Name: generation and 3-dimensional quantitation of arterial lesions in mice using optical projection tomography
Uploaded: 2015-05-26T13:00:00
Duration: 11 min 45 s
Description: Watch this Scientific Journal Video about Generation and 3-Dimensional Quantitation of Arterial Lesions in Mice Using Optical Projection Tomography at JoVE.com

This work was supported by studentships from the University of Edinburgh (NSK) and Carnegie Trust (LL; Henry Dryerre scheme) and funding from the British Heart Foundation (PWFH, BRW, DJW; RG/05/008; PG/05/007; PG/08/068/25461) and Wellcome Trust (JRS, BRW, DJW; 08314/Z/07/Z). The authors are grateful to support for their work provided by the BHF-funded Centre of Research Excellence award to the Centre for Cardiovascular Science.
The authors are particularly grateful for advice from Professor Masataka Sata (University of Tokushima) and Dr Igor Chersehnev (in Dr Ernane Reis&#8217; group at Mount Sinai School of Medicine) on establishment of the surgical models of neointimal lesion production. The video produced and made available by Sata et al.(http://plaza.umin.ac.jp/~msata/english.htm) was particularly useful.

1. Surgical Induction of Neointimal Lesions in the Mouse Femoral Artery
<ol>
	<li>Experiments using animals should be performed in accordance with national and institutional ethics requirements. All surgery should be performed using appropriate aseptic technique. Induction of neointimal lesions is achieved using a modification of the technique described by Roque et al.12 and Sata et al.13.</li>
	<li>Weigh male C57Bl6/J mice (Age 10-12 weeks; weight 25-30 g) then anaesthetize by delivering 4-5% isoflurane in an induction chamber. Once anesthesia has been induced, transfer the mouse to a heated mat to maintain body temperature at 37 &#176;C. Continue administration of isoflurane (2-3%) via a mask.</li>
	<li>Once an appropriate level of anesthesia has been induced (lack of response to toe pinch), provide analgesic cover by administration of buprenorphine (0.1 mg/kg-1). Then place the mouse in a supine position and shave the ventral surface of the left hindlimb.</li>
	<li>Make an incision to expose the muscles of the upper hindlimb and, between the bifurcation with the popliteal artery and the abdominal wall, use blunt dissection to isolate the femoral artery and vein from the femoral nerve. Irrigate the wound as required using 1% w/v lignocaine.</li>
	<li>Place proximal (close to the abdominal wall) and distal (immediately below the branch with the popliteal artery) temporary ligatures (6/0 Mersilk) around the femoral artery and vein to control blood flow. Then isolate the popliteal artery (for approximately 2-5 mm distal to the branch with the femoral artery) and ligate distally. Place a second, untied ligature beneath the popliteal artery.</li>
	<li>Make a small incision (arteriotomy) in the popliteal artery, immediately distal to the branch with the femoral artery, preventing bleeding by applying pressure to the proximal temporary ligature. Advance a straight, sprung 0.014&#8221; guidewire 1-1.5 cm along the femoral artery in the direction of the abdominal wall and leave in place for 30 sec (Figure 1A).</li>
	<li>Remove the guidewire and ligate the popliteal artery above the arteriotomy, using the ligature placed for that purpose, and taking care not to occlude the femoral artery. 
	NOTE: For ligation-induced injury. Neointimal remodeling without intraluminal injury can be induced by ligating the femoral or popliteal arteries (Figure 1B and 1C). To achieve this follow steps 1.1-1.5. However, do not make the arteriotomy but (avoiding step 1.6) either (i) ligate the popliteal artery immediately distal to the femoral artery or (ii) ligate the common femoral artery at the branch point with the popliteal artery. Then proceed with step 1.8.</li>
	<li>Remove temporary ligatures, close the wound with a discontinuous external suture (5/0 Mersilk) and apply EMLA cream (2.5% lidocaine, 2.5% prilocaine). Allow the animals to regain consciousness (usually 5-10 min) and ensure they are moving freely around their cage (slight lameness may be evident in the affected leg but this should resolve over the first 2-3 days after surgery) before returning to holding rooms. Mice do not have to be housed singly after surgery.</li>
	<li>Allow the animals to recover for up to 3 months. Small lesions will begin to appear ~7 days after wire injury and will reach a stable maximum size after ~ 21-28 days.</li>
</ol>
2. Induction of Atherosclerotic Lesions in the Apolipoprotein E-/- Mice
<ol>
	<li>Administer western diet (0.2% cholesterol; Research Diets, USA) to male, 6 week old ApoE-null mice (bred in house) for 12 weeks.</li>
	<li>Atherosclerotic lesions are often visible on gross inspection of the aortic arch and its major branches (Figure 2).</li>
</ol>
3. Analysing Arterial Lesions using Optical Projection Tomography (OPT)
NOTE: OPT images of lesions in murine femoral arteries and aortic arch samples were obtained using an optical projection tomograph.
<ol>
	<li>Euthanize mice by transcardiac perfusion fixation and exsanguination under terminal anesthesia (80 mg/kg sodium pentobarbital), using heparinised (10 U/ml) phosphate buffered saline (PBS) followed by 10% neutral buffered formalin.</li>
	<li>Isolate femoral arteries or the aortic arch and its major branches (left carotid artery, left subclavian artery, brachiocephalic trunk), as appropriate, and remove extraneous peri-adventitial material. Post-fix in 10% buffered formalin O/N, before storage in 70% ethanol until needed.</li>
	<li>Embed arteries in 1.5% low melting point agarose, pre-filtered through Whatman 113 V paper. Attach each sample to a magnetic OPT mount with cyanoacrylate adhesive with the vessel axis in line with that of the mount. Trim excess agarose to a conical shape. Dehydrate in 100% methanol for at least 12 hr.</li>
	<li>Clear vessels by immersion (for 12-24 hr) in a mixture of benzyl alcohol and benzyl benzoate (1:2 v/v).</li>
	<li>Place cleared samples in a calibrated tomograph. Set resolution to 1,024 x 1,024, and determine an optical magnification that allows the entire area of interest to be seen. OPT volume is isotropic the z-axis is reconstructed to the same resolution (i.e., 1,024 x 1,024 x 1,024), voxel size ~200 &#181;m. This may represent an over-estimate of resolution as there are likely to be reconstruction artifacts. Adjust sample position so that it rotates upon its own axis in the center of the field of view in the bright-field, transmission channel.</li>
	<li>In the GFP1 filter emission channel (excitation filter 425 nm with 40 nm band-pass; emission filter: 475 nm long pass), focus the specimen and adjust exposure time to maximize the dynamic range of the resulting image (avoid over-saturation). Scan the vessel in the GFP1 emission channel only, with a 0.9&#176;rotation step.</li>
	<li>At completion, confirm quality of data acquisition using DataViewer software. Remove specimen from the scanner.</li>
	<li>To allow subsequent histological analysis, place sample in 100% methanol for &#62;24 hr before processing to paraffin wax as normal.</li>
</ol>
4. Image Reconstruction and Analysis
Tomographic re-construction by filtered back-projection is performed using NRecon software or similar. Reconstructions can be performed unattended, in batches.
<ol>
	<li>Improve image quality by compensating for misalignment and adjusting image intensity levels.</li>
	<li>Check the quality of image reconstruction using DataViewer software.</li>
	<li>Identify the appropriate section of the sample for analysis. Keep this length consistent between vessels if luminal dimensions are to be recorded.</li>
	<li>Define the outline of the lesions by manually tracing the appropriate border for 1 in every 50 re-constructed cross-sections.</li>
	<li>Check each interleaved cross-section to ensure computer-generated interpolations are correct. Manually adjust the border where necessary.</li>
	<li>Set the grey-level threshold so that only the lesion is selected and export the measurement data.</li>
	<li>For each scan, define a vertical region of interest containing the lesion and trace the border between media and neointima (i.e., the position of the internal elastic lamina) for every 50th scan-line. Interpolate intima/media borders for the interleaved scan lines in software, and verify and correct the fit where required. Further segment this defined three dimensional volume to a manually-defined intensity threshold to produce a binary image set in which white pixels represent neointima and black pixels represent patent lumen.</li>
	<li>Measurements taken include: total lesion volume (object volume), luminal volume (total volume &#8211; object volume) and the distribution of lesion and lumen cross-sectional area along the axial length of the studied vessel.</li>
</ol>

<ol>
	<li>Luis, A. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atherosclerosis.">Atherosclerosis.</a> Nature. 407, 233-241 (2000).</li><li>Ross, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atherosclerosis&#8211;an+inflammatory+disease.">Atherosclerosis&#8211;an inflammatory disease.</a> N Engl J Med. 340, 115-126 (1999).</li><li>Deuse, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Imaging+In-Stent+Restenosis:+An+Inexpensive,+Reliable,+and+Rapid+Preclinical+Model.">Imaging In-Stent Restenosis: An Inexpensive, Reliable, and Rapid Preclinical Model.</a> J Vis Ex. (31), (2009).</li><li>McAteer, M. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantification+and+3D+reconstruction+of+atherosclerotic+plaque+components+in+apolipoprotein+E+knockout+mice+using+ex+vivo+high-resolution+MRI.">Quantification and 3D reconstruction of atherosclerotic plaque components in apolipoprotein E knockout mice using ex vivo high-resolution MRI.</a> Arterioscler Thromb Vasc Biol. 24, 2384-2390 (2004).</li><li>Martinez, H. G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Microscopic+Computed+Tomography-Based+Virtual+Histology+for+Visualization+and+Morphometry+of+Atherosclerosis+in+Diabetic+Apolipoprotein+E+Mutant+Mice.">Microscopic Computed Tomography-Based Virtual Histology for Visualization and Morphometry of Atherosclerosis in Diabetic Apolipoprotein E Mutant Mice.</a> Circulation. 120, 821-822 (2009).</li><li>Langheinrich, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Atherosclerotic+Lesions+at+Micro+CT:+Feasibility+for+Analysis+of+Coronary+Artery+Wall+in+Autopsy+Specimens.">Atherosclerotic Lesions at Micro CT: Feasibility for Analysis of Coronary Artery Wall in Autopsy Specimens.</a> Radiology. 231, 675-681 (2004).</li><li>Ambrosi, C. M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Virtual+histology+of+the+human+heart+using+optical+coherence+tomography.">Virtual histology of the human heart using optical coherence tomography.</a> J Biomed Opt. 14, 054002 (2009).</li><li>Ku, G. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Photoacoustic+microscopy+with+2-micron+transverse+resolution.">Photoacoustic microscopy with 2-micron transverse resolution.</a> J Biomed Opt. 15, 021302 (2010).</li><li>Sharpe, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+projection+tomography+as+a+tool+for+3D+microscopy+and+gene+expression+studies.">Optical projection tomography as a tool for 3D microscopy and gene expression studies.</a> Science. 296, 541-545 (2002).</li><li>Sharpe, J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+projection+tomography.">Optical projection tomography.</a> Annu Rev Biomed Eng. 6, 209-228 (2004).</li><li>Kirkby, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+3-Dimensional+Imaging+of+Murine+Neointimal+and+Atherosclerotic+Lesions+by+Optical+Projection+Tomography.">Quantitative 3-Dimensional Imaging of Murine Neointimal and Atherosclerotic Lesions by Optical Projection Tomography.</a> PloS ONE. 6 (2), e16906 (2011).</li><li>Roque, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Mouse+model+of+femoral+artery+denudation+injury+associated+with+the+rapid,+accumulation+of+adhesion+molecules+on+the+luminal+surface+and+recruitment+of+neutrophils.">Mouse model of femoral artery denudation injury associated with the rapid, accumulation of adhesion molecules on the luminal surface and recruitment of neutrophils.</a> Arterioscler Thromb Vasc Biol. 20, 335-342 (2000).</li><li>Sata, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+mouse+model+of+vascular+injury+that+induces+rapid+onset+of+medial+cell+apoptosis+followed+by+reproducible+neointimal+hyperplasia.">A mouse model of vascular injury that induces rapid onset of medial cell apoptosis followed by reproducible neointimal hyperplasia.</a> J Mol Cell Cardiol. 32, 2097-2104 (2000).</li><li>Richards-Kortum, R., Sevick-Muraca, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Quantitative+optical+spectroscopy+for+tissue+diagnosis.">Quantitative optical spectroscopy for tissue diagnosis.</a> Annu Rev Phys Chem. 47, 555-606 (1996).</li><li>Kirkby, N. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Non-endothelial+cell+endothelin-B+receptors+limit+neointima+formation+following+vascular+injury.">Non-endothelial cell endothelin-B receptors limit neointima formation following vascular injury.</a> Cardiovascular Research. 95, 19-28 (2012).</li><li>Kipari, T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=11-hydroxysteroid+dehydrogenase+type+1+deficiency+in+bone+marrow-derived+cells+reduces+atherosclerosis.">11-hydroxysteroid dehydrogenase type 1 deficiency in bone marrow-derived cells reduces atherosclerosis.</a> FASEB J. 27 (4), 1519-1531 (2013).</li><li>Mackinnon, A. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Inhibition+of+galectin-3+reduces+atherosclerosis+in+apolipoprotein+E+deficient+mice.">Inhibition of galectin-3 reduces atherosclerosis in apolipoprotein E deficient mice.</a> Glycobiology. 23 (6), 654-663 (2013).</li><li>Kumar, A., Lindner, V. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remodeling+with+neointima+formation+in+the+mouse+carotid+artery+after+cessation+of+blood+flow.">Remodeling with neointima formation in the mouse carotid artery after cessation of blood flow.</a> Arterioscler Thromb Vasc Biol. 17, 2238-2244 (1997).</li><li>Walls, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correction+of+artefacts+in+optical+projection+tomography.">Correction of artefacts in optical projection tomography.</a> Phys Med Biol. 50, 4645-4665 (2005).</li><li>Walls, J. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Resolution+improvement+in+emission+optical+projection+tomography.">Resolution improvement in emission optical projection tomography.</a> Phys Med Biol. 52, 2775-2790 (2007).</li><li>Bucher, D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Correction+methods+for+three-dimensional+reconstructions+from+confocal+images:+I.+tissue+shrinking+and+axial+scaling.">Correction methods for three-dimensional reconstructions from confocal images: I. tissue shrinking and axial scaling.</a> Journal of Neuroscience Methods. 100, 135-143 (2000).</li><li>Alanentalo, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Tomographic+molecular+imaging+and+3D+quantification+within+adult+mouse+organs.">Tomographic molecular imaging and 3D quantification within adult mouse organs.</a> Nat Methods. 4, 31-33 (2007).</li></ol>

The authors have no competing financial interest.

3-dimensional analysis has great potential for replacing or adding to the 2-dimensional histological techniques that still underpin the majority of investigations of arterial lesion formation. Here OPT is shown in small murine arteries (with murine femoral arteries probably representing the smallest vessels that can be analyzed successfully using this technique). It is, however, also suitable for use with arteries (and lesions) from other species, including small-to-medium sized human vessels; our group has successfully used the technique to analyze lesions in rabbit aorta (Bezuidenhout et al.; unpublished). OPT promises faster analysis and increased structural information compared with traditional histology and has the advantage of not preventing subsequent analysis of the sample using both histological and immunohistochemical techniques.
The images produced using OPT gave anatomical detail, showing sites of lesion formation and the size of lesions in these areas. The arteries used in these investigations are probably close to the limit of resolution for the technique and image quality is therefore impaired to a certain degree by artifacts (probably resulting from rotation misalignment, incomplete clearing, reflection/refraction at the agarose vertices and focusing problems). Despite this, the details required (i.e., layers of the vessel wall) remain discernable and therefore the technique is extremely useful for the quantification of individual layers. Indeed, images could be quantified rapidly and reproducibly to provide measurements of lesion and luminal volume in plaque-bearing sections of the vessel, as well as cross-sectional areas of the lesion and lumen at selected sites in the sample. Large (aorta) and medium sized (femoral, carotid, subclavian) murine arteries &#8211; those generally used for analysis of atherosclerotic and neotintimal lesion formation in mice &#8211; were successfully analyzed using this method. Indeed we have now used OPT to demonstrate the effect of pharmacological interventions and genetic manipulation on atherosclerotic and neointimal lesion size. For example, endothelin receptor blockade altered neointimal lesion formation whereas selective deletion of the endothelin B receptor from the vascular endothelium did not15. In atherosclerosis prone mice, genetic deletion of the enzymes 11&#946;-HSD116 or galectin 317 were shown to reduce the size of atherosclerotic lesions.
Quantification of lesion volume is an obvious benefit of OPT. It gives a more informative indication of the total lesion burden in an artery4 than is usually obtained with histological methods. Analyzing the entire lesion reduces selection bias and error that will inevitably occur when discrete sections of a vessel are chosen for analysis. Production of longitudinal lesion profiles is a further strength of OPT, emphasized by the comparison of lesions induced by different types of injury13,16 (Figure 5). For example, both complete ligation and wire-insertion induced almost total occlusion close to the femero-popliteal bifurcation. Wire injury, however, produced lesions that extended along the entire length of the scanned section, whereas lesions induced by arterial ligation rapidly diminished in size and disappear. This pattern&#160;is consistent with the greater extent of injury caused by insertion of the angioplasty guidewire. Generating similar results using histological sections is expensive, time consuming and labor intensive.
The advantages of OPT include the quality of the images it produces and its relative speed and simplicity (we have routinely scanned 20 vessels per day). Image quality appears superior, or at least comparable, to other methods for generating 3-dimensional images ex vivo (such as MRI and micro- CT), yet OPT requires shorter scan times (integration time for our studies was typically 1-2sec/image) and is less expensive. Sample preparation extends over several days but requires little labor, vessels can be prepared in batches, and data can be acquired in one session. Consequently, throughput is high and does not require extended use of the scanner. Importantly, the non-destructive nature of OPT means it can be used to identify sites of interest for immunohistochemical examination; thus reducing the amount of cutting and staining required. It is possible that development of high resolution ultrasound will provide an alternative method for volumetric quantification of lesions in arteries this size, but the authors are unaware of any publications that demonstrate this application.
Perhaps unsurprisingly, image quality in OPT is inferior to microscopic techniques (which can, of course, only be performed on smaller samples). Proposed refinements to reconstruction of data may address this limitation by allowing future improvement of image quality19,20. Another methodological concern is that tissue processing alters characteristics of the sample. For example the lipophilic nature of the clearing agent, benzyl alcohol/benzyl benzoate (BABB), is likely to remove lipid from atherosclerotic lesions, whilst prior dehydration may cause shrinkage (although, of course, dehydration and lipid removal steps are also a feature of sample preparation for embedding in paraffin wax). BABB was used in this investigation as, in comparison with hydrophilic clearing agents (e.g. glycerol21) it causes only small changes in morphology.
There are several possibilities for further development and refinement of OPT, particularly with regard to tracking the 3-dimensional arrangement of key cells and signaling factors involved in arterial remodeling. The strong autofluorescence of arterial tissue, which is such an advantage in the generation of anatomical images, is not quenched by existing methods of bleaching22 and may restrict the use of fluorescent probes to assess RNA and protein distribution patterns. The use of colorimetric probes (e.g. &#946;-galactosidase) visualized by transmission imaging may overcome this limitation.
To conclude, OPT has great potential for 3-dimensional imaging of lesions in the intima of murine arteries. It represents a considerable advance on 2-dimensional methods which are generally labor intensive and do not effectively represent total lesion volume. OPT is relatively fast, convenient and non-destructive. New developments in image analysis promise to further increase the power and utility of the technique.

The formation of arterial lesions is central to the high morbidity and mortality associated with cardiovascular disease1. Lesion formation is considered to be caused by an unfettered inflammatory response to arterial injury2. Atherosclerotic lesions form slowly in response to chronic injury to the arterial wall whereas restenotic lesions develop rapidly following acute mechanical damage (for example, after stent implantation). The mechanisms that contribute to development of arterial lesions have been clarified considerably by the use of appropriate animal models, often in combination with relevant genetic manipulations1.
Analysis of lesion size and composition has classically depended heavily on ex vivo, 2&#8211;dimensional histology (although this is changing with the development of improved methods for in vivo and ex vivo detection and analysis of lesions in small animals3). Histological analysis of arterial lesions is labor intensive, time consuming and provides limited information of 3-dimensional structure. For example, lesion burden is commonly assessed by measuring the cross-sectional area of a lesion (either at randomly selected sites or at the site of maximum occlusion). This provides an incomplete analysis of overall lesion burden. Whole-mount 3-dimensional imaging technology provides a possible solution to this problem but surprisingly few suitable approaches have been described. This may be due predominantly to the size of mouse arteries which are too large for single-photon confocal microscopy but too small for magnetic resonance imaging (MRI)4 and X-ray computed tomography (CT)5. Application of ex vivo MRI and micro CT to the study of atherosclerotic lesions in mice suggests they offer limited resolution, even in relatively large arteries. Added to this, the relatively long acquisition times required limit throughput (and increase scanning costs)4,6.
Development of new optical imaging modalities (such as optical coherence tomography3,7 and photo-acoustic tomography8) offers much potential for improving imaging of lesions in murine arteries. Similar potential is shown by optical projection tomography (OPT) which was developed to allow analysis of mouse embryos. OPT was designed to image specimens ranging from ~0.3-10 mm in diameter9. Transmission imaging records the opacity of a semi-translucent sample to polychromatic visible light and, can be used for identification of anatomical structures. Emission imaging records emission of light following excitation at specific wavelengths from endogenous (e.g., collagen, elastin) and exogenous fluorophores in the sample. This can also provide anatomical information (since different tissue components can differ in the type and density of autofluorescent species present). In addition, distribution of immunoreactivity or gene expression can be determined with the use of appropriate fluorescent probes10. For either imaging mode (transmission or emission), light is focused to a charge-coupled device to allow iterative image capture as the sample rotates (usually 400 images at 0.9&#176; increments). These can be used for calculation of volume by standard tomographic reconstruction methods (such as filtered back-projection (using a cone algorithm) or iterative reconstruction).
This video demonstrates our novel application of OPT for rapid, quantifiable and cost-effective 3-dimensional analysis of atherosclerotic and neointimal lesions, as previously described in Kirkby et al.11. The technique was shown to be suitable for quantifying lesion size in three commonly used models: (i) femoral artery wire-injury; (ii) femoral artery ligation, and (iii) diet-induced atherosclerosis in apolipoprotein E deficient (apoE-/-) mice.

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			<td height="22" style="height:22px;width:195px;">Operating Microscope</td>
			<td style="width:180px;">Zeiss, Germany</td>
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			<td height="22" style="height:22px;width:195px;">Anaesthetic Machine</td>
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			<td height="22" style="height:22px;width:195px;">Bead Steriliser</td>
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			<td height="22" style="height:22px;width:195px;">Heated Mat</td>
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			<td style="width:180px;">Cook Inc, USA</td>
			<td style="width:137px;">C-PMS-251</td>
			<td style="width:180px;">0.014&#8221;</td>
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			<td height="22" style="height:22px;width:195px;">Suture Silk</td>
			<td style="width:180px;">Fine Science Tools, UK</td>
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			<td style="width:180px;">Bioptonics, UK</td>
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			<td height="22" style="height:22px;width:195px;">Magnetic OPT Mount</td>
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			<td height="22" style="height:22px;width:195px;">Computer</td>
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			<td style="width:180px;">Skyscan, Belgium</td>
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			<td style="width:180px;">Merial Animal Health Ltd, UK</td>
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			<td height="43" style="height:43px;width:195px;">Vetergesic</td>
			<td style="width:180px;">Alstoe Animal Health Ltd, UK</td>
			<td style="width:137px;">N/A</td>
			<td style="width:180px;">0.3mg/ml</td>
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			<td height="43" style="height:43px;width:195px;">1% Lignocaine</td>
			<td style="width:180px;">Hamlen Pharmaceuticals, UK</td>
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			<td height="43" style="height:43px;width:195px;">Sodium Pentobarbital</td>
			<td style="width:180px;">Ceva Animal Health Ltd, UK</td>
			<td style="width:137px;">N/A</td>
			<td style="width:180px;"></td>
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		<tr height="22">
			<td height="22" style="height:22px;width:195px;">Western Diet</td>
			<td style="width:180px;">Research Diets, USA</td>
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			<td height="22" style="height:22px;width:195px;">Heparin (Mucous)</td>
			<td style="width:180px;">Leo Laboratories, UK</td>
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			<td style="width:180px;">25, 0000 Units</td>
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			<td height="22" style="height:22px;width:195px;">Neutral Buffered Formalin</td>
			<td style="width:180px;">Sigma, UK</td>
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			<td height="22" style="height:22px;width:195px;">Ethanol</td>
			<td style="width:180px;">VWR BDH Prolabo, UK</td>
			<td style="width:137px;">20821.33</td>
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			<td height="22" style="height:22px;width:195px;">Agarose</td>
			<td style="width:180px;">Invitrogen, UK</td>
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			<td height="22" style="height:22px;width:195px;">Filter Paper</td>
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			<td style="width:180px;">Whatman</td>
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			<td height="22" style="height:22px;width:195px;">Cyanoacrylate adhesive</td>
			<td style="width:180px;">Henkel, UK</td>
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			<td height="22" style="height:22px;width:195px;">Methanol</td>
			<td style="width:180px;">VWR BDH Prolabo, UK</td>
			<td style="width:137px;">20856.296</td>
			<td style="width:180px;">100%</td>
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generation and 3-dimensional quantitation of arterial lesions in mice using optical projection tomography

The generation and analysis of vascular lesions in appropriate animal models is a cornerstone of research into cardiovascular disease, generating important information on the pathogenesis of lesion formation and the action of novel therapies. Use of atherosclerosis-prone mice, surgical methods of lesion induction, and dietary modification has dramatically improved understanding of the mechanisms that contribute to disease development and the potential of new treatments.
Classically, analysis of lesions is performed ex vivo using 2-dimensional histological techniques. This article describes application of optical projection tomography (OPT) to 3-dimensional quantitation of arterial lesions. As this technique is non-destructive, it can be used as an adjunct to standard histological and immunohistochemical analyses.
Neointimal lesions were induced by wire-insertion or ligation of the mouse femoral artery whilst atherosclerotic lesions were generated by administration of an atherogenic diet to apoE-deficient mice.
Lesions were examined using OPT imaging of autofluorescent emission followed by complementary histological and immunohistochemical analysis. OPT clearly distinguished lesions from the underlying vascular wall. Lesion size was calculated in 2-dimensional sections using planimetry, enabling calculation of lesion volume and maximal cross-sectional area. Data generated using OPT were consistent with measurements obtained using histology, confirming the accuracy of the technique and its potential as a complement (rather than alternative) to traditional methods of analysis.
This work demonstrates the potential of OPT for imaging atherosclerotic and neointimal lesions. It provides a rapid, much needed ex vivo technique for the routine 3-dimensional quantification of vascular remodelling.

Preliminary scanning of healthy (unlesioned) murine femoral arteries (n = 5) demonstrated that transmission imaging did not provide useful images. This was a consequence of the cleared arteries becoming too transparent (rather than too opaque) for transmission imaging.However, this is beneficial for emission imaging as there is no absorbance/scattering of the emitted signal . In contrast, femoral arteries autofluoresce strongly in the emission channel, with the greatest signal following excitation at 405&#8211;445 nm (consistent with a 410 nm excitation peak for elastin14). 2-dimensional slices reconstructed from these images clearly distinguished the media from the lumen and adventitia and lumen.
In murine femoral arteries harvested 28 days after wire- (n = 6) or ligation- (n = 5) induced injury neointimal thickening was evident in non-tomographic emission projections (Figure 3A). In reconstructed 2-dimensional slices, concentric neointimal lesions could be distinguished from the media by their weaker emission (Figure 3B and&#160;Figure S1).
OPT emission images of whole mount samples of the aortic arch and its major branches from atherosclerotic mice (n = 8) identified lesions with the anticipated anatomical distribution (i.e., in the lesser curvature of the aortic arch, the brachiocephalic artery, and the origins of the left carotid and left subclavian arteries (Figure 4A). Cross-sectional images indicated that these were typically eccentric lesions and were readily distinguished from the media and lumen (Figure 4B, Figures S2 and S3).
Processing arteries for histological analysis following OPT confirmed the non-destructive nature of OPT, with sections successfully stained using histological (United States Trichrome, Picrosirius red) and immunohistochemical (&#945;-SMA, Mac-2) techniques (Figures 3C and 4C).
Measurement of lesion size using OPT has been shown to be consistent with measurements obtained using image analysis of histological sections taken from the same artery11.
Planimetric measurements of lesion area obtained by OPT and histology correlated closely by linear regression for wire- (R2 = 0.92) and ligation-induced (R2 = 0.89) neointimal lesions and atherosclerotic plaques (R2 = 0.85). An important benefit of OPT is its ability to enable 3-dimensional analysis. By developing volumetric quantification of lesions with this technique, we were able to record lesion volumes in wire- (0.1100 &#177; 0.0091 mm3; n = 6) and ligation-injured femoral arteries (0.0200 &#177; 0.0089 mm3; n = 5) and also in atherosclerotic brachiocephalic arteries (0.180 &#177; 0.018 mm3; n = 8). Measurements were highly reproducible (coefficients of variation 5.4%, 11.4% and 4.8%, respectively, n = 4) for all types of lesion. Neointimal lesions in wire-injured vessels were larger (p &#60;0.0001) than those produced by ligation, consistent with the greater degree of damage inflicted by the former.
The data generated could also be expressed as lesion profiles (Figure 5) and rendered for dynamic, qualitative evaluation (see Figures S1-S3). This approach clearly demonstrated the extent of lesion formation in response to different injury procedures and highlighted the uneven distribution of lesion formation in injured vessels.
<img alt="Figure 1" src="/files/ftp_upload/50627/50627fig1.jpg" /> 
Figure 1: Methods for initiating lesion formation in murine femoral artery.&#160;(A) Retrograde insertion of an angioplasty guidewire into the femoral artery, by means of an arteriotomy in the popliteal artery stimulates lesion formation in response to stretch injury and removal of the endothelium. Blood flow is re-established over the injured section of vessel. (B) Neointimal proliferation in the absence of intraluminal stretch, denudation or interruption to blood flow can be induced by ligating either the femoral or the popliteal artery immediately distal to the femoral artery bifurcation. (C) A more severe non-denuding injury/ proliferation response can be induced by ligating both the femoral and popliteal arteries across the branch point of the common femoral artery. This technique will also block blood flow in the distal portion of the femoral artery.
<img alt="Figure 2" src="/files/ftp_upload/50627/50627fig2.jpg" /> 
Figure 2: Characteristic deposition of atheroma in the mouse aortic arch.&#160;Atherosclerosis prone (Apolipopotein E deficient mice) fed a high cholesterol western diet for 12 weeks develop a characteristic pattern of lesion deposition in the aortic arch and its major branches. As demonstrated, lesions are visible (arrows), by gross inspection under a dissecting microscope, in the aortic arch, the brachiocephalic artery, and in the ostia of the left carotid artery&#160;and left subclavian artery.&#160;
<img alt="Figure 3" src="/files/ftp_upload/50627/50627fig3.jpg" /> 
Figure 3: Lesion formation following ligation of the left femoral artery.&#160;(A) Non-tomographic fluorescence emission images (inverted to increase clarity &#8211; dark regions correspond to stronger emission) allow identification of intimal thickening (red arrowheads). (B) Distinct vascular regions and the lumen can be distinguished in tomographic reconstructions. (C) Histological analysis (United States trichrome) emphasises the clear resemblance with images obtained using OPT. Scale bars in (A-C) are 200 mm. Adapted from Kirkby et al.11 Scale bars in (A-C) are 200 &#181;m.
<img alt="Figure 4" src="/files/ftp_upload/50627/50627fig4.jpg" /> 
Figure 4: Imaging of atheroma in the aortic arch of atherosclerosis prone mice.&#160;(A) Atheroma (red arrowheads) is readily apparent in non-tomographic images (inverted so that darker regions indicate stronger emission, thus improving clarity) of the aortic arch, in sites predicted as atheroma-bearing by inspection under light microscopy (see Figure 2). (B) This pattern of distribution is confirmed in tomographic cross-sections. (C) Histological (United States trichrome) staining shows close similarity with tomographic sections, and immunohistochemistry using several different antibodies emphasises the complementary nature of OPT with traditional approaches to lesion analysis. Scale bars in (A&#8211;B) are 1 mm; Scale bar in (C) is 250 &#181;m. RSA, right subclavian artery; RCA, right carotid artery; LCA, left carotid artery; LSA, left subclavian artery; BCA, brachiocephalic artery; AAo, ascending aorta; DAo, descending aorta. Adapted from Kirkby et al.11
<img alt="Figure 5" src="/files/ftp_upload/50627/50627fig5.jpg" /> 
Figure 5: Analysis of lesion and lumen profiles indicates varying extent of neointimal proliferation in response to different methods of arterial injury.&#160;Optical projection tomography allows lesion and lumen cross sectional measurements to be plotted against distance along the femoral artery. This clearly demonstrates that, compared with an uninjured artery (A), partial ligation (B) produces small, relatively discrete lesions, whereas total ligation (C) produces complete occlusion at the site of ligation but the lesion does not extend far along the artery. Intraluminal wire injury (D) produces a lesion that almost completely occludes the distal portion of the sample and extends along the entire length of the scanned section of artery. Adapted from Kirkby et al.11
Figure S1.&#160;Animated reconstruction of cross-sectional images obtained from a mouse femoral artery following ligation injury.This type of animated image is useful for both qualitative and quantitative analysis. As the animation moves from the proximal to the distal sections of the artery the gradual development of an occlusive neointima, discernible from the lumen and the media, is readily apparent. Side branches can be easily identified and there is evident luminal occlusion and outward remodelling of the artery as the lesion increases in size. Complete occlusion of the vessel occurs once the site of ligation is reached. Adapted from Kirkby et al.11
Figure S2.&#160;Animated reconstruction of cross-sectional images of an aortic arch from an atherosclerosis-prone mouse.&#160;The animation commences with cross-sections of the ascending (left &#8211; which appears first) and descending (right) aorta. Small lesions appear in the ascending aorta as the scan moves in the direction of the aortic arch. The images then move through the arch to show the heavily lesioned ostia of the brachiocephalic (left), left carotid (middle) and left subclavian (right) arteries. As the scan moves distally along these branches the lesions gradually reduce and disappear, first in the subclavian artery, then in the carotid and finally in the brachiocephalic artery. Interestingly, the lesion in the brachiocephalic artery moves onto the flow divider as this vessel divides into the right carotid and right subclavian arteries. Adapted from Kirkby et al.11
Figure S3.&#160;Animated, volume-rendered image of an aortic arch from an atherosclerosis-prone mouse.&#160;Optical projection tomography allows generation of 3-dimensional images, in this case demonstrating lesion distribution in the aortic arch of an apolipoprotein E deficient mouse. (A) Atheroma is present in the expected sites (throughout the brachiocephalic artery, in the ostia of the left carotid and subclavian arteries and in the lesser curvature of the aortic arch). (B) Segmentation and rendering of lesion (shown in red) bearing cross-sections emphasises the distribution of plaques when superimposed on the original image. Adapted from Kirkby et al.11

Watch this Scientific Journal Video about Generation and 3-Dimensional Quantitation of Arterial Lesions in Mice Using Optical Projection Tomography at JoVE.com

Generation and 3-Dimensional Quantitation of Arterial Lesions in Mice Using Optical Projection Tomography

Ex vivo analysis of arterial lesions from animal models of cardiovascular disease classically relies on histological and immunohistochemical techniques. These provide 2-dimensional measurements in 3-dimensional lesions. This manuscript describes the generation of arterial lesions for quantitative analysis in 3-dimensions using optical projection tomography.

The generation and analysis of vascular lesions in appropriate animal models is a cornerstone of research into cardiovascular disease, generating ...

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Research

JoVE Journal

Medicine

Doppler Optical Coherence Tomography of Retinal Circulation

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double circular scan (CDCS) that scans around the optic nerve head at 3.40 mm and 3.75 mm diameters. The double concentric circles are performed 6 times consecutively over 2 sec. The CDCS scan is saved with Doppler shift information from which flow can be calculated. The standard clinical protocol calls for 3 CDCS scans made with the OCT beam passing through the superonasal edge of the pupil and 3 CDCS scan through the inferonal pupil. This double-angle protocol ensures that acceptable Doppler angle is obtained on each retinal branch vessel in at least 1 scan. The CDCS scan data, a 3-dimensional volumetric OCT scan of the optic disc scan, and a color photograph of the optic disc are used together to obtain retinal blood flow measurement on an eye. We have developed a blood flow measurement software called "Doppler optical coherence tomography of retinal circulation" (DOCTORC). This semi-automated software is used to measure total retinal blood flow, vessel cross section area, and average blood velocity. The flow of each vessel is calculated from the Doppler shift in the vessel cross-sectional area and the Doppler angle between the vessel and the OCT beam. Total retinal blood flow measurement is summed from the veins around the optic disc. The results obtained at our Doppler OCT reading center showed good reproducibility between graders and methods (&lt;10%). Total retinal blood flow could be useful in the management of glaucoma, other retinal diseases, and retinal diseases. In glaucoma patients, OCT retinal blood flow measurement was highly correlated with visual field loss (R2&gt;0.57 with visual field pattern deviation). Doppler OCT is a new method to perform rapid, noncontact, and repeatable measurement of total retinal blood flow using widely available Fourier-domain OCT instrumentation. This new technology may improve the practicality of making these measurements in clinical studies and routine clinical practice.

Total retinal blood flow is measured by Doppler optical coherence tomography and semi-automated grading software.

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double ...

Modeling and Imaging 3-Dimensional Collective Cell Invasion

A defining characteristic of cancer malignancy is invasion and metastasis 1. In some cancers (e.g. glioma 2), local invasion into surrounding healthy tissue is the root cause of disease and death. For other cancers (e.g. breast, lung, etc.), it is the process of metastasis, in which tumor cells move from a primary tumor mass, colonize distal sites and ultimately contribute to organ failure, that eventually leads to morbidity and mortality 3. It has been estimated that invasion and metastasis are responsible for 90&#37; of cancer deaths 4. As a result, there has been intense interest in identifying the molecular processes and critical protein mediators of invasion and metastasis for the purposes of improving diagnosis and treatment 5.
A challenge for cancer scientists is to develop invasion assays that sufficiently resemble the in vivo situation to enable accurate disease modeling 6. Two-dimensional cell motility assays are only informative about one aspect of invasion and do not take into account extracellular matrix (ECM) protein remodeling which is also a critical element. Recently, research has refined our understanding of tumor cell invasion and revealed that individual cells may move by elongated or rounded modes 7. In addition, there has been greater appreciation of the contribution of collective invasion, in which cells invade in strands, sheets and clusters, particularly in highly differentiated tumors that maintain epithelial characteristics, to the spread of cancer 8.
We present a refined method 9 for examining the contributions of candidate proteins to collective invasion 10. In particular, by engineering separate pools of cells to express different fluorescent proteins, it is possible to molecularly dissect the activities and proteins required in leading cells versus those required in following cells. The use of RNAi provides the molecular tool to experimentally disassemble the processes involved in individual cell invasion as well as in different positions of collective invasion. In this procedure, mixtures of fluorescently-labeled cells are plated on the bottom of a Transwell insert previously filled with Matrigel ECM protein, then allowed to invade "upwards" through the filter and into the Matrigel. Reconstruction of z-series image stacks, obtained by confocal imaging, into three-dimensional representations allows for visualization of collectively invading strands and analysis of the representation of fluorescently-labeled cells in leading versus following positions.

Models of tumor cell invasion into three-dimensional extracellular matrix better reflect the in vivo situation than two-dimensional motility assays. Using matrix invasion assays combined with confocal imaging of fluorescently-labeled cells, detailed information on invasion modes and the distinct contributions of leading versus following cells can be obtained.

A defining characteristic of cancer malignancy is invasion and metastasis 1. In some cancers (e.g. glioma 2), local invasion into surrounding healthy ...

3-Dimensional Resin Casting and Imaging of Mouse Portal Vein or Intrahepatic Bile Duct System

In organs, the correct architecture of vascular and ductal structures is indispensable for proper physiological function, and the formation and maintenance of these structures is a highly regulated process. The analysis of these complex, 3-dimensional structures has greatly depended on either 2-dimensional examination in section or on dye injection studies. These techniques, however, are not able to provide a complete and quantifiable representation of the ductal or vascular structures they are intended to elucidate. Alternatively, the nature of 3-dimensional plastic resin casts generates a permanent snapshot of the system and is a novel and widely useful technique for visualizing and quantifying 3-dimensional structures and networks.
A crucial advantage of the resin casting system is the ability to determine the intact and connected, or communicating, structure of a blood vessel or duct. The structure of vascular and ductal networks are crucial for organ function, and this technique has the potential to aid study of vascular and ductal networks in several ways. Resin casting may be used to analyze normal morphology and functional architecture of a luminal structure, identify developmental morphogenetic changes, and uncover morphological differences in tissue architecture between normal and disease states. Previous work has utilized resin casting to study, for example, architectural and functional defects within the mouse intrahepatic bile duct system that were not reflected in 2-dimensional analysis of the structure1,2, alterations in brain vasculature of a Alzheimer's disease mouse model3, portal vein abnormalities in portal hypertensive and cirrhotic mice4, developmental steps in rat lymphatic maturation between immature and adult lungs5, immediate microvascular changes in the rat liver, pancreas, and kidney in response in to chemical injury6.
Here we present a method of generating a 3-dimensional resin cast of a mouse vascular or ductal network, focusing specifically on the portal vein and intrahepatic bile duct. These casts can be visualized by clearing or macerating the tissue and can then be analyzed. This technique can be applied to virtually any vascular or ductal system and would be directly applicable to any study inquiring into the development, function, maintenance, or injury of a 3-dimensional ductal or vascular structure.

A method of visualizing and quantifying the 3-dimensional structure of mouse hepatic portal vein or intrahepatic bile duct is described. This resin cast technique can also be applied to other ductal or vascular systems and allows for in situ visualization or quantification of a system's intact communicating architecture.

In  organs, the correct architecture of vascular and ductal structures is  indispensable for proper physiological function, and the formation and  ...

Near Infrared Optical Projection Tomography for Assessments of &beta;-cell Mass Distribution in Diabetes Research

By adapting OPT to include the capability of imaging in the near infrared (NIR) spectrum, we here illustrate the possibility to image larger bodies of pancreatic tissue, such as the rat pancreas, and to increase the number of channels (cell types) that may be studied in a single specimen. We further describe the implementation of a number of computational tools that provide: 1/ accurate positioning of a specimen's (in our case the pancreas) centre of mass (COM) at the axis of rotation (AR)2; 2/ improved algorithms for post-alignment tuning which prevents geometric distortions during the tomographic reconstruction2 and 3/ a protocol for intensity equalization to increase signal to noise ratios in OPT-based BCM determinations3. In addition, we describe a sample holder that minimizes the risk for unintentional movements of the specimen during image acquisition. Together, these protocols enable assessments of BCM distribution and other features, to be performed throughout the volume of intact pancreata or other organs (e.g. in studies of islet transplantation), with a resolution down to the level of individual islets of Langerhans.

Near Infrared Optical Projection Tomography for Assessments of &amp;#946;-cell Mass Distribution in Diabetes Research

We describe the adaptation of optical projection tomography (OPT)1 to imaging in the near infrared spectrum, and the implementation of a number of computational tools. These protocols enable assessments of pancreatic &beta;-cell mass (BCM) in larger specimens, increase the multichannel capacity of the technique and increase the quality of OPT data.

By adapting OPT to include the capability of imaging in the near infrared (NIR) spectrum, we here illustrate the possibility to image larger bodies of ...

In Vivo, Percutaneous, Needle Based, Optical Coherence Tomography of Renal Masses

Optical coherence tomography (OCT) is the optical equivalent of ultrasound imaging, based on the backscattering of near infrared light. OCT provides real time images with a 15 &#181;m axial resolution at an effective tissue penetration of 2-3 mm. Within the OCT images the loss of signal intensity per millimeter of tissue penetration, the attenuation coefficient, is calculated. The attenuation coefficient is a tissue specific property, providing a quantitative parameter for tissue differentiation. 
Until now, renal mass treatment decisions have been made primarily on the basis of MRI and CT imaging characteristics, age and comorbidity. However these parameters and diagnostic methods lack the finesse to truly detect the malignant potential of a renal mass. A successful core biopsy or fine needle aspiration provides objective tumor differentiation with both sensitivity and specificity in the range of 95-100%. However, a non-diagnostic rate of 10-20% overall, and even up to 30% in SRMs, is to be expected, delaying the diagnostic process due to the frequent necessity for additional biopsy procedures. 
We aim to develop OCT into an optical biopsy, providing real-time imaging combined with on-the-spot tumor differentiation. This publication provides a detailed step-by-step approach for percutaneous, needle based, OCT of renal masses.

In Vivo, Percutaneous, Needle Based, Optical Coherence Tomography of Renal Masses

Optical coherence tomography (OCT) is a high resolution imaging technique that allows analysis of tissue specific optical properties providing the means for tissue differentiation. We developed needle based OCT, providing real-time imaging combined with on-the-spot tumor differentiation. This publication describes a method for percutaneous, needle based OCT of renal masses.

Optical coherence tomography (OCT) is the optical equivalent of ultrasound imaging, based on the backscattering of near infrared light. OCT provides real ...

Ultrahigh Resolution Mouse Optical Coherence Tomography to Aid Intraocular Injection in Retinal Gene Therapy Research

HR-SD-OCT is utilized to monitor the progression of photoreceptor degeneration in live mouse models, assess the delivery of therapeutic agents into the subretinal space, and to evaluate toxicity and efficacy in vivo. HR-SD-OCT uses near infrared light (800-880 nm) and has optics specifically designed for the unique optics of the mouse eye with sub-2-micron axial resolution. Transgenic mouse models of outer retinal (photoreceptor) degeneration and controls were imaged to assess the disease progression. Pulled glass microneedles were used to deliver sub retinal injections of adeno-associated virus (AAV) or nanoparticles (NP) via a trans-scleral and trans-choroidal approach. Careful positioning of the needle into the subretinal space was required prior to a calibrated pressure injection, which delivers fluid into the sub retinal space. Real time subretinal surgery was conducted on our retinal imaging system (RIS). HR-SD-OCT demonstrated progressive uniform retinal degeneration due to expression of a toxic mutant human mutant rhodopsin (P347S) (RHOP347S) transgene in mice. HR-SD-OCT allows rigorous quantification of all the retinal layers. Outer nuclear layer (ONL) thickness and photoreceptor outer segment length (OSL) measurements correlate with photoreceptor vitality, degeneration, or rescue. The RIS delivery system allows real-time visualization of subretinal injections in neonatal (~P10-14) or adult mice, and HR-SD-OCT immediately determines success of delivery and maps areal extent. HR-SD-OCT is a powerful tool that can evaluate the success of subretinal surgery in mice, in addition to measuring vitality of photoreceptors in vivo. HR-SD-OCT can also be used to identify uniform animal cohorts to evaluate the extent of retinal degeneration, toxicity, and therapeutic rescue in preclinical gene therapy research studies.

Here we demonstrate a novel approach to using high resolution spectral-domain optical coherence tomography (HR-SD-OCT) to assist delivery of gene therapy agents into the subretinal space, assess its areal coverage, and characterize photoreceptor vitality.

HR-SD-OCT is utilized to monitor the progression of photoreceptor degeneration in live mouse models, assess the delivery of therapeutic agents into the ...

In Vivo Imaging of Cx3cr1gfp/gfp Reporter Mice with Spectral-domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy

Spectral domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) are extensively used in experimental ophthalmology. In the present protocol, mice expressing green fluorescent protein (gfp) under the promoter of Cx3cr1 (BALB/c-Cx3cr1gfp/gfp) were used to image microglia cells in vivo in the retina. Microglia are resident macrophages of the retina and have been implicated in several retinal diseases1,2,3,4,5,6. This protocol provides a detailed approach for generation of retinal B-scans, with SD-OCT, and imaging of microglia cell distribution in Cx3cr1gfp/gfp mice with SLO in vivo, using an ophthalmic imaging platform system. The protocol can be used in several reporter mouse lines. However, there are some limitations to the protocol presented here. First, both SLO and SD-OCT, when used in the high-resolution mode, collect data with high axial resolution but the lateral resolution is lower (3.5 &#181;m and 6 &#181;m, respectively). Moreover, the focus and saturation level in SLO is highly dependent on parameter selection and correct alignment of the eye. Additionally, using devices designed for human patients in mice is challenging due to the higher total optical power of the mouse eye compared to the human eye; this can lead to lateral magnification inaccuracies7, which are also dependent on the magnification by the mouse lens among others. However, despite that the axial scan position is dependent upon lateral magnification, the axial SD-OCT measurements are accurate8.

In Vivo Imaging of Cx3cr1gfp/gfp Reporter Mice with Spectral-domain Optical Coherence Tomography and Scanning Laser Ophthalmoscopy

This protocol describes how high-resolution imaging techniques such as spectral domain optical coherence tomography and scanning laser ophthalmoscopy can be utilized in small rodents, using an ophthalmic imaging platform system, to obtain information on retinal thickness and microglial cell distribution, respectively.

Spectral domain optical coherence tomography (SD-OCT) and scanning laser ophthalmoscopy (SLO) are extensively used in experimental ophthalmology. In the ...

Ablation of Ischemic Ventricular Tachycardia Using a Multipolar Catheter and 3-dimensional Mapping System for High-density Electro-anatomical Reconstruction

Ventricular tachycardia (VT) in patients with ischemic cardiomyopathy mainly results from endocardial scars after myocardial infarction; those scars represent zones of slow conduction that allow the occurrence and maintenance of reentrant circuits. Catheter ablation enables substrate modification of those low voltage areas and thus can help to alter the scar tissue in such a way that arrhythmias cannot appear anymore. Hospitalizations of concerned patients decrease, quality of life and outcome rise. Consequently, VT ablation represents a growing field in electrophysiology, especially for patients with endocardial scars in ischemic heart disease after myocardial infarction. However, ablation of ventricular tachycardia remains one of the most challenging procedures in the electrophysiology lab. Precise scar definition and localization of abnormal potentials are critical for ablation success. The following manuscript describes the use of a multipolar mapping catheter and 3-dimensional (3D) mapping system to create a high density electro-anatomical map of the left ventricle including a precise scar representation as well as mapping of fractionated and late potentials in order to allow a highly accurate substrate modification.

With the following protocol, we provide an approach to Ventricular Tachycardia (VT) ablation using high density mapping with a multipolar catheter and 3D mapping system enhancing the success of the procedure.

Ventricular tachycardia (VT) in patients with ischemic cardiomyopathy mainly results from endocardial scars after myocardial infarction; those scars ...

Quantitative Analysis of Cellular Composition in Advanced Atherosclerotic Lesions of Smooth Muscle Cell Lineage-Tracing Mice

Atherosclerosis remains the leading cause of death worldwide and, despite countless preclinical studies describing promising therapeutic targets, novel interventions have remained elusive. This is likely due, in part, to a reliance on preclinical prevention models investigating the effects of genetic manipulations or pharmacological treatments on atherosclerosis development rather than the established disease. Also, results of these studies are often confounding because of the use of superficial lesion analyses and a lack of characterization of lesion cell populations. To help overcome these translational hurdles, we propose an increased reliance on intervention models that employ investigation of changes in cellular composition at a single cell level by immunofluorescent staining and confocal microscopy. To this end, we describe a protocol for testing a putative therapeutic agent in a murine intervention model including a systematic approach for animal dissection, embedding, sectioning, staining, and quantification of brachiocephalic artery lesions. In addition, due to the phenotypic diversity of cells within late-stage atherosclerotic lesions, we describe the importance of using cell-specific, inducible lineage tracing mouse systems and how this can be leveraged for unbiased characterization of atherosclerotic lesion cell populations. Together, these strategies may assist vascular biologists to more accurately model therapeutic interventions and analyze atherosclerotic disease and will hopefully translate into a higher rate of success in clinical trials.

We propose a standardized protocol to characterize the cellular composition of late-stage murine atherosclerotic lesions including systematic methods of animal dissection, tissue embedding, sectioning, staining, and analysis of brachiocephalic arteries from atheroprone smooth muscle cell lineage tracing mice.

Atherosclerosis remains the leading cause of death worldwide and, despite countless preclinical studies describing promising therapeutic targets, novel ...

High-Throughput Analysis of Optical Mapping Data Using ElectroMap

Optical mapping is an established technique for high spatio-temporal resolution study of cardiac electrophysiology in multi-cellular preparations. Here we present, in a step-by-step guide, the use of ElectroMap for analysis, quantification, and mapping of high-resolution voltage and calcium datasets acquired by optical mapping. ElectroMap analysis options cover a wide variety of key electrophysiological parameters, and the graphical user interface allows straightforward modification of pre-processing and parameter definitions, making ElectroMap applicable to a wide range of experimental models. We show how built-in pacing frequency detection and signal segmentation allows high-throughput analysis of entire experimental recordings, acute responses, and single beat-to-beat variability. Additionally, ElectroMap incorporates automated multi-beat averaging to improve signal quality of noisy datasets, and here we demonstrate how this feature can help elucidate electrophysiological changes that might otherwise go undetected when using single beat analysis. Custom modules are included within the software for detailed investigation of conduction, single file analysis, and alternans, as demonstrated here. This software platform can be used to enable and accelerate the processing, analysis, and mapping of complex cardiac electrophysiology.

This protocol describes the setup and use of ElectroMap, a MATLAB-based open-source software platform for analysis of cardiac optical mapping data. ElectroMap provides a versatile high-throughput tool for analysis of optical mapping voltage and calcium datasets across a wide range of cardiac experimental models.

Optical mapping is an established technique for high spatio-temporal resolution study of cardiac electrophysiology in multi-cellular preparations. Here we ...