Name: high-resolution fiber-optic microendoscopy for in situ cellular imaging
Uploaded: 2011-01-11T22:01:00
Duration: 13 min 49 s
Description: Watch this Scientific Journal Video about High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging at JoVE.com

This research was partly funded by the National Institutes of Health, grant R01 EB007594, the Department of Defense Breast Cancer Research Program, proposal BCO74699P7, and the Susan G. Komen Foundation grant 26152/98188972.

1. Microendoscope Assembly
The high-resolution microendoscope described here (figure 1a) should be considered as a base configuration with several variations possible in assembly and application. We describe in detail here an embodiment of the platform which is designed to be used with proflavine as a fluorescent contrast agent. Proflavine is a bright nuclear stain with peak absorption and emission wavelengths of 445 nm and 515 nm respectively. The use of other contrast agents will require the user to select excitation, emission, and dichroic filters appropriately. Several elements of the high-resolution microendoscope are generic and may be obtained from multiple vendors. For example, optomechanical positioning components are available from Thorlabs, Newport, Linos among others. Compact CCD cameras are available from companies including Point Grey Research, Prosilica, and Retiga; camera sensitivity should be chosen with consideration of the brightness of the fluorophore to be used, as well as the desired frame rate. High-power light emitting diodes (LEDs) may be obtained from Luxeon, Cree, and Nichia among others. Fiber-optic bundles are available from Sumitomo, Fujikura, and Schott. In selecting components for a specific application, the user should consider the inherent relationships involved in fluorescence microscopy between fluorophore concentration, photobleaching, illumination intensity, camera sensitivity, gain, and exposure time.
<ol>
<li>Connect the 6" cage rods to the 1.5" cage rods, to form a pair of 7.5" long rods. Screw these rods into one face of the fold mirror unit. Screw the 0.5" rods into the opposite face. Slide the cage cube onto the cage rods, via the two lower through holes. Screw the 2" rods into the side face of the cage cube (figure 1b).</li>
<li>Attach the camera to a cage plate by using a C-mount to SM1 adapter. Secure the cage plate on the 0.5" cage rods, flush with the face of the fold mirror unit.</li>
<li>Insert the "tube" lens into a 3" long lens tube and secure the lens with a retaining ring. The focal length of the lens should be selected such that the cores of the fiber-optic bundle are sampled by at least two pixels when projected onto the camera. Drop the emission filter into the tube on top of the first retaining ring, and add another ring to secure the filter in place. Observe the filter orientation convention indicated by the filter manufacturer. Screw the lens tube into the side of the cage cube nearest to the CCD camera. Note that in figure 1c, this lens and filter are shown without the 3" lens tube for clarity.</li>
<li>Connect the camera to a computer and view the image on screen. Direct the cage assembly at a distant object and slide the cage cube along the rails until an image appears in focus. Lock down the cage cube at this location. (This is a simple method of ensuring that the tube lens will form a focused image when combined with the infinity-corrected objective lens).</li>
<li>Insert the dichroic mirror into the holder and place at 45&deg; in the cage cube.</li>
<li>Screw the objective lens, via a RMS to SM1 thread adapter and an adjustable lens tube, into the face of the cage cube opposite the tube lens holder. A z-translator may be used in place of the adjustable lens tube for easier focusing. Screw an SMA connector into a cage plate and mount this on the rods, approximately at the working distance of the objective lens.</li>
<li>Mount an LED on a cage plate and slide onto the end of the 2" rods. Add a lens to a 0.5" lens tube such that when this tube is screwed into the side of the cage cube, it will form an image of the LED that fills the back aperture of the objective lens. This (Kohler illumination) configuration will ensure that the proximal face of the fiber-optic bundle is uniformly illuminated. Add the excitation filter to the 0.5" lens tube and secure in place with a retaining ring (figure 1c).</li>
<li>Attach a SMA connector to a fiber-optic bundle. Screw the SMA connectorized bundle into the SMA receptacle mounted on the cage rods. Direct the distal end of the bundle towards a broadband light source (fluorescent lighting will suffice) and observe the image of the bundle proximal face on the CCD camera. Adjust the position of the objective lens by screwing in or out of the cage cube until the fiber bundle image appears in focus. The individual cores should be clearly visible (Figure 2).</li>
</ol>
2. GRIN Lens Assembly
The spatial resolution of the microendoscope can be increased by attaching a micro-lens or lens assembly to the distal tip of the fiber bundle. These optics are configured such that instead of placing the bundle tip directly on to the tissue, the tip is imaged onto the tissue surface with demagnification, thereby increasing the spatial sampling frequency imposed by the light-guiding cores of the fiber bundle. The degree of demagnification corresponds to the increase in spatial resolution, and at the same time, to a proportionate decrease in field-of-view. Gradient index (GRIN) lens components are compatible with fiber-optics and are available from GrinTech, NSG, Schott, among others, and can be directly bonded to the distal tip of a fiber bundle.
<ol>
<li>Select a GRIN lens with the desired magnification and working distance for your application. Ensure that the diameter of the lens exceeds that of the fiber bundle you plan to work with. We recommend that the fiber bundle and GRIN lens be mounted on separate 3-axis manual positioning stages under a low power microscope or stereoscope for accurate alignment prior to bonding.</li>
<li>Place a drop of optical adhesive (eg. Norland UV curing adhesive) on either the lens or bundle face. Bring the two components into contact by using the manual positioners. Expose the interface to UV light for the dose recommended by the manufacturer.</li>
<li>To protect the GRIN lens and the bonded interface, a short length of aluminum capillary tubing (Small Parts Inc.) can be used to enclose the joint. Slide the tubing over the joint and secure in place with epoxy. Heat shrink tubing can be used to finish the assembly.</li>
</ol>
3. Microendoscope Imaging
<ol>
<li>Apply the contrast agent to the cells or tissue to be imaged. With proflavine (0.01% w/v in PBS), in vitro imaging of cells in culture can be performed by brief incubation (&lt; 1 minute) and thorough rinsing. Imaging of ex vivo tissue specimens or in vivo tissues is possible following topical application of the dye. Uptake of proflavine under these conditions has been found to be near-instantaneous, with imaging possible within a few seconds and lasting for several minutes.</li>
<li>Place the fiber optic bundle in light contact with the sample to be imaged. When imaging cells in culture or ex vivo tissue specimens, we recommend mounting the distal end of the fiber bundle in a secure fixture with manual positioning stages on XYZ axes for stability during imaging.</li>
</ol>
4. Representative Results:

When assembled correctly, the microendoscope will operate as an epi-fluorescence microscope, relayed through a coherent fiber-optic bundle. For optimal imaging results, attention should be paid to ensuring that three key conditions are met:
<ol>
<li>The proximal face of the fiber bundle should be imaged onto the CCD camera without defocus, in order to achieve the full resolution of the system. Figure 2a,b,c demonstrate a portion of a fiber bundle imaged with poor focus, slight defocus, and good focus, respectively. The optimum focus is found by adjusting the axial position of the objective lens relative to the bundle face.</li>
<li>The proximal face of the fiber bundle should be uniformly illuminated over its full diameter (field-of-view). As described in the Protocol Text (1.7), this is achieved by configuring the illumination optics for Kohler illumination. Figure 2d shows an image acquired when a uniform fluorescent sample is illuminated in this preferred configuration, with Figure 2e demonstrating the corresponding result under critical illumination. In the latter case, the structure of the LED is imaged onto the fiber bundle face, resulting in the appearance of this unwanted pattern superimposed upon the true sample structure.</li>
<li>Both the proximal and distal faces of the fiber bundle should be clean and free of scratches and chips. Figure 2f demonstrates the presence of debris attached to the bundle face, with damage in the form of a small chip at 5 o'clock on the fiber perimeter. Debris can be removed from the bundle faces by cleaning in the same fashion as conventional fiber-optic connectors, with lens paper and isopropanol, or standard fiber-optic cleaning tools. If either end of the fiber bundle is scratched or chipped, or if the bundle breaks along its length, the face may be polished flat by standard manual, or mechanical polishing techniques. We recommend 12-15 &mu;m lapping paper for an initial coarse polish, with a final polish on 0.5-1.0 &mu;m paper.</li>
</ol>
Figure 3a demonstrates imaging of 1483 cells in vitro, following labeling with proflavine and light placement of the bare fiber bundle on the sample. Figure 3b demonstrates the improvement in spatial resolution and reduction in field-of-view provided by a 2.5x GRIN lens bonded to the bundle tip. Movie 1 demonstrates in vivo imaging of the mammary fat pad in a mouse model. Here, a fiber bundle with 0.5 mm outer diameter (330 &mu;m field-of-view) was passed through a 21-gauge needle and advanced into the tissue. Fat cells are clearly visible, with motion due to the cardiac cycle apparent in this acquisition at 15 frames per second. Figure 3c demonstrates imaging of the oral mucosa in a healthy human volunteer, this time using a larger fiber bundle with 1.5 mm outer diameter (1.4 mm field-of-view). In all examples shown, proflavine was used as a nuclear labeling fluorescent contrast agent.

 <img src="/files/ftp_upload/2306/2306fig1.jpg" alt="Figure 1" /> 
Figure 1. Assembling the high-resolution microendoscope (HRME). (a) Schematic diagram of the HRME system. (b) Assembly of the main optomechanical support structure. (c) Addition of optical elements, illumination LED, and CCD camera. (d) Photograph of the HRME system, packaged in a 10" x 8" x 2.5" enclosure.
 <img src="/files/ftp_upload/2306/2306fig2.jpg" alt="Figure 2" /> 
Figure 2. Setting up the HRME. Examples of imaging with the fiber-optic bundle in (a) poor focus, (b) close to good focus, (c) ideal focus. In (d), a uniform fluorescent target at the bundle's distal tip is imaged under Kohler (uniform) illumination. (e) A uniform fluorescent target imaged under critical illumination, with the source structure apparent on the object. (f) Loose tissue and cells can stick to the fiber bundle face, which is also prone to minor damage at its periphery.
 <img src="/files/ftp_upload/2306/2306fig3.jpg" alt="Figure 3" /> 
Figure 3. Imaging with the HRME. (a) 1483 cells in vitro, imaged with a bare fiber bundle (IGN-08/30) following labeling with proflavine 0.01% (w/v). (b) The same 1483 cell culture as shown in (a), imaged with a fiber bundle with 2.5x GRIN lens attached. (c) Image of normal human oral mucosa in vivo, following topical application of proflavine 0.01% (w/v).
Movie 1. Imaging the mammary fat pad of a mouse via insertion of a 450 &mu;m outer diameter fiber bundle within the lumen of a 21-gauge needle passed into the tissue. Proflavine 0.01% (w/v) was delivered to the imaging site through the same needle prior to insertion of the imaging fiber. <a href="https://www.jove.com/files/ftp_upload/2306/5-11-1 2306_Pierce_movie1.avi">Click here to watch video</a>

<ol>
	<li>Pierce, M. C., Javier, D. J., Richards-Kortum, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optical+contrast+agents+and+imaging+systems+for+detection+and+diagnosis+of+cancer.">Optical contrast agents and imaging systems for detection and diagnosis of cancer.</a> Int. J. Cancer. 123, 1979-1990 (2008).</li><li>Muldoon, T. J., Pierce, M. C., Nida, D. L., Williams, M. D., Gillenwater, A., Richards-Kortum, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Subcellular-resolution+molecular+imaging+within+living+tissue+by+fiber+microendoscopy.">Subcellular-resolution molecular imaging within living tissue by fiber microendoscopy.</a> Opt. Express. 15, 16413-16423 (2007).</li><li>Muldoon, T. J., Anandasabapathy, S., Maru, D., Richards-Kortum, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High-resolution+imaging+in+Barrett's+esophagus:+a+novel,+low-cost+endoscopic+microscope.">High-resolution imaging in Barrett's esophagus: a novel, low-cost endoscopic microscope.</a> Gastrointest. Endosc. 68, 737-744 (2008).</li><li>Muldoon, T. J., Thekkek, N., Roblyer, D., Maru, D., Harpaz, N., Potack, J., Anandasabapathy, S., Richards-Kortum, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Evaluation+of+quantitative+image+analysis+criteria+for+the+high-resolution+microendoscopic+detection+of+neoplasia+in+Barrett's+esophagus.">Evaluation of quantitative image analysis criteria for the high-resolution microendoscopic detection of neoplasia in Barrett's esophagus.</a> J. Biomed. Opt. 15, 026027-026027 (2010).</li><li>Zhong, W., Celli, J. P., Rizvi, I., Mai, Z., Spring, B. Q., Yun, S. H., Hasan, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+high-resolution+fluorescence+microendoscopy+for+ovarian+cancer+detection+and+treatment+monitoring.">In vivo high-resolution fluorescence microendoscopy for ovarian cancer detection and treatment monitoring.</a> Br. J. Cancer. 101, 2015-2022 (2009).</li><li>Dubaj, V., Mazzolini, A., Wood, A., Harris, M. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Optic+fibre+bundle+contact+imaging+probe+employing+a+laser+scanning+confocal+microscope.">Optic fibre bundle contact imaging probe employing a laser scanning confocal microscope.</a> J. Microsc. 207, 108-117 (2002).</li><li>Dromard, T., Ravaine, V., Ravaine, S., L&#233;v&#234;que, J. -. L., Sojic, N. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Remote+in+vivo+imaging+of+human+skin+corneocytes+by+means+of+an+optical+fiber+bundle.">Remote in vivo imaging of human skin corneocytes by means of an optical fiber bundle.</a> Rev. Sci. Inst. 78, 053709-05 (2007).</li><li>Udovich, J. A., Kirkpatrick, N. D., Kano, A., Tanbakuchi, A., Utzinger, U., Gmitro, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Spectral+background+and+transmission+characteristics+of+fiber+optic+imaging+bundles.">Spectral background and transmission characteristics of fiber optic imaging bundles.</a> Appl. Opt. 47, 4560-4568 (2008).</li><li>Barretto, R. P. J., Messerschmidt, B., Schnitzer, M. J. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=In+vivo+fluorescence+imaging+with+high-resolution+microlenses.">In vivo fluorescence imaging with high-resolution microlenses.</a> Nat. Methods. 6, 511-512 (2009).</li><li>Rouse, A. R., Kano, A., Udovich, J. A., Kroto, S. M., Gmitro, A. F. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Design+and+demonstration+of+a+miniature+catheter+for+a+confocal+microendoscope.">Design and demonstration of a miniature catheter for a confocal microendoscope.</a> Appl. Opt. 43, 5763-5771 (2004).</li><li>Kester, R. T., Christenson, T., Richards-Kortum, R., Tkaczyk, T. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Low+cost,+high+performance,+self-aligning+miniature+optical+systems.">Low cost, high performance, self-aligning miniature optical systems.</a> Appl. Opt. 48, 3375-3384 (2009).</li></ol>

MP and DY have nothing to disclose. RRK holds patents relating to microendoscopic imaging platforms.

The high-resolution microendoscopy technique described here provides researchers in the basic biomedical and clinical research areas with a flexible, robust, and cost-effective method for visualizing cellular detail in situ. We have described a protocol for assembling the imaging system and demonstrated its use in cell culture in vitro, and in animal, and human tissues in vivo. While the imaging results presented here used proflavine as a fluorescent contrast agent, other groups have demonstrated versions of the system with LED illumination wavelengths and filters chosen to match excitation / emission spectra of other dyes 5-7.
Resolution and field-of-view are initially determined by the core-to-core spacing and imaging diameter of the fiber-optic bundle. We have used bundles with approximately 4 &mu;m core-core spacing, and imaging diameters of 330 &mu;m (movie 1), 720 &mu;m (Figure 2, Figure 3a,b), and 1400 &mu;m (Figure 3c). The smaller bundles can be passed through narrower gauge needles and are significantly more flexible than the larger fibers. We and others 8 have, in some cases, noted the appearance of autofluorescence emissions from the fiber bundle itself. When attempting to excite fluorophores at UV wavelengths, or collect emission in the red spectral range, attention should be paid to the level of fiber bundle autofluorescence contributing to the overall measured signal.
While most of the high-resolution microendoscopy work reported to-date has used a bare fiber bundle, additional magnification can be provided by use of GRIN lenses bonded to the distal tip. GRIN lenses offer a straightforward and economical way to increase spatial resolution, though their susceptibility to optical aberrations and limited NA is well recognized. If GRIN lens performance is inadequate for a particular application, hybrid GRIN / spherical lens objectives 9 or miniature objective lens assemblies 10-11 can be employed.
The high-resolution microendoscope described here essentially operates as a wide-field epi-fluorescence microscope; therefore no optical sectioning (as in confocal or nonlinear microscopy) is to be expected. In our experience, using 455 nm excitation light and topical proflavine as a contrast agent, light is primarily collected from a depth corresponding to a few cell layers.
This protocol ought to enable the reader to assemble the high-resolution microendoscope on the benchtop, with a compact footprint of 10" x 8". If desired, the system may be enclosed in a box and the electrical components (LED and camera) powered by a battery pack (Figure 1d). Many compact cameras can be powered by the IEEE-1394 (Firewire) and USB ports of the host computer.

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		<div>
		<table border="1">
		<thead>
		<tr>
		<th>Material Name</th>
		<th>Type</th>
		<th>Company</th>
		<th>Catalogue Number</th>
		<th>Comment</th>
		</tr>
		</thead>
		<tbody>
		
<tr>
<td>CCD camera</td>
<td>&nbsp;</td>
<td>Point Grey Research</td>
<td>GRAS-14S5M</td>
<td>&nbsp;</td>
<tr>
<td>LED</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>M455L2</td>
<td>Selected for use with proflavine &#x2013; other fluorophores may require different parts</td>
</tr>
<tr>
<td>Excitation filter</td>
<td>&nbsp;</td>
<td>Semrock</td>
<td>452/45</td>
<td>Selected for use with proflavine &#x2013; other fluorophores may require different parts</td>
</tr>
<tr>
<td>Emission filter</td>
<td>&nbsp;</td>
<td>Semrock</td>
<td>550/88</td>
<td>Selected for use with proflavine &#x2013; other fluorophores may require different parts</td>
</tr>
<tr>
<td>Dichroic mirror</td>
<td>&nbsp;</td>
<td>Chroma</td>
<td>485 DCLP</td>
<td>Selected for use with proflavine &#x2013; other fluorophores may require different parts</td>
</tr>
<tr>
<td>Objective lens</td>
<td>&nbsp;</td>
<td>Thorlabs (Olympus)</td>
<td>RMS 10X</td>
<td>&nbsp;</td>
<tr>
<td>Tube lens</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>AC-254-150-A1</td>
<td>Select focal length to achieve required magnification to CCD</td>
</tr>
<tr>
<td>Condenser lens</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>ACL2520</td>
<td>&nbsp;</td>
<tr>
<td>Cage cube unit</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>C6W, B1C, B3C, B5C, SM1CP2</td>
<td>&nbsp;</td>
<tr>
<td>Cage rods and plates</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>ER05 (x4), ER1.5 (x2), ER2 (x2), ER6 (x2), CP02 (x3)</td>
<td>&nbsp;</td>
<tr>
<td>Fold mirror unit</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>KCB1, PF10-03-G01</td>
<td>&nbsp;</td>
<tr>
<td>Lens tubes</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>SM1L05, SM1L30, SM1V05 (or SM1Z)</td>
<td>&nbsp;</td>
<tr>
<td>Adapters / couplers</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>SM1A3, SM1A9, SM1T2 (x2)</td>
<td>&nbsp;</td>
<tr>
<td>SMA connectors</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>SM1SMA, 11040A</td>
<td>&nbsp;</td>
<tr>
<td>LED driver</td>
<td>&nbsp;</td>
<td>Thorlabs</td>
<td>LEDD1B TPS001</td>
<td>&nbsp;</td>
<tr>
<td>Fiber optic bundle</td>
<td>&nbsp;</td>
<td>Sumitomo</td>
<td>IGN-08/30</td>
<td>Larger or smaller bundles are available (Sumitomo / Fujikura)</td>
</tr>		</tbody>
		</table>
		</div>

high-resolution fiber-optic microendoscopy for in situ cellular imaging

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution. Traditionally, multiple experiments are run in parallel, with individual samples removed from the study at sequential time points for evaluation by light microscopy. Several intravital techniques have been developed, with confocal, multiphoton, and second harmonic microscopy all demonstrating their ability to be used for imaging in situ 1. With these systems, however, the required infrastructure is complex and expensive, involving scanning laser systems and complex light sources. Here we present a protocol for the design and assembly of a high-resolution microendoscope which can be built in a day using off-the-shelf components for under US$5,000. The platform offers flexibility in terms of image resolution, field-of-view, and operating wavelength, and we describe how these parameters can be easily modified to meet the specific needs of the end user.
We and others have explored the use of the high-resolution microendoscope (HRME) in in vitro cell culture 2-5, in excised 6 and living animal tissues 2,5, and in human tissues in vivo 2,7. Users have reported the use of several different fluorescent contrast agents, including proflavine 2-4, benzoporphyrin-derivative monoacid ring A (BPD-MA) 5, and fluoroscein 6,7, all of which have received full, or investigational approval from the FDA for use in human subjects. High-resolution microendoscopy, in the form described here, may appeal to a wide range of researchers working in the basic and clinical sciences. The technique offers an effective and economical approach which complements traditional benchtop microscopy, by enabling the user to perform high-resolution, longitudinal imaging in situ.

Watch this Scientific Journal Video about High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging at JoVE.com

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

In many biological and clinical situations it is advantageous to study cellular processes as they evolve in their native microenvironment. Here we describe the assembly and use of a low-cost fiber-optic microscope which can provide real time imaging in cell culture, animal studies, and clinical patient studies.

High-resolution Fiber-optic Microendoscopy for in situ Cellular Imaging

Many biological and clinical studies require the longitudinal study and analysis of morphology and function with cellular level resolution.  ...

high-resolution-fiber-optic-microendoscopy-for-situ-cellular

Research

JoVE Journal

Bioengineering

High Resolution 3D Imaging of Ex-Vivo Biological Samples by Micro CT

Non-destructive volume visualization can be achieved only by tomographic techniques, of which the most efficient is the x-ray micro computerized tomography (&mu;CT).
High resolution &mu;CT is a very versatile yet accurate (1-2 microns of resolution) technique for 3D examination of ex-vivo biological samples1, 2. As opposed to electron tomography, the &mu;CT allows the examination of up to 4 cm thick samples. This technique requires only few hours of measurement as compared to weeks in histology. In addition, &mu;CT does not rely on 2D stereologic models, thus it may complement and in some cases can even replace histological methods3, 4, which are both time consuming and destructive. Sample conditioning and positioning in &mu;CT is straightforward and does not require high vacuum or low temperatures, which may adversely affect the structure. The sample is positioned and rotated 180&deg; or 360&deg;between a microfocused x-ray source and a detector, which includes a scintillator and an accurate CCD camera, For each angle a 2D image is taken, and then the entire volume is reconstructed using one of the different available algorithms5-7. The 3D resolution increases with the decrease of the rotation step. The present video protocol shows the main steps in preparation, immobilization and positioning of the sample followed by imaging at high resolution.

High Resolution 3D Imaging of Ex-Vivo Biological Samples by Micro CT

Non-destructive volume visualization can be achieved only by tomographic techniques, of which the most efficient is the x-ray micro computerized tomography ( CT).

Non-destructive volume visualization can be achieved only by tomographic techniques, of which the most efficient is the x-ray micro computerized ...

Video-rate Scanning Confocal Microscopy and Microendoscopy

Confocal microscopy has become an invaluable tool in biology and the biomedical sciences, enabling rapid, high-sensitivity, and high-resolution optical sectioning of complex systems. Confocal microscopy is routinely used, for example, to study specific cellular targets1, monitor dynamics in living cells2-4, and visualize the three dimensional evolution of entire organisms5,6. Extensions of confocal imaging systems, such as confocal microendoscopes, allow for high-resolution imaging in vivo7 and are currently being applied to disease imaging and diagnosis in clinical settings8,9.
Confocal microscopy provides three-dimensional resolution by creating so-called "optical sections" using straightforward geometrical optics. In a standard wide-field microscope, fluorescence generated from a sample is collected by an objective lens and relayed directly to a detector. While acceptable for imaging thin samples, thick samples become blurred by fluorescence generated above and below the objective focal plane. In contrast, confocal microscopy enables virtual, optical sectioning of samples, rejecting out-of-focus light to build high resolution three-dimensional representations of samples.
Confocal microscopes achieve this feat by using a confocal aperture in the detection beam path. The fluorescence collected from a sample by the objective is relayed back through the scanning mirrors and through the primary dichroic mirror, a mirror carefully selected to reflect shorter wavelengths such as the laser excitation beam while passing the longer, Stokes-shifted fluorescence emission. This long-wavelength fluorescence signal is then passed to a pair of lenses on either side of a pinhole that is positioned at a plane exactly conjugate with the focal plane of the objective lens. Photons collected from the focal volume of the object are collimated by the objective lens and are focused by the confocal lenses through the pinhole. Fluorescence generated above or below the focal plane will therefore not be collimated properly, and will not pass through the confocal pinhole1, creating an optical section in which only light from the microscope focus is visible. (Fig 1). Thus the pinhole effectively acts as a virtual aperture in the focal plane, confining the detected emission to only one limited spatial location.
Modern commercial confocal microscopes offer users fully automated operation, making formerly complex imaging procedures relatively straightforward and accessible. Despite the flexibility and power of these systems, commercial confocal microscopes are not well suited for all confocal imaging tasks, such as many in vivo imaging applications. Without the ability to create customized imaging systems to meet their needs, important experiments can remain out of reach to many scientists.
In this article, we provide a step-by-step method for the complete construction of a custom, video-rate confocal imaging system from basic components. The upright microscope will be constructed using a resonant galvanometric mirror to provide the fast scanning axis, while a standard speed resonant galvanometric mirror will scan the slow axis. To create a precise scanned beam in the objective lens focus, these mirrors will be positioned at the so-called telecentric planes using four relay lenses. Confocal detection will be accomplished using a standard, off-the-shelf photomultiplier tube (PMT), and the images will be captured and displayed using a Matrox framegrabber card and the included software.

The complete construction of a custom, real-time confocal scanning imaging system is described. This system, which can be readily used for video-rate microscopy and microendoscopy, allows for an array of imaging geometries and applications not accessible using standard commercial confocal systems, at a fraction of the cost.

Confocal microscopy has become an invaluable tool in biology and the biomedical sciences, enabling rapid, high-sensitivity, and high-resolution optical ...

Cellular Lipid Extraction for Targeted Stable Isotope Dilution Liquid Chromatography-Mass Spectrometry Analysis

The metabolism of fatty acids, such as arachidonic acid (AA) and linoleic acid (LA), results in the formation of oxidized bioactive lipids, including numerous stereoisomers1,2. These metabolites can be formed from free or esterified fatty acids. Many of these oxidized metabolites have biological activity and have been implicated in various diseases including cardiovascular and neurodegenerative diseases, asthma, and cancer3-7. Oxidized bioactive lipids can be formed enzymatically or by reactive oxygen species (ROS). Enzymes that metabolize fatty acids include cyclooxygenase (COX), lipoxygenase (LO), and cytochromes P450 (CYPs)1,8. Enzymatic metabolism results in enantioselective formation whereas ROS oxidation results in the racemic formation of products.
While this protocol focuses primarily on the analysis of AA- and some LA-derived bioactive metabolites; it could be easily applied to metabolites of other fatty acids. Bioactive lipids are extracted from cell lysate or media using liquid-liquid (l-l) extraction. At the beginning of the l-l extraction process, stable isotope internal standards are added to account for errors during sample preparation. Stable isotope dilution (SID) also accounts for any differences, such as ion suppression, that metabolites may experience during the mass spectrometry (MS) analysis9. After the extraction, derivatization with an electron capture (EC) reagent, pentafluorylbenzyl bromide (PFB) is employed to increase detection sensitivity10,11. Multiple reaction monitoring (MRM) is used to increase the selectivity of the MS analysis. Before MS analysis, lipids are separated using chiral normal phase high performance liquid chromatography (HPLC). The HPLC conditions are optimized to separate the enantiomers and various stereoisomers of the monitored lipids12. This specific LC-MS method monitors prostaglandins (PGs), isoprostanes (isoPs), hydroxyeicosatetraenoic acids (HETEs), hydroxyoctadecadienoic acids (HODEs), oxoeicosatetraenoic acids (oxoETEs) and oxooctadecadienoic acids (oxoODEs); however, the HPLC and MS parameters can be optimized to include any fatty acid metabolites13.
Most of the currently available bioanalytical methods do not take into account the separate quantification of enantiomers. This is extremely important when trying to deduce whether or not the metabolites were formed enzymatically or by ROS. Additionally, the ratios of the enantiomers may provide evidence for a specific enzymatic pathway of formation. The use of SID allows for accurate quantification of metabolites and accounts for any sample loss during preparation as well as the differences experienced during ionization. Using the PFB electron capture reagent increases the sensitivity of detection by two orders of magnitude over conventional APCI methods. Overall, this method, SID-LC-EC-atmospheric pressure chemical ionization APCI-MRM/MS, is one of the most sensitive, selective, and accurate methods of quantification for bioactive lipids.

This protocol will demonstrate the extraction and analysis of free and esterified bioactive fatty acids from cells. Fatty acids are accurately quantified using stable isotope dilution, chiral liquid chromatography, electron capture atmospheric chemical ionization multiple reaction monitoring mass spectrometry (SID-LC-ECAPCI-MRM/MS).

The metabolism of fatty acids, such as arachidonic acid (AA) and linoleic acid (LA), results in the formation of oxidized bioactive lipids, including ...

Continuous High-resolution Microscopic Observation of Replicative Aging in Budding Yeast

We demonstrate the use of a simple microfluidic setup, in which single budding yeast cells can be tracked throughout their entire lifespan. The microfluidic chip exploits the size difference between mother and daughter cells using an array of micropads. Upon loading, cells are trapped underneath these micropads, because the distance between the micropad and cover glass is similar to the diameter of a yeast cell (3-4 &mu;m). After the loading procedure, culture medium is continuously flushed through the chip, which not only creates a constant and defined environment throughout the entire experiment, but also flushes out the emerging daughter cells, which are not retained underneath the pads due to their smaller size. The setup retains mother cells so efficiently that in a single experiment up to 50 individual cells can be monitored in a fully automated manner for 5 days or, if necessary, longer. In addition, the excellent optical properties of the chip allow high-resolution imaging of cells during the entire aging process.

We describe here the operation of a microfluidic device that allows continuous and high-resolution microscopic imaging of single budding yeast cells during their complete replicative and/or chronological lifespan.

We demonstrate the use of a simple microfluidic setup, in which single budding yeast cells can be tracked throughout their entire lifespan. The ...

High-resolution Spatiotemporal Analysis of Receptor Dynamics by Single-molecule Fluorescence Microscopy

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., kinetics, coexistence of different states and populations, transient interactions), which are typically hidden in ensemble measurements, such as those obtained with standard biochemical or microscopy methods. Thus, dynamic events, such as receptor-receptor interactions, can be followed in real time in a living cell with high spatiotemporal resolution. This protocol describes a method based on labeling with small and bright organic fluorophores and total internal reflection fluorescence (TIRF) microscopy to directly visualize single receptors on the surface of living cells. This approach allows one to precisely localize receptors, measure the size of receptor complexes, and capture dynamic events such as transient receptor-receptor interactions. The protocol provides a detailed description of how to perform a single-molecule experiment, including sample preparation, image acquisition and image analysis. As an example, the application of this method to analyze two G-protein-coupled receptors, i.e., &#946;2-adrenergic and &#947;-aminobutyric acid type B (GABAB) receptor, is reported. The protocol can be adapted to other membrane proteins and different cell models, transfection methods and labeling strategies.

This protocol describes how to use total internal reflection fluorescence microscopy to visualize and track single receptors on the surface of living cells and thereby analyze receptor lateral mobility, size of receptor complexes as well as to visualize transient receptor-receptor interactions. This protocol can be extended to other membrane proteins.

Single-molecule microscopy is emerging as a powerful approach to analyze the behavior of signaling molecules, in particular concerning those aspect (e.g., ...

Preparation of Mica Supported Lipid Bilayers for High Resolution Optical Microscopy Imaging

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction with other compounds, such as drugs or peptides. However SLB characteristics differ depending on the support used. 
Commonly used techniques for SLB imaging and measurements are single molecule fluorescence microscopy, FCS and atomic force microscopy (AFM). Because most optical imaging studies are carried out on a glass support, while AFM requires an extremely flat surface (generally mica), results from these techniques cannot be compared directly, since the charge and smoothness properties of these materials strongly influence diffusion. Unfortunately, the high level of manual dexterity required for the cutting and gluing thin slices of mica to the glass slide presents a hurdle to routine use of mica for SLB preparation. Although this would be the method of choice, such prepared mica surfaces often end up being uneven (wavy) and difficult to image, especially with small working distance, high numerical aperture lenses. Here we present a simple and reproducible method for preparing thin, flat mica surfaces for lipid vesicle deposition and SLB preparation. Additionally, our custom made chamber requires only very small volumes of vesicles for SLB formation. The overall procedure results in the efficient, simple and inexpensive production of high quality lipid bilayer surfaces that are directly comparable to those used in AFM studies.

We present a method of preparing mica supported lipid bilayers for high resolution microscopy. Mica is transparent and flat on an atomic scale, but rarely used in imaging because of handling difficulties; our preparation results in even deposition of the mica sheet, and reduces the material used in bilayer preparation.

Supported lipid bilayers (SLBs) are widely used as a model for studying membrane properties (phase separation, clustering, dynamics) and its interaction ...

Multimodal Imaging and Spectroscopy Fiber-bundle Microendoscopy Platform for Non-invasive, In Vivo Tissue Analysis

Recent fiber-bundle microendoscopy techniques enable non-invasive analysis of in vivo tissue using either imaging techniques or a combination of spectroscopy techniques. Combining imaging and spectroscopy techniques into a single optical probe may provide a more complete analysis of tissue health. In this article, two dissimilar modalities are combined, high-resolution fluorescence microendoscopy imaging and diffuse reflectance spectroscopy, into a single optical probe. High-resolution fluorescence microendoscopy imaging is a technique used to visualize apical tissue micro-architecture and, although mostly a qualitative technique, has demonstrated effective real-time differentiation between neoplastic and non-neoplastic tissue. Diffuse reflectance spectroscopy is a technique which can extract tissue physiological parameters including local hemoglobin concentration, melanin concentration, and oxygen saturation. This article describes the specifications required to construct the fiber-optic probe, how to build the instrumentation, and then demonstrates the technique on in vivo human skin. This work revealed that tissue micro-architecture, specifically apical skin keratinocytes, can be co-registered with its associated physiological parameters. The instrumentation and fiber-bundle probe presented here can be optimized as either a handheld or endoscopically-compatible device for use in a variety of organ systems. Additional clinical research is needed to test the viability of this technique for different epithelial disease states.

Multimodal Imaging and Spectroscopy Fiber-bundle Microendoscopy Platform for Non-invasive, In Vivo Tissue Analysis

The assembly and use of a multimodal microendoscope is described which can co-register superficial tissue image data with tissue physiological parameters including hemoglobin concentration, melanin concentration, and oxygen saturation. This technique can be useful for evaluating tissue structure and perfusion, and can be optimized for individual needs of the investigator.

Recent fiber-bundle microendoscopy techniques enable non-invasive analysis of in vivo tissue using either imaging techniques or a combination of ...

Proper Positioning and Restraint of a Rat Hind Limb for Focused High Resolution Imaging of Bone Micro-architecture Using In Vivo Micro-computed Tomography

The use of in vivo micro-computed tomography (&#181;CT) is a powerful tool which involves the non-destructive imaging of internal structures at high resolutions in live animal models. This allows for repeated imaging of the same rodent over time. This feature not only reduces the total number of rodents required in an experimental design and thereby reduces the inter-subject variation that can arise, but also allows researchers to assess longitudinal or life-long responses to an intervention. To acquire high quality images that can be processed and analyzed to more accurately quantify outcomes of bone micro-architecture, users of in vivo &#181;CT scanners must properly anesthetize the rat, and position and restrain the hind limb. To do this, it is imperative that the rat be anesthetized to a level of complete relaxation, and that pedal reflexes are lost. These guidelines may be modified for each individual rat, as the rate of isoflurane metabolism can vary depending on strain and body size. Proper technique for in vivo &#181;CT image acquisition enables accurate and consistent measurement of bone micro-architecture within and across studies.

Proper Positioning and Restraint of a Rat Hind Limb for Focused High Resolution Imaging of Bone Micro-architecture Using In Vivo Micro-computed Tomography

This paper instructs users of in vivo micro-computed tomography (&#181;CT) scanners how to anesthetize, correctly position and restrain the hind limb of a rat for minimal movement during high-resolution imaging of the tibia. The result is high quality images that can be processed to accurately quantify bone micro-architecture.

The use of in vivo micro-computed tomography (&#181;CT) is a powerful tool which involves the non-destructive imaging of internal structures at high ...

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

This paper elaborates the sample preparation protocols required to obtain optimal domain patterns using the Bitter method, focusing on the extra steps compared to standard metallographic sample preparation procedures. The paper proposes a novel bespoke rig for dynamic domain imaging with in situ BH (magnetic hysteresis) measurements and elaborates the protocols for the sensor preparation and the use of the rig to ensure accurate BH measurement. The protocols for static and ordinary dynamic domain imaging (without in situ BH measurements) are also presented. The reported method takes advantage of the convenience and high sensitivity of the traditional Bitter method and enables in situ BH measurement without interrupting or interfering with the domain wall movement processes. This facilitates establishing a direct and quantitative link between the domain wall movement processes&#8211;microstructural feature interactions in ferritic steels with their BH loops. This method is anticipated to become a useful tool for the fundamental study of microstructure&#8211;magnetic property relationships in steels and to help interpret the electromagnetic sensor signals for non-destructive evaluation of steel microstructures.

Optimized Setup and Protocol for Magnetic Domain Imaging with In Situ Hysteresis Measurement

This paper elaborates the sample and sensor preparation procedures and the protocols for using the test rig particularly for dynamic domain imaging with in situ BH measurements in order to achieve optimal domain pattern quality and accurate BH measurements.

This paper elaborates the sample preparation protocols required to obtain optimal domain patterns using the Bitter method, focusing on the extra steps ...

High Resolution 3D Imaging of the Human Pancreas Neuro-insular Network

Using traditional histological methods, researchers are hampered in their ability to image whole tissues or organs in large-scale 3D. Histological sections are generally limited to &#60;20 &#181;m as formalin fixed paraffin section on glass slides or &#60;500 &#181;m for free-floating fixed sections. Therefore, extensive efforts are required for serial sectioning and large-scale image reconstruction methods to recreate 3D for samples &#62;500 &#181;m using traditional methods. In addition, light scatters from macromolecules within tissues, particularly lipids, prevents imaging to a depth &#62;150 &#181;m with most confocal microscopes. To reduce light scatter and to allow for deep tissue imaging using simple confocal microscopy, various optical clearing methods have been developed that are relevant for rodent and human tissue samples fixed by immersion. Several methods are related and use protein crosslinking with acrylamide and tissue clearing with sodium dodecyl sulfate (SDS). Other optical clearing techniques used various solvents though each modification had various advantages and disadvantages. Here, an optimized passive optical clearing method is described for studies of the human pancreas innervation and specifically for interrogation of the innervation of human islets.

Here, we present a protocol to image human pancreas sections in three dimensions (3D) using optimized passive clearing methods. This manuscript demonstrates these procedures for passive optical clearing followed by multiple immunofluorescence staining to identify key elements of the autonomic and sensory neural networks innervating human islets.