This work was carried out with the use of facilities and resources at the VA Puget Sound Health Care Center. The work is that of the author and does not necessarily reflect the position or policy of the Department of Veterans Affairs or the United States government. Dr Tang is currently funded via the VA (Merit 5 I01 BX004975-02).

Animal experiments were performed according to a protocol approved by the University of Washington Institutional Animal Care and Use Committee.
1. Scanner preparation
<ol>
	<li>Adjust the scanner height so that the distance to the scanned subject is approximately 30 cm.</li>
	<li>Turn on the imager and launch the associated software.</li>
	<li>Open the Measurement program. If the software is correctly communicating with the scanner, the infrared laser turn on warning will appear.</li>
	<li>Calibrate the machine with manufacturer provided standards (not shown in the video and will depend on the specific model of machine being used).</li>
	<li>Adjust the scanner settings to be appropriate for the background material and lighting setup in the room.
	<ol>
		<li>Set the gain levels DC FLUX and CONC, per the manufacturer&#39;s instructions (not shown in the video).</li>
		<li>Set the Background Threshold by pointing the laser beam at the black background material, and press Auto BK Set.</li>
	</ol>
	</li>
</ol>
2. Mouse pre-scanning preparation
<ol>
	<li>Set up the isoflurane induction chamber with appropriate scavenging of the waste gas. 
	NOTE: Placing the induction chamber on a warming pad will help prevent mouse temperature loss during anesthesia induction.</li>
	<li>Turn on the homeothermic blanket, which is placed in the scanning area underneath a nonreflective surface (in this case a black neoprene fabric). Set the homeothermic blanket to maintain a body temperature of 37 &#176;C.</li>
	<li>Position the temperature probe for the homeothermic blanket and lubricant so they are ready for insertion.</li>
	<li>Place the anesthesia mask and scavenging system in the scanning area.</li>
	<li>Anesthetize the mouse with an isoflurane vaporizer. Set the oxygen rate to 1 L/min of flow and adjust the isoflurane to 4% for anesthesia induction. Turn on the flow to the anesthesia induction chamber, and the mouse breathing rate will slow. Adequate anesthesia is achieved when the mouse loses its righting reflex.</li>
	<li>Transfer the mouse to an anesthetic mask/nose cone with attached waste gas scavenger and adjust the isoflurane to 1.5%. 
	NOTE: This anesthesia level is generally adequate to keep the mouse lying relatively still during scanning, but is not intended to provide surgical levels of anesthesia, so the depth of anesthesia is not checked. Changing the isoflurane level causes changes in heartbeat, respiration, and dermal perfusion, so a consistent percentage should be used throughout any time course experiment and for all experimental subjects. Alternative anesthetic techniques such as IP injection of ketamine xylazine can also be used, but the same anesthetic technique should be used throughout any time course study as different anesthetics affect dermal perfusion differently.</li>
	<li>(Optional depending on scanning area) If the planned region of interest to be scanned is covered by fur, use a small electric trimmer or depilatory cream to remove the hair from the region of interest. 
	NOTE: The depilatory cream should be completely removed, and the mouse skin dried prior to scanning.</li>
	<li>Place the mouse in the appropriate scanning position on the black nonreflective surface covering the homeothermic blanket, confirming that both hindlimbs remain on the heat source throughout equilibration and scanning (Figure 1). 
	NOTE: It is important to maintain both feet on the homeothermic blanket to prevent regional variation in temperature.</li>
	<li>Insert the lubricated rectal temperature probe associated with the homeothermic blanket.</li>
	<li>Equilibrate the mouse temperature to desired scanning temperature (37 &#176;C); approximately 5-10 minutes.</li>
	<li>Select Scanner Setup, which can be accessed from the top menu or from the scanner setup icon. Adjust the scan area by changing the X-Y coordinates to accommodate the region of interest. Scan speed will depend on the scan resolution. Higher resolution will result in longer scan times. For repeat scanning focusing on global perfusion, as opposed to higher resolution focusing on anatomic perfusion, a scan speed of 4 ms/pixel is adequate. 
	&#8203;NOTE: Higher resolution and single scan should be considered if the researcher is attempting to directly study the developing collateral circulation (best imaged in the ventral thigh and calf where it is closer to the skin). Repeated scan at lower resolution/speed (e.g., 4 ms/pixel) is adequate when assessing global perfusion to the end organ of the mouse footpad. The software shown in the video automatically loads the previously used template for scanning area, speed, and resolution when restarted, or it can be retrieved from a stored file if different regions of interest are being used for various experiments.</li>
	<li>If performing repeat scans, select the Repeat and Line Scan tab. The number of scans can be changed (in this case 3 scans) as well as the repeat interval. The minimum time for the repeat interval would be the estimated scanning time, which is shown in the grayed-out area on the right of the box determined by scan area and scan resolution. Adding a few seconds allows the user to pause and potentially reposition the mouse if needed between scans.</li>
</ol>
3. Scanning
<ol>
	<li>Select the Image Scan tab and select the Mark button. The laser will move to outline the scanning area. Adjust the mouse position so that the target to be scanned is within the marked area. 
	NOTE: For footpad or footpad and calf scanning, prone positioning with the hindlimbs extended provides a more consistent region of interest than supine positioning. The femoral artery and saphenous artery and collaterals are very close to the ventral surface of the thigh and calf, so supine positioning is preferred if using these regions of interest.</li>
	<li>Start repeated measurement by selecting the Repeat Scanning icon and press the Play Button to initiate the scan.</li>
	<li>Confirm the scanning distance in the pop-up window and click OK to start scanning.</li>
	<li>Monitor the mouse during scanning for mouse movement; if the mouse moves sufficiently that the hindpaws are no longer in the scanning region in the middle of a scan, restart the scan. Small variations in mouse hindpaw position can be accommodated for in the analysis software.</li>
	<li>Monitor the mouse temperature during the scanning process as it may fluctuate even with the use of the homeothermic blanket. If there is too much variation in the mouse temperature, this may result in significant variation between scans. Generally, a temperature range of 36.8-37.2 &#176;C will result in acceptable data.</li>
	<li>Save the captured scan under the Save as window with a file name that includes mouse identifier and timepoint for easier data analysis. Enter mouse and timepoint details if desired in the subject details window.</li>
	<li>Turn off the isoflurane and remove the rectal temperature probe.</li>
	<li>Disinfect the rectal temperature probe with 70% ethanol so it is ready for use in the next mouse.</li>
	<li>Allow the mouse to recover from anesthesia to the point where it displays a righting reflex by flipping from the supine position to the prone position prior to returning it to the cage. 
	&#8203;NOTE: Recovery can be carried out either on a warming blanket for isoflurane since recovery is very quick or in a warmed recovery cage for ketamine/xylazine.</li>
</ol>
4. Capturing LDPI data (Figure 3)
<ol>
	<li>Open the imaging review software program.</li>
	<li>Go to the file menu, open, and locate the saved file.</li>
	<li>Select the ROI icon from the toolbar.</li>
	<li>Select the Add Polygon button.</li>
	<li>Trace the region of interest (ROI) for the control hindlimb using the mouse. Polygon tracing does not have to be exact as the gray background will not be included in the calculated averages.</li>
	<li>Repeat steps 4.3-4.5&#160;for the surgical hindlimb.</li>
	<li>Choose the Statistics icon to open the Image ROIs Statistics Results (PU) window.</li>
	<li>Export the results for Polygon 1 (control hindlimb) and Polygon 2 (surgical hindlimb) to a data collection worksheet via copy/paste.</li>
</ol>
5. Analysis
<ol>
	<li>Capture the data as Surgical/Control ratio for each scan.</li>
	<li>Use the averaged surgical/control for all three scans for the data point for that particular mouse at that timepoint. Because of biologic variability in the response to hindlimb ischemia, in general 8-10 mice are required per timepoint to achieve reproducible results with ~10% standard error. 
	NOTE: Before allowing the mouse to recover from anesthesia, it is worthwhile to perform a quick analysis of the repeated scans to check if the data is too variable (e.g., more than 100-150 perfusion units different between scans 1-3). High variation between repeated scans suggests the mouse was not completely equilibrated during the scan (Figure 2), and a repeat scan can be performed without losing a datapoint, which would occur if the images are not analyzed until a later date. Changing the color palette to optimize the dynamic range of displayed flux values may be necessary to better display scan variation (Figure 2).</li>
</ol>

<ol><li>Varma, P., Stineman, M. G., Dillingham, T. R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Epidemiology+of+limb+loss%5BTitle%5D)+AND+%22Physical+Medicine+and+Rehabilitation+Clinics+of+North+America%22%5BJournal%5D)">Epidemiology of limb loss.</a> Physical Medicine and Rehabilitation Clinics of North America. 25 (1), 1-8 (2014).</li>
<li>Farber, A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Chronic+Limb-Threatening+Ischemia%5BTitle%5D)+AND+%22New+England+Journal+of+Medicine%22%5BJournal%5D)">Chronic Limb-Threatening Ischemia.</a> New England Journal of Medicine. 379 (2), 171-180 (2018).</li>
<li>Abularrage, C. J., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Evaluation+of+the+microcirculation+in+vascular+disease%5BTitle%5D)+AND+%22Journal+of+Vascular+Surgery%22%5BJournal%5D)">Evaluation of the microcirculation in vascular disease.</a> Journal of Vascular Surgery. 42 (3), 574-581 (2005).</li>
<li>Houben, A., Martens, R. J. H., Stehouwer, C. D. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Assessing+Microvascular+Function+in+Humans+from+a+Chronic+Disease+Perspective%5BTitle%5D)+AND+%22Journal+of+the+American+Society+of+Nephrology%22%5BJournal%5D)">Assessing Microvascular Function in Humans from a Chronic Disease Perspective.</a> Journal of the American Society of Nephrology. 28 (12), 3461-3472 (2017).</li>
<li>Mahe, G., Humeau-Heurtier, A., Durand, S., Leftheriotis, G., Abraham, P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Assessment+of+skin+microvascular+function+and+dysfunction+with+laser+speckle+contrast+imaging%5BTitle%5D)+AND+%22Circulation%3A+Cardiovascular+Imaging%22%5BJournal%5D)">Assessment of skin microvascular function and dysfunction with laser speckle contrast imaging.</a> Circulation: Cardiovascular Imaging. 5 (1), 155-163 (2012).</li>
<li>Murray, A. K., Herrick, A. L., King, T. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Laser+Doppler+imaging%3A+a+developing+technique+for+application+in+the+rheumatic+diseases%5BTitle%5D)+AND+%22Rheumatology+%28Oxford%29%22%5BJournal%5D)">Laser Doppler imaging: a developing technique for application in the rheumatic diseases.</a> Rheumatology (Oxford). 43 (10), 1210-1218 (2004).</li>
<li>Greco, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Repeatability%2C+reproducibility+and+standardisation+of+a+laser+Doppler+imaging+technique+for+the+evaluation+of+normal+mouse+hindlimb+perfusion%5BTitle%5D)+AND+%22Sensors+%28Basel%29%22%5BJournal%5D)">Repeatability, reproducibility and standardisation of a laser Doppler imaging technique for the evaluation of normal mouse hindlimb perfusion.</a> Sensors (Basel). 13 (1), 500-515 (2012).</li>
<li>Sonmez, T. T., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((A+novel+laser-Doppler+flowmetry+assisted+murine+model+of+acute+hindlimb+ischemia-reperfusion+for+free+flap+research%5BTitle%5D)+AND+%22PLoS+One%22%5BJournal%5D)">A novel laser-Doppler flowmetry assisted murine model of acute hindlimb ischemia-reperfusion for free flap research.</a> PLoS One. 8 (6), 66498(2013).</li>
<li>Gargiulo, S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Effects+of+some+anesthetic+agents+on+skin+microcirculation+evaluated+by+laser+Doppler+perfusion+imaging+in+mice%5BTitle%5D)+AND+%22BMC+Veterinary+Research%22%5BJournal%5D)">Effects of some anesthetic agents on skin microcirculation evaluated by laser Doppler perfusion imaging in mice.</a> BMC Veterinary Research. 9, 255(2013).</li>
<li>Ankri-Eliahoo, G., Weitz, K., Cox, T. C., Tang, G. L. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((p27%28kip1%29+Knockout+enhances+collateralization+in+response+to+hindlimb+ischemia%5BTitle%5D)+AND+%22Journal+of+Vascular+Surgery%22%5BJournal%5D)">p27(kip1) Knockout enhances collateralization in response to hindlimb ischemia.</a> Journal of Vascular Surgery. 63 (5), 1351-1359 (2016).</li>
<li>McEnaney, R. M., Shukla, A., Madigan, M. C., Sachdev, U., Tzeng, E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((P2Y2+nucleotide+receptor+mediates+arteriogenesis+in+a+murine+model+of+hind+limb+ischemia%5BTitle%5D)+AND+%22Journal+of+Vascular+Surgery%22%5BJournal%5D)">P2Y2 nucleotide receptor mediates arteriogenesis in a murine model of hind limb ischemia.</a> Journal of Vascular Surgery. 63 (1), 216-225 (2016).</li>
<li>Padgett, M. E., McCord, T. J., McClung, J. M., Kontos, C. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Methods+for+Acute+and+Subacute+Murine+Hindlimb+Ischemia%5BTitle%5D)+AND+%22Journal+of+Visualized+Experiments%22%5BJournal%5D)">Methods for Acute and Subacute Murine Hindlimb Ischemia.</a> Journal of Visualized Experiments. (112), e54166(2016).</li>
<li>Niiyama, H., Huang, N. F., Rollins, M. D., Cooke, J. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Murine+model+of+hindlimb+ischemia%5BTitle%5D)+AND+%22Journal+of+Visualized+Experiments%22%5BJournal%5D)">Murine model of hindlimb ischemia.</a> Journal of Visualized Experiments. (23), e1035(2009).</li>
<li>Chalothorn, D., Faber, J. E. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Strain-dependent+variation+in+collateral+circulatory+function+in+mouse+hindlimb%5BTitle%5D)+AND+%22Physiological+Genomics%22%5BJournal%5D)">Strain-dependent variation in collateral circulatory function in mouse hindlimb.</a> Physiological Genomics. 42 (3), 469-479 (2010).</li>
<li>Helisch, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Impact+of+mouse+strain+differences+in+innate+hindlimb+collateral+vasculature%5BTitle%5D)+AND+%22Arteriosclerosis%2C+Thrombosis%2C+and+Vascular+Biology%22%5BJournal%5D)">Impact of mouse strain differences in innate hindlimb collateral vasculature.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 26 (3), 520-526 (2006).</li>
<li>Faber, J. E., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Aging+causes+collateral+rarefaction+and+increased+severity+of+ischemic+injury+in+multiple+tissues%5BTitle%5D)+AND+%22Arteriosclerosis%2C+Thrombosis%2C+and+Vascular+Biology%22%5BJournal%5D)">Aging causes collateral rarefaction and increased severity of ischemic injury in multiple tissues.</a> Arteriosclerosis, Thrombosis, and Vascular Biology. 31 (8), 1748-1756 (2011).</li>
<li>Forrester, K. R., Stewart, C., Tulip, J., Leonard, C., Bray, R. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Comparison+of+laser+speckle+and+laser+Doppler+perfusion+imaging%3A+measurement+in+human+skin+and+rabbit+articular+tissue%5BTitle%5D)+AND+%22Medical+%26+Biological+Engineering+%26+Computing%22%5BJournal%5D)">Comparison of laser speckle and laser Doppler perfusion imaging: measurement in human skin and rabbit articular tissue.</a> Medical & Biological Engineering & Computing. 40 (6), 687-697 (2002).</li>
<li>Briers, J. D. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Laser+Doppler%2C+speckle+and+related+techniques+for+blood+perfusion+mapping+and+imaging%5BTitle%5D)+AND+%22Physiological+Measurement%22%5BJournal%5D)">Laser Doppler, speckle and related techniques for blood perfusion mapping and imaging.</a> Physiological Measurement. 22 (4), 35-66 (2001).</li>
<li>Heeman, W., Steenbergen, W., van Dam, G., Boerma, E. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Clinical+applications+of+laser+speckle+contrast+imaging%3A+a+review%5BTitle%5D)+AND+%22Journal+of+Biomedical+Optics%22%5BJournal%5D)">Clinical applications of laser speckle contrast imaging: a review.</a> Journal of Biomedical Optics. 24 (8), 1-11 (2019).</li>
<li>Nguyen, T., Davidson, B. P. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Contrast+Enhanced+Ultrasound+Perfusion+Imaging+in+Skeletal+Muscle%5BTitle%5D)+AND+%22Journal+of+Cardiovascular+Imaging%22%5BJournal%5D)">Contrast Enhanced Ultrasound Perfusion Imaging in Skeletal Muscle.</a> Journal of Cardiovascular Imaging. 27 (3), 163-177 (2019).</li>
<li>Zaccagnini, G., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Magnetic+Resonance+Imaging+Allows+the+Evaluation+of+Tissue+Damage+and+Regeneration+in+a+Mouse+Model+of+Critical+Limb+Ischemia%5BTitle%5D)+AND+%22PLoS+One%22%5BJournal%5D)">Magnetic Resonance Imaging Allows the Evaluation of Tissue Damage and Regeneration in a Mouse Model of Critical Limb Ischemia.</a> PLoS One. 10 (11), 0142111(2015).</li>
<li>Penuelas, I., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((PET+as+a+measurement+of+hindlimb+perfusion+in+a+mouse+model+of+peripheral+artery+occlusive+disease%5BTitle%5D)+AND+%22Journal+of+Nuclear+Medicine%22%5BJournal%5D)">PET as a measurement of hindlimb perfusion in a mouse model of peripheral artery occlusive disease.</a> Journal of Nuclear Medicine. 48 (13), 1216-1223 (2007).</li>
<li>Jia, Y., Qin, J., Zhi, Z., Wang, R. K. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Ultrahigh+sensitive+optical+microangiography+reveals+depth-resolved+microcirculation+and+its+longitudinal+response+to+prolonged+ischemic+event+within+skeletal+muscles+in+mice%5BTitle%5D)+AND+%22Journal+of+Biomedical+Optics%22%5BJournal%5D)">Ultrahigh sensitive optical microangiography reveals depth-resolved microcirculation and its longitudinal response to prolonged ischemic event within skeletal muscles in mice.</a> Journal of Biomedical Optics. 16 (8), 086004(2011).</li>
<li>Turaihi, A. H., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Combined+Intravital+Microscopy+and+Contrast-enhanced+Ultrasonography+of+the+Mouse+Hindlimb+to+Study+Insulin-induced+Vasodilation+and+Muscle+Perfusion%5BTitle%5D)+AND+%22Journal+of+Visualized+Experiments%22%5BJournal%5D)">Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion.</a> Journal of Visualized Experiments. (121), e54912(2017).</li>
<li>Liu, C., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Enhanced+autophagy+alleviates+injury+during+hindlimb+ischemia%2Freperfusion+in+mice%5BTitle%5D)+AND+%22Experimental+and+Therapeutic+Medicine%22%5BJournal%5D)">Enhanced autophagy alleviates injury during hindlimb ischemia/reperfusion in mice.</a> Experimental and Therapeutic Medicine. 18 (3), 1669-1676 (2019).</li>
<li>Liu, D. L., Svanberg, K., Wang, I., Andersson-Engels, S., Svanberg, S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Laser+Doppler+perfusion+imaging%3A+new+technique+for+determination+of+perfusion+and+reperfusion+of+splanchnic+organs+and+tumor+tissue%5BTitle%5D)+AND+%22Lasers+in+Surgery+and+Medicine%22%5BJournal%5D)">Laser Doppler perfusion imaging: new technique for determination of perfusion and reperfusion of splanchnic organs and tumor tissue.</a> Lasers in Surgery and Medicine. 20 (4), 473-479 (1997).</li>
<li>Jing, Y., Bai, F., Chen, H., Dong, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Using+Laser+Doppler+Imaging+and+Monitoring+to+Analyze+Spinal+Cord+Microcirculation+in+Rat%5BTitle%5D)+AND+%22Journal+of+Visualized+Experiments%22%5BJournal%5D)">Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat.</a> Journal of Visualized Experiments. (135), e56243(2018).</li>
<li>Zhang, D., Li, S., Wang, S., Ma, H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((An+evaluation+of+the+effect+of+a+gastric+ischemia-reperfusion+model+with+laser+Doppler+blood+perfusion+imaging%5BTitle%5D)+AND+%22Lasers+in+Medical+Science%22%5BJournal%5D)">An evaluation of the effect of a gastric ischemia-reperfusion model with laser Doppler blood perfusion imaging.</a> Lasers in Medical Science. 21 (4), 224-228 (2006).</li>
<li>Fitzal, F., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/pubmed?term=((Circulatory+changes+after+prolonged+ischemia+in+the+epigastric+flap%5BTitle%5D)+AND+%22Journal+of+Reconstructive+Microsurgery%22%5BJournal%5D)">Circulatory changes after prolonged ischemia in the epigastric flap.</a> Journal of Reconstructive Microsurgery. 17 (7), 535-543 (2001).</li>
</ol>

Dr Tang has no conflicts of interest to disclose.

Consistent technique is critical for obtaining reliable results with LDPI. The same anesthetic, temperature settings, mouse position, and region of interest should be used throughout the entire time course. Different anesthetic agents will result in higher or lower perfusion values9. Isoflurane anesthesia is convenient because of its rapid onset and emergence as well as overall safety. A consistent percentage of isoflurane should be used as depth of anesthesia with this vasodilatory agent may alte...

Skin ulceration with inadequate wound healing is a leading cause of amputations in human patients1. Adequate wound healing requires higher levels of arterial perfusion than are needed to maintain intact skin, which is compromised in patients with peripheral arterial disease2,3,4. Several other rheumatologic conditions and diabetes can also lead to disturbed and inadequate skin microcirculation to heal wounds5,6. Many diabetic patients have concomitant peripheral arterial disease, placing them at especially high risk for amputation. Laser Doppler perfusion imaging (LDPI) is used in clinical situations to evaluate the skin microcirculation, as well as in research situations to evaluate blood flow and blood flow recovery after experimental hindlimb ischemia, ischemia-reperfusion, and microsurgical flaps7.
The LDPI system projects a low power laser beam that is deflected by a scanning mirror to move over a region of interest. This differs from Laser Doppler flowmetry, which provides a perfusion measurement for the small area of tissue in direct contact with the flowmetry probe8. When the laser beam interacts with moving blood in the microvasculature, it undergoes a Doppler frequency shift, which is photodetected by the scanner and converted to arbitrary perfusion units. Because LDPI is a light-based technique, it is limited in terms of depth of penetration to 0.3-1 mm, meaning that for the most part dermal perfusion is assessed7. Dermal flow can be altered by skin temperature and the sympathetic nervous system, which may be affected by various anesthetic agents9. Measurements from the optical laser are also affected by ambient lighting conditions, skin pigmentation, and can be blocked by overlying fur or hair7.
LDPI is the most commonly used research technique to monitor perfusion recovery after ischemia because it is noninvasive, does not require contrast administration, and has quick scan times allowing data collection on multiple animals. This makes it ideal to help determine whether treatments aimed at therapeutic arteriogenesis or angiogenesis are effective in small animal models. Blood flow recovery after hindlimb ischemia as measured by LDPI correlates well with collateral artery development when assessed by other means such as Microfil casting or micro-CT10,11. The goal of this protocol is to demonstrate the assessment of hindlimb perfusion using LDPI.

<table><tbody><tr><td>Black nonreflective material</td><td></td><td></td><td>Fabric store, black neoprene recommended by company</td></tr><tr><td>F/air cannister</td><td>A.M. Bickford Inc</td><td>80120</td><td></td></tr><tr><td>Homeothermic blanket with rigid metal probe</td><td>Harvard Apparatus</td><td></td><td>Also comes with flexible probe, but this is less durable</td></tr><tr><td>Isoflurane Anesthesia machine</td><td>Drager</td><td></td><td>Multiple manufacturers</td></tr><tr><td>Isoflurane induction chamber</td><td>VetEquip</td><td>941444</td><td>2 L chamber</td></tr><tr><td>Moor laser Doppler perfusion imager</td><td>Moor Instruments</td><td>MoorLDI2-IR</td><td>Higher resolution imager (MoorLDI2-HIR)</td></tr><tr><td>Mouse Anesthesia nose cone</td><td></td><td></td><td>Multiple manufacturers</td></tr><tr><td>Nair</td><td>Nair</td><td></td><td></td></tr><tr><td>Oxygen tank</td><td></td><td></td><td>Multiple manufacturers</td></tr><tr><td>Surgilube</td><td>Multiple distributors</td><td></td><td></td></tr></tbody></table>

laser doppler perfusion imaging in the mouse hindlimb

Blood flow recovery is a critical outcome measure after experimental hindlimb ischemia or ischemia-reperfusion. Laser Doppler perfusion imaging (LDPI) is a common, noninvasive, repeatable method for assessing blood flow recovery. The technique calculates overall blood flow in the sampled tissue from the Doppler shift in frequency caused when a laser hits moving red blood cells. Measurements are expressed in arbitrary perfusion units, so the contralateral non-intervened upon leg is usually used to help control measurements. Measurement depth is in the range of 0.3-1 mm; for hindlimb ischemia, this means that dermal perfusion is assessed. Dermal perfusion is dependent on several factors&#8212;most importantly skin temperature and anesthetic agent, which must be carefully controlled to result in reliable readings. Furthermore, hair and skin pigmentation can alter the ability of the laser to either reach or penetrate to the dermis. This article demonstrates the technique of LDPI in the mouse hindlimb.

Successful LDPI should result in consistent repeated measures scans, with no more than 100-150 perfusion unit variation (corresponding to about 10% of the usual mean perfusion for the mouse footpad) between the three scans (Figure 2). As demonstrated in Figure 2, repeat scans help determine that the mouse has been appropriately equilibrated so that the ischemic/control ratio best reflects the underlying blood flow as opposed to variation in dermal perfusion caus...

Watch this Scientific Journal Video about Laser Doppler Perfusion Imaging in the Mouse Hindlimb at JoVE.com

Laser Doppler Perfusion Imaging in the Mouse Hindlimb

Here, we present a protocol that demonstrates the technique and necessary controls for Laser Doppler perfusion imaging to measure blood flow in the mouse hindlimb.

Blood flow recovery is a critical outcome measure after experimental hindlimb ischemia or ischemia-reperfusion. Laser Doppler perfusion imaging (LDPI) is ...

laser-doppler-perfusion-imaging-in-the-mouse-hindlimb

Research

JoVE Journal

Medicine

5.8K Views.  University of Washington. Here, we present a protocol that demonstrates the technique and necessary controls for Laser Doppler perfusion imaging to measure blood flow in the mouse hindlimb.

Video: Laser Doppler Perfusion Imaging in the Mouse Hindlimb

Programming Stem Cells for Therapeutic Angiogenesis Using Biodegradable Polymeric Nanoparticles

Controlled vascular growth is critical for successful tissue regeneration and wound healing, as well as for treating ischemic diseases such as stroke, heart attack or peripheral arterial diseases. Direct delivery of angiogenic growth factors has the potential to stimulate new blood vessel growth, but is often associated with limitations such as lack of targeting and short half-life in vivo. Gene therapy offers an alternative approach by delivering genes encoding angiogenic factors, but often requires using virus, and is limited by safety concerns. Here we describe a recently developed strategy for stimulating vascular growth by programming stem cells to overexpress angiogenic factors in situ using biodegradable polymeric nanoparticles. Specifically our strategy utilized stem cells as delivery vehicles by taking advantage of their ability to migrate toward ischemic tissues in vivo. Using the optimized polymeric vectors, adipose-derived stem cells were modified to overexpress an angiogenic gene encoding vascular endothelial growth factor (VEGF). We described the processes for polymer synthesis, nanoparticle formation, transfecting stem cells in vitro, as well as methods for validating the efficacy of VEGF-expressing stem cells for promoting angiogenesis in a murine hindlimb ischemia model.

We describe the method of programming stem cells to overexpress therapeutic factors for angiogenesis using biodegradable polymeric nanoparticles. Processes described include polymer synthesis, transfecting adipose-derived stem cells in vitro, and validating the efficacy of programmed stem cells to promote angiogenesis in a murine hindlimb ischemia model.

Controlled vascular growth is critical for successful tissue regeneration and wound healing, as well as for treating ischemic diseases such as stroke, ...

Bioengineering

Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory alterations of the spinal cord. In this article, our goal was to use both Laser Doppler imaging and monitoring to analyze the change of BF after spinal cord injury. Both the laser Doppler image scanner and the probe/monitor were being employed to obtain each readout. The data of LDPI provided a local distribution of BF, which gave an overview of perfusion around the injury site and made it accessible for comparative analysis of BF among different locations. By intensely measuring the probing area over a period of time, a combined probe was used to simultaneously measure the BF and oxygen saturation of the spinal cord, showing overall spinal cord perfusion and oxygen supply. LDF itself has a few limitations, such as relative flux, sensitivity to movement, and biological zero signal. However, the technology has been applied in clinical and experimental study due to its simple setup and rapid measurement of BF.

Here we present a combination of laser Doppler perfusion imaging (LDPI) and laser Doppler perfusion monitoring (LDPM) to measure spinal cord local blood flows and oxygen saturation (SO2), as well as a standardized procedure for introducing spinal cord trauma on rat.

Laser Doppler flowmetry (LDF) is a noninvasive method for blood flow (BF) measurement, which makes it preferable for measuring microcirculatory ...

Behavior

Murine Model of Hindlimb Ischemia 

In the United States, peripheral arterial disease (PAD) affects about 10 million individuals, and is also prevalent worldwide. Medical therapies for symptomatic relief are limited. Surgical or endovascular interventions are useful for some individuals, but long-term results are often disappointing. As a result, there is a need for developing new therapies to treat PAD. The murine hindlimb ischemia preparation is a model of PAD, and is useful for testing new therapies. When compared to other models of tissue ischemia such as coronary or cerebral artery ligation, femoral artery ligation provides for a simpler model of ischemic tissue. Other advantages of this model are the ease of access to the femoral artery and low mortality rate. 
In this video, we demonstrate the methodology for the murine model of unilateral hindimb ischemia. The specific materials and procedures for creating and evaluating the model will be described, including the assessment of limb perfusion by laser Doppler imaging. This protocol can also be utilized for the transplantation and non-invasive tracking of cells, which is demonstrated by Huang et al.1.

Murine Model of Hindlimb Ischemia

The surgical procedure for induction of unilateral hindlimb ischemia is demonstrated, with confirmation of ischemia by laser Doppler perfusion imaging.

In the United States, peripheral arterial disease (PAD) affects about 10 million individuals, and is also prevalent worldwide.  Medical therapies for ...

Biology

Osmotic Drug Delivery to Ischemic Hindlimbs and Perfusion of Vasculature with Microfil for Micro-Computed Tomography Imaging

Preclinical research in animal models of peripheral arterial disease plays a vital role in testing the efficacy of therapeutic agents designed to stimulate microcirculation. The choice of delivery method for these agents is important because the route of administration profoundly affects the bioactivity and efficacy of these agents1,2. In this article, we demonstrate how to locally administer a substance in ischemic hindlimbs by using a catheterized osmotic pump. This pump can deliver a fixed volume of aqueous solution continuously for an allotted period of time. We also present our mouse model of unilateral hindlimb ischemia induced by ligation of the common femoral artery proximal to the origin of profunda femoris and epigastrica arteries in the left hindlimb. Lastly, we describe the in vivo cannulation and ligation of the infrarenal abdominal aorta and perfusion of the hindlimb vasculature with Microfil, a silicone radiopaque casting agent. Microfil can perfuse and fill the entire vascular bed (arterial and venous), and because we have ligated the major vascular conduit for exit, the agent can be retained in the vasculature for future ex vivo imaging with the use of small specimen micro-CT3.

We show here the in vivo insertion of an osmotic pump for constant local drug delivery and the creation of hindlimb ischemia in a mouse model. Moreover, the hindlimb vasculature is perfused with Microfil, a silicone radiopaque agent, to prepare for micro-computed tomography (micro-CT) imaging.

Preclinical research in animal models of peripheral arterial disease plays a vital role in testing the efficacy of therapeutic agents designed to ...

Methods for Acute and Subacute Murine Hindlimb Ischemia

Peripheral artery disease (PAD) is a leading cause of cardiovascular morbidity and mortality in developed countries, and animal models that reliably reproduce the human disease are necessary to develop new therapies for this disease. The mouse hindlimb ischemia model has been widely used for this purpose, but the standard practice of inducing acute limb ischemia by ligation of the femoral artery can result in substantial tissue necrosis, compromising investigators&#39; ability to study the vascular and skeletal muscle tissue responses to ischemia. An alternative approach to femoral artery ligation is the induction of gradual femoral artery occlusion through the use of ameroid constrictors. When placed around the femoral artery in the same or different locations as the sites of femoral artery ligation, these devices occlude the artery over 1 - 3 days, resulting in more gradual, subacute ischemia. This results in less substantial skeletal muscle tissue necrosis, which may more closely mimic the responses seen in human PAD. Because genetic background influences outcomes in both the acute and subacute ischemia models, consideration of the mouse strain being studied is important in choosing the best model. This paper describes the proper procedure and anatomical placement of ligatures or ameroid constrictors on the mouse femoral artery to induce subacute or acute hindlimb ischemia in the mouse.

Surgical induction of hindlimb ischemia in the mouse is useful to examine angiogenesis, however this is compromised in certain inbred mouse strains that display marked ischemia-induced tissue necrosis. Methods are described to induce subacute limb ischemia using ameroid constrictors to circumvent this problem through the induction of gradual arterial occlusion.

Peripheral artery disease (PAD) is a leading cause of cardiovascular morbidity and mortality in developed countries, and animal models that reliably ...

Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate postprandial delivery of nutrients and hormones to insulin-sensitive tissues. We here describe a technique for combining intravital microscopy (IVM) and contrast-enhanced ultrasonography (CEUS) of the adductor compartment of the mouse hindlimb to simultaneously visualize muscle resistance arteries and perfusion of the microcirculation in vivo. Simultaneously assessing insulin's effect at multiple levels of the vascular tree is important to study relationships between insulin's multiple vasoactive effects and muscle perfusion. Experiments in this study were performed in mice. First, the tail vein cannula is inserted for the infusion of anesthesia, vasoactive compounds and ultrasound contrast agent (lipid-encapsulated microbubbles). Second, a small incision is made in the groin area to expose the arterial tree of the adductor muscle compartment. The ultrasound probe is then positioned at the contralateral upper hindlimb to view the muscles in cross-section. To assess baseline parameters, the arterial diameter is assessed and microbubbles are subsequently infused at a constant rate to estimate muscle blood flow and microvascular blood volume (MBV). When applied before and during a hyperinsulinemic-euglycemic clamp, combined IVM and CEUS allow assessment of insulin-induced changes of arterial diameter, microvascular muscle perfusion and whole-body insulin sensitivity. Moreover, the temporal relationship between responses of the microcirculation and the resistance arteries to insulin can be quantified. It is also possible to follow-up the mice longitudinally in time, making it a valuable tool to study changes in vascular and whole-body insulin sensitivity.

Insulin-induced vasodilation regulates muscle perfusion and increases the microvascular surface area (microvascular recruitment) available for solute exchange between blood and tissue interstitium. Combined intravital microscopy and contrast-enhanced ultrasonography is presented to simultaneously assess insulin&#39;s action at the larger vessels and the microcirculation in vivo.

It has been demonstrated that insulin's vascular actions contribute to regulation of insulin sensitivity. Insulin's effects on muscle perfusion regulate ...

Laser Doppler: A Tool for Measuring Pancreatic Islet Microvascular Vasomotion In Vivo

As a functional status of microcirculation, microvascular vasomotion is important for the delivery of oxygen and nutrients and the removal of carbon dioxide and waste products. The impairment of microvascular vasomotion might be a crucial step in the development of microcirculation-related diseases. In addition, the highly vascularized pancreatic islet is adapted to support endocrine function. In this respect, it seems possible to infer that the functional status of pancreatic islet microvascular vasomotion might affect pancreatic islet function. Analyzing the pathological changes of the functional status of pancreatic islet microvascular vasomotion may be a feasible strategy to determine contributions that pancreatic islet microcirculation makes to related diseases, such as diabetes mellitus, pancreatitis, etc. Therefore, this protocol describes using a laser Doppler blood flow monitor to determine the functional status of pancreatic islet microvascular vasomotion, and to establish parameters (including average blood perfusion, amplitude, frequency, and relative velocity of pancreatic islet microvascular vasomotion) for evaluation of the microcirculatory functional status. In a streptozotocin-induced diabetic mouse model, we observed an impaired functional status of pancreatic islet microvascular vasomotion. In conclusion, this approach for assessing pancreatic islet microvascular vasomotion in vivo may reveal mechanisms relating to pancreatic islet diseases.

Laser Doppler: A Tool for Measuring Pancreatic Islet Microvascular Vasomotion In Vivo

Pancreatic islet microvascular vasomotion regulates islet blood distribution and maintains the physiological function of islet &#946; cells. This protocol describes using a laser Doppler monitor to determine the functional status of pancreatic islet microvascular vasomotion in vivo and to assess the contributions of pancreatic islet microcirculation to pancreatic-related diseases.

As a functional status of microcirculation, microvascular vasomotion is important for the delivery of oxygen and nutrients and the removal of carbon ...

Multiphoton Intravital Imaging for Monitoring Leukocyte Recruitment during Arteriogenesis in a Murine Hindlimb Model

Arteriogenesis strongly depends on leukocyte and platelet recruitment to the perivascular space of growing collateral vessels. The standard approach for analyzing collateral arteries and leukocytes in arteriogenesis is ex vivo (immuno-) histological methodology. However, this technique does not allow the measurement of dynamic processes such as blood flow, shear stress, cell-cell interactions, and particle velocity. This paper presents a protocol to monitor in vivo processes in growing collateral arteries during arteriogenesis utilizing intravital imaging. The method described here is a reliable tool for dynamics measurement and offers a high-contrast analysis with minimal photo-cytotoxicity, provided by multiphoton excitation microscopy. Prior to analyzing growing collateral arteries, arteriogenesis was induced in the adductor muscle of mice by unilateral ligation of the femoral artery.
After the ligation, the preexisting collateral arteries started to grow due to increased shear stress. Twenty-four hours after surgery, the skin and subcutaneous fat above the collateral arteries were removed, constructing a pocket for further analyses. To visualize blood flow and immune cells during in vivo imaging, CD41-fluorescein isothiocyanate (FITC) (platelets) and CD45-phycoerythrin (PE) (leukocytes) antibodies were injected intravenously (i.v.) via a catheter placed in the tail vein of a mouse. This article introduces intravital multiphoton imaging as an alternative or in vivo complementation to the commonly used static ex vivo (immuno-) histological analyses to study processes relevant for arteriogenesis. In summary, this paper describes a novel and dynamic in vivo method to investigate immune cell trafficking, blood flow, and shear stress in a hindlimb model of arteriogenesis, which enhances evaluation possibilities notably.

The recruitment of leukocytes and platelets constitutes an essential component necessary for the effective growth of collateral arteries during arteriogenesis. Multiphoton microscopy is an efficient tool for tracking cell dynamics with high spatio-temporal resolution in vivo and less photo-toxicity to study leukocyte recruitment and extravasation during arteriogenesis.

Arteriogenesis strongly depends on leukocyte and platelet recruitment to the perivascular space of growing collateral vessels. The standard approach for ...

High-Resolution Three-Dimensional Imaging of the Footpad Vasculature in a Murine Hindlimb Gangrene Model

Peripheral arterial disease (PAD) is a significant cause of morbidity resulting from chronic exposure to atherosclerotic risk factors. Patients suffering from its most severe form, chronic limb-threatening ischemia (CLTI), face substantial impairments to daily living, including chronic pain, limited walking distance without pain, and nonhealing wounds. Preclinical models have been developed in various animals to study PAD, but mouse hindlimb ischemia remains the most widely used. There can be significant variation in response to ischemic insult in these models depending on the mouse strain used and the site, number, and means of arterial disruption. This protocol describes a unique method combining femoral artery and vein electrocoagulation with the administration of a nitric oxide synthase (NOS) inhibitor to reliably induce footpad gangrene in Friend Virus B (FVB) mice that resembles the tissue loss of CLTI. While traditional means of assessing reperfusion such as laser Doppler perfusion imaging (LDPI) are still recommended, intracardiac perfusion of the lipophilic dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) is used to label the vasculature. Subsequent whole-mount confocal laser scanning microscopy allows for high-resolution, three-dimensional (3D) reconstruction of footpad vascular networks that complements traditional means of assessing reperfusion in hindlimb ischemia models.

The present protocol describes a unique, clinically relevant model of peripheral arterial disease that combines femoral artery and vein electrocoagulation with the administration of a nitric oxide synthase inhibitor to induce hindlimb gangrene in FVB mice. Intracardiac DiI perfusion is then used for high-resolution, three-dimensional imaging of the footpad vasculature.

Peripheral arterial disease (PAD) is a significant cause of morbidity resulting from chronic exposure to atherosclerotic risk factors. Patients suffering ...

Periorbital Laser Doppler Flowmetry for MCAO-Induced Ischemic Stroke in Rodents

Periorbital Placement of a Laser Doppler Probe for Cerebral Blood Flow Monitoring Prior to Middle Cerebral Artery Occlusion in Rodent Models

Middle cerebral artery occlusion (MCAO) is the gold-standard method for preclinical modeling of ischemic stroke in rodents. However, successful occlusion is not guaranteed by even the most skilled surgical hands. Errors primarily occur when the filament is not placed at the correct depth and include instances of either no infarction or vessel perforation, which can cause death. Laser Doppler flowmetry (LDF) is a reliable technique that provides real-time feedback on regional cerebral blood flow (CBF) during the MCAO procedure. Here we demonstrate a rapid technique for periorbital placement of a laser Doppler probe for measurement of CBF in both mice and rats. Our rationale was to simplify LDF implementation, encouraging widespread usage for improved surgical reliability. The technique eliminates the need for skull thinning and specialized equipment, with placement at the periorbital region rather than dorsal placement, promoting efficiency and ease of adoption. The protocol described here encompasses presurgical preparations, periorbital Doppler probe placement, and post-operative care. Representative results include visual depictions of procedural elements along with representative LDF tracings illustrating successful MCAO surgeries, with instances of unsuccessful filament placement leading to complications. The protocol illustrates LDF in confirming proper filament placement and offers a simplified procedure compared to alternative methods.

Author Spotlight: Advancing Stroke Research with Periorbital Doppler Monitoring of Regional Cerebral Blood Flow in Rodent Models

A minimally invasive surgical procedure is shown here, which involves placing the laser Doppler probe onto the skull over the distal region of the middle cerebral artery (MCA), a periorbital location suitable for rats and mice, to assess blood flow during transient MCA occlusion.

Middle cerebral artery occlusion (MCAO) is the gold-standard method for preclinical modeling of ischemic stroke in rodents. However, successful occlusion ...

Laser Doppler Perfusion Imaging in the Mouse Hindlimb

Podsumowanie

Przeglądaj więcej filmów

Programming Stem Cells for Therapeutic Angiogenesis Using Biodegradable Polymeric Nanoparticles

Using Laser Doppler Imaging and Monitoring to Analyze Spinal Cord Microcirculation in Rat

Murine Model of Hindlimb Ischemia

Osmotic Drug Delivery to Ischemic Hindlimbs and Perfusion of Vasculature with Microfil for Micro-Computed Tomography Imaging

Methods for Acute and Subacute Murine Hindlimb Ischemia

Combined Intravital Microscopy and Contrast-enhanced Ultrasonography of the Mouse Hindlimb to Study Insulin-induced Vasodilation and Muscle Perfusion

Laser Doppler: A Tool for Measuring Pancreatic Islet Microvascular Vasomotion In Vivo

Multiphoton Intravital Imaging for Monitoring Leukocyte Recruitment during Arteriogenesis in a Murine Hindlimb Model

High-Resolution Three-Dimensional Imaging of the Footpad Vasculature in a Murine Hindlimb Gangrene Model

Periorbital Placement of a Laser Doppler Probe for Cerebral Blood Flow Monitoring Prior to Middle Cerebral Artery Occlusion in Rodent Models