A systematic review of the use of near-infrared fluorescence imaging in patients with peripheral artery disease

Quantitative perfusion assessment using indocyanine green during surgery - current applications and recommendations for future use

PURPOSE

Incorrect assessment of tissue perfusion carries a significant risk of complications in surgery. The use of near-infrared (NIR) fluorescence imaging with Indocyanine Green (ICG) presents a possible solution. However, only through quantification of the fluorescence signal can an objective and reproducible evaluation of tissue perfusion be obtained. This narrative review aims to provide an overview of the available quantification methods for perfusion assessment using ICG NIR fluorescence imaging and to present an overview of current clinically utilized software implementations.

METHODS

PubMed was searched for clinical studies on the quantification of ICG NIR fluorescence imaging to assess tissue perfusion. Data on the utilized camera systems and performed methods of quantification were collected.

RESULTS

Eleven software programs for quantifying tissue perfusion using ICG NIR fluorescence imaging were identified. Five of the 11 programs have been described in three or more clinical studies, including Flow® 800, ROIs Software, IC Calc, SPY-Q™, and the Quest Research Framework®. In addition, applying normalization to fluorescence intensity analysis was described for two software programs.

CONCLUSION

Several systems or software solutions provide a quantification of ICG fluorescence; however, intraoperative applications are scarce and quantification methods vary abundantly. In the widespread search for reliable quantification of perfusion with ICG NIR fluorescence imaging, standardization of quantification methods and data acquisition is essential.

Evaluation of the Angiosome Concept Using Near-Infrared Fluorescence Imaging with Indocyanine Green

BACKGROUND

The angiosome concept is defined as the anatomical territory of a source artery within all tissue layers. When applying this theory in vascular surgery, direct revascularization (DR) is preferred to achieve increased blood flow toward the targeted angiosome of the foot in patients with lower extremity arterial disease (LEAD). This study evaluates the applicability of the angiosome concept using quantified near-infrared (NIR) fluorescence imaging with indocyanine green (ICG).

METHODS

This study included patients undergoing an endovascular- or surgical revascularization of the leg between January 2019 and December 2021. Preinterventional and postinterventional ICG NIR fluorescence imaging was performed. Three angiosomes on the dorsum of the foot were determined: the posterior tibial artery (hallux), the anterior tibial artery (dorsum of the foot) and the combined angiosome (second to fifth digit). The angiosomes were classified from the electronic patient records and the degree of collateralization was classified based on preprocedural computed tomography angiography and/or X-ray angiography. Fluorescence intensity was quantified in all angiosomes. A subgroup analysis based on endovascular or surgical revascularized angiosomes, and within critical limb threatening ischemia (CLTI) patients was performed.

RESULTS

ICG NIR fluorescence measurements were obtained in 52 patients (54 limbs) including a total of 157 angiosomes (121 DR and 36 indirect revascularizations [IR]). A significant improvement of all perfusion parameters in both the directly and indirectly revascularized angiosomes was found (P-values between <0.001-0.007). Within the indirectly revascularized angiosomes, 90.6% of the scored collaterals were classified as significant. When comparing the percentual change in perfusion parameters between the directly and indirectly revascularized angiosomes, no significant difference was seen in all perfusion parameters (P-values between 0.253 and 0.881). Similar results were shown in the CLTI patients subgroup analysis, displaying a significant improvement of perfusion parameters in both the direct and indirect angiosome groups (P-values between <0.001 and 0.007), and no significant difference when comparing the percentual parameter improvement between both angiosome groups (P-values between 0.134 and 0.359). Furthermore, no significant differences were observed when comparing percentual changes of perfusion parameters in directly and indirectly revascularized angiosomes for both endovascular and surgical interventions (P-values between 0.053 and 0.899).

CONCLUSIONS

This study proves that both DR and IR of an angiosome leads to an improvement of perfusion. This suggests that interventional strategies should not only focus on creating in-line flow to the supplying angiosome. One can argue that the angiosome concept is not applicable in patients with LEAD.

Systematic Review of Innovative Diagnostic Tests for Chronic Exertional Compartment Syndrome

The diagnosis chronic exertional compartment syndrome is traditionally linked to elevated intracompartmental pressures, although uncertainty regarding this diagnostic instrument is increasing. The aim of current review was to evaluate literature for alternative diagnostic tests. A search in line with PRISMA criteria was conducted. Studies evaluating diagnostic tests for chronic exertional compartment syndrome other than intracompartmental pressure measurements were included. Bias and quality of studies were evaluated using the Oxford Levels of Evidence and the QUADAS-2 instrument. A total of 28 studies met study criteria (MRI n=8, SPECT n=6, NIRS n=4, MRI and NIRS together n=1, miscellaneous modalities n=9). Promising results were reported for MRI (n=4), NIRS (n=4) and SPECT (n=3). These imaging techniques rely on detecting changes of signal intensity in manually selected regions of interest in the muscle compartments of the leg. Yet, diagnostic tools and protocols were diverse. Moreover, five studies explored alternative modalities serving as an adjunct, rather than replacing pressure measurements. Future research is warranted as clinical and methodological heterogeneity were present and high quality validation studies were absent. Further optimization of specific key criteria based on a patient's history, physical examination and symptom provocation may potentially render intracompartmental pressure measurement redundant.

Use of fluorescence imaging during lymphatic surgery: A Delphi survey of experts worldwide

BACKGROUND

Fluorescence imaging with indocyanine green is increasingly used during lymphedema patient management. However, to date, no guidelines exist on when it should and should not be used or how it should be performed. Our objective was to have an international panel of experts identify areas of consensus and nonconsensus in current attitudes and practices in fluorescence imaging with indocyanine green use during lymphedema surgery patient management.

METHODS

A 2-round Delphi study was conducted involving 18 experts in the use of fluorescence imaging during lymphatic surgery, all asked to vote on 49 statements on patient preparation and contraindications (n = 7 statements), indocyanine green dosing and administration (n = 10), fluorescence imaging uses and potential advantages (n = 16), and potential disadvantages and training needs (n = 16).

RESULTS

Consensus ultimately was reached on 40/49 statements, including consistent consensus regarding the value of fluorescence imaging with indocyanine green in almost all facets of lymphedema patient management, including early detection, assessing disease extent, preoperative work-up, surgical planning, intraoperative guidance, monitoring short- and longer-term outcomes, quality control, and resident training. All experts felt it was very safe, while 94% felt it should be part of routine care and that indocyanine green was superior to colored dyes and ultrasound. Nonetheless, there also was consensus that limited high-quality evidence remains a barrier to its widespread use and that patients should still be provided with specific information and asked to sign specific consent for both fluorescence imaging and indocyanine green.

CONCLUSION

Fluorescence imaging with or without indocyanine green appears to have several roles in lymphedema prevention, diagnosis, assessment, and treatment.

Theranostic potential of graphene quantum dots for multiple sclerosis

Nanomedicine offers great promise to solve healthcare problems using nanotechnology. Theranostics provide imaging/diagnosis and therapy simultaneously. Novel agents that target both the neuroinflammation and neurodegeneration component of multiple sclerosis (MS) are required. Progress has been achieved in developing smart, surface decorated nanoparticles that effectively transport the therapeutic drug into the central nervous system (CNS). Graphene quantum dots (GQDs) can be traced in vivo by fluorescence imaging due to their unique optical properties. They can also traverse the blood-brain barrier (BBB) and deliver drugs into the CNS. Moreover, GQDs have low cytotoxicity and higher biocompatibility. Therefore, GQDs can be utilized to design novel multifunctional nanocarrier theranostic tools for MS.

AVOID; a phase III, randomised controlled trial using indocyanine green for the prevention of anastomotic leakage in colorectal surgery

INTRODUCTION

Anastomotic leakage (AL) is one of the major complications after colorectal surgery. Compromised tissue perfusion at the anastomosis site increases the risk of AL. Several cohort studies have shown that indocyanine green (ICG) combined with fluorescent near-infrared imaging is a feasible and reproducible technique for real-time intraoperative imaging of tissue perfusion, leading to reduced leakage rates after colorectal resection. Unfortunately, these studies were not randomised. Therefore, we propose a randomised controlled trial to assess the value of ICG-guided surgery in reducing AL after colorectal surgery.

METHODS AND ANALYSIS

A multicentre, randomised controlled clinical trial will be conducted to assess the benefit of ICG-guided surgery in preventing AL. A total of 978 patients scheduled for colorectal surgery will be included. Patients will be randomised between the Fluorescence Guided Bowel Anastomosis group and the Conventional Bowel Anastomosis group. The primary endpoint is clinically relevant AL (defined as requiring active therapeutic intervention or reoperation) within 90 days after surgery. Among the secondary endpoints are 30-day clinically relevant AL, all-cause postoperative complications, all-cause and AL-related mortality, surgical and non-surgical reinterventions, total surgical time, length of hospital stay and all-cause and AL-related readmittance.

ETHICS AND DISSEMINATION

This protocol has been approved by the Medical Ethical Committee Leiden-Den Haag-Delft (METC-LDD) and is registered at ClinicalTrials.gov and trialregister.nl. The results of this study will be reported through peer-reviewed publications and conference presentations.

TRIAL REGISTRATION NUMBER

NCT04712032; NL7502.

Angiosome-guided endovascular revascularization for treatment of diabetic foot ulcers with peripheral artery disease

OBJECTIVE

Because diabetic foot ulcers (DFUs) are difficult to heal and cause huge economic losses to society, accelerating their healing has become extremely important. The purpose of this study was to evaluate the effect of revascularization based on the angiosome concept on DFU.

MATERIALS AND METHODS

Between January 2018 and July 2020, 112 consecutive legs with DFUs in 111 patients who were discharged from the vascular surgery department of our hospital were retrospectively evaluated. The legs were assigned to two groups depending on whether direct arterial flow to the foot ulcer based on the angiosome concept was achieved. Comparisons of the ulcer healing rate, mean time to ulcer healing, major amputation rate, survival rate, and major amputation-free survival rate between the angiosome direct revascularization (DR) and angiosome indirect revascularization (IR) groups were performed.

RESULTS

DR was achieved in 71 legs (63%) compared with IR in 41 legs. The ulcer healing rate (70.4% in the DR group vs. 34.1% in the IR group, P < 0.01), the mean time to ulcer healing (7.01 ± 4.26 months vs. 10.09 ± 3.24months, P < 0.01), the survival rate (90.1% vs. 53.7%, P < 0.01), and the major amputation-free survival rate (81.7% vs. 48.8%, P < 0.01) were significantly higher in the DR group than in the IR group. Undergoing DR did not significantly reduce the major amputations rate compared with IR (13.4% and 34.1%, respectively, P = 0.15), but there might be a trend. In multivariate models, DR remained a significant predictor for ulcer healing (HR, 7.07; 95% confidence interval, 6.54-7.60, P < 0.01). Opening multiple infrapopliteal arteries in the DR group compared with restoring only one infrapopliteal artery did not significantly improve the the ulcer healing rate (P = 0.59), the mean time to ulcer healing (P = 0.70), major amputation rate (P = 0.83), the survival rate (P = 0.31), and the major amputation-free survival rate(P = 0.40).

CONCLUSIONS

Attaining a direct arterial flow based on the angiosome concept may be important for ulcer healing, survival, and amputation-free survival in diabetic foot patients. Opening multiple infrapopliteal arteries in DR patients may not improve the ulcer healing, survival, major amputation or amputation-free survival compared with single DR vessel patency.

Normalization of Time-Intensity Curves for Quantification of Foot Perfusion Using Near-Infrared Fluorescence Imaging With Indocyanine Green

PURPOSE

Near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) is gaining popularity for the quantification of tissue perfusion, including foot perfusion in patients with lower extremity arterial disease (LEAD). However, the absolute fluorescence intensity is influenced by patient-and system-related factors limiting reliable and valid quantification. To enhance the quality of quantitative perfusion assessment using ICG NIR fluorescence imaging, normalization of the measured time-intensity curves seems useful.

MATERIALS AND METHODS

In this cohort study, the effect of normalization on 2 aspects of ICG NIR fluorescence imaging in assessment of foot perfusion was measured: the repeatability and the region selection. Following intravenous administration of ICG, the NIR fluorescence intensity in both feet was recorded for 10 mins using the Quest Spectrum platform^®. The effect of normalization on repeatability was measured in the nontreated foot in patients undergoing unilateral revascularization preprocedural and postprocedural (repeatability group). The effect of normalization on region selection was performed in patients without LEAD (region selection group). Absolute and normalized time-intensity curves were compared.

RESULTS

Successful ICG NIR fluorescence imaging was performed in 54 patients (repeatability group, n = 38; region selection group, n = 16). For the repeatability group, normalization of the time-intensity curves displayed a comparable inflow pattern for repeated measurements. For the region selection group, the maximum fluorescence intensity (Imax) demonstrated significant differences between the 3 measured regions of the foot (P = .002). Following normalization, the time-intensity curves in both feet were comparable for all 3 regions.

CONCLUSION

This study shows the effect of normalization of time-intensity curves on both the repeatability and region selection in ICG NIR fluorescence imaging. The significant difference between absolute parameters in various regions of the foot demonstrates the limitation of absolute intensity in interpreting tissue perfusion. Therefore, normalization and standardization of camera settings are essential steps toward reliable and valid quantification of tissue perfusion using ICG NIR fluorescence imaging.

Intra-operative assessment of the vascularisation of a cross section of the meniscus using near-infrared fluorescence imaging

PURPOSE

The purpose of this study was to assess whether the vascularisation of the meniscus could be visualised intra-operatively using near-infrared fluorescence (NIRF) imaging with indocyanine green (ICG) in patients undergoing total knee arthroplasty (TKA).

METHODS

The anterior horn (i.e., Cooper classification: zones C and D) of the meniscus that was least affected (i.e., least degenerative) was removed during TKA surgery in ten patients to obtain a cross section of the inside of the meniscus. Thereafter, 10 mg of ICG was injected intravenously, and vascularisation of the cross section of the meniscus was assessed using the Quest spectrum NIRF camera system. We calculated the percentage of patients in whom vascularisation was observed intra-operatively using NIRF imaging compared to immunohistochemistry.

RESULTS

Meniscal vascularisation using NIRF imaging was observed in six out of eight (75%) patients in whom vascularisation was demonstrated with immunohistochemistry. The median extent of vascularisation was 13% (interquartile range (IQR) 3-28%) using NIRF imaging and 15% (IQR 11-23%) using immunohistochemistry.

CONCLUSION

This study shows the potential of NIRF imaging to visualise vascularisation of the meniscus, as vascularisation was observed in six out of eight patients with histologically proven meniscal vascularisation.

LEVEL OF EVIDENCE

IV.

Predicting Clinical Outcomes in a Diabetic Foot Ulcer Population Using Fluorescence Imaging

OBJECTIVE

To retrospectively evaluate a cohort of patients with diabetic foot ulcers to determine if the rate of microcirculatory flow detected by fluorescence imaging within the wound and surrounding tissue is associated with healing outcomes.

METHODS

Tissue perfusion parameters used for the current analysis were the ingress rate (IR) within the wound bed (R01) and in an area remote from the wound (REF), as well as time to first blush. Wounds were then categorized based on their outcome (healed, healing, chronic nonhealing, partial foot amputation, proximal amputation below the knee) and compared between patients with positive or negative wound healing outcomes.

RESULTS

The final study cohort included 61 wounds and demonstrated that a higher IR within R01 and REF areas was significantly associated with positive outcomes, whereas time to first blush was not. A two-predictor logistic model found a significant relationship between IR (R01 and REF) and odds of wound healing.

CONCLUSIONS

Fluorescence imaging evaluation of a diabetic foot ulcer can provide valuable information on healing outcomes that can help determine if a wound is progressing toward healing and therefore may help inform the need for advanced wound modalities, referrals, and amputation.

Perfusion Patterns in Patients with Chronic Limb-Threatening Ischemia versus Control Patients Using Near-Infrared Fluorescence Imaging with Indocyanine Green

In assessing the severity of lower extremity arterial disease (LEAD), physicians rely on clinical judgements supported by conventional measurements of macrovascular blood flow. However, current diagnostic techniques provide no information about regional tissue perfusion and are of limited value in patients with chronic limb-threatening ischemia (CLTI). Near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) has been used extensively in perfusion studies and is a possible modality for tissue perfusion measurement in patients with CLTI. In this prospective cohort study, ICG NIR fluorescence imaging was performed in patients with CLTI and control patients using the Quest Spectrum Platform^® (Middenmeer, The Netherlands). The time–intensity curves were analyzed using the Quest Research Framework. Fourteen parameters were extracted. Successful ICG NIR fluorescence imaging was performed in 19 patients with CLTI and in 16 control patients. The time to maximum intensity (seconds) was lower for CLTI patients (90.5 vs. 143.3, p = 0.002). For the inflow parameters, the maximum slope, the normalized maximum slope and the ingress rate were all significantly higher in the CLTI group. The inflow parameters observed in patients with CLTI were superior to the control group. Possible explanations for the increased inflow include damage to the regulatory mechanisms of the microcirculation, arterial stiffness, and transcapillary leakage.

Optical Imaging in the Second Near Infrared Window for Vascular Bioimaging

Optical imaging in the second near infrared region (NIR-II, 1000-1700 nm) provides higher resolution and deeper penetration depth for accurate and real-time vascular anatomy, blood dynamics, and function information, effectively contributing to the early diagnosis and curative effect assessment of vascular anomalies. Currently, NIR-II optical imaging demonstrates encouraging results including long-term monitoring of vascular injury and regeneration, real-time feedback of blood perfusion, tracking of lymphatic metastases, and imaging-guided surgery. This review summarizes the latest progresses of NIR-II optical imaging for angiography including fluorescence imaging, photoacoustic (PA) imaging, and optical coherence tomography (OCT). The development of current NIR-II fluorescence, PA, and OCT probes (i.e., single-walled carbon nanotubes, quantum dots, rare earth doped nanoparticles, noble metal-based nanostructures, organic dye-based probes, and semiconductor polymer nanoparticles), highlighting probe optimization regarding high brightness, longwave emission, and biocompatibility through chemical modification or nanotechnology, is first introduced. The application of NIR-II probes in angiography based on the classification of peripheral vascular, cerebrovascular, tumor vessel, and cardiovascular, is then reviewed. Major challenges and opportunities in the NIR-II optical imaging for vascular imaging are finally discussed.

Near-infrared fluorescence imaging with indocyanine green for quantification of changes in tissue perfusion following revascularization

OBJECTIVES

Current diagnostic modalities for patients with peripheral artery disease (PAD) mainly focus on the macrovascular level. For assessment of tissue perfusion, near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) seems promising. In this prospective cohort study, ICG NIR fluorescence imaging was performed pre- and post-revascularization to assess changes in foot perfusion.

METHODS

ICG NIR fluorescence imaging was performed in 36 patients with PAD pre- and post-intervention. After intravenous bolus injection of 0.1 mg/kg ICG, the camera registered the NIR fluorescence intensity over time on the dorsum of the feet for 15 min using the Quest Spectrum Platform®. Time-intensity curves were plotted for three regions of interest (ROI): (1) the dorsum of the foot, (2) the forefoot, and (3) the hallux. Time-intensity curves were normalized for maximum fluorescence intensity. Extracted parameters were the maximum slope, area under the curve (AUC) for the ingress, and the AUC for the egress. The non-treated contralateral leg was used as a control group.

RESULTS

Successful revascularization was performed in 32 patients. There was a significant increase for the maximum slope and AUC egress in all three ROIs. The most significant difference was seen for the maximum slope in ROI 3 (3.7%/s to 6.6%/s, p < 0.001). In the control group, no significant differences were seen for the maximum slope and AUC egress in all ROIs.

CONCLUSIONS

This study shows the potential of ICG NIR fluorescence imaging in assessing the effect of revascularization procedures on foot perfusion. Future studies should focus on the use of this technique in predicting favorable outcome of revascularization procedures.

Assessment of Tissue Viability Following Amputation Surgery Using Near-Infrared Fluorescence Imaging With Indocyanine Green

BACKGROUND

Patients with chronic limb threatening ischemia have a risk of undergoing a major amputation within 1 year of nearly 30% with a substantial risk of re-amputation since wound healing is often impaired. Quantitative assessment of regional tissue viability following amputation surgery can identify patients at risk for impaired wound healing. In quantification of regional tissue perfusion, near-infrared (NIR) fluorescence imaging using Indocyanine Green (ICG) seems promising.

METHODS

This pilot study included adult patients undergoing lower extremity amputation surgery due to peripheral artery disease or diabetes mellitus. ICG NIR fluorescence imaging was performed within 5 days following amputation surgery using the Quest Spectrum Platform^Ⓡ. Following intravenous administration of ICG, the NIR fluorescence intensity of the amputation wound was recorded for 10 minutes. The NIR fluorescence intensity videos were analyzed and if a fluorescence deficit was observed, this region was marked as "low fluorescence." All other regions were marked as "normal fluorescence."

RESULTS

Successful ICG NIR fluorescence imaging was performed in 10 patients undergoing a total of 15 amputations. No "low fluorescence" regions were observed in 11 out of 15 amputation wounds. In 10 out of these 11 amputations, no wound healing problems occurred during follow-up. Regions with "low fluorescence" were observed in 4 amputation wounds. Impaired wound healing corresponding to these regions was observed in all wounds and a re-amputation was necessary in 3 out of 4. When observing time-related parameters, regions with low fluorescence had a significantly longer time to maximum intensity (113 seconds vs. 32 seconds, P = 0.003) and a significantly lesser decline in outflow after five minutes (80.3% vs. 57.0%, P = 0.003).

CONCLUSIONS

ICG NIR fluorescence imaging was able to predict postoperative skin necrosis in all four cases. Quantitative assessment of regional perfusion remains challenging due toinfluencing factors on the NIR fluorescence intensity signal, including camera angle, camera distance and ICG dosage. This was also observed in this study, contributing to a large variety in fluorescence intensity parameters among patients. To provide surgeons with reliable NIR fluorescence cut-off values for prediction of wound healing, prospective studies on the intra-operative use of this technique are required. The potential prediction of wound healing using ICG NIR fluorescence imaging will have a huge impact on patient mortality, morbidity as well as the burden of amputation surgery on health care.

Quantitative dynamic near-infrared fluorescence imaging using indocyanine green for analysis of bowel perfusion after mesenteric resection

SIGNIFICANCE

Near-infrared (NIR) fluorescence imaging using indocyanine green (ICG) has proven to be a feasible application for real-time intraoperative assessment of tissue perfusion, although quantification of NIR fluorescence signals is pivotal for standardized assessment of tissue perfusion.

AIM

Four patients are described with possible compromised bowel perfusion after mesenteric resection. Based on these patients we want to emphasize the difficulties in the quantification of NIR fluorescence imaging for perfusion analysis.

APPROACH

During image-guided fluorescence assessment, 5 mg of ICG (2.5  mg  /  ml) was intravenously administered by the anesthesiologist. NIR fluorescence imaging was done with the open camera system of Quest Medical Imaging. Fluorescence data taken from the regions of interest (bowel at risk, transition zone of bowel at risk and adjacent normally perfused bowel, and normally perfused reference bowel) were quantitatively analyzed after surgery for fluorescence intensity-and perfusion time-related parameters.

RESULTS

Bowel perfusion, as assessed clinically by independent surgeons based on NIR fluorescence imaging, resulted in different treatment strategies, three with excellent clinical outcome, but one with a perfusion related complication. Post-surgery quantitative analysis of fluorescence dynamics showed different patterns in the affected bowel segment compared to the unaffected reference segments for the four patients.

CONCLUSIONS

Similar intraoperative fluorescence results could lead to different surgical treatment strategies, which demonstrated the difficulties in interpretation of uncorrected fluorescence signals. Real-time quantification and standardization of NIR fluorescence perfusion imaging could probably aid surgeons in the nearby future.

Perfusion Parameters in Near-Infrared Fluorescence Imaging with Indocyanine Green: A Systematic Review of the Literature

(1) Background: Near-infrared fluorescence imaging is a technique capable of assessing tissue perfusion and has been adopted in various fields including plastic surgery, vascular surgery, coronary arterial disease, and gastrointestinal surgery. While the usefulness of this technique has been broadly explored, there is a large variety in the calculation of perfusion parameters. In this systematic review, we aim to provide a detailed overview of current perfusion parameters, and determine the perfusion parameters with the most potential for application in near-infrared fluorescence imaging. (2) Methods: A comprehensive search of the literature was performed in Pubmed, Embase, Medline, and Cochrane Review. We included all clinical studies referencing near-infrared perfusion parameters. (3) Results: A total of 1511 articles were found, of which, 113 were suitable for review, with a final selection of 59 articles. Near-infrared fluorescence imaging parameters are heterogeneous in their correlation to perfusion. Time-related parameters appear superior to absolute intensity parameters in a clinical setting. (4) Conclusions: This literature review demonstrates the variety of parameters selected for the quantification of perfusion in near-infrared fluorescence imaging.

Real-time fluorescence imaging in intraoperative decision making for cancer surgery

Fluorescence-guided surgery is an intraoperative optical imaging method that provides surgeons with real-time guidance for the delineation of tumours. Currently, in phase 1 and 2 clinical trials, evaluation of fluorescence-guided surgery is primarily focused on its diagnostic performance, although the corresponding outcome variables do not inform about the added clinical benefit of fluorescence-guided surgery and are challenging to assess objectively. Nonetheless, the effect of fluorescence-guided surgery on intraoperative decision making is the most objective outcome measurement to assess the clinical value of this imaging method. In this Review, we explore the study designs of existing trials of fluorescence-guided surgery that allow us to extract information on potential changes in intraoperative decision making, such as additional or more conservative resections. On the basis of this analysis, we offer recommendations on how to report changes in intraoperative decision making that result from fluorescence imaging, which is of utmost importance for the widespread clinical implementation of fluorescence-guided surgery.

Correlation between ankle-brachial index and thermography measurements in patients with peripheral arterial disease

OBJECTIVES

To correlate the ankle-brachial index and photographic thermography findings in patients with peripheral arterial disease.

METHODS

Photographic thermography was performed at the foot level, and ankle-brachial index was measured in 72 lower limbs of 53 patients with peripheral arterial disease who were divided into calcified artery, patients with an ankle-brachial index greater than 1.4; and non-calcified artery classified as asymptomatic, mild, moderate, and severe on the basis of peripheral arterial disease severity. Fisher's exact test was used for categorical data, and Wilcoxon test was used for numerical data.

RESULTS

Spearman's correlation analysis showed a strong correlation (R = 0.7) between the ankle-brachial index and the mean plantar temperature in patients without lower limb artery calcification. Linear regression yielded the predictor equation Y = 3.296 × X + 29.75, wherein ankle-brachial index (X) can be predicted on the basis of temperature values. Spearman's correlation test showed no significance (p = 0.2174) in patients with arterial calcification. Kruskal-Wallis test with post hoc analysis using Dunn's test for multiple comparisons showed that the mean plantar temperature was lower in patients with arterial calcification.

CONCLUSION

Photographic thermography findings show a strong correlation with ankle-brachial index in patients with non-calcified arteries.

Cell-Based Tracers as Trojan Horses for Image-Guided Surgery

Surgeons rely almost completely on their own vision and palpation to recognize affected tissues during surgery. Consequently, they are often unable to distinguish between different cells and tissue types. This makes accurate and complete resection cumbersome. Targeted image-guided surgery (IGS) provides a solution by enabling real-time tissue recognition. Most current targeting agents (tracers) consist of antibodies or peptides equipped with a radiolabel for Positron Emission Tomography (PET) and Single Photon Emission Computed Tomography (SPECT), magnetic resonance imaging (MRI) labels, or a near-infrared fluorescent (NIRF) dye. These tracers are preoperatively administered to patients, home in on targeted cells or tissues, and are visualized in the operating room via dedicated imaging systems. Instead of using these 'passive' tracers, there are other, more 'active' approaches of probe delivery conceivable by using living cells (macrophages/monocytes, neutrophils, T cells, mesenchymal stromal cells), cell(-derived) fragments (platelets, extracellular vesicles (exosomes)), and microorganisms (bacteria, viruses) or, alternatively, 'humanized' nanoparticles. Compared with current tracers, these active contrast agents might be more efficient for the specific targeting of tumors or other pathological tissues (e.g., atherosclerotic plaques). This review provides an overview of the arsenal of possibilities applicable for the concept of cell-based tracers for IGS.

Vascular Assessment of the Lower Extremity with a Chronic Wound

Peripheral arterial disease (PAD) affects many individuals worldwide and is associated with increased morbidity and mortality. Controversy exists on whether or not to screen asymptomatic patients. Further complicating this is that many patients with a chronic lower extremity wound are often asymptomatic. PAD and traditional noninvasive vascular studies may be inaccurate in providing a correct diagnosis. A review of current and novel vascular assessment modalities along with their benefits and limitations are presented here. A combination of these vascular assessments may help improve accuracy in diagnosis, providing timely care to those patients in need.

Assessment of foot perfusion: Overview of modalities, review of evidence, and identification of evidence gaps

Patients with critical limb ischemia have nonhealing wounds and/or ischemic rest pain and are at high risk for amputation and mortality. Accurate evaluation of foot perfusion should help avoid unnecessary amputation, guide revascularization strategies, and offer efficient surveillance for patency. Our aim is to review current modalities of assessing foot perfusion in the context of the practical clinical management of patients with critical limb ischemia.

Fluorescence angiography compared to toe blood pressure in the evaluation of severe limb ischemia

Background: Severity of limb ischemia in peripheral arterial disease (PAD) patients is usually evaluated by clinical assessment and toe blood pressure (TBP) or transcutaneous oxygen pressures (TcPO 2). Indocyanin green angiography (IGA) is a promising tool generating a foot cartography of skin microvascular perfusion. However, there is no consensus about the fluorescence parameters that should be used to evaluate ischemia. The purpose of this cross-sectional evaluation and 3-month clinical follow-up was to determine the best fluorescence parameter for the evaluation of severe PAD, using TBP as reference. Patients and methods: IGA was realized in patients with clinical suspicion of CLI in addition to TBP and TcPO 2. Parameters from the time intensity fluorescence curve measured on the foot were compared with TBP (primary reference), and with TcPO2. Clinical outcomes (amputation, revascularization, death) were recorded at 3 months follow-up. Results: Thirty-four patients were included and IGA could be analysed in 29 of them. When all limbs were studied, no significant correlation was found between any of the measured fluorescence parameters (saturation time, ingress slope, amplitude, delay) and TBP pressure neither TCPO2. In the limbs with CLI, a significant correlation between the TBP and amplitude on the forefoot was found. According to the outcome, none of the fluorescence parameters showed a significant prognostic value in contrast to the significant results for TBP and TcPO2. Conclusions: In this study, quantitative analysis of IGA parameters did not show any prognostic value, nor was there any significant statistical association with well-established prognostic parameters such as TBP and TcPO 2 in patients with suspected CLI. A correlation was found between amplitude and TBP in patients with CLI. Topographical information such as perfusion heterogeneity was not evaluated and remains a valuable target to be investigated.

Mini-Platform for Off-On Near-Infrared Fluorescence Imaging Using Peptide-Targeting Ligands

Here, we propose a zwitterionic near-infrared (NIR) fluorophore-tryptophan (Trp) conjugate with a cleavable linker as a minimal-sized versatile platform (MP) for the preparation of peptide ligand-based off-on type molecular probes. The zwitterionic NIR fluorophore in MP undergoes fluorescence quenching via a photoinduced electron transfer mechanism when in close proximity to tryptophan, and nonspecific binding with serum proteins is minimized by the zwitterionicity of the fluorophore. The linker can be cleaved inside cancer cells in response to tumor-associated stimuli. As a proof-of-concept experiment, ATTO655 was covalently linked with Trp via a diarginine linker to form an MP. A cyclic peptide consisting of Arg-Gly-Asp-d-Phe-Lys (cRGD) was used as a cancer-targeting ligand and was conjugated to the MP to form cRGD-MP. The NIR fluorescence of cRGD-MP could be selectively turned on inside the target cancer cells, thereby enabling specific fluorescence imaging of integrin α_vβ₃-overexpressing cancer cells in vitro and in vivo.