In Patients with Severe Peripheral Arterial Disease, Revascularization-Induced Improvement in Lower Extremity Ischemia Can Be Detected by Laser Speckle Contrast Imaging of the Fluctuation in Blood Perfusion after Local Heating

Smartphone-Based Rigid Endoscopy Device with Hemodynamic Response Imaging and Laser Speckle Contrast Imaging

Modern smartphones have been employed as key elements in point-of-care (POC) devices due to remarkable advances in their form factor, computing, and display performances. Recently, we reported a combination of the smartphone with a handheld endoscope using laser speckle contrast imaging (LSCI), suggesting potential for functional POC endoscopy. Here, we extended our work to develop a smartphone-combined multifunctional handheld endoscope using dual-wavelength LSCI. Dual-wavelength LSCI is used to monitor the changes in dynamic blood flow as well as changes in the concentration of oxygenated (HbO2), deoxygenated (Hbr), and total hemoglobin (HbT). The smartphone in the device performs fast acquisition and computation of the raw LSCI data to map the blood perfusion parameters. The flow imaging performance of the proposed device was tested with a tissue-like flow phantom, exhibiting a speckle flow index map representing the blood perfusion. Furthermore, the device was employed to assess the blood perfusion status from an exteriorized intestine model of rat in vivo during and after local ischemia, showing that blood flow and HbO2 gradually decreased in the ischemic region whereas hyperemia and excess increases in HbO2 were observed in the same region right after reperfusion. The results indicate that the combination of LSCI with smartphone endoscopy delivers a valuable platform for better understanding of the functional hemodynamic changes in the vasculatures of the internal organs, which may benefit POC testing for diagnosis and treatment of vascular diseases.

2D perfusion angiography: an alternative method to evaluate endovascular intervention for acute lower limb ischemia

BACKGROUND

Despite advances in endovascular techniques to treat acute limb ischemia (ALI), evaluation of clinical outcomes for revascularization remains challenging, especially the accurate quantification of post-endovascular limb perfusion. This study aimed to investigate the accuracy and value of 2D perfusion angiography to evaluate endovascular intervention for ALI.

METHODS

A total of 47 patients with ALI were retrospectively analyzed. The transcutaneous oxygen partial pressure (TcPO2) was obtained using laser Doppler blood perfusion monitoring. The ankle-brachial index (ABI) and angiographic images were obtained before and after endovascular intervention. iFlow imaging was used to obtain color-coded images. Regions of interest (ROIs) at the femoral head, knee joint, and ankle joint were selected to obtain the time to peak (TTP). The differences in the TTP between the knee and femoral head regions (TTP difference in the knee area) and between the ankle and knee regions (TTP difference in the ankle area) were observed. The TTP, ABI, and TcPO2 between the complete response (CR), partial response (PR), no response (NR), and amputation (AM) groups were compared. The correlation between TTP changes in the ankle area (ΔTTP) and changes in ABI (ΔABI)/changes in TcPO2 (ΔTcPO2) was analyzed.

RESULTS

There was a significant increase in both TcPO2 and ABI compared with the pre-intervention values (27.75 ± 5.32 vs 40.92 ± 4.62, and 0.35 ± 0.16 vs 0.79 ± 0.15, respectively, all p < 0.01). The post-intervention TTP differences in the knee areas (5.12 ± 2.45 s) and ankle areas (6.93 ± 4.37 s) were significantly faster than pre-intervention TTP differences (7.03 ± 2.57 s and 10.66 ± 4.07 s, respectively, all p < 0.05). The post-operative TTP in the ankle area, post-operative TTP difference in the ankle area, and ΔTTP in the AM group were higher than the values in the CR and PR groups. The ΔTTP demonstrated strong correlation with ΔABI (r = -0.722, p < 0.01) and ΔTcPO2 (r = -0.734, p < 0.01).

CONCLUSIONS

2D perfusion angiography with enhanced visual and quantitative analysis exhibits great potential to evaluate the efficacy of endovascular intervention, and provides a quantitative and sensitive tool to evaluate post-endovascular limb perfusion for ALI patients.

Development of a Non-Invasive Local Heating Load Test to Detect Severe Limb Ischemia Within 200 seconds

Purpose

To establish a non-invasive test method for the rapid detection of severe ischemia (SI) in the limbs in patients with peripheral arterial disease (PAD).

Methods

Between November 2019 and May 2021, 22 patients admitted for PAD to 2 hospitals agreed to participate in the study. All patients underwent a local heating load (LHL) test. SI was defined as at least 1 ankle-brachial index value of <.4 and/or transcutaneous oximetry value of <30 mmHg. The other cases were classified as mild-to-moderate ischemia (MMI). The LHL test was performed simultaneously with 15 minutes of heating and measurement by attaching a blood flow meter measuring probe combined with a warmer to the patient’s dorsal foot. Evaluation consisted of 200-s periods from the start of heating to 800 seconds. For each period, perfusion value (PV) was evaluated, and slope was calculated graphically based on linear regression as PV fluctuation per minute. Test accuracy was calculated using a receiver operating characteristic curve.

Results

Twenty-four limbs of 18 patients were finally evaluated; 4 patients (2 with missing data, 1 with collagen disease, and 1 with embolism) were excluded, with 13 and 11 limbs in the SI and MMI groups, respectively. The SI group showed a significantly lower slope value in the first 200 seconds and lower PV at 200 seconds and thereafter. From the slope value, it was possible to detect SI with 85% sensitivity and 73% specificity at 200 seconds. PV could be determined with higher accuracy in periods after 200 seconds, with 85% sensitivity and 82% specificity at 800 seconds.

Conclusions

Our non-invasive LHL test could be used as a rapid screening test to detect SI in limbs within 200 seconds, as well as a more accurate test to detect ischemia within 800 seconds.

Comprehensive imaging of microcirculatory changes in the foot during endovascular intervention - A technical feasibility study

Chronic limb-threatening ischemia (CLTI) has a major impact on patient's lives and is associated with a heavy health care burden with high morbidity and mortality. Treatment by endovascular intervention is mostly based on macrocirculatory information from angiography and does not consider the microcirculation. Despite successful endovascular intervention according to angiographic criteria, a proportion of patients fail to heal ischemic lesions. This might be due to impaired microvascular perfusion and variations in the supply to different angiosomes. Non-invasive optical techniques for microcirculatory perfusion and oxygen saturation imaging have the potential to provide the interventionist with additional information in real-time, supporting clinical decisions during the intervention. This study presents a novel multimodal imaging system, based on multi-exposure laser speckle contrast imaging and multi-spectral imaging, for continuous use during endovascular intervention. The results during intervention display spatiotemporal changes in the microcirculation compatible with expected physiological reactions during balloon dilation, with initially induced ischemia followed by a restored perfusion, and local administration of a vasodilator inducing hyperemia. We also present perioperative and postoperative follow-up measurements with a pulsatile microcirculation perfusion. Finally, cases of spatial heterogeneity in the observed oxygen saturation and perfusion are discussed. In conclusion, this technical feasibility study shows the potential of the methodology to characterize changes in microcirculation before, during, and after endovascular intervention.

Multispectral optoacoustic tomography of peripheral arterial disease based on muscle hemoglobin gradients-a pilot clinical study

Background

Current imaging assessment of peripheral artery disease (PAD) relies on anatomical cross-sectional visualizations of the affected arteries. Multispectral optoacoustic tomography (MSOT) is a novel molecular imaging technique that provides direct and label-free visualizations of soft tissue perfusion and oxygenation.

Methods

MSOT was prospectively assessed in a pilot trial in healthy volunteers (group n₁=4, mean age 31, 50% male and group n₃=4, mean age 37.3, 75% male) and patients with intermittent claudication (group n₂=4, mean age 72, 75% male, PAD stage IIb). We conducted cuff-induced ischemia (group n₁) and resting state measurements (groups n₂ and n₃) over the calf region. Spatially resolved mapping of oxygenated (HbO₂), deoxygenated (Hb) and total (THb) hemoglobin, as well as oxygen saturation (SO₂), were measured via hand-held hybrid MSOT-Ultrasound based purely on hemoglobin contrast.

Results

Calf measurements in healthy volunteers revealed distinct dynamics for HbO₂, Hb, THb and SO₂ under cuff-induced ischemia. HbO₂, THb and SO₂ levels were significantly impaired in PAD patients compared to healthy volunteers (P<0.05 for all parameters). Revascularization led to significant improvements in HbO₂ of the affected limb.

Conclusions

Clinical MSOT allows for non-invasive, label-free and real-time imaging of muscle oxygenation in health and disease with implications for diagnostics and therapy assessment in PAD.

Real-time video-rate perfusion imaging using multi-exposure laser speckle contrast imaging and machine learning

SIGNIFICANCE

Multi-exposure laser speckle contrast imaging (MELSCI) estimates microcirculatory blood perfusion more accurately than single-exposure LSCI. However, the technique has been hampered by technical limitations due to massive data throughput requirements and nonlinear inverse search algorithms, limiting it to an offline technique where data must be postprocessed.

AIM

To present an MELSCI system capable of continuous acquisition and processing of MELSCI data, enabling real-time video-rate perfusion imaging with high accuracy.

APPROACH

The MELSCI algorithm was implemented in programmable hardware (field programmable gate array) closely interfaced to a high-speed CMOS sensor for real-time calculation. Perfusion images were estimated in real-time from the MELSCI data using an artificial neural network trained on simulated data. The MELSCI perfusion was compared to two existing single-exposure metrics both quantitatively in a controlled phantom experiment and qualitatively in vivo.

RESULTS

The MELSCI perfusion shows higher signal dynamics compared to both single-exposure metrics, both spatially and temporally where heartbeat-related variations are resolved in much greater detail. The MELSCI perfusion is less susceptible to measurement noise and is more linear with respect to laser Doppler perfusion in the phantom experiment (R2  =  0.992).

CONCLUSIONS

The presented MELSCI system allows for real-time acquisition and calculation of high-quality perfusion at 15.6 frames per second.

2D perfusion DSA with an open-source, semi-automated, color-coded software for the quantification of foot perfusion following infrapopliteal angioplasty: a feasibility study

BACKGROUND

Foot perfusion has been recently implemented as a new tool for optimizing outcomes of peripheral endovascular procedures. A custom-made, two-dimensional perfusion digital subtraction angiography (PDSA) algorithm has been implemented to quantify outcomes of endovascular treatment of critical limb ischemia (CLI), assist intra-procedural decision-making, and enhance clinical outcomes.

METHODS

The study was approved by the Hospital's Ethics Committee. This prospective, single-center study included seven consecutive patients scheduled to undergo infrapopliteal endovascular treatment of CLI. Perfusion blood volume (PBV), mean transit time (MTT), and perfusion blood flow (PBF) maps were extracted by analyzing time-intensity curves and signal intensity on the perfused vessel mask. Mean values calculated from user-specified regions of interest (ROIs) on perfusion maps were employed to evaluate pre- and post-endovascular treatment condition. Measurements were performed immediately after final PDSA.

RESULTS

In total, five patients (aged 54 ± 16 years, mean ± standard deviation) were analyzed, as two patients were excluded due to significant motion artifacts. Post-procedural MTT presented a mean decrease of 19.1% for all patients and increased only in 1 of 5 patients, demonstrating in 4/5 patients an increase in tissue perfusion after revascularization. Overall mean PBF and PBV values were also analogously increased following revascularization (446% and 69.5% mean, respectively) and in the majority of selected ROIs (13/15 and 12/15 ROIs, respectively).

CONCLUSIONS

Quantification of infrapopliteal angioplasty outcomes using this newly proposed, custom-made, intra-procedural PDSA algorithm was performed using PBV, MTT, and PBF maps. Further studies are required to determine its role in peripheral endovascular procedures ( ClinicalTrials.gov Identifier: NCT04356092).

Applicability of Transcutaneous Oxygen Tension Measurement in the Assessment of Chronic Limb-Threatening Ischemia

Transcutaneous oxygen tension measurement (TcPO₂) is widely applied for the evaluation of chronic limb-threatening ischemia (CLTI). Nevertheless, studies that focused on the clinical value of TcPO₂ have shown varying results. We identified factors that potentially play a role in TcPO₂ measurement variation such as probe placement, probe temperature, and the use of a reference probe. In this review of the current literature, we assessed the application of these factors. A systematic search was conducted. Parameters that were assessed were probe placement, probe temperature, and mentioning and/or use of a reference probe. In total, 36 articles were eligible for analysis. In 24 (67%) studies, probes were placed on specific anatomical locations. Seven (19%) studies placed probes, regardless of the location of the ulcer, adjacent to an ischemic lesion or ulcer (perilesion). Selected temperature setting of the probe differed; in 18 (50%), a default probe temperature of 44°C was selected, and in 13 (36%), a different temperature was selected. In 31 (84%) studies, the use of a reference probe was not reported. Transcutaneous oxygen tension measurement is applied diversely in patients with CLTI. Homogeneity in TcPO₂ protocols is warranted for reliable clinical application and to compare future TcPO₂ research.

Assessment of the Severity of Ischaemia and the Outcomes of Revascularisation in Peripheral Arterial Disease Patients Based on the Skin Microcirculatory Response to a Thermal Load Test

Objective

This study investigated the skin microcirculatory response to a thermal load test using a laser Doppler flowmetry device to evaluate the severity of limb ischaemia and the outcomes of revascularisation in patients with peripheral arterial disease (PAD).

Methods

A total of 34 PAD patients (39 limbs) including 17 critical limb ischaemia (CLI) patients (21 limbs) who underwent revascularisation were enrolled. The skin microcirculation of the dorsal side of the affected foot was investigated for 15 minutes after local heating. The tests were performed both before and after revascularisation, and several parameters gleaned from the microcirculatory fluctuations were analysed and compared with the ankle brachial pressure index and the transcutaneous oxygen tension (tcPO₂) values.

Results

Among the parameters, significant differences were observed between the CLI patients and patients with claudication with regard to the increasing phase time (T_inc), the difference in the perfusion values at the onset and the peak of the transient increase in blood perfusion (PΔ), the slope of the transient increase in blood perfusion (S_in), and the slope of the decrease in blood perfusion after the peak (S_de). In CLI patients, the PΔ, S_in, and S_de values increased significantly after revascularisation. In the patients with claudication, the changes in the parameters after revascularisation were not statistically significant. The S_de showed the most statistically significant correlation with the tcPO₂ value (ρ .759, p < .001).

Conclusions

Thermal load testing can be used to evaluate the severity of limb ischaemia in patients with PAD.

•

New thermal load testing for evaluation of the severity of limb ischaemia is presented.

•

Skin blood flow response to thermal load was investigated by laser Doppler flowmetry.

•

Thermal load testing can be used to evaluate the severity of limb ischaemia.