Detection of Peripheral Arterial Disease Within the Foot Using Vascular Optical Tomographic Imaging: A Clinical Pilot Study

Spatial-Temporal Oxygenation Mapping Using a Near-Infrared Optical Scanner: Towards Peripheral Vascular Imaging

Near-infrared spectroscopy (NIRS)-based peripheral perfusion, or microcirculation, can be used to assess the severity of peripheral vascular dysfunction. A low-cost, portable non-contact near-infrared optical scanner (NIROS) was developed for spatio-temporal mapping of tissue oxygenation and perfusion in tissues. In vivo validation studies were carried out on control subjects (n = 3) to assess the ability of NIROS to measure real-time oxygenation changes in response to an occlusion paradigm on the dorsum of the hand. NIROS captured real-time tissue oxygenation changes with 95% correlation when compared to a commercial device. A feasibility peripheral imaging study was performed in a mouse model (n = 5) of chronic kidney disease (CKD) induced vascular calcification to assess differences in microcirculatory peripheral tissue oxygenation. The tissue oxygenation (in terms of oxy-, deoxy-, and total hemoglobin changes) due to the occlusion paradigm was distinctly different prior to (week-6) and after the onset of vascular calcification (week-12) in the murine tails. Future work will involve extensive studies to correlate these microcirculatory tissue oxygenation changes in the peripheral tail to the vascular calcification in the heart.

Postintervention monitoring of peripheral arterial disease wound healing using dynamic vascular optical spectroscopy

SIGNIFICANCE

Due to the persistence of chronic wounds, a second surgical intervention is often necessary for patients with peripheral arterial disease (PAD) within a year of the first intervention. The dynamic vascular optical spectroscopy system (DVOS) may assist physicians in determining patient prognosis only a month after the first surgical intervention.

AIM

We aim to assess the DVOS utility in characterizing wound healing in PAD patients after endovascular intervention.

APPROACH

The DVOS used near-infrared light ( 670 < λ < 850    nm ) to record hemodynamic response to a cuff inflation in 14 PAD patients with lower limb ulcers immediately before, immediately after, and at a first follow-up 3 to 4 weeks after intervention. Ankle-brachial index (ABI) and arterial duplex ultrasound (A-DUS) measurements were obtained when possible.

RESULTS

The total hemoglobin plateau time differed significantly between patients with ulcers that reduced in size ( N = 9 ) and patients with ulcers that did not ( N = 5 ) 3 to 4 weeks after intervention ( p  value < 0.001 ). Data correlated strongly (89% sensitivity, 100% specificity, and AUC = 0.96 ) with long-term wound healing. ABI and A-DUS measurements were not statistically associated with wound healing.

CONCLUSIONS

This pilot study demonstrates the potential of the DVOS to aid physicians in giving accurate long-term wound healing prognoses 1 month after intervention.

Measurement of Revascularization Effect Using Near Infrared Spectroscopy in Below the Knee Arteries

Background

Current methods evaluating tissue ischemia are based mainly on evaluating blood flow and not tissue perfusion. However, diabetes mainly affects small vessels and blood flow evaluation is insufficient. The aim of the trial was to evaluate the feasibility of NIRS in measuring perfusion changes during chronic total occlusion (CTO) revascularization in below the knee (BTK) arteries.

Methods

A prospective observational study was performed. During the endovascular revascularization procedure, tissue oxygenation changes were measured using three NIRS sensors. Postoperative angiographies and 30 days wound healing was evaluated.

Results

The study enrolled 30 patients with chronic limb threatening ischemia, occluded below the knee arteries, Rutherford 5. Mean age 74.7 ± 11.2 years, 16 (53%) of the patients had diabetes mellitus, 10 (33%) had end-stage renal disease. A statistically significant NIRS rSO 2 increase was observed on sensors near the wound after the revascularization, p = 0.001. Thirty days follow-up visits included 27 patients, because 3 patients had died. Comparing good wound healing group with poor wound healing group intraoperative NIRS rSO 2 increase difference was statistically significant, p = 0.017.

Conclusions

The study confirmed tissue perfusion increase could be detected using NIRS during revascularization of below the knee arteries. An intraoperative increase of NIRS rSO 2 proved to predict wound healing results.

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.

Biophotonics methods for functional monitoring of complications of diabetes mellitus

The prevalence of diabetes complications is a significant public health problem with a considerable economic cost. Thus, the timely diagnosis of complications and prevention of their development will contribute to increasing the length and quality of patient life, and reducing the economic costs of their treatment. This article aims to review the current state-of-the-art biophotonics technologies used to identify the complications of diabetes mellitus and assess the quality of their treatment. Additionally, these technologies assess the structural and functional properties of biological tissues, and they include capillaroscopy, laser Doppler flowmetry and hyperspectral imaging, laser speckle contrast imaging, diffuse reflectance spectroscopy and imaging, fluorescence spectroscopy and imaging, optical coherence tomography, optoacoustic imaging and confocal microscopy. Recent advances in the field of optical noninvasive diagnosis suggest a wider introduction of biophotonics technologies into clinical practice and, in particular, in diabetes care units.

Detecting hemodynamic changes in the foot vessels of diabetic patients by photoacoustic tomography

Limb perfusion monitoring is critical for diabetes mellitus (DM) patients as they are vulnerable to vascular complications due to prolonged hyperglycemia. However, current clinical approaches are ineffective in vascular imaging and in assessing vascular function in lower limbs. In this work, a concave ultrasound transducer array-based photoacoustic tomography (PAT) system was used to image the foot dorsal section of a subject, and a total of seven DM patients and seven healthy volunteers were enrolled in this study. Hemodynamic changes in foot vessels during vascular occlusion as well as oxygen saturation (SO₂ ) in rest were analyzed for both groups. The results obtained showed that DM patients have a unique peripheral hemodynamic response to occlusion and a lower level SO₂ , compared to that for healthy subjects. This suggests that PAT has the potential to detect vascular dysfunction in DM patients and to measure the effect of treatment.

A systematic review of diagnostic techniques to determine tissue perfusion in patients with peripheral arterial disease

Introduction: Peripheral arterial disease (PAD) may cause symptoms due to impaired tissue perfusion of the lower extremity. So far, assessment of PAD is mainly performed by determination of stenosis or occlusion in the large arteries and does not focus on microcirculation. Several diagnostic techniques have been recently introduced that may enable tissue perfusion measurements in the lower limb; however, most have not yet been implemented in clinical daily practice. This systematic review provides an overview of these diagnostic techniques and their ability to accurately detect PAD by peripheral tissue perfusion. Areas covered: A literature search was performed for articles that described a diagnostic technique to determine tissue perfusion in patients with known PAD compared with healthy controls. Expert opinion: So far, transcutaneous oxygen measurements are most often used to measure tissue oxygenation in PAD patients, but evidence seems too low to define this technique as a gold standard, and implementing this technique for home monitoring is difficult. New potentially suitable diagnostic tests should be non-invasive, contact-free, and quick. Further research is needed for all of these techniques before broad implementation in clinical use is justified, in hospital, and for home monitoring.

Photoacoustic assessment of hemodynamic changes in foot vessels

Monitoring the blood supply in the lower extremities is critical for individuals who are vulnerable to vascular dysfunction. Current clinical approaches are ineffective in observing hemodynamic changes in peripheral vessels. In this paper, we investigate the potential of photoacoustic tomography (PAT) as an alternative way to in vivo monitor hemodynamic changes in foot vessels. High spatial and temporal resolution maps of hemoglobin in major arteries and veins are shown. Results from twelve human subjects are presented here to visualize vascular perfusion of healthy volunteers in two age groups (young vs aged). Significant differences between the two groups are observed and verify the declining in vascular function with aging, highlighting the potential of PAT as a new tool to evaluate vascular function in the lower extremities.

Modeling of the hemodynamics in the feet of patients with peripheral artery disease

To simulate the hemodynamic effects in the feet in response to a thigh cuff occlusion, we have developed a multi-compartmental model in which the circulatory system for the leg is represented by its electrical equivalents. Dynamic vascular optical tomographic imaging data previously obtained from 20 patients with peripheral artery disease (PAD) and 20 healthy subjects is used to test the model. Analyzing the clinical data with the support of the model yields diagnostic specificity and sensitivity in the 90-95% range, significantly higher than previously reported.

Photoacoustic computed tomography of human extremities

We present a method of imaging angiographic structures in human extremities, including hands, arms, legs, and feet, using a newly developed photoacoustic computed tomography (PACT) system. The system features deep penetration (1.8 cm in muscular tissues) with high spatial and temporal resolutions. A volumetric image is acquired within 5 to 15 s while each cross sectional image is acquired within 100  μs. Therefore, we see no blurring from motion in the imaging plane. Longitudinal and latitudinal cross-sectional images of a healthy volunteer clearly show the vascular network of each appendage and highlight the system's ability to image major and minor vasculatures, without the use of an external contrast or ionizing radiation. We also track heartbeat-induced arterial movement at a two-dimensional frame rate of 10 Hz. This work substantiates the idea that PACT could be used as a noninvasive method for imaging human vasculatures.

Non-contact dynamic diffuse optical tomography imaging system for evaluating lower extremity vasculature

A novel multi-view non-contact dynamic diffuse optical tomographic imaging system for the clinical evaluation of vasculature in the lower extremities is presented. The system design and implementation are described in detail, including methods for simultaneously obtaining and reconstructing diffusely reflected and transmitted light using a system of mirrors and a single CCD camera. The system and its performance using numeric simulations and optical phantoms. Measurements of a healthy foot in vivo demonstrates the potential of the system in assessing perfusion within the foot.

Direct approach to compute Jacobians for diffuse optical tomography using perturbation Monte Carlo-based photon "replay"

Perturbation Monte Carlo (pMC) has been previously proposed to rapidly recompute optical measurements when small perturbations of optical properties are considered, but it was largely restricted to changes associated with prior tissue segments or regions-of-interest. In this work, we expand pMC to compute spatially and temporally resolved sensitivity profiles, i.e. the Jacobians, for diffuse optical tomography (DOT) applications. By recording the pseudo random number generator (PRNG) seeds of each detected photon, we are able to "replay" all detected photons to directly create the 3D sensitivity profiles for both absorption and scattering coefficients. We validate the replay-based Jacobians against the traditional adjoint Monte Carlo (aMC) method, and demonstrate the feasibility of using this approach for efficient 3D image reconstructions using in vitro hyperspectral wide-field DOT measurements. The strengths and limitations of the replay approach regarding its computational efficiency and accuracy are discussed, in comparison with aMC, for point-detector systems as well as wide-field pattern-based and hyperspectral imaging systems. The replay approach has been implemented in both of our open-source MC simulators - MCX and MMC (http://mcx.space).

Peripheral vascular disease assessment in the lower limb: a review of current and emerging non-invasive diagnostic methods

BACKGROUND

Worldwide, at least 200 million people are affected by peripheral vascular diseases (PVDs), including peripheral arterial disease (PAD), chronic venous insufficiency (CVI) and deep vein thrombosis (DVT). The high prevalence and serious consequences of PVDs have led to the development of several diagnostic tools and clinical guidelines to assist timely diagnosis and patient management. Given the increasing number of diagnostic methods available, a comprehensive review of available technologies is timely in order to understand their limitations and direct future development effort.

MAIN BODY

This paper reviews the available diagnostic methods for PAD, CVI, and DVT with a focus on non-invasive modalities. Each method is critically evaluated in terms of sensitivity, specificity, accuracy, ease of use, procedure time duration, and training requirements where applicable.

CONCLUSION

This review emphasizes the limitations of existing methods, highlighting a latent need for the development of new non-invasive, efficient diagnostic methods. Some newly emerging technologies are identified, in particular wearable sensors, which demonstrate considerable potential to address the need for simple, cost-effective, accurate and timely diagnosis of PVDs.

Chromophore decomposition in multispectral time-resolved diffuse optical tomography

Multicomponent phantom measurements are carried out to evaluate the ability of multispectral time domain diffuse optical tomography in reflectance geometry to quantify the position and the composition of small heterogeneities at depths of 1-1.5 cm in turbid media. Time-resolved data were analyzed with the Mellin-Laplace transform. Results show good localization and correct composition gradation of objects but still a lack of absolute material composition accuracy when no a priori geometry information is known.

Critical Limb Ischemia: An Expert Statement

Critical limb ischemia (CLI), the most advanced form of peripheral artery disease, is associated with significant morbidity, mortality, and health care resource utilization. It is also associated with physical, as well as psychosocial, consequences such as amputation and depression. Importantly, after a major amputation, patients are at heightened risk of amputation on the contralateral leg. However, despite the technological advances to manage CLI with minimally invasive technologies, this condition often remains untreated, with significant disparities in revascularization and amputation rates according to race, socioeconomic status, and geographic region. Care remains disparate across medical specialties in this rapidly evolving field. Many challenges persist, including appropriate reimbursement for treating complex patients with difficult anatomy. This paper provides a comprehensive summary that includes diagnostic assessment and analysis, endovascular versus open surgical treatment, regenerative and adjunctive therapies, and other important aspects of CLI.

Ambulatory diffuse optical tomography and multimodality physiological monitoring system for muscle and exercise applications

Ambulatory diffuse optical tomography (aDOT) is based on near-infrared spectroscopy (NIRS) and enables three-dimensional imaging of regional hemodynamics and oxygen consumption during a person’s normal activities. Although NIRS has been previously used for muscle assessment, it has been notably limited in terms of the number of channels measured, the extent to which subjects can be ambulatory, and/or the ability to simultaneously acquire synchronized auxiliary data such as electromyography (EMG) or electrocardiography (ECG). We describe the development of a prototype aDOT system, called NINscan-M, capable of ambulatory tomographic imaging as well as simultaneous auxiliary multimodal physiological monitoring. Powered by four AA size batteries and weighing 577 g, the NINscan-M prototype can synchronously record 64-channel NIRS imaging data, eight channels of EMG, ECG, or other analog signals, plus force, acceleration, rotation, and temperature for 24+ h at up to 250 Hz. We describe the system’s design, characterization, and performance characteristics. We also describe examples of isometric, cycle ergometer, and free-running ambulatory exercise to demonstrate tomographic imaging at 25 Hz. NINscan-M represents a multiuse tool for muscle physiology studies as well as clinical muscle assessment.

Key Concepts in Critical Limb Ischemia: Selected Proceedings from the 2015 Vascular Interventional Advances Meeting

Over 500,000 patients each year are diagnosed with critical limb ischemia (CLI), the most severe form of peripheral artery disease. CLI portends a grim prognosis; half the patients die from a cardiovascular cause within 5 years, a rate that is 5 times higher than a matched population without CLI. In 2014, the Centers for Medicare and Medicaid Services paid approximately $3.6 billion for claims submitted by hospitals for inpatient and outpatient care delivered to patients with CLI. Although significant advances in diagnosis, treatment, and follow-up of patients with CLI have been made, many challenges remain. In this article, we summarize selected presentations from the 2015 Vascular Interventional Advances Conference related to the modern demographics, diagnosis, and management of patients with CLI.

Reproducibility of parameters of postocclusive reactive hyperemia measured by diffuse optical tomography

The application of near-infrared spectroscopy (NIRS) to assess microvascular function has shown promising results. An important limitation when using a single source-detector pair, however, is the lack of depth sensitivity. Diffuse optical tomography (DOT) overcomes this limitation using an array of sources and detectors that allow the reconstruction of volumetric hemodynamic changes. This study compares the key parameters of postocclusive reactive hyperemia measured in the forearm using standard NIRS and DOT. We show that while the mean parameter values are similar for the two techniques, DOT achieves much better reproducibility, as measured by the intraclass correlation coefficient (ICC). We show that DOT achieves high reproducibility for muscle oxygen consumption (ICC: 0.99), time to maximal HbO2 (ICC: 0.94), maximal HbO2 (ICC: 0.99), and time to maximal HbT (ICC: 0.99). Absolute reproducibility as measured by the standard error of measurement is consistently smaller and close to zero (ideal value) across all parameters measured by DOT compared to NIRS. We conclude that DOT provides a more robust characterization of the reactive hyperemic response and show how the availability of volumetric hemodynamic changes allows the identification of areas of temporal consistency, which could help characterize more precisely the microvasculature.