Jennifer W. Hoi

Imaging of vascular dynamics within the foot using dynamic diffuse optical tomography to diagnose peripheral arterial disease

Peripheral Arterial Disease (PAD) is the narrowing of the functional area of the artery generally due to atherosclerosis. It affects between 8-12 million people in the United States and if untreated this can lead to ulceration, gangrene and ultimately amputation. The current diagnostic method for PAD is the ankle-brachial index (ABI). The ABI is a ratio of the patient’s systolic blood pressure in the foot to that of the brachial artery in the arm, a ratio below 0.9 is indicative of affected vasculature. However, this method is ineffective in patients with calcified arteries (diabetic and end-stage renal failure patients), which falsely elevates the ABI recording resulting in a false negative reading. In this paper we present our results in a pilot study to deduce optical tomography’s ability to detect poor blood perfusion in the foot. We performed an IRB approved 30 patient study, where we imaged the feet of the enrolled patients during a five stage dynamic imaging sequence. The patients were split up into three groups: 10 healthy subjects, 10 PAD patients and 10 PAD patients with diabetes and they were imaged while applying a pressure cuff to their thigh. Differences in the magnitude of blood pooling in the foot and rate at which the blood pools in the foot are all indicative of arterial disease.

A Non-Contact Fiber-Less Diffuse Optical Tomographic System for Dynamic Imaging of the Feet with Peripheral Artery Disease

We present a new design for a non-contact fiber-free diffuse optical tomography system capable of simultaneously capturing multiple views of feet for dynamic imaging of foot vasculature.

A reduced-space basis function neural network method for diffuse optical tomography

We propose here a reduced space image reconstruction method that makes use of basis function neural network (BFNN) within a framework of PDE-constrained algorithm. This method reduces the solution space using the basis function approach, and finds the optimal solution through the learning process of neural network. The basis function approach improves the ill-posed nature of an original inverse problem, reducing the number of unknowns as well as regularizing the solution automatically. The proposed method was applied to breast cancer imaging, and the reconstruction performance was evaluated on how well the method can identify the tumor location in breast tissue. The results show that the BFNN method gives better results in the identification of tumor location than the traditional element-based reconstruction method.

Characterizing infantile hemangiomas with a near-infrared spectroscopic handheld wireless device

Infantile hemangiomas (IH) are common vascular growths that occur in 5-10% of neonates and have the potential to cause disfiguring and even life-threatening complications. Currently, no objective tool exist to monitor either progression or treatment of IH. To address this unmet clinical need, we have developed a handheld wireless device (HWD) that uses diffuse optical spectroscopy for the assessment of IH. The system employs 4 wavelengths (l=780nm, 805nm, 850nm, and 905nm) and 6 source-detector pairs with distances between 0.6 and 20 mm. Placed on the skin surface, backreflection data is obtained and a multispectral evolution algorithm is used to determine total hemoglobin concentration and tissue oxygen saturation. First results of an ongoing pilot study involving 13 patients (average enrollment age = 25 months) suggest that an increase in hypoxic stress over time can lead to the proliferation of IH. Involuting IH lesions showed an increase in tissue oxygen saturation as well as a decrease in total hemoglobin.

Non-contact continuous-wave diffuse optical tomographic system to capture vascular dynamics in the foot

Dynamic optical tomographic imaging has shown promise in diagnosing and monitoring peripheral arterial disease (PAD), which affects 8 to 12 million in the United States. PAD is the narrowing of the arteries that supply blood to the lower extremities. Prolonged reduced blood flow to the foot leads to ulcers and gangrene, which makes placement of optical fibers for contact-based optical tomography systems difficult and cumbersome. Since many diabetic PAD patients have foot wounds, a non-contact interface is highly desirable. We present a novel non-contact dynamic continuous-wave optical tomographic imaging system that images the vasculature in the foot for evaluating PAD. The system images at up to 1Hz by delivering 2 wavelengths of light to the top of the foot at up to 20 source positions through collimated source fibers. Transmitted light is collected with an electron multiplying charge couple device (EMCCD) camera. We demonstrate that the system can resolve absorbers at various locations in a phantom study and show the system’s first clinical 3D images of total hemoglobin changes in the foot during venous occlusion at the thigh. Our initial results indicate that this system is effective in capturing the vascular dynamics within the foot and can be used to diagnose and monitor treatment of PAD in diabetic patients.

Modeling of the blood flow in the lower extremities for dynamic diffuse optical tomography of peripheral artery disease

Peripheral Arterial Disease (PAD) is caused by a reduction of the internal diameters of the arteries in the upper or lower extremities mainly due to atherosclerosis. If not treated, its worsening may led to a complete occlusion, causing the death of the cells lacking proper blood supply, followed by gangrene that may require chirurgical amputation. We have recently performed a clinical study in which good sensitivities and specificities were achieved with dynamic diffuse optical tomography. To gain a better understanding of the physiological foundations of many of the observed effects, we started to develop a mathematical model for PAD. The model presented in this work is based on a multi-compartment Windkessel model, where the vasculature in the leg and foot is represented by resistors and capacitors, the blood pressure with a voltage drop, and the blood flow with a current. Unlike existing models, the dynamics induced by a thigh-pressure-cuff inflation and deflation during the measurements are taken into consideration. This is achieved by dynamically varying the resistances of the large veins and arteries. By including the effects of the thigh-pressure cuff, we were able to explain many of the effects observed during our dynamic DOT measurements, including the hemodynamics of oxy- and deoxy-hemoglobin concentration changes. The model was implemented in MATLAB and the simulations were normalized and compared with the blood perfusion obtained from healthy, PAD and diabetic patients. Our preliminary results show that in unhealthy patients the total system resistance is sensibly higher than in healthy patients.

Detection of peripheral arterial disease using dynamic diffuse optical tomography of vascular dynamics in the foot

We present dynamic diffuse optical tomography (DDOT) results from a 34-patient study for detecting peripheral arterial disease and patients with and without diabetes. DDOT achieved a sensitivity of 80% and a specificity of 70%.

Contact-free diffuse optical tomography system for dynamic imaging of peripheral vasculature

We present a dynamic contact-free system capable of imaging at 1Hz using 20 collimated source fibers at two wavelengths and an electron multiplying charge coupled device (EMCCD) camera for imaging vascular dynamics in the foot.

Optical Infantile Hemangiomas Assessment with a Handheld Wireless Near-Infrared Spectroscopic Device

A handheld wireless device has been developed to assess the progression of infantile hemangioma lesions. Results from an on-going pilot study are presented.

Dynamic contact-free continuous-wave diffuse optical tomography system for the detection of vascular dynamics within the foot

We present a dynamic contact-free continuous-wave diffuse optical tomography system for the detection and monitoring of peripheral arterial disease (PAD) in the foot. Peripheral Arterial Disease (PAD) is the narrowing of the functional area of the artery generally due to atherosclerosis. It affects between 8-12 million people in the United States and if untreated this can lead to ulceration, gangrene and ultimately amputation. Contact-Free imaging is highly desirable, due to the presence of ulcerations and gangrene in many patients affected by PAD. The system uses an electron multiplying charge coupled device (EMCCD) camera for detection to achieve a dynamic range of 86 dB with a frame rate of 1 Hz using 20 collimated source fibers and 2 wavelengths. We present first clinical results showing 3D images of total hemoglobin changes in response to a dynamic thigh cuff.