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BiographyThis project will examine the effectiveness of ARFI in evaluating the mechanical properties of arteries, particularly in identifying diffuse atherosclerosis and differentiating between soft and hard plaques. Clinical effectiveness of ARFI will be examined by conducting clinical trials. Approximately sixteen normal, healthy volunteers in two age groups (18-25 and over 45) and sixteen patients with peripheral vascular disease with be recruited each year for examination of their popliteal artery. Results from this study will compared to other metrics such as the Rose Questionnaire, Ankle-Brachial Index, and standard risk assessment forms (smoking, diet, age) in order to gauge the effectiveness of this new method. ARFI images will be collected over the entire cardiac cycle; it is hypothesized that subjects with diffuse atherosclerosis will show little differentiation in terms of vessel displacement over the cardiac cycle.
Twenty-four patients with diagnosed peripheral vascular disease and twenty-seven volunteers with no predeposition for vascular disease have had their popliteal arteries imaged using ARFI. The results are promising suggesting that healthy vascular tissue exhibit a uniform response to an ARFI interrogation with noticeable demarcation between the vascular wall and surrounding tissue. Plaques identified in the conventional Bmode image are well visualized in the corresponding ARFI image.
One challenge with ARFI imaging is that the applied force changes substantially based on arterial depth and tissue attenuation and can vary between patients. Other metrics other than displacement (which is force based) will be studied including tissue recovery time, time to maximum displacement, and ratio of displacement during systole vs displacement during diastole. The systolic vs diastolic ratio appears particularly to be promising with preliminary results suggesting that a statistically significant relationship exists between the subject groups and the systolic/diastolic ratio of displacement.
It is hoped that by analyzing the data and looking for information more dependent on inherent tissue properties rather than force will provide more clinically relevant information. For example, to study the effects of arterial pressure on ARFI imaging, phantom vessels constructed from cyrogels will be pressurized in a water tank and imaged using ARFI imaging over different gauge pressures. Both single layer cryogel vessels and vessels with embedded plaques have been successfully constructed this year. Previous plaque models used a concentric plaque approach. Now, both hard and soft eccentric plaques of variable size can be accurately modeling in cyrogel.
Ex-vivo arteries will also be pressurized and studied using ARFI imaging. The vessels will then be dissected to compare histology. A finite element model may be developed to create a deeper understanding of the mechanical effects of displacing tissue with radiation force. It is hoped that such a model will allow more accurate estimates of tissue stiffness and thus arterial health.