Next Generation Non-Invasive Imaging for Peripheral Arterial Disease

Peripheral arterial disease (PAD) affects millions of patients in the United States and has been a key focus of research for our group at the Southern Arizona Limb Salvage Alliance (SALSA). PAD is caused by genetic factors as well as hyperlipidemia, smoking, hypertension and diabetes. Care for patients with PAD focuses on medical optimization, mechanical optimization, wound care and surgical revascularization, without which patients have a large degree of impairment resulting from chronic wounds and amputations.
A major advancement in management of PAD dates to data from the 1970’s and 1980’s regarding the use of ankle-brachial indices (ABIs) and toe plethysmography (calculation of systolic toe pressure). These measurements quantify the blood supply to the lower extremity (Bone et al). These measurements guide daily clinical practice and are obtained on nearly every patient seen in the Podiatry clinic and Vascular Surgery clinic. These parameters help greatly, but are not ideal for the reasons enumerated below:
1) ABIs are technician-dependant and can vary by as much as 20% from exam to exam.
2) ABIs are inaccurate in patients with diabetes (because blood vessels become calcified and are poorly or not compressible). This a particularly glaring problem when 50-80% of our patients are now diabetic.
3) Toe pressure, although more accurate than ABIs, are also eschewed in diabetic patients.
4) Toe Pressure cannot be obtained in patients who have had toe amputations.
5) ABI and toe pressure cannot differentiate between specific regions of blood supply—there are 4-6 different regions of blood supply for the foot called Angiosomes. Data show that region-specific blood revascularization results in improved wound healing.

For these reasons we are interested in developing improved techniques for non-invasive imaging of the lower extremity to quantify blood supply. There are several novel options for us to pursue, but there are no good data to determine which of the new non-invasive imaging modalities are the best. These new imaging modalities include Spatial Frequency Domain Imaging (SFDI), Magnetic Resonance Imaging (MRI), Multispectral Optoacoustic Tomography (MOST), Diffuse Speckle Contrast Analysis (DSCA—Pedra). These imaging modalities are non-invasive, rapid, easy to perform and pose no risk for our patients.