Application of BOLD Magnetic Resonance Imaging for Evaluating Regional Volumetric Foot Tissue Oxygenation: A Feasibility Study in Healthy Volunteers

Abstract

Objectives To evaluate the feasibility and repeatability of applying blood oxygen level-dependent (BOLD) magnetic resonance (MR) imaging in the feet to quantify regional dynamic changes in tissue oxygenation during proximal cuff occlusion and reactive hyperemia. Subjects and Methods Ten healthy male subjects underwent BOLD and T1-weighted imaging of the feet on two separate occasions using a 3T scanner. Dynamic changes in BOLD signal intensity were assessed before and during proximal cuff occlusion of the thigh and during reactive hyperemia, and BOLD time course data was evaluated for the time-to-half ischemic minimum, minimum ischemic value, peak hyperemic value, time-to-peak hyperemia, time-to-half peak hyperemia, and end value. T1-weighted images were used for segmentation of volumes of interest (VOI) in anatomical regions of the foot (heel, toes, dorsal foot, medial and lateral plantar foot). Repeatability of vascular responses was assessed for each foot VOI using semi-automated image registration and quantification of serial BOLD images. Results The heel VOI demonstrated a significantly higher peak hyperemic response, expressed as percent change from baseline BOLD signal intensity, compared to all other VOIs of the foot (heel, 7.4±1.2%; toes, 5.6±0.8%; dorsal foot, 5.7±1.6%; medial plantar, 5.6±1.7%; lateral plantar, 5.6±1.5%; P<0.05). Additionally, the lateral plantar VOI had a significantly lower terminal signal intensity value (i.e., end value) when compared to all foot VOIs (P<0.05). BOLD MR imaging was repeatable between visits in all foot VOIs, with no significant differences between study visits for any of the evaluated functional indices. Conclusions BOLD MR imaging offers a repeatable technique for volumetric assessment of regional foot tissue oxygenation. Future application of BOLD imaging in the feet of patients with peripheral vascular disease may permit serial evaluation of regional tissue oxygenation and allow for improved assessment of therapeutic interventions targeting specific sites of the foot.

SPECT/CT Imaging: A Noninvasive Approach for Evaluating Serial Changes in Angiosome Foot Perfusion in Critical Limb Ischemia

“…TcPO 2 is the only widely utilized tool in the clinical setting for assessing foot perfusion; however, TcPO 2 is superficial in nature, does not have a large field-of-view, and often does not allow for assessment of the plantar surface of the foot. In addition, while MR-based imaging approaches such as contrast-enhanced imaging, 12 arterial spin labeling, 13,14 and blood oxygen level dependent 11,15 can quantify volumetric tissue oxygenation and perfusion of the lower extremities, these approaches are not capable of measuring perfusion under resting conditions and generally require pharmacological, reactive hyperemia, or exercise stress paradigms. Our radiotracer-based imaging approach with SPECT/CT imaging has previously demonstrated utility for quantifying regional volumetric perfusion under resting conditions in both the preclinical 10 and clinical 9 setting and offers a fast and straightforward imaging protocol for assessing limb perfusion in a patient population at high risk for lower extremity ulceration and am-putation.…”

“…1) using a previously developed image analysis tool kit (BioImage Suite) that our team has previously utilized for evaluating regional skeletal muscle perfusion 9,10 and oxygenation. 11 Average radiotracer uptake was assessed from coregistered SPECT images within the CT-defined 3D angiosomes of the foot. Average SPECT image intensity values were normalized to injected radiotracer dose (mCi) and patient body weight (kg) to generate standardized uptake values (SUVs).…”

“…2) using a previously published automated technique that allowed for alignment of serial images. 9,11 The relative percent change in SUV within each angiosome was calculated from the pre-to post-revascularization time point.…”

Perfusion Assessment in Critical Limb Ischemia: Principles for Understanding and the Development of Evidence and Evaluation of Devices: A Scientific Statement From the American Heart Association

“…The difference in signal is measurable with heavily T2* weighted sequences. 76 A study by Bajwa and colleagues 77 assessed BOLD MRI as a tool for measuring calf muscle perfusion in patients with CLI. They showed statistically significant interuser and interscan reproducibility.…”

Radiotracer Imaging Allows for Noninvasive Detection and Quantification of Abnormalities in Angiosome Foot Perfusion in Diabetic Patients With Critical Limb Ischemia and Nonhealing Wounds

“…Current clinical imaging tools have limitations related to assessment of microvascular disease in patients with PAD and are commonly restricted to evaluating microvascular perfusion within superficial tissue or only allow for evaluation of major vessel blood flow and morphology. 17 Although magnetic resonance-based approaches, such as blood oxygen level dependent, 18 , 19 arterial spin labeling, 20 , 21 and contrast-enhanced imaging, 22 are capable of quantifying 3D tissue oxygenation and perfusion, these approaches do not allow for assessment of resting foot perfusion and generally require exercise, pharmacological, or reactive hyperemia paradigms to produce quantifiable signals. Radiotracer-based perfusion imaging with single photon emission computed tomography (SPECT)/computed tomography (CT) offers some advantages over conventional imaging techniques by allowing for serial volumetric assessment of regional microvascular perfusion in the lower extremities under resting conditions without the need for iodine- or gadolinium-based contrast agents.…”