Exploring the Dynamics of Ischemia and Reactive Hyperemia With Skeletal Muscle Blood Oxygen Level Dependent MRI in Patients With Peripheral Artery Disease, Age‐Matched Controls, and Young Healthy Subjects

ABSTRACT Background Skeletal muscle blood oxygen level dependent (BOLD) MRI is a technique for assessing vascular function in peripheral limbs. In patients, however, an increased frequency of atypical response patterns has been observed, warranting investigation into its underlying causes. Purpose To explore the dynamics of cuff‐induced ischemia and reactive hyperemia with BOLD MRI, focusing on the occurrence, quantification, and interpretation of frequent atypical cuff‐induced response patterns. Study Type Secondary assessment of prospectively collected datasets. Population Seventeen peripheral artery disease (PAD) patients (age: 64–80 years, ankle‐brachial index (ABI) range: 0.4–0.8), 8 age‐matched controls (age: 64–82 years, ABI range: 1–1.2), and 14 young controls (age: 22–39 years). Field Strength/Sequence ‐weighted multi‐echo gradient‐echo sequence with 11 equidistant echo‐times at 3T. Assessment A transverse slice of the calf was imaged repeatedly during an upper‐thigh cuff compression cycle consisting of 1‐min baseline, 5‐min arterial occlusion (cuff inflated) and 5‐min reactive hyperemia (cuff deflated). ‐mapping with ROI‐wise analysis of the soleus and gastrocnemius muscles produced ‐time curves and previously established metrics, including the hyperemic upslope () and time‐to‐peak (TTP) were assessed. The time‐curves were surveyed to identify the frequency and type of deviations from expected. ‐time curves of soleus were further analyzed by fitting a parameterized function to derive additional metrics including depth of the undershoot on cuff release and deviation from a monotonic T2* decrease. Ankle‐brachial index (ABI) served as a clinical reference for comparisons. Statistical Tests Non‐parametric 2‐tailed Wilcoxon rank‐sum tests to assess differences between patients and age‐matched controls. A p value < 0.05 was considered significant. Results Atypical cuff‐induced response patterns in PAD patients included a negative cuff‐induced transient (42%, soleus) and non‐monotonic declines in during cuffing (58%, soleus). While these contributed to increased variabilities in patients, (−0.63 ms/s) and TTP (62.8 s) between patients and age‐matched controls. Data Conclusion HS up and TTP provided means to quantify calf muscle responses to cuffing. Specific cases of non‐monotonous decrease during cuffing suggest the detection of venous valve leakages in inter‐muscular veins. Insufficient cuff pressure produced curves with absent ischemic plateau and weak hyperemic responses, the recognition of which is important to prevent physiological misinterpretations of curves and derived metrics. Evidence Level 1. Technical Efficacy 3.