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

Figures

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  FIGURE 1. (A) Positioning of leg, pressure cuff and flex coil (top). Cuff compression cycle during dynamic T2* mapping (below), showing the duration of each measurement phase and the time points for cuff inflation and deflation. (B) The first of 207 sets of multi‐echo gradient‐echo acquisitions, where the 11 equidistant echo times range from 2 to 40 ms. (C) T2*−map generated from the first set of echoes. (D) Regions of interest covering the soleus (blue), and the lateral (red) and medial (green) gastrocnemius muscles. (E) The descriptive model (gray) fitted to the soleus ROI‐median T2*‐time curve (blue) and the derived perfusion related metrics: T2*init initial T2*; ISdown initial downslope; posDevLength positive deviation length; posDevMagn positive deviation magnitude; ∆ UST undershoot transient magnitude; rel. T2*max relative maximum T2*; ∆T2*max baseline subtracted maximum T2*; HSup hyperemic up‐slope; TTHP time to half peak; TTP time to peak; TTHR time to half recovery. Levels and slopes illustrated with arrows, time and level intervals illustrated with double‐headed arrows.

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  FIGURE 2. Data overview based on ROI‐wise time curves from the soleus muscle in PAD patients (red, n = 17), age‐matched controls (green, n = 8) and young controls (blue, n = 14). Subplots show (A) T2*‐time curves from all subject groups, (B) violin plot covering the initial T2* values for the three groups, (C) initial T2* subtracted T2*‐time curves and (D) groupwise median (lines) and IQR (shaded) T2*‐time curves.

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  FIGURE 3. Summary of the data survey. BOLD time curve characteristics from a young healthy subject (A) and patients with peripheral artery disease (B–G). In the first and second columns, curve traits are annotated, while the subsequent columns detail the number and percentage of occurrences in each subject group and muscle.

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  FIGURE 4. Ankle brachial index (ABI) and perfusion‐related BOLD metrics obtained via semi‐quantitative curve analyses applied to the soleus muscle in PAD patients (n = 17), age‐matched controls (n = 8) and young controls (n = 14). Metric‐wise display of individual estimates (left), and 2‐sided violin plots (right), grouped such that the estimated histogram profiles of patients are placed to the left and the two control groups are placed to the right in each violin. BOLD perfusion related metrics include T2*init initial T2*; ISdown initial downslope; posDevLength positive deviation length; posDevMagn positive deviation magnitude; MIV minimal ischemic value; ∆ UST undershoot transient magnitude, HPV hyperemic peak value; ∆T2*max baseline subtracted maximum T2*; HSup hyperemic up‐slope, TTHP time to half peak; TTP time to peak; TTHR time to half recovery.

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  FIGURE A1. A sequence of non‐monotonic decrease (yellow) of sample‐length 4 illustrating the principle used for derivings the metrics posDevLength (positive deviation length) and pesDevMagn (positive deviation magnitude).