Agreement between multiparametric MRI (PIVOT), Doppler ultrasound, and near-infrared spectroscopy-based assessments of skeletal muscle oxygenation and perfusion

Abstract

Skeletal muscle perfusion and oxygenation are commonly evaluated using Doppler ultrasound and near-infrared spectroscopy (NIRS) techniques. However, a recently developed magnetic resonance imaging (MRI) sequence, termed PIVOT, permits the simultaneous collection of skeletal muscle perfusion and T2* (an index of skeletal muscle oxygenation).

Purpose: To determine the level of agreement between PIVOT, Doppler ultrasound, and NIRS-based assessments of skeletal muscle perfusion and oxygenation.

Methods: Twelve healthy volunteers (8 females, 25 ± 3 years, 170 ± 11 cm, 71.5 ± 8.0 kg) performed six total reactive hyperemia protocols. During three of these reactive hyperemia protocols, Tissue Saturation Index (TSI) and oxygenated hemoglobin (O₂Hb) were recorded from the medial gastrocnemius (MG) and tibialis anterior (TA), and blood flow velocity was recorded from the popliteal artery (BFv_pop) via Doppler Ultrasound. The other three trials were performed inside the bore of a 3 T MRI scanner, and the PIVOT sequence was used to assess perfusion (PIVOT_perf) and oxygenation (T2*) of the medial gastrocnemius and tibialis anterior muscles. Positive incremental areas under the curve (iAUC) and times to peak (TTP) were calculated for each variable, and the level of agreement between collection methods was evaluated via Bland-Altman analyses and Spearman's Rho correlation analyses.

Results: The only significant bivariate relationships observed were between the T2* vs. TSI iAUC and PIVOT_perf vs. BFv_pop values recorded from the MG. Significant mean differences were observed for all comparisons (all P ≤ 0.038), and significant proportional biases were observed for the PIVOT_perf vs. tHb TTP (R² = 0.848, P < 0.001) and T2* vs. TSI TTP comparisons in the TA (R² = 0.488, P = 0.011), and the PIVOT_perf vs. BFv_pop iAUC (R² = 0.477, P = 0.013) and time to peak (R² = 0.851, P < 0.001) comparisons in the MG.

Conclusions: Our findings suggest that the PIVOT technique has, at best, a moderate level of agreement with Doppler ultrasound and NIRS assessment methods and is subject to significant proportional bias. These findings do not challenge the accuracy of either measurement technique but instead reflect differences in the vascular compartments, sampling volumes, and parameters being evaluated.

Keywords: Leg blood flow; Muscle oxygenation; NIRS; Perfusion.

Figure 1.

A representative high-resolution image of the lower leg (Panel A). The medial gastrocnemius (MG) and the tibialis anterior (TA) muscles are indicated in red and blue, respectively. Superimposed are the approximated near-infrared spectroscopy (NIRS) photon fields, represented by a series of gradient red crescents with peak penetration depths equal to one-half of the source- (S_1,2,3) detector (D₁) separation distance. Average values of subcutaneous adipose tissue thickness (ATT), directly beneath each of the NIRS devices, are represented by white double-sided arrows. Representative tracings of near-infrared spectroscopy (NIRS) -derived tissue saturation index (TSI, open-diamonds), oxygenated hemoglobin saturation (O₂Hb, black-circles), deoxygenated hemoglobin saturation (HHb, open-circles), total hemoglobin saturation (tHb, black-squares), and PIVOT-derived skeletal muscle T2* (solid black line) of the MG (Panel B) and TA (Panel C) following the release of an ischemic pressure cuff are shown. Representative tracings of popliteal blood flow velocity (Bfv_pop, solid black line), assessed via Doppler ultrasound, and arterial spin labeling (ASL) -derived skeletal muscle perfusion in the MG (black dashed-line) and the TA (black dotted line) are shown following cuff release. Values in Panels B-C are expressed as a percent change(Δ) from the end of the 5-minute ischemic cuff occlusion period.

Figure 2.

Bland-Altman analyses comparing the levels of agreement between the incremental area under the curve (iAUC) values of popliteal blood flow velocity (BFv_pop), assessed via Doppler ultrasound, and PIVOT-derived skeletal muscle perfusion (PIVOT_perf) of the medial gastrocnemius (MG) and the tibialis anterior (TA) are represented in panels A & B. Comparisons between PIVOT_perf and near-infrared spectroscopy (NIRS) -derived total hemoglobin saturation (tHb) of the MG and TA (Panels C & D). Comparisons between PIVOT-derived skeletal muscle T2* and NIRS-derived tissue saturation index (TSI) of the MG and TA (Panels E & F). Comparisons between T2* and NIRS-derived oxygenated hemoglobin saturation (O₂Hb) of the MG and TA (Panels G & H).

Figure 3.

Bland-Altman analyses comparing the levels of agreement between the time-to-peak (TTP) values of popliteal blood flow velocity (BFv_pop), assessed via Doppler ultrasound, and PIVOT-derived skeletal muscle perfusion (PIVOT_perf) of the medial gastrocnemius (MG) and the tibialis anterior (TA) are represented in panels A & B. Comparisons between PIVOT_perf and near-infrared spectroscopy (NIRS) - derived total hemoglobin saturation (tHb) of the MG and TA (Panels C & D). Comparisons between PIVOT-derived skeletal muscle T2* and NIRS-derived tissue saturation index (TSI) of the MG and TA (Panels E & F). Comparisons between T2* and NIRS-derived oxygenated hemoglobin saturation (O₂Hb) of the MG and TA (Panels G & H).