Department of Radiology and Imaging Sciences, University of Utah , Salt Lake City, Utah.
Division of Geriatrics, Department of Internal Medicine, University of Utah , Salt Lake City, Utah.
Am J Physiol Heart Circ Physiol. 2019 Jan 1;316(1):H201-H211. doi: 10.1152/ajpheart.00537.2018. Epub 2018 Nov 2.
Peripheral artery disease (PAD) in the lower extremities often leads to intermittent claudication. In the present study, we proposed a low-dose DCE MRI protocol for quantifying calf muscle perfusion stimulated with plantar flexion and multiple new metrics for interpreting perfusion maps, including the ratio of gastrocnemius over soleus perfusion (G/S; for assessing the vascular redistribution between the two muscles) and muscle perfusion normalized by whole body perfusion (for quantifying the muscle's active hyperemia). Twenty-eight human subjects participated in this Institutional Review Board-approved study, with 10 healthy subjects ( group A) for assessing interday reproducibility and 8 healthy subjects ( group B) for exploring the relationship between plantar-flexion load and induced muscle perfusion. In a pilot group of five elderly healthy subjects and five patients with PAD ( group C), we proposed a protocol that measured perfusion for a low-intensity exercise and for an exhaustion exercise in a single MRI session. In group A, perfusion estimates for calf muscles were highly reproducible, with correlation coefficients of 0.90-0.93. In group B, gastrocnemius perfusion increased linearly with the exercise workload ( P < 0.05). With the low-intensity exercise, patients with PAD in group C showed substantially lower gastrocnemius perfusion compared with elderly healthy subjects [43.4 (SD 23.5) vs. 106.7 (SD 73.2) ml·min·100 g]. With exhaustion exercise, G/S [1.0 (SD 0.4)] for patients with PAD was lower than both its low-intensity level [1.9 (SD 1.3)] and the level in elderly healthy subjects [2.7 (SD 2.1)]. In conclusion, the proposed MRI protocol and the new metrics are feasible for quantifying exercise-induced muscle hyperemia, a promising functional test of PAD. NEW & NOTEWORTHY To quantitatively map exercise-induced hyperemia in calf muscles, we proposed a high-resolution MRI method shown to be highly reproducible and sensitive to exercise load. With the use of low contrast, it is feasible to measure calf muscle hyperemia for both low-intensity and exhaustion exercises in a single MRI session. The newly proposed metrics for interpreting perfusion maps are promising for quantifying intermuscle vascular redistribution or a muscle's active hyperemia.
下肢外周动脉疾病（PAD）常导致间歇性跛行。在本研究中，我们提出了一种低剂量 DCE MRI 方案来定量测量足底屈肌刺激引起的小腿肌肉灌注，并提出了多个新的灌注图解释指标，包括比目鱼肌与腓肠肌灌注比值（G/S；用于评估两块肌肉之间的血管再分布）和全身灌注标准化的肌肉灌注（用于量化肌肉的主动充血）。28 名健康受试者参加了这项经机构审查委员会批准的研究，其中 10 名健康受试者（A 组）用于评估日内可重复性，8 名健康受试者（B 组）用于探索足底屈肌负荷与诱导肌肉灌注之间的关系。在一个由五名老年健康受试者和五名 PAD 患者组成的试点组（C 组）中，我们提出了一种方案，该方案可在单次 MRI 检查中测量低强度运动和疲劳运动的灌注。在 A 组中，小腿肌肉的灌注估计具有高度的可重复性，相关系数为 0.90-0.93。在 B 组中，腓肠肌灌注随运动负荷线性增加（P<0.05）。在低强度运动中，C 组中的 PAD 患者的腓肠肌灌注明显低于老年健康受试者[43.4（23.5）ml·min·100 g 比 106.7（73.2）ml·min·100 g]。在疲劳运动中，PAD 患者的 G/S[1.0（0.4）]低于其低强度水平[1.9（1.3）]和老年健康受试者的水平[2.7（2.1）]。总之，所提出的 MRI 方案和新指标可用于定量测量运动引起的肌肉充血，这是一种有前途的 PAD 功能测试。创新点：为了定量绘制小腿肌肉运动引起的充血图，我们提出了一种高分辨率 MRI 方法，该方法被证明具有高度的可重复性，并且对运动负荷敏感。使用低对比度，在单次 MRI 检查中测量低强度和疲劳运动的小腿肌肉充血是可行的。用于解释灌注图的新指标有望用于量化肌肉间血管再分布或肌肉的主动充血。
