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WORKS IN PROGRESS: CARDIAC IMAGING

Skeletal Muscle Microvascular Flow in Progressive Peripheral Artery Disease

Assessment With Continuous Arterial Spin-Labeling Perfusion Magnetic Resonance Imaging

Wen-Chau Wu, PhD^_*,#, Emile Mohler, III, MD, Sarah J. Ratcliffe, PhD, Felix W. Wehrli, PhD^_*, John A. Detre, MD^_*,|| and Thomas F. Floyd, MD^,||,_*

^_* Department of Radiology, Hospital of University of Pennsylvania, Philadelphia, Pennsylvania
Department of Medicine (Vascular Medicine), Hospital of University of Pennsylvania, Philadelphia, Pennsylvania
Department of Biostatistics and Epidemiology, Hospital of University of Pennsylvania, Philadelphia, Pennsylvania
Department of Anesthesiology and Critical Care, Hospital of University of Pennsylvania, Philadelphia, Pennsylvania
^|| Department of Neurology, Hospital of University of Pennsylvania, Philadelphia, Pennsylvania
^# Graduate Institute of Clinical Medicine, National Taiwan University, Taipei, Taiwan

Manuscript received December 2, 2008; revised manuscript received February 24, 2009, accepted March 10, 2009.

^_* Reprint requests and correspondence: Dr. Thomas F. Floyd, Departments of Neurology and Anesthesiology & Critical Care, The Hospital of University of Pennsylvania, 3400 Spruce Street, Philadelphia, Pennsylvania 19104 (Email: Thomas.Floyd{at}uphs.upenn.edu).

Objectives: We present the novel application of continuous arterial spin-labeling (CASL) magnetic resonance imaging (MRI) for the measurement of calf muscle perfusion in subjects with progressive peripheral arterial disease (PAD).

Background: Peripheral arterial disease is largely considered to be a disease of conduit vessels. The impact of PAD upon microvascular flow in the end-organ, muscle, remains unknown. Continuous arterial spin-labeling is a noninvasive MRI method capable of measuring microvascular flow and might assist in our understanding of the impact of PAD upon the microvasculature.

Methods: Forty subjects with varying degrees of PAD and 17 age-matched PAD-free subjects were recruited and underwent measurement of the ankle-to-brachial index (ABI) and CASL. Peak hyperemic flow (PHF) and time-to-peak (TTP) were computed and assessed as a function of ABI and calf muscle group.

Results: An ABI dependence was found in both PHF (p = 0.04) and TTP (p < 10^–4). Whereas TTP increased almost immediately with increasing PAD severity, PHF was, in contrast, relatively well preserved until later stages of disease.

Conclusions: The CASL flow measurements correlate with disease state as measured by ABI and demonstrate preserved microvascular flow reserve in the presence of early to intermediate vascular disease.

Key Words: arterial spin-labeling • magnetic resonance imaging • peripheral arterial disease • skeletal muscle

Abbreviations and Acronyms   ABI = ankle-to-brachial index   ASL = arterial spin labeling   CASL = continuous arterial spin-labeling   GstrcM = gastrocnemius muscle   MRI = magnetic resonance imaging   PAD = peripheral arterial disease   PHF = peak hyperemic flow   SolM = soleus muscle   T1 = longitudinal relaxation time constant   T2 = transverse relaxation time constant   TTP = time-to-peak

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