title: Arterial spin labeling MR imaging reproducibly measures peak-exercise calf muscle perfusion: a study in patients with peripheral arterial disease and healthy volunteers.
abstract: OBJECTIVE
  This study hypothesized that arterial spin labeling (ASL) magnetic resonance (MR) imaging at 3-T would be a reliable noncontrast technique for measuring peak exercise calf muscle blood flow in both healthy volunteers and patients with peripheral arterial disease (PAD) and will discriminate between these groups.
  
  
  BACKGROUND
  Prior work demonstrated the utility of first-pass gadolinium-enhanced calf muscle perfusion MR imaging in patients with PAD. However, patients with PAD often have advanced renal disease and cannot receive gadolinium.
  
  
  METHODS
  PAD patients had claudication and an ankle brachial index of 0.4 to 0.9. Age-matched normal subjects (NL) had no PAD risk factors and were symptom-free with exercise. All performed supine plantar flexion exercise in a 3-T MR imaging scanner using a pedal ergometer until exhaustion or limiting symptoms and were imaged at peak exercise with 15 averaged ASL images. Peak perfusion was measured from ASL blood flow images by placing a region of interest in the calf muscle region with the greatest signal intensity. Perfusion was compared between PAD patients and NL and repeat testing was performed in 12 subjects (5 NL, 7 PAD) for assessment of reproducibility.
  
  
  RESULTS
  Peak exercise calf perfusion of 15 NL (age: 54 ± 9 years) was higher than in 15 PAD patients (age: 64 ± 5 years, ankle brachial index: 0.70 ± 0.14) (80 ± 23 ml/min - 100 g vs. 49 ± 16 ml/min/100 g, p < 0.001). Five NL performed exercise matched to PAD patients and again demonstrated higher perfusion (84 ± 25 ml/min - 100 g, p < 0.002). As a measure of reproducibility, intraclass correlation coefficient between repeated studies was 0.87 (95% confidence interval [CI]: 0.61 to 0.96). Interobserver reproducibility was 0.96 (95% CI: 0.84 to 0.99).
  
  
  CONCLUSIONS
  ASL is a reproducible noncontrast technique for quantifying peak exercise blood flow in calf muscle. Independent of exercise time, ASL discriminates between NL and PAD patients. This technique may prove useful for clinical trials of therapies for improving muscle perfusion, especially in patients unable to receive gadolinium.
authors.affiliation: Department of Medicine, University of Virginia Health System, Charlottesville, Virginia 22908, USA.
authors.forename: Amy W
authors.initials: AW
authors.lastname: Pollak
authors.forename: Craig H
authors.initials: CH
authors.lastname: Meyer
authors.forename: Frederick H
authors.initials: FH
authors.lastname: Epstein
authors.forename: Ronny S
authors.initials: RS
authors.lastname: Jiji
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Hunter
authors.forename: Joseph M
authors.initials: JM
authors.lastname: Dimaria
authors.forename: John M
authors.initials: JM
authors.lastname: Christopher
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Kramer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D055109:Ankle Brachial Index / Q000379:methods; D001158:Arteries / Q000473:pathology* / Q000503:physiopathology; D005080:Exercise Test / Q000379:methods*; D005260:Female; D006801:Humans; D007866:Leg / Q000098:blood supply*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D008875:Middle Aged; D018482:Muscle, Skeletal / Q000098:blood supply* / Q000503:physiopathology; D058729:Peripheral Arterial Disease / Q000175:diagnosis*; D012039:Regional Blood Flow / Q000502:physiology*; D015203:Reproducibility of Results; D012720:Severity of Illness Index