title: Combined large field-of-view MRA and time-resolved MRA of the lower extremities: impact of acquisition order on image quality.
abstract: OBJECTIVE
  Different approaches exist for hybrid MRA of the calf station. So far, the order of the acquisition of the focused calf MRA and the large field-of-view MRA has not been scientifically evaluated. Therefore the aim of this study was to evaluate if the quality of the combined large field-of-view MRA (CTM MR angiography) and time-resolved MRA with stochastic interleaved trajectories (TWIST MRA) depends on the order of acquisition of the two contrast-enhanced studies.
  
  
  METHODS
  In this retrospective study, 40 consecutive patients (mean age 68.1 ± 8.7 years, 29 male/11 female) who had undergone an MR angiographic protocol that consisted of CTM-MRA (TR/TE, 2.4/1.0 ms; 21° flip angle; isotropic resolution 1.2mm; gadolinium dose, 0.07 mmol/kg) and TWIST-MRA (TR/TE 2.8/1.1; 20° flip angle; isotropic resolution 1.1mm; temporal resolution 5.5s, gadolinium dose, 0.03 mmol/kg), were included. In the first group (group 1) TWIST-MRA of the calf station was performed 1-2 min after CTM-MRA. In the second group (group 2) CTM-MRA was performed 1-2 min after TWIST-MRA of the calf station. The image quality of CTM-MRA and TWIST-MRA were evaluated by 2 two independent radiologists in consensus according to a 4-point Likert-like rating scale assessing overall image quality on a segmental basis. Venous overlay was assessed per examination.
  
  
  RESULTS
  In the CTM-MRA, 1360 segments were included in the assessment of image quality. CTM-MRA was diagnostic in 95% (1289/1360) of segments. There was a significant difference (p<0.0001) between both groups with regard to the number of segments rated as excellent and moderate. The image quality was rated as excellent in group 1 in 80% (514/640 segments) and in group 2 in 67% (432/649), respectively (p<0.0001). In contrast, the image quality was rated as moderate in the first group in 5% (33/640) and in the second group in 19% (121/649) respectively (p<0.0001). The venous overlay was disturbing in 10% in group 1 and 20% in group 2 (p=n.s.).
  
  
  CONCLUSIONS
  If a combined hybrid MRA approach with large field-of-view and time-resolved MRA is acquired the large field-of-view MRA should be acquired first in order for optimal image quality.
authors.affiliation: Institute of Clinical Radiology and Nuclear Medicine, University Medical Center Mannheim, Medical Faculty Mannheim, Heidelberg University, Germany. Philipp.Riffel@umm.de
authors.forename: Philipp
authors.initials: P
authors.lastname: Riffel
authors.forename: Stefan
authors.initials: S
authors.lastname: Haneder
authors.forename: Ulrike I
authors.initials: UI
authors.lastname: Attenberger
authors.forename: Joachim
authors.initials: J
authors.lastname: Brade
authors.forename: Stefan O
authors.initials: SO
authors.lastname: Schoenberg
authors.forename: Henrik J
authors.initials: HJ
authors.lastname: Michaely
mesh_terms: D000368:Aged; D000465:Algorithms; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D035002:Lower Extremity / Q000033:anatomy & histology*; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013382:Subtraction Technique