title: Clinical assessment of standard and generalized autocalibrating partially parallel acquisition diffusion imaging: effects of reduction factor and spatial resolution.
abstract: OBJECTIVE
  PI improves routine EPI-based DWI by enabling higher spatial resolution and reducing geometric distortion, though it remains unclear which of these is most important. We evaluated the relative contribution of these factors and assessed their ability to increase lesion conspicuity and diagnostic confidence by using a GRAPPA technique.
  
  
  METHODS
  Four separate DWI scans were obtained at 1.5T in 48 patients with independent variation of in-plane spatial resolution (1.88 mm(2) versus 1.25 mm(2)) and/or reduction factor (R = 1 versus R = 3). A neuroradiologist with access to clinical history and additional imaging sequences provided a reference standard diagnosis for each case. Three blinded neuroradiologists assessed scans for abnormalities and also evaluated multiple imaging-quality metrics by using a 5-point ordinal scale. Logistic regression was used to determine the impact of each factor on subjective image quality and confidence.
  
  
  RESULTS
  Reference standard diagnoses in the patient cohort were acute ischemic stroke (n = 30), ischemic stroke with hemorrhagic conversion (n = 4), intraparenchymal hemorrhage (n = 9), or no acute lesion (n = 5). While readers preferred both a higher reduction factor and a higher spatial resolution, the largest effect was due to an increased reduction factor (odds ratio, 47 ± 16). Small lesions were more confidently discriminated from artifacts on R = 3 images. The diagnosis changed in 5 of 48 scans, always toward the reference standard reading and exclusively for posterior fossa lesions.
  
  
  CONCLUSIONS
  PI improves DWI primarily by reducing geometric distortion rather than by increasing spatial resolution. This outcome leads to a more accurate and confident diagnosis of small lesions.
authors.affiliation: Department of Radiology, Stanford University, Stanford, California, USA. drjalal@uw.edu
authors.forename: J B
authors.initials: JB
authors.lastname: Andre
authors.forename: G
authors.initials: G
authors.lastname: Zaharchuk
authors.forename: N J
authors.initials: NJ
authors.lastname: Fischbein
authors.forename: M
authors.initials: M
authors.lastname: Augustin
authors.forename: S
authors.initials: S
authors.lastname: Skare
authors.forename: M
authors.initials: M
authors.lastname: Straka
authors.forename: J
authors.initials: J
authors.lastname: Rosenberg
authors.forename: M G
authors.initials: MG
authors.lastname: Lansberg
authors.forename: S
authors.initials: S
authors.lastname: Kemp
authors.forename: C A C
authors.initials: CA
authors.lastname: Wijman
authors.forename: G W
authors.initials: GW
authors.lastname: Albers
authors.forename: N E
authors.initials: NE
authors.lastname: Schwartz
authors.forename: R
authors.initials: R
authors.lastname: Bammer
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002138:Calibration; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods / Q000592:standards*; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods / Q000592:standards*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods / Q000592:standards*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D020521:Stroke / Q000473:pathology*; D014481:United States