title: Comparison of positron emission tomography diffusion-weighted imaging (PET/DWI) registration quality in a PET/MR scanner: Zoomed DWI vs. Conventional DWI.
abstract: OBJECTIVE
  To compare zoomed diffusion-weighted imaging (z-DWI) with reduced field of view (FOV) by spatially selective radiofrequency pulses and conventional echo planar imaging (EPI) DWI (c-DWI) with regard to registration quality using positron emission tomography / magnetic resonance (PET/MR) in patients with malignant tumors.
  
  
  METHODS
  Fludeoxyglucose (18(F) ) PET imaging, c-DWI, and z-DWI were conducted simultaneously in 21 patients with known or suspected malignancy using a PET/MR system. A fusion image showing the largest tumor area was generated for analysis. Registration accuracy between PET and DWI was assessed based on the area of maximum overlap and central point displacement of the tumor. EPI factor, echo time (TE), matching area, and displacement were compared between c-DWI and z-DWI by paired t-test. Agreement of apparent diffusion coefficient (ADC) acquired by the two sequences were also assessed with linear regression s and Bland-Altman plot analysis.
  
  
  RESULTS
  Thirty-two lesions were detected on both PET and DWI (mean size 536.3 ± 471.8 mm(2) ). At least one lesion was found in all subjects. In all cases, EPI factor was smaller with z-DWI than c-DWI (43.1 ± 15.6 vs. 62.0 ± 10.0, P < 0.0001), and TE was also shorter for z-DWI (53.6 ± 3.6 msec vs. 65.2 ± 3.6 msec, P < 0.0001). Registration accuracy was better with z-DWI in 30 of 32 lesions (93.8%), and both average matching area and central point displacement were significantly improved (79.8 ± 18.1% vs. 61.8 ± 22.9%, P < 0.0001 and 3.92 ± 2.69 mm vs. 7.51 ± 4.07 mm, P < 0.0001). ADC values calculated with c-DWI and z-DWI showed good agreement.
  
  
  CONCLUSIONS
  Zoomed DWI reduces image distortion and provides better registration accuracy with PET images.
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Sagiyama
authors.affiliation: Department of Molecular Imaging and Diagnosis, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Yuji
authors.initials: Y
authors.lastname: Watanabe
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Ryotaro
authors.initials: R
authors.lastname: Kamei
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Baba
authors.affiliation: Department of Clinical Radiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Honda
mesh_terms: D000368:Aged; D016477:Artifacts; D038524:Diffusion Magnetic Resonance Imaging; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000737:chemistry; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009369:Neoplasms / Q000000981:diagnostic imaging*; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: PET/MR; image fusion; spatially selective RF pulse; zoomed-EPI DWI