title: Image quality improvement in three-dimensional time-of-flight magnetic resonance angiography using the subtraction method for brain and temporal bone diseases.
abstract: BACKGROUND
  Time-of-flight (TOF) magnetic resonance (MR) angiography is based on flow-related enhancement using the T1-weighted spoiled gradient echo, or the fast low-angle shot gradient echo sequence. However, materials with short T1 relaxation times may show hyperintensity signals and contaminate the TOF images. The objective of our study was to determine whether subtraction three-dimensional (3D) TOF MR angiography improves image quality in brain and temporal bone diseases with unwanted contaminations with short T1 relaxation times.
  
  
  METHODS
  During the 12-month study period, patients who had masses with short T1 relaxation times noted on precontrast T1-weighted brain MR images and 24 healthy volunteers were scanned using conventional and subtraction 3D TOF MR angiography. The qualitative evaluation of each MR angiogram was based on signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR) and scores in three categories, namely, (1) presence of misregistration artifacts, (2) ability to display arterial anatomy selectively (without contamination by materials with short T1 relaxation times), and (3) arterial flow-related enhancement.
  
  
  RESULTS
  We included 12 patients with intracranial hematomas, brain tumors, or middle-ear cholesterol granulomas. Subtraction 3D TOF MR angiography yielded higher CNRs between the area of the basilar artery (BA) and normal-appearing parenchyma of the brain and lower SNRs in the area of the BA compared with the conventional technique (147.7 ± 77.6 vs. 130.6 ± 54.2, p < 0.003 and 162.5 ± 79.9 vs. 194.3 ± 62.3, p < 0.001, respectively) in all 36 cases. The 3D subtraction angiography did not deteriorate image quality with misregistration artifacts and showed a better selective display of arteries (p < 0.0001) and arterial flow-related enhancement (p < 0.044) than the conventional method.
  
  
  CONCLUSIONS
  Subtraction 3D TOF MR angiography is more appropriate than the conventional method in improving the image quality in brain and temporal bone diseases with unwanted contaminations with short T1 relaxation times.
authors.affiliation: Department of Medical Imaging, Chung Shan Medical University Hospital, Taichung, Taiwan, ROC.
authors.forename: Shu-Hui
authors.initials: SH
authors.lastname: Peng
authors.forename: Chao-Yu
authors.initials: CY
authors.lastname: Shen
authors.forename: Ming-Chi
authors.initials: MC
authors.lastname: Wu
authors.forename: Yue-Der
authors.initials: YD
authors.lastname: Lin
authors.forename: Chun-Huang
authors.initials: CH
authors.lastname: Huang
authors.forename: Ruei-Jin
authors.initials: RJ
authors.lastname: Kang
authors.forename: Yeu-Sheng
authors.initials: YS
authors.lastname: Tyan
authors.forename: Teng-Fu
authors.initials: TF
authors.lastname: Tsao
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001847:Bone Diseases / Q000175:diagnosis*; D001927:Brain Diseases / Q000175:diagnosis*; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods* / Q000592:standards; D007223:Infant; D018810:Magnetic Resonance Angiography / Q000379:methods* / Q000592:standards; D008297:Male; D008875:Middle Aged; D013701:Temporal Bone
keywords: contamination; hematoma; magnetic resonance angiography; subtraction