title: Dual energy bone subtraction in computed tomography angiography of extracranial-intracranial bypass: feasibility and limitations.
abstract: OBJECTIVE
  To assess the feasibility of dual energy (DE)-CTA images with DE-bone removal (DEBR) for visualization of extra- to intracranial (EC/IC) arterial bypass compared to digital subtraction angiography (DSA).
  
  
  METHODS
  Prospectively, 24 patients underwent DE-CTA and DSA for evaluation of EC/IC-bypass. Using 5-point scales (0=poor to 4=excellent) two examiners rated image quality, quality of bone removal, and vessel integrity of bypass for three segments (extracranial, trepanation, intracranial) in CTA images with and without DEBR in comparison to DSA. Scores were evaluated by Friedmann's- and post-hoc Wilcoxon rank test.
  
  
  RESULTS
  Image quality was high in CTA with and without DEBR and DSA (3.78 ± 0.36, 3.78 ± 0.36, 3.27 ± 0.46). No significant bone remnants were present using DEBR. Mean scores of bypass visualization were not significantly different for the extra- and intracranial segments. However, in the trepanation segment pseudo-lesions of the bypass were present in DEBR-CTA (6 out 24 cases) with a negative effect on visualization scores compared to DSA (p < 0.05).
  
  
  CONCLUSIONS
  CTA with DEBR for assessment of EC/IC-bypass is feasible with reliable removal of cranial bones. Readers should be aware of a potential pitfall showing focal pseudostenosis/-occlusion of the bypass close to bone at the trepanation margin.
authors.affiliation: Department of Clinical Radiology, University Hospital of Münster, Albert-Schweitzer-Strasse 33, 48149 Münster, Germany. akemmling@web.de
authors.forename: André
authors.initials: A
authors.lastname: Kemmling
authors.forename: Ingo
authors.initials: I
authors.lastname: Nölte
authors.forename: Christoph
authors.initials: C
authors.lastname: Groden
authors.forename: Steffen
authors.initials: S
authors.lastname: Diehl
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D015901:Angiography, Digital Subtraction / Q000379:methods*; D001842:Bone and Bones / Q000000981:diagnostic imaging*; D002561:Cerebrovascular Disorders / Q000000981:diagnostic imaging / Q000628:therapy*; D003952:Diagnostic Imaging / Q000379:methods; D005240:Feasibility Studies; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods; D011871:Radiology / Q000379:methods; D014057:Tomography, X-Ray Computed / Q000379:methods*