Using standard nonenhanced axial scans for cerebral CT angiography bone elimination: Feasibility study

Objective: To investigate the feasibility of using standard nonenhanced axial-mode scans as precontrast scans for bone elimination in cerebral CT angiography (CTA). Materials and methods: A consecutive dataset of 32 patients who had both cerebral nonenhanced CT (NECT) (scanned in axial mode) and subtraction CTA (scanned in helical mode) examinations between April and August 2008 were retrospectively analyzed. For each patient, both axial-and helical-mode, NECT scans were processed by using the matched mask bone elimination (MMBE) method. Bone masks generated from axial-and helical-mode NECT scans were quantitatively compared by using overlapping analyses. The diagnostic quality and noise level of the resultant, maximum intensity projection, images by using 2 different bone masks were visually evaluated by 2 neuroradiologists independently using a 5-point scale (inferior, 1; worse, 2; equivalent, 3; better, 4; superior, 5). The effective doses to patients were estimated by using a dose-length product method. Results: Of the 28 (87.5%) patients without intrascan movements, overlap rates between axial-and helical-mode bone masks ranged from 99.2% to 99.9% (mean, 99.7% ± 0.2%). The mean diagnostic quality and noise level scores of resultant maximum intensity projection images given by 2 neuroradiologists were 3.0 ± 0.3 and 2.5 ± 0.5, respectively. The effective dose to patients with a routine brain CTA examination can be reduced from 1.16 to 0.78 mSv (16 cm, field-of-view) by using the proposed method if standard axial-mode NECT scans of the head are readily available. Conclusion: We found that using standard axial-mode NECT scans for bone elimination in helical-mode CTA is feasible. This method can further lower radiation dose without compromising the diagnostic quality.