Shuai Leng PhD, Presenter: Nothing to Disclose

John Ignatius Lane MD, Abstract Co-Author: Nothing to Disclose

Kelly Karl Koeller MD, Abstract Co-Author: Nothing to Disclose

Felix E. Diehn MD, Abstract Co-Author: Nothing to Disclose

Robert James Witte MD, Abstract Co-Author: Nothing to Disclose

Michael Robert Bruesewitz, Abstract Co-Author: Nothing to Disclose

Thomas J. Vrieze RT, Abstract Co-Author: Nothing to Disclose

Cynthia H. McCollough PhD, Abstract Co-Author: Research Grant, Siemens AG

To assess spatial resolution and image noise for a temporal bone CT imaging method that uses an ultra-high resolution (UHR) scan mode combined with iterative reconstruction (IR), and to compare to a protocol with reduced dose efficiency due to use of z-axis collimation (zUHR).

Patients with prior temporal bone CT scans acquired using a zUHR protocol who received a follow-up scan using the UHR+IR technique were identified. Left and right side of temporal bone images were reconstructed in axial, coronal and Poschl planes. Spatial resolution was evaluated independently by 3 neuroradiologists with focus on the following structures: round and oval windows, incudomallear joint, incudostapedial joint, spiral lamina in the basal turn, and scutum. The zUHR and UHR+IR images were displayed side by side, with the order randomized and blinded to the readers. The following grading scale was applied to the UHR+IR images (relative to the zUHR images): 1=inferior resolution, degrades visualization, 2=slightly inferior resolution, not affect visualization, 3=equivalent, 4=slightly superior resolution, not affect visualization, 5=superior resolution, improves visualization. Image noise was measured in regions of interest over the posterior fossa and compared.

8 patients with 16 sets (left and right side) of temporal bones were identified, of which 3 sets were excluded due to surgery between the two exams (13 left). The average scores across readers for spatial resolution on the UHR+IR images compared to zUHR were 3.4, 3.5 and 2.9 in axial, coronal and Poschl planes, respectively, indicating comparable or slightly better spatial resolution using the UHR+IR technique. Wilcoxon signed-rank test showed significant differences (p<0.05) for axial and coronal planes. A paired t-test showed significantly lower noise for UHR+IR compared to zUHR (p<0.05), with a mean noise reduction of 32% (17 to 49%). This translates to a potential dose reduction of 54% (31 to 74%) as radiation dose is inversely proportional to the square of image noise in CT.

The UHR+IR scan mode has similar or slightly better resolution relative to the zUHR mode, but significantly lower (32%) image noise. An estimated 50% dose reduction may be achievable using the UHR+IR mode.

Substantial dose reduction can likely be achieved for temporal bone CT imaging using the investigated combined UHR+IR technique.

Leng, S, Lane, J, Koeller, K, Diehn, F, Witte, R, Bruesewitz, M, Vrieze, T, McCollough, C, Image Quality and Radiation Dose Assessment in Temporal Bone CT Using an Ultra High Resolution Mode and an Iterative Reconstruction Algorithm Temporal Bone CT: Improved Image Quality and Potential for Decreased Radiation Dose Using an Ultra High Resol.  Radiological Society of North America 2013 Scientific Assembly and Annual Meeting, December 1 - December 6, 2013 ,Chicago IL. http://archive.rsna.org/2013/13023016.html