Tabassum A. Kennedy MD, Presenter: Nothing to Disclose

Timothy Peter Szczykutowicz PhD, Abstract Co-Author: Equipment support, General Electric Company Research Grant, Siemens AG

Sara Rademacher Nace MD, Abstract Co-Author: Nothing to Disclose

Kevin Royalty MS, MBA, Abstract Co-Author: Employee, Siemens AG

Sebastian Schafer, Abstract Co-Author: Consultant, Siemens AG

Samuel P. Gubbels MD, Abstract Co-Author: Nothing to Disclose

Brian Gartrell MD, Abstract Co-Author: Nothing to Disclose

There have been substantial developments in C-Arm CT acquisitions (CACT), particularly in the setting of implantable devices and focusing on small volume, high contrast targets. The purpose of this study was to image the temporal bone and compare the image quality and relative radiation dose to the ocular lens between multidetector CT (MDCT) and CACT using a cadaveric model before and after cochlear electrode (CE) implantation.

Four cadaveric heads were scanned on a C-Arm biplane system with CT capability, and on a clinical 64-slice MDCT. Each head was scanned with 2 different CACT modes: a small field ov view (FOV) and full FOV mode. The small FOV mode utilized 6.5 cm x 11 cm coverage, 0.154 mm detector pitch and 0.2mm slice thickness. The full FOV mode utilized 6.5 cm x 38 cm coverage, 0.308 mm detector pitch and 0.2 mm slice thickness.  For MDCT scans, a clinical temporal bone protocol was used with a 0.531 pitch, noise index 6.7, acquisition slice thickness 2.5 mm, and axial bone reconstructions of 0.625 mm. Dose measurements were performed using thermoluminescent dosimeters (TLDs). The relative dose to the lens was measured with TLD chips placed under the eyelids of whole cadaver heads.  Separate scans were acquired of each cadaver head both before and after CE implantation. Image quality was qualitatively evaluated by a panel of experienced neuroradiologists including the position of the implanted CE.

The image quality of MDCT and CACT temporal bone images was judged to be equivalent for clinical evaluation  prior to CE implantation. CACT was superior to MDCT in localizing the intracochelar position of the CE. The radiation dose to the lens was 15 times lower in small FOV CACT compared to MDCT and 1.9 lower in full FOV CACT compared to MDCT. There was no significant difference in radiation dose between the pre and post implant acquisitions.

Due to the geometry of the scan range and collimation of the CACT system, a substantial dose reduction was observed for CACT over MDCT for the lens. Our data suggests equivalent spatial resolution for clinically relevant temporal bone structures prior to CE implantation and improved visibility of intracochlear position of the CE after implantation.

Future applications of C-arm CT systems include intraoperative cochlear implant staging from delivery under fluoroscopic guidance to post-delivery assessment of surgical position.

Kennedy, T, Szczykutowicz, T, Nace, S, Royalty, K, Schafer, S, Gubbels, S, Gartrell, B, Comparative Cadaver Study of MDCT and C-Arm CT Imaging of the Temporal Bone before and after Cochlear Electrode Implantation: Image Quality and Dose Distribution.  Radiological Society of North America 2014 Scientific Assembly and Annual Meeting, - ,Chicago IL. http://archive.rsna.org/2014/14012099.html