Daniel Kolditz, Presenter: Employee, Artemis Imaging GmbH

Marcel Beister, Abstract Co-Author: Employee, Artemis Imaging GmbH

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Consultant, Bayer AG Founder, CT Imaging GmbH Scientific Advisor, CT Imaging GmbH Shareholder, CT Imaging GmbH Founder, Artemis Imaging GmbH CEO, Artemis Imaging GmbH Shareholder, Artemis Imaging GmbH

Generally, the complete breast cross-section is scanned in breast CT to avoid truncation artifacts in the reconstructed images. The aim of this study was to develop and evaluate a volume-of-interest (VOI) approach to increase image quality for a sub-volume at reduced total dose.

The VOI approach accepts taking two consecutive scans. It starts with a low-dose overview (OV) scan of the complete breast cross-section and a low-resolution reconstruction aiming at soft-tissue assessment for general orientation, initial diagnosis and the VOI selection. To examine specific structures more closely, higher resolution and a respective dose increase, limited to the VOI, are necessary. For this, the VOI is scanned with a narrowed collimation, a higher detector resolution and a higher dose to ensure better local image quality. For reconstruction the truncated VOI projections are completed with information of the prior OV scan in a filtered backprojection algorithm or an iterative reconstruction technique. Image quality parameters as spatial resolution, noise and lesion visibility were evaluated and compared to a simple standard scan both by simulations and measurements with an experimental breast CT scanner. The dose reduction potential was investigated in measurements using a calibrated ionization chamber and thermoluminescence dosimeters and in simulations using a Monte Carlo tool (ImpactMC, CT Imaging GmbH, Erlangen, Germany) to assess 3D dose distributions and average glandular dose (AGD).

Compared to a standard scan with 6 mGy AGD, the OV scan taken at only 1.5 mGy AGD provided sufficient image quality for orientation and detection of microcalcification clusters due to their high contrast. The successive VOI scan allowed resolving this cluster of 100 µm microcalcifications. The VOI technique worked in this case with an accumulated AGD of only 3.3 (= 1.5 + 1.8) mGy, while providing more specific information locally.

The proposed approach allows imaging of sub-volumes with higher resolution at reduced total dose whenever prior information regarding the cross-section is available. The dose reduction depends on the size of the VOI related to the total volume to be examined.

The VOI technique is of definite interest whenever looking at specific structures in detail without a dose penalty. It can also be employed for dose-intensive procedures when repeated scans are taken.

Kolditz, D, Beister, M, Kalender, W, Volume-of-Interest Imaging for High Image Quality at Reduced Dose in Dedicated Female Breast CT.  Radiological Society of North America 2011 Scientific Assembly and Annual Meeting, November 26 - December 2, 2011 ,Chicago IL. http://archive.rsna.org/2011/11008972.html