Christine Niebler MS, Presenter: Nothing to Disclose

Yiannis Kyriakou, Abstract Co-Author: Nothing to Disclose

Christian Penssel PhD, Abstract Co-Author: Nothing to Disclose

Willi A. Kalender PhD, Abstract Co-Author: Consultant, Siemens AG Founder, VAMP GmbH Scientific Advisor, VAMP GmbH Shareholder, VAMP GmbH

To provide high-resolution 3D images of a volume of interest (VOI) at low patient dose using a variable isocenter C-arm system.

A low-dose, low-resolution scan (localization scan) with collimators fully open was used for a survey in which the position of the VOI was localized. In a second scan the rotation center and the collimation were chosen according to the position and size of the VOI. The second scan (high-resolution VOI scan) could be performed with higher dose in order to provide a high-resolution 3D reconstruction with low noise. We use a prototype C-arm flat-panel detector system equipped with a large flat panel detector of 40 cm × 30 cm. The approach was evaluated using anthropomorphic phantoms with different imagequality evaluation inserts. A thin tungsten wire insert was used for the determination of the modulation transfer function (MTF) in the VOI. A high resolution pattern was used for visual evaluation. Homogeneous regions of the anthropomorphic phantom were used for the investigation of the noise behaviour in- and outside the VOI. Truncation problems were solved as described in a separate paper. Dose was calculated with a Monte Carlo tool (ImpactMC, VAMP GmbH, Erlangen, Germany) and was measured using a calibrated ionisation chamber in cylindrical PMMA phantoms of 16 cm and 32 cm diameter.

Without a loss of generality, results are given for 25 cm (full field) and local 8 cm VOI as an example. The evaluation of the MTF indicated a resolution of 3.3 lp/mm at the 10% value. Images of a stent confirmed the high resolution. The cumulative dose for the two scans (low-dose localization and high-dose highresolution VOI scan) was found to be 30%-60% lower than the dose of a respective standard scan over the full volume at the same resolution level. This was due to the reduction of the highly exposed volume.

The approach of using two separate scans offers significant benefits with respect to high-resolution imaging of a VOI. With appropriate beam collimation cumulative patient dose is reduced even for better image quality in the VOI.

Volume of interest (VOI) scans can be made with high resolution, yet limited total patient dose.

Niebler, C, Kyriakou, Y, Penssel, C, Kalender, W, High-Resolution Volume-of-Interest Imaging at Reduced Patient Dose Using a Flat-Panel C-Arm System with Variable Isocenter.  Radiological Society of North America 2006 Scientific Assembly and Annual Meeting, November 26 - December 1, 2006 ,Chicago IL. http://archive.rsna.org/2006/4428473.html