Bernd Ohnesorge PhD, PRESENTER: Nothing to Disclose

Abstract: HTML Purpose: To optimize the X-ray tube voltage with regard to signal-to-noise ratio and patient dose for CT angiographic examinations (CTAs), in particular for cardio-thoracic applications. Methods and Materials: In contrast enhanced studies, such as CT angiographic examinations, the contrast-to-noise ratio for fixed patient dose increases with decreasing X-ray tube voltage. As a consequence, to obtain a given contrast-to-noise ratio, patient dose can be reduced by choosing lower kV-settings. We performed phantom measurements using small tubes filled with diluted iodine contrast agent embedded in plexiglass phantoms with different diameters. We measured the CT-value (in Hounsfield Units HU) of the iodine contrast agent, image noise and dose in terms of the CTDI value for X-ray tube voltages of 80 kV, 100 kV and 120 kV using a Sensation 16 multi-slice scanner (Siemens, Forchheim, Germany). To confirm our results, we performed a patient study on 20 human subjects scheduled for CTAs of the coronary arteries and for thoracic CTAs. We used 80 kV for 6 patients, 100 kV for 7 patients and 120 kV for 7 patients. Two independent readers rated the images with regard to diagnostic quality, sufficient contrast enhancement and image noise. Results: Compared to a standard scan with 120kV, the same contrast-to-noise ratio in a 32 cm phantom, corresponding to an average adult, is obtained with 0.49 times the dose for 80 kV (1.3 times the mAs) and 0.69 times the dose (1.1 times the mAs) for 100 kV. Ideally, 80 kV should be used for CTAs at lowest patient dose. In practice, however, the use of 80 kV for larger patients is limited by the available mA-reserves of the X-ray tube, leading to a loss of diagnostic quality due to excessive image noise (3 out of 6 patients). In these patients, 100 kV is a good compromise and the preferable choice for CT angiographic examinations. Conclusion: Using 100 kV for cardio-thoracic CTAs yields diagnostic image quality at 30% less dose compared to standard scans with 120 kV.  (T.G.F., B.M.O., C.S., S.S. are employees of Siemens Medical Solutions.) Questions about this event email: bernd.ohnesorge@siemens.com

Ohnesorge PhD, B, Optimization of the X-Ray Tube Voltage for CT Angiographic Examinations of the Thorax.  Radiological Society of North America 2003 Scientific Assembly and Annual Meeting, November 30 - December 5, 2003 ,Chicago IL. http://archive.rsna.org/2003/3104670.html