Einfluss von kollimation und pitch auf die patientendosis und die abbildungsqualitat bei der spiral-computertomographie des thorax

Purpose: The aim of the study was to optimize the scan parameters for spiral-CT of the thorax. Methods: Using a Somatom AR-SP (Siemens AG, Erlangen) CT-unit, four different scanning protocols (collimation/table feed) were compared: A (5/10), B (10/10), C (10/15), D (10/20). High contrast resolution in the xy-plane and in the z-direction were investigated with special phantoms. Noise levels were measured using a water phantom, the radiation exposure of lung parenchyma was investigated using an Alderson- Rando-Phantom. An anthropoid chest phantom was scanned to compare the image quality of the four protocols. Results: Protocol A showed the best resolution in the z-direction; the resolution in the xy-plane was equal for all protocols. Image noise in the center of the water phantom was 58 HU for protocol A and 40 HU for the other three. The following equivalent organ dose were measured for lung parenchyma: A 14 mSv, B 29 mSv, C 20 mSv, D 14 m5v. Conclusion: Scanning protocols with small collimation and a pitch of 2 are characterised by low radiation exposure and excellent resolution in the z- direction. These parameters seem to be most suitable for lung scanning.