Tradeoffs in helical CT: the effects of collimation and pitch on dose, noise, and slice sensitivity profiles

Michael F. McNitt-Gray; Chris H. Cagnon; Tim D. Solberg

doi:10.1117/12.237804

11 April 1996 Tradeoffs in helical CT: the effects of collimation and pitch on dose, noise, and slice sensitivity profiles

Michael F. McNitt-Gray, Chris H. Cagnon, Tim D. Solberg

Author Affiliations +

Proceedings Volume 2708, Medical Imaging 1996: Physics of Medical Imaging; (1996) https://doi.org/10.1117/12.237804
Event: Medical Imaging 1996, 1996, Newport Beach, CA, United States

Abstract

To investigate the tradeoffs that occur in helical CT scanning due to the different combinations of pitch and collimation available. These tradeoffs affect patient dose, image noise and slice sensitivity profiles. For both a single and dual detector helical CT scanners, different combinations of pitch and collimation were investigated. For each combination, patient dose was estimated using calculations from TLD measurements made with a standard CTDI phantom. Noise was measured using a homogeneous water phantom. Slice sensitivity profiles were measured using phantoms approximating impulse functions. For each scanner, the effects on noise, slice thickness and radiation dose of variations in pitch and collimation were reported. In addition, the tradeoffs between combinations of pitch and collimation that utilize the same table speed were examined. As an example, the single helical scanner can obtain a table speed of 10 mm/s using either: (1) a collimation of 10 mm and a pitch of 1, or by (2) collimating to 5 mm and using a pitch of 2. Assuming a constant mA, the radiation dose decreases from 1.2 rad at the center to .71 rad at the center, when going from the first to the second technique. The image noise increases from a standard deviation of 4.1 to 5.7; and the slice sensitivity profile decreases from 10.46 mm to 6.55 mm. Results for other pitch and collimation combinations are reported as well as the results for the dual helical scanner. For a fixed table movement speed, thinner slices with higher pitches give better z-axis resolution and lower patient dose while increasing image noise.

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Michael F. McNitt-Gray, Chris H. Cagnon, and Tim D. Solberg "Tradeoffs in helical CT: the effects of collimation and pitch on dose, noise, and slice sensitivity profiles", Proc. SPIE 2708, Medical Imaging 1996: Physics of Medical Imaging, (11 April 1996); https://doi.org/10.1117/12.237804

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