Share Email Print
cover

Proceedings Paper

Tradeoffs in helical CT: the effects of collimation and pitch on dose, noise, and slice sensitivity profiles
Author(s): Michael F. McNitt-Gray; Chris H. Cagnon; Tim D. Solberg
Format Member Price Non-Member Price
PDF $14.40 $18.00

Paper 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.

Paper Details

Date Published: 11 April 1996
PDF: 11 pages
Proc. SPIE 2708, Medical Imaging 1996: Physics of Medical Imaging, (11 April 1996); doi: 10.1117/12.237804
Show Author Affiliations
Michael F. McNitt-Gray, UCLA School of Medicine (United States)
Chris H. Cagnon, UCLA School of Medicine (United States)
Tim D. Solberg, UCLA School of Medicine (United States)


Published in SPIE Proceedings Vol. 2708:
Medical Imaging 1996: Physics of Medical Imaging
Richard L. Van Metter; Jacob Beutel, Editor(s)

© SPIE. Terms of Use
Back to Top