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Evaluation of the Impact of Body Size and Tube Output Limits in the Optimization of Fast Scanning with High-Pitch Dual Source CT


J Ramirez Giraldo

J Ramirez Giraldo1, A. Mileto2, L.Hurwitz2, D. Marin2, (1) Siemens Medical Solutions USA, Inc (2) Duke University Medical Center, Durham NC, 27710

Presentations

TH-C-18A-12 Thursday 10:15AM - 12:15PM Room: 18A

Purpose: To evaluate the impact of body size and tube power limits in the optimization of fast scanning with high-pitch dual source CT (DSCT).

Methods: A previously validated MERCURY phantom, made of polyethylene, with circular cross-section of diameters 16, 23, 30 and 37cm, and connected through tapered sections, was scanned using a second generation DSCT system. The DSCT operates with two independently controlled x-ray tube generators offering up to 200 kW power reserve (100 kW per tube). The entire lenght of the phantom (42cm) was scanned with two protocols using: A)Standard single-source CT (SSCT) protocol with pitch of 0.8, and B) DSCT protocol with high-pitch values ranging from 1.6 to 3.2 (0.2 steps). All scans used 120 kVp with 150 quality reference mAs using automatic exposure control. Scanner radiation output (CTDIvol) and effective mAs values were extracted retrospectively from DICOM files for each slice. Image noise was recorded. All variables were assessed relative to phantom diameter.

Results: With standard-pitch SSCT, the scanner radiation output (and tube-current) were progressively adapted with increasing size, from 6 mGy (120 mAs) up to 15 mGy (270 mAs) from the thinnest (16cm) to the thickest diameter (37 cm), respectively. By comparison, using high-pitch (3.2), the scanner output was bounded at about 8 mGy (140 mAs), independent of phantom diameter. Although relative to standard-pitch, the high-pitch led to lower radiation output for the same scan, the image noise was higher, particularly for larger diameters. To match the radiation output adaptation of standard-pitch, a high-pitch mode of 1.6 was needed, with the advantage of scanning twice as fast.

Conclusion: To maximize the benefits of fast scanning with high-pitch DSCT, the body size and tube power limits of the system need to be considered such that a good balance between speed of acquisition and image quality are warranted.

Funding Support, Disclosures, and Conflict of Interest: JCRG is an employee of Siemens Medical Solutions USA Inc.


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