Room: Room 205
Purpose: To develop and evaluate the performance of an automatic patient size-specific noise index (SSNI) adjustment algorithm with respect to CT image quality and radiation dose on the Revolution CT (GE Healthcare, Waukesha, WI).
Methods: Five different sized anthropomorphic phantoms (water equivalent diameters [Dw]: 25.1, 31.0, 32.6, 35.9, and 39.2 cm) were used. An abdominal CT angiography (CTA) protocol was used as reference: 120 kV, 25 noise index (NI), and 1.25mm slice thickness. Using a previously developed technique as a starting point, five noise adjustment strength levels were developed ranging from no noise adjustment to strong noise adjustment across phantom size, relative to a reference size of 28.9 Dw. Each phantom was scanned on a Revolution CT at each SSNI level. A radiologist evaluated all image sets using a 5-point Likert scale for noise (1=far too low noise/high dose, 3= good noise/dose tradeoff, 5=far too high noise/low dose) and a 3-point Likert scale for diagnostic acceptability (1=not acceptable, 2=probably acceptable, 3=acceptable).
Results: SSNI increases NI for phantoms larger than the reference size, while the opposite is true for phantoms smaller than the reference size. SSNI varied between 21.8 and 38.0 across all phantom sizes and SSNI strengths, corresponding to CTDIvol changes of +37.1% (strongest SSNI, smallest phantom) and -64.4% (strongest SSNI, largest phantom) relative to the CTDIvol for that phantom at the reference NI of 25. Individual noise Likert scores ranged from 2 to 5, and average noise Likert scores (averaged across phantom size) ranged from 3.2 to 3.8. Individual diagnostic acceptability Likert scores ranged from 2 to 3, and average diagnostic acceptability Likert scores ranged from 2.4 to 2.8.
Conclusion: Implementation of SSNI along with appropriate selection of SSNI strength on Revolution CT may yield a more optimal dose/noise trade-off relative to constant NI across patient size.
Funding Support, Disclosures, and Conflict of Interest: Franco Rupcich and Dominic Crotty are employees of GE Healthcare. Harold Litt has nothing to disclose.