The Optimization of CT Protocols Using Plots of CTDIvol and of Max and Min MA Versus Patient Size for Actual Clinical Scans Using Automatic Exposure Control (AEC)
F Ranallo*, T Szczykutowicz, University of Wisconsin, Madison, WIWE-C-103-4 Wednesday 10:30AM - 12:30PM Room: 103
Purpose: To determine the usefulness of the knowledge of CTDIvol and mA variations as a function of patient size for optimizing scan parameters in CT imaging using AEC.
Methods: Data was collected from actual patient scans for a number of different CT protocols such as standard chest, body, head, vascular imaging, and pediatric body. A GE LightSpeed VCT scanner was used in Smart mA mode in which the user can select the Noise Index, and the maximum and minimum mA allowed during mA modulation. For each different protocol the CTDIvol, minimum mA, maximum mA and patient size where determined for at least 40 patients, along with information on when the mA had reached its specified minimum or maximum value. Plots were made of the CTDIvol versus patient size and of the maximum and minimum mA versus patient size.
Results: Initial results demonstrated a significant variation in CTDIvol over the range of adult patient sizes of more than a factor of ten for abdominal imaging. The observation that clinical scans frequently reached the minimum allowed mA indicated that reduction of the rotation time and lowering of the minimum mA parameter would allow lower patient dose and better operation of the AEC system. These results also led us to create separate protocols for small, medium, and large patients, each with a different optimized Noise Index, kV, rotation time, and mA range. These were created in consultation with our radiologists in determining the lowest dose that would provide a clinically acceptable image after the AEC was deemed to be operating optimally.
Conclusion: The above analysis can provide significant help in improving CT protocols and lowering patient dose. The plots of CTDIvol versus patient size also helped to educate radiologists in the dose variations to be expected for a range of patient sizes.
Funding Support, Disclosures, and Conflict of Interest: Equipment grant from GE healthcare.
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