Program Information
Prospective Determination of Manufacturer Calculated CTDIVOL for Use in CT Protocol Development and Optimization
R Herrera*, D Gauntt , UAB University of Alabama, Birmingham, Birmingham, AL
Presentations
SU-K-201-6 (Sunday, July 30, 2017) 4:00 PM - 6:00 PM Room: 201
Purpose: Accrediting organizations encourage performing optimization of CT protocols. We seek to determine, a priori, the manufacturer’s calculated CTDIVOL based on scan and reconstruction parameters, and to apply this to the development and optimization of new CT protocols. This requires understanding the relationship between CTDIVOL, patient size and AEC parameters.
Methods: Semi-anthropomorphic abdominal phantoms with spine insert were used to investigate the relationship between CT scan parameters and the prospective CTDIVOL displayed on a GE-HD750 scanner and a Philips-iCT256 scanner: the accuracy of the displayed CTDIVOL was previously verified. Six sizes of semi-anthropomorphic phantoms were used, with water-equivalent diameter (DW) ranging from 13cm to 36cm. Each phantom was scanned using an abdomen protocol, where AP and LAT topograms are used to determine the tube current for a helical acquisition. After acquiring the topograms, various scan parameters were varied and prospective CTDIVOL and tube current recorded. This data was used to generate a model of CTDIVOL as a function of patient size and acquisition settings. Helical acquisitions were performed for selected settings; the mean CT number in soft tissue and the spine, and the noise standard deviation in soft tissue were recorded.
Results: For tube voltages ranging from 80kV to 140kV, and DW ranging from 13cm to 36cm, our model predicts the CTDIVOL as a function of acquisition parameters and patient size, with relative RMS-errors of 3.0% for the GE scanner, and 7.4% for the Philips scanner. We also find that CNR decreases monotonically with increasing kV for all DW.
Conclusion: Relationships are established for the behavior of the pre-calculated CTDIVOL and bone/soft tissue contrast, with the following parameters: AEC parameter (Noise Index/Dose-Right Index), and water-equivalent diameter. These relationships allow us to create simple rules-of-thumb that can be easily applied in the optimization of CTDIVOL during protocol development.
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