(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose:
Purpose of the study is to evaluate dose modulations and optimize standardization of scan protocols in CT scanners from two major manufacturers.
Methods:
Experiments were performed using Catphan504-phantom with Teflon slip-rings that simulated small(20-cm), normal(30-cm) and medium-to-large(35-cm) patient-sizes. Phantom was scanned using manufacturers’ modulation algorithms, “3D-Modulation” in a Philips (Ingenuity-128), and “CareDose4D” on Siemens-scanner (Somatom-FORCE). Multiple “reference-doses” (8.5, 10.5, 13.5mGy) were set at 32-cm for Siemens, corresponding to multiple “dose-right-index” (DRI=16,18,20,22) for Philips-scanner. Images were reconstructed using default iterative-algorithms(iDose=4) for Philips-scanner and ADMIRE=3 (Siemens-scanner). Siemens picked the “optimal”-kVp within CareDose4D-algorithm whereas for Philips-scanner, tube-kVps were manually varied (80,100,120,140) for each DRI settings. Iodine-contrast enhancement was measured with an iodine-containing vial at various kVps. The performance of modulation algorithms in-terms-of noise-uniformity and CNR was compared using subjective and quantitative approaches. Similar comparison was made within Philips-scanner to determine the optimized kVp at a given patient size. The derived optimal kVp is compared with CareDose4D-algorithm.
Results:
With given reference-dose (Siemens) or DRI (Philips), modulations by manufacturers showed similarity in its dose-delivery and noise changes over patient-sizes, with higher doses and higher noise as patient-size increased, more prominent for the lower kVp (80- and 100-kVp) in Philips-scanner. Using “dose merit” quantified as CNR normalized by scan-dose, optimal kVp for the Philips’s modulation is 80-kVp for 20-25 cm, 100-kVp for 25-30 cm patient, and 120-kVp for 30-35 cm patient. For Siemens, corresponding kVp auto-selected by Caredose4D was 90,100, and 110-kVp, indicating a similar trend. With optimally-chosen kVps for both scanners, noise at given dose is similar, with slightly reduced noise in Siemens(<10%) across patient sizes.
Conclusion:
The dose modulation algorithms in both scanners have similar behaviors in image-noise variation across patient-sizes. The appropriate size specific kVp as-per patient size in Philips-scanner is experimentally determined, and consistent with the CareDose4D choice in Siemens-scanner.
Keywords
Not Applicable / None Entered.
Taxonomy
IM- CT: Quantitative imaging/analysis
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