Experimental setups for new CBCT scan protocols. (a) Standard-dose head, low-dose head, and high-quality head scans with a head CTDI phantom (16 cm in diameter); (b) pelvis, pelvis spotlight, and low-dose thorax scans with a body CTDI phantom (32 cm in diameter). Note that both CTDI phantoms are in the length of 15.2 cm.
Varian OBI x-ray tube geometries for each full-fan mode and half-fan mode. Full-fan mode uses full-bowtie filter and half-bowtie is used for half-fan mode. Note that the opening of the blades (collimators) is different in each mode.
CT images of the CATPHAN 504 phantom for the image quality tests of (a) HU verification (module: CTP 404), (b) spatial linearity (CTP 404), (c) spatial resolution (CTP 528), (d) contrast resolution (CTP 515), and (e) HU uniformity (CTP 486).
Visualization of the 2D dose distribution for each new CBCT scan protocol: (a) Head, (b) pelvis, (c) pelvis spot light, and (d) low-dose thorax scans. The start and end points for the partial-angle scan was marked in Fig. 4(a). Note that the color scale is in the unit of mGy.
HU linearity test for the new CBCT protocols. Legends are as follows: CBSDH: Standard-dose head; CBLDH: Low-dose head; CBHQH: High-quality head; CBPEL: Pelvis; CBPSL: Pelvis spotlight; CBLDT: Low-dose thorax; CBFFold: Old full-fan; and CBHFold: Old half-fan. The negCriteria and posCriteria represent the acceptance criteria of ±40 HU.
CBCT images for the HU uniformity test obtained from (a) CBHQH (partial-angle scan) and (b) CBPEL (full-angle scan) protocols. Note the crescent effect at the interface of the two different density materials in the Fig. 6(a).
(a) Cross-sectional profiles obtained from standard head scan and (b) from standard body scan. The solid circle, open square, and open circle denote the profiles acquired at center, middle, and edge location in the CT phantoms.
Longitudinal profiles acquired from standard head and standard body scan. Note the dose drops at the edge location.
Detailed scan parameters and values for new and old CBCT scan protocols.
CTDI values and comparisons between the CTDI values acquired from method (1)–(4). The CTDI differences were calculated by following equation: . Note that the abbreviations IC and MC represent ion chamber measurements and Monte Carlo simulations.
Results of image quality QA tests for new and old CBCT scan protocols. Note that all the QA data of the old protocols are referenced from Ref. 14. The HU differences were calculated by following equation: . Note that the abbreviation n.HU represents nominal HU.
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