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Sci‐PM Sat ‐ 01: Imaging performance of a bench‐top megavoltage CT scanner
Author(s) -
Monajemi T,
Tu D,
Fallone B,
Rathee S
Publication year - 2005
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.2031060
Subject(s) - imaging phantom , optics , scanner , detective quantum efficiency , image resolution , detector , linearity , physics , medical imaging , materials science , attenuation , tomosynthesis , optical transfer function , nuclear medicine , image quality , mammography , computer science , computer vision , artificial intelligence , medicine , quantum mechanics , image (mathematics) , cancer , breast cancer
The ultimate goal of this project is to create a focused 2D MV detector with high detective quantum efficiency so reasonable low contrast resolution (LCR) at low dose can be obtained in MVCT. As an initial step an 80‐element detector is fabricated by tiling 8‐element CdWO 4(element size 0.275 × 0.8 × 1 cm 3 ) and photodiode arrays on an arc (radius = 110 cm). A precision rotary stage and its control are added to create a third generation CT scanner. The attenuation of Co 60and 6 MV beams are measured as a function of solid water thickness, fit to a second order polynomial to correct for spectral hardening artifacts. A calibration procedure was established to remove ring artifacts caused by distinctly asymmetric line spread functions at the ends of 8‐element blocks. Low contrast resolution as a function of dose and object size, the signal to noise ratio (SNR) as a function of dose, and linearity of CT numbers with density were quantified. Throwing away one‐ninth of collected projection angles to reduce the dose per image adversely affects the resolution in 6 MV images; 15 mm targets at 1.5% are visible at 7cGy. Low contrast target of 1.5% at 6 mm is visible in Co 60at 2cGy. LCR in objects stays approximately constant while dose is reduced from 17 to 2cGy. Contrast decreases with diameter decrease. SNR 2 from a uniform phantom increases linearly with dose (R 2 =0.9977). CT numbers as a function of the density show a linear trend (R 2 =0.9923).