| ORIGINAL ARTICLE |
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| Year : 2006 | Volume
: 31
| Issue : 1 | Page : 28-35 |
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Performance evaluation of a dedicated computed tomography scanner used for virtual simulation using in-house fabricated CT phantoms
DS Sharma1, SD Sharma2, KK Sanu2, S Saju1, DD Deshpande1, S Kannan2
1 Department of Medical Physics, Tata Memorial Hospital, Parel, Mumbai, India
2 Radiological Physics and Advisory Division, Bhabha Atomic Research Center, Anushaktinagar, Mumbai, India
Correspondence Address:
S D Sharma
Radiological Physics & Advisory Division, Bhabha Atomic Research Centre, CT&CRS Building, Anushaktinagar, Mumbai - 400 094
India
 Source of Support: None, Conflict of Interest: None  | Check |
DOI: 10.4103/0971-6203.25667
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Comprehensive tests on single slice CT scanner was carried out using in-house fabricated phantoms/test tools following AAPM recommended methods to independently validate the auto-performance test (APT) results. Test results of all the electromechanical parameters were found within the specified limits. Radiation and sensitivity profile widths were within ± 0.05 cm of the set slice thickness. Effective energy corresponding to nominal kVp of 80, 110 and 130 were 49.99, 55.08 and 59.48 keV, respectively. Percentage noise obtained by APT was 1.32% while the independently measured value was 0.38%. Observed contrast resolutions by independent method at 0.78% and 12% contrast difference were 4 mm and 1.25 mm (= 4 lp/cm) respectively. However, high contrast resolution (limiting spatial resolution) by APT at 50, 10 and 2% MTF levels were 9, 12.5 and 14.1 lp/cm respectively. Difference in calculated and measured CT numbers of water, air, teflon, acrylic, polystyrene and polypropylene were in the range of 0 to 24 HU, while this difference was 46 and 94 HU in case of nylon and bakelite respectively. The contrast scale determined using CT linearity phantom was 1.998×10-4 cm-1/CT number. CT dose index (CTDI) and weighted CTDI (CTDIw) measured at different kVp for standard head and body phantoms were smaller than manufacturer-specified and system-calculated values and were found within the manufacturer-specified limit of ± 20%. Measured CTDIs on surface (head: 3.6 cGy and body: 2.6 cGy) and at the center (3.3 cGy, head; and 1.2 cGy, body) were comparable to reported values of other similar CT scanners and were also within the industry-quoted CTDI range. Comprehensive QA and independent validation of APT results are necessary to obtain baseline data for CT virtual simulation. |
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