Abstract
PurposeThe purpose of this study is to assess the performance of computer-aided detection (CAD) software in detecting and measuring polyps for CT Colonography, based on an in vitro phantom study.Material and methodsA colon phantom was constructed with a PVC pipe of 3.8 cm diameter. Nine simulated polyps of various sizes (3.2mm-25.4mm) were affixed inside the phantom that was placed in a water bath. The phantom was scanned on a 64-slice CT scanner with tube voltage of 120 kV and current of 205 mAs. Two separate scans were performed, with different slice thickness and reconstruction interval. The first scan (thin) had a slice thickness of 1mm and reconstruction interval 0.5mm. The second scan (thick) had a slice thickness of 2mm and reconstruction interval of 1mm. Images from both scans were processed using CT Colonography software that automatically segments the colon phantom and applies CAD that automatically highlights and provides the size (maximum and minimum diameters, volume) of each polyp. Two readers independently measured each polyp (two orthogonal diameters) using both 2D and 3D views. Readers’ manual measurements (diameters) and automatic measurements from CAD (diameters and volume) were compared to actual polyp sizes as measured by mechanical calipers.ResultsAll polyps except the smallest (3.2mm) were detected by CAD. CAD achieved 100% sensitivity in detecting polyps ≥6mm. Mean errors in CAD automated volume measurements for thin and thick slice scans were 8.7% and 6.8%, respectively. Almost all CAD and manual readers’ 3D measurements overestimated the size of polyps to variable extent. Both over- and underestimation of polyp sizes were observed in the readers’ manual 2D measurements. Overall, Reader 1 (expert) had smaller mean error than Reader 2 (non-expert).ConclusionCAD provided accurate size measurements for all polyps, and results were comparable to the two readers' manual measurements
Highlights
Intensity modulated radiotherapy (IMRT) utilises small beamlets of ionising radiation to provide a highKhamfongkhruea et al Biomed Imaging Interv J 2012; 8(1):e5This page number is not for citation purposes use a respiratory gating system
The measurements by MapCheck show the gamma index of the planned absolute dose distribution in static and moving targets with gating, resulting in more than 96% passing for all dose rates
The absolute dose distribution measured by film for the static target was agreeable with the value of moving target with gating
Summary
Intensity modulated radiotherapy (IMRT) utilises small beamlets of ionising radiation to provide a highKhamfongkhruea et al Biomed Imaging Interv J 2012; 8(1):e5This page number is not for citation purposes use a respiratory gating system. Chen et al [5] studied the dosimetric effects caused by the respiratory motion during IMRT by using Kodak EDR2 films. They concluded that, without the gating system, the dose distribution of the stationary phantom was different from the moving one. Duan et al [7] studied the dosimetric effect of respiration-gated beam with IMRT delivery Their results suggested that low dose rate can reduce the effect of delay and catch-up cycle. Lin et al [2] determined the effect of radiation dose rate with moving target and the gated treatment using step-and-shoot IMRT delivery. The high dose rate gated stepand-shoot IMRT was dosimetrically accurate, shortened the delivery time, and was safe to use clinically
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