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Objective:To investigate the effect of different scanning modes, detector width and location in detector on high and low contrast resolution of wide-detector CT image.Methods:The Catphan600 phantom with high and low contrast resolution modules was scanned with GE Revolution CT at the same CTDI vol. The scans were performed with the detector widths of 40, 80 and 160 mm for sequential scanning mode and with the detector width/pitch combinations of 40 mm/0.516, 40 mm/0.984, 80 mm/0.508 and 80 mm/0.992 for spiral scanning mode. The resolution modules were placed at the adjacent region between two sequential scans, central and foot side edge in the longitudinal scanning range seperately. The subjective evaluation of the high and low contrast resolution was performed by two radiologists. Results:The high contrast resolution was 8 LP/cm at adjacent region between two sequential scans with the detector width of 80 mm or 160 mm in sequential scanning mode, and at the pitch of 0.5 in spiral scanning mode, while it was 7 LP/cm for the rest of detector combinations. The distinguishable diameter was 3 mm at 1% low contrast resolution at foot side edge with the detector widths of 80 mm or 160 mm in the sequential scanning mode, and it was 2 mm for all the other conditions. The distinguishable diameter was 2 mm at 1% low contrast resolution with the detector width of 40 mm and pitch 0.516 in the spiral scanning mode and it was worse with the wider detector and larger pitch.Conclusions:For the wide-detector CT, scanning mode, detector width, location in detector and pitches will affect the high and low contrast resolution to some degree. Appropriate selection should be done according to actual needs in clinical practice.
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OBJECTIVE@#Based on the Magphan phantom,a baseline value of low contrast resolution was established,and the stability of the imaging performance of the system was monitored.Drift and correction were found in time to give full play to the performance of the device.@*METHODS@#The general test evaluation method for low-contrast resolution was not suitable for the characteristics of long-term monitoring equipment performance changes,and the test evaluation of low-contrast resolution that incorporates the -test method in statistical principle was proposed.@*RESULTS@#By analyzing and evaluating the test results of the low contrast resolution of the standard water model image,and verifying the correctness of the evaluation method,according to the correct test method,the test statistic value was used as the low contrast resolution value of the MRI equipment to test the boundary of the region.The value was used as a baseline value for low contrast resolution to establish a long-term stable quality assurance system.@*CONCLUSIONS@#In this paper,the data of the low contrast resolution test on Magphan phantom was in line with practical experience,therefore the test method of low contrast resolution was verified.The baseline value of the indicator can be established based on the detection and evaluation method of low contrast resolution based on phantom,then to ensure the stability of the imaging performance of the system.
Subject(s)
Contrast Media , Magnetic Resonance Imaging , Phantoms, ImagingABSTRACT
Objective To analyze the performance differences of CT scanners with different detector rows between different manufacturers,and to provide the basis for the rational allocation and use of these CT scanners.Methods According to the result from the sentinel surveillance in 2014,a total of 148 medical institutions were equipped with CT scanners in 16 districts of Beijing,including general hospital(53),cancer hospital(5),TCM hospitals(25),children′s hospitals(2),community hospitals(30)and other specialized medical institutions(33).According to the principle of simple random sampling,40 medical institutions are selected,including 14 general hospitals,1 cancer hospital,7 Chinese medicine hospitals,1 children′s hospital,8 community hospitals and 9 other specialized medical institutions.A total of 141 CT scanners are selected from all CT sets of the selected medical institutions from 2012 to 2014.According to GB 17589-2011 X-ray computed tomography device quality assurance testing status test,four parameters related closely to image quality were tested,including CT value(water),noise,high contrast resolution,and low contrast detectability.Results No significant differences were found in CT value(water),noise and low contrast detectability among CT scanners produced by different manufacturers(P＞0.05),whereas high contrast resolution was found to have a remarkable difference(χ2＝34.706,P＜0.05).Significant differences were found in noise,high contrast resolution and low resolution detectability between the CT scanners with ＜64 detector rows and ≥64 detector rows(χ2＝6.978,10.040,15.973,P＜0.05).However,there is no difference in CT value(water)(P＞0.05).For less-than-64 detector row CT scanners,no significant difference was found in CT value(water),noise and low contrast detectability among different manufacturers(P＞0.05).only high contrast resolution differed remarkably(χ2＝9.941,P＜0.05).For more-than-or equal-to-64 detector row CT scanners,CT value(water)and noise have no differences among different manufacturers(P ＞0.05),whereas,there were significant difference in high contrast resolution and low contrast detectability(χ2＝31.376,32.967,P＜0.05).Conclusions There were a few differences in the performance testing of CT scanners from different manufacturers,and the less-than-64 detector row CT scanners have advantages in noise and low contrast detectability compared with the more-than-64 detector row CT scanners,whereas the latter have advantages in high contrast resolution and scanning time,allowing its wider application in medical institutions with more special diseases.
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Objective To evaluate and compare the radiation dose and image quality of the new generation of whole body mobile CT (BodyTom CT) with commonly used fixed CT.Methods The image quality was evaluated with CATPHAN 500 performance test body model.The radiation dose was measured by conventional 100 mm pen ionization chamber and PMMA body phantom and head phantom (head diameter 160 mm,phantom diameter 320 rm and width 140 mm).Results The spatial and contrast resolution of BodyTom CT images were similar to two kinds of fixed CT(P ＞ 0.05).The CNR of image with BodyTom CT decreased by about 20％:In head scan mode,significantly lower than that with Philps 64 slice CT and Toshiba 320 slice CT (with soft,t =-4.82,-6.98,P ＜ 0.05;with standard,t =-20.60,-20.09,P ＜0.05);in body scan mode,significantly lower than that with Philps 64 slice CT and Toshiba 320 slice CT (with soft,t =-5.67,-12.82,P ＜ 0.05;with standard,t =-3.39,-9.18,P ＜ 0.05;with sharp,t =-3.88,-3.21,P ＜0.05).The radiation dose with BodyTom CT was significantly higher than that with fixed CT:in body model,22.97％ than that with Philps 64(t=9.48,P＜0.05),29.6％ than that with Toshiba 320 slice CT(t =11.66,P ＜0.05);in head model,29.76％ than that with Philps 64 slice CT(t=23.44,P＜0.05),33.22％ than that with Toshiba 320 slice CT(t=23.11,P＜0.05).Conclusions The radiation dose with mobile CT was over 20％ higher than that with routine multi-row CT while with the similar image quality.
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Objective To explore the feasibility and reasonable of low-dose scan on abdominal angiography in 64-slice spiral helical CT. Methods Phantom test: at 120 KV and from 200 mAs to 30 mAs at an interval of 10 mAs in each image acquisition, it was measured standard deviation (SD) of CT number, high contrast resolution and low contrast resolution, and then analyzed the relationship between the three parameters and the mAs values. Three mAs values were chosen to undertake clinical analysis.Clinical analysis: 90 randomly selected objects with abdominal angiography were divided into three groups,scanning with above three mAs values.Measurement of the SD value at the plain scan images was performed and the enhanced low-dose scan images were used post-processing with three-dimensional volume reconstruction (VR). The VR images were classified into three grades (excellent, moderate, bad) with the blind evaluation of three CT radiologists. The quality-correlation analysis was used between the standard deviation (SD) values of plain scan image and abdominal angiography VR image. Results According to the quality-correlation analysis between the standard deviation (SD) value of plain scan image and abdominal angiography VR image, the area under curve in receiver-operated characteristic (ROC) analysis was 0.921, 0.906 and 0.893 in each three group, respectively. Conclusions The low-dose scan of abdominal angiography is feasible. 80mAs can ensure better image quality. The enhanced scan probably can use 60mAs when the SD value is less than 5.78 in the plain scan; but when the SD value of plain scan is greater than 11.8, the enhanced scan is used best 100 mAs or higher.