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In this study, we evaluated the dose response of MAGAT (Methacrylic Acid Gelatin gel and THPC) normoxic polymer gel dosimeters based on the X-ray CT scanner. To perform this study, we determined the proper ratio of the gel composition and acquired X-ray scan parameters. MAGAT gel dosimeters were manufactured using MAA (MethacrylicAcid) and gelatin of various concentration, irradiated up to 20 Gy. We obtained the 20 CT images from the irradiated gel dosimeters by using on a Phillips Brilliance Big Bore CT scanner with the various scan parameters. This CT images were used to determine the N(CT)-dose response, dose sensitivity and dose resolution As an amount of MAA and gelatin were increase, the slope and intercept were increase in each MAGAT gel dosimeter with various concentration of the N(CT)-dose response curve. The dose sensitivity was 0.38+/-0.08 to 0.859+/-0.1 and increased were amount of the MAA was increased or the gelatin was decreased. However, the change of gelatin concentration was very small compare to MAA. The Dose resolution (D(delta)(95%)) varies considerably from 2.6 to 6 Gy, dependent on dose resolution and CT image noise. The slope and dose sensitivity was almost ident verywith the variation of the tube voltage, tube current and slice thickness in the dose response curve, but the noise (standard deviation of averamalg CT number) was decreased when the tube voltage, tube current and slice thickness are increase. The optimal MAGAT polymer gel dosimeter based on the CT were evaluated to determine the CT imaging scan parameters of the maximum tube voltage, tube current and slice thickness (commonly used in clinical) using the composition ratio of a 9% MAA, 8% gelatin and 83% water. This study could get proper composition ratio and scan parameter evaluating dose response of MAGAT normoxic polymer gel dosimeter using CT scanner.
Subject(s)
Gelatin , Noise , Polymers , Tomography Scanners, X-Ray Computed , WaterABSTRACT
Objective To study the effects on tissue CT number caused by scan protocols.Methods The phantom was repeatedly scanned in different protocols by changing only one of parameters,such as X-ray tube voltage,mAs and recon kernel,while other parameters were ketp unchanged.The CT number of different materials in phantom were measured and analyzed.Results The CT numbers of tissues changed remarkably with the tube voltage and had different relativity for different tissues.The CT numbers had positive correlation with kV for such maierials as polyethyle,lexan,perspex,but for teflon the correlation was negative.The mAs and recon kernel had no effects on CT number.Conclusions The CT number of tissue changes with scanning X-ray tube voltage,so the setting of scan parameters should be taken into account in image diagnosis and radiotherapy.
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Objective To study the scan parameter of spiral CT angiography in aortic dissection.Methods 34 cases with aortic dissection successively underwent SCTA were studied retrospectively.The CT scan parameters,methods of posteriorimage treating were reviewed and analysed one by one.Results In 34 cases,32 cases were diagnosed as aortic dissection and classified correctly,in accordance with the result of operation and DSA,the quality of image was satisfied and the rate of success at least above 88.9%.The use of main scan parameters:(1)the ascend aortic dissection:slice thickness 4 mm,reconstruction interval 2 mm,pitch 1.25;tube current 175 mA;(2)involed in ascend,arch,descend and throacic aorta dissection:slice thickness 5 mm,reconstruction interval 2～3 mm,pitch 1.5;tube current 150 mA;(3)involved in abdominal aortic dissection:slice thickness 6～8 mm,reconstruction interval 2～3 mm,pitch 1.5 or 1.75;tube current 125 mA.The tube voltage all were 120 kV,the dosage of contrast media was 90～100 ml;the delayed scan time was choiced 20 second in throacic aortic and 25 second in abdominal aortic.The posterior image methods main used MPR,SSD,MIP and VR. Conclusion To set a sensible scaning plan,choose and match scan parameters properly according to the scaning length,can avoid the shortage of restrain SCTA scaning length and get satisfied image.
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Objective To study the factors effect on the measurement of CT value.Methods CT water phantom was scanned using the regular condition of scaning first,then changed one of scaning conditions (thick slice, exposure capacity, reconstruction of function, kV, FOV and CT-scanner) to scan the water phantom again. The CT value (mean?SD) of image region of interest (ROI) was compared in two conditions. Results The mean CT value in the opposite ROI in thick slice 5mm and exposure capacity 150 mAs was similar to that in thick slice 10mm and exposure capacity 300mAs, the reconstruction of function Fc80 was lower Fc10 , the 130kV was distinct higher 120Kv in mean of CT value respectively.The SD(noise) in thick slice 5mm was near to the exposure capacity 150mAs, while in contrast to the thick slice 10mm and the exposure capacity 300mAs was obvious increased , but the reconstruction of function Fc80 was distinct higher Fc10, the 130kV was slightly lower 120Kv in SD(noise) respectively . All of mean CT value and the noise in the small field were higher in the middle field ,when CT imaging in the water phantom of the single small field .This result was also received when the old Toshiba CT-scanner was compared with the new GE CT-scanner in the differ water plantom.Conclusion The CT value is not constant and can’t act as a diagnostic standred.