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Objective To investigate the effects of X-ray beam hardening from contrast agent on CT values on CTA images.Methods The 20 mL syringes were numbered 1 to 26.The syringe 1,4,7,23 and 20 were filled with 1 mL,0.8 mL,0.6 mL,0.4 mL and 0.2 mL of iodine contrast medium (300 mg I/mL),respectively,and then mixed each of them with 0.9％ NaC1 solution to get a total of 20 mL solution in each syringe.The rest of 26 syringes were filled with 20 mL of 0.9％ NaC1 solution,as the experimental group to simulate carotid artery CTA examination.Matched 26 numbered syringes were filled with 20 mL 0.9％ NaC1 solution respectively,as control group to simulate plain scan.CT scans were performed,CT values were measured,and then the difference of CT values of 0.9 ％ NaCl solution in two groups was analyzed statistically.Results The mean,maximum and minimum CT values of saline in the experimental group vs control group were (-0.139±10.322) HU vs (5.585±2.939) HU,14.6 HU vs 9.7 HU,-23.8 HU vs-2.4 HU,respectively,and the differences were significant (t=2.695,P＜0.05).The CT values of saline around the high concentrations of iodine solution showed a large fluctuation range.Conclusion The X ray beam hardening effects caused by high concentration of iodine contrast on carotid artery CTA phase,may cause significant fluctuations of CT values.
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Objective To investigate the effect of the multi-material artifact reduction (MMAR) algorithm of wide-detector CT system in reducing the beam hardening artifacts in brain CT imaging. Methods Nine tubes with various iodine concentrations (0.1-16.0 mgI/ml) were placed in a uniform phantom filled with soft-tissue equivalent material. The phantom was scanned using different combinations of the tube voltage and current as follows:80 kV/530 mA, 100 kV/295 mA, 120 kV/190 mA and 140 kV/135 mA. The scanning was performed using the GE Discovery 750 and GE Revolution CT scanners, respectively. The CT values and standard deviations of the uniform areas between tubes were measured. The artifact index (AI) was calculated by using the standard deviation value outside the tubes as background noise. The artifact index values under different kV/mA combinations with different scanners were compared. CT brain images of 36 patients (n=18 on Discovery CT and n=18 on Revolution CT) were randomly selected. CT values of normal brain tissue and dark bands areas in the posterior fossa were measured for each case. The AI was calculated for these cases as for the phantom study. Paired t test was performed for phantom data analysis, and independent t test was performed for the clinical cases data analysis. Results The average AI values with Revolution CT(4.96±1.39, 4.80±1.57, 4.56±1.45, 4.76±1.57) were smaller than those of Discovery 750 (11.90 ± 6.61, 11.17 ± 5.61, 8.85 ± 4.59, 8.77 ± 3.85) under different tube voltage settings(t=3.714, 4.186, 3.745, 4.634,P<0.001). The higher the iodine concentration difference between tube pairs was, the higher the artifact index;As for clinical data, the difference in AI values between Revolution CT(2.31 ± 0.95) and Discovery 750(3.91 ± 1.32) was found statistically significant(t=4.066,P<0.001). Conclusion The multi-material artifact reduction algorithm implemented on the wide-detector Revolution CT scanner can significantly reduce beam hardening artifacts.
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Objective To investigate the effect of the multi-material artifact reduction (MMAR) algorithm of wide-detector CT system in reducing the beam hardening artifacts in brain CT imaging. Methods Nine tubes with various iodine concentrations (0.1-16.0 mgI/ml) were placed in a uniform phantom filled with soft-tissue equivalent material. The phantom was scanned using different combinations of the tube voltage and current as follows:80 kV/530 mA, 100 kV/295 mA, 120 kV/190 mA and 140 kV/135 mA. The scanning was performed using the GE Discovery 750 and GE Revolution CT scanners, respectively. The CT values and standard deviations of the uniform areas between tubes were measured. The artifact index (AI) was calculated by using the standard deviation value outside the tubes as background noise. The artifact index values under different kV/mA combinations with different scanners were compared. CT brain images of 36 patients (n=18 on Discovery CT and n=18 on Revolution CT) were randomly selected. CT values of normal brain tissue and dark bands areas in the posterior fossa were measured for each case. The AI was calculated for these cases as for the phantom study. Paired t test was performed for phantom data analysis, and independent t test was performed for the clinical cases data analysis. Results The average AI values with Revolution CT(4.96±1.39, 4.80±1.57, 4.56±1.45, 4.76±1.57) were smaller than those of Discovery 750 (11.90 ± 6.61, 11.17 ± 5.61, 8.85 ± 4.59, 8.77 ± 3.85) under different tube voltage settings(t=3.714, 4.186, 3.745, 4.634,P<0.001). The higher the iodine concentration difference between tube pairs was, the higher the artifact index;As for clinical data, the difference in AI values between Revolution CT(2.31 ± 0.95) and Discovery 750(3.91 ± 1.32) was found statistically significant(t=4.066,P<0.001). Conclusion The multi-material artifact reduction algorithm implemented on the wide-detector Revolution CT scanner can significantly reduce beam hardening artifacts.
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Objective To compare the displayed inner diameter of coronary stent by high definition(HD)and gem?stone spectral imaging(GSI)using dynamic cardiac and coronary artery phantom. Methods Five different types of coro?nary stents(internal diameter, 3.10 mm±0.55 mm;strut thickness, 0.12 mm±0.04 mm)were placed into a pulsating cardiac phantom(ALPHA 1-VT PC, Fuyo Corporation, Japan). The stent phantom was scanned by 3 systems, gemstone spectral im?aging(GSI), spiral scan(S)and HD. All the spectral imaging data were analyzed using GSI viewer to reconstruct the VMS (monochromic spectral) images(60-140 keV). Image noise(N), signal-to-noise ratio(SNR), contrast-to-noise ratio(CNR) and inner diameter were compared between images acquired through these 3 systems. Results SNRs in images of S and HD were higher than that of GSI(P0.05). The visible diameter(%)measurements of HD(0.85 ± 0.06)was significant higher than that of the other 2 scan systems and most close to the width of those stent’s actual size.(GSI:0.40±0.16, 0.48±0.13, 0.50±0.14, 0.51±0.13, 0.45±0.05,0.52±0.13, 0.53±0.13, 0.53±0.13, 0.53±0.13, S:0.53±0.14, P<0.05). Conclusion There was no significant dif?ferences in image quality among the images acquired by these 3 systems when the heart rate was set to 60 beats per min. Comparing to GSI and S, HD can produce best represent images to the known inner diameter of coronary stent.
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Objective To evaluate the image quality of hand tendons by using spectral CT,compared with conventional CT ima-ges.Methods Forty patients scanned with spectral CT were enrolled.The 65keV of optimal contrast-to-noise ratio (Optimal CNR) for viewing hand tendons was selected.The image quality of monochromatic GSI images (65 keV)and conventional CT images were compared with two different methods including subjective method and objective method by two radiologists respectively.Results In subjective method,the image quality in GSI images was superior to conventional CT images (P <0.05).And in objective method, the beam-hardening artifacts in the phalanges of fingers space were reduced markedly with hand tendons displaying more clearly in GSI images (P <0.05 ).There was no significant difference between the two radiologists in both methods with good correlation (Kappa=0.75,Kappa=0.85).Conclusion Spectral CT with the optimal 65keV monochromatic images could reduce the artifacts and increase image quality significantly in hand tendons imaging.It might be a very useful supplementary imaging method in detec-ting tendon diseases in routine work.
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Objective: To discuss the methods and experience of 64-slice spiral CT which used in infant cases with congenital heart disease, to select the appropriate scan parameters for reducing artifact and the radiation dose. Methods: Thirty-five cases with congenital heart disease were arranged CT examination by using Philips Brilliance 64-slice spiral CT scanner with Blous Tracking techniques. Results: All the images of the heart chambers, pulmonary artery, pulmonary vein, the ascending aorta and the descending aorta contrast agent filling showed good and had clear display. The density of superior vena cava is moderate. The various vascular CT value is approximate, no hardening artifacts. The atrioventricular of Cardiac and vascular of contrast agent filled fully and had clear boundary, no significant artifacts and no effect on the impact reconstruction. Conclusion: Appropriate adjustment of scanning parameters can reduce hardening artifact and the impact of artifacts. Following the principle of as low as reasonably achievable (ALARA) can obtain diagnostic images and reduce radiation damage to the infant.
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PURPOSE : The purpose of this study was to develop the radiographic technique for detecting the demineralization which is known as indication of dental caries MATERIALS AND METHODS : This technique was based on the comparing of multiple radiographs which was irradiated by multiple X-ray spectra. For the meaningful comparing, the multiple radiographs were reconstructed to the dosimetrically consistent images using a standard material. The difference of resulting images of same target with multiple spectra represents the difference of response of material as regards the spectra. RESULTS : We have found about 10% of demineralization of dental hard tissues particularly in the proximal region through the analyzing of differences. CONCLUSION : Most intriguing thing in this investigation was that the method to analyze difference shows us to an anatomic structure of dental hard tissues even if absolute values of optical density were excluded during the procedures.
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Dental CariesABSTRACT
PURPOSE: The accurate dosimerty of independent collimator equipped for 6MV and 15MV X-ray beam was investigated to search for the optimal correction factor. METHODS AND MATERIALS: The field size factors, beam quality and dose distribution were measured by using 6MV, 15MV X-ray. Field size factors were measured from 3X3cm2 to 35X35cm2 by using 0.6cc ion chamber (NE 2571) at Dmax. Beam qualities were measured at different field sizes, off-axis distances and depths. Isodose distributions at different off-axis distance using 10X10cm field were also investigated and compared with symmetric field. RESULTS: 1) Relative field size factors was different along lateral distance with maximum changes in 3.1% for 6MV and 5% for 15MV. But the field size factors of asymmetric fields were identical to the modified central-axis values in symmetric fileld, which corrected by off-axis ratio at Dmax.2) The HVL and PDD was decreased by increasing off-axis distance. PDD was also decreased by increasing depth For field size more than 5X5cm2 and depth less than 15cm, PDD of asymmetric field differs from that of symmetric one (0.5~2% for 6MV and 0.4~1.4% for 15MV).3) The measured isodose curves demonstrate divergence effects and reduced doses adjacent to the edge close to the flattening filter center was also observed. CONCLUSION: When asymmetric collimator is used, calcutation of MU must be corrected with off-axis and PDD with a caution of underdose in central axis.