The phantom study of bismuth shielding combined with organ tube current modulation in brain CT / 中华放射医学与防护杂志

Objective:To evaluate the application value of bismuth shielding combined with organ tube current modulation (X-care) in brain CT scanning by measuring the radiation dose of sensitive organs.Methods:The head and neck phantom was scanned with Siemens dual source CT at the same volume CT dose index (CTDI vol) by X-care, bismuth shielding and x-care combined with bismuth shielding, and by dual energy CT angiography (DE-CTA) with and without bismuth shielding. The CT values of cerebral vessels, adjacent brain tissues and cerebrospinal fluid and image noise were measured, and the contrast noise ratio of cerebral vessels and brain parenchyma was calculated. Organ dose equivalent ( HT) was calculated by placing thermoluminescent personal dosimeter (TLD), and CTDI vol and dose length product (DLP) were recorded after each scan. Results:Under the same CTDI vol, the mean values of HT, lens with X-care, Bi shielding and X-care combined with Bi shielding were(37.89 ± 2.00), (42.20 ± 2.96) and (28.21 ± 1.31) mSv, respectively, significantly lower than those of conventional sequence scanning( F=186.52, P<0.05). The values of HT, thyroid with Bi shielding and X-care combined with Bi shielding were (0.77 ± 0.07) and (0.89 ± 0.08) mSv, lower than those of routine brain scan and X-care( F=103.26, P<0.05). The values of HT, lens and HT, thyroidof DE-CTA with bismuth shielding were (11.56 ± 1.04) and (0.32 ± 0.03) mSv, respectively, significantly lower than those without bismuth shielding( t=5.07, P<0.05). There was no significant difference in noise and CNR in routine brain scan between with and without X-care, bismuth shielding and X-care combined with bismuth shielding. There was no significant difference in noise and CNR in dual energy CTA scanning between with and without Bi shielding. Conclusions:Using bismuth shielding and organ tube current modulation, we can significantly reduce organ dose of lens and thyroid during brain CT scanning without sacrificing the image quality.

Effectiveness of iterative metal artifact reduction for reduction of metal artifact in chest CT scanning / 中国医学影像技术

Objective To assess the effectiveness of iterative metal artifact reduction (IMAR) on metal artifacts reduction in thorax scan.Methods Thoracic phantom with two pedicle screws implanted in both sides of the T5 vertebrae was used,with the scan parameters of 130 kV and CARE Dose 4D,the phantom was scanned with and without the screws respectively.Images without screws were reconstructed with FBP.Images with screws were reconstructed with FBP and IMAR respectively.Three ROIs were selected on tissues including aorta,pulmonary and paravertebral soft tissue on image slice adjacent to the screws.The CT value and standard deviations (noise) of ROIs were measured,and the deviation of CT value (△HU) was calculated as the difference between CT values in images with and without screws.Twenty-six cases who received chest CT examination and with pedicle screw implant in scanning range were collected.The scanning parameters and image reconstruction methods were the same as phantom scan.The CT value (HU) of metal artifacts adjacent to vertebrae and dorsal soft tissue was measured,and the image quality of reconstructed image by two skilled radiologists independently was evaluated.Results In the phantom after implanted screws,the noise were significantly reduced by IMAR compared to FBP in all the three ROIs of aorta,pulmonary and paravertebral soft tissue (P＜0.05),and the △HU was significantly smaller in IMAR compared to that with FBP (P＜0.01).In 26 patients,there were significant differences in CT value of vertebral bone tissue and dorsal soft tissue between FBP and IMAR (P＜0.05),and the subjective evaluation scores of the two image reconstruction methods showed a statistically significant difference (P＜0.05).Conclusion IMAR can significantly reduce streak artifacts of metal implant and adjuste the CT values of artifact affected tissues to make it more close to the true value without metal implant.

Evaluation on Ability to Detect the Intracranial Hematoma with Different Density Using C-Arm Cone-beam Computed Tomography Based on Animal Model / 生物医学工程学杂志

This study aims to evaluate the ability of C-arm cone-beam CT to detect intracranial hematomas in canine models. Twenty one healthy canines were divided into seven groups and each group had three animals. Autologous blood and contrast agent (3 mL) were slowly injected into the left/right frontal lobes of each animal. Canines in the first group, the control group, were only injected with autologous blood without contrast agent. Each animal in all the 7 groups was scanned with C-arm cone-beam CT and multislice computed tomography (MSCT) after 5 minutes. The attenuation values and their standard deviations of the hematoma and uniformed brain tissues were measured to calculate the image noise, signal to noise ratio (SNR) and contrast to noise ratio (CNR). A scale with scores 1-3 was used to rate the quality of the reconstructed image of different hematoma as a subjective evaluation, and all the experimental data were processed with statistical treatment. The results revealed that when the density of hematoma was less than 65 HU, hematomata were not very clear on C-arm CT images, and when the density of hematoma was more than 65 HU, hematomata showed clearly on both C-arm CT and MSCT images and the scores of them were close. The coherence between the two physicians was very reliable. The same results were obtained with C-arm cone-beam CT and MSCT grades in measuring SD value, SNR, and CNR. The reasonable choice of density detection range of intracranial hematoma with C-arm cone-beam CT could be effectively applied to monitoring the intracranial hemorrhage during interventional diagnosis and treatment.

Image quality evaluation of virtual monoenergetic spectral images obtained in two types of dual energy CT based on noise level / 中华放射学杂志

Objective To investigate the image quality difference of the virtual monochromatic spectral(VMS) images synthesized from fast kilovoltage switching and dual-source dual-energy CT for a given radiation dose. Methods A plurality of disposable syringes containing 15 mg/ml iodine contrast agent and saline were placed on the surface of the male anthropomorphic phantom consisting ofhead neck and torso, GE HD750 gemstone spectral imaging and Siemens Somatom Definition Flash dual energy CT protocols were performed on the phantom for a same dose(volume CT dose index 6.52 mGy), and VMS images (40, 60, 70, 80, 100, 120, 140 keV) were reconstructed and obtained(VMSkV switching and VMSdual-source image), respectively. The objective image noise, iodine signal noise ratio(SNR), iodine contrast noise ratio (CNR) and CT values were measured. The results were analyzed using the paired t test and ANOVA. Results All VMS iodine CT values were gradually decreased with the increasing of keV , and iodine CT values on VMSdual-source images were greater than on VMSkV switching images(P<0.05), VMSkV switching iodine CT values in descending order from the head , chest, abdomen at less than 100 keV,while most VMSdual-source iodine CT values were highest on chest(P<0.05). VMSdual-source and VMSkV switching image noise were highest at 40 keV and successively raised from the head, chest , abdomen. VMSkV switching image noise gradually decreased with the increase of keV in the range of 40 to 70 keV , gradually increased up to the trough after 70 keV from 80 keV gradually decreased, while VMSdual-source image noise was lowest at 70 keV or 80 keV , and then with the keV increased gradually increased. Image noise on VMSkV switching images in the range of 40 to 100 keV were higher than that on VMSdual-source images and lower in the range of 100 to 140 keV at most part(P<0.05). VMSdual-source and VMSkV switching iodine SNR were highest at 40 keV or 60 keV,SNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head and abdomen(P<0.05) . VMSdual-source and VMSkV switching iodine CNR were highest at 60 keV,CNR on VMSdual-source images are greater than on VMSkV switching images except 40 keV images on head 100 keV and 120 keV on abdomen(P<0.05).SNR and CNR decreased from the head, chest, abdomen (P<0.05). Conclusion VMS images synthesized from fast kilovoltage switching and dual-source dual-energy CT have different image quality performance at most keV and body parts, but VMS imaging at approximately 70 keV yielded lower image noise, and at approximately 60 keV yielded highest SNR and CNR.

Correlation of acquisition time of C-arm cone-beam CT with image quality and radiation doseduring cerebral angiography using an anthropomorphic head phantom / 中华放射学杂志

Objective To investigate the influence of acquisition time of C-arm cone-beam CT on image quality and radiation dose of cerebral angiography.Methods C-arm cone-beam CT of cerebral angiography was performed on the male anthropomorphic head phantom,with DynaCT imaging mode and the acquisition time of 5 s,8 s and 20 s were used.Scanning was performed with each acquisition time for three times,and VR,MIP and MPR images were reconstructed.The attenuation values and their standard deviations of intracranial segment of the internal carotid artery (ICA),middle cerebral artery(MCA),anterior cerebral artery(ACA) and uniformed brain tissues were measured to calculate the image noise,signal to noise ratio (SNR) and contrast to noise ratio (CNR).We used the image noise,SNR and CNR as the objective standard to evaluate the image quality,and One-way ANOVA analysis of variance was used to assess the difference among them.A scale with scores 1 to 5 was used to rate the quality of the reconstructed image of ICA,MCA,ACA as a subjective evaluation,the difference among the evaluation scores were analyzed using Kruskal-wallis.We recorded the dose area product (DAP) of each acquisition time and the effective dose(ED) was calculated to assess the radiation dose,the difference among them were analyzed using One-way ANOVA analysis of variance.Results In C-arm cone beam CT 20 s imaging,the SNR of intracranial segment of the ICA,M CA,ACA were 22.29± 1.41,29.36 ±0.11 and 23.13 ±2.10 respectively,in 5 s imaging13.83 ±0.61,14.65 ±0.16 and 12.79±0.19 respectively,in 8 s imaging 14.92±0.96,18.97 ± 1.24 and 16.65 ±0.46 respectively,all the results showed a significant difference (F valued 58.19,327.29,52.74 respectively,all P valued＜0.01),the CNR of 20 s imaging were higher than that of 5 s and 8 s imaging,the Noise of ICA,MCA,ACA and the uniformed brain tissues of 20 s imaging were lower than that of 5 s and 8 s imaging,all the results showed significant difference (all P valued＜0.01).The subjective evaluation scores of VR imaging of 5 s,8 s and 20 s were 3.61 ±0.49,4.06±0.53,4.72±0.45 respectively,the scores of MIP imaging were 3.42±0.50,3.83±0.65 and 4.50±0.51 respectively,the scores of MPR imaging were 2.83±0.45,3.14±0.35 and 3.67±0.49 respectively,all the results showed significant difference (x2 valued 51.29,42.25 and 43.56 respectively,all P valued ＜0.01).The DAP values in C-arm cone beam CT 5 s,8 s and 20 s imaging were (9.11 ±0.18),(13.81±0.75)and(58.62±0.62)Gy· cm2,ED values were (0.91 ±0.02),(1.38±0.75)and(5.84± 0.11) mSv,all the results showed significant difference (F valued 3 720.30 and 3 654.85 respectively,all P valued＜0.01).Conclusion The image quality and radiation dose of C-arm cone-beam computed tomography are closely correlated with acquisition time.

Comparison of pulmonary nodule detection rate and accuracy in low-dose chest CT between iterative reconstruction algorithm and filtered back proj ection algorithm / 吉林大学学报(医学版)

Objective To compare the differences of pulmonary nodule detection rates between iterative reconstruction (sinogram affirmed iterative reconstruction,SAFIRE)algorithm and filtered back projection (FBP) algorithm in chest CT, and to evaluate the detection accuracy.Methods Three groups of tube voltage values of 80,100,and 120 kV were defaulted on the new dual-source CT,with automatic mAs care dose 4D technology, the chest phantom with simulated pulmonary nodules was scanned, then the images were reconstructed with FBP and SAFIRE (grade 1-5 ),respectively. The detection rates of simulated pulmonary nodules in the chest CT images reconstructed of SAFIRE (grade 1-5 )and FBP were compared, and their diameters and CT values were measured.Results With the same tube voltage, no significant difference was found in the detection rate of simulated pulmonary nodules between SAFIRE (grade 1-5 )and FBP (P>0.05 ), the diameter deviation of simulated nodules of SAFIRE (grade 3 )was less than FBP, and the difference in the average CT value of the simulated nodules between SAFIRE (grade 3)and FBP was not statistically significant (P>0.05);the simulated nodule detection rate of 100 kV was equivalent to the detection rate of 120 kV,the simulated nodule (-800 HU and 3 mm )detection rate of 80 kV was less than that of 120 kV;as the tube voltage reduced,or simulated nodule diameter decreased,or the density of simulated nodule reduced,the nodule’s diameter deviation was increased. Conclusion Compared with FBP,the capabilities of SAFIRE in pulmonary nodule detection in different densities and different sizes are same,and SAFIRE algorithm is helpful for accurate displaying of pulmonary nodules,and it can be used for low-dose CT lung cancer screening program.

Application of Monte Carlo software in estimating patients' radiation dose during CCTA and confirmation by anthropomorphic phantom study / 中华放射医学与防护杂志

Objective To evaluate the accuracy and efficiency of the Monte Carlo software in measuring the radiation dose to the patients who received the CCTA (Coronary Computed Tomography Angiography) examination.Methods A anthropomorphic chest phantom underwent CCTA using three scan parameters (tube voltage 80 kV,100 kV and 120 kV).Computer Software ImpactDose 2.0 was used to compute the chest organ dose on the basis of the three groups tube voltage CT scan characteristic,and the stimulation results of ImpactDose 2.0 software was verified by use of anthropomorphic phantom thermoluminescence dosimeter experiment method.Results For all the measured organs except for lung,the absorbed organ dose and effective dose of three groups of tube voltages of CCTA measured by the InpactDose 2.0 was lower than those as measured by anthropomorphic phantom study.The relative error of both methods was within ± 50％.Conclusions Monte Carlo software can be used to estimate the levels of radiation dose during CCTA examination with a tolerable error within the acceptable range.