| Objective:To study the radiation dose of High-performance cardiac CT (256-slice CT and 320-slice CT) which advent in recent years, and the radiation dose contribution and distribution irradiated to sensitive organs and tissues surrounding the heart in the cardiac CT scanning.Method and Materials:The homemade thermoluminescent dosimeter. (TLD) was laid with the simulated human body model. The simulated human body model was scanned with 64-slice CT (axial scan),256-slice CT (axial scan and spiral scan) and 320-slice CT (1 beat and 2 beats) under routine protocols. The average absorbed doses of the thyroid, breast, heart, esophagus, spinal cord, lung, liver, colon and stomach, and the absorbed dose distributions of these tissues and organs were compared with the five scan types to explore the dosimetric advantages formed with the high-performance CT in the cardiac scanning (as opposed to 64-axis scan). Coronary CT angiograms obtained with 256-slice row CT were retrospectively evaluated in 68 clinical patients. An prospective electrocardiographic (ECG) gating was evaluated in 34 patients (group A). The routine retrospectively gated helical technique was then evaluated in 34 consecutive patients (group B). All images were evaluated for image quality, estimated radiation dose.Result:The statistical analysis of experimental data was done with the software of SPSS17.0as follows:1) Thyroid:As 64-slice CT scan compared with 256-slice CT axial scan and 320-slice CT(one beat), F= 16.409, P values were 0.000 and 0.001 respectively, P< 0.05, the differences were significant; while as 64-slice axial scan compared with 256-slice spiral scan and 320-slice (two beat), P values were 0.224 and 0.778 respectively, P> 0.05, the differences were not statistically significant.2) Breast:As 64-slice axial scan compared with that in the other four types, F=40.368, P values were 0.002, 0.000,0.000 and 0.001 respectively, P< 0.05, the differences were significant. 3) Spinal cord:As 64-slice CT axial scan compared with that in the other four scan types, F=10.131, P values were 0.000,0.001,0.000 and 0.001 respectively, P< 0.05, the differences were significant.4) Esophagus:As 64-slice CT axial scanning compared with that in the other four types, F=10.829, P values were 0.001,0.001,0.000 and 0.000 respectively, P< 0.05, this indicates a significant difference.5) Heart:As 64-slice CT axial scan compared with that in the other four types, F=,28.911, P values were 0.000,0.000,0.000 and 0.000 respectively, P< 0.05, the differences were significant.6) Lungs:As 64-slice CT compared with that in the other four types, F=10.362, P values were 0.001,0.001,0.001 and 0.001 respectively, P< 0.05, the differences were significant.7) Liver:As 64-slice CT compared with 256-slice spiral scan and 320-slice CT of 2 beats, F=1.808,P values were 0.188 and 0.177, the differences were not statistically significant; while as compared with 256-slice axial scan and 320-slice CT of 1 beats, P values were 0.039 and 0.022, the differences were significant.8) Stomach:As 64-slice CT scan compared with that in other four types scanning types, F=59.609, P values were 0.000,0.000,0.000 and 0.001 respectively, P< 0.05, this indicates a significant difference.9) Colon:As 64-slice CT axial scan compared with that in the other four types, F=2.312, P values were 0.175, 0.323,0.145 and 0.294 respectively, P> 0.05, the differences were not statistically significant.10) The average CTDI for group A was (16.92±1.16) mGy, and the average CTDI for group B was (54.31±3.87) mGy, P< 0.05, there was significant difference (t=-53.99,P<0.001). The mean image SNR for group A and group B were (22.66±9.49) and (20.11±9.54) respectively, P> 0.05, there was no significant difference (t=1.12, P=0.27). The mean image CNR for group A and group B were (19.24±8.36) and (16.83±8.47) respectively, P> 0.05, there was no significant difference(t=1.18, P=0.24).Conclusion:1) Analysis of radiation dosimetry:Through conventional cardiac CT scanning, High-performance CT (256-slice CT and 320-slice CT) has advantage of radiation dosimetry on average absorbed dose of each tissue than 64-slice CT axial scan.2) Radiation protection of sensitive tissue:cardiac CT scanning will not only produce absorbed dose of tissue but also produce absorbed dose of relative tissue. Thus, sensitive tissue such as thyroid, liver, stomach and colon should be protected during cardiac scanning.3) Selection of clinical application:one beat of 320-slice CT and axial scan of 256-slice CT should be first choice during clinical cardiac CT scanning, and the radiation dose should be reduced while maintaining image quality. |
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