Radiation exposure in perfusion CT of the brain.

OBJECTIVE: This study aimed to show the simulation of the radiation exposure of the brain during perfusion measurements multi-detector-CT. MATERIAL AND METHODS: The effective dose and different organ doses were measured with thermoluminescent dosimeters in an Alderson-Rando phantom and compared with the data of a simulation program (CT-Expo V1.6) for varying scan protocols with different tube voltages (in kilovolts) and constant parameters for tube current (270 mAs), scan length (28.8 mm), scan time (40 seconds), slice thickness (24 × 1.2 mm), and number of scans (40) for multi-detector-CT perfusion measurements of the brain. RESULTS: The thermoluminescent dosimeter measurements yielded effective doses of 3.8 mSv (80 kV), 8.6 mSv (100 kV), 14.1 mSv (120 kV), and 22.2 mSv (140 kV). These values were in line with the data from the simulation program CT-Expo V1.6. The organ doses varied between 97 and 556 mGy (brain), 10.7 and 80.9 mGy (eye lens), 9.6 and 46 mGy (bone marrow), 1.2 and 6.7 mGy (thyroid gland), and 4.1 to 22.3 mGy (skin). The maximum local skin dose ranged from 355 mGy (80 kV) to 1855 mGy (140 kV) in the directly exposed part of the skin. CONCLUSIONS: The radiation exposure during perfusion measurements of the brain is strongly dependent on the tube voltage and can vary widely even if the other exposure parameters remain constant. Maximum organ doses up to 556 mGy (brain) can be measured. Even if we never reached local organ doses that can cause a direct radiation injury, the review of the tube voltages implemented by the vendor is mandatory beside the limitation of the scanned area by clinical examination and the reduction of the number of scans. Simulation programs are a valuable tool for dose measurements.

The value of dual-energy CTA for control of surgically clipped aneurysms.

OBJECTIVE: Comparison of image quality in DE-CTA with and without automatic head bone removal (BR) versus CTA with 16-detectors as a tool in postoperative evaluation of patients after neurosurgical clipping. METHODS: In this study 30 aneurysms that had undergone neurosurgical clipping were included: 18 with DE-CTA and 12 with conventional CTA. The images were further processed using the volume rendering technique (VRT) and BR. Two experienced neuroradiologists reviewed the images regarding the severity of artefacts surrounding the clip, visibility of the vessels and remnant necks. The results were compared with DSA images, if performed. RESULTS: Significantly fewer disturbances by artefacts were observed in DE-CTA versus CTA in a 16-row system. Visibility of the surrounding vessels was satisfying in both techniques and there were comparable results with DSA with only one exception. All images produced with 140 kV provided fewer artefacts than those with 80 kV. CONCLUSION: DE-CTA provides better image quality with fewer disturbances by clip artefact, a satisfying evaluation of remnant aneurysm necks and the surrounding vessels. As this method is easily performed and readily accessible with fast image post-processing using BR it provides an opportunity to avoid invasive DSA in the evaluation of suspected aneurysm rests.