Low-dose dental computed tomography: significant dose reduction without loss of image quality.

PURPOSE: To measure and reduce the patient dose during computed tomography (CT) for dental applications. MATERIAL AND METHODS: Lithium fluoride thermoluminescent dosimeters were implanted in a tissue-equivalent humanoid phantom (Alderson-Rando-Phantom) to determine doses to the thyroid gland, the active bone marrow, the salivary glands, and the eye lens. Dental CT was performed with spiral CT and a dental software package. The usual dental CT technique was compared with a new dose-reduced protocol, which delivered best image quality at lowest possible radiation dose, as tested in a preceding study. Image quality was analysed using a human anatomic head preparation. In addition, the radiation dose was compared with panoramic radiography and digital volume tomography (DVT). Eight radiologists evaluated all images in a blinded fashion. A Wilcoxon rank pair test was used for statistical evaluation. RESULTS: Radiation dose could be reduced by a factor of 9 (max.) with the new dose-reduced protocol (e.g. bone marrow dose from 23.6 mSv to 2.9 mSv; eye lens from 0.5 mSv to 0.3 mSv; thyroid gland from 2.5 mSv to 0.5 mSv; parotid glands from 2.3 mSv to 0.4 mSv). Dose reduction did not reduce image quality or diagnostic information. CONCLUSION: A considerable dose reduction without loss of diagnostic information is achievable in dental CT. As radiation exposure of the presented low-dose protocol is expected to be in the same range as DVT, low-dose dental CT might be superior to DVT, because CT can be used to evaluate soft tissues as well.

[Low-dosage dental CT]. / Niedrigdosis Dental-CT.

PURPOSE: The intention of this study was to reduce patient dose during dental CT in the planning for osseointegrated implants. METHODS AND MATERIALS: Dental CTs were performed with a spiral CT (Somatom Plus 4, Siemens) and a dental software package. Use of the usual dental CT technique [1] (120 kVp; 165 mA, 1 s rotation time, 165 mAs; pitch factor 1) was compared with a new protocol (120 kVp; 50 mA; 0.7 s rotation time; 35 mAs; pitch factor 2) which delivered the best image quality at the lowest possible radiation dose, as tested in a preceding study. Image quality was analysed using a human anatomic head preparation. Four radiologists analysed the images independently. A Wilcoxon rank pair-test was used for statistic evaluation. The doses to the thyroid gland, the active bone marrow, the salivary glands, and the eye lens were determined in a tissue-equivalent phantom (Alderson-Rando Phantom) with lithium fluoride thermoluminescent dosimeters at the appropriate locations. RESULTS: By mAs reduction from 165 to 35 and using a pitch factor of 2, the radiation dose could be reduced by a factor of nine (max.) (e.g., the bone marrow dose could be reduced from 23.6 mSv to 2.9 mSv, eye lens from 0.5 mSv to 0.3 mSv, thyroid gland from 2.5 mSv to 0.5 mSv, parotid glands from 2.3 mSv to 0.4 mSv). The dose reduction did not lead to an actual loss of image quality or diagnostic information. CONCLUSION: A considerable dose reduction without loss of diagnostic information is achievable in dental CT. Dose-reducing examination protocols like the one presented may further expand the use of preoperative dental CT.

[Aspects of radiation protection in cardiovascular brachytherapy]. / Strahlenschutzaspekte in der kardiovaskulären Brachytherapie.

In the scope of cardiovascular brachytherapy beta- as well as gamma-ray emitting radionuclides are used. The handling of radioactive sources is within the range of the radiation protection regulations (Strahlenschutzverordnung [StrlSch V]). According to EU guidelines an amendment of the StrlSch V is required by May 2000. The connected reduction of dose limits now should already be taken into consideration when planning irradiation facilities, likewise in cardiovascular brachytherapy. Temporary regulations for equipment that was already in operation before May 2000 are not planned in the new StrlSch V.

[Effect of collimation and pitch on radiation exposure and image quality in spiral CT of the thorax]. / Einfluss von Kollimation und Pitch auf die Patientendosis und die Abbildungsqualität bei der Spiral-Computertomographie des Thorax.

PURPOSE: The aim of the study was to optimize the scan parameters for spiral-CT of the thorax. METHODS: Using a Somatom AR-SP (Siemens AG, Erlangen) CT-unit, four different scanning protocols (collimation/table feed) were compared: A (5/10), B (10/10), C (10/15), D (10/20). High contrast resolution in the xy-plane and in the z-direction were investigated with special phantoms. Noise levels were measured using a water phantom, the radiation exposure of lung parenchyma was investigated using an Alderson-Rande-Phantom. An anthropoid chest phantom was scanned to compare the image quality of the four protocols. RESULTS: Protocol A showed the best resolution in the z-direction; the resolution in the xy-plane was equal for all protocols. Image noise in the center of the water phantom was 58 HU for protocol A and 40 HU for the other three. The following equivalent organ dose were measured for lung parenchyma: A 14 mSv, B 29 mSv, C 20 mSv, D 14 mSv. CONCLUSION: Scanning protocols with small collimation and a pitch of 2 are characterised by low radiation exposure and excellent resolution in the z-direction. These parameters seem to be most suitable for lung scanning.