Department of ORL, head and neck surgery

ABSTRACT Purpose: CBCT systems for head examinations especially in otorhinolaryngology offer better than required image quality at relatively low purchasing costs. Due to this fact the number of dedicated head scanners increases steadily. Regarding image quality in relation to patient dose these systems are frequently not optimized. Examination parameter optimization is an iterative process, which should be done carefully by physicians in cooperation with physicists. After a successful optimization, Monte Carlo Simulations can be used to quantify the dose reduction to the patient. Methods: Images of an anatomic head phantom were obtained using different settings of kVp, mAs and rotation angle (360°, 210°). The resulting images were anonymized and the examination parameters were removed. Radiologists and otorhinolaryngologists evaluated these images and rated them into excellent image quality, good image quality, bad image quality and not readable. Based on the ratings new parameters for the adequate image quality were set. The dose reduction was calculated using Monte Carlo simulations. Results: The organ dose of radiation sensitive organs was reduced significantly. The dose reductions compared to the standard settings are: eyes: 85%, eye lenses: 88%, salivary glands: 40%, thyroid: 60%, blood vessels: 40%, brain: 60%, teeth: 80% and tonsils: 65%. Dose reduction was best, when a short scan (210° rotation angle) was used, where the eyes are not in the direct exposure field. Conclusions: The results show the potential for dose optimizations in otorhinolaryngological CBCT examinations compared to standard vendor settings without loss in diagnostic information. Furthermore this study points out the great opportunities that Monte Carlo-based dose-calculations methods offer to quantify the increase of dose efficiency after examination protocol optimizations. It could also be shown that CBCT has advantages when doing short scan mode around the rear head. This protects radiation sensitive organs such as the eye lenses from being directly radiated.

Imaging of the anterior skull base and paranasal sinuses is essential before surgery of the nose and paranasal sinuses. It is important to know individual anatomical variations to define a "dangerous ethmoid" to prevent complications such as considerable bleeding or injury to the brain. This study aimed to analyze the relevant parameters with special regard to age-dependent differences. This was a retrospective, single center study of 865 patients. Data from cone beam computed tomography (CBCT) of 116 patients less than 18 years of age and 749 adult patients were analyzed. Keros type, the course of the anterior ethmoid artery, the course of the uncinate process and the angle between the lateral lamella and the cribriform of the olfactory fossa were evaluated. Different frequencies of the course of the uncinate process between young and adult persons could be shown: onset at the lamina papyracea 67% vs. 64%; onset at the skull base, 22% vs. 26%; and onset at the middle turb...

With the Bonebridge, a new bone-anchored hearing aid has been available since March 2012. The objective of the study was to analyse the visualisation of the implant itself as well as its impact on the representation of the bony structures of the petrosal bone in CT, MRI and cone beam CT (CBCT). The Bonebridge was implanted unilaterally in two completely prepared human heads. The radiological imaging by means of CBCT, 64-slice CT, 1.5-T and 3.0-T MRI was conducted both preoperatively and postoperatively. The images were subsequently evaluated from both the ENT medical and nd radiological perspectives. As anticipated, no visualisation of the implant or of the petrosal bones could be realised on MRI because of the interactive technology and the magnet artefact. In contrast, an excellent evaluability of the implant itself as well as of the surrounding neurovascular structures (sinus sigmoideus, skull base, middle ear, inner ear, inner auditory canal) was exhibited in both the CT and in ...

CONCLUSION These results show the feasibility of dose optimization for paranasal sinuses examinations while maintaining image quality. Using the 180° rotation parameter for image generation, keeps the eye lenses out of the direct exposure field resulting in significant dose reduction. This is important with the new knowledge about the higher radiation sensitivity of the eye. Further research in this field is necessary, not only for the improvement of radiation health of the patients but also as a base for the creation of guidelines and standards for CBCT-examinations. It was also shown, that Monte Carlo simulations offer a great possibility to calculate dose reduction potential after protocol optimization. BACKGROUND To reduce the patient dose for paranasal sinuses examinations with a CBCT-unit while maintaining adequate image quality. DISCUSSION The images acquired at 90kVp, 8mA with 360° rotation had the highest diagnostic quality and deposited the highest dose to the eye lenses (...