Optimierung der Bildqualität bei der MR-Darstellung der Hundenase und des Hundeohres

Recognising and evaluating pathological changes requires knowledge about the imaging of the anatomic-physiological organic structures with the applied imaging techniques. The MRT features a sequence-dependent contrast of the tissue, which results from the selected TE and TR. Hence, the individual sequences must be checked regarding their applicability to present the particular structures. Optimising the different parameters enables detailed imaging of the dog nose and ear. First studies were carried out using phantoms in order to put as few dogs as possible under the stress of general anaesthesia. Thereby, the multi-purpose phantom (SIEMENS), being suitable for evaluating basic quality parameters such as resolution and slice-thickness-dependent SNR, did not enable the required evaluation of susceptibility artefacts. The application of a sponge phantom, simulating the fine nose structures, was also not suitable to replace studies on living dogs in respect of the susceptibility differences. Furthermore, these studies were necessary because of the need to consider artefacts resulting from blood flow. Finally, studies on living dogs to optimise the contrast, oversampling and the spatial resolution could be limited to a small number. The MRI-Scans both of the dog nose and the dog ear were judged by experts, as the fineness of the structures did not allow measurement of objective quality parameters such as the CNR or the SNR. The present study shows that different sequences must be applied for detailed imaging of the dog nose and ear. Due to its low-noise, but detailed and high-contrast imaging the SE-sequence was judged most suitable for the studies on the dog nose. The disadvantage of the long measurement time of 12 min 51 s was not evaluated. As the TSE2000-sequence achieved similarly good results and has a significantly shorter measurement time of 8 min 21 s, this sequence is recommended for the anatomical imaging of the dog nose. Pathological cases were only studied exemplarily due to their small number. Yet, good pathology imaging with high contrast to the surrounding tissue is expected as a result of the high resolution of the optimised sequences. The best rating regarding the imaging of the dog ear was given to the CISS-sequence because of the exceptional high resolution of the slice thickness and the high T2-weighting, leading to a hyper-intense imaging of the cochlea. For a detailed visualisation and evaluation of the inner ear structures, above all the semicircular ducts of the vestibular organ, 3D reconstructions proved to be particularly suitable. To enable an optimal illustration of all planes of the 3D projection, isotropic voxels should be applied by adjusting the effective slice thickness and the pixel size. Detailed imaging was achieved by choosing voxels as small as possible. At the MRT used in this work the CISS-sequence featured a high plane resolution of 0.39 mm x 0.39 mm, though the minimal slice thickness of 0.95 mm led to asymmetrical voxels, which proved to be disadvantageous regarding an optimal 3D reconstruction. The DESS-sequence, rated second best, turned out to be better suited because of the minimal measurement of 0.6 mm in z-dimension and therefore nearly isotropic voxels. Compared with the CISS-sequence the demarcation of the tympanic cavity from the surrounding tissue was judged more appropriate, while the cochlea was indeed depicted significantly lower by the DESS-sequence. Hence, the applied sequence has to be chosen with regard to the structure of interest. In summary, a very good implementation of a detailed and high-contrast imaging of the fine nasal structures was achieved by optimising the sequences. The studies on the dog ear showed good results concerning the tympanic cavity and the cochlea, while only partial or no imaging of the semicircular ducts and ossicles was possible. With the use of more powerful MRT a better resolution and greater signal strength of the tissue structures can be expected. Thereby, a more detailed imaging of the semicircular ducts might be possible. This and whether higher signal strength of the ossicles is sufficient for their imaging has to be investigated in further studies. Pathological results differ in MRT imaging due to the specific T1- and T2-times. Therefore, the application of optimised sequences for clinical diagnosis requires further systematic studies on different pathology cases to optimise the tissue contrast.