Application of frozen Thiel-embalmed specimens for radiotherapy delineation guideline development: a method to create accurate MRI-enhanced CT datasets.

PURPOSE: Thiel embalming followed by freezing in the desired position and acquiring CT + MRI scans is expected to be the ideal approach to obtain accurate, enhanced CT data for delineation guideline development. The effect of Thiel embalming and freezing on MRI image quality is not known. This study evaluates the above-described process to obtain enhanced CT datasets, focusing on the integration of MRI data obtained from frozen, Thiel-embalmed specimens. METHODS: Three Thiel-embalmed specimens were frozen in prone crawl position and MRI scanning protocols were evaluated based on contrast detail and structural conformity between 3D renderings from corresponding structures, segmented on corresponding MRI and CT scans. The measurement error of the dataset registration procedure was also assessed. RESULTS: Scanning protocol T1 VIBE FS enabled swift differentiation of soft tissues based on contrast detail, even allowing a fully detailed segmentation of the brachial plexus. Structural conformity between the reconstructed structures on CT and MRI was excellent, with nerves and blood vessels imported into the CT scan never intersecting with the bones. The mean measurement error for the image registration procedure was consistently in the submillimeter range (range 0.77-0.94 mm). CONCLUSION: Based on the excellent MRI image quality and the submillimeter error margin, the procedure of scanning frozen Thiel-embalmed specimens in the treatment position to obtain enhanced CT scans is recommended. The procedure can be used to support the postulation of delineation guidelines, or for training deep learning algorithms, considering automated segmentations.

White matter asymmetries in human situs inversus totalis.

Diffusion weighted imaging (DWI) was used to investigate white matter asymmetries in participants with situs inversus totalis (SIT) and matched controls. Regardless of visceral condition, hemispheric differences were found for the arcuate fasciculus (ARC) and the superior longitudinal fasciculus (SLF), which are involved in language and visuospatial functioning, respectively. The ARC appears lateralized to the left hemisphere, analogous to the left lateralization of functional areas associated with language. The SLF, on the other hand, is lateralized to the right, corresponding with rightward lateralization of visuospatial functioning. Interestingly, SIT participants show a significantly lower number of streamlines in the Uncinate Fasciculus (UNC). In addition, UNC volume appears associated with measures of cognitive performance, a finding in line with previously reported performance differences between SIT participants and controls.

Atypical brain functional segregation is more frequent in situs inversus totalis.

Most humans show typical brain functional specialization with language and praxis favoring left hemisphere lateralization and spatial attention and face recognition showing right hemisphere dominance. Lateralization of these cognitive functions was investigated using fMRI in participants with complete visceral reversal and matched control participants. While most participants revealed typical brain organization, atypical functional segregation was significantly more frequent in participants with visceral reversal. Interestingly, some left handers maintained typical functional segregation but showed complete reversal of all cognitive functions regardless of visceral organization. Cognitive performance, as measured with a neuropsychological test battery, was significantly predicted by the degree of atypical functional segregation of praxis and spatial attention. Increased deviation from typical functional segregation paired with lower cognitive performance. The findings suggest that typical functional segregation reflects an optimal evolutionary solution with deviations being associated with reduced cognitive performance.

Brain structural and functional asymmetry in human situs inversus totalis.

Magnetic resonance imaging was used to investigate brain structural and functional asymmetries in 15 participants with complete visceral reversal (situs inversus totalis, SIT). Language-related brain structural and functional lateralization of SIT participants, including peri-Sylvian gray and white matter asymmetries and hemispheric language dominance, was similar to those of 15 control participants individually matched for sex, age, education, and handedness. In contrast, the SIT cohort showed reversal of the brain (Yakovlevian) torque (occipital petalia and occipital bending) compared to the control group. Secondary findings suggested different asymmetry patterns between SIT participants with (n = 6) or without (n = 9) primary ciliary dyskinesia (PCD, also known as Kartagener syndrome) although the small sample sizes warrant cautious interpretation. In particular, reversed brain torque was mainly due to the subgroup with PCD-unrelated SIT and this group also included 55% left handers, a ratio close to a random allocation of handedness. We conclude that complete visceral reversal has no effect on the lateralization of brain structural and functional asymmetries associated with language, but seems to reverse the typical direction of the brain torque in particular in participants that have SIT unrelated to PCD. The observed differences in asymmetry patterns of SIT groups with and without PCD seem to suggest that symmetry breaking of visceral laterality, brain torque, and language dominance rely on different mechanisms.

Magnetic resonance imaging of third molars: developing a protocol suitable for forensic age estimation.

BACKGROUND: Established dental age estimation methods in sub-adults study the development of third molar root apices on radiographs. In living individuals, however, avoiding ionising radiation is expedient. Studying dental development with magnetic resonance imaging complies with this requirement, adding the advantage of imaging in three dimensions. AIM: To elaborate the development of an MRI protocol to visualise all third molars for forensic age estimation, with particular attention to the development of the root apex. SUBJECTS AND METHODS: Ex vivo scans of porcine jaws and in vivo scans of 10 volunteers aged 17-25 years were performed to select adequate sequences. Studied parameters were T1 vs T2 weighting, ultrashort echo time (UTE), fat suppression, in plane resolution, slice thickness, 3D imaging, signal-to-noise ratio, and acquisition time. A bilateral four-channel flexible surface coil was used. Two observers evaluated the suitability of the images. RESULTS: T2-weighted images were preferred to T1-weighted images. To clearly distinguish root apices in (almost) fully developed third molars an in plane resolution of 0.33 × 0.33 mm2 was deemed necessary. Taking acquisition time limits into account, only a T2 FSE sequence with slice thickness of 2 mm generated images with sufficient resolution and contrast. UTE, thinner slice T2 FSE and T2 3D FSE sequences could not generate the desired resolution within 6.5 minutes. CONCLUSION: Three Tesla MRI of the third molars is a feasible technique for forensic age estimation, in which a T2 FSE sequence can provide the desired in plane resolution within a clinically acceptable acquisition time.

Brachial plexus 3D reconstruction from MRI with dissection validation: a baseline study for clinical applications.

PURPOSE: The present study aimed to establish a baseline for detailed 3D brachial plexus reconstruction from magnetic resonance imaging (MRI). Concretely, the goal was to determine the individual brachial plexus anatomy with maximum detail and accuracy achievable, as yet irrespective of whether the methods used could be economically and practically applied in the clinical setting. MATERIALS AND METHODS: Six embalmed cadavers were randomly taken for MRI imaging of the brachial plexus. Detailed two-dimensional (2D) segmentation for all brachial plexus parts was done. The 2D brachial plexus segmentations were 3D reconstructed using Mimics(®) software. Then, these 3D reconstructions were anatomically validated by dissection of the cadavers. After finalising the cadaver experiments, brachial plexus MRIs were obtained in three healthy male volunteers and the same reconstruction procedure as in vitro was followed. RESULTS: A procedure was developed for brachial plexus 3D reconstruction based on MRI without the use of any contrast agent. Anatomical validation of six cadaver brachial plexus reconstructions showed high correspondence with the dissected brachial plexuses. Anatomical variations of the main branches were equally present in the 3D reconstructions generated. However, there were also some differences that related to the difference between the surface anatomy of the nerve and the internal nerve structure. In vivo, it was possible to reconstruct the complete brachial plexus in such a manner that normal-appearing BPs were derived in a reproducible way. CONCLUSIONS: This study showed that the described procedure results in accurate and reproducible brachial plexus 3D reconstructions.