From Phineas Gage and Monsieur Leborgne to H.M.: Revisiting Disconnection Syndromes.

On the 50th anniversary of Norman Geschwind's seminal paper entitled 'Disconnexion syndrome in animal and man', we pay tribute to his ideas by applying contemporary tractography methods to understand white matter disconnection in 3 classic cases that made history in behavioral neurology. We first documented the locus and extent of the brain lesion from the computerized tomography of Phineas Gage's skull and the magnetic resonance images of Louis Victor Leborgne's brain, Broca's first patient, and Henry Gustave Molaison. We then applied the reconstructed lesions to an atlas of white matter connections obtained from diffusion tractography of 129 healthy adults. Our results showed that in all 3 patients, disruption extended to connections projecting to areas distant from the lesion. We confirmed that the damaged tracts link areas that in contemporary neuroscience are considered functionally engaged for tasks related to emotion and decision-making (Gage), language production (Leborgne), and declarative memory (Molaison). Our findings suggest that even historic cases should be reappraised within a disconnection framework whose principles were plainly established by the associationist schools in the last 2 centuries.

Volume rendering of visible human data for an anatomical virtual environment.

In this work, we utilize the axial anatomical human male sections from the National Library of Medicine's Visible Human Project to generate three-dimensional (3-D) volume representations of the human male subject. The two-dimensional (2-D) projection images were produced by combining ray tracing techniques with automated image segmentation routines. The resultant images provide accurate and realistic volumetric representations of the Visible Human data set which is ultimately needed in medical virtual environment simulation. Ray tracing techniques provide methods by which 2-D volume views of a 3-D voxel array can be produced. The cross-sectional images can be scanned at different angles to produce rotated views of the voxel array. By combining volume views at incremental angles over 360 degrees a full volumetric representation of the voxel array, in this case the human male data set, can be computer generated and displayed without the speed and memory limitations of trying to display the entire data array. Additional texture and feature information can be obtained from the data by applying optical property equations to the ray scans. The imaging effects that can be added to volume renderings using these equations include shading, shadowing, and transparency. The automated segmentation routines provide a means to distinguish between various anatomical structures of the body. These routines can be used to differentiate between skin, fat, muscle, cartilage, blood vessels, and bone. By combining automated segmentation routines with the ray-tracing techniques, 2-D volume views of various anatomical structures and features can be isolated from the full data set. Examples of these segmentation abilities are demonstrated for the human male data set which include volume views of the skeletal systems, the musculoskeletal system, and part of the vascular system. The methods described above allow us to generate lifelike images, NURBS surface models, and realistic texture maps of specific anatomical structures. We have the capability to generate images that are both accurate and lifelike, much like photographic anatomical atlases. We can also generate images, models, and textures that have the clarity of medical artwork/illustrations, by highlighting the coloring of the ray traced structures with conventional colors instead of the natural color of the specimen. We are currently in the process of generating a comprehensive reference atlas of volume rendered images of the human body, soon to be published by Mosby-Year Book. The segmentation techniques needed to create this atlas also offer the accuracy and realism needed to create surface models and texture maps for a virtual environment for surgery simulation.

Linear measurements in 2-dimensional pelvic floor imaging: the impact of slice tilt angles on measurement reproducibility.

OBJECTIVE: Magnetic resonance imaging techniques have improved the study of female pelvic dysfunction. However, disagreements between magnetic resonance measurements and their derived 3-dimensional reconstructions were noted. We tested the hypothesis that these discrepancies stemmed from variations in magnetic resonance acquisition angle. STUDY DESIGN: Images from the pelvis of the Visible Human Female (a thinly sliced cadaveric image data set) were obtained. Slices in the axial plane were rotated around pivot points in the pelvis to yield a set of similar-appearing para-axial images. A parameter that described the maximum anterior-posterior dimension of the levator hiatus was defined. This levator hiatus parameter was measured on all of the rotated images and compared with an expected value that was calculated from trigonometry. The levator hiatus was also measured on a group of similar-appearing slices rotated slightly around a defined point. RESULTS: In 1 group of slices, expected levator hiatus variation was 1.5 to 6.1%, whereas measured variation was 4% to 15%. Among the similar-appearing rotated slices, 4.8% to 16.0% variations were seen in the levator hiatus. CONCLUSION: Identical measurements made on radiologic images can vary widely. Slice acquisition must be standardized to avoid errors in data comparison.

3D visualisation of the middle ear and adjacent structures using reconstructed multi-slice CT datasets, correlating 3D images and virtual endoscopy to the 2D cross-sectional images.

The 3D imaging of the middle ear facilitates better understanding of the patient's anatomy. Cross-sectional slices, however, often allow a more accurate evaluation of anatomical structures, as some detail may be lost through post-processing. In order to demonstrate the advantages of combining both approaches, we performed computed tomography (CT) imaging in two normal and 15 different pathological cases, and the 3D models were correlated to the cross-sectional CT slices. Reconstructed CT datasets were acquired by multi-slice CT. Post-processing was performed using the in-house software "3D Slicer", applying thresholding and manual segmentation. 3D models of the individual anatomical structures were generated and displayed in different colours. The display of relevant anatomical and pathological structures was evaluated in the greyscale 2D slices, 3D images, and the 2D slices showing the segmented 2D anatomy in different colours for each structure. Correlating 2D slices to the 3D models and virtual endoscopy helps to combine the advantages of each method. As generating 3D models can be extremely time-consuming, this approach can be a clinically applicable way of gaining a 3D understanding of the patient's anatomy by using models as a reference. Furthermore, it can help radiologists and otolaryngologists evaluating the 2D slices by adding the correct 3D information that would otherwise have to be mentally integrated. The method can be applied to radiological diagnosis, surgical planning, and especially, to teaching.