Tractography of peripheral nerves and skeletal muscles.

The assessment of human peripheral nerves and skeletal muscles by means of diffusion tensor imaging and tractograpy has been a recent area of research. These techniques have been successfully applied in both volunteers and patients, providing non-invasively, quantitative microstructural parameters (mainly mean fractional anisotropy and apparent diffusion coefficient) and offering a three-dimensional visualization tool of nerves and muscles fibers. DTI and tractography may reveal abnormalities that are beyond the resolution of conventional MR techniques and hence open the way to potential clinical applications. In this article, we will first summarize the current state of DTI and tractography in the evaluation of peripheral nerves and skeletal muscles as well as their potential future clinical applications. Then, we will address important technical considerations, which understanding is necessary to appropriately apply DTI and tractograhy, and in order to understand the current limitations of these innovative and promising techniques.

Diffusion tensor imaging and tractography of the median nerve in carpal tunnel syndrome: preliminary results.

The purpose was to demonstrate the feasibility of in vivo diffusion tensor imaging (DTI) and tractography of the human median nerve with a 1.5-T MR scanner and to assess potential differences in diffusion between healthy volunteers and patients suffering from carpal tunnel syndrome. The median nerve was examined in 13 patients and 13 healthy volunteers with MR DTI and tractography using a 1.5-T MRI scanner with a dedicated wrist coil. T1-weighted images were performed for anatomical correlation. Mean fractional anisotropy (FA) and mean apparent diffusion coefficient (ADC) values were quantified in the median nerve on tractography images. In all subjects, the nerve orientation and course could be detected with tractography. Mean FA values were significantly lower in patients (p=0.03). However, no statistically significant differences were found for mean ADC values. In vivo assessment of the median nerve in the carpal tunnel using DTI with tractography on a 1.5-T MRI scanner is possible. Microstructural parameters can be easily obtained from tractography images. A significant decrease of mean FA values was found in patients suffering from chronic compression of the median nerve. Further investigations are necessary to determine if mean FA values may be correlated with the severity of nerve entrapment.

In vivo MR tractography of thigh muscles using diffusion imaging: initial results.

The aims of this preliminary study were (1) to demonstrate the feasibility of providing in vivo 3D architecture of human thigh muscles using tractography on a 1.5T magnet, and (2) to assess the value of tractography images to obtain averaged microstructural parameters, i.e., the fractional anisotropy (FA) and the mean apparent diffusion coefficient (ADC), over the whole thigh. Five healthy volunteers were included in this study. Their right thighs were imaged using diffusion tensor imaging and gradient-echo T2* sequences. Muscular tractography was performed on each muscle. MR tractography provided a good approach of the muscle shape and of the orientation of the muscle fibers. There was no aberration in the color-encoding scheme nor in the luminosity assigned to each fiber. In contrast, tendons were not drawn in any of the muscles studied. FA values ranged from 0.27 to 0.38. Mean ADC values ranged from 0.76 to 0.96 x 10(-3) mm2/s. Our study demonstrated the feasibility of providing in vivo 3D architecture of human thigh muscles using tractography on a 1.5T magnet, and of determining muscular microstructural parameters (FA and ADC). Musculoskeletal radiologists should be aware of these new developments that may provide complementary information on muscles to the usual sequences.

Surgical views from three-dimensional digital subtraction angiography for the planning of aneurysm surgery.

AIM: To develop a semi-automatic protocol helping to present directly and quickly three-dimensional digital subtraction angiography (3D-DSA) data in an orientation that reproduces exactly the neurosurgeon's intraoperative view. METHOD: Post-processing of 3D-DSA data (volume-rendering) was performed on an Integris workstation (Philips, Best); surgical views were obtained by visualization of the patient's head through a frontopterional approach: the 3D volume was turned 135 degrees in the sagittal plane (around the X axis) and rotated by 45 degrees and 60 degrees in the coronal plane (around the Y axis). The protocol was evaluated on a consecutive series of nine patients who had ruptured or asymptomatic anterior circulation aneurysms requiring surgical treatment. Frontopterional views of angiographic 3D data were compared with intraoperative views. RESULTS: The proposed semi-automatic algorithm is simple, fast and reproducible, and displays the 3D data in an orientation identical to the intraoperative views. The surgical anatomy of the anterior communicating artery was best reproduced with a coronal rotation of 60 degrees , with a coronal rotation of 45 degrees for the other aneurysm locations. In each case, the surgical reconstructions allowed a more accurate analysis of the vascular anatomy around the aneurysm, and facilitated pre- and perioperative planning. CONCLUSION: The present protocol displays angiographic 3D data in a projection that exactly reproduces the vascular anatomy through a frontopterional approach. It may help neurosurgeons to better anticipate any potential difficulties during access and clip-positioning arising due to the specific vascular anatomy of a given patient.

Contrast-enhanced MR angiography of supraaortic vessels: the effect of voxel size on image quality.

BACKGROUND AND PURPOSE: Several acquisition strategies may be used for imaging supraaortic vessels by using contrast-enhanced MR angiography. The purpose of this study was to assess the effect of voxel size on image quality of MR angiograms. METHODS: Fourty-four patients underwent 3D MR angiography in the coronal plane. Patients were randomly assigned into two groups according to the voxel size of MR angiograms: group 1 referred to a 1.3 x 1.29 x 1.25-mm voxel size and group 2 to a 0.95 x 0.76 x 0.82 mm voxel size. Signal-to-noise ratios (SNRs) were measured and image artifacts were analyzed by consensus between observers. The delineation of the arterial lumen was independently ranked on a four-point scale (1 = not assessable; 2 = poor delineation; 3 = fair delineation; 4 = optimal delineation). RESULTS: The overall interobserver agreement for the delineation of the arterial lumen was good (K = .84, P < .0001), with a rank significantly higher in group 2 (68% of arteries graded as 4) compared with group 1 (76% graded as 3). SNRs were significantly higher by using the conventional resolution technique, with a negative correlation between SNRs and artery delineation (P < .0001). Image artifacts, however, were more frequent with the high-resolution technique, including wrap-around artifacts and signal fall-off at the origin of the great vessels. CONCLUSION: MR angiograms with a decreased voxel size improve the delineation of cervical carotid and vertebral arteries, despite reduced SNRs and additional artifacts.