aThe influence of passive shortening and stretching of the calf muscles on diffusion characteristics was investigated. The diffusion tensor was measured in transverse slices through the lower leg of eight healthy volunteers (29 W 7 years) on a 3 T whole-body MR unit in three different positions of the foot (40-plantarflexion, neutral ankle position (0-), and S10-dorsiflexion in the ankle). Maps of the mean diffusivity, the three eigenvalues of the tensor and fractional anisotropy (FA) were calculated. Results revealed a distinct dependence of the mean diffusivity and FA on the foot position and the related shortening and stretching of the muscle groups. The tibialis anterior muscle showed a significant increase of 19% in FA with increasing dorsiflexion, while the FA of the antagonists significantly decreased ($20%). Regarding the mean diffusivity of the diffusion tensor, the muscle groups showed an opposed response to muscle elongation and shortening. Regarding the eigenvalues of the diffusion tensor, l 2 and l 3 showed significant changes in relation to muscle length. In contrast, no change in l 1 could be found. This work reveals significant changes in diffusional characteristics induced by passive muscle shortening and stretching.

A sequence for echoplanar diffusion tensor imaging of musculature was developed using a stimulated echo preparation. The strategy was optimized in order to obtain reliable diffusion tensor data in a short measuring time. Image distortion problems due to eddy currents arising from long-lasting diffusion sensitizing gradients could be overcome by insertion of additional gradient pulses in the TM interval of the stimulated echo preparation. In contrast to former approaches with similar intention, the proposed strategy does not influence the stimulated echo signal itself and does not lead to prolonged echo time as in the case of spin echo methods. Phantom measurements were performed to compare eddy current induced distortion effects in diffusion weighted images. The diffusion tensor in the musculature of the lower leg was investigated in four healthy subjects and maps of the trace and the three eigenvalues of the diffusion tensor, fractional anisotropy maps, and angle maps were calculated. MR diffusion tensor imaging (DTI) has been widely used over the past decade in order to measure molecular water diffusion in vivo (1-13) and has been proven to be a powerful noninvasive tool for providing additional information about microstructure and pathology of tissues.In human tissues, diffusion is partly restricted by barriers such as cell membranes or large protein molecules. Diffusion in white matter or skeletal musculature is, therefore, not rotationally invariant but more enhanced in the direction of the longitudinal axis of the fibers compared to perpendicular directions. Although several tissue compartments with exchanging water molecules are involved, the diffusion behavior of tissue is often described by a symmetric second rank tensor in a simplified model (2). DTI techniques assess the diffusion sensitive signal attenuations caused by diffusion sensitizing gradients along several independent directions. Since a symmetric second rank tensor is characterized by six independent components, at least six independent directions for the diffusion gradients must be assessed in order to calculate the entire tensor.When conventional techniques are used for diffusion weighted imaging, the final images often show marked artifacts due to irregular motion induced phase shifts. Those problems can be solved by additional scans for phase correction (14). In addition, diffusion tensor imaging with at least six diffusion directions tends to become time consuming. Single-shot echo planar imaging (EPI) is rather robust even under conditions involving slight motion of the tissue under investigation and is, therefore, mainly used for DTI examinations.A few studies have been reported on DTI applications outside the brain. Those reports mainly focused on studies in kidney (6 -8), skeletal musculature (9 -12), and tongue (13). Musculature has a much shorter T 2 /T 1 ratio than brain, especially for higher magnetic fields (water in musculature at 1.5 T: T 1 Ϸ 1000 ms, T 2 Ϸ 30 ms (15)). For this reason, signal-to-noise ratio (SNR) in diffusio...

Purpose: To investigate the lumbar intervertebral discs (IVDs) by MRI in the morning and evening after a diurnal load cycle. Changes in MR characteristics (T2-weighted imaging, T2-and apparent diffusion coefficient [ADC] -mapping) during the course of the day were visualized and analyzed visually and quantitatively. The length of the lumbar spine was measured in between the lower anterior edge of Th12 and the upper anterior edge of S1. T2 changes and diffusion characteristics of the vertebral disc tissue were investigated with a higher spatial resolution than in former studies. Materials and Methods:In six males, lumbar IVDs were investigated in the morning and evening. T2-maps and ADC maps were generated. Data were analyzed by selecting regions of interest (ROI) in the annulus fibrosus (AF), nucleus pulposus (NP), and an intermediate area.Results: From morning to evening, T2 decreased in the center of the NP (Ϫ7.9%; P ϭ 0.001) and the intermediate voxels (Ϫ6.4%; P Ͻ 0.0005). T2 increased (8.5%; P Ͻ 0.048) in the AF. ADC decreased in the AF (Ϫ5.2%; P ϭ 0.007) and the intermediate ROIs (Ϫ2.2%; P ϭ 0.004). There was no significant change of ADC in the NP (Ϫ1.6%; P ϭ 0.242).Conclusion: T2 and diffusion (ADC) changes of IVDs in humans were investigated with a spatial differentiation between NP and AF. T2 and ADC turned out to be sensitive parameters in investigating changes in the MR characteristics of the IVD matrix during a day. Highly resolved MR imaging and parameter mapping is expected to be an interesting tool in characterizing structural changes in the vertebral disc architecture in an early stage of degeneration.

Purpose: To determine age-related changes in MR properties as T2 and T2* relaxation times, fat content, and magnetization transfer in the human calf, and comparison of these effects in different muscle groups. Materials and Methods:Studies were performed on 12 "younger" (mean, 31.2 Ϯ 6.1 years) and 11 "older" healthy adult individuals (mean, 66.1 Ϯ 7.8 years). The tibialis anterior muscle, the soleus muscle and the gastrocnemius muscle were examined at rest in a 3 Tesla whole-body MR unit. T2 and T2*, muscular fat content and magnetization transfer ratios (MTR) were determined. Results of the two age groups were compared, and differences between the muscle groups were investigated. Results:Increase of T2 and muscular fat was detected with age with significant difference between the age groups. The extent of fatty infiltration was much more variable for the "older" group. For both age groups, the tibialis anterior muscle showed the lowest fat content with 1.2 Ϯ 0.4% in the "young" group and 2.3 Ϯ 0.7% in the "older" group. A strong correlation between fat content and T2 was found, while the groups did not significantly differ regarding T2*. Decrease in the MTR could only be shown for the tibialis anterior muscle with age. Conclusion:Age-related changes in healthy human calf musculature were found. Further studies might show possible correlations of age-dependent changes with physical efficiency and susceptibility to diseases like type 2 diabetes. IN AN AGING SOCIETY, the quality of life for the elderly becomes more and more important. This includes physical activity, physical fitness, and health. It is known that senescence goes along with impairment in muscle function, reduction in bone density, and loss in joint mobility. For this reason, in the past years an increasing number of studies investigating the influence of aging on muscular functionality and metabolism have been performed; muscular atrophy and fiber composition are major research areas, because age-associated muscle atrophy is associated with muscular weakness and fatigability (1). It is known from histological studies that muscle volume decreases with age (2,3), with type II fibers more affected (4 -6).In contrast to histological studies, MR techniques have the advantage of noninvasive tissue characterization in vivo offering information about muscle structure, metabolism, and architecture in one examination. Different MR methods are available for determination of relaxation times and magnetization transfer, quantification of muscular lipids, and assessment of perfusion patterns and diffusion properties.To our knowledge there exists only one previous study focusing on muscle aging and transverse relaxation times (7), although measurement of T2 and T2* relaxation times has been reported to be useful in the assessment of muscle atrophy (8), the analysis of denervation effects (9,10), and the muscular metabolic state (11,12).Another useful parameter characterizing the composition of tissues is magnetization transfer contrast (MTC) (13,14). The MT imag...

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