Biomedical subjects

Kai Uffmann

Publications and source records attributed to Kai Uffmann.

5 recordsLinked to original sources

PubMed2006

Accelerating MR elastography: a multiecho phase-contrast gradient-echo sequence.

PURPOSE: To demonstrate the feasibility of using a multiecho phase-contrast (PC) gradient-echo sequence with motion-sensitizing gradient (MSG) to accelerate MR elastography (MRE) acquisitions in comparison to single-echo PC sequences. MATERIALS AND METHODS: The sequence was implemented and compared with a conventional single-echo sequence as the standard of reference in both agarose phantoms and in vivo in the biceps of three healthy volunteers. For reconstruction of the elasticity modulus, a local frequency estimation (LFE) algorithm was used. ETL factors of 1-16 were evaluated. RESULTS: Phantom experiments demonstrated excellent consistency between single-echo and multiecho measurements in terms of wave equivalency, SNR, and reconstructed shear modulus. Additionally, the in vivo MRE examinations showed an excellent correspondence to the single-echo results. Minor loss of wave amplitude was observed at higher ETL factors. CONCLUSION: The results demonstrate that a multiecho sequence is suitable for accelerating MRE in nearly homogeneous tissue, such as muscle. It provides equivalent elasticity values in a significantly reduced scan time compared to a single-echo sequence. The maximum achievable ETL factor must be individually determined for the target tissue.

Acceleration↗

PubMed2005

A diffusion tensor imaging analysis of gender differences in water diffusivity within human skeletal muscle.

The diffusive properties of adjacent muscles at rest were evaluated in male (n = 12) and female (n = 12) subjects using diffusion tensor imaging (DTI). The principle, second and third eigenvalues, trace of the diffusion tensor [Tr(D)], and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated from the diffusion tensor. Seven muscles were investigated in this study from images acquired of the left calf: the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus and peroneus longus. A mathematical model was also derived that relates the eigenvalues of the diffusion tensor to the muscle fiber volume fraction, which is defined as the volume of muscle fibers within a well-defined arbitrary muscle volume. Females on average had higher eigenvalues and Tr(D) compared with males, with the majority of muscles being statistically different between the sexes. In contrast, males on average had higher e and FA than females, with the large plantar flexors--soleus, lateral gastrocnemius, and medial gastrocnemius--producing statistically different results. The behavior of the mathematical model for variations in fiber volume fraction produced similar trends to those seen when the experimental data were fit to the model. The model predicts that a larger volume fraction of skeletal muscle in males is devoted to fibers than in females, but the true underlying source of the gender discrepancy remains unclear. Although the model does not fully account for other transport processes, it does provide some insight into the limiting factors that affect the diffusion of water in skeletal muscle measured by DTI.

Adult↗

PubMed2004

Cerebral activation using a MR-compatible piezoelectric actuator with adjustable vibration frequencies and in vivo wave propagation control.

Functional magnetic resonance imaging (fMRI) studies are increasingly used in patients with brain tumors near the sensory motor cortex for planning of therapy. Passive stimuli can be helpful for reproducible results. The purpose of our study was to investigate frequency and amplitude dependencies of cerebral activation patterns using a vibratory stimulus that involves sensory and motor function and allows exact adjustment of vibratory frequencies and direct control of penetration depth into the tissue. Fifteen volunteers were studied with fMRI during vibratory stimulation of the right biceps muscle utilizing a block design (frequencies: 150 and 300 Hz, amplitudes: 400, 600, and 800 microm). In addition, visualization of the wave propagation into the biceps tissue itself was performed with a modified phase contrast sequence. A specially developed MR-compatible mechanical oscillator was used to apply the vibrotactile sensations. fMRI revealed activation of the left primary somatosensory cortex during application of both vibratory frequencies. Additionally, activity of the primary and supplementary motor cortex was revealed using 150-Hz stimuli, while only minimal at 300 Hz. The activity strength correlated with increasing stimulus amplitudes and the visualized penetration depth. Activation of motor areas was more pronounced at the beginning of the rest period. In conclusion, sensory motor areas can be activated using a piezoelectric actuator, with less pronounced motor area activation at higher frequencies. Our setup allowed local control of stimulus penetration through the tissue correlated to central activation, providing objective stimulus control. The pronounced activation of the motor cortex during the rest condition may reflect the subjective feeling of arm movement after the end of the stimulus.

Adolescent↗

PubMed2004

In vivo elasticity measurements of extremity skeletal muscle with MR elastography.

MR elastography (MRE) has been shown to be capable of non-invasively measuring tissue elasticity even in deep-lying regions. Although limited studies have already been published examining in vivo muscle elasticity, it is still not clear over what range the in vivo elasticity values vary. The present study intends to produce further information by examining four different skeletal muscles in a group of 12 healthy volunteers in the age range of 27-38 years. The examinations were performed in the biceps brachii, the flexor digitorum profundus, the soleus and the gastrocnemius. The average shear modulus was determined to be 17.9 (+/- 5.5), 8.7 (+/- 2.8), 12.5 (+/- 7.3) and 9.9 (+/- 6.8) kPa for each muscle, respectively. To ascertain the reproducibility of the examination, the stiffness measurements in two volunteers were repeated seven times for the biceps brachii. These examinations yielded a mean shear modulus of 11.3 +/-.7 and 13.3 +/- 4.7 kPa for the two subjects. For elasticity reconstruction, an automated reconstruction algorithm is introduced which eliminates variation due to subjective manual image analysis. This study yields new information regarding the expected variation in muscle elasticity in a healthy population, and also reveals the expected variability of the MRE technique in skeletal muscle.

Adult↗

PubMed2004

Diffusive sensitivity to muscle architecture: a magnetic resonance diffusion tensor imaging study of the human calf.

The aim of this study was to examine the diffusive properties of adjacent muscles at rest, and to determine the relationship between diffusive and architectural properties, which are task-specific to muscles. The principle, second, and third eigenvalues, trace of the diffusion tensor, and two anisotropic parameters, ellipsoid eccentricity (e) and fractional anisotropy (FA), of various muscles in the human calf were calculated by diffusion tensor imaging (DTI). Linear correlations of the calculated parameters to the muscle physiological cross-sectional area (PCSA), which is proportional to maximum muscle force, were performed to ascertain any linear relation between muscle architecture and diffusivity. Images of the left calf were acquired from six healthy male volunteers. Seven muscles were investigated in this study. These comprised the soleus, lateral gastrocnemius, medial gastrocnemius, posterior tibialis, anterior tibialis, extensor digitorum longus, and peroneus longus. All data were presented as the mean and standard error of the mean (SEM). In general, differences in diffusive parameter values occurred primarily between functionally different muscles. A strong correlation was also found between PCSA and the third eigenvalue, e, and FA. A mathematical derivation revealed a linear relationship between PCSA and the third eigenvalue as a result of their dependence on the average radius of all fibers within a single muscle. These findings demonstrated the ability of DTI to differentiate between functionally different muscles in the same region of the body on the basis of their diffusive properties.

Diffusion Magnetic Resonance Imaging↗