Fritz Schick

An MRI technique with high selectivity and sensitivity to the signal components in the chemical shift range of methylene and methyl protons of fatty acids has been developed for noninvasive assessment of muscular fat in vivo. A spoiled gradient‐echo sequence with spatial‐spectral excitation by six equidistant pulses with 2°‐(−9°)‐17°‐(−17°)‐9°‐(−2°) and a multi‐echo train (TE = 16, 36, 56, 76, 96, and 116 ms) allowed a series of images to be recorded with a receiver bandwidth of 78 Hz per pixel. SIs from phantoms with lipid contents between 0.1% and 100% were compared to those from pure water. Thirty healthy volunteers underwent fat‐selective imaging of their lower leg, and parallel localized proton spectroscopy of the tibialis anterior and the soleus muscle by a single‐voxel stimulated echo acquisition mode (STEAM) technique (TR = 2 s, TE = 10 ms, TM = 15 ms). Results show a high correlation (r = 0.91) between fat imaging and the spectroscopic approach in the soleus muscle, considering the percentage total fat content of musculature. The correlation coefficient was clearly lower (r = 0.55) in the tibialis anterior muscle due to signal contaminations from adjacent subcutaneous fat in the images, inhomogeneous fat distribution, and generally lower lipid content in this muscle. Applications of the new imaging technique showed marked intra‐ and interindividual variability in the spatial distribution of lipids in the musculature of the lower leg. No significant correlation of the muscular fat with the thickness of the subcutaneous fat layer was found. In addition, the body mass index does not appear to determine muscular fat content, except in very obese cases. Magn Reson Med 47:720–727, 2002.

The influence of a short‐term elevation of free fatty acids (FFAs) on intramyocellular lipids (IMCL) under hyperinsulinemic conditions was monitored in five healthy male subjects in the course of a 5‐hr hyperinsulinemic glucose clamp. During the glucose clamp a lipid emulsion (Intralipid 20®) and heparin were administered intravenously. IMCL was quantified in the tibialis anterior (TA) and the soleus (SOL) muscle by ¹H‐MRS. A rapid elevation of the IMCL pool was found in both muscles (61% in TA and 22% in SOL) in the 5‐hr time period. A control hyperinsulinemic glucose clamp in the same study group, repeated without elevation of circulating FFAs, did not lead to significant changes in IMCL for both muscles. The present study shows for the first time that only the combination of high concentrations of FFAs and insulin lead to marked storage of lipids in skeletal muscle cells in humans. Magn Reson Med 45:179–183, 2001.

A systematic evaluation of the potential quality of magnetic resonance images recorded in the presence of metallic stents was performed on a low‐field open imager operating at 0.2 T and on a high‐field closed unit operating at 1.0 T. Eight different stent types were examined by two‐dimensional gradient‐echo sequences with echo times of 4 and 10 msec and by a fast spin‐echo technique. In addition, a three‐dimensional gradient‐echo sequence was applied with an echo time of 2.4 msec. A set of sequence and slice parameters was used on both scanners. Thus, artifacts due to susceptibility effects depending on the magnetic field strength could be distinguished from radiofrequency shielding effects in the lumen of the stents (independent of the field strength). Nine different orthogonal orientations of the stent axis and the image (in terms of slice, read, and phase‐encoding direction) were tested, and the artifacts (extension of signal void and visibility of the lumen) were compared. The optimal strategy for visualization of vascular and perivascular regions outside the stents was fast spin‐echo imaging with the stent axis and read direction parallel to the static field. Susceptibility‐induced signal void in gradient‐echo images was minimal using the three‐dimensional approach. Increased transmitter amplitudes above usual values provided clearly improved insight in the lumen using gradient‐echo sequences. J. Magn. Reson. Imaging 2000;12:606–615.

Frequency‐selective chemical shift magnetic resonance (MR) imaging was applied on the calf musculature and the abdomen of a patient with acquired generalized lipoatrophy (AGL; Lawrence syndrome), a very rare syndrome affecting selectively several types of adipose tissue accompanied by alterations in glucose and energy metabolism. In addition, ¹H‐MRS was used for assessment of intra‐ (IMCL) and extramyocellular lipid stores (EMCL) in the skeletal musculature of the calf. Results from the AGL patient were compared with an age‐matched group of five healthy volunteers. Fat‐selective imaging of the calf revealed a total lack of subcutaneous adipose tissue. No EMCL signal was found in the spectra from the soleus muscle of the AGL patient. IMCL signals were present in the spectra but were clearly lower than in the controls (14% of normal value in the soleus muscle). In abdominal images, subcutaneous fat signal was not detectable, as in the calf, but nearly normal conditions were shown for visceral adipose tissue between abdominal organs. Fat‐selective images showed the liver with high signal intensity, indicating hepatic steatosis combined with hepatosplenomegaly. Modern chemical shift‐selective MR imaging and localized spectroscopy allow a noninvasive and quantitative assessment of tissue composition in patients with disorders of carbohydrate and lipid metabolism. J. Magn. Reson. Imaging 2000;12:306–310.