Jan Weis

Reduced oxygenation in diabetic rat kidneys measured by T2* weighted magnetic resonance micro-imaging.

By applying invasive techniques for direct measurements of oxygen tension, we have reported decreased kidney oxygenation in experimental diabetes in rats. However, the non-invasive MRI technique utilizing the BOLD effect provides several advantages with the possibility to perform repetitive measurements in the same animals and in human subjects. In this study, we applied a modified single gradient echo micro-imaging sequence to detect the BOLD effect in kidneys of diabetic rats and compared the results to normoglycemic controls. All measurements were performed on inactin-anaesthetized adult male Wistar Furth rats. Diabetes was induced by streptozotocin (45 mg/kg) 14 days prior to MRI-analysis. Sixteen T2*-weighted image records (B0=1.5 T) were performed using radiofrequency spoiled gradient echo sequence with 2.6 ms step increments of TE (TE1=12 ms), while TR (75 ms) and bandwidth per pixel (71.4 Hz) were kept constant. T2* maps were computed by mono-exponential fitting of the pixel intensities. Relaxation rates R2* (1/T2*) in cortex and outer stripe of the outer medulla were similar in both groups (cortex for controls 22.3 +/- 0.4 vs. diabetics 23.1 +/- 1.8 Hz and outer stripe of outer medulla for controls 24.9 +/- 0.4 vs. diabetics 26.4 +/- 1.8 Hz; n=4 in both groups), whereas R2* was increased in the inner stripe of the outer medulla in diabetic rats (diabetics 26.1 +/- 2.4 vs. controls 18.8 +/- 1.4 Hz; n=4, P<0.05). This study demonstrates that experimental diabetes in rats induces decreased oxygenation of the renal outer medulla. Furthermore, the proposed T2*-weighted MR micro-imaging technique is suitable for detection of regional changes in kidney oxygenation in experimental animal models.

Chemical shift artifact-free microscopy: spectroscopic microimaging of the human skin.

A spectroscopic imaging technique with high spatial resolution was used for the study of human skin in vivo. The measurements were performed using a whole‐body magnetic resonance system (1.5 T) with standard gradients and a standard 8‐cm diameter circular surface coil. A decisive gain in signal‐to‐noise ratio was achieved by reducing the receiver bandwidth of the imaging system to values less than ±5 kHz. The chemical shift misregistration was eliminated by post‐detection data processing. The method was tested on different kinds of skin, on the foot sole and head. Water, fat, and chemical shift artifact‐free images were obtained with resolution 0.107 × 0.143 mm in plane and slice thickness 1 mm. A major advantage of the spectroscopic imaging procedure is that the pulse sequence can be optimized for the maximum signal‐to‐noise ratio. There is no need for special modification of the sequence to circumvent the chemical shift artifacts (water, fat suppression, etc.). Magn Reson Med 41:904–908, 1999.

Noninvasive monitoring of brain temperature during mild hypothermia

The main purpose of this study was to verify the feasibility of brain temperature mapping with high-spatial- and reduced-spectral-resolution magnetic resonance spectroscopic imaging (MRSI). A secondary goal was to determine the temperature coefficient of water chemical shift in the brain with and without internal spectral reference. The accuracy of the proposed MRSI method was verified using a water and vegetable oil phantom. Selective decrease of the brain temperature of pigs was induced by intranasal cooling. Temperature reductions between 2 degrees C and 4 degrees C were achieved within 20 min. The relative changes in temperature during the cooling process were monitored using MRSI. The reference temperature was measured with MR-compatible fiber-optic probes. Single-voxel (1)H MRS was used for measurement of absolute brain temperature at baseline and at the end of cooling. The temperature coefficient of the water chemical shift of brain tissue measured by MRSI without internal reference was -0.0192+/-0.0019 ppm/degrees C. The temperature coefficients of the water chemical shift relative to N-acetylaspartate, choline-containing compounds and creatine were -0.0096+/-0.0009, -0.0083+/-0.0007 and -0.0091+/-0.0011 ppm/degrees C, respectively. The results of this study indicate that MRSI with high spatial and reduced spectral resolutions is a reliable tool for monitoring long-term temperature changes in the brain.

The earliest MR imaging and proton MR spectroscopy abnormalities in adult-onset Krabbe disease

Background –  Adult‐onset Krabbe disease is an uncommon form of leukodystrophy. Its magnetic resonance imaging (MRI) and magnetic resonance spectroscopy (MRS) manifestations are not well documented.

Assessment of lipids in skeletal muscle by LCModel and AMARES.

To process single voxel spectra of the human skeletal muscle by using an advanced method for accurate, robust, and efficient spectral fitting (AMARES) and by linear combination of model spectra (LCModel). To determine absolute concentrations of extra‐ (EMCL) and intramyocellular lipids (IMCL).

Assessment of lipids in skeletal muscle by high‐resolution spectroscopic imaging using fat as the internal standard: Comparison with water referenced spectroscopy

The main purpose of the study was to compare proton (1H) single‐voxel MR spectroscopy (MRS) with high‐spatial‐resolution spectroscopic imaging (MRSI) to determine the lipid content in human skeletal muscle. Unsuppressed water line was used as a concentration reference in the processing of single‐voxel spectra. The spectrum from yellow bone marrow with a 100% fat content and probe with the vegetable oil served as internal and external reference for high‐spatial‐resolution MRSI, respectively. Very good correlation was found between lipid concentrations measured by water referenced single‐voxel MRS and high‐spatial‐resolution MRSI with yellow bone marrow as the internal standard. Excellent correlation was found between total lipid concentrations estimated by high‐spatial‐resolution MRSI with vegetable oil as the external fat standard and yellow bone marrow as the internal reference. From comparison of single‐voxel MRS and MRSI approaches, it follows that relaxation correction of the reference water and methylene fat line is inevitable in processing the standard single‐voxel spectra. The high‐resolution MRSI approach is recommended to avoid the problem of relaxation corrections and enables using vegetable oil as the external fat standard. Magn Reson Med 59:1259–1265, 2008.

Lipid content in the musculature of the lower leg: Evaluation with high-resolution spectroscopic imaging

A novel spectroscopic imaging method with high spectral and spatial resolution was developed for the specific goal of assessing muscle fat. Sensitivity to the methylene and methyl protons of fatty acids was improved by the use of a binomial 1 1 excitation pulse instead of the standard radiofrequency (RF) pulse. Acceptable measurement time is achieved by using a narrow spectral bandwidth (6 ppm). The spectral resolution is sufficient to resolve extramyocellular (EMCL) and intramyocellular (IMCL) lipids. A post‐detection data processing scheme that permits correction of spectral artifacts caused by chemical shifts, spectral line aliasing, and magnetic field inhomogeneities is suggested. The lipid content in different lower leg muscles was evaluated. Muscle fiber orientation was taken into account in assessing quantities of EMCL and IMCL. The proposed technique allows small amounts of inhomogeneously distributed muscle lipids to be quantified. Magn Reson Med 54:152–158, 2005.

High-resolution spectroscopic imaging of the human skin

High-resolution water, fat and chemical shift artefact-free images of different areas of the skin were obtained on a whole-body MR unit (1.5 T) with commercial receiver surface coil with a diameter of 25 mm and high-power gradients (23 mT/m). Sufficient signal-to-noise ratio was achieved by lowering receiver bandwidth to +/-10 kHz or lower and shortening the echo time to 11 (13) ms. Spectroscopic image data sets were acquired with resolution 0.102 x 0.133 mm in plane and slice thickness 0.5 mm. The results demonstrate that it is possible to produce high-quality water and fat micro-images of the skin layers using only a few chemical shift encoding steps in a clinically reasonable time (approximately 2 minutes per slice).

In vivo 31P-MR spectroscopy in normal pregnancy, early and late preeclampsia: A study of placental metabolism

INTRODUCTION Preeclampsia affects about 3% of pregnancies and the placenta is believed to play a major role in its pathophysiology. Lately, the role of the placenta has been hypothesised to be more pronounced in preeclampsia of early (<34 weeks) rather than late (≥ 34 weeks) onset. (31)P Magnetic Resonance Spectroscopy (MRS) enables non-invasive, in vivo studies of placental metabolism. Our aim was to study placental energy and membrane metabolism in women with normal pregnancies and those with early and late onset preeclampsia. METHODS The study population included fourteen women with preeclampsia (five with early onset and nine with late onset preeclampsia) and sixteen women with normal pregnancy (seven with early and nine with late pregnancy). All women underwent a (31)P-MRS examination of the placenta. RESULTS The phosphodiester (PDE) spectral intensity fraction of the total (31)P signal and the phosphodiester/phosphomonoester (PDE/PME) spectral intensity ratio was higher in early onset preeclampsia than in early normal pregnancy (p = 0.03 and p = 0.02). In normal pregnancy the PDE spectral intensity fraction and the PDE/PME spectral intensity ratio increased with increasing gestational age (p = 0.006 and p = 0.001). DISCUSSION Since PDE and PME are related to cell membrane degradation and formation, respectively, our findings indicate increased cell degradation and maybe also decreased cell proliferation in early onset preeclampsia compared to early normal pregnancy, and with increasing gestational age in normal pregnancy. CONCLUSIONS Our findings could be explained by increased apoptosis due to ischaemia in early onset preeclampsia and also increased apoptosis with increasing gestational age in normal pregnancy.

Two-dimensional spectroscopic imaging for pretreatment evaluation of prostate cancer: comparison with the step-section histology after radical prostatectomy

PURPOSE To minimize user and vendor dependence of the spectrum processing of prostate spectra, to measure the ratio of choline (Cho) plus creatine (Cr) to citrate (Cit) in the prostate tissue of normal volunteers and cancer patients, and to compare the results with pathologic findings after radical prostatectomy. MATERIALS AND METHODS Four healthy volunteers and 13 patients with prostate cancer were measured. Measurements were performed using two-dimensional magnetic resonance spectroscopic imaging (MRSI) and endorectal coil. A standard vendors spectrum processing approach has been modified. An original feature of this methodology was the combination of vendor-optimized and user-independent spectrum preprocessing in the scanner and user-independent quantitation in the environment of an MRUI software package. (Cho+Cr)/Cit ratio was used for the classification of prostate tissue. Results were compared with histopathology after radical prostatectomy. RESULTS Eight of 13 cancer patients were classified as suspicious or very suspicious for cancer at spectroscopy, three were ambiguous for cancer and two patients were evaluated as false negative. A considerable overlap of metabolite ratios at various Gleason score was found. CONCLUSION The proposed spectrum processing has the potential to improve the accuracy and user independency of the (Cho+Cr)/Cit quantitation. This study confirmed the previous results that a considerable overlap of (Cho+Cr)/Cit ratios exists at various Gleason score levels.