Rapid fat/water assessment in knee bone marrow with inner-volume RARE spectroscopic imaging.

An inner-volume modification of a spectroscopic imaging technique based on RARE (rapid acquisition with relaxation enhancement) sequences is shown to provide, in less than 1 minute, spectra suitable for fat/water peak-area integration from selected imaging columns containing more than 1,000 5 x 5 x 1-mm voxels. A limitation is the unavoidable T2 weighting of the spectral peaks, which influences estimations of true fat/water composition from the spectra. Studies obtained in the knees of healthy volunteers demonstrate the ability of the technique to enable characterization of the two major proton peaks in bone marrow. Data collected at two or more effective TEs are suitable for extrapolation of fat/water estimates to zero TE.     

Hematopoietic reconstitution after bone marrow transplantation: Assessment with MR imaging and H-1 localized spectroscopy

Magnetic resonance (MR) studies were performed in 14 patients as early as possible (21–110 days) after bone marrow transplantation (BMT). MR characteristics of lumbar vertebral bone marrow were studied with T1-weighted spin-echo imaging, water- and fatselective imaging with a frequency-selective excitation technique, and point-resolved spatially localized proton spectroscopy. Signals from water and fat protons and their T1 and T2 values were analyzed. Water proton signal intensity correlated well with cellularity within bone marrow, as determined with parallel iliac crest biopsies. The fraction of signal from water in red bone marrow of patients with allogeneic transplants from siblings (four cases) was significantly higher than in four patients with autologous transplants. The latter showed very low cellularity in the period of about 4 weeks after BMT because of the cytotoxic pretreatment of the bone marrow. The MR results in six patients with allogeneic transplants from unrelated donors ranged widely, depending on the complications after BMT. Analysis of data obtained with the different techniques showed that water- and fat-selective MR imaging and spectroscopic methods are useful for noninvasive monitoring of hematopoietic reconstitution after BMT.     

Initial experience with dynamic MR imaging in evaluation of normal bone marrow versus malignant bone marrow infiltrations in humans

The purpose of this study was (a) evaluation of dynamic contrast-enhanced MR imaging of normal bone marrow versus malignant bone marrow infiltrations in patients with proven B-cell-type chronic lymphocytic leukemia (B-CLL) and (b) correlation with the clinical stage according to Binet (stages A, B, C) and response to therapy. Bone marrow imaging of the lumbar spine, pelvis, and proximal femurs was performed at 1.5 T in 45 patients without known malignancy and in 30 patients with B-CLL. The differences between opposed-phase and in-phase dynamic gradient-echo sequences before and up to 10 minutes after intravenous application of .1 mmol/kg body weight of gadolinium-diethylenetriamine penta-acetic acid (Gd-DTPA) were evaluated in normal bone marrow. The contrast-enhancement patterns of normal and malignant bone marrow were compared using the opposed-phase dynamic gradient-echo sequence. Ten of the patients with bone marrow infiltrations (Binet stage C) additionally underwent MR imaging follow-up during therapy. Opposed-phase gradient echo sequences demonstrated a signal decrease of normal bone marrow, and in-phase gradient echo sequences demonstrated a signal increase of normal bone marrow after administration of Gd-DTPA. The dynamic signal intensity time courses differed significantly (P < .05) between Binet stages B and C and controls as well as among the three Binet stages of B-CLL. In the 10 patients followed during therapy, MR imaging sensitively demonstrated response (n = 6), nonresponse (n = 2), or relapse after initial response (n = 2). In out-of-phase imaging, both normal bone marrow and initial bone marrow infiltration in CLL stage Binet A show signal decrease after administration of contrast agent, whereas there is increase in signal intensity in higher-grade bone marrow infiltration in Binet stage B or C disease. The signal loss of normal bone marrow in out-of-phase imaging is a phase effect rather than a T2* effect. The differentiation of initial from higher-grade bone marrow infiltration on out-of-phase images relies solely on a shift in the fat/water ratio.     

Fast spin-echo MR imaging of the abdomen: Contrast optimization and artifact reduction

The effects of various fast spin-echo (FSE) magnetic resonance (MR) imaging parameters and artifact reduction techniques on FSE image contrast and quality were studied. The authors performed 139 abdominal MR examinations, comparing standard FSE images (echo train length [ETL] = 8, echo space [E-space] = 17 msec, bandwidth = ±16-kHz) with FSE images with an ETL of 16 (n = 22) or FSE images with a ±32-kHz bandwidth and an E-space of 11-14 msec (n = 22). FSE artifact reduction techniques were evaluated with spectral fat saturation (n = 40) or with a new flow compensation FSE sequence (n = 55). Images of liver lesions were reviewed qualitatively and with contrast-to-noise ratio (C/N) measurements. Decreasing the time of echo train sampling produced superior image quality, with increased anatomic sharpness, less image artifact, and improved liver-lesion C/N. Images obtained with an ETL of 16 showed more image blurring and a 23% decrease in relative contrast and 28% decrease in relative C/N for liver tumors. Increasing the bandwidth reduced E-space, producing a 12% decrease in background noise. Artifact reduction with fat saturation or flow compensation produced images with less ghosting artifact and superior overall image quality, with 39% and 20% increases in liver-tumor C/N, respectively. FSE image quality and contrast in the depiction of hepatic disease can be optimized with careful selection of imaging parameters and the use of artifact reduction techniques.     

Does vertebral bone marrow fat content correlate with abdominal adipose tissue,lumbar spine bone mineral density,and blood biomarkers in women with type 2 diabetes mellitus?

Purpose:

To compare vertebral bone marrow fat content quantified with proton MR spectroscopy (¹H‐MRS) with the volume of abdominal adipose tissue, lumbar spine volumetric bone mineral density (vBMD), and blood biomarkers in postmenopausal women with and without type 2 diabetes mellitus (T2DM).

Materials and Methods:

Thirteen postmenopausal women with T2DM and 13 age‐ and body mass index‐matched healthy controls were included in this study. All subjects underwent ¹H‐MRS of L1–L3 to quantify vertebral bone marrow fat content (FC) and unsaturated lipid fraction (ULF). Quantitative computed tomography (QCT) was performed to assess vBMD of L1–L3. The volumes of abdominal subcutaneous/visceral/total adipose tissue were determined from the QCT images and adjusted for abdominal body volume (SAT_adj/VAT_adj/TAT_adj). Fasting blood tests included plasma glucose and HbA1c.

Results:

Mean FC showed an inverse correlation with vBMD (r = ?0.452; P < 0.05) in the whole study population. While mean FC was similar in the diabetic women and healthy controls (69.3 ± 7.5% versus 67.5 ± 6.1%; P > 0.05), mean ULF was significantly lower in the diabetic group (6.7 ± 1.0% versus 7.9 ± 1.6%; P < 0.05). SAT_adj and TAT_adj correlated significantly with mean FC in the whole study population (r = 0.538 and r = 0.466; P < 0.05). In contrast to the control group, significant correlations of mean FC with VAT_adj and HbA1c were observed in the diabetic group (r = 0.642 and r = 0.825; P < 0.05).

Conclusion:

This study demonstrated that vertebral bone marrow fat content correlates significantly with SAT_adj, TAT_adj, and lumbar spine vBMD in postmenopausal women with and without T2DM, but with VAT_adj and HbA1c only in women with T2DM. J. Magn. Reson. Imaging 2012;35:117‐124. © 2011 Wiley Periodicals, Inc.

     

Chronic lymphocytic leukemia: Changes in bone marrow composition and distribution assessed with quantitative MRI

The purposes of this study were (α) to determine the prevalence of bone marrow abnormalities in patients with chronic lymphocytic leukemia (CLL) using quantitative MR assessment of axial marrow composition and peripheral marrow distribution; (b) to assess the agreement between both quantitative MR methods and compare their sensitivities to detect marrow alterations; and (c) to correlate MR findings with clinical and laboratory parameters. Twenty-nine consecutive patients with biopsy-proven CLL were investigated on a .5-T MR imager to determine bulk T1 relaxation times of the vertebral bone marrow and proportion of proximal femur surface area occupied by nonfatty marrow on coronal T1-weighted MR images of one hip. Of the 29 patients, 12 (41%) had abnormal increase in lumbar marrow T1 values (>600 msec) and 16 (55%) had increased proportion of surface area occupied by non-fatty marrow in the proximal femur (>+1 SD compared to normal values determined in sex- and age-matched healthy subjects). The results of both quantitative MR methods were normal in 12 patients and abnormal in 11 patients (agreement, 79%). Patients with alterations in peripheral marrow distribution had significantly higher T1 relaxation times (P = .001) than those with normal peripheral marrow. Patients with abnormal marrow composition or distribution at MRI had significantly higher blood and marrow lymphocytosis than patients without these features. In conclusion, the agreement between both quantitative MR methods suggests a parallelism between changes in axial marrow composition and in peripheral marrow distribution in patients with CLL. The limits of quantitative MRI in CLL must be kept in mind, because quantitative MR methods failed to detect leukemic marrow infiltration in 41% of patients.     

Reproducibility of MR perfusion and 1H spectroscopy of bone marrow

Purpose

To determine the reproducibility of proton (¹H) magnetic resonance (MR) spectroscopy and dynamic contrast‐enhanced MR imaging in a clinical setting for the assessment of marrow fat fraction and marrow perfusion in longitudinal studies.

Materials and Methods

In all, 36 subjects (17 females, 19 males, mean age 72.9 ± 2.9 years) who underwent MR spectroscopy and/or dynamic contrast‐enhanced perfusion imaging of the proximal femur were asked to return after 1 week for a repeat MR examination.

Results

Reproducibility of ¹H MR spectroscopy in all bone areas tested was high, ranging from 0.78–0.85, with the highest reproducibility being in the femoral head and lowest in the femoral neck. Reproducibility of paired perfusion measurements ranged from 0.59 (enhancement slope femoral head) to 0.98 (enhancement maximum acetabulum). Overall reproducibility of ¹H MR spectroscopy and dynamic contrast‐enhanced imaging tended to be best in areas with the highest inherent fat fraction or perfusion.

Conclusion

Reproducibility of ¹H MR spectroscopy or perfusion imaging is sufficiently high to warrant these techniques being applied to the longitudinal study of bone diseases. J. Magn. Reson. Imaging 2009;29:1438–1442. © 2009 Wiley‐Liss, Inc.     

Time after excision and temperature alter ex vivo tissue relaxation time measurements

Previously unreported effects of tissue storage were recently observed in the authors' experimental magnetic resonance (MR) studies. To evaluate the effect of elapsed time after excision and storage temperature on tissue relaxation time measurements, tissue samples from the liver, pancreas, kidney, testis, spleen, and brain were obtained in rats. T1 and T2 were first measured within 5 minutes of excision, and between subsequent measurements, tubes were kept in a water bath at 40°C, at room temperature (28°C), or in an ice bath (4°C). Cellular and organellar integrity was assessed with electron microscopy and correlated with the MR findings. At 40°C (20-MHz spectrometer), the T1 of liver decreased from 280 msec ± 8 to 212 msec ± 10 during the first 60 minutes; the T1 of pancreas decreased from 276 msec ± 3 to 208 msec ± 2. Other tissues showed less than a 5% decrease in T1. T2 changes were smaller than T1 changes in all tissues. Electron microscopy of pancreatic acinar cells showed postmortem changes in mitochondria evolving over the first 60 minutes after death. Manganese loading experiments implicated mitochondrial manganese stores in the observed enhanced postmortem decrease in T1. This study calls into question reported relaxation time data for liver and pancreas. MR studies of excised tissues must account for time and temperature to prevent systematic experimental errors.     

Differentiation between hemangiomas and cysts of the liver with nonenhanced MR imaging: Efficacy of T2 values at 1.5 T

The authors studied the utility of non-contrast-agent-enhanced magnetic resonance (MR) imaging for differentiating cysts and cavernous hemangiomas of the liver. Nineteen patients with hemangiomas (51 lesions) and 16 with cysts (30 lesions) were studied with a 1.5-T MR imager. T2 values were calculated with the two-point method to evaluate the efficacy of T2 values in the differentiation between hemangiomas and cysts of the liver. For lesions larger than 1 cm, the mean T2 value of cysts (306 msec ± 156) was significantly longer than that of hemangiomas (113 msec ± 15) (P < .0001); there was no overlap of the ranges for T2 values of hemangiomas and cysts. All cysts larger than 1 cm could be differentiated from hemangiomas by using a threshold T2 value of 140 msec. This study suggests that calculated T2 values permit differentiation between hemangiomas and cysts larger than 1 cm at 1.5 T.     

Regional metabolite T2 in the healthy rhesus macaque brain at 7T

Although the rhesus macaque brain is an excellent model system for the study of neurological diseases and their responses to treatment, its small size requires much higher spatial resolution, motivating use of ultra‐high‐field (B₀) imagers. Their weaker radio‐frequency fields, however, dictate longer pulses; hence longer TE localization sequences. Due to the shorter transverse relaxation time (T₂) at higher B₀s, these longer TEs subject metabolites to T₂‐weighting, that decrease their quantification accuracy. To address this we measured the T₂s of N‐acetylaspartate (NAA), choline (Cho), and creatine (Cr) in several gray matter (GM) and white matter (WM) regions of four healthy rhesus macaques at 7T using three‐dimensional (3D) proton MR spectroscopic imaging at (0.4 cm)³ = 64 μl spatial resolution. The results show that macaque T₂s are in good agreement with those reported in humans at 7T: 169 ± 2.3 ms for NAA (mean ± SEM), 114 ± 1.9 ms for Cr, and 128 ± 2.4 ms for Cho, with no significant differences between GM and WM. The T₂ histograms from 320 voxels in each animal for NAA, Cr, and Cho were similar in position and shape, indicating that they are potentially characteristic of “healthy” in this species. Magn Reson Med 59:1165–1169, 2008. © 2008 Wiley‐Liss, Inc.     

Age- and sex-specific differences in the 1H-spectrum of vertebral bone marrow

Correct interpretation of 1H magnetic resonance (MR) studies of the red vertebral bone marrow in patients with disorders of the hematopoietic system requires knowledge of the dependence of the proton spectrum on age and sex. Infiltration of malignant cells causes a decreased red bone marrow fat signal, which is reversed upon successful treatment. The aim of this study was to establish a database of normal water/fat relations from a large group of volunteers. In all, 154 healthy volunteers from 11 to 95 years of age were examined using a 1.5-T MR system (ACS-NT, Philips). A volume of 2-8 ml in the center of a normal vertebral body was selected for spectroscopy using the PRESS sequence without water suppression (TR/TE 2 sec/40 msec). Signal intensities and T2 times of lipid and water resonances were determined. The relative fat signal intensity was calculated corrected for T2 relaxation. The relative proportion of protons in the fat signal increases with age from 24% in the age group 11-20 years to 54% in the group > or = 61 years. The proportion of fat in the vertebral bone marrow in female subjects is less than that in male subjects in the same age group (statistically significant at P < or = 0.01). In the central age group between 31 and 50 years, the difference is largest, at 12%; in the youngest and oldest age group this difference is small. T2 times are neither age nor sex dependent.     

Contrast-enhanced MR myelography in spontaneous intracranial hypotension: description of an artefact imitating CSF leakage

In contrast-enhanced (CE) MR myelography, hyperintense signal outside the intrathecal space in T1-weighted sequences with spectral presaturation inversion recovery (SPIR) is usually considered to be due to CSF leakage. We retrospectively investigated a hyperintense signal at the apex of the lung appearing in this sequence in patients with SIH (n = 5), CSF rhinorrhoea (n = 2), lumbar spine surgery (n = 1) and in control subjects (n = 6). Intrathecal application of contrast agent was performed in all patients before MR examination, but not in the control group. The reproducible signal increase was investigated with other fat suppression techniques and MR spectroscopy. All patients and controls showed strongly hyperintense signal at the apex of the lungs imitating CSF leakage into paraspinal tissue. This signal increase was identified as an artefact, caused by spectroscopically proven shift and broadening of water and lipid resonances (1–2 ppm) in this anatomical region. Only patients with SIH showed additional focal enhancement along the spinal nerve roots and/or in the spinal epidural space. In conclusion CE MR myelography with spectral selective fat suppression shows a reproducible cervicothoracic artefact, imitating CSF leakage. Selective water excitation technique as well as periradicular and epidural contrast collections may be helpful to discriminate between real pathological findings and artefacts.     

Quantitative chemical shift imaging of vertebral bone marrow in patients with Gaucher disease.

To evaluate extent of bone marrow involvement and disease severity in Gaucher patients, results of modified Dixon quantitative chemical shift imaging (QCSI) of the lumbar spine were correlated with quantitative analysis of marrow triglycerides and glucocerebrosides and with quantitative determination of splenic volume at magnetic resonance (MR) imaging. High-field-strength MR spectra of surgical marrow specimens were dominated by a single fat and a water peak, validating use of QCSI. QCSI showed average vertebral marrow fat fractions of 10% +/- 8 in Gaucher patients (normal adult averages, 29% +/- 6). Relaxation times for lipid and water approximated normal averages; bulk T1 values were significantly longer, reflecting decreased marrow fat. Glucocerebroside concentrations were higher in Gaucher marrow and inversely correlated with triglyceride concentrations. Extent of marrow infiltration determined by fat fraction measurements correlated with disease severity measured by splenic enlargement. These results show that as Gaucher cells infiltrate bone marrow and displace normal marrow adipocytes, bulk T1 increases due to the higher T1 of water compared with that of fat. QCSI provides a sensitive, noninvasive technique for evaluating bone marrow involvement in Gaucher disease.     

Precise and accurate measurement of proton T1 in human brain in vivo: Validation and preliminary clinical application

Precise and accurate inversion-recovery (PAIR) magnetic resonance (MR) measurements of T1 were obtained in eight brain regions and cerebrospinal fluid of 26 healthy volunteers. Accuracy of the technique was assessed by measuring T1 in small fluid volumes with the PAIR technique and with two independent spectroscopic techniques. The mean difference between T1 measured with PAIR and with the two spectroscopic techniques was 3.1% ± 1.3. The precision (reproducibility) of measurements with the PAIR technique was excellent. The coefficient of variation (CV) across 16 measurements in a head phantom was 2.0%, compared with a CV of 2.7% across 45 separate measurements in a single subject. The within-subject CV was 1.8% ± 0.6 in white matter and 1.4% ± 1.0 in basal ganglia. The between-subject CV in 26 healthy volunteers was 3.6% ± 0.6 in white matter and 4.1% ± 1.9 in basal ganglia. Comparison between a patient with an active recurrent brain tumor and an agematched patient with an inactive brain tumor showed that T1 was significantly elevated throughout the brain of the active-tumor patient, especially in white matter tracts, even though no tumor or edema was detected in the white matter on standard MR images. Comparisons between five brain tumor patients and four healthy volunteers of similar age showed that T1 was significantly and substantially elevated throughout the white matter tracts and in the caudate nucleus, putamen, and thalamus. These results are consistent with the hypothesis that white matter tracts are selectively vulnerable to edema and that T1 increases in white matter are a sensitive indicator of patient status or tumor aggressiveness.     

Protonen-MR-Spektroskopie des Wirbelsäulenkörpermarks Analyse des physiologischen Signalverhaltens

Background. Magnetic resonance imaging has shown to be a sensitive method for diagnostics of the red bone marrow, the composition of which changes physiologically and during pathological processes. However, the interpretation of MRI in patients with disorders of the red bone marrow is very difficult. The aim of this study was the characterization of the proton spectrum of healthy bone marrow and its age- and sex-dependent changes to obtain a data basis for measurements in patients. Methods. 154 healthy volunteers have been examined. After imaging, a spectroscopic measurement was performed to determine the relative intensities of fat and water, and their respective T2 times. Results. While T2 (water: 46.9 ms and fat: 75.4 ms) does not depend on age or sex, the relative signal intensity of fat increases by about 6% per decade. In the age groups between 31 and 50 years it diverses significantly between men (43.5%) and woman (32.5%) (p≤0.01, Mann-Whitney-Test. Conclusions. Proton spectroscopy can increase the reliability of diagnosis by offering information on composition of the marrow. The analysis of spectroscopic measurements requires exact knowledge about normal physiological values.     

Quantification of vertebral bone marrow fat content using 3 Tesla MR spectroscopy: reproducibility, vertebral variation, and applications in osteoporosis

Purpose:

To determine the reproducibility of proton MR spectroscopy (¹H‐MRS) for assessing vertebral bone marrow adiposity at 3 Tesla (T); to evaluate variation of marrow adiposity at different vertebral levels; and to demonstrate the feasibility of using ¹H‐MRS at 3T for evaluating marrow adiposity in subjects with low bone density.

Materials and Methods:

Single voxel MRS was acquired at vertebral body L1 to L4 at 3T in 51 postmenopausal females including healthy controls (n = 13) and patients with osteoporosis/osteopenia (n = 38). Marrow fat contents were compared between vertebral levels and between groups using analysis of variance (ANOVA). Six subjects were scanned twice to evaluate technique reproducibility.

Results:

The average coefficient of variation of vertebral marrow fat content quantification was 1.7%. Marrow fat content significantly increased from L1 to L4. The average fat content was significantly elevated in patients with osteoporosis/osteopenia compared with controls, adjusted for age and body mass index (P < 0.05).

Conclusion:

In vivo MRS at high field strength provides reliable measurement of marrow adiposity with excellent reproducibility and can be a valuable tool for providing complementary information on bone quality and potentially also fracture risk. J. Magn. Reson. Imaging 2011;33:974–979. © 2011 Wiley‐Liss, Inc.     

Reduced-bandwidth method for F-19 imaging of perflubron.

A reduced-bandwidth imaging method has been developed to eliminate the chemical shift artifacts in magnetic resonance (MR) imaging of the blood substitute perflubron (PFB) and simultaneously enhance the signal-to-noise ratio (SNR). The two strongest spectral peaks, which have relatively long T2 values (247 and 471 msec), were used. When the receiver bandwidth is reduced substantially by increasing the data acquisition time Ts, the bandwidth across the object becomes less than the chemical shift frequency. The reduced bandwidth eliminates misregistration by displaying the images corresponding to multiple spectral peaks on the same image plane simultaneously. An additional gain due to the reduced bandwidth is the reduced thermal Gaussian noise. Unfortunately, the increased Ts results in an increased TE, which causes the signal to be attenuated by T2 relaxation. The optimum measured Ts (and TE) values for successful image separation and maximum SNR were 120 and 144 msec for the two spectral peaks, respectively. The long TE also suppresses the rest of the downfield spectral peak cluster of PFB. The degree of magnetic field inhomogeneity and tissue susceptibility across the object may cause some limitations in the application of this technique; however, a composite radio-frequency pulse that will allow use of additional spectral lines and/or localized volume imaging techniques may be incorporated to overcome these limitations.     

Localized proton MR spectroscopy of the brain in children

Small-voxel (3.0–8.0 cm³), magnetic resonance (MR) imaging–guided proton MR spectroscopy was performed in 54 patients (aged 6 days to 19 years) with intracranial masses (n = 16), neurodegenerative disorders (n = 34), and other neurologic diseases (n = 4) and in 23 age-matched control subjects without brain disease. A combined short TE (18 msec) stimulatedecho acquisition mode (STEAM) and long TE (135 and/or 270 msec) spin-echo point-resolved spatially localized spectroscopy (PRESS) protocol, using designed radio-frequency pulses, was performed at 1.5 T. STEAM spectra revealed short T2 and/or strongly coupled metabolites; prominent resonances were obtained from N-acetyl aspartate (NAA), choline-containing compounds (Cho), and total creatine (tCr). Lactate was well resolved with the long TE PRESS sequence. Intracranial tumors were readily differentiated from cerebrospinal fluid (CSF) collections. All tumors showed low NAA, high Cho, and reduced tCr levels. Neurodegenerative disorders showed low or absent NAA levels and enhanced mobile lipid, glutamate and glutamine, and inositol levels, consistent with neuronal loss, gliosis, demyelination, and amino acid neuro-toxicity. Preliminary experience indicates that proton MR spectroscopy can contribute in the evaluation of central nervous system abnormalities of infants and children.     

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.     

Automated spectral analysis III: Application to in Vivo proton MR Spectroscopy and spectroscopic imaging

An automated method for analysis of in vivo proton magnetic resonance (MR) spectra and reconstruction of metabolite distributions from MR spectroscopic imaging (MRSI) data is described. A parametric spectral model using acquisition specific, a priori information is combined with a wavelet-based, nonparametric characterization of baseline signals. For image reconstruction, the initial fit estimates were additionally modified according to a priori spatial constraints. The automated fitting procedure was applied to four different examples of MRS data obtained at 1.5 T and 4.1 T. For analysis of major metabolites at medium TE values, the method was shown to perform reliably even in the presence of large baseline signals and relatively poor signal-to-noise ratios typical of in vivo proton MRSI. identification of additional metabolites was also demonstrated for short TE data. Automated formation of metabolite images will greatly facilitate and expand the clinical applications of MR spectroscopic imaging.