Stimulated Echo Acquisition Mode Research Articles

Fat fractions and spectral T2 values in vertebral bone marrow in HIV- and non-HIV-infected men: a 1H spectroscopic imaging study.

Fat fractions and spectral T2 values of fat and water within the vertebral marrow of non-HIV- and HIV-infected men were measured with the use of a Carr-Purcell-Meiboom-Gill (CPMG) line scan spectroscopic imaging sequence. The fat fraction for the HIV-infected men (0.29 +/- 0.08) was significantly lower (P < 0.05, Student's unpaired t-test) than the fat fraction found in non-HIV-infected men (0.40 +/- 0.12). The mean water and fat T2 values did not differ between the two groups, and did not show any systematic dependence on fat fraction over the wide range of fat fractions encountered in this study. The marrow water and fat T2 values measured with the CPMG approach were markedly longer than the spectral T2 values reported by other groups using the more common point-resolved spectroscopy (PRESS) and stimulated-echo acquisition mode (STEAM) acquisitions. Proton spectroscopic studies of vertebral marrow revealed differences between non-HIV- and HIV-infected men that may prove useful for studying the effects of this disease and/or antiretroviral agents on body composition.

Dependence of the Spin-Spin Relaxation Time of Water in Collagen Gels on Collagen Fiber Directions

In this study, we investigated the effect of structural differences in collagen fibers in relation to the spin-spin (T2) relaxation time of surrounding water molecules. We propose a simple experimental model of the magic angle effect based on magnetically oriented collagen gels. Experiments were performed with a 4.7T magnetic resonance imaging (MRI) system with a quadrature radio frequency coil operated at 200 MHz for 1H resonance. Collagen gels were polymerized from collagen solutions exposed to a 4.7T magnetic field for 120 min. The T2 relaxation time was measured with the Carr-Purcell-Meiboom-Gill (CPMG) sequence. The apparent diffusion coefficient (ADC) was measured with the stimulated echo acquisition mode (STEAM) sequence with a motion-probing gradient (MPG). Orienting the collagen fibers at an angle of about 55 degrees to the main magnetic field caused an increase in the T2 relaxation times of water molecules in the collagen gels. The ADC in the direction parallel to the fibers was larger than that in the direction perpendicular to the fibers. The increase in the T2 relaxation time and ADC are attributed to a change in the magnetic interaction between the water molecules and collagen fibers.

Quantification of metabolic differences in the frontal brain of depressive patients and controls obtained by 1H-MRS at 3 Tesla.

This study compared metabolic differences in the frontal brain of depressed patients versus age- and sex-matched controls using proton magnetic resonance spectroscopy and absolute quantification of metabolites (NAA, Cr, Cho, mI) at 3 Tesla. Short-echo-time stimulated echo acquisition mode (TE/TM/TR=20/30/6000 milliseconds) was applied in the prefrontal region of 17 depressed patients and 17 age- and sex-matched controls. Metabolic ratios, ie, N-acetyl-aspartate/creatine (Cr), choline/Cr, and myo-inositol/Cr, and absolute concentrations (using internal water as a reference together with LCModel-based spectra fitting) were calculated and compared between groups and published reference data. Metabolic ratios showed significantly lower N-acetyl-aspartate/Cr (P = 0.016/0.006, left/right), choline/Cr (P = n.s./0.016), and myo-inositol/Cr (P = 0.022/0.026) for depressive patients versus controls. However, depressive patients showed significantly higher absolute concentrations of Cr (P = 0.017/0.0004) compared with controls with no differences in all other metabolites estimated. The authors demonstrate that absolute quantification of metabolite concentration is essential in properly identifying pathologic differences of brain metabolites in depression.

Spettroscopia protonica, perfusione e diffusione RM dell'encefalo nella sclerosi tuberosa

Tuberous Sclerosis Complex (TSC) is a genetic disease affecting multiple systems. Brain is one of the most frequently involved organ and the standard intracranial hallmarks are cortical tuberous (CT), subependymal nodules (SEN) and giant cell astrocytoma (GCA). MRI findings are characteristic and are included among the diagnostic criteria set out by Roach. Functional MR acquisitions such as proton spectroscopy (1HMRS), perfusion (ASL-PI) and diffusion (DWI and DTI) are additional tools to conventional imaging which allow a deeper understanding of “in vivo” physiology and pathology of the brain. We have variably applied 1H MRS, ASL-PI and DWI- DTI in a series of patients with definite diagnosis of TSC. The aim was to assess the strength of these techniques in the clinical management of the most impaired patients, i.e. those with refractory epilepsy or with suspected GCA. Combined brain MR studies were performed in 15 patients with definite diagnosis of TSC using a 1.5 T MR system (Signa Horizon LX, GE Medical System, Milwaukee, Wis) with a maximum gradient capability of 23 mT/m and a slew rate of 120 T/m/s. 1H MRS was applied in 12 cortical tubers and one GCA. A short TE stimulated echo acquisition mode (STEAM) technique (TR = 2010 ms, TE = 30 ms, mixing time ? 13.7 ms, 128 scans, VOI dimension = 3.4 cc) was performed. Raw data were analysed off-line with the Spectral Analysis General Electric/Interactive Data Language (SAGE/IDL). The following metabolites were evaluated: N-acetyl-aspartate (NAA, at 2.01 ppm), Creatine/Phosphocreatine (Cr, at 3.05 ppm), Choline-containing compounds (Cho, at 3.25 ppm), Myo-Inositol (mI, at 3.56 ppm) and if detectable Lactate (Lac, at 1.33 ppm). Ratio of signal amplitude of each metabolite versus Cr signal was calculated. Results were compared to cortical 1HMRS data of 20 age-matched healthy subjects. Multislice ASL-PI was used to measure CBF in 6 patients. CBF measurement was obtained using single-shot, GE-EPI images with FOV = 24 cm × 15 cm and acquisition matrix of 64 × 40, resulting in an in-plane resolution of 3.75 mm. CBF values have been compared with those obtained in 46 healthy subjects (age ranging from 4 to 76 years). DWI was performed in 5 patients, using an interleaved single-shot pulsed field gradient spin-echo sequence described by Stejskal and Tanner. The diffusion tensor (DTI) has been measured from seven MR images, the first one with bvalue ? 0 and the other six with a bvalue = 1000 sec/mm2 and diffusion gradient applied along the noncollinear directions (1,0,1), (-1,0,1), (0,1,1), (0,1,-1), (1,-1,0), (-1,1,0). The diffusion weighted images (TR = 8000 ms, FOV = 24 cm × 24 cm, matrix = 128 × 128, slice thickness 5 mm) have been repeated four times to improve signal to noise ratio and processed by a Matlab 5.12 code to solve analytically Dij values and to calculate the Trace, VR, FA and LI maps. 1H MRS acquired on CT presented a metabolic profile characterized by a marked increase of mI, a decrease of NAA and normal Cho. Lac was never detected. On the contrary the suspected GCA demonstrated Cho signal increase. In 4 patients ASL-PI demonstrated a marked CBF reduction in cortical regions corresponding with MRI-FLAIR confirmed locations of cortical tubers (15/28 ml/100g/min). Three of these studies revealed also isolated cortical hyperperfusion (160/198 ml/100g/min) corresponding to normal MRI in two cases and to a small cortical dysplasia in one. All of these patients were epileptics. Global CBF was significantly reduced in two patients without any focal cortical flow abnormalities. Both patients were not affected by epilepsy and MRI demonstrated many small and scattered cortical lesions. Of little use turned out DWI and DTI, since TS lesions demonstrated similar diffusion values compared to other type of glial lesions. Among the techniques here evaluated, 1HMRS and ASL-PI have revealed interesting results for a deeper comprehension of TSC. 1H MRS increases the diagnostic confidence in those cases presenting solitary cortical-subcortical lesions and allows a non-invasive longitudinal evaluation of the potential biological transformation of SEN into GCA. CBF hypoperfusion in ASL-PI is in agreement with SPECT and PET studies of TSC, confirming therefore that cortical dysplasias are brain areas metabolically depressed and functionally inert. Focal cortical hyperperfusion detected in three cases could be related to epileptogenic foci. This hypothesis need to be further investigated by means of multimodality functional neuroimaging (MRI, ASL-PI, PET and EEG) in order to test the ASL-PI capability of visualizing the epileptogenic laterality and of identification of the trigger epileptic foci.

Human immunodeficiency virus 1-associated minor motor disorders: perfusion-weighted MR imaging and H MR spectroscopy.

To investigate whether advanced magnetic resonance (MR) imaging techniques such as diffusion-weighted (DW) and perfusion-weighted (PW) MR imaging and hydrogen 1 (1H) MR spectroscopy can depict functional and pathophysiologic mechanisms in patients who have minor motor deficits (MMDs) associated with human immunodeficiency virus 1 (HIV-1). Thirty-two patients with results seropositive for HIV-1 and different degrees of HIV-1-related MMD underwent conventional brain MR imaging, as well as DW and PW MR imaging and 1H MR spectroscopy of the basal ganglia. PW MR imaging data were computed pixel by pixel for creation of time-to-peak, relative regional cerebral blood volume, and bolus amplitude parameter maps. In addition, quantitative regional cerebral blood flow (rCBF) maps were calculated with respect to the arterial input function by using the singular value decomposition algorithm. For 1H MR spectroscopy, a stimulated echo acquisition mode 20, or STEAM 20, sequence was used. Spectra were fit for determination of the signal intensities of the different metabolites. According to psychomotor testing results, patients were divided into three groups: group 1, 10 patients with normal motor function; group 2, eight patients with psychomotor slowing for the first time; and group 3, 14 patients who had had sustained pathologic psychomotor slowing for at least 6 months before the MR imaging examination. No patients had an abnormality at either conventional or DW MR imaging. PW MR imaging depicted significantly elevated rCBF in group 2 patients (P =.039, analysis of variance [ANOVA]) and significantly elevated myo-inositol-to-creatine ratio levels in group 3 patients (P =.020, ANOVA). Quantitative PW MR imaging and 1H MR spectroscopy can depict pathologic changes in patients who have HIV-1-related MMD but normal clinical examination and conventional MR imaging findings.

Reproducibility of metabolite concentration evaluated by intraclass correlation coefficient using clinical MR apparatus.

The purpose of this study was to evaluate the reproducibility of in vivo quantitative proton MR spectroscopy (MRS) by repeated-measure analysis of variance and intraclass correlation coefficient (ICC) including assessment of both inter- and intrasubject variation. The concentration of metabolites was quantified using long-TR and short-TE stimulated-echo acquisition mode sequences with a quadrature head coil. All preparation procedures for MRS measurement except volume of interest determination were done by an automatic preparation scanning system equivalent to a clinical setting. Analyses were conducted by an LCModel running based on our original basis set by two different reference methods. The ICC showed a good correlation (r = 0.61-0.99) in any metabolite and almost the same value between the two different reference methods, but the concentration of myoinositol had a large intersubject variation. Our results suggest that the reproducibility of quantified metabolite concentration is acceptable in the clinical setting regardless of the reference method, although quantified values may have different intersubject variations.

Proton magnetic resonance spectroscopy with metabolite nulling reveals regional differences of macromolecules in normal human brain.

To quantify the macromolecular content in different anatomic brain regions and to evaluate an age dependency of the macromolecular concentrations. A short echo time Stimulated Echo Acquisition Mode (STEAM) sequence was used without and with inversion recovery metabolite nulling in 8-12 healthy volunteers. Quantitation was achieved by an extended LCModel, and macromolecular resonances at 0.9, 1.4, 2.1, and 3.0 ppm were evaluated. In the cerebellum, the 1.4, 2.1, and 3.0 ppm resonances were highest compared to all other regions (P < 0.02); the 0.9 ppm resonance was significantly higher than that of pons (P < 0.01). In the motor cortex, the 0.9, 1.4, and 2.1 ppm resonances were higher than those of white matter and pons (P < 0.02). Pons and white matter did not differ significantly from each other. A significant correlation of the macromolecular concentrations with the age could not be found. There were higher macromolecular concentrations in the cerebellum and motor cortex than in pons or white matter. These were probably due to the higher portions of gray matter in these volumes of interest (VOIs) than in the other regions.

Maturation of the human fetal brain as observed by 1H MR spectroscopy.

Proton MRS was used to monitor cerebral metabolite tissue levels in 35 normal fetuses during development in the gestational age range of 30-41 weeks. First, MRI in three orthogonal orientations was performed. A volume of interest (VOI) (15-43 cc) of fetal brain tissue was then selected for (1)H MRS. For localization, two pulse sequences (stimulated echo acquisition mode (STEAM) at TE = 20 ms, and point-resolved spectroscopy (PRESS) at TE = 135 ms) were applied. The MR spectra of the brain showed signals for inositol (Ino), choline (Cho), creatine (Cr), and N-acetyl (NA) compounds. From 30 to 41 weeks the absolute tissue level of NA, and the ratios of NA/Cr and NA/Cho increased, whereas the ratio of Cho/Cr decreased. These changes reflect maturation of the brain. Considering the diagnostic value of proton MRS in pediatric neurology, this new approach may also be useful for characterizing pathological conditions in the fetal brain.

GABA X2 multiplet measured pre- and post-administration of vigabatrin in human brain.

This work demonstrates, in solution and in human brain at 3 tesla, that the X(2)-multiplet of the A(2)M(2)X(2) proton spin system of GABA at 2.315 ppm can be readily resolved from that of the overlapping background, particularly the glutamate multiplet, i.e., the PQ multiplet of the glutamate AMNPQ spin system. Prior to experiment, the values of the stimulated echo acquisition mode (STEAM) sequence parameters TE and TM that maximized the GABA-X(2) discrimination from its background (i.e., 168 ms and 28 ms, respectively) were determined numerically. The determination was made by calculating the spectral response of all contributing metabolites to the STEAM sequence throughout TE/TM space. A baseline GABA concentration (mean +/- standard deviation (SD) of the mean) of 0.78 +/- 0.04 mM was estimated from spectra acquired from a 3 x 3 x 3 cm(3) volume in the parieto-occipital cortex of eight normal control subjects. Five of the eight control subjects were also studied 24 hr post-administration of a single dose of 50 mg.kg(-1) vigabatrin. Four of the five showed increases in GABA in the range of 15-120% of their baseline level.

RETRACTED: Proton MR spectroscopic changes in Parkinson's diseases after thalamotomy

To investigate whether there are significant changes in regional brain metabolism in patients with Parkinson's disease before and after thalamotomy using proton magnetic resonance spectroscopy (1H MRS). Fifteen patients underwent 15 stereotactic thalamotomies for control of medically refractory parkinsonian tremor. Single-voxel 1H MRS was carried out on a 1.5 T unit using stimulated-echo acquisition mode (STEAM) sequence (TR/TM/TE, 2000/14/20 ms). Spectra were obtained from substantia nigra, thalamus and putamen areas with volumes of interests (7-8 ml) in patients before and after the surgery. Metabolite ratios of NAA/Cho, NAA/Cr and Cho/Cr were calculated from relative peak area measurements. We evaluated alterations of metabolite ratios in brain metabolism in Parkinson's disease patients with clinical outcome following thalamotomy. NAA/Cho ratios showed generally low levels in substantia nigra and thalamus in Parkinson's disease patients with clinical improvement following thalamotomy. In 80% (12/15) patients, decreased NAA/Cho ratios were observed from the selected voxels in substantia nigra after thalamic surgery (P<0.05). The ratios were also significantly decreased in thalamus in 67% (10/15) patients with clinical improvement (P<0.05). Our results suggest that NAA/Cho ratio may be a valuable criterion for evaluation of Parkinson's disease patients with the clinical improvement following surgery. 1H MRS may be a useful utility for the aid in better understanding the pathophysiologic process in Parkinson's disease patients on the basis of the variation of NAA/Cho ratio.

Fast in vivo water quantification in rat brain oedema based on T(1) measurement at high magnetic field.

In vivo water content determination based on magnetic resonance (MR) method is of importance in clinical practice as well as in animal studies to follow up the treatment given in order to reduce brain oedema. The methods proposed in the literature so far are largely time consuming. The aim of this study was to find a fast in vivo water quantification method having real advantage for patients suffering from critical conditions. Cold injury was applied to provoke brain oedema in fourteen rats. T(1) values of both the oedematous area and the contralateral normal cortex were determined by two independent methods 24 hours after the cold impact. First, from a series of images recorded by inversion recovery spin echo (IRSE) sequence and then by progressive saturation experiment performed by localised MR spectroscopy using stimulated echo acquisition mode (STEAM). To reduce the acquisition time, a two-element repetition time array was optimised for the STEAM experiment, whereas four inversion times were used for T(1) mapping. Both methods were validated against gel phantoms with known T(1) values. After the MR measurements the animals were sacrificed and the water contents of the regions of interest were determined by gravimetric wet-dry method. The reciprocals of the in vivo measured T(1) values were correlated with the reciprocals of the brain water contents. STEAM experiment showed stronger correlation (r=0.96) than IRSE (r=0.93). In addition, STEAM provided more accurate T(1) values in the phantom study. Determination of brain water content based on T1 measurement does work also at high magnetic field. Determination of brain water content by Magnetic Resonance Spectroscopy is feasible within 2 minutes. Using the presented fast method, water content can be determined within a couple of minutes in animal experiments as well as in the daily clinical practice.

Proton MRS in Kennedy disease: Absolute metabolite and macromolecular concentrations

To investigate whether glutamine and glutamate (Glx) were elevated in Kennedy Disease (KD), and whether pathological proteins were spectroscopically visible as altered macromolecular (MM) resonances. Ten patients with KD and twelve healthy volunteers were investigated using a stimulated echo acquisition mode (STEAM) spectroscopy sequence with metabolite-nulling. The concentrations of Glx remained unchanged in KD. An increased myo-inositol (Ins), and elevated MM at 0.9 ppm were found within the motor area. The N-acetyl-aspartate (NAA)/creatine (Cr) ratio was negatively correlated to the number of cytosine adenosine guanine (CAG) repeats in the motor area. The elevated MM at 0.9 ppm may be attributed to a pathologically altered protein in KD. Additionally, the changes of Ins point to a clinically unexpected involvement of the motor cortex. The correlation of NAA/Cr with the number of CAG repeats indicates a link between metabolites and genetic failure.

Predicting breast cancer response to chemotherapy using quantitative magnetic resonance (MR) imaging

Change in tumour volume may be a relatively late manifestation of chemotherapy response in patients with inoperable breast cancer. Recent studies suggest that quantifying water apparent diffusion coefficient (ADC), microvessel permeability (Ktrans) or water to fat signal ratio (WFR), using magnetic resonance (MR) imaging or spectroscopy, may provide an early indication of ultimate treatment response. Imaging and spectroscopy were carried out prior to chemotherapy (TP0) and shortly after the second (TP2) and final courses. ADC was measured using echo planar imaging (EPI) (maximum diffusion gradient weighting 680 s/mm2); Ktrans was measured using dynamic T1-weighted gradient echo imaging (13 s temporal resolution); WFR was measured using stimulated echo acquisition mode (STEAM) spectroscopy (TE 135 ms); tumour volume was measured using high resolution, three dimensional, post contrast, fat-suppressed images (manually traced regions of interest). Preliminary results from five (of 35 recruited) women who have completed their chemotherapy course (standard regimen involving 5-fluorouracil, epirubicin and cyclophosphamide) demonstrated that all tumours responded. Both the TP2:TP0 MRI volume ratio and the corresponding Ktrans ratio accurately predicted response in all five cases. The corresponding ADC and WFR ratios predicted response in three out of five and four out of five cases, suggesting that they may be less reliable indicators of final treatment efficacy. Results from 25 out of 35 women (course completed) will be presented.

MRI of muscular fat.

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 degrees -(-9 degrees )-17 degrees -(-17 degrees )-9 degrees -(-2 degrees ) 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.

Silicone breast implants: correlation between implant ruptures, magnetic resonance spectroscopically estimated silicone presence in the liver, antibody status and clinical symptoms.

To determine the impact of implant integrity on clinical symptoms and antibody status in women with silicone breast implants (SBIs). Ninety consecutive women were examined by means of magnetic resonance imaging (MRI) to assess the integrity of their silicone breast implants. The presence of silicone in the liver was estimated by (1)H localized stimulated echo acquisition mode (STEAM) magnetic resonance spectroscopy (MRS). Results were correlated with patients' complaints, as evaluated by a standardized questionnaire, physical examination by a rheumatologist and antibody screening. Breast MRI revealed defects in 24 patients (26.6%); in 13 (54.2%) of these women, silicone was detected in the liver by MRS. Of the 66 patients with MRI-estimated intact implants, 15 (22.7%) had apparent silicone in their liver, arguing for gel bleeding. Clinically, two patients had had rheumatoid arthritis before SBIs, whereas the other patients revealed no typical symptoms of arthritis or connective tissue disease (CTD). The patients with MRS evidence of silicone in the liver had no statistically significant differences in their complaints with the exception of the most frequent symptom, tingling/numbness of the fingers (82.1 vs 51.6%, P=0.006). A positive pattern of antinuclear antibodies (ANA) was obtained in 13 of the 28 MRS-positive patients (46.4%) and in 15 of the 62 MRS-negative patients (24.2%, P=0.033). However, in only one of these 28 ANA-positive patients was a specific weak antibody titre against SS-A detected by ELISA. Implant integrity has no major impact on rheumatic symptoms of women with SBIs. This finding supports the standpoint that silicone does not cause either a specific CTD or any other distinct disease entity. However, the moderately increased incidences of ANA-positivity and neuropathy-associated symptoms require explanation.

Restoration of motion-related signal loss and line-shape deterioration of proton MR spectra using the residual water as intrinsic reference.

A postprocessing method to restore motion-related signal loss and line-shape deterioration in single-volume proton MR spectroscopy (MRS) is presented. Each acquisition is corrected by its phase offset and frequency shift, extracted from the residual water signal prior to averaging. Requirements are good gradient selection and selective suppression of CSF in residual water. Stimulated echo acquisition mode (STEAM) spectra (TE = 30 ms) were analyzed using the LCModel program to study gains in metabolite signal and spectral quality in five brain regions. Increases of total N-acetyl-aspartate concentrations of up to 5% were observed. The method may be beneficial for clinical examinations of less compliant subjects and for dynamic spectroscopy.

Reliable detection of macromolecules in single-volume 1H NMR spectra of the human brain.

In short echo time proton MR spectra of the brain, resonances from macromolecules are visible. The macromolecular resonances in the 0.5-2.0 ppm region can be affected by lipid contamination arising from fat-containing regions outside the selected volume of interest (VOI). This study demonstrates that considerable lipid contamination may remain in stimulated echo acquisition mode (STEAM) spectra even if the spoiling of unwanted coherences is sufficient and the VOI is placed 2 cm or more away from fat-containing regions. The observed contamination was attributed to residual remote out-of-volume excitation, although only very small out-of-slice ripples of less than 0.2% of the in-slice excitation were found in the calculated excitation profile of the RF pulses. Spatial presaturation of fat-containing regions led to a sufficient suppression of the contamination and enabled the detection of highly reproducible macromolecular resonances. Thus, in single-volume spectroscopy as well as in spectroscopic imaging (SI or CSI), the combination of volume selection and outer volume presaturation, each in three dimensions, is highly recommended to ensure accurate detection and reliable evaluation of even small pathological alterations in macromolecules, e.g., proteins or lipids, or other resonances in the 0.5-2.0 ppm region.

The fetus at term: in utero volume-selected proton MR spectroscopy with a breath-hold technique--a feasibility study.

In three healthy gravidas at 38 and 39 weeks gestation, fetal MR spectroscopy was performed with a breath-hold technique by using the following pulse sequences: single voxel point-resolved spectroscopy, or PRESS, for liver and heart studies and stimulated-echo acquisition mode, or STEAM, for brain studies. Signal peaks of lipid from heart and liver were detected, as were the signal peaks of choline, creatine, and N-acetylaspartate from fetal brain. Findings demonstrated the feasibility of performing proton MR spectroscopy to assess mobile fetal structures.

A precise and user‐independent quantification technique for regional comparison of single volume proton MR spectroscopy of the human brain

The aim of this work was to study and correct the influence of varying coil load and local B1 field in single volume MR spectroscopy. A simple, precise, and user-independent way to adjust the transmitter gain has been developed and validated. It is based on a fit of the localized signal to flip angle variation around 90°. This method proved to be robust against B1 gradients and suitable for in vivo applications. Local B1 correction was combined with an external reference and decomposition of the volume into CSF and tissue to obtain a comprehensive absolute quantification of tissue water content and metabolite concentrations in human brain. STEAM localized spectra of parietal and insular gray matter and subparietal white matter (n = 11, TE = 30 ms) were analyzed using a linear combination of model spectra (LCModel). Coefficients of variation (CV) between 1.5% and 4% were obtained for the tissue water content (1–2% in a single subject). The CVs of major metabolite concentrations (4–21%) were dominated by the errors of the spectral analysis. The largest B1 variation in the in vivo experiments (range 30%) was due to changes in coil load. Differences in regional sensitivity due to B1 inhomogeneity (parietal: 8% and 9%; insular: 16%) were found to be the second largest source of variation. Correction for local B1 improved standard deviations and intra-subject reproducibility. On average, sensitivity was 9% less in insular than in parietal gray matter. If ignored, significant differences were introduced for water and N-acetyl-aspartate or were obscured for creatine and cholines. Hence, local sensitivity correction proved to be necessary for regional comparison of absolute metabolite concentrations. Copyright © 2000 John Wiley & Sons, Ltd. Abbreviations used: Cho choline containing compounds CSF cerebro-spinal fluid CV coefficient of variation ins GM insular gray matter pa WM parietal white matter pmp GM paramedian-parietal gray matter RF radio-frequency Rtra linear transmitter reference SD standard deviation SNR signal-to-noise ratio SPGR spoiled gradient echo STEAM stimulated echo acquisition mode tCr total creatine TG transmitter gain tNAA total N-acetyl aspartate TWC tissue water content VOI volume of interest

Quantitative proton magnetic resonance spectroscopy of focal brain lesions

The diagnostic value of single-voxel proton magnetic resonance spectroscopy (2 T, stimulated echo acquisition mode, TR = 6,000 ms, TE = 20 ms, 4-5 mL volumes-of-interest) was assessed for a differentiation of focal brain lesions of unknown etiology in 17 patients 1-14 years of age. Absolute metabolite concentrations were compared with age-matched control subjects and an individual control region. Most of the brain tumors were characterized by strongly reduced total N -acetylaspartyl compounds and marked increases of myo -inositol and choline-containing compounds, consistent with a lack of neuroaxonal tissue and a proliferation of glial cells. Lactate was elevated in only four patients. When using this pattern for a metabolic discrimination of brain tumors from other focal lesions, proton spectroscopy correctly identified 14 of 17 abnormalities, as confirmed by histologic examination after neurosurgical intervention. One false-positive tumor diagnosis was a severe reactive gliosis mimicking a typical tumor spectrum. Two inconclusive cases comprised an astrocytoma with moderately elevated myo -inositol but reduced choline-containing compounds and a patient with an abscess leading to a marked reduction of all metabolites but strong contributions from mobile lipids. In summary, quantitative proton spectroscopy has considerable clinical value for preoperative characterization of focal brain lesions.