Biomedical subjects

G B Matson

Publications and source records attributed to G B Matson.

At least 19 recordsLinked to original sources

PubMed2000

Hippocampal structures: anteroposterior N-acetylaspartate differences in patients with epilepsy and control subjects as shown with proton MR spectroscopic imaging.

PURPOSE: To determine the distribution of proton metabolites along the long axis of the hippocampus. MATERIALS AND METHODS: Proton magnetic resonance (MR) spectroscopic imaging measurements were performed in the hippocampi of 14 control subjects and nine patients with unilateral mesial temporal lobe epilepsy. RESULTS: Control subjects showed significantly lower ratios of N-acetylaspartate (NAA) to choline-containing compounds (Ch) and creatine plus phosphocreatine (CR) (NAA/[Cr + Ch]) in the anterior as compared with the posterior part of the hippocampus. Furthermore, a similar anteroposterior (AP) difference in NAA/(Cr + Ch) values was found in both ipsilateral and contralateral hippocampi of patients. In the patients compared with the control subjects, ipsilateral NAA/(Cr + Ch) levels were reduced in every part of hippocampal tissue with an average reduction of 17%, and contralateral NAA/(Cr + Ch) was reduced by about 10%. In the patients compared with the control subjects, the proportional reduction in ipsilateral NAA/(Cr + Ch) was greatest in voxels from anterior hippocampal regions. CONCLUSION: AP differences could be a result of fewer neurons in the anterior compared with the posterior hippocampus or of the increasing thickness of the hippocampus from posterior to anterior, which leads to different contributions from adjacent tissue. Measurements of T2 showed that T2 differences are probably not responsible for these changes.

Adult↗

PubMed1999

A practical double-tuned 1H/31P quadrature birdcage headcoil optimized for 31P operation.

A double-tuned 1H/31P birdcage head coil for use with humans at 1.5 T is described. The coil was designed for proton-decoupled 31P excitation and reception and incorporated a number of practical features including optimized sensitivity for 31P, quadrature operation at 1H and 31P frequencies, and a radiofrequency (RF) mirror for improved B1 homogeneity. The design achieved similar B1 homogeneity at both 31P and 1H frequencies. Inductive matching was used to accommodate samples with large loading differences. A facile method for tuning and matching over a variety of sample loadings is presented, along with capacitively shortened bazookas for suppression of cable braid currents. The proton sensitivity, although down by approximately a factor of two compared with an optimized 1H birdcage head coil, was still ample for shimming and generation of scout images. Advantages of the design are discussed and proton-decoupled 31P spectra of human brain are presented.

Adenosine Triphosphate↗

PubMed1999

Spectral simulations incorporating gradient coherence selection.

Computer-aided methods can considerably simplify the use of the product operator formalism for theoretical analysis of NMR phenomena, which otherwise becomes unwieldy for anything but simple spin systems and pulse sequences. In this report, two previously available programming approaches using symbolic algebra (J. Shriver, Concepts Magn. Reson. 4, 1-33, 1992) and numerical simulation using object-oriented programming (S. A. Smith, T. O. Levante, B. H. Meier, and R. R. Ernst, J. Magn. Reson. A 106, 75-105, 1994) have been extended to include the use of gradient operators for simulation of spatially localized NMR spectroscopy and gradient coherence selection. These methods are demonstrated using an analysis of the response of an AX(3) spin system to the STEAM pulse sequence and verified with experimental measurements on lactate.

Computer Simulation↗

PubMed1998

Multiple-echo proton spectroscopic imaging using time domain parametric spectral analysis.

A multiple-echo MR spectroscopic imaging (MRSI) method is presented that enables improved metabolite imaging in the presence of local field inhomogeneities and measurement of transverse relaxation parameters. Short echo spacing is used to maximize signal energy from inhomogeneously line-broadened resonances, and time domain parametric spectral analysis of the entire echo train is used to obtain sufficient spectral resolution from the shortened sampling periods. Optimal sequence parameters for 1H MRSI are determined by computer simulation, and performance is compared with conventional single-echo acquisition using phantom studies at a field strength of 4.7 T. A preliminary example for use at 1.5 T is also presented using phantom and human brain MRSI studies. This technique is shown to offer improved performance relative to single-echo MRSI for imaging of metabolites with shortened T2* values due to the presence of local field inhomogeneities. Additional advantages are the intrinsic measurement of metabolite T2 values and determination of metabolite integrals without T2 weighting, thereby facilitating quantitative metabolite imaging.

Aspartic Acid↗

PubMed1998

Measurement of chemical shifts and coupling constants for glutamate and glutamine.

Proton chemical shifts and coupling constants were obtained for glutamate and glutamine in water (D2O) at pH = 6.6. Initial chemical shift and coupling constant values obtained from experimental spectra were refined using a spectral simulation and optimization program to get a complete set of values that could not otherwise be measured directly from the experimental spectra due to strong spin-spin couplings. These values are essential for automated spectral fitting procedures that require a priori information.

Brain↗

PubMed1998

Regional distribution of interictal 31P metabolic changes in patients with temporal lobe epilepsy.

PURPOSE: We compared the 31P metabolites in different brain regions of patients with temporal lobe epilepsy (TLE) with those from controls. METHODS: Ten control subjects and 11 patients with TLE were investigated with magnetic resonance imaging (MRI) and [31P]MR spectroscopic imaging (MRSI). [31P]MR spectra were selected from a variety of brain regions inside and outside the temporal lobe. RESULTS: There were no asymmetries of inorganic phosphate (Pi), pH, or phosphomonoesters (PME) between regions in the left and right hemispheres of controls. In patients with TLE, Pi and pH were higher and PME was lower throughout the entire ipsilateral temporal lobe as compared with the contralateral side and there were no significant asymmetries outside the temporal lobe. The degree of ipsilateral/contralateral asymmetry for all three metabolites was substantially greater for the temporal lobe than for the frontal, occipital, and parietal lobes, and these asymmetries provided additional data for seizure localization. As compared with levels in controls, Pi and pH were increased and PME were decreased on the ipsilateral side in patients with TLE. There were changes in Pi, pH, and PME on the contralateral side in persons with epilepsy as compared with controls, contrary to changes on the ipsilateral side. CONCLUSIONS: Our findings provide some insight into the metabolic changes that occur in TLE and may prove useful adjuncts for seizure focus lateralization or localization.

Adult↗

PubMed1997

Hippocampal N-acetylaspartate in neocortical epilepsy and mesial temporal lobe epilepsy.

Previous magnetic resonance spectroscopy (MRS) studies have shown that N-acetylaspartate (NAA) is reduced not only in the ipsilateral but also in the contralateral hippocampus of many patients with mesial temporal lobe epilepsy (mTLE). The reason for the contralateral damage is not clear. To test whether the hippocampus is also damaged if the focus is outside the hippocampus, we have measured patients with neocortical epilepsy (NE). Therefore, the goals of this study were to determine if hippocampal NAA is reduced in NE and if hippocampal NAA discriminates NE from mTLE. MRS imaging (MRSI) studies were performed on 10 NE patients and compared with MRSI results in 23 unilateral mTLE patients and 16 controls. The results show that, in contrast to mTLE, NAA was not reduced in the hippocampus of NE patients, neither ipsilateral nor contralateral to the seizure focus. These results suggest that repeated seizures do not cause secondary damage to the hippocampus. The absence of spectroscopic differences in NE may help to distinguish NE from mTLE.

Adult↗

PubMed1997

Presurgical multimodality neuroimaging in electroencephalographic lateralized temporal lobe epilepsy.

The purpose of this study was to compare 2-[18F]fluoro-2-deoxy-D-glucose positron emission tomography (FDG-PET), hippocampal volumetry (HV), T2 relaxometry, and proton magnetic resonance spectroscopic imaging (1H-MRSI) in the presurgical neuroimaging lateralization of patients with nonlesional, electroencephalogram (EEG)-defined unilateral temporal lobe epilepsy (TLE). Twenty-five patients were prospectively studied, along with age-matched controls. T2 relaxometry examinations were performed in 13 patients. Comparison of FDG-PET, HV, and 1H-MRSI was possible in 23 patients. FDG-PET lateralized 87% of patients, HV 65%, N-acetyl aspartate (NAA)/(choline [Cho] + creatine [Cr]) 61%, and [NAA] 57%. Combined HV and NAA/(Cho + Cr) results lateralized 83% of the patients, a value similar to PET. Of 10 patients with normal magnetic resonance imaging (MRI) scans, 2 were lateralized with HV, 6 with FDG-PET, 4 with NAA/(Cho + Cr), and 3 with [NAA]. T2 relaxometry lateralized no patients without hippocampal atrophy. Bilateral abnormality was present in 29 to 33% of patients with 1H-MRSI measures and 17% with HV. Only hippocampal atrophy correlated with postoperative seizure-free outcome. FDG-PET remains the most sensitive imaging method to correlate with EEG-lateralized TLE. Both FDG-PET and 1H-MRSI can lateralize patients with normal MRI, but only the presence of relative unilateral hippocampal atrophy is predictive of seizure-free outcome. Bilaterally abnormal MRI and 1H-MRSI measures do not preclude good surgical outcome.

Adult↗

PubMed1997

Correlation of seizure frequency with N-acetyl-aspartate levels determined by 1H magnetic resonance spectroscopic imaging.

Using 1H MRSI, we measured N-acetyl-aspartate (NAA), a neuronal marker, in the seizure focus of 16 patients with partial epilepsy. Decreasing NAA correlated with increasing seizure frequency in frontal lobe epilepsy (r = -0.72, p < 0.02) and a similar trend was present in temporal lobe epilepsy (r = -.60, p < 0.06). NAA was not related to the duration of epilepsy. We conclude that patients with higher seizure frequency have evidence of greater neuron loss or dysfunction.

Adolescent↗

PubMed1997

Temporal lobe epilepsy: bilateral hippocampal metabolite changes revealed at proton MR spectroscopic imaging.

PURPOSE: To determine which proton magnetic resonance (MR) spectroscopic imaging measures are best for lateralizing the seizure focus in patients who have temporal lobe epilepsy with and in those without hippocampal atrophy on MR images, the extent of contralateral abnormalities, and whether there is a correlation between MR spectroscopic imaging findings and surgical outcome. MATERIALS AND METHODS: MR spectroscopic imaging was performed in 16 adult patients with temporal lobe epilepsy and unilateral electroencephalographic findings and in 16 adult control subjects. Eleven patients underwent surgery; all patients underwent MR imaging. RESULTS: Nine patients had hippocampal atrophy on MR images. An ipsilateral decrease in the N-acetylaspartate concentration or the ratio of N-acetylaspartate to the sum of creatine and choline (N-acetylaspartate/ [creatine + choline]) was found in all patients. Decreased contralateral N-acetylaspartate concentration, N-acetylaspartate/(creatine + choline), or N-acetylaspartate concentration and N-acetylaspartate/(creatine + choline) were detected in eight patients (50%), which suggests bilateral abnormalities not detected with MR imaging. In the five patients who underwent surgery and did not show hippocampal atrophy on MR images, successful and unsuccessful outcomes were correctly predicted with N-acetylaspartate concentration. CONCLUSION: Decreased N-acetylaspartate concentration is not due solely to hippocampal atrophy. Contralateral abnormalities are much more frequent than expected. MR spectroscopic imaging is valuable in the presurgical evaluation of epilepsy.

Adult↗

PubMed1996

Comparison of k-space sampling schemes for multidimensional MR spectroscopic imaging.

For clinical 31P MR spectroscopic imaging (MRSI) studies, where signal averaging is necessary, some improvement of sensitivity and spatial response function may be achieved by acquiring data over a spherical k-space volume and varying the number of averages acquired in proportion to the desired spatial filter. Eight different k-space sampling schemes are compared through simulations that provide graphs of the spatial response functions (SRF), and tabulations of voxel volumes, relative signal-to-noise ratios (SNR), and relative data collection efficiencies (SNR per unit volume over the same time). All schemes were based on practical experiments, each of which could be implemented in the same length of time. The results show that in comparison with cubic k-space sampling with the same number of signal averages at each point, spherical and acquisition-weighted k-space sampling can be used to achieve reduced Gibbs ringing along the principal axes directions, and thus reduced contamination from adjacent tissue in these directions, without degradation of voxel volume or SNR.

Computer Simulation↗

PubMed1995

Proton magnetic resonance spectroscopic imaging in patients with frontal lobe epilepsy.

Proton magnetic resonance spectroscopic imaging (1H MRSI) has demonstrated decreased N-acetyl compounds (NA) in the epileptogenic hippocampus in patients with temporal lobe epilepsy. We studied 8 patients with frontal lobe epilepsy and found mean NA/creatine (Cr) in the epileptogenic frontal lobe decreased by 27% compared with that of the contralateral homologous region (1.81 +/- 0.36 vs 2.49 +/- 0.60, p < 0.008). In every patient, NA/Cr was decreased in the epileptogenic region by at least 5%. These findings suggest that 1H MRSI may be useful in the presurgical evaluation of patients with frontal lobe epilepsy.

Aspartic Acid↗

PubMed1994

Phosphorus magnetic resonance spectroscopic imaging in patients with frontal lobe epilepsy.

Phosphorus magnetic resonance spectroscopic imaging has previously demonstrated localized metabolic abnormalities within the epileptogenic region in patients with temporal lobe epilepsy, including alkalosis, increased inorganic phosphate level, and decreased phosphomonoester levels. We studied 8 patients with frontal lobe epilepsy, finding interictal alkalosis in the epileptogenic region compared to the contralateral frontal lobe in all patients (7.10 +/- 0.05 vs 7.00 +/- 0.06, p < 0.001). Seven patients exhibited decreased phosphomonoester levels in the epileptogenic frontal lobe compared to the contralateral frontal lobe (16.0 +/- 6.0 vs 23.0 +/- 4.0, p < 0.01). In contrast to findings in temporal lobe epilepsy, inorganic phosphate level was not increased in the epileptogenic region. Based on values derived from normal control subjects, 5 patients had elevated pH in the seizure focus and 2 patients had decreased phosphomonoesters while none had abnormalities in the contralateral frontal lobe. These data suggest that magnetic resonance spectroscopy will be useful in the presurgical evaluation of patients with frontal lobe epilepsy.

Adolescent↗

PubMed1994

Biochemical alterations in multiple sclerosis lesions and normal-appearing white matter detected by in vivo 31P and 1H spectroscopic imaging.

The goals of the current study were threefold: first, to confirm previous single volume proton (1H) magnetic resonance spectroscopy results of reduced N-acetyl aspartate (NAA, a putative marker of neurons) in multiple sclerosis (MS) white matter lesions using multiple volume 1H magnetic resonance spectroscopic imaging (MRSI); second, to measure the phospholipid metabolites phosphomonoesters and phosphodiesters in such lesions using phosphorus (31P) MRSI; and third, to test the hypothesis that biochemical changes occur in the normal-appearing (on spin echo T2-weighted magnetic resonance images) white matter in patients with MS. Thirteen subjects with clinically definite MS were studied with both 1H and 31P MRSI, and 19 controls were studied with either 1H MRSI, 31P MRSI, or both. MS lesion, MS normal-appearing white matter, and region-matched control spectra from the centrum semiovale were analyzed. The major findings of this study were that in both white matter lesions and normal-appearing white matter in patients with MS, the metabolite ratio NAA/creatine and the total 31P peak integrals were significantly reduced compared with controls. In addition, in MS lesions NAA/choline and phosphodiesters/total 31P were significantly reduced compared with controls, and in MS normal-appearing white matter there was a trend for NAA/choline to be reduced compared with controls. In normal-appearing white matter in patients with MS, total creatine and phosphocreatine were significantly increased compared to controls, as detected with both 1H (total creatine peak integrals) and 31P (phosphocreatine/total 31P) MRSI techniques. These results suggest reduced neuronal density and altered phospholipid metabolites in white matter lesions in patients with MS.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1994

In vivo detection of myelin phospholipids in multiple sclerosis with phosphorus magnetic resonance spectroscopic imaging.

The goal of this study was to investigate myelin phospholipids in vivo in multiple sclerosis lesions and normal-appearing white matter by evaluating the spectral broad component from phosphorus 31 magnetic resonance spectroscopic imaging data. The phospholipid broad component was reduced nearly 35% (p < 0.001) in both lesions and in normal-appearing white matter in multiple sclerosis subjects compared to control subjects, suggesting reduced myelin phospholipid concentration or altered relaxation times.

Adult↗

PubMed1994

Reduced phase encoding in spectroscopic imaging.

The effect of different spatial-encoding (k-space) sampling distributions are evaluated for magnetic resonance spectroscopic imaging (MRSI) using Fourier reconstruction. Previously, most MRSI studies have used square or cubic k-space functions, symmetrically distributed. These studies examine the conventional k-space distribution with spherical distribution, and 1/2 k-space acquisition, using computer simulation studies of the MRSI acquisition for three spatial dimensions and experimental results. Results compare the spatial response function, Gibbs ringing effects, and signal contamination for different spatial-encoding distribution functions. Results indicate that spherical encoding, in comparison with cubic encoding, results in a modest improvement of the response function with approximately equivalent spatial resolution for the same acquisition time. For spin-echo acquired data, reduced acquisition times can readily be obtained using 1/2 k-space methods, with a concomitant reduction in signal to noise ratio.

Adenosine Triphosphate↗

PubMed1994

An integrated program for amplitude-modulated RF pulse generation and re-mapping with shaped gradients.

Efficient generation of amplitude modulated, frequency selective RF pulses has been demonstrated by the Shinnar-Le Roux (SLR) algorithm. In the present article, we provide an overview of a relatively comprehensive computer program that includes a version of the SLR algorithm and also incorporates an algorithm for re-mapping a selective RF pulse onto a new dwell time with modulated gradients. The re-mapping may be used to reduce SAR, or to shorten the RF pulse time by increasing the gradient and RF strength in regions where the original RF pulse amplitude was low. The program includes additional useful features including a Bloch equations algorithm, and pulse scaling, to enable examination of pulse profiles under a variety of conditions such as RF inhomogeneity and even nuclear relaxation. The program, MATPULSE, was developed with the MATLAB for Windows programming language and makes extensive use of the MATLAB graphical user interface (GUI) features to generate a user-friendly interface. A number of examples are provided to illustrate the capabilities of the MATPULSE program.

Image Processing, Computer-Assisted↗

PubMed1994

Molar quantitation of in vivo proton metabolites in human brain with 3D magnetic resonance spectroscopic imaging.

A method for molar quantitation of in vivo proton metabolites in human brain with three-dimensional (3D) proton magnetic resonance spectroscopic imaging (MRSI) is described. The method relies on comparison of brain and calibration phantom measurements, with corrections for coil loading, and spin-lattice and spin-spin relaxation times. A 3D proton MRSI pulse sequence was developed which acquires two echoes and enables acquisition of both the TMS coil loading reference phantom and proton metabolite signals from a single experiment. With the aqueous fraction (tissue water) taken into account, the calculated molar concentrations from 24 centrum semiovale white matter voxels from 4 control subjects were (mmol/l +/- SD): N-acetyl aspartate = 14.6 +/- 2.8, total creatine+phosphocreatine = 6.0 +/- 1.2, total choline = 1.9 +/- 0.4. These values are equivalent to previously reported results obtained from single volume localized proton magnetic resonance spectroscopy.

Aspartic Acid↗