Mark A. Brown

Time-domain combination of MR spectroscopy data acquired using phased-array coils

A new method for efficiently processing MRS data acquired with phased‐array coils is presented. The method consists of performing phase compensation (i.e., redefining the signal phase relative to a common reference) of the signals in the time domain prior to combining the signals. The resulting spectra are equivalent to those obtained by previously published methods for phased‐array spectral data processing (i.e., processing the signals individually and then combining them in the frequency domain). The method allows spectra acquired with phased‐array coils to be processed as efficiently as those acquired with non‐phased‐array coils. Both single voxel spectroscopy (SVS) and chemical shift imaging (CSI) data sets may be processed by this method. Magn Reson Med 52:1207–1213, 2004.

Breath‐hold 3D gradient‐echo MR imaging of the lung parenchyma: Evaluation of reproducibility of image quality in normals and preliminary observations in patients with disease

This study evaluates the reproducibility and image quality of a three‐dimensional (3D) gradient‐echo sequence for imaging the lung parenchyma, with and without gadolinium administration, using a 2D spoiled gradient‐echo sequence for comparison. Twenty patients without lung disease (normals) and five patients with lung disease (lung disease) underwent paired 2D and 3D gradient‐echo sequences, without contrast (24 patients) and with contrast (18 patients). Images were retrospectively reviewed independently in a blinded fashion by two investigators. Artifacts and demonstration of central lung, peripheral lung, heart, pulmonary arteries, and esophagus were evaluated. Image quality of the central lung was rated as fair or good in 5 and 4 (reader one and two) patients with non‐contrast 2D gradient‐echo, 24 and 25 patients with non‐contrast 3D gradient‐echo, 3 and 1 patient(s) with contrast‐enhanced 2D gradient‐echo, and 19 and 19 patients with contrast‐enhanced 3D gradient‐echo imaging. Differences in image quality between 2D and 3D sequences were significant (P < 0.001). Heart‐related phase artifacts were negligible in 2 and 0 patients with non‐contrast 2D gradient‐echo, 23 and 25 patients with non‐contrast 3D gradient‐echo, 0 and 0 patients with contrast‐enhanced 2D gradient‐echo, and 17 and 19 patients with contrast‐enhanced 3D gradient‐echo imaging. Differences in heart‐related phase artifact in the central lung between 2D and 3D sequences were significant (P = 0.001). Infiltrates, lung cancer, and pulmonary metastasis were better shown on the gadolinium‐enhanced 3D gradient‐echo sequences than on the other sequences. Breath‐hold 3D gradient‐echo imaging results in good image quality and negligible image artifacts and is superior to 2D spoiled gradient‐echo imaging. Preliminary results in patients with disease appear promising. J. Magn. Reson. Imaging 2000;11:195–200.

Magnetic resonance imaging of pulmonary parenchymal disease using a modified breath-hold 3D gradient-echo technique: Initial observations

To determine the potential of a modified breath‐hold 3D gradient‐echo technique for visualizing pulmonary parenchymal diseases.

Accurate quantification of visceral adipose tissue (VAT) using water‐saturation MRI and computer segmentation: Preliminary results

To describe and evaluate the accuracy of water‐saturation MRI and a computer segmentation program for quantification of visceral adipose tissue (VAT).

ANTISCATTER GRIDS FOR LOW-ENERGY NEUTRON RADIOGRAPHY.

Background fogging from scattered neutrons is an inherent problem in neutron radiography of hydrogenous substances such as biological tissue (1, 2). This report describes the antiscatter grids that the authors have developed for thermal and epithermal neutron radiography. The design follows the standard technics used in roentgenography except for the choice of materials. Since aluminum is radiolucent to low-energy neutrons, it is employed to separate the neutron opaque planes that define the small acceptance solid angle. Cadmium and indium are the neutron opaque materials used for the thermal and epithermal grids, respectively. Because neutron capture in both cadmium and indium results in prompt gamma cascades, these grids are suggested primarily for neutron radiography tech nics utilizing image transfer foils (3). Atkins (2) has built a similar grid with boron as the opaque material. Even though this grid is significantly less efficient, gamma rays are not produced in boron; thus direct neutron radiograp...

In vivo estimation of gamma‐aminobutyric acid levels in the neonatal brain

Gamma‐aminobutyric acid (GABA) is the major inhibitory neurotransmitter in the brain, and plays a key role in brain development. However, the in vivo levels of brain GABA in early life are unknown. Using edited MRS, in vivo GABA can be detected as GABA+ signal with contamination of macromolecule signals. GABA+ is evaluated as the peak ratio of GABA+/reference compound, for which creatine (Cr) or water is typically used. However, the concentrations and T1 and T2 relaxation times of these references change during development. Thus, the peak ratio comparison between neonates and children may be inaccurate. The aim of this study was to measure in vivo neonatal brain GABA+ levels, and to investigate the dependency of GABA levels on brain region and age. The basal ganglia and cerebellum of 38 neonates and 12 children were measured using GABA‐edited MRS. Two different approaches were used to obtain GABA+ levels: (i) multiplying the GABA/water ratio by the water concentration; and (ii) multiplying the GABA+/Cr by the Cr concentration. Neonates exhibited significantly lower GABA+ levels compared with children in both regions, regardless of the approach employed, consistent with previous ex vivo data. A similar finding of lower GABA+/water and GABA+/Cr in neonates compared with children was observed, except for GABA+/Cr in the cerebellum. This contrasting finding resulted from significantly lower Cr concentrations in the neonate cerebellum, which were approximately 52% of those of children. In conclusion, care should be taken to consider Cr concentrations when comparing GABA+/Cr levels between different‐aged subjects.