Biomedical subjects

B R Barker

Publications and source records attributed to B R Barker.

3 recordsLinked to original sources

PubMed1991

Absence of exercise-induced MRI enhancement of skeletal muscle in McArdle's disease.

To assess the role of glycogenolysis in mediating exercise-induced increases in muscle water as monitored by changes in muscle proton relaxation times on magnetic resonance imaging (MRI) and cross-sectional area (CSA), five patients with myophosphorylase deficiency (MPD) were compared with seven controls. Absolute and relative work loads were matched during ischemic handgrip and graded cycling, respectively. Relaxation times of active muscle did not increase after handgrip in MPD (T1: 1 +/- 14%, P greater than 0.1; T2: 4 +/- 4%, P greater than 0.1) but did in controls (T1: 59 +/- 30%, P less than 0.005; T2: 26 +/- 9%, P less than 0.005). The volume of exercised muscles, estimated by CSA, increased in both groups after handgrip (controls: 13.8 +/- 3.5%, n = 7, P less than 0.0001; MPD: 7.5 +/- 1.5%, n = 4, P less than 0.005), but the change was greater in controls (P less than 0.02). Ischemic handgrip in controls resulted in a large increase in finger flexor signal intensity (SI) on short tau-inversion recovery images (25 +/- 7%, n = 3; P less than 0.005 compared with preexercise) and a further increase with subsequent reflow (43 +/- 11%, n = 3; P less than 0.001 compared with rest); in MPD, SI did not increase. The ratio of active to inactive muscle SI did not increase from rest to maximal cycle exercise in MPD (0 +/- 20%, n = 2, P greater than 0.1) but did in normals (73 +/- 36%, n = 3; P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1987

Lipid/water ratio of bone marrow measured by phase-encoded proton nuclear magnetic resonance spectroscopy.

Proton NMR spectroscopy (spatially resolved) at 0.7 Tesla with a whole body superconducting magnet was performed on bone marrow from human lumbar spine to measure the lipid/water ratio. Phase-encoded proton spectroscopy was performed by using (1) a spin-echo sequence with selective 90 degrees and 180 degrees rf pulses on the Z and X axes; (2) 64 different phase encodes along the Y axis; and (3) echo acquisition with no gradient. The lipid/water ratios also were measured by the Folch chemical extraction technique. The set of phase-encoded spectra obtained from the spine demonstrates the chemical difference between the vertebral disk (large water peak and no lipid peak) and the marrow (smaller water peak and detectable lipids). Lipid/water ratios were lower than the chemically measured ratios. The phase-encoded proton spectroscopic technique presented in this study allowed rapid acquisition of localized spectra from the bone marrow in each of three vertebral bodies of the intact human spine. This technique provided a measure of the mobile lipid/water ratio weighted by relaxation times.

Body Water↗

PubMedDate not supplied

A MRI gradient waveform model for automated sequence calibration.

In order to set up magnetic resonance imaging (MRI) procedures of arbitrary voxel dimensions, slice orientation, and sequence timing in a reasonable time, some form of automatic gradient pulse calibration is required. One such method, involving simulation of gradient waveforms, is presented. Waveforms are modeled based on measurements of the step response. The model used divides each transition into three time regions: a "start" region in the first 0.3 ms, a "slew" region, and a "tail" region representing decay of the eddy current compensation error. In the "slew" region, the time derivative of the gradient, G' (t), is expressed as a function of G(t). The first two regions are nonlinear with respect to demand. The mean error in the simulated gradient is generally less than 0.04 mT m-1 in spin echo sequences. Image signal/noise ratios resulting from sequences calibrated using the model are within 5% of those of empirically calibrated sequences.

Calibration↗