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J Houseman

Publications and source records attributed to J Houseman.

7 recordsLinked to original sources
PubMed2000

The relationship between the apparent diffusion coefficient measured by magnetic resonance imaging, anoxic depolarization, and glutamate efflux during experimental cerebral ischemia.

A reduction in the apparent diffusion coefficient (ADC) of water measured by magnetic resonance imaging (MRI) has been shown to occur early after cerebrovascular occlusion. This change may be a useful indicator of brain tissue adversely affected by inadequate blood supply. The objective of this study was to test the hypothesis that loss of membrane ion homeostasis and depolarization can occur simultaneously with the drop in ADC. Also investigated was whether elevation of extracellular glutamate ([GLU]e) would occur before ADC changes. High-speed MRI of the trace of the diffusion tensor (15-second time resolution) was combined with simultaneous recording of the extracellular direct current (DC) potential and on-line [GLU]e from the striatum of the anesthetized rat. After a control period, data were acquired during remote middle cerebral artery occlusion for 60 minutes, followed by 30 minutes of reperfusion, and cardiac arrest-induced global ischemia. After either focal or global ischemia, the ADC was reduced by 10 to 25% before anoxic depolarization occurred. After either insult, the time for half the maximum change in ADC was significantly shorter than the corresponding DC potential parameter (P < 0.05). The [GLU]e remained at low levels during the entire period of varying ADC and DC potential and did not peak until much later after either ischemic insult. This study demonstrates that ADC changes can occur before membrane depolarization and that high [GLU]e has no involvement in the early rapid ADC decrease.

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PubMed1997

Localized q-space imaging of the mouse brain.

Localized q-space imaging was used to obtain water displacement profiles from mouse brain. These profiles take the form of unidirectional diffusive displacement probability distributions. Two groups of mice were studied, a normal group and a group in which surgery had been performed to produce a unilateral reduction in the supply of blood to the forebrain. q-Space measurements were made both in vivo and postmortem. The displacement profiles were characterized using the summary parameter prob[d < 10], which is the proportion of water molecules that undergo a net diffusive displacement that is less than +/-10 microm, during the diffusion period (50 ms). The range of prob[d < 10] values in the normal group was 0.71 to 0.77 in vivo compared with 0.78 to 0.87 in the impaired hemisphere of the surgically treated group. An increase in prob[d < 10] occurred postmortem to yield values in the range 0.79 to 0.81 and 0.80 to 0.89 in the normal and surgically treated group, respectively. These observations are consistent with the diffusion-weighted image intensity changes that occur after a period of ischemia.

Animals↗
PubMed1994

q-Space imaging of the brain.

q-Space imaging (Callaghan, J. Magn. Reson. 88, 493 (1990)) has been used to obtain mouse brain water displacement profiles. These profiles take the form of a unidirectional incoherent-displacement probability density distribution. Two groups of mice were studied, a normal group and one in which surgery had been performed to reduce the supply of blood to the forebrain. In the normal group the incoherent displacement of water was reduced postmortem. Four of the surgically treated mice yielded displacement profiles that resembled those obtained postmortem; the remaining two were near normal. This study demonstrates the feasibility of in vivo q-space imaging. The displacement profile changes that occur subsequent to an interruption of the forebrain blood supply are consistent with the hyperintensity changes seen in diffusion-weighted imaging.

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PubMed1994

Monitoring the initial expansion of focal ischaemic changes by diffusion-weighted MRI using a remote controlled method of occlusion.

The purpose of the present study was to quantify the early changes which occur on diffusion-weighted imaging following focal cerebral ischaemia. We have developed a method for the remote occlusion of the middle cerebral artery in the rat, allowing early changes to be monitored and images to be acquired before and after ischaemia under identical conditions. Sequential diffusion-weighted images were acquired before and for up to 6 h following the occlusion. The data show that a hyperintense area appears soon after occlusion which expands during the first 2 h. It has previously been shown that the hyperintensity observed after ischaemia is linked to events associated with energy failure. Our findings are in good agreement with previous pathophysiological studies of focal ischaemia, which suggest a growing of the energy depleted area. In conclusion, our data extend the usefulness of diffusion-weighted imaging to the study of the early spatial evolution of the most compromised area after focal ischaemia. Diffusion-weighted imaging may constitute a very powerful tool to investigate pharmacological therapies which may interact with this evolution, both in experimental and clinical studies.

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PubMed1992

Perfusion and diffusion MR imaging.

Diffusion-weighted images of the rat brain were obtained using the pulsed-gradient spin-echo method. An attempt was made to extract perfusion-related parameters from signal intensity data taken from the caudate-putamen region of the images, by using a nonlinear least-squares calculation to fit the Le Bihan biexponential expression (Le Bihan et al., Radiology, 168, 497 (1988)) to the data. The perfusion-related parameters could not be obtained with sufficient accuracy to be useful, although the perfusion-weighted images appear to contain meaningful qualitative information. An analysis of the perfusion model is presented and shows why the Le Bihan pseudo-diffusion coefficient is particularly difficult to measure with reasonable accuracy.

Animals↗
PubMed1985

Retinal blood flow in the cat following periods of light and darkness.

Estimates of flow velocity in retinal arterioles of seven cat eyes were obtained using high-speed cine Indocyanine Green absorption angiography in the near-infra-red waveband, following alternate 30 min periods of light and darkness. Simultaneous estimates of vessel calibre were obtained by micrometry of the cine image. Comparisons of values obtained after periods of light adaptation with the preceeding and subsequent periods of darkness show no significant changes in vessel calibre (at P greater than 0.95 level, confidence limits +/- 17% of the mean) while three of 14 comparisons show significant but inconsistent changes in linear flow velocity (at P greater than 0.95 level, confidence limits +/- 22% of the mean). A significant decrease (41%) in b-wave amplitude was seen in six of seven experiments after dark adaptation subsequent to exposure to light for a total of 60 min.

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