O'Shea, Jacqueline Mary; (1998) Magnetic resonance imaging studies of cell volume changes in the isolated turtle cerebellum. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis examines the relationship between certain magnetic resonance image (MRI) parameters and the properties of brain tissue studied in vitro. The importance of this derives from the fact that various pathological conditions of brain tissue in vivo can be identified using MRI protocols, but the relationship to underlying physiological changes is easier to study in vitro. The anoxia resistant turtle cerebellum is free of haemodynamic effects and responds to anisosmotic challenge as an osmometer. Apparatus was developed to maintain this preparation within a MRI magnet. Hypotonic solutions, causing cell swelling, led to decreases in apparent diffusion coefficient (ADC) and increases in the MR relaxation time T2; cell shrinking was associated with increases in ADC and decreases in T2. These effects were compared with simple models of the dynamics of tissue compartments, diffusion and relaxation. The ADC data fitted a two compartment model, with fast exchange between extracellular (EC) and intracellular (IC) space. The relaxation data are not well fitted in this way and seem to involve interaction between relaxation and compartment volumes. Directional differences of ADC were observed in relation to tissue micro- and macrostructure. The MRI measurements were weakly anisotropic, although with the available techniques it was not possible to assign the effects in a clear manner to the known oriented and layered arrays of cerebellar cells. Techniques were applied to separate the signals from EC and IC compartments, using (i) an EC contrast agent (Gd-DTPA), and (ii) imaging techniques in which MR sequence parameters influence the visibility of water in a compartment. A lower ADC observed in the presence of the contrast agent is consistent with the conclusions from other data that ADCIC<ADCEC although interpretation of the data may be complicated by intercompartmental exchange and susceptibility effects due to the contrast agent.

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