Water diffusion measurements in perfused human hippocampal slices undergoing tonicity changes

Abstract

Diffusion MRI has the potential to probe the compartmental origins of MR signals acquired from human nervous tissue. However, current experiments in human subjects require long diffusion times, which may confound data interpretation due to the effects of compartmental exchange. To investigate human nervous tissue at shorter diffusion times, and to determine the relevance of previous diffusion studies in rat hippocampal slices, water diffusion in 20 perfused human hippocampal slices was measured using a wide-bore 17.6-T magnet equipped with 1000-mT/m gradients. These slices were procured from five patients undergoing temporal lobectomy for epilepsy. Tissue viability was confirmed with electrophysiological measurements. Diffusion-weighted water signal attenuation in the slices was well-described by a biexponential function (R 2 > 0.99). The mean diffusion parameters for slices before osmotic perturbation were 0.686 ؎ 0.082 for the fraction of fast diffusing water (F fast ), 1.22 ؎ 0.22 ؋ 10 -3 mm 2 /s for the fast apparent diffusion coefficient (ADC), and 0.06 ؎ 0.02 ؋ 10 -3 mm 2 /s for the slow ADC. Slice perturbations with 20% hypotonic and 20% hypertonic artificial cerebrospinal fluid led to changes in F fast of -8.2% and ؉10.1%, respectively (ANOVA, P < 0.001). These data agree with previous diffusion studies of rat brain slices and human brain in vivo, and should aid the development of working models of water diffusion in nervous tissue, and thus increase the clinical utility of diffusion MRI.

Microstructural changes in ischemic cortical gray matter predicted by a model of diffusion‐weighted MRI

“…Cell swelling induces changes of the extracellular tortuosity and, hence, to the ADC [9,10]. Our model predicts that an extracellular tortuosity of ϳ1.4 is associated with normal levels of ADC, as depicted in Fig.…”

“…The volume fractions did not agree with the fractions expected from histology (i.e., slow-diffusing intracellular fraction of ϳ80% and fast-diffusing extracellular fraction of ϳ20%). In the study by Shepherd et al (10), (using perfused human hippocampal slices) a distinct difference between the slow-and the fast-diffusion coefficient was shown using biexponential diffusion analysis, where the fast-diffusing component was ascribed to the largest cellular fraction. Similarly, Inglis et al (11) found the slow-and fast-diffusion components to be 44% and 56%, respectively, while spectroscopic T 2 relaxation measurements yielded volume fractions of 17% and 83% with values of 41 msec and 94 msec, respectively.…”

Magnetization transfer studies of the fast and slow tissue water diffusion components in the human brain

“…[1][2][3][4][5][6][7][8][9] These values represent a paradoxical reversal of what may be anticipated for the volume fractions if one assigns the fast diffusion coefficient component to the extracellular water and the slow diffusion coefficient component to the intracellular water. 38 However, even if these volume fractions appear to be opposite of what they should be for extra-and intracellular water, the direction of the change of the apparent volume fractions which have accompanied physiological manipulations of the actual intra-and extracellular compartments by stroke, 8 osmotic or pharmacological manipulation, 6,7 and development from newborn to adult, 5 have actually been consistent with this simple assignment. Indeed, using the Karger equations for a two-compartment model, which includes the effects of water exchange, 35 it is possible to consider moderate exchange rates.…”

“…[1][2][3][4][5][6] The assignment of the fast and slow tissue water diffusion components to extra-and intracellular water, respectively, has been discussed, if not universally espoused, as a possibility in these [1][2][3][4][5][6] and several other related works. [7][8][9][10][11][12][13][14][15] This assignment remains intriguing but controversial since restricted diffusion effects alone can lead to decay curves which appear to be biexponential in form but do not require an underlying assumption of two or more distinct water compartments. [15][16][17][18][19][20][21][22] We hypothesize that if the physical basis of empirically useful biexponential decay analyses is two distinct water compartments with widely disparate diffusion coefficients, then it would reasonably follow that the two compartments might have substantially different magnetization transfer ratios.…”

Transient signal changes in diffusion‐weighted stimulated echoes during neuronal stimulation at 3T

“…The b-values for the PRE are obtained by using T M ϭ 0 and replacing ⌬ STE with ⌬ PRE in Eqs. [11] and [12]. Sequence parameters are taken from Table 1.…”