Functional neuroimaging with diffusion-weighted MRI

第２４回　生体・生理工学シンポジウ

Effect of Cell Membrane Water Permeability on Diffusion-Weighted MR signal: a Study using Expression-controlled Aquaporin4 Cells

We performed multi-b-value and multi-diffusion-time DWI on AQP4-nonexpressed (noAQ) and AQP4-expressed (AQ) cells to investigate the effect that CMP has on diffusion-weighted magnetic resonance signal. Significant signal differences between the noAQ and AQ cells were observed only at high b-values. Diffusion-time dependent ADC changes were also observed, but there were no significant differences between the noAQ and AQ cell samples.ISMRM 20th Annual Meeting & Exhibitio

Diffusion-Weighted TE-dependent fMRI Signal in Rat Somatosensory Cortex at 7 T

Recently, diffusion-weighted (DW) fMRI signal changes have been reported to increase at high diffusion-weightings (b-values) [1-4]. It has been suggested that DW-fMRI signal courses might reflect vessel-size specific extravascular (EV) BOLD [1], persistent blood signal and changes in cerebral blood volume [2,3], or cell swelling directly linked to brain activation [4]. Berfication of any these mechanismsmight lead to a significantly enhanced understanding of the functional response. The aim of this study was to investigate the signal change dependency over a relatively broad range of imaging parameters. The experiments were performed on a-chloralose anaesthetised rats at 7 T using electrical forepaw stimulation with b-values in the range O-200 s/mm2 and echo-times of 30, 60 and 90 ms.17th Scientific Meeting & Exhibitio

Diffusion-weighted fMRI signal in rat somatosensory cortex at 7T

Diffusion-weighted fMRI has attracted some as a technique that might provide information more directly correlated with actual neural activity than BOLD fMRI.A number of interpretations have been proposed for the diffusion-weighted signal,however many questions remain unanswered.To further examine the dependence of fMRI on b-value,somatosensory forepaw stimulation was conducted on alpha-chloralose anesthetised rats at 7 T.Functional images were acquired at five b-values(b=0,200.800.1400and2000s/mm2)and two echo-times(TE=30and60ms). The mean signal changes from all rats showed a clear difference in signal amplitude between data acquired at differentTEs, although the response shape is qualitatively similar.In contrast to previous human data,the positive stimulus-correlated signal change and post-stimulus undershoot showed a slight downward (but insignificant)trend with increased b-value.Note that the undershoot persists for higher b-values.The IV contribution to the TE=60 ms data may be substantially attenuated because of the relatively short T2 of blood at7T.第36回日本磁気共鳴医学

Effect of Cell Membrane Water Permeability on Diffusion-Weighted MR Signal: A Study Using Expression-Controlled Aquaporin4 Cells

Diffusion-weighted magnetic resonance imaging (DWI) plays an important role in diagnosing diseases such as brain infarction and cancer. Although it is understood that signal attenuation is due to the diffusion of water molecules, a reliable quantitative signal model relating tissue parameters and signal contrast remains to be established. Cell membrane water permeability (CMP) is one factor that may affect DWI signal contrast. Aquaporin4 (AQP4) is a channel located in the cell membrane that is known to facilitate water exchange and therefore affect CMP and perhaps DWI contrast. In this study, we performed multi-b-value and multi-diffusion-time DWI on AQP4-nonexpressed (noAQ) and AQP4-expressed (AQ) cells to investigate the effect that CMP has on diffusion-weighted magnetic resonance signal

Compartmentalized Diffusion-Weighted Fmri Signal in Alpha-Chloralose Anesthetized Rat Somatosensory Cortex at 7 T.

2008 World Molecular Imaging Congres

Signal contributions to heavily diffusion-weighted functional magnetic resonance imaging investigated with multi-SE-EPI acquisitions.

Diffusion-weighted (DW) functional magnetic resonance imaging (fMRI) signal changes have been noted as a promising marker of neural activity. Although there is no agreement on the signal origin, the blood oxygen level dependent (BOLD) effect has figured as one of the most likely sources. In order to investigate possible BOLD and non-BOLD contributions to the signal, DW fMRI was performed on normal volunteers using a sequence with two echo-planar acquisitions after pulsed-gradient spin-echo. Along with the changes to the signal amplitude (ΔS/S) measured at both echo-times, this sequence allowed changes to the transverse relaxation rate (ΔR2) to be estimated for multiple b-values during hypercapnia (HC) and visual stimulation (VS). ΔS/S and ΔR2 observed during HC were relatively insensitive to increasing b-value. On the other hand, ΔS/S demonstrated a clear dependence on b-value at both echo-times for VS. In addition, ΔR2 during the latter half of VS was significantly more negative at b=1400s/mm(2) than for the time-courses at lower b-value, but ΔR2 during the post-stimulus undershoot was independent of b-value. The results have been discussed in terms of two models: the standard intravascular-extravascular model for fMRI and a three-compartment model (one intra- and two extravascular compartments). Within these interpretations the results suggest that the majority of the response is linked to changes in transverse relaxation, but possible contributions from other sources may not be ruled out

Effects of chewing on cognitive processing speed.

In recent years, chewing has been discussed as producing effects of maintaining and sustaining cognitive performance. We have reported that chewing may improve or recover the process of working memory; however, the mechanisms underlying these phenomena are still to be elucidated. We investigated the effect of chewing on aspects of attention and cognitive processing speed, testing the hypothesis that this effect induces higher cognitive performance. Seventeen healthy adults (20-34 years old) were studied during attention task with blood oxygenation level-dependent functional (fMRI) at 3.0 T MRI. The attentional network test (ANT) within a single task fMRI containing two cue conditions (no cue and center cue) and two target conditions (congruent and incongruent) was conducted to examine the efficiency of alerting and executive control. Participants were instructed to press a button with the right or left thumb according to the direction of a centrally presented arrow. Each participant underwent two back-to-back ANT sessions with or without chewing gum, odorless and tasteless to remove any effect other than chewing. Behavioral results showed that mean reaction time was significantly decreased during chewing condition, regardless of speed-accuracy trade-off, although there were no significant changes in behavioral effects (both alerting and conflict effects). On the other hand, fMRI analysis revealed higher activations in the anterior cingulate cortex and left frontal gyrus for the executive network and motor-related regions for both attentional networks during chewing condition. These results suggested that chewing induced an increase in the arousal level and alertness in addition to an effect on motor control and, as a consequence, these effects could lead to improvements in cognitive performance

Behaviour of Compartmentalized Diffusion-Weighted fMRI Signal from Human Brain during Hypercapnia

Recently, it has been suggested that diffusion-weighted fMRI could provide a more direct method of observing neuronal activity. In this study, signal originated from brain during hypercapnia and visual stimulation diffusion-weighted fMRI experiments was decomposed into intravascular, fast-diffusion phase, and slow-diffusion phase components. It was concluded that the slow-diffusion phase signal change must reflect the neural activation, although the exact mechanism remains unclear.16th Scientific Meeting & Exhibitio

Time-course of deltaR2 during visual stimulation and hypercapnia diffusion-weighted fMRI experiments

It has been suggested that the BOLD effect contributes to heavily diffusion-weighted (DW) fMRI signal changes. The BOLD effect is usually interpreted as a change in transverse relaxation rate (deltaR2). In this study, deltaR2 during visual stimulation (VS) and hypercapnia (HC) DW fMRI experiments was estimated using a multiple spin-echo EPI acquisitions after motion-probing gradients. deltaR2 showed dependence on b-value during VS, but not during HC. The results suggest that deltaR2 at high b-value may demonstrate a higher sensitivity to neuronal activation than at lower b-values.18th Scientific Meeting & Exhibitio