Diffusion Tensor Imaging (DTI) is an advanced magnetic resonance imaging (MRI) technique. DTI provides quantitative information at microstuructural level via its parameter indices e.g. mean diffusivity (MD) and fractional anisotropy (FA). It also allows for visualization of neuron fibres through a specific technique called fibre tractography. Leukoaraiosis is an asymptomatic pathological condition of the brain white matter which appears hyperintense on T2-weighted MRI images. Association of leukoaraiosis with age and ischemic heart disease have been previously reported. The objective of this study is to compare MD and FA values measured in various areas of the brain white matter (WM), grey matter (GM), and cerebrospinal fluid (CSF) in humans using DTI. 30 subjects with leukoaraiosis and 12 subjects without leukoaraiosis underwent brain scan using GE 1.5 Tesla MRI system. Region of interests were located in the CSF and various WM and GM areas. Comparison of MD and FA values was made between leukoaraiosis tissue (LA) and normal appearing brain tissue (NABT) measured within the same leukoaraiosis subjects, and with normal brain tissue (CONTROL) of healthy control subjects. LA demonstrated a significantly higher MD and lower FA compared to NABT and CONTROL in frontal and occipital WM areas. No differences were observed in MD in any brain region between NABT and CONTROL. Whereas no differences were observed in FA between NABT and CONTROL except in the occipital WM. Fibre tractography showed 31.7% to 56.1% lesser fibre tracts in LA subjects compared to CONTROL subjects. Significant differences were found between pathological tissue compared to normal appearing brain tissue and normal brain tissue. Fibre tractography exposed reduced number of neural fibres in leukoaraiosis subjects as compared to normal subjects.
Objective: A baseline functional magnetic resonance imaging (fMRI) study was carried out on a healthy right-handed male subject to attain further insights into the basic neuronal control mechanisms of bimanual and unimanual movements of hand fingers, an area that is still not fully understood. Methods : The study used the basic unimanual and bimanual movements of the left- and right-hand fingers to stimulate neuronal activity in the cerebral cortices. The subject was instructed to sequentially press his fingers either unimanually (UNI) or bimanually (BIM), against the thumb in a consistent alternative manner during the functional scans. The data were analysed using the MATLAB and SPM2 software packages. Results : Brain activations obtained via the F-test indicate a larger activation area as compared to that obtained from the T-test. The results showed that, the activated brain regions due to the self-paced finger movements are the precentral and postcentral gyrii covering the primary motor, premotor and somatosensory primer areas. The activestate signal intensity was found to be significantly (p < 0.05) higher than that of the resting-state. For UNI, brain activation showed contra-laterality with a larger activation area and a higher signal intensity at the point of maximum intensity for the left-hand finger
movement (UNIleft) compared to the right-hand finger movement (UNIright). Small ipsilateral activations were observed during UNIright and UNIleft. For BIM, the activation was observed in both hemispheres with the right hemisphere showing a higher signal intensity and coverage. The results support the fact that for a right-handed person performing either UNI or BIM type of movement, the activated motor area on the right hemisphere of the brain (movement of the left hand fingers) experience a higher intensity and larger coverage of hemodynamic response compared to the left hemisphere of the brain (movement of the right hand fingers). Analyses performed on the activated regions of interest (ROI) by
comparing the unimanual and bimanual types of activations revealed that during BIM, there are voxels in the left hemisphere controlling the movement of the left hand fingers (BIMleft) and voxels in the right hemisphere controlling the movement of the right hand fingers (BIMright). The interactions observed in this study resemble the existence of interhemispheric connection between both hemispheres during BIM. Conclusion : Although this is a single subject study, the hemodynamic response and the neuronal control mechanism in the cerebral cortices based on the BOLD mechanism can be studied and evaluated using fMRI and SPM.
Objective: This study investigates functional specialisation in, and effective connectivity between the
precentral gyrus (PCG) and supplementary motor area (SMA) in seven right handed female subjects.
Methods: Unimanual (UNIright and UNIleft) and bimanual (BIM) self-paced tapping of hand fingers were
performed by the subjects to activate PCG and SMA. Brain activations and effective connectivity were
analysed using statistical parametric mapping (SPM), dynamic causal modeling (DCM) and Bayesian
model selection (BMS) and were reported based on group fixed (FFX) and random (RFX) effects
analyses. Results: Group results showed that the observed brain activation for UNIright and UNIleft fulfill contralateral behavior of motor coordination with a larger activation area for UNIright. The activation for BIM occurs in both hemispheres with BIMright showing higher extent of activation as compared to BIMleft. Region of interest (ROI) analyses reveal that the number of activated voxel (NOV) and percentage of signal change (PSC) on average is higher in PCG than SMA for all tapping conditions. However, comparing between hemispheres for both UNI and BIM, higher PSC is observed in the right PCG and the left SMA. DCM and BMS results indicate that most subjects prefer PCG as the intrinsic input for UNIright and UNIleft. The input was later found to be bi-directionally connected to SMA for UNIright. The bi-directional model was then used for BIM in the left and right hemispheres. The model was in favour of six out of seven subjects. DCM results for BIM indicate the existence of interhemispheric connectivity between the right and left hemisphere PCG. Conclusion: The findings strongly support the existence of functional specialisation and integration i.e. effective connectivity in human brain during finger tapping and can be used as baselines in determining the probable motor coordination pathways and their connection strength in a population of subjects.
Optimum combination of voxel size resolution and b-value for whole brain imaging has been determined. Data images
were acquired using a 1.5T magnetic resonance imaging (MRI) system (GE Signa HDxt). Diffusion tensor imaging (DTI)
scan was performed on phantom and a human volunteer. Six protocols which consist of various combination of voxel
size and b-value were evaluated. Measurement of signal-to-noise ratio (SNR) and DTI parameter indices were carried out
for both phantom and in-vivo studies. Due consideration was given to a combination of parameters yielding sufficient
SNR with DTI values comparable to those obtained from previous reported studies. For the phantom study, SNR ≥ 20 was
found in all of the protocols except for a combination of voxel size of 2.0 × 2.0 × 2.0 mm3
with b-value of 1200 s/mm2
(V2.0 B1200) and that of voxel size of 2.0 × 2.0 × 2.0 mm3
with b-value of 1000 s/mm2
(V2.0 B1000). For in-vivo study,
all protocols presented SNR > 20. It was found that a combination of voxel size of 2.5 × 2.5 × 2.5 mm3
with b-value of
1000 s/mm2
(V2.5 B1000) and that of voxel size of 2.5 × 2.5 × 2.5 mm3
with b-value of 700 s/mm2
(V2.5 B700) displayed
the most comparable ADC and FA values with references. In terms of anatomic coverage, V2.5 B700 was found better
than V2.5 B1000 as it assures coverage of the whole brain. In conclusion, a combination of voxel size of 2.5 × 2.5 × 2.5
mm3
with b-value of 700 s/mm2
was considered as optimum parameters for brain DTI.
High sensitivity signal detection for a sparse temporal sampling (STS) functional magnetic resonance imaging (fMRI) is compensated by the increase in the number of scans (Ns) and consequently the scan time. A long scan time would result in fatigue and restlessness in participants, while a short scan time is undesirable for an STS-fMRI due to insufficient Ns for averaging. The purpose of this study was to determine the Ns practically sufficient for a sparse fMRI study. Eighteen participants were presented with white noise during a sparse fMRI scan. The height extent of activation was determined via t statistics and region of interest (ROI) based percentage of signal change (PSC). The t statistics and PSC for Heschl’s gyrus (HG) and superior temporal gyrus (STG) during which the participants listened to the white noise were calculated for different number of scans which were 6, 12, 18, 24, 30 and 36. The t statistics and PSC values calculated for the bilateral HG and STG qualitatively indicated a minimal change over Ns = 12 to 36. Both ROIs showed a consistent common right lateralization of activation for all Ns, indicating the right-hemispheric dominance of auditory cortex in processing white noise stimulus. It was proposed that for a sparse fMRI study, Ns may practically fall between 12 and 36