Ahmad Nazlim Yusoff

This study observed the properties of gelatin as tissue-mimicking materials for quality assessment of image quality in the quantitative T2 MRI method. Images for spin-spin relaxation time (T2) measurement were acquired using MRI 3 Tesla system. T2 values were measured by acquiring T2 images from gelatin samples as tissue-mimicking materials with five different concentrations: 10%, 15%, 20%, 25%, and 30%. The decay rate of signal intensity values over various echo-time (TE) was used to plot an exponential graph for T2 values, with spin-spin relaxation rate (R2) as the reciprocal of T2. The signal intensities and T2 values were observed to determine the relation between gelatin concentration and those parameters. The gelatin concentration is inversely proportional to T2 value, but no relation is found between gelatin concentration and signal intensity. The result shows that gelatin concentration of 30% has potential for tissue-mimicking materials for white matter and spinal cord. This study is potentially developed for further studies of tissue-mimicking materials for phantom development in quantitative MRI.

This study aimed to investigate different short-term memory capacities (STMC) on resting brain of healthy individuals particularly the neuropsychology and connectivity behaviors. The outcomes may serve as a baseline for clinical diagnosis of memory decline due to aging and mental disorders. It was hypothesized that resting brain of low and typical STMC individuals behaves differently. Thirty-nine healthy young male adults were recruited from local universities. They were categorized as typical or low STMC based on their scores in the Malay Version of the Auditory-Verbal Learning Test (MVAVLT). A resting-state functional magnetic resonance imaging (rs-fMRI) was conducted and data were analyzed using statistical parametric mapping (SPM) and dynamic causal modeling (DCM). Nine neuropsychological assessments were significantly higher (p < 0.05) in typical STMC participants compared with low STMC participants. Four activation clusters survived the contrast "Low > Typical" uncorrected at set and cluster levels threshold (p_FWE < 0.05). A causal model containing these clusters as nodes found that there is no preference on negative or positive connectivity among typical and low STMC groups. Nevertheless, implementing a reduced connection scheme revealed more significant connections for the low STMC group. To conclude, the low STMC participants scored lower in all neuropsychological assessments, but a higher activation profile with more areas being connected effectively as compared with the typical STMC group. The results suggest a higher resting neural activity and communication among certain brain areas in low STMC individuals that the brain could have executed as a compensation strategy.

Object This study aimed to evaluate the relaxivity and uniformity of agarose gel phantoms added with relaxation modifiers. It is hypothesized that the modifiers could manipulate the T1 and T2 relaxations as well as the signal uniformity. Materials and methods Twenty agarose gel phantoms with different GdCl₃ and FeCl₃ volume fractions were prepared. The phantoms were scanned using a 3-T scanner implementing a turbo spin echo sequence to acquire T1 and T2 images. The SNR of the images were computed using Image-J software from 1, 3, and 25 regions-of-interest (ROIs) and were inverted as T1 and T2 curves. Results With the increase in relaxation modifier content, T1 SNR increased at a faster rate at very short TR and reached saturation at TR well below 400 ms. Agarose gel phantoms containing GdCl₃ showed a higher saturation value as compared to phantoms containing FeCl₃. For T2 SNR, differences between plots are observed at low TE. As TE gets larger, the SNR between plots is incomparable. The SNR for both groups was uniform among 1, 3, and 25 ROIs. Discussions It can be concluded that GdCl₃ and FeCl₃ solutions can be used as effective relaxation modifiers to reduce T1 but not T2 relaxation times.

Background: Resting-state functional magnetic resonance imaging (rs-fMRI) can evaluate brain functional connectivity without requiring subjects to perform a specific task. This rs-fMRI is very useful in patients with cognitive decline or unable to respond to tasks. However, long scan durations have been suggested to measure connectivity between brain areas to produce more reliable results, which are not clinically optimal. Therefore, this study aims to evaluate a shorter scan duration and compare the scan duration of 10 and 15 min using the rs-fMRI approach. Methods: Twenty-one healthy male and female participants (seventeen right-handed and four left-handed), with ages ranging between 21 and 60 years, were recruited. All participants underwent both 10 and 15 min of rs-fMRI scans. The present study evaluated the default mode network (DMN) areas for both scan durations. The areas involved were the posterior cingulate cortex (PCC), medial prefrontal cortex (mPFC), left inferior parietal cortex (LIPC), and right inferior parietal cortex (RIPC). Fifteen causal models were constructed and inverted using spectral dynamic causal modelling (spDCM). The models were compared using Bayesian Model Selection (BMS) for group studies. Result: The BMS results indicated that the fully connected model was the winning model among 15 competing models for both 10 and 15 min scan durations. However, there was no significant difference in effective connectivity among the regions of interest between the 10 and 15 min scans. Conclusion: Scan duration in the range of 10 to 15 min is sufficient to evaluate the effective connectivity within the DMN region. In frail subjects, a shorter scan duration is more favourable.

Background: Agar has been commonly used as one of the materials to fabricate magnetic resonance imaging phantoms in the past few decades. In this study, eleven agar gel phantoms with different iron (III) oxide (Fe₂O₃) masses were prepared. This study was aimed to evaluate the signal-to-noise ratio (SNR) uniformity and stability of agar gel phantoms with and without the addition of Fe₂O₃ at two different time points (TPs). Fe₂O₃ powder was used as a relaxation modifier to manipulate and produce various SNR, T1 and T2 values. These phantoms were scanned using turbo spin echo pulse sequence to produce T1- and T2-measurement images. The SNR was then computed by plotting 1, 3 and 25 regions of interest on the images using ImageJ software. The T1 and T2 relaxation equations were then fitted to the experimental results of SNR versus TR and SNR versus TE curves for the determination of saturation (SNR_o), T1 and T2 values. Results: The results demonstrated that the agar gel phantoms were able to maintain SNR uniformity but not SNR stability after 4 weeks of phantom preparation. The change in the water content and microstructure of the phantoms have no significant effect on T2 relaxation but on T1 relaxation. The T1 and T2 of the agar gel phantoms were minimally affected although there was a systemic increase in the content of the Fe₂O₃ powder. Conclusions: It can be concluded that the agar gel phantoms exhibited the characteristics of SNR uniformity, but they showed instability of SNR at TP2. The Fe₂O₃ in powder form is not an effective relaxation modifier to reduce the T1 and T2 when it is introduced into the agar gel phantoms. Dissolved nanosized particles should be the focus of future studies.

The present study examined the impact of white noise on word recall performance and brain activity in 40 healthy adolescents, split in two groups (normal and low) depending on their auditory working memory capacity (AWMC). Using functional magnetic resonance imaging, participants performed a backward recall task under four different signal-to-noise ratio (SNR) conditions: 15, 10, 5, and 0-dB SNR. Behaviorally, normal AWMC individuals scored significantly higher than low AWMC individuals across noise levels. Whole-brain analyses showed brain activation not to be statistically different between groups across noise levels. In the normal group, a significant positive relationship was found between performance and number of activated voxels in the right superior frontal gyrus. In the low group, significant positive correlations were found between performance and number of activated voxels in left superior frontal gyrus, left inferior frontal gyrus, and left anterior cingulate cortex. These findings suggest that the strategic structure involved in the enhancement of AWM performance may differ in normal and low AWMC individuals.

Magnetic resonance signal change is expected to be different between normal, glaucoma suspect (GS) and Primary Open Angle Glaucoma (POAG) subjects. Functional magnetic resonance imaging (fMRI) technique was employed to investigate the differences. This multiple subject studies were carried out to characterize the percentage of signal change (PSC) in Brodmann Area (BA) 17, 18 and 19 of the visual cortex. The block designed fMRI was implemented. The subjects were requested to focus on the black and white checkerboard stimulus of the visual world (A, B and CD), visual field (EF) and visual area (G). The data were analysed using Statistical Parametric Mapping (SPM8) via Matlab platform. results showed that GS subjects have the highest PSC, followed by normal and POAG subjects. However, no significant difference was observed in PSC between BA17, 18 and 19 for normal, GS and POAG groups with p = 0.0869, p = 0.0688 and p = 0.2690, respectively. In conclusion, none of the BA can be suggested to be the most dominant area in responding to the visual stimuli used in this study.

Enhancing divergent thinking skills via creativity stimulation training has proven to increase performance in creativity, and caused changes in neuronal responses. However, the studies on effective connectivity between these regions has yet to be explored. This study aims to identify the most optimum connectivity model between left angular gyrus (AG), left precuneus (PCU) and medial prefrontal cortices (mPFC) during divergent thinking task in 36 healthy volunteers. All participants performed a behavioral alternative use test (AUT) and were divided into two groups, in which experimental group received creativity training, and control group were void of it. Both groups then underwent functional magnetic resonance imaging (fMRI) data acquisition, in which participants were instructed to alternative use test (AUT) of the common household object visually projected to them in the MRI bore. Post-fMRI AUT assessment was also done. Data were analysed using Statistical Parametric Mapping (SPM12) and Dynamic Causal Modelling (DCM12.5) software. Findings revealed full bidirectional connectivity between left AG, left PCU and mPFC during execution of alternative use generation. Creativity stimulation training has impacted in the change of input centre to be on left AG in the control group and mPFC in the experimental group, implying different divergent thinking strategies among participants who attended the creativity training.