Quantative analysis of brain white matter using diffusion tensor imaging

Penyelidikan ini mengenai aplikasi pengimejan tensor difusi (DTI) dalam kajian tentang leukoaraiosis dan jirim putih normal. Empat objektif utama yang telah digariskan dalam kajian ini telah tercapai. Sebuah fantom kepala telah digunakan dan sejumlah 15 subjek normal dan 51 subjek leukoaraiosis telah mengambil bahagian dalam kajian ini. Sejumlah 5128 hirisan telah dianalisis dalam kerja ini. Pengimejan otak telah dijalankan menggunakan sistem pengimejan resonan magnet (MRI) 1.5 Tesla. Keupayaan mendapatkan data DTI dan membina trektografi gentian untuk kajian leukoaraiosis telah dikaji. Hasil yang didapati menunjukkan kebolehan DTI untuk membezakan leukoaraiosis daripada jirim putih normal. Trektografi gentian telah menunjukkan perbezaan struktur yang jelas bagi gentian saraf dalam kawasan jirim putih. Dapat disimpulkan data DTI dan pembinaan trektografi gentian untuk penilaian leukoaraiosis didapati boleh dilaksanakan. This research is concerned with the application of diffusion tensor imaging (DTI) in the study of leukoaraiosis and normal white matter. Four main objectives outlined in the study have been achieved. A head phantom was used and a total of 15 normal subjects and 51 leukoaraiosis subjects participated in the study. A total of 5128 slices were analysed in this work. Brain imaging was performed using 1.5 Tesla MRI system. Feasibility of acquiring DTI data and constructing fiber tracts for leukoaraiosis study was investigated. Results obtained showed capability of DTI to distinguish leukoaraiosis from normal white matter. Fiber tractography exhibited a good structural differentiation of nerve fibers in the white matter region. Acquiring DTI data and constructing fiber tractography for assessment of leukoaraiosis was found to be feasible

Determination of optimum combination of voxel size and b-value for brain diffusion tensor imaging

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

A Review: Photonic Devices Used for Dosimetry in Medical Radiation

Numerous instruments such as ionization chambers, hand-held and pocket dosimeters of various types, film badges, thermoluminescent dosimeters (TLDs) and optically stimulated luminescence dosimeters (OSLDs) are used to measure and monitor radiation in medical applications. Of recent, photonic devices have also been adopted. This article evaluates recent research and advancements in the applications of photonic devices in medical radiation detection primarily focusing on four types; photodiodes – including light-emitting diodes (LEDs), phototransistors—including metal oxide semiconductor field effect transistors (MOSFETs), photovoltaic sensors/solar cells, and charge coupled devices/charge metal oxide semiconductors (CCD/CMOS) cameras. A comprehensive analysis of the operating principles and recent technologies of these devices is performed. Further, critical evaluation and comparison of their benefits and limitations as dosimeters is done based on the available studies. Common factors barring photonic devices from being used as radiation detectors are also discussed; with suggestions on possible solutions to overcome these barriers. Finally, the potentials of these devices and the challenges of realizing their applications as quintessential dosimeters are highlighted for future research and improvements

Modeling and simulation of blood flow analysis on simplified aneurysm models

Nowadays, the cerebral aneurysm is an abnormal focal dilation of a brain artery which is considered as a serious and potentially life-threatening condition. The rupture of an aneurysm causes subarachnoid hemorrhage (SAH) and is associated with high rates of morbidity and mortality. A better understanding of the mechanisms underlying aneurysm pathophysiology is crucial for the development of new preventive procedures and therapeutic strategies. This study focuses on the modeling and simulation of the blood flow analysis using simplified aneurysm models to perform early prediction on the geometrical effects of hemodynamics. The investigation involves three simplified models of aneurysms reconstructed using Solidworks 2019, in which the aneurysms are developed at the bifurcation. The qualitative comparison of the hemodynamics between three models was obtained and the geometrical effects were evaluated. The results show that the differences in shape and geometry on aneurysms affect the hemodynamics trend and are capable to apply for further understanding of problems regarding hemodynamics in the patient

Study of extracted geometry effect on patient-specific cerebral aneurysm model with different threshold coefficient (Cthres)

The recent diagnostic assessment of cerebrovascular disease makes use of computational fluid dynamics (CFD) to quantify blood flow and determine the hemodynamics factors contributing to the disease from patient-specific models. However, compliant and anatomical patient-specific geometries are generally reconstructed from the medical images with different threshold values subjectively. Therefore, this paper tends to present the effect of extracted geometry with different threshold coefficient, Cthres by using a patient-specific cerebral aneurysm model. A set of medical images, digital subtraction angiography (DSA) images from the real patient diagnosed with internal carotid artery (ICA) aneurysm was obtained. The threshold value used to extract the patient-specific cerebral aneurysm geometry was calculated by using a simple threshold determination method. Several threshold coefficients, Cthres such as 0.2, 0.3, 0.4, 0.5 and 0.6 were employed in the image segmentation creating three-dimensional (3D) realistic arterial geometries that were then used for CFD simulation. As a result, we obtained that the volume of patient-specific cerebral aneurysm geometry decreases as the threshold coefficient, Cthres increases. There is dislocation of artery attached to the ICA aneurysm geometry occurred at a high threshold coefficient, Cthres. Besides, the physical changes also bring remarkable physiological effect on the wall shear stress (WSS) distribution and velocity flow field at patient-specific cerebral aneurysm geometry reconstructed with different threshold coefficient, Cthres

Modeling and simulation of blood flow analysis on simplified aneurysm models

Nowadays, the cerebral aneurysm is an abnormal focal dilation of a brain artery which is considered as a serious and potentially life-threatening condition. The rupture of an aneurysm causes subarachnoid hemorrhage (SAH) and is associated with high rates of morbidity and mortality. A better understanding of the mechanisms underlying aneurysm pathophysiology is crucial for the development of new preventive procedures and therapeutic strategies. This study focuses on the modeling and simulation of the blood flow analysis using simplified aneurysm models to perform early prediction on the geometrical effects of hemodynamics. The investigation involves three simplified models of aneurysms reconstructed using Solidworks 2019, in which the aneurysms are developed at the bifurcation. The qualitative comparison of the hemodynamics between three models was obtained and the geometrical effects were evaluated. The results show that the differences in shape and geometry on aneurysms affect the hemodynamics trend and are capable to apply for further understanding of problems regarding hemodynamics in the patient

Study of extracted geometry effect on patient-specific cerebral aneurysm model with different threshold coefficient (Ctℎres )

The recent diagnostic assessment of cerebrovascular disease makes use of computational fluid dynamics (CFD) to quantify blood flow and determine the hemodynamics factors contributing to the disease from patient-specific models. However, compliant, and anatomical patient-specific geometries are generally reconstructed from the medical images with different threshold values subjectively. Therefore, this paper tends to present the effect of extracted geometry with different threshold coefficient, Ctℎres by using a patient-specific cerebral aneurysm model. A set of medical images, digital subtraction angiography (DSA) images from the real patient diagnosed with internal carotid artery (ICA) aneurysm was obtained. The threshold value used to extract the patient-specific cerebral aneurysm geometry was calculated by using a simple threshold determination method. Several threshold coefficients, Ctℎres such as 0.2, 0.3, 0.4, 0.5 and 0.6 were employed in the image segmentation creating three-dimensional (3D) realistic arterial geometries that were then used for CFD simulation. As a result, we obtained that the volume of each patient-specific cerebral aneurysm geometry decreases as the threshold coefficient, Ctℎres increases. There is dislocation of artery attached to the ICA aneurysm geometry occurred at a high threshold coefficient, Ctℎres . Besides, the physical changes also bring remarkable physiological effect on the wall shear stress (WSS) distribution and velocity flow field at the patient-specific cerebral aneurysm geometry reconstructed with different threshold coefficient, Ctℎre

Investigation into Physical and Pathophysiological Changes of Hemodynamics on Segmented Patient-Specific Cerebral Aneurysm Models through Computational Analysis

Growth and rupture of human cerebral aneurysm are risky as both of these stages may lead to human organ dysfunction arisen from neurological disorders. The rupture of cerebral aneurysm can even lead to fatal hemorrhaging and other serious health issues. Several sets of medical images from patients have been utilized to reconstruct patient-specific cerebral aneurysm model geometries with different threshold value through image segmentation for computational analysis. In this paper, the physical and pathophysiological changes on hemodynamics, namely geometry volume, inlet area, outlet area, wall shear stress (WSS) distribution, and velocity flow field in the particular models are discussed. A prediction on the location where the aneurysm grows and ruptures has been made. Besides, the model geometries have been validated with varied mesh size. The simulation results show that the mesh size which is applied on the model geometry has significant effect on the generated WSS and velocity values, when varying within certain range. From the findings, the mesh size is one of the important elements which should be optimized, other than the threshold value used for model geometry reconstruction

Reconstruction of patient-specific cerebral aneurysm model through image segmentation

The diagnostic assessment of cerebrovascular disease makes use of computational simulation as a predicting tool to determine hemodynamics factor contributing to the disease from patient-specific models which imitate the actual shape of the object of interest. However, the patient-specific models are generally reconstructed from the medical images subjectively. Image segmentation is commonly performed to produce object of interest with high visualization. In order to produce patient-specific anatomical model, a systematic adjustment on image intensity was performed in this study. This paper tends to present the reconstruction of three-dimensional (3D) patient-specific cerebral aneurysm model through systematic image segmentation by using threshold coefficients

Relationship between volume of leukoaraiosis spot and degree of tissue damage: a quantitative diffusion tensor imaging study

Diffusion tensor imaging (DTI) offers parameter indices, namely, mean diffusivity (MD) and fractional anisotropy (FA). Leukoaraiosis is a brain white matter hyperintensity as observed on fluid-attenuated inversion recovery (FLAIR) images. In this study, we attempt to assess leukoaraiosis at its specific spot using a new parameter, namely, lesion-to-normal appearing white matter ratio (LNR). LNR was then used to investigate the relationship between the volume of leukoaraiosis spot and the degree of tissue damage. This study involved 49 leukoaraiosis subjects who altogether contributed to 274 leukoaraiosis spots. The MD, FA, and volume were measured at each spot. LNR was calculated by comparing the MD values of the spot with those of the surrounding normal-appearing white matter (NAWM). The correlation between MD, FA, and LNR with leukoaraiosis volume was then analysed. The leukoaraiosis tissues generally exhibited higher MD (103.97 ± 12.32 × 10-5 mm2/s) and lower FA (0.31 ± 0.08) values than the NAWM tissues (79.30 ± 4.76 × 10-5 mm2/s and 0.41 ± 0.09, respectively). LNR values were found to range from 0.04 to 1.63. The results showed an insignificant association between the leukoaraiosis volume and LNR [r = −.055, p = .368], whereas a very weak association was shown with MD [r = −.196,p =.001] and FA [r = .268, p < .001]. The volume of the leukoaraiosis spot does not necessarily indicate the degree of tissue damage. By using LNR instead of MD, an accurate analysis was performed since the variability of MD for NAWM surrounding the lesion is taken into account