Woon-Kwan Chung

A Study on Comparison of Cardiac Ejection Fraction Values Measured in Myocardium SPECT and Cine MRI

This study examined the correlation between MR cine and myocardium Single-photon emission computed tomography (SPECT) by comparing the measured cardiac ejection fractions. The usefulness of cardiac MRI was also evaluated. Ten patients (8 men, 2 women and average age of 58.6 years), who underwent a myocardium SPECT scan and cardiac cine MRI scan among patients who visited the hospital for the chief complaint of cardiac disorder from June 1, 2010 to February 10, 2011, were enrolled in this study. The cardiac ejection fraction was calculated from the images obtained in both scans. The data was used to examine the correlation. The regression equation the cardiac ejection fraction values of the 10 patients obtained in myocardium SPECT and MRI cine was Y = 1.12X�8.91 (R 2 = 0.78, significance of F = 0.001639, and confidence level of 95%). The results were significant when the cardiac ejection fraction obtained from MRI cine was compared with that obtained from myocardium SPECT. Overall, a cardiac examination using MRI enables an investigation of not only the ejection fraction but also the ED and ES volumes, stroke volume, wall thickness, and wall thickening in a higher spatial resolution despite the examination being conducted once. This examination is believed to be very useful for diagnosing patients with cardiac disease.

Studies on the Ability to Detect Lesions According to the Changes in the MR Diffusion Weighted Images

This study evaluated the ability of Diffusion-Weight Image (DWI), which is one of pulse sequences used in MRI based on the T2 weighted images, to detect samples placed within phantoms according to their size. Two identically sized phantoms, which could be inserted into the breast coil bilaterally, were prepared. Five samples with different sizes were placed in the phantoms, and the T2 weighted images and DWI were obtained. The Breast 2 channel coil of SIEMENS MAGNETOM Avanto 1.5 Tesla equipment was used for the experiments. 2D T2 weighted images were obtained using the following parameters: TR/TE = 6700/74 msec, Thickness/gap = 5/1 mm, Inversion Time (TI) = 130 ms, and matrix = 224 × 448. The parameters of DWI were that TR/TE = 8100/ 90 msec, Thickness/gap = 5/1 mm, matrix = 128 × 128, Inversion Time = 185 ms, and b-value = 0, 100, 300, 600, 1000 s/mm. The ratio of the sample volume on DWI compared to the T2 weighted images, which show excellent ability to detect lesions on MR images, was presented as the mean b-value. The measured b-value of the samples was obtained: 0.5 × 0.5 cm = 0.33/0.34 square × cm (103%), 1 × 1 cm = 1.28/1.25 square × cm (102.4%), 1.5 × 1.5 cm = 2.28/2.67 square x cm (85.39%), 2 × 2 cm = 3.56/4.08 square x cm (87.25%), and 2.5 × 2.5 cm = 7.53/8.77 square × cm (85.86%). In conclusion, the detection ability by the size of a sample was measured to be over 85% compared to T2 weighted image, but the detection ability of DWI was relatively lower than that of T2 weighted image.

Dose assessment according to changes in algorithm in cardiac CT

The principal objective of this study was to determine the effects of the application of the adaptive statistical iterative reconstruction (ASIR) technique in combination with another two factors (body mass index (BMI) and tube potential) on radiation dose in cardiac computed tomography (CT). For quantitative analysis, regions of interest were positioned on the central region of the great coronary artery, the right coronary artery, and the left anterior descending artery, after which the means and standard deviations of measured CT numbers were obtained. For qualitative analysis, images taken from the major coronary arteries (right coronary, left anterior descending, and left circumflex) were graded on a scale of 1–5, with 5 indicating the best image quality. Effective dose, which was calculated by multiplying the value of the dose length product by a standard conversion factor of 0.017 for the chest, was employed as a measure of radiation exposure dose. In cardiac CT in patients with BMI of less than 25 kg/m2, the use of 40% ASIR in combination with a low tube potential of 100 kVp resulted in a significant reduction in the radiation dose without compromising diagnostic quality. Additionally, the combination of the 120 kVp protocol and the application of 40% ASIR application for patients with BMI higher than 25 kg/m2 yielded similar results.

Survey on low-dose medical radiation exposure in occupational workers: the effect on hematological change

This study examined the changes in the hematological index caused by low-dose medical radiation exposure in workers in a medical radiation-exposed environment. The cumulative dose was obtained using thermoluminescent dosimeters over a 9-year period, and the changes in hematological index count (red blood cells (RBCs), hemoglobin, platelets, white blood cells (WBCs), monocytes, lymphocytes, neutrophils, basophils, and eosinophils) were examined in both the occupational workers and controls. In total, 370 occupational workers and 335 controls were compared. The analysis led to the following observations: (1) The average cumulative dose in males and females was 9.65±15.2 and 4.82±5.55 mSv, respectively. (2) In both males and females, there was a very low correlation between the occupation period and the cumulative dose (r<±0.25). (3) When the occupation period was longer, the WBC counts both decreased and increased in the male workers and the RBC counts were lower in the workers than in the control group (p<0.05). In females, the WBC counts both decreased and increased in the workers and the eosinophil counts were lower in the workers than in the control group (p<0.01). (4) When the cumulative dose was large, the lymphocyte counts decreased in male workers and the platelet count was lower in the workers than in the control group (p<0.05). In females, the lymphocyte count and RBC count were lower in the workers than in the control group (p<0.05). Abnormal distributions of some blood indices were observed in the occupational radiation workers compared with the controls. Attempts were made to limit radiation exposure to personnel, but the employees did not always follow the preset rules. Actually, the adverse effects of low-level radiation were attributed to probability. Overall, workers should obey the radiation protection regulations provided by the government and a national system of radiation protection is needed.

Evaluation of the radiation dose to a phantom for various X-ray exposure factors performed using the dose area product in digital radiography

The aim of this study is to measure the dose area product (DAP) in digital radiography by using a DAP meter to determine the X-ray exposure. Pediatric X-ray examinations can be obtained for any radiographic examinations using the selected radiographic examination parameters (kVp and mAs), the DAP information recorded. The best peak signal-to-noise ratio (PSNR) at a fixed tube voltage of 70 kVp was obtained at tube currents of 20 and 32 mA, whereas the best PSNR at a fixed tube current of 25 mA was obtained at a tube voltage of 73 kVp. The fixed tube voltage of 70 kVp and the fixed tube current of 25 mA could help to obtain the best image quality and depict the spatial resolution of an anthropomorphic torso phantom radiographic examination. The normalized data over the DAP were provided to determine the patient dose from radiography.

A PC-based water level controller for nuclear steam generators

Abstract An adaptive control was proposed early by Na and No (1990) for the control of the water level of steam generators. In this work the algorithm of the controller is changed a little. In order to know if this controller is robust in modeling errors and in high frequency measurement noises in controlling the water level of steam generators, a scaled-down steam generator is made which has the dimension of nearly one-tenth of the reference height and pressure, and 1/10,000 of its power. The controller is studied experimentally by implementing it to the mock-up of a nuclear steam generator. It is known that the controller is robust in unmodelled dynamics.

The Study of Radiation Damage Mechanism on Ultra-Structures of Leukocytes and Platelets in Rat Cells

ABSTRACT The principal objective of this study was to assess the mechanisms relevant to radiation-induced damage to multicore leukocytes and platelets, using a Transmission Electron Microscope (TEM). In this study, in the group subjected to 5 Gy irradiation, platelet size was reduced by 25%, and the cell membranes were thick and not clearly visible. On the 20-day and 30-day observations, passed leukocytes and mitochondrial damage were shown to be increased. The mass of glycogen granules was also reduced. In the 7 Gy irradiation group, platelet size was even more profoundly reduced. In the erythrocytes, most echinocytes, which generally exhibit burrs, were irregularly shaped, and sickle cells were observed. In the observation of leukocytes, no evidence of radiation damage was detected in the primary or secondary granules. Damage to the nuclear membrane and cell membrane was increased. The outline of the centrosome was somewhat dim. In the 7 Gy irradiation group, no damage was detected in specific granules of the basophil. Phagocytosis of amoebal movement was observed. In some parts of the lymphocyte, nuclei were divided or formed a space between the nucleus and cytoplasm and were sensitive to radiation.

Quantitative Analysis of T1 Weighted Images due to Change in TI by Using the Inversion Recovery in 3.0T Brain MRI Examination

Although 3.0T magnetic resonance imaging (MRI) has the advantages of a higher signal to noise ratio (SNR) and contrast than 1.5T MRI, there are limitations on the contrast between white and grey matter because of the long T1 recovery time when T1 images are obtained using the Spin Echo Technique. To overcome this, T1 weighted images are obtained occasionally using the inversion recovery (IR) technique, which employs a relatively long TR. The aim of this study was to determine the optimal TI in a brain examination when a T1 weighted image is obtained using the IR technique. Eight participants (male: 7, female: 1, average age: 34 ± 14.11) with a normal diagnosis were targeted from February 18, 2012 to February 27, 2012, and the contrast between white and grey matter as well as the contrast to noise ratio (CNRs) in each participant were measured. The CNRs of white matter and grey matter were highest at TI = 600, 650, 750, 900, 1050 and 1100 ㎳ when the TR was 1100, 1400, 1700, 2000, 2300 and 2600 ms, respectively. Therefore, as the TIs were 44.425 ± 0.877% of the TRs in the TR range of 1400-2300 ms, the optimal T1 weighted images that describe the contrast between white and grey matter can be obtained if the TIs are compensated for with 44.425 ± 0.877% of the TRs in the time of setting TIs.

Reduction in radiation dose with reconstruction technique in the brain perfusion CT

The principal objective of this study was to verify the utility of the reconstruction imaging technique in the brain perfusion computed tomography (PCT) scan by assessing reductions in the radiation dose and analyzing the generated images. The setting used for image acquisition had a detector coverage of 40 mm, a helical thickness of 0.625 mm, a helical shuttle mode scan type and a rotation time of 0.5 s as the image parameters used for the brain PCT scan. Additionally, a phantom experiment and an animal experiment were carried out. In the phantom and animal experiments, noise was measured in the scanning with the tube voltage fixed at 80 kVp (kilovolt peak) and the level of the adaptive statistical iterative reconstruction (ASIR) was changed from 0% to 100% at 10% intervals. The standard deviation of the CT coefficient was measured three times to calculate the mean value. In the phantom and animal experiments, the absorbed dose was measured 10 times under the same conditions as the ones for noise measurement before the mean value was calculated. In the animal experiment, pencil-type and CT-dedicated ionization chambers were inserted into the central portion of pig heads for measurement. In the phantom study, as the level of the ASIR changed from 0% to 100% under identical scanning conditions, the noise value and dose were proportionally reduced. In our animal experiment, the noise value was lowest when the ASIR level was 50%, unlike in the phantom study. The dose was reduced as in the phantom study.

Tooth Distortion as a Function of Arch Form in Cone Beam Computed Tomography

ABSTRACT The cone beam computed tomography enables conducting measurement of length and area in the space where it is impossible to conduct such measurement compared to panorama. The cone beam computed tomography also enables making three-dimensional diagnosis and establishing treatment plan. In this experiment, the cone beam computed tomography was used to analyze image distortion of anatomical structure whose location was different between panorama and reconstructed panoramic image. Multiplanar reformation image was obtained after radiography of mandibular dentition. Then, the axial image was examined to obtain cross-sectional images of teeth that ranged from the right second molar to the left second molar before diameter of crown was measured and compared. Based on the cross-section that was radiographed by using the cone beam computed tomography, comparison was made between reconstructed panorama and standard panorama. According to the results of comparison, diameter of crown was measured with a slight difference of around 0.03 mm between the cone beam computed tomography cross-sectional image and the reconstructed image. It was also found that panorama caused image distortion with the large error of around 0.95 mm. Based on these results, it was confirmed that the cone beam computed tomography panorama that was reconstructed in consideration of patients anatomical structure showed less distortion than the existing panorama. It was also confirmed that depending on distance, there was decrease in reliability of measurement of anatomical structure whose location was different in the existing panoramic image. It is necessary to develop methods and various programs in the future to improve poor image information that is obtained from the cone beam computed tomography and panorama examination.