• Nuclear Medicine and Molecular Imaging
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• v.40 no.1
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• pp.40-47
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• 2006

Purpose: The aim of this study was to examine the effects of attenuation correction (AC) and scatter correction (SC) on the quantification of PET count rates. Materials and Methods: To assess the effects of AC and SC $^{18}F$-FDG PET images of phantom and cat brain were acquired using microPET R4 scanner. Thirty-minute transmission images using $^{68}Ge$ source and emission images after injection of FDG were acquired. PET images were reconstructed using 2D OSEM. AC and SC were applied. Regional count rates were measured using ROIs drawn on cerebral cortex including frontal, parietal, and latral temporal lobes and deep gray matter including head of caudate nucleus, putamen and thalamus for pre- and post-AC and SC images. The count rates were then normalized with the injected dose per body weight. To assess the effects of AC, count ratio of "deep gray matter/cerebral cortex" was calculated. To assess the effects of SC, ROIs were also drawn on the gray matter (GM) and white matter (WM), and contrast between them ((GM-WM)/GM was measured. Results: After the AC, count ratio of "deep gray matter/cerebral cortex" was increased by $17{\pm}7%$. After the SC, contrast was also increased by $12{\pm}3%$. Conclusion: Relative count of deep gray matter and contrast between gray and white matters were increased after AC and SC, suggesting that the AC would be critical for the quantitative analysis of cat brain PET data.

• Investigative Magnetic Resonance Imaging
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• v.6 no.2
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• pp.120-128
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• 2002

Purpose : To demonstrate that the relaxographic method provides additional information such as the distribution of relaxation times and water content which are poentially applicable to clinical medicine. Materials and Methods : First, the computer simulation was performed with the generated relaxation data to verify the accuracy and reliabilility of the relaxographic method (CONTINI). Secondly, in or der to see how well the CONTIN quantifies and resolves the two different ${T_1}$ environments, we calculated the oil to water peak area ratios and identified peak positions of ${T_1}-distribution$ curve of the phantom solutions, which consist of four centrifugal tubes (10 ml) filled with the compounds of 0, 10, 20, 30% of corn oil and distilled water, using CONTIN. Finally, inversion recovery MR images for a volunteer are acquired for each TI ranged from 40 to 1160 msec with TR/TE=2200/20 msec. From the 3 different ROIs (GM, WM, CSF), CONTIN analysis was performed to obtain the ${T_1}$-distribution curves, which gave peak positions and peak area of each ROI location. Results : The simulation result shows that the errors of peak positions were less in the higher peak (centered ${T_1}=600$ msec) than in the lower peak (centered ${T_1}=150$ msec) for all SNR but the errors of peak areas were larger in the higher peak than in the lower peak. The CONTIN analysis of the measured relaxation data of phantoms revealed two peaks between 20 and 60 msec and between 500 and 700 msec. The analysis gives the peak area ratio as oil 10%: oil 20%: oil 30% = 1:1.3:1.9, which is different from the exact ratio, 1:2:3. For human brain, in ROI 3 (CSF), only one component of -distributions was observed whereas in ROI 1(GM) and in ROI 2 (WM) we observed two components of ${T_1}-distribution$. For the WM and CSF there was great agreement between the observed ${T_1}-relaxation$ times and the reported values. Conclusion : we demonstrated that the relaxographic method provided additional information such as the distribution of relaxation times and water content, which were not available in the routine relaxometry and ${T_1}/{T_2}$ mapping techniques. In addition, these additional information provided by relaxographic analysis may have clinical importance.

• Progress in Medical Physics
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• v.23 no.3
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• pp.177-187
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• 2012

Magnetic resonance angiography (MRA) techniques are widely used in diagnosis of vascular disorders such as hemadostenosis and aneurism. Especially, phase contrast (PC) MRA technique, which is a typical non contrast-enhanced MRA technique, provides not only the anatomy of blood vessels but also flow velocity. In this study, we developed the 2- and 3-dimensional PC MRA pulse sequences for a low magnetic field MRI system. Vessel images were acquired using 2D and 3D PC MRA and the velocities of the blood flow were measured in the superior sagittal sinus, straight sinus and the confluence of the two. The 2D PC MRA provided the good quality of vascular images for large vessels but the poor quality for small ones. Although 3D PC MRA gave more improved visualization of small vessels than 2D PC MRA, the image quality was not enough to be used for diagnosis of the small vessels due to the low SNR and field homogeneity of the low field MRI system. The measured blood velocities were $25.46{\pm}0.73cm/sec$, $24.02{\pm}0.34cm/sec$ and $26.15{\pm}1.50cm/sec$ in the superior sagittal sinus, straight sinus and the confluence of the two, respectively, which showed good agreement with the previous experimental values. Thus, the developed PC MRA technique for low field MRI system is expected to provide the useful velocity information to diagnose the large brain vessels.

• Journal of the Korean Society of Radiology
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• v.12 no.1
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• pp.47-52
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• 2018

Brain perfusion CT scanning is often employed usefully in clinical conditions as it accurately and promptly provides information about the perfusion state of patients having acute ischemic stroke with a lot of time constraints and allows them to receive proper treatment. Despite those strengths of it, it also has a serious weakness that Lens may be exposed to a lot of dose of radiation in it. In this study, as a way to reduce the dose of radiation to Lens in brain perfusion CT scanning, this researcher conducted an experiment with Bismuth shielding and change of patients' position. TLD (TLD-100) was placed on both lens using the phantom (PBU-50), and then, in total 4 positions, parallel to IOML, parallel to IOML (Bismuth shielding), parallel to SOML, and parallel to SOML (Bismuth shielding), brain perfusion scanning was done 5 times for each position, and dose to Lens were measured. Also, to examine how the picture quality changed in different positions, 4 areas of interest were designated in 4 spots, and then, CT number and noise changes were measured and compared. According to the results of conducting one-way ANOVA on the doses measured, as the significance probability was found to be 0.000, so there was difference found in the doses of radiation to crystalline lenses. According to the results of Duncan's post-hoc test, with the scanning of being parallel to IOML as the reference, the reduction of 89.16% and 89.66% was observed in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding) respectively, so the doses to Lens reduced significantly. Next, in the scanning of being parallel to IOML (Bismuth shielding), the reduction of 37.12% was found. According to the results, reduction in the doses of radiation was found the most significantly both in the scanning of being parallel to SOML and that of being parallel to SOML (Bismuth shielding). With the limit of the equivalent dose to Lens as the reference, this researcher conducted comparison with the dose to occupational exposure and dose to Public exposure in the scanning of being parallel to IOML and found 39.47% and 394.73% respectively; however in the scanning of being parallel to SOML (Bismuth shielding), considerable reduction was found as 4.08% and 40.8% respectively. According to the results of evaluation on picture quality, every image was found to meet the evaluative standards of phantom scanning in terms of the measurement of CT numbers and noise. In conclusion, it would be the most useful way to reduce the dose of radiation to Lens to use shields in brain perfusion CT scanning and adjust patients' position so that their lens will not be in the field of radiation.

• Investigative Magnetic Resonance Imaging
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• v.13 no.2
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• pp.117-126
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• 2009

Purpose : A numerical method of designing a multiple quantum filter (MQF) is presented for the optimum detection of myo-inositol (mI), an important brain metabolite, by using in vivo proton nuclear magnetic resonance spectroscopy ($^1$-HMRS). Materials and Methods : Starting from the characterization of the metabolite, the filter design includes the optimization of the sequence parameters such as the two echo times (TEs), the mixing time (TM), and the flip angle and offset frequency of the 3rd $90^{\circ}$ pulse which converts multiple quantum coherences (MQCs) back into single quantum coherences (SQCs). The optimized filter was then tested both in phantom and in human brains. Results : The results demonstrate that the proposed MQF can improve the signal-to-background ratio of the target metabolite by a factor of more than three by effectively suppressing the signal from the background metabolites. Conclusion : By incorporating a numerical method into the design of MQFs in $^1$-HMRS the spectral integrity of a target metabolite, in particular, with a complicated spin system can be substantially enhanced.

• Proceedings of the Korean Society of Medical Physics Conference
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• 2004.11a
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• pp.85-87
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• 2004

We fabricated flexible thermoradiotherapy probes to alternated combination with Interstitial hyperthermia and Brachyradiotherapy thermoradiotherapy probe was coated by gold plate on polyethylene brachytherapy probe. When Agar phantom was heated 15 minute with 30 W radiofrequency power, temperature increased as 5oC for polyethylene probe and 20oC for gold coated polyethylene probe. We observed that the 1 cm square array would heat a volume with a 1.25 cm radius circular field cross section to therapeutic temperatures (90% relative SAR using Tm) and the 2 cm square array with a 1.75 cm radius rectangular field with central inhomogeneity. With 2 cm long electrode implants, we observed that the 1 cm square array would heat a 3 cm long sagittal section to therapeutic temperature (90% relative SAR using Tm). The histopathological changes associated with RF heating of normal canine brains have been correlated with thermal distributions. RF needle electrode heating was applied for 50 min to generate tissue temperatures of 43${\circ}$C. We obtained a quarter of the heated tissue material immediately after heating and sacrificed at intervals from 7${\sim}$30 days. The acute stage was demonstrated by liquefactive necrosis, pyknosis of neuronal element in the gray matter. Mild gliosis occurring around the necrosis was demonstrated in the last sacrificed (days30)canine brain.

• The Journal of Korean Society for Radiation Therapy
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• v.31 no.1
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• pp.75-81
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• 2019

Purpose: Helmet type bolus for 3D printer is being manufactured because of the disadvantages of Bolus materials when photon beam is used for the treatment of scalp malignancy. However, PLA, which is a used material, has a higher density than a tissue equivalent material and inconveniences occur when the patient wears PLA. In this study, we try to treat malignant scalp tumors by using M3 wax helmet with 3D printer. Methods and materials: For the modeling of the helmet type M3 wax, the head phantom was photographed by CT, which was acquired with a DICOM file. The part for helmet on the scalp was made with Helmet contour. The M3 Wax helmet was made by dissolving paraffin wax, mixing magnesium oxide and calcium carbonate, solidifying it in a PLA 3D helmet, and then eliminated PLA 3D Helmet of the surface. The treatment plan was based on Intensity-Modulated Radiation Therapy (IMRT) of 10 Portals, and the therapeutic dose was 200 cGy, using Analytical Anisotropic Algorithm (AAA) of Eclipse. Then, the dose was verified by using EBT3 film and Mosfet (Metal Oxide Semiconductor Field Effect Transistor: USA), and the IMRT plan was measured 3 times in 3 parts by reproducing the phantom of the head human model under the same condition with the CT simulation room. Results: The Hounsfield unit (HU) of the bolus measured by CT was $52{\pm}37.1$. The dose of TPS was 186.6 cGy, 193.2 cGy and 190.6 cGy at the M3 Wax bolus measurement points of A, B and C, and the dose measured three times at Mostet was $179.66{\pm}2.62cGy$, $184.33{\pm}1.24cGy$ and $195.33{\pm}1.69cGy$. And the error rates were -3.71 %, -4.59 %, and 2.48 %. The dose measured with EBT3 film was $182.00{\pm}1.63cGy$, $193.66{\pm}2.05cGy$ and $196{\pm}2.16cGy$. The error rates were -2.46 %, 0.23 % and 2.83 %. Conclusions: The thickness of the M3 wax bolus was 2 cm, which could help the treatment plan to be established by easily lowering the dose of the brain part. The maximum error rate of the scalp surface dose was measured within 5 % and generally within 3 %, even in the A, B, C measurements of dosimeters of EBT3 film and Mosfet in the treatment dose verification. The making period of M3 wax bolus is shorter, cheaper than that of 3D printer, can be reused and is very useful for the treatment of scalp malignancies as human tissue equivalent material. Therefore, we think that the use of casting type M3 wax bolus, which will complement the making period and cost of high capacity Bolus and Compensator in 3D printer, will increase later.

• Progress in Medical Physics
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• v.13 no.4
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• pp.209-217
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• 2002

There have been many studies on the application of the reciprocal advantages of multimodality image to define accurate target volume in the Process of radiation treatment planning. For the proper use of the multimodality images, the registration works between different modality images should be performed in advance. In this study, we selected chamfer matching method and mutual information method as most popular methods in recent image registration studies considering the registration accuracy and clinical practicality. And the two registration methods were analyzed to deduce the optimal registration method according to the characteristics of images. Lung phantom of which multimodality images could be acquired was fabricated and CT, MRI and SPECT images of the phantom were used in this study. We developed the registration program which can perform the two registration methods properly and analyzed the registration results which were produced by the developed program in many different images' conditions. Although the overall accuracy of the registration in both chamfer matching method and mutual information method was acceptable, the registration errors in SPECT images which had lower resolution and in degraded images of which data were removed in some part were increased when chamfer matching method was applied. Especially in the case of degraded reference image, chamfer matching methods produce relatively large errors compared with mutual information method. Mutual information method can be estimated as more robust registration method than chamfer matching method in this study because it did not need the prerequisite works, the extraction of accurate contour points, and it produced more accurate registration results consistently regardless of the images' characteristics. The analysis of the registration methods in this study can be expected to provide useful information to the utilization of multimodality images in delineating target volume for radiation treatment planning and in many other clinical applications.

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.12
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• pp.180-188
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• 2014

It is very important accurate diagnosis and quick treatment in cerebrovascular disease, i.e. stenosis or occlusion that could be caused by risk factors such as poor dietary habits, insufficient exercise, and obesity. Time-of-flight magnetic resonance angiography (TOF-MRA), it is well known as diagnostic method without using contrast agent for cerebrovascular disease, is the most representative and reliable technique. Nevertheless, it still has measurement errors (also known as overestimation) for length of stenosis and area of occlusion in celebral infarction that is built by accumulation and rupture of plaques generated by hemodynamic turbulence. The purpose of this study is to show clinical trial feasibility for 3D-SPACE T2, which is improved by using signal attenuation effects of fluid velocity, in diagnosis of cerebrovascular disease. To model angiostenosis, strictures of different proportions (40%, 50%, 60%, and 70%) and virtual blood stream (normal saline) of different velocities (0.19 ml/sec, 1.5 ml/sec, 2.1 ml/sec, and 2.6 ml/sec) by using dialysis were made. Cross-examinations were performed for 3D-SPACE T2 and TOF-MRA (16 times each). The accuracy of measurement for length of stenosis was compared in all experimental conditions. 3D-SPACE 2T has superiority in terms of accuracy for measurements of the length of stenosis, compared with TOF-MRA. Also, it is robust in fast blood stream and large stenosis than TOF-MRA. 3D-SPACE 2T will be promising technique to increase diagnosis accuracy in narrow complex lesions as like two cerebral small vessels with stenosis, created by hemodynamic turbulence.

• The Korean Journal of Nuclear Medicine
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• v.39 no.1
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• pp.49-56
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• 2005

Purpose: Dedicated animal PET is useful equipment for the study of new PET tracer. recently, microPET R4 was installed in the Korea institute of radiology and medical science. In this study, we measured the characteristics of scanner. Materials and methods: Resolution was measured using a line source (F-18:65 ${\mu}Ci$, inner diameter: 0.5 mm). The line source was put in the axial direction and was moved from the center of field of view to outside with 1 mm interval. PET images were reconstructed using a filtered back-protection and ordered subset expectation maximization. line source (16.5 ${\mu}Ci$, 78 mm) was put on the tenter of axial direction to measure the sensitivity when the deadtime was under 1%. Images were acquired during 4 minutes respectively from center to 39 mm outward. Delayed count was subtracted from total count and then decay was corrected for the calculation of sensitivity. Noise equivalent count ratio and scatter fraction were calculated using cylindrical phantom. Results: Spatial resolution of reconstructed image using filtered back-projection was 1.86 mm(radial), 1.95 mm(tangential), 1.95 mm(axial) in the tenter of field of view, and 2.54 mm, 2.8 mm, 1.61 mm in 2 cm away from the center respectively. Sensitivity was 2.36% at the center of transaxial field of view. Scatter fraction was 20%. Maximal noise equivalent count ratio was 66.4 kcps at 242 kBq/mL. Small animal images were acquired for confirmation of performance. Conclusion: Performance characteristics of microPET R4 were similar with reported value. So this will be a useful tool for small animal imaging.