• The Korean Journal of Nuclear Medicine
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• v.32 no.6
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• pp.490-496
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• 1998

Purpose: We evaluated brain perfusion SPECT findings of MELAS syndrome and mitochondrial myopathy in correlation with MR imaging in search of specific imaging features. Materials and Methods: Subjects were five patients (four females and one male; age range, 1 to 25 year) who presented with repeated stroke-like episodes, seizures or developmental delay or asymptomatic but had elevated lactic acid in CSF and serum. Conventional non-contrast MR imaging and Tc-99m-ethyl cysteinate dimer (ECD) brain perfusion SPECT were Performed and imaging features were analyzed. Results: MRI demonstrated increased T2 signal intensities in the affected areas of gray and white matters mainly in the parietal (4/5) and occipital lobes (4/5) and in the basal ganglia (1/5), which were not restricted to a specific vascular territory. SPECT demonstrated decreased perfusion in the corresponding regions of MRI lesions. In addition, there were perfusion defects in parietal (1 patient), temporal (2), and frontal (1) lobes and basal ganglia (1) and thalami (2). In a patient with mitochondrial myopathy who had normal MRI, decreased perfusion was noted in left parietal area and bilateral thalami. Conclusion: Tc-99m ECD SPECT imaging in patients with MELAS syndrome and mitochondrial myopathy showed hypoperfusion of parieto-occipital cortex, basal ganglia, thalamus and temporal cortex, which were not restricted to a specific vascular territory. There were no specific imaging features on SPECT. The significance of abnormal perfusion on SPECT without corresponding MR abnormalities needs to be evaluated further in larger number of patients.

• Investigative Magnetic Resonance Imaging
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• v.16 no.1
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• pp.25-30
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• 2012

Purpose : To compare the enhancement pattern of normal facial nerves on 3D-FLAIR and 3D-T1-FFE-F) sequences at 3.0 T MR units. Materials and Methods: We assessed 20 consecutive subjects without a history of facial nerve abnormalities who underwent temporal bone MRI with contrast enhancement between January 2008 and March 2009. Two neuroradiologists independently reviewed pre-/post-enhanced 3D-T1-FFE-FS and 3D-FLAIR images respectively with 2-week interval to assess the enhancement of normal facial nerves divided into five anatomical segments. The degree of enhancement in each segment was graded as none, mild or strong, and the results of 3D-FLAIR and 3D-T1-FFE-FS image sets were compared. Results: On 3D-FLAIR images, one of the two reviewers observed mild enhancement of the genu segment in two (10%) subjects. On 3D-T1-FFE-FS images, at least one segment of the facial nerve was enhanced in 13 (65%) subjects. At least one reviewer found that 17 of the 100 segments showed enhancement on 3D-T1-FFE-FS images, with the mastoid segment being the most commonly enhanced. Interobserver agreement on 3D-T1-FFE-FS images was good for enhancement of the normal facial nerve (${\kappa}$= 0.589). Conclusion: In contrast to 3D-T1-FFE-FS, normal facial nerve segments rarely showed enhancement on 3D-FLAIR images.

• Investigative Magnetic Resonance Imaging
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• v.5 no.1
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• pp.33-37
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• 2001

Purpose : The water exchange rate between bulk water and bound water is an important parameter in deciding the efficiency of paramagnetic contrast agents. In this study, we evaluated the water exchange rates of various Gd-chelates using oxygen-17 NMR technique. Material and Methods : The samples (Gd-DTPA, Gd-DTPA-BMA, Gd-DOTA, Gd-EOB-DTPA) were prepared by mixing 5% $^{17}O-enriched$ water (Isotech, USA). The pH of the samples was adjusted to physiological value [pH=7.0] by buffer solution. The variable temperature $^{17}O-NMR$ measurements were performed using Bruker-600 (14.1 T, 81.3 MHz) spectrometer. Bruker VT-1000 temperature control units were used to stabilize the temperature. The $^{17}O$ spin-spin relaxation times (T2) were measured using Carr-Purcell-Meiboom-Gill (CPMG)I pulse sequence with 24 echo trains. The variable temperature T2 relaxation data were then fitted into Solomon-Bloembergen equations using least square fit algorithm to estimate the water exchange times. Results : From the measured $^{17}O-NMR$ relaxation rates, the determined water exchange rates at 300K are $0.42{\;}{\mu}s$ for Gd-DTPA, $1.99{\;}{\mu}s$ for Gd-DTPA-BMA, $0.27{\;}{\mu}s$ for Gd-DOTA, and $0.11{\;}{\mu}s$ for Gd-EOB-DTPA. The Gd-DTPA-BMA showed slowest exchange whereas Gd-EOB-DTPA had fastest water exchange rate. In addition, it was found that the water exchange rates (${\tau}_m$) of all samples had exponential temperature dependence with different decay constant. Conclusion : $^{17}O-NMR$ relaxation rate measurements, when combined with variable temperature technique, provide a solid tool for studying water exchange rate, which is very important in investigating the detailed mechanism of relaxation enhancement effect of the paramagnetic contrast agents.

• Investigative Magnetic Resonance Imaging
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• v.3 no.2
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• pp.146-153
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• 1999

Purpose : To evaluate the proton MR spectroscopy (MRS) findings of early and late ischemic infarcts and to compare these MRS findings with clinical symptoms. Materials and Methods : We obtained MRs spectra of 28 consecutive patients with early ischemic infarct (15 me, 13 women) between 2-10 (mean 6.2) days after stroke onset. Follow-up MRS was carried out between 20-32 (mean 25) days in 12 patients. The MRs spectra were acquired at 1.5T MR unit using single voxel technique with PRESS sequence, TR of 2000ms, TE of 288 (144)ms, and voxel size of 2cm x 2cm x 2cm in the three areas; an infarct lesion, the brain parenchyma adjacent to the lesion, and contralateral normal brain parenchyma. The NAA/creatine, choline/creatine, and lactate/creatine ratios were calculated in each spectrum. The spectra of MRS were compared with clinical symptoms. Results : In early infarct, decreased NAA/creatine ratio (n=22) and increased lactate/creatine ratio (n=25) were found in the infarct lesion. Choline/creastine ratio was within normal range (n=25). On follow-up MRS in late stage, NAA/creatine ratio in the infarct lesion decreased further (n=5), did not change (n=6), or increased (n=1). Lactate/creatine ratio became less elevated (n=10), or did not changed (n=2). Choline/creatine ratio had a trend for increase. The decreased NAA/creatine and increased lactate/creatine ratios were correlated well with the severity of symptoms, respectively. Conclusion : Decreased NAA/creatine and increased lactate/creatine ratios were common MRS findings characteristic in early ischemic infarct and correlated well with clinical severity. On follow-up MRS in late stage, NAA/creatine ratio decreased further or did not change, and lactate/creatine ratio became less elevated.

• Investigative Magnetic Resonance Imaging
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• v.15 no.1
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• pp.32-40
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• 2011

Purpose : The purpose of this study was to investigate the microstructural changes according to aging on the thickness and signal intensity (SI) of the cortical gray matter (GM) and white matter (WM) on the T2-, fluid-attenuated inversion recovery (FLAIR) and T1-weighted MR images in normal subjects. Materials and Methods : The 10, 20, 30, 40, 50, 60, 70, 80 and 90 year age groups of men and women (each 10 individuals) who underwent routine brain MRI, including the T2-, FLAIR and T1-weighted images, were selected for this study. We measured the thickness and the SI of the cortical GM and WM at the postcentral gyrus, which has an even thickness at the level of centrum semiovale, on the axial scans and we calculated the mean values of the thickness ratio of the gray/white matter (TRGW) and the signal intensity ratio of the gray/white matter (SRGW), and we compared the ratios of each age group. Results : On the T2-weighted images, the TRGWs were 0.81 and 0.79 at the age of 10 and they were 0.73 and 0.71 at the age of 90 in the men and women, respectively. So, the GM thickness was decreased more than the WM thickness was with aging. On the FLAIR images, the TRGWs were 1.09 and 1.00 at the age of 10 and they were 1.11 and 0.95 at the age of 70 in the men and women, respectively. On the T1-weighted images, the TRGWs were 0.66 and 0.80 at the age of 10, and the ratio was changed to 0.90 and 0.78 at the age of 90 in the men and women, respectively. On the T2-weighted image, the SRGWs were 1.53 and 1.43 at the age of 10, and they were 1.23 and 1.27 at the age of 90 in the men and women, respectively. On the FLAIR images, the SRGWs were 1.23 and 1.25 at the age of 10 and they were 1.06 and 1.05 at the age of 90 in the men and women, respectively. On the T1-weighted images, the SRGWs were 0.86 and 0.85 at the age of 10, and they were 0.90 and 0.87 at the age of 90 in the men and women, respectively. Conclusion : We suggest that the age-related microstructural changes of the thickness and the SI of the cortical GM and WM on the T2-, FLAIR and T1-weighted images are unique, and so this knowledge will be helpful to differentiate neurodegenerative disease from normal aging of the brain.

• Investigative Magnetic Resonance Imaging
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• v.18 no.2
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• pp.107-119
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• 2014

Purpose : To efficiently evaluate phased array coil performance using a software tool box with which we can make visual comparison of the sensitivity of every coil element between the real experiment and EM simulation. Materials and Methods: We have developed a $C^{{+}{+}}$- and MATLAB-based software tool called Phased Array Coil Evaluator (PACE). PACE has the following functions: Building 3D models of the coil elements, importing the FDTD simulation results, and visualizing the coil sensitivity of each coil element on the ordinary Cartesian coordinate and the relative coil position coordinate. To build a 3D model of the phased array coil, we used an electromagnetic 3D tracker in a stylus form. After making the 3D model, we imported the 3D model into the FDTD electromagnetic field simulation tool. Results: An accurate comparison between the coil sensitivity simulation and real experiment on the tool box platform has been made through fine matching of the simulation and real experiment with aids of the 3D tracker. In the simulation and experiment, we used a 36-channel helmet-style phased array coil. At the 3D MRI data acquisition using the spoiled gradient echo sequence, we used the uniform cylindrical phantom that had the same geometry as the one in the FDTD simulation. In the tool box, we can conveniently choose the coil element of interest and we can compare the coil sensitivities element-by-element of the phased array coil. Conclusion: We expect the tool box can be greatly used for developing phased array coils of new geometry or for periodic maintenance of phased array coils in a more accurate and consistent manner.

• Investigative Magnetic Resonance Imaging
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• v.18 no.4
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• pp.303-313
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• 2014

Purpose : In-vivo conductivity reconstruction using transmit field ($B_1{^+}$) information of MRI was proposed. We assessed the accuracy of conductivity reconstruction in the presence of statistical noise in complex $B_1{^+}$ map and provided a parametric model of the conductivity-to-noise ratio value. Materials and Methods: The $B_1{^+}$ distribution was simulated for a cylindrical phantom model. By adding complex Gaussian noise to the simulated $B_1{^+}$ map, quantitative conductivity estimation error was evaluated. The quantitative evaluation process was repeated over several different parameters such as Larmor frequency, object radius and SNR of $B_1{^+}$ map. A parametric model for the conductivity-to-noise ratio was developed according to these various parameters. Results: According to the simulation results, conductivity estimation is more sensitive to statistical noise in $B_1{^+}$ phase than to noise in $B_1{^+}$ magnitude. The conductivity estimate of the object of interest does not depend on the external object surrounding it. The conductivity-to-noise ratio is proportional to the signal-to-noise ratio of the $B_1{^+}$ map, Larmor frequency, the conductivity value itself and the number of averaged pixels. To estimate accurate conductivity value of the targeted tissue, SNR of $B_1{^+}$ map and adequate filtering size have to be taken into account for conductivity reconstruction process. In addition, the simulation result was verified at 3T conventional MRI scanner. Conclusion: Through all these relationships, quantitative conductivity estimation error due to statistical noise in $B_1{^+}$ map is modeled. By using this model, further issues regarding filtering and reconstruction algorithms can be investigated for MREPT.

• Investigative Magnetic Resonance Imaging
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• v.6 no.2
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• pp.129-136
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• 2002

Purpose : To evaluate the usefulness of MRCP in the diagnosis of the variable causes of common bile duct(CBD) dilatation, except stone or tumor Materials and methods : Twenty-six patients(M:F=15:11, mean age; 62 years) with both MRCP and ERCP were included in this study. Dynamic MRCP(n=12) and contrast-enhanced MRI(n=10) of abdomen were also added. Dilatation of CBD, intrahepatic ducts and pancreatic duct was evaluated, including coexistence of intrahepatic ductal stone, pancreatic pseudocyst, and papillary or papillary edema. The criteria of CBD dilatation was over than 7mm(n= 21, without cholecystectomy) or 10 mm(n=5, with cholecystecto-my) in diameter on T2-weighted coronal image. Results : The mean diameter of CBD was 12.7mm without cholecystectomy(9-19 mm) and 13.0 mm with cholecystectomy(10-15mm), respectively(p 〉0.05). Cholangitis(n=11, 42.3%), chronic pancreatitis(n=8, 30.8%), stenosis of distal CBD(n= 6, 23.1%), periampullary diverticulum(n=3, 11.5%), stenosis of ampulla of Vater(n=2, 7.7%), dysfunction of sphincter of Oddi(n=2, 7.7%), acute focal pancreatitis in the pancreatic head(n=2, 7.7%), papillitis(n=1, 3.8%), pseudocyst in the pancre atic head(n = 1, 3.8%), and ascaris in CBD(n=1, 3.8%) were noted. Pancreatic duct dilatation(n=10, 38.5%) and duodenal diverticulum(n=3, 11.5%) were also seen on MRC P. On dynamic MRCP(12 patients), distal CBD was visualized in 2 patients(16.7%), which was not shown on routine MRCP. Only 1 patient(10.0%) showed papillitis with slightly enhancing papilla on contrast-enhanced MRI (10 patients). Conclusion : MRCP was thought to be helpful in the evaluation of the causes of CBD dilatation, not caused by stone or tumor, especially in the cases of stenosis of distal CBD and chronic pancreatitis, dysfunction of sphincter of Oddi on dynamic MRCP and cholangitis and pericholangitic abnormality on contrast-enhanced MRI.

• Investigative Magnetic Resonance Imaging
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• v.18 no.1
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• pp.1-6
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• 2014

Purpose : $T_2{^*}$ relaxation time which includes susceptibility information represents unique feature of tissue. The objective of this study was to investigate $T_2{^*}$ relaxation times of the normal glandular tissue and fat of breast using a 3T MRI system. Materials and Methods: Seven-echo MR Images were acquired from 52 female subjects (age $49{\pm}12 $years; range, 25 to 75) using a three-dimensional (3D) gradient-echo sequence. Echo times were between 2.28 ms to 25.72 ms in 3.91 ms steps. Voxel-based $T_2{^*}$ relaxation times and $R_2{^*}$ relaxation rate maps were calculated by using the linear curve fitting for each subject. The 3D regions-of-interest (ROI) of the normal glandular tissue and fat were drawn on the longest echo-time image to obtain $T_2{^*}$ and $R_2{^*}$ values. Mean values of those parameters were calculated over all subjects. Results: The 3D ROI sizes were $4818{\pm}4679$ voxels and $1455{\pm}785$ voxels for the normal glandular tissue and fat, respectively. The mean $T_2{^*}$ values were $22.40{\pm}5.61ms$ and $36.36{\pm}8.77ms$ for normal glandular tissue and fat, respectively. The mean $R_2{^*}$ values were $0.0524{\pm}0.0134/ms$ and $0.0297{\pm}0.0069/ms$ for the normal glandular tissue and fat, respectively. Conclusion: $T_2{^*}$ and $R_2{^*}$ values were measured from human breast tissues. $T_2{^*}$ of the normal glandular tissue was shorter than that of fat. Measurement of $T_2{^*}$ relaxation time could be important to understand susceptibility effects in the breast cancer and the normal tissue.

• Investigative Magnetic Resonance Imaging
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• v.17 no.4
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• pp.294-307
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• 2013

Purpose : To investigate the correlations between Seoul Neuropsychological Screening Battery (SNSB) scores and the gray matter volumes (GMV) in patients with Alzheimer's disease (AD) and mild cognitive impairment (MCI) and cognitively normal (CN) elderly subjects with correcting the genotypes. Materials and Methods: Total 75 subjects were enrolled with 25 subjects for each group. The apolipoprotein E (APOE) epsilon genotypes, SNSB scores, and the 3D T1-weighted images were obtained from all subjects. Correlations between SNSB scores and GMV were investigated with the multiple regression method for each subject group using both voxel-based and region-of-interest-based analyses with covariates of age, gender, and the genotype. Results: In the AD group, Rey Complex Figure Test (RCFT) delayed recall scores were positively correlated with GMV. In the MCI group, Seoul Verbal Learning Test (SVLT) scores were positively correlated with GMV. In the CN group, GMV negatively correlated with Boston Naming Test (K-BNT) scores and Mini-Mental State Examimation (K-MMSE) scores, but positively correlated with RCFT scores. Conclusion: When we used covariates of age, gender, and the genotype, we found statistically significant correlations between some SNSB scores and GMV at some brain regions. It may be necessary to further investigate a longitudinal study to understand the correlation.