Usefulness of ACR MRI Phantom for Quality Assurance of MRI Instruments

PURPOSE: To examine whether the ACR phantom could be used in quality standards for magnetic resonance imaging (MRI) instruments in Korea. MATERIALS AND METHODS: We conducted the phantom test using the ACR MRI phantom in 20 MRI instruments currently used in Korea. According to ACR criteria, we acquired the phantom images which were then assessed by the following seven tests: geometric accuracy, high spatial resolution, slice thickness accuracy, slice position accuracy, image intensity uniformity, percent signal ghosting, and low contrast object detectability. The phantom images were interpreted by three experienced radiologists according to ACR criteria. Then, we examined the failure rate of each test and evaluated the inter-observer variation in the measurements and test failure. RESULTS: The failure rate of each test could be broken into the following components: geometric accuracy (11-21%), high contrast spatial resolution (10-15%), slice thickness accuracy (6-22%), slice position accuracy (5-17%), image intensity uniformity (6%), percent signal ghosting (16%), and low contrast object detectability (8-10%). In this series, all the failure rates were less than 30%. In addition, no inter-observer variation was seen in the measurements and test failure. CONCLUSION: ACR MRI phantom promises to be established as the standard phantom for MRI instruments in Korea because of its objectivity in assessing the phantom images.

The Correlation of Motor Impairment and Fractional Anisotropy in Diffusion Tensor Imaging in Post-stroke Hemiplegic Patients

OBJECTIVE: Diffusion tensor imaging (DTI) fully characterizes water molecule mobility, allowing an exploration of fiber tract integrity and orientation in the human brain. The purpose of this study was to investigate the correlation between motor impairment and the changes of fractional anisotropy (FA) in the internal capsule in post-stroke hemiplegic patients. METHOD: Six normal subjects and 19 post-stroke hemiplegic patients who had a lesion in the internal capsule were included in this study. DTI was performed with a 3.0 Tesla MR at the mean interval of 28.2 days after stroke. Motor impairment was assessed with the Motricity Index and Trunk Control Test at the time of the imaging study. FA was measured in anterior limb and posterior limb of internal capsule. RESULTS: FA reduced significantly in the affected region compared with the other unaffected region in patients and normal region in controls. FA in the affected posterior limb of the internal capsule was correlated with the Motricity Index score of the affected upper limb (r=0.642, p<0.05). CONCLUSION: DTI can be helpful to evaluate motor impairment of the upper limb in post-stroke hemiplegic patients.

Quantitative Evaluation of Liver Function with MRI Using Gd-EOB-DTPA

OBJECTIVE: Gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) is a newly developed MR contrast agent. After intravenous injection, Gd-EOB-DTPA is gradually taken up by the hepatocytes and eventually excreted via the biliary pathway without any change to its chemical structure. Because of these characteristics, it can be used as a tracer for quantitative liver function testing. The purpose of this study is to develop a noninvasive method of quantitation of the hepatic function using Gd-EOB-DTPA through the deconvolution analysis. MATERIALS AND METHODS: Adult New Zealand white rabbits (n = 10, average body weight = 3.5 kg) were used in the present study. Hepatic injury was induced to by the intragastric administration of carbon tetrachloride (CCl4) three times a week for three weeks. Liver enzyme (aspartate aminotransferase, AST; alanine aminotransferase, ALT) levels and the plasma indocyanine green (ICG) retention rate 15 minutes after an intravenous injection of ICG (ICG R15), was checked before and after the three-week administration of CCl4. At the end of experimental period, an observer "blinded" to the treatment given the rabbits performed the histological examination. MRI studies were performed before and after the three-week administration of CCl4 on a 1.5 T scanner using a human extremity coil. After intravenous bolus injection of Gd-EOB-DTPA (0.3 mL of Gd-EOB-DTPA freshly prepared in 2.7 mL of normal saline) through the ear vein, the 250 axial single level dynamic MR images were obtained using a fast low angle shot (FLASH, TR/TE = 11/4.2 msec, flip angle = 15, acquisition time 1 second, slice thickness = 5 mm, matrix = 128x128, field of view = 120 mm) sequence with 1.5 sec time intervals. The time-intensity curves were obtained at the abdominal aorta and the liver parenchyma that was devoid of blood vessels. Deconvolution analysis of the aortic (input function) and hepatic parenchymal (output function) time-intensity curves was performed with a modified Fourier transform technique to calculate the hepatic extraction fraction (HEF). The presence and type of hepatic injury were determined by the histopathologic examination and statistical analysis of the changes of the hepatic enzyme levels, the ICG R15 and Gd-EOB-DTPA HEF values between the time before and after CCl4 administration with Wicoxon signed rank test. Correlation between the Gd-EOB-DTPA HEF and the change of the ICG R15 were analyzed with Pearson's correlation coefficient. RESULTS: Histopathologic examination showed findings that were compatible with hepatic fibrosis caused by chronic liver injury. The initial blood biochemical studies before the administration of carbon tetrachloride showed that the mean AST and ALT levels were 39.8+/-5.2 IU/L and 59.1+/-11.7 IU/L, respectively. The AST and ALT levels increased to 138.4+/-50.5 IU and 172.0+/-71.6 IU/L, respectively, after the three week administration of CCl4. The ALT and AST levels were significantly increased after the three weeks of CCl4 administration (p=0.018). The ICG R15 values were 4.47+/-2.08% and 19.43+/-3.98% before and after three-week administration of CCl4, respectively. The ICG R15 values were significantly increased after hepatic injury (p=0.018). After normalizing the HEF as 100% in each rabbit before CCl4 administration, the deconvoluted curve after CCl4 administration revealed less hepatocyte extraction efficiency with a mean value of 77.7+/-3.6. There was a significant correlation between the HEF and changes of the ICG R15 by the Pearson correlation coefficient assessment (correlation coefficient = -0.965, p=0.000). CONCLUSION: The Gd-EOB-DTPA HEF could be calculated from deconvolution analysis of aortic and hepatic parenchymal time-intensity curves obtained by dynamic MRI. The Gd-EOB-DTPA HEF was well correlated with changes of the ICG R15, which is the most common parameter used in the quantitative estimation of the hepatic function. The Gd-EOB-DTPA HEF is a direct, noninvasive technique for the quantitative evaluation of liver function. It could be a promising alternative for the determination of noninvasive hepatic function in those patients with liver disease.

The Effects of Essential Aroma Oils on Brain Activation: Olfactory Functional MRI and c-Fos Expression / 대한이비인후과학회지

BACKGROUND AND OBJECTIVES: For centuries, fragrance had beneficial psychological and physiological effects on humans. Aromatherapy, the use of concentrated essential oils extracted from herbs, flowers, and other parts of plants to treat various diseases, is becoming more commonly accepted within the health service. However, there are very few published articles, which provide a sound rationale for the use of aromatherapy as a medical intervention. The purpose of this study was to find a scientific explanation for the effect of aromatherapy by investigating 1. whether or not essential aroma oils caused increased brain activity and 2. which areas of the brain were activated by the essential aroma oils. MATERIALS AND METHODS: Olfactory fMRI (functional magnetic resonance imaging), which is capable of monitoring and recording regional pathophysiological fluctuations in living brains, was performed on 11 healthy adult humans during exposure to essential aroma oils (lavender and lemon oils) and buthanol. The c-fos immunohistochemical staining was also performed on brain tissues of 24 Mongolian gerbils after exposure to the essential aroma oils. RESULTS: In the human fMRI study, the olfactory cortex was activated in all subjects by the essential aroma oils and buthanol. Additionally, lavender oil also activated the hearing and language-related regions of brain. In the animal study, similar results were observed: immunoreactive cells were detected in the hearing and language related regions of gerbil brains that had been exposed to lavender oil. CONCLUSION: The lavender oil activated not only the olfactory region but also the hearing and language-related regions of the brain. These results imply that the essential aroma oil introduced through the olfactory pathway has effects on other regions of the brain.

Multi-Component Relaxation Study of Human Brain Using Relaxographic Analysis

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 reliablility of the relaxographic method (CONTIN). Secondly, in order to see how well the CONTIN quantifies and resolves the two different T1 environments, we calculated the oil to water peak area ratios and identified peak positions of T1-distribution curve of the phantom solutions, which consist of four centrifugal tubes (10ml) 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 T1-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 T1=600 msec) than in the lower peak (centered T1=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 T1-distribution. For the WM and CSF there was great agreement between the observed T1-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 T1/T2 mapping techniques. In addition, these additional information provided by relaxographic analysis may have clinical importance.

(17)O NMR Study On Water Exchange Rate of Paramagnetic Contrast Agents

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 MEHTODS: 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) 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 microsecond for Gd-DTPA, 1.99 microsecond for Gd-DTPA-BMA, 0.27 microsecond for Gd-DOTA, and 0.11 microsecond 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 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.

Contrast-Enhanced Magnetic Resonance Angiography: Dose the Test Dose Bolus Represent the Main Dose Bolus Accurately?

OBJECTIVE: To determine whether the time-intensity curves acquired by test and main dose contrast injections for MR angiography are similar. MATERIALS AND METHODS: In 11 patients, repeated contrast-enhanced 2D-turbo-FLASH scans with 1-sec interval were obtained. Both test and main dose time-intensity curves were acquired from the abdominal aorta, and the parameters of time-intensity curves for the test and main boluses were compared. The parame-ters used were arterial and venous enhancement times, arterial peak enhance-ment time, arteriovenous circulation time, enhancement duration and enhance-ment expansion ratio. RESULTS: Between the main and test boluses, arterial and venous enhance-ment times and arteriovenous circulation time showed statistically significant correlation (p < 0.01), with correlation coefficients of 0.95, 0.92 and 0.98 respectively. Although the enhancement duration was definitely greater than infusion time, reasonable measurement of the end enhancement point in the main bolus was impossible. CONCLUSION: Only arterial and venous enhancement times and arteriovenous circulation time of the main bolus could be predicted from the test-bolus results. The use of these reliable parameters would lead to improvements in the scan timing method for MR angiography.

Contrast-Enhanced Magnetic Resonance Angiography: Dose the Test Dose Bolus Represent the Main Dose Bolus Accurately?

OBJECTIVE: To determine whether the time-intensity curves acquired by test and main dose contrast injections for MR angiography are similar. MATERIALS AND METHODS: In 11 patients, repeated contrast-enhanced 2D-turbo-FLASH scans with 1-sec interval were obtained. Both test and main dose time-intensity curves were acquired from the abdominal aorta, and the parameters of time-intensity curves for the test and main boluses were compared. The parame-ters used were arterial and venous enhancement times, arterial peak enhance-ment time, arteriovenous circulation time, enhancement duration and enhance-ment expansion ratio. RESULTS: Between the main and test boluses, arterial and venous enhance-ment times and arteriovenous circulation time showed statistically significant correlation (p < 0.01), with correlation coefficients of 0.95, 0.92 and 0.98 respectively. Although the enhancement duration was definitely greater than infusion time, reasonable measurement of the end enhancement point in the main bolus was impossible. CONCLUSION: Only arterial and venous enhancement times and arteriovenous circulation time of the main bolus could be predicted from the test-bolus results. The use of these reliable parameters would lead to improvements in the scan timing method for MR angiography.

Low-dose Contrast-enhanced Magnetic Resonance Angiography with Less than the Standard Dose of Gadolinium Chelate: Comparison with Conventional Digital Subtraction Angiography

PURPOSE: To evaluate the effectiveness of contrast-enhanced MR angiography (CEM-RA)using gadolinium chelate at less than the standard dose. MATERIALS AND METHODS: Eight patients with occlusive arterial disease underwent 16 CEMRA scans of the lower extremities following bolus injection of 0.075 mmol/kg gadolinium, using a 1.5T scanner and 3D-turbo-FLASH sequence. The arterial phase was compared with that obtained by digital subtraction angiography (DSA). After grouping arteries according to their diameter, arterial detectability (AD), stenosis grad-ing (SG), and the detectability of significant stenosis (SD) were compared. RESULTS: The AD of CEMRA showed high specificity (Sp, 98%-100%) in all groups, and sensitivity (Sn) was high (>90%) in groups I, II, and III. SG showed a correlation coefficient of 0.65* and 0.60* in groups I and II, though CEMRA tended to overesti-mate. SD was high (Sn,100%) in all groups, but Sp was low(<70%). CONCLUSION: Low-dose CEMRA is an excellent way to exclude significant arterial ob-struction in the lower extremities, even in small arteries. Stenosis grading was possible in large arteries but consideration must be paid to the technique 's overestimating characteristic.

The Optimization of Scan Timing for Contrast-Enhanced Magnetic Resonance Angiography

OBJECTIVE: To determine the optimal scan timing for contrast-enhanced magnetic resonance angiography and to evaluate a new timing method based on the arteriovenous circulation time. MATERIALS AND METHODS: Eighty-nine contrast-enhanced magnetic resonance angiographic examinations were performed mainly in the extremities. A 1.5T scanner with a 3-D turbo-FLASH sequence was used, and during each study, two consecutive arterial phases and one venous phase were acquired. Scan delay time was calculated from the time-intensity curve by the traditional (n = 48) and/or the new (n = 41) method. This latter was based on arteriovenous circulation time rather than peak arterial enhancement time, as used in the traditional method. The numbers of first-phase images showing a properly enhanced arterial phase were compared between the two methods. RESULTS: Mean scan delay time was 5.4 sec longer with the new method than with the traditional. Properly enhanced first-phase images were found in 65% of cases (31/48) using the traditional timing method, and 95% (39/41) using the new method. When cases in which there was mismatch between the target vessel and the time-intensity curve acquisition site are excluded, erroneous acquisition occurred in seven cases with the traditional method, but in none with the new method. CONCLUSION: The calculation of scan delay time on the basis of arteriovenous circulation time provides better timing for arterial phase acquisition than the traditional method.

A Suggestion of New Integrated Prognostic Factor for Aortic Aneurysm: Ta n gential Stress Index

PURPOSE: To construct a useful index for use as a prognostic factor in cases of aortic aneurysm. MATERIALS AND METHODS: Using CT or EBT, we studied nine ruptured aortic aneurysms, 40 unruptured aneurysms, and 42 normalaortas, measuring aortic diameter and wall thickness. Systolic, mean or diastolic blood pressure was used as apressure parameter. Tangential stress(TS) and the tangential stress index ( TSI) were calculated by modified Laplace's law. RESULTS: Average diastolic TS's (TSI's) were 1938 (4.13), 905 (1.84) and 554 (0.94) in rupturedaneurysm, unruptured aneurysm and normal groups, respectively (p<0.01). ROC curves of diastolic TS and TSI wereseen in a "useful study" zone. With a threshold of 1230 (2.90) for TS (TSI), the sensitivity and thespecificity for differentiation of ruptured and unruptured aneurysms were 100% (100%) and 75% (88%), and thepositive and the negative predictive values were 47% (64%) and 100% (100%), respectively (p<0.01). Amongsystolic, mean and diastolic TS 's and TS I 's, the diastolic TSI showed the highest specificity at its maximalsensitivity. CONCLUSION: Diastolic TSI is a more accurate prognostic factor for aortic aneurysm.