PURPOSE: In-vivo conductivity reconstruction using transmit field (B1+) information of MRI was proposed. We assessed the accuracy of conductivity reconstruction in the presence of statistical noise in complex B1 + map and provided a parametric model of the conductivity-to-noise ratio value. MATERIALS AND METHODS: The B1+ distribution was simulated for a cylindrical phantom model. By adding complex Gaussian noise to the simulated B1+ 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 B1+ 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 B1+ phase than to noise in B1+ 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 B1+ map, Larmor frequency, the conductivity value itself and the number of averaged pixels. To estimate accurate conductivity value of the targeted tissue, SNR of B1+ 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 B1+ map is modeled. By using this model, further issues regarding filtering and reconstruction algorithms can be investigated for MREPT.
Evaluation Studies as Topic ; Magnetic Resonance Imaging ; Noise* ; Radius ; Signal-To-Noise Ratio

OBJECTIVES: To increase the booster vaccination rate, the Korean government legislated a measles vaccination for elementary school students in 2001, requiring parents to submit a certificate of vaccination upon the admission of the students to elementary school. The purpose of this study was to evaluate the validity of measles vaccination certificates which were issued to parents. METHODS: Using questionnaire survey data of 890 general practitioners and 9,235 parents in 2005, we investigated the evidence for booster vaccination certificates of measles. RESULTS: In the survey of general practitioners, 59.5% of the certificates depended on the medical records of clinic, 13.5% was immunization booklets, 23.7% was re-immunizations, 1.9% was confirmation of record of other clinics, and 1.4% was parents' statements or requests without evidence. In the survey of parents, 36.2% of the certificates depended on the medical records of clinic, 43.4% was immunization booklets, 18.0% was reimmunizations, and 2.4% was parents statements or requests without evidence. CONCLUSIONS: Our findings show that a majority of the booster vaccination certificates of measles was issued on the basis of documented vaccinations and it means that the implementation of the law requiring the submission of elementary school students' vaccination certificates has been very successful in Korea.
Adult ; Aged ; *Certification ; Documentation ; Female ; Humans ; Korea ; Male ; Measles Vaccine/*administration & dosage ; Medical Records ; Middle Aged ; Parents ; Questionnaires ; *Schools ; Vaccination/legislation & jurisprudence/*standards/statistics & numerical data

Visualization of the tissue loss tangent property can provide distinct contrast and offer new information related to tissue electrical properties. A method for non-invasive imaging of the electrical loss tangent of tissue using magnetic resonance imaging (MRI) was demonstrated, and the effect of loss tangent was observed through simulations assuming a hyperthermia procedure. For measurement of tissue loss tangent, radiofrequency field maps (B1+ complex map) were acquired using a double-angle actual flip angle imaging MRI sequence. The conductivity and permittivity were estimated from the complex valued B1+ map using Helmholtz equations. Phantom and ex-vivo experiments were then performed. Electromagnetic simulations of hyperthermia were carried out for observation of temperature elevation with respect to loss tangent. Non-invasive imaging of tissue loss tangent via complex valued B1+ mapping using MRI was successfully conducted. Simulation results indicated that loss tangent is a dominant factor in temperature elevation in the high frequency range during hyperthermia. Knowledge of the tissue loss tangent value can be a useful marker for thermotherapy applications.
Fever ; Hyperthermia, Induced ; Magnetic Resonance Imaging ; Magnets

OBJECTIVES: Obsessive-compulsive disorder (OCD) is a chronic and disabling psychiatric disorder. The duration of untreated illness (DUI) has been suggested as one of the predictors of clinical course and outcome in various psychiatric disorders. There is increasing evidence that cognitive dysfunction is associated with the prognosis of OCD. The aim of this study was to investigate the influence of DUI on the neurocognitive functions in patients with OCD. METHODS: Sixty-two patients with a DSM-IV diagnosis of OCD from the outpatient clinic were included in this study. We defined the short DUI if the DUI was 2-year or less and the long DUI if it was longer than 2-year. Neurocognitive functions were assessed by visuospatial memory function test and 4 subsets of K-WAIS such as vocabulary, arithmetic, block design and picture arrangement. Differences in neurocognitive functions as well as clinical variables between OCD patients with short DUI and those with long DUI were investigated. Correlation analyses were also performed to determine the correlation between DUI and neurocognitive functions. RESULTS: Compared with the short DUI group, the long DUI group performed worse in the block design test, which measures executive function. The long DUI group also had a higher level of compulsive symptom severity than the short DUI group. However, the DUI was not correlated with neurocognitive functions. CONCLUSIONS: Findings in this preliminary study suggest that the long DUI in patients with OCD is associated with more severe executive dysfunction. Studies with larger samples and longitudinal design are needed to further confirm the prognostic role of the DUI in OCD.
Ambulatory Care Facilities ; Diagnosis ; Diagnostic and Statistical Manual of Mental Disorders ; Executive Function ; Humans ; Memory ; Obsessive-Compulsive Disorder* ; Prognosis ; Vocabulary