Simultaneous Unwrapping Phase and Error Recovery from Inhomogeneity (SUPER) for Quantitative Susceptibility Mapping of the Human Brain

PURPOSE: The effect of global inhomogeneity on quantitative susceptibility mapping (QSM) was investigated. A technique referred to as Simultaneous Unwrapping Phase with Error Recovery from inhomogeneity (SUPER) is suggested as a preprocessing to QSM to remove global field inhomogeneity-induced phase by polynomial fitting. MATERIALS AND METHODS: The effect of global inhomogeneity on QSM was investigated by numerical simulations. Three types of global inhomogeneity were added to the tissue susceptibility phase, and the root mean square error (RMSE) in the susceptibility map was evaluated. In-vivo QSM imaging with volunteers was carried out for 3.0T and 7.0T MRI systems to demonstrate the efficacy of the proposed method. RESULTS: The SUPER technique removed harmonic and non-harmonic global phases. Previously only the harmonic phase was removed by the background phase removal method. The global phase contained a non-harmonic phase due to various experimental and physiological causes, which degraded a susceptibility map. The RMSE in the susceptibility map increased under the influence of global inhomogeneity; while the error was consistent, irrespective of the global inhomogeneity, if the inhomogeneity was corrected by the SUPER technique. In-vivo QSM imaging with volunteers at 3.0T and 7.0T MRI systems showed better definition in small vascular structures and reduced fluctuation and non-uniformity in the frontal lobes, where field inhomogeneity was more severe. CONCLUSION: Correcting global inhomogeneity using the SUPER technique is an effective way to obtain an accurate susceptibility map on QSM method. Since the susceptibility variations are small quantities in the brain tissue, correction of the inhomogeneity is an essential element for obtaining an accurate QSM.

Índice de aclaramiento pulmonar en pediatría / Lung clearance index

The rate of lung clearance is a measure of the ventilation inhomogeneity determined during multiple breath washout (MBW). Higher values of lung clearance index (LCI) indicate greater ventilation inhomogeneity. The test is performed during tidal breathing, needs little cooperation and coordination, and can be done in all age groups. Different tracer gases can be used; the most common are gas nitrogen as resident gas and sulfohexafluoride (SF6) as an exogenous gas.LCI has been used in various pediatric diseases, such as asthma, bronchopulmonary dysplasia and especially in patients with cystic fibrosis (CF), where high LCI values had been a more sensitive tool that spirometry to detect the early disease and bronchiectasis. It has also been used to monitor the progression of early lung disease, since the value of LCI in preschoolers predicted FEV1 in children of school age. Finally, in patients older than 6 years LCI has proven to be a useful tool to assess response to interventions in patients with normal lung function test. In conclusion the use of LCI is very promising in CF patients with early stages of the disease, and in the clinical monitoring of patients with CF. Its role in other respiratory diseases such as asthma, is still to be determined.

El índice de aclaramiento de pulmón (LCI) es una medida de la falta de homogeneidad de ventilación determinado durante el lavado pulmonar de múltiples respiraciones (MBW). Los valores más altos de LCI indican mayor inhomogeneidad de ventilación. La prueba se realiza durante respiración corriente y necesita poca cooperación y coordinación, por lo que se puede realizar en todos los grupos de edad. Pueden utilizarse diferentes gases trazadores; los más comunes son el nitrógeno como gas residente y sulfohexafluoride (SF6) como gas exógeno.LCI ha sido utilizado en diferentes enfermedades en pediatría, tales como asma, displasia broncopulmonar y especialmente fibrosis quística (FQ). En esta última los valores elevados de LCI son una herramienta más sensible quela espirometría para la detección de la enfermedad pulmonar precoz y bronquiectasias. También ha sido utilizado para monitorizar la progresión de la enfermedad pulmonar, ya que el valor de LCI en los niños en edad preescolar predice el VEF1 en edad escolar. Finalmente en pacientes mayores de 6 años LCI ha demostrado ser una herramienta útil para evaluarla respuesta a intervenciones en pacientes con función pulmonar normal. En conclusión el uso de LCI es muy prometedor en pacientes con FQ en etapa precoz de la enfermedad, su rolen el monitoreo clínico de los pacientes con FQ. En otras enfermedades de las vías respiratorias, como el asma, esto aún está por definirse.

Accuracy of dose planning for prostate radiotherapy in the presence of metallic implants evaluated by electron spin resonance dosimetry

Radiotherapy is one of the main approaches to cure prostate cancer, and its success depends on the accuracy of dose planning. A complicating factor is the presence of a metallic prosthesis in the femur and pelvis, which is becoming more common in elderly populations. The goal of this work was to perform dose measurements to check the accuracy of radiotherapy treatment planning under these complicated conditions. To accomplish this, a scale phantom of an adult pelvic region was used with alanine dosimeters inserted in the prostate region. This phantom was irradiated according to the planned treatment under the following three conditions: with two metallic prostheses in the region of the femur head, with only one prosthesis, and without any prostheses. The combined relative standard uncertainty of dose measurement by electron spin resonance (ESR)/alanine was 5.05%, whereas the combined relative standard uncertainty of the applied dose was 3.35%, resulting in a combined relative standard uncertainty of the whole process of 6.06%. The ESR dosimetry indicated that there was no difference (P>0.05, ANOVA) in dosage between the planned dose and treatments. The results are in the range of the planned dose, within the combined relative uncertainty, demonstrating that the treatment-planning system compensates for the effects caused by the presence of femur and hip metal prostheses.

Background Gradient Correction using Excitation Pulse Profile for Fat and T2* Quantification in 2D Multi-Slice Liver Imaging

PURPOSE: The objective of this study was to develop background gradient correction method using excitation pulse profile compensation for accurate fat and T2* quantification in the liver. MATERIALS AND METHODS: In liver imaging using gradient echo, signal decay induced by linear background gradient is weighted by an excitation pulse profile and therefore hinders accurate quantification of T2* and fat. To correct this, a linear background gradient in the slice-selection direction was estimated from a B0 field map and signal decays were corrected using the excitation pulse profile. Improved estimation of fat fraction and T2* from the corrected data were demonstrated by phantom and in vivo experiments at 3 Tesla magnetic field. RESULTS: After correction, in the phantom experiments, the estimated T2* and fat fractions were changed close to that of a well-shimmed condition while, for in vivo experiments, the background gradients were estimated to be up to approximately 120 microT/m with increased homogeneity in T2* and fat fractions obtained. CONCLUSION: The background gradient correction method using excitation pulse profile can reduce the effect of macroscopic field inhomogeneity in signal decay and can be applied for simultaneous fat and iron quantification in 2D gradient echo liver imaging.

Development of in-house software to calculate dose for intensity-modulated radiation therapy based on lung CT-patient data.

Background: In external radiotherapy, the delivered dose is calculated from the treatment planning system. Various types of software have been used to verify the patient dose distribution. Objective: Develop the in-house software (ISOFT) to calculate dose in intensity-modulated radiotherapy (IMRT) based on lung CT-patient data by combining the modified Clarkson integration with 3D-beam subtraction method. Materials and methods: An ISOFT was developed for 6MV X-rays Varian Clinac21EX linear accelerator and the CT-based patient data. The multileaf collimators (MLCs) file from the Varian Eclipse treatment planning was transferred to the ISOFT. The ISOFT was used to calculate the dose distribution with correction of tissue inhomogeneity. To test the accuracy of the ISOFT, the normal MLC-shaped fields and IMRT plans were measured in a water phantom and in a thorax phantom, respectively. Then, these measurements were compared with the doses calculated from the ISOFT and the Varian Eclipse treatment planning system. Results: The deviation between the measurements and calculations by the ISOFT for MLC-shaped fields in the water phantom fell within 0.5%. There were mostly higher calculated doses in lung compared with the measured result in the thorax phantom. The overestimated doses due to loss of scattering in the low-density materials were considered less in all methods of calculation. The measured lung dose difference from the ISOFT was within 5% criterion of acceptability. Conclusion: The ISOFT can be used conveniently to verify dose calculation in heterogeneous media.

Water-Fat Imaging with Automatic Field Inhomogeneity Correction Using Joint Phase Magnitude Density Function at Low Field MRI

PURPOSE: A new inhomogeneity correction method based on two-point Dixon sequence is proposed to obtain water and fat images at 0.35T, low field magnetic resonance imaging (MRI) system. MATERIALS AND METHODS: Joint phase-magnitude density function (JPMF) is obtained from the in-phase and out-of-phase images by the two-point Dixon method. The range of the water signal is adjusted from the JPMF, and 3D inhomogeneity map is obtained from the phase of corresponding water volume. The 3D inhomogeneity map is used to correct the inhomogeneity field iteratively. RESULTS: The proposed water-fat imaging method was successfully applied to various organs. The proposed 3D inhomogeneity correction algorithm provides good performances in overall multi-slice images. CONCLUSION: The proposed water-fat separation method using JPMF is robust to field inhomogeneity. Three dimensional inhomogeneity map and the iterative inhomogeneity correction algorithm improve water and fat imaging substantially.

Accurate Localization of Metal Electrodes Using Magnetic Resonance Imaging

PURPOSE: Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. MATERIALS AND METHODS: Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional (90degrees view) and 45degrees oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. RESULTS: There was least field inhomogeneity along the 45degrees line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with 45degrees oblique-view was coincided regardless of susceptibility. And with 45degrees oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the 45degrees oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. CONCLUSION: We suggested the method for accurate localization of electrode using 45degrees oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.

Accurate Localization of Metal Electrodes Using Magnetic Resonance Imaging

PURPOSE: Localization using MRI is difficult due to susceptibility induced artifacts caused by metal electrodes. Here we took an advantage of the B0 pattern induced by the metal electrodes by using an oblique-view imaging method. MATERIALS AND METHODS: Metal electrode models with various diameters and susceptibilities were simulated to understand the aspect of field distortion. We set localization criteria for a turbo spin-echo (TSE) sequence usingconventional (90degrees view) and 45degrees oblique-view imaging method through simulation of images with various resolutions and validated the criteria usingphantom images acquired by a 3.0T clinical MRI system. For a gradient-refocused echo (GRE) sequence, which is relatively more sensitive to field inhomogeneity, we used phase images to find the center of electrode. RESULTS: There was least field inhomogeneity along the 45degrees line that penetrated the center of the electrode. Therefore, our criteria for the TSE sequence with 45degrees oblique-view was coincided regardless of susceptibility. And with 45degrees oblique-view angle images, pixel shifts were bidirectional so we can detect the location of electrodes even in low resolution. For the GRE sequence, the 45degrees oblique-view anglemethod madethe lines where field polarity changes become coincident to the Cartesian grid so the localization of the center coordinates was more facilitated. CONCLUSION: We suggested the method for accurate localization of electrode using 45degrees oblique-view angle imaging. It is expected to be a novelmethodto monitoring an electrophysiological brain study and brain neurosurgery.

Evaluation of the Secondary Particle Effect in Inhomogeneous Media for Proton Therapy Using Geant4 Based MC Simulation / 의학물리

In proton therapy, the analysis of secondary particles is important due to delivered dose outside the target volume and thus increased potential risk for the development of secondary cancer. The purpose of this study is to analyze the influence of secondary particles from proton beams on fluence and energy deposition in the presence of inhomogeneous material by using Geant4 simulation toolkit. The inhomogeneity was modeled with the condition that the adipose tissue, bone and lung equivalent slab with thickness of 2 cm were inserted at 30% (Plateau region) and 80% (Bragg peak region) dose points of maximum dose in Bragg curve. The energy of proton was varied with 100, 130, 160 and 190 MeV for energy dependency. The results for secondary particles were presented for the fluence and deposited energy of secondary particles at inhomogeneous condition. Our study demonstrates that the fluence of secondary particles is neither influenced insertion of inhomogeneties nor the energy of initial proton, while there is a little effect by material density. The deposited energy of secondary particles has a difference in the position placed inhomogeneous materials. In the Plateau region, deposited energy of secondary particles mostly depends on the density of inserted materials. Deposited energy in the Bragg region, in otherwise, is influenced by both density of inserted material and initial energy of proton beams. Our results suggest a possibility of prediction about the distribution of secondary particles within complex heterogeneity.

Ultrasonography of the salivary glands in primary Sjogren's syndrome with positive anti Ro/SS-A antibody / 대한내과학회지

BACKGROUND/AIMS: This study sought to evaluate the diagnostic value of salivary gland ultrasonography in primary Sjogren's syndrome with anti-Ro/SS-A antibody. The secondary goal was to assess the relationship between the grade of parenchymal inhomogeneity and the anti-Ro/SS-A antibody titer or clinical manifestations. METHODS: The parotid and submandibular glands were examined ultrasonographically in 30 patients having primary Sjogren's syndrome with anti-Ro/SS-A antibody and 30 control subjects with no evidence of Sjogren's syndrome. The ultrasonographic definition of parenchymal inhomogeneity of the salivary glands was blurred glandular borders, multiple hyperechoic bands, and hypoechoic areas. The parenchymal inhomogeneity of the glands was categorized into four grades. RESULTS: Parenchymal inhomogeneity of the parotid gland was seen in 25 (83.3%) patients with primary Sjogren's syndrome and 2 (6.7%) control subjects. Of these cases, the submandibular gland showed parenchymal inhomogeneity in 24 (80%) patients with primary Sjogren's syndrome and 2 (6.7%) control subjects. The sensitivity and specificity of parenchymal inhomogeneity of the parotid gland were 83.3% and 93.3%, respectively, and 80% and 93.3% for the submandibular gland. The grade of ultrasonographic parenchymal inhomogeneity was related to a diagnosis of Sjogren's syndrome (p<0.001) and the time of dissolution of the wafer, but had no relationship with the anti-Ro/SS-A antibody titer. A high degree of interobserver agreement was found in the assessment of parenchymal abnormalities of the salivary gland (parotid gland: kappa=0.859; submandibular gland: kappa=0.837). CONCLUSIONS: Salivary gland ultrasonography is a useful method for visualizing glandular structural changes and making a diagnosis of primary Sjogren's syndrome.

Estimation of Inhomogeneity Correction Factor in Small Field Dosimetry / 의학물리

In this study, we estimated inhomogeneity correction factor in small field. And, we evaluated accuracy of treatment planning and measurement data which applied inhomogeneity correction factor or not. We developed the Inhomogeneity Correction Phantom (ICP) for insertion of inhomogeneity materials. The inhomogeneity materials were 12 types in each different electron density. This phantom is able to adapt the EBT film and 0.125 cc ion chamber for measurement of dose distribution and point dose. We evaluated comparison of planning and measurement data using ICP. When we applied to inhomogeneity correction factor or not, the average difference was 1.63% and 10.05% in each plan and film measurement data. And, the average difference of dose distribution was 10.09% in each measurement film. And the average difference of point dose was 0.43% and 2.09% in each plan and measurement data. In conclusion, if we did not apply the inhomogeneity correction factor in small field, it shows more great difference in measurement data. The planning system using this study shows good result for correction of inhomogeneity materials. In radiosurgery using small field, we should be correct the inhomogeneity correction factor, more exactly.

Tissue Inhomogeneity Correction in Clinical Application of Transmission Dosimetry to Head and Neck Cancer Radiation Treatment / 대한방사선종양학회지

PURPOSE: To confirm the reproducibility of in vivo transmission dosimetry system and the accuracy of the algorithms for the estimation of transmission dose in head and neck radiation therapy patients. MATERIALS AND MEHTODS: From September 5 to 18, 2001, transmission dose measurements were performed when radiotherapy was given to brain or head and neck cancer patients. The data of 35 patients who were treated more than three times and whose central axis of the beam was not blocked were analyzed in this study. To confirm the reproducibility of this system, transmission dose was measured before daily treatment and then repetitively every hour during the treatment time, with a field size of 10x10 cm2 and a delivery of 100 MU. The accuracy of the transmission dose calculation algorithms was confirmed by comparing estimated dose with measured dose. To accurately estimate transmission dose, tissue inhomogeneity correction was done. RESULTS: The measurement variations during a day were within +/-0.5% and the daily variations in the checked period were within +/-1.0%, which were acceptable for system reproducibility. The mean errors between estimated and measured doses were within +/-5.0% in patients treated to the brain, +/-2.5% in head, and +/-5.0% in neck. CONCLUSION: The results of this study confirmed the reproducibility of our system and its usefulness and accuracy for daily treatment. We also found that tissue inhomogeneity correction was necessary for the accurate estimation of transmission dose in patients treated to the head and neck.

Ventricular Inhomogeneity and Beat-to-beat QT Interval Variability after Surgical Repair of Tetralogy of Fallot

PURPOSE: The object of this study is to determine whether QT interval variability in patients with postoperative tetralogy of Fallot increases. METHODS: We enrolled 41 patients who had total correction of tetralogy of Fallot, and 31 healthy controls. They were 6-12 years old. Patients were divided into 2 groups : arrhythmia-positive patients(n=10) who had ventricular premature contractions more than 30/hour or who had couplets, and arrhythmia-negative patients(n=31). We selected the 10-minute arrhythmia-free portion of 24-hour ambulatory ECG recorded during sleep(1-3AM). We selected the 2nd beat of recordings for a template, then found the QT interval for each beat. The method was that T-wave shape best matches template T-wave under the time-stretch model. The mean heart rate and variance and mean QT interval and variance were computed and then a QT variability index(QTVI)-which represents the log ratio between QT interval variability and heart rate variability-was derived. RESULTS: Postoperative tetralogy of Fallot patients with/without ventricular arrhythmia showed significantly increased QTVI compared with the control(-0.481+/-0.310/-0.661+/-0.376 vs -1.200+/-0.380, P<0.0001). There was a trend that QTVI in patients with ventricular arrhythmia increased more than in patients without ventricular arrhythmia, but there were no statistical significances. CONCLUSION: QT interval variability increased in repaired tetralogy of Fallot patients with/without ventricular arrhythmia compared with the control. And this finding indicates that inhomogeneity of temporal ventricular repolarization exists in repaired tetralogy of Fallot patients.