Modified Dixon Method Research Articles

Anisotropy of elastic and photoelastic properties of lithium niobate crystals

The elastic and photoelastic constants of lithium niobate crystals and the attenuation coefficients of acoustic waves at room temperature have been determined by the Bragg diffraction of light by sound. The components of the photoelasticity tensor were determined by the modified Dixon method. The obtained values of the constants were used to determine the anisotropy of the effective elastic and photoelastic constants with a change in the direction of propagation of acoustic waves in the (100) symmetry plane, for different directions of the wave vector and polarization of light relative to the sound wave vector. It is shown that, for certain geometries of the Bragg light diffraction, there is a correlation between the orientation dependences of the effective elastic and photoelastic constants in the investigated plane. The results of the study can be used to analyze the anisotropy of the photoelastic properties of lithium niobate crystals and determine the diffraction geometry with the highest efficiency of Bragg light diffraction.

Prospective study of change in liver function and fat in patients with colorectal liver metastases undergoing preoperative chemotherapy: protocol for the CLiFF Study

IntroductionPreoperative chemotherapy in patients undergoing resection for colorectal liver metastases (CLM) improves oncological outcomes. However, chemotherapy-associated liver injury (occurring in two patterns: vascular and fat deposition) is a real clinical...

Non-Invasive, Fast and Reliable Assessment of Age- And Gender-Related Pancreas and Liver Fat Content in Completely Healthy Individuals: Modified Dixon Method with 3 Tesla Magnetic Resonance Imaging

Acquiring the content of liver fat related to age and gender, and iron signal time as well as fat content values in pancreas and muscle tissue in healthy subjects with normal body mass index (BMI), by using Modified Dixon (mDixon) magnetic resonance imaging.

Estimation of hepatic fat fraction using modified Dixon magnetic resonance imaging techniques: effect of liver cirrhosis

PurposeTo evaluate modified Dixon MRI techniques in hepatic fat estimation and to assess the effect of cirrhosis. Methods235 patients who underwent liver MRI were included. Correlation between modified Dixon techniques with MRS was assessed. Accuracy of MR techniques in hepatic fat estimation was calculated, and the result was compared between patients with/without liver cirrhosis. ResultsCorrelation between modified Dixon and MRS was better in group without liver cirrhosis, and accuracy of modified Dixon method was higher in group without liver cirrhosis. ConclusionsModified Dixon techniques estimate hepatic fat fraction noninvasively, but the result can be influenced by the presence of liver cirrhosis.

Assessment of the Quality of Breast MR Imaging Using the Modified Dixon Method and Frequency-Selective Fat Suppression: A Phantom Study.

To obtain objective and concrete data by physically assessing the quality of breast magnetic resonance images based on the fat-suppression effect by the modified Dixon method (mDixon) and frequency-selective fat suppression (e-Thrive) using an original lipid-content breast phantom that could easily reveal the influence of non-uniform fat suppression in breast magnetic resonance imaging. The fat-suppression uniformity was approximately seven times superior when using mDixon compared with when using e-Thrive. mDixon appears to have a significant advantage.

Comparison among T1-Weighted Magnetic Resonance Imaging, Modified Dixon Method, and Magnetic Resonance Spectroscopy in Measuring Bone Marrow Fat

Introduction. An increasing number of studies are utilizing different magnetic resonance (MR) methods to quantify bone marrow fat due to its potential role in osteoporosis. Our aim is to compare the measurements of bone marrow fat among T1-weighted magnetic resonance imaging (MRI), modified Dixon method (also called fat fraction MRI (FFMRI)), and magnetic resonance spectroscopy (MRS). Methods. Contiguous MRI scans were acquired in 27 Caucasian postmenopausal women with a modified Dixon method (i.e., FFMRI). Bone marrow adipose tissue (BMAT) of T1-weighted MRI and bone marrow fat fraction of the L3 vertebra and femoral necks were quantified using SliceOmatic and Matlab. MRS was also acquired at the L3 vertebra. Results. Correlation among the three MR methods measured bone marrow fat fraction and BMAT ranges from 0.78 to 0.88 (P < 0.001) in the L3 vertebra. Correlation between BMAT measured by T1-weighted MRI and bone marrow fat fraction measured by modified FFMRI is 0.86 (P < 0.001) in femoral necks. Conclusion. There are good correlations among T1-weighted MRI, FFMRI, and MRS for bone marrow fat quantification. The inhomogeneous distribution of bone marrow fat, the threshold segmentation of the T1-weighted MRI, and the ambiguity of the FFMRI may partially explain the difference among the three methods.

Dual Double‑gradient‑echo MRI for Liver Fat Content Analysis

We have devised a modified Dixon method for analyzing fatty infiltration of the liver using a dual double- gradient-echo (DDGRE) sequence. To correct the T2* decay, fourfold echo images were obtained by out-of-phase (TE = 2.3/6.9 ms) and in-phase (4.6/9.2 ms) double-echo sets during a single breath-hold scan on a 1.5 T MRI. The liver fat fractions obtained using the DDGRE method were determined in patients with fatty liver and in healthy volunteers as controls. Moreover, the fat fractions determined in vitr ou sing the DDGRE method were compared with those determined by the conventional double-gradient-echo method, other MRI methods, and X-ray CT. The average fat fractions in patients with fatty liver obtained with the DDGRE method was over 10%, and was significantly greater than those in healthy volunteers. The fat fraction of the phantom obtained with the DDGRE method showed the closest agreement with the actual fat content. The DDGRE method with a single breath-hold makes it possible to simply and accurately analyze fatty infiltration of the liver.

Introduction of fast MR imaging in the assessment of hepatic steatosis

We determined the utility of fast gradient echo techniques (modified Dixon method) in the assessment of hepatic fat content. Fast spoiled gradient echo was performed on bovine liver/corn oil homogenates with known fat fractions (FF E) to assess the accuracy of fat quantitation (FF MRI). The pulse sequence was manipulated via alterations in TE (echo time), TR (repetition time), and α (flip angle). In vivo studies were then performed using breath-holding maneuvers on normal adult volunteers and subjects at risk to develop hepatic steatosis, with cystic fibrosis or morbid obesity. At out-of-phase, TE, TR, and α were 2.1 ms, 7.3 ms, and 30–50° and in-phase TE, TR, and α were 4.2 ms, 9.3 ms, and 30–50°; FF MRI correlated well with FF E. An elevated fat fraction was observed in a high percentage of subjects with cystic fibrosis and morbid obesity. Fast gradient echo techniques were used successfully in the assessment of hepatic steatosis. The reduced acquisition times permitted in vivo analysis on adults and children using breath hold maneuvers.

Systemic Bone Marrow Disorders

In a prospective clinical study, 26 patients (22 with malignant lymphoma and 4 with myelofibrosis) and 9 healthy volunteers were examined by conventional magnetic resonance and proton chemical shift imaging (CSI; modified Dixon method). On the basis of the CSI data, a quantitative evaluation of the relative fat and water signal fractions in regions of interest of the femur, pelvis, and spine was performed. In 16 of 17 patients with biopsy-proven bone marrow disorders, CSI revealed a significant reduction in the fat fraction of the bone marrow relative to that of normal volunteers. The visual assessment could detect only 14 of the 17 pathological cases.

Knochenmarkveränderungen bei Morbus Hodgkin: MR-Tomographie und Chemical Shift Imaging

A patient with Hodgkin's disease, who had received various forms of treatment, was examined by MR tomography and scintigraphy; the results are discussed together with the findings of the bone marrow biopsy. A spectroscopic imaging technique (modified Dixon method) and quantitative evaluation of the fat and water components of the RF signal provide new diagnostic information that may improve the differential diagnosis. Serial examinations following supra-lethal therapy and bone marrow transplantation have been able to show changes in the bone marrow and these could be evaluated quantitatively.

1H-spectroscopic imaging using a modified Dixon method

Inhomogeneities of the static magnetic field and the different susceptibilities of the various types of tissue are a serious problem for all imaging methods of spectral separation of fat and water. In the Dixon method this problem is solved by using the absolute values of the image signals for the separation. In image regions where the fat signal is greater than the water signal, however, this results in an incorrect assignment of the computed solutions. A modified Dixon method was developed to easily carry out the spectral separation completely over the entire image by interactively building up a phase correction matrix after the data acquisition. The spectral delineation of the fat tissue finds an interesting application in the treatment planning with fast neutrons in accounting for the increase in dose.

Single-acquisition chemical-shift imaging of a binary system with use of stimulated echoes.

A method for separating binary chemical-shift components with a single image data acquisition by means of stimulated echoes is demonstrated. With a strategy analogous to the modified Dixon method, three stimulated echoes were acquired to form three complex images. In each of the images, the complex pixel intensities were imparted, by design of the pulse sequence, with a phase factor carrying chemical-shift or field inhomogeneity information. With these three images, true fat/water separation can be obtained in biologic tissues. Studies at high field strength (4.7 T) on a toluene phantom, a pseudo-binary chemical-shift system, were used to evaluate the applicability of the method. Its clinical feasibility was demonstrated on a healthy human subject in a 0.6-T whole-body imaging system.