Chemical Shift Selective Saturation Research Articles

Water-Fat Separation for the Knee on a 50 mT Portable MRI Scanner.

The Dixon method is frequently employed in clinical and scientific research for fat suppression, because it has lower sensitivity to static magnetic field inhomogeneity compared to chemical shift selective saturation or its variants and maintains image signal-to-noise ratio (SNR). Recently, research on very-low-field (VLF < 100 mT) magnetic resonance imaging (MRI) has regained popularity. However, there is limited literature on water-fat separation in VLF MRI. Here, we present a modified two-point Dixon method specifically designed for VLF MRI. Most experiments were performed on a homemade 50 mT portable MRI scanner. The receiving coil adopted a homemade quadrature receiving coil. The data were acquired using spin-echo and gradient-echo sequences. We considered the T2* effect, and added priori information to existing two-point Dixon method. Then, the method used regional iterative phasor extraction (RIPE) to extract the error phasor. Finally, least squares solutions for water and fat were obtained and fat signal fraction was calculated. For phantom evaluation, water-only and fat-only images were obtained and the local fat signal fractions were calculated, with two samples being 0.94 and 0.93, respectively. For knee imaging, cartilage, muscle and fat could be clearly distinguished. The water-only images were able to highlight areas such as cartilage that could not be easily distinguished without separation. This work has demonstrated the feasibility of using a 50 mT MRI scanner for water-fat separation. To the best of our knowledge, this is the first reported result of water-fat separation at a 50 mT portable MRI scanner.

T1 강조 경추자기공명영상에 대한 최적의 지방소거기법의 정량적 평가: TSE-CHESS 과 TSE-SPAIR 의 비교

Abstract he purpose of this study is to know clinical usefulness for fat suppression of the body curved portion compared with TSE-CHESS and TSE-SPAIR technique. A total of 25 normal volunteers without cervical spine disease were studied on a 3.0 T MRI scanner. As a quantitative analysis, PSNRs and CNRs were evaluated by using two methods for fat suppression of the body curved portion. As a results, PSNRs and CNRs for fat suppression were significantly greater for the TSE-SPAIR technique compared to TSE-CHESS technique. In conclusion, this study showed that a TSE-SPAIR technique has improved PSNRs and CNRs for evaluating of fat suppression in the body curved portion. These conclusions in the future will be provided information in diagnosis of fat suppression for the body curved portion. Kye Words : Magnetic Resonance Imaging, CHEmical shift Selective Saturation, SPectrally selective Adiabatic Inversion Recovery, Turbo Spin Echo Received 4 September 2013, Revised 27 September 2013Accepted 20 November 2013Corresponding Author: Eun-Hoe Goo(Department of Radiological Science, Cheongju University)Email: eunhoegoo@gmail.co.krⒸ The Society of Digital Policy & Management. All rights reserved. This is an open-access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.otg/licenses/by-nc/3.0), which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is ISSN: 1738-1916 properly cited.

Comparison of the effects of the CHESS sequence and the SPAIR sequence for fat saturation

This study compared the abilities of the chemical-shift selective saturation(CHESS) and the spectrally-adiabatic inversion recovery (SPAIR) fat-saturation techniques to resolve the recent problems in fat saturation caused by areas of changing volume such as the head and the neck and by metal artifacts when T1 fat-saturation techniques representing the anatomical images and T2 fat-saturation techniques representing pathological images are used. To compare the abilities of CHESS and SPAIR, we acquired images of the head and the neck and of the pelvis, and we compared the contrast-to-noise ratios (CNRs) and the signal-to-noise ratios (SNRs) of the signals from the flexed body parts. Images were taken of the abdomens, heads and necks, and pelvises of 15 men and 15 women (30 in total). In all scanning techniques, the SNRs and the CNRs were calculated based on a quantitative analysis method with a view to obtaining uniform data. According to the study results, the CNRs of the SPAIR and the CHESS techniques for the pelvis in the T1-weighted image were 55.10 and 67.23, respectively. The SNRs of the SPAIR technique were70.61 for muscle and 15.50 for fat whereas the SNRs of the CHESS technique were 79.23 for muscle and 12.00 for fat. For the pelvis in the T2-weighted image, the CNRs of the SPAIR and the CHESS technique were 12.50 and 16.66, respectively. The SNRs of the SPAIR technique were 16.98 for muscle and 5.14 for fat. In contrast, the SNRs of the CHESS technique were 27.90 for muscle and 11.23 for fat. Consequently, the signal intensity was higher in the CHESS than in the SPAIR technique. Nevertheless, with regard to the clinical usefulness, the image quality was higher in the SPAIR technique than in the CHESS technique.

TH-A-218-01: Managing Fat in MRI: A Technical Perspective

Water and fat are the two predominant sources of signal for in vivo MRI. Because fat is omnipresent in many parts of our body and because fat appears bright in many types of basic MR images, it is often essential to be able to successfully suppress the fat signal. Chemical shift selective saturation (CHESS) and short‐tau inversion recovery (STIR) are the two well‐known techniques for this purpose. Despite their widespread use and success, CHESS and STIR have fundamental limitations and as a consequence, poor fat suppression is one of the most frequently‐encountered image quality issues in clinical practice. Further, it is difficult to implement the CHESS or STIR‐based techniques for some emerging applications such as fast dynamic imaging. Another MRI technique for managing fat that has gained increasing clinical use only in the last few years was first published by Tom Dixon in 1984. The original idea of the so‐called Dixon techniques is to collect two images that have water and fat signals in‐phase and 180o out‐of‐phase, respectively. These two images can be added and subtracted to yield a “water‐only” image and a “fat‐only” image. Thus, the Dixon techniques have the potential for simultaneous fat suppression and fat quantification. Additionally, it was recognized and is now demonstrated that the Dixon techniques can be made highly insensitive to magnetic field inhomogeneity and highly SNR and scan time efficient. In this talk, I will provide an overview of some major development of the techniques for managing fat in MRI. I will focus particularly on the physical basis as well as the respective pros and cons of the different fat management techniques in MRI. Learning Objectives: 1. Understand the physical basis and advantages and disadvantages of several major fat management techniques in MRI 2. Understand some major issues and technical development of the Dixon techniques for water and fat imaging 3. Understand some remaining challenges and future opportunities for fat imaging and applications by MRI

Postsurgical Spinal Magnetic Resonance Imaging With Iterative Decomposition of Water and Fat With Echo Asymmetry and Least-Squares Estimation

Magnetic resonance imaging (MRI) is the most popular follow-up study for patients who have undergone spinal surgery. However, the image quality often becomes poor because of artifacts from metal implants and/or from failed fat suppression, which obscure diagnosis. Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) is a new fat suppression method that is less affected by inhomogeneity of the magnetic field. Here, we compared postsurgical spinal MRI with IDEAL versus chemical shift selective saturation (CHESS). For 35 patients who had spinal surgery, we examined T2-weighted fast spin-echo sagittal images of the spine with both IDEAL and CHESS. Two radiologists evaluated the degrees of fat suppression and spinal canal projection from 0 (least/worst) to 2 (most/best). Fat suppression and spinal canal scores for IDEAL were statistically higher than those for CHESS (P < 0.05). Iterative decomposition of water and fat with echo asymmetry and least-squares estimation is clinically useful for postoperative spinal MRI.

Fast spin‐echo triple‐echo Dixon: Initial clinical experience with a novel pulse sequence for fat‐suppressed T2‐weighted abdominal MR imaging

To evaluate a prototype fast spin echo (FSE) triple-echo-Dixon (fTED) technique for breath-hold, fat-suppressed, T2-weighted abdominal imaging. Forty patients underwent breath-hold T2-weighted abdominal imaging with fTED and conventional fast recovery (FR) FSE with chemical shift-selective saturation (CHESS). FRFSE and fTED images were compared for overall image quality, homogeneity of fat suppression, image sharpness, anatomic detail, and phase artifact. Depiction of disease was recorded separately for FRFSE and fTED images. FTED successfully reconstructed water-only and fat-only images from source images in all 40 cases. Water and fat separation was perfect in 36 (0.90) patients. Homogeneity of fat suppression was superior on the fTED images in 38 (0.95) of 40 cases. FTED images showed better anatomic detail in 27 (0.68), and less susceptibility artifact in 20 (0.50). FRFSE images showed less vascular pulsation artifact in 30 (0.75) cases, and less phase artifact in 21 (0.53) cases. There was no difference in depiction of disease for FRFSE and fTED images. FTED is a robust sequence providing breath-hold T2-weighted images with superior fat suppression, excellent image quality, and at least equal depiction of disease compared to conventional breath-hold T2-weighted FRFSE imaging.

Expansion of the spectral bandwidth by spatial and chemical shift selective saturation in high-speed magnetic resonance spectroscopic imaging.

A new spectral bandwidth expansion technique for high-speed magnetic resonance spectroscopic imaging (MRSI) based on an echo-planar technique is presented. This expansion can be achieved by spatial and chemical shift selective saturation without increasing the total measurement time. In addition, displacement along the slice-select direction due to chemical-shift differences between the measured compounds is also suppressed. Experimental results are shown using a phantom consisting of benzene and acetone. High spatial resolution (1 x 1 mm2) and wide spectral bandwidth (1.5-1.8 kHz; the effective spectral bandwidth has been doubled) are obtained without the displacement along the slice-select direction.

5446384 Simultaneous imaging of multiple spectroscopic components with magnetic resonance

Magnetic resonance images of selected chemical species are generated by the application of a multi-band radio-frequency excitation pulse. The radio-frequency pulse excites an arbitrary number of spectral bands. As the imaging phase encoding gradient pulse is advanced, the phase of each excitation band is advanced by a unique amount. This causes the signals from the spins in a particular band to appear at a position in the phase encoding direction which is the stem of the spin position and an offset arising from the phase increment given to that excitation band. Additional selectivity of selected chemical species can be accomplished by combining the multi-band excitation with chemical shift selective saturation radio-frequency pulses and echo-time modulation.

Rapid in vivo proton shimming

A rapid and completely automated method of adjusting the magnetic field (B0) homogeneity for in vivo proton spectroscopy and imaging is described. B0 inhomogeneity maps are generated by a gradient-recalled echo pulse sequence in which the frequency dispersion is chosen to eliminate the effects of the fat/water chemical shift. Low-order shim values are derived by magnitude-weighted least-squares fits to the B0 maps and automatically applied as DC offsets to the X, Y, and Z gradient amplifiers. Imaging with chemical shift selective saturation is used as a measure of the efficacy of the technique. Results indicate that AUTOSHIM improves the overall homogeneity: however, local high-order field distortions which cannot be corrected by linear gradients are generated by certain air/tissue and bone/tissue morphology. In such cases a "Zoom SHIM" may be applied over a limited region of interest for local homogeneity improvement at the expense of other regions. It is suggested that such scans are a necessity for recording the homogeneity during clinical MR spectroscopy.