Chemical Shift Selective Sequence Research Articles

Comparison between 3-point Dixon- and CHESS-based OMERACT-recommended MRI protocols in hands of patients with suspicion of early rheumatoid arthritis

PurposeTo compare fat suppression effectiveness, image quality and disease activity scores between MRI protocols based on the Dixon method and the Chemical Shift Selective (CHESS) technique in hands of patients with suspicion of early rheumatoid arthritis (RA). MethodBoth hands of 28 patients (19 women; mean age 45.2 years old) with suspicion of early RA were prospectively imaged with Dixon- and CHESS-based OMERACT recommended protocols at 1.5 T including fat-suppressed T2-weighted and contrast-enhanced T1-weighted imaging. Two radiologists (R1/R2) separately assessed effectiveness of fat suppression and determined RAMRIS scores woth the Dixon- and CHESS-based protocols. R1 repeated the RAMRIS scoring and measured contrast-to-noise ratios (CNRs) on Dixon and CHESS images. Statistics included 2-way ANOVA test for the comparison of CNRs and Bland-Altman methodology for inter-technique and intra-observer agreement (p < 0.05). ResultsFat suppression failure occurred in up to 1 patient with the Dixon- and 25 patients with the CHESS-based protocols. CNRs were significantly higher on T1-weighted and lower on T2-weighted Dixon images than on the corresponding CHESS images (p ≤ 0.042). Median bias of the difference between Dixon- and CHESS-based RAMRIS scores was not significantly different from 0 (−0.8 to +1.0 and −1.1 to +1.4 for R1/R2). Median bias of the difference between RAMRIS scores at first and second readings was significantly different from 0 with the CHESS-based protocols (−0.8 to +1.7) but not with the Dixon-based protocols (+0.0 to +1.0). ConclusionsDixon sequences yield more effective fat suppression and more reproducible RAMRIS scoring than CHESS sequences in hands with suspicion of early RA.

Conspicuity of Malignant Liver Tumors on Diffusion-Weighted Imaging With Short tau Inversion Recovery After Gadolinium Ethoxybenzyl Diethylenetriaminepentaacetic Acid Administration.

Diffusion-weighted imaging (DWI) has been used for the detection and characterization of liver tumors because it has excellent contrast resolution. DWI using short tau inversion recovery (STIR) can improve tumor-to-liver contrast after gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) administration that shortens the T1 relaxation of liver parenchyma. To quantitatively and qualitatively compare the conspicuity of malignant liver tumors on DWI after Gd-EOB-DTPA administration between STIR and chemical shift selective (CHESS) sequences. Single-institution retrospective study. Fifty-seven patients with histologically confirmed malignant liver tumors were evaluated. Low b-value DWIs with STIR and CHESS sequences 18-20 minutes after Gd-EOB-DTPA administration were acquired at 1.5T. Tumor contrast-to-noise ratio (CNR) and visual grade of tumor conspicuity on DWI between STIR and CHESS sequences were compared. Paired Student's t-test and the Wilcoxon signed rank-test were applied. P < 0.05 was considered statistically significant. The mean tumor CNR and visual grade of tumor conspicuity on DWI were significantly higher for STIR than for CHESS (both P < 0.001). Regardless of the presence of chronic liver disease, the mean CNR (normal liver 33.5 ± 19.8 vs. 15.7 ± 12.2, P < 0.001; chronic liver disease 19.6 ± 11.0 vs. 9.2 ± 7.8, P < 0.001) and the visual conspicuity grade (normal liver 3.36 ± 0.64 vs. 2.56 ± 0.77, P < 0.001; chronic liver disease 2.94 ± 0.80 vs. 2.25 ± 0.84, P = 0.001) were significantly higher for STIR than for CHESS. Mean CNR and the visual conspicuity grade were also significantly higher for STIR than for CHESS in patients with hepatocellular carcinomas (CNR 18.1 ± 10.5 vs. 8.8 ± 7.2, P < 0.001; visual grade 2.88 ± 0.83 vs. 2.22 ± 0.87, P = 0.001) or metastases (CNR 35.0 ± 19.3 vs. 16.2 ± 13.1, P < 0.001; visual grade 3.45 ± 0.51 vs. 2.59 ± 0.73, P < 0.001). DWI using STIR may be more helpful for depicting malignant liver tumors after Gd-EOB-DTPA administration compared with DWI using CHESS. 3 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2019;49:565-573.

Fat suppression at three-dimensional T1-weighted MR imaging of the hands: Dixon method versus CHESS technique.

To compare the effectiveness of fat suppression and the image quality of the Dixon method with those of the chemical shift-selective (CHESS) technique in hands of normal subjects at non-enhanced three-dimensional (3D) T1-weighted MR imaging. Both hands of 14 healthy volunteers were imaged with 3D fast spoiled gradient echo (FSPGR) T1-weighted Dixon, 3D FSPGR T1-weighted CHESS and 3D T1-weighted fast spin echo (FSE) CHESS sequences in a 1.5T MR scanner. Three radiologists scored the effectiveness of fat suppression in bone marrow (EFSBM) and soft tissues (EFSST) in 20 joints per subject. One radiologist measured the signal-to-noise ratio (SNR) in 10 bones per subject. Statistical analysis used two-way ANOVA with random effects (P<0.0083), paired t-test (P<0.05) and observed agreement to assess differences in effectiveness of fat suppression, differences in SNR and interobserver agreement. EFSBM was statistically significantly higher for the 3D FSPGR T1-weighted Dixon than for the 3D FSPGR T1-weighted CHESS sequence and the 3D FSE T1-weighted CHESS sequence (P<0.0001). EFSST was statistically significantly higher for the 3D FSPGR T1-weighted Dixon than for the 3D FSPGR T1-weighted CHESS sequence (P<0.0011) and for the 3D FSE T1-weighted CHESS sequence in the axial plane (P=0.0028). Mean SNR was statistically significantly higher for 3D FSPGR T1-weighted Dixon sequence than for 3D FSPGR T1-weighted CHESS and 3D FSE T1-weighted CHESS sequences (P<0.0001). The Dixon method yields more effective fat suppression and higher SNR than the CHESS technique at 3D T1-weighted MR imaging of the hands.

Fat suppression at 2D MR imaging of the hands: Dixon method versus CHESS technique and STIR sequence

ObjectiveTo compare the effectiveness of fat suppression and the signal-to-noise ratio (SNR) of the Dixon method with those of the CHESS (Chemical Shift-Selective) technique and STIR (Short Tau Inversion Recovery) sequence in hands of normal subjects at 2D MR imaging. Material and methods14 healthy volunteers (mean age of 29.4 years) consented to have both hands prospectively imaged with SE T1 Dixon, T1 CHESS, T2 Dixon, T2 CHESS and STIR sequences in a 1.5T MR scanner. Three radiologists scored the effectiveness of fat suppression in bone marrow (EFSBM) and soft tissues (EFSST) in 20 joints per subject. One radiologist measured the SNR in 10 bones per subject. Statistical analysis used two-way ANOVA with random effects, paired t-test and observed agreement to assess differences in effectiveness of fat suppression, differences in SNR and inter-observer agreement. ResultsEFSBM was statistically significantly higher for T1 Dixon than for T1 CHESS and for T2 Dixon than for T2 CHESS (p<0.0001). EFSBM was significantly higher for T2 Dixon than for STIR in the coronal plane (p=0.0020). The SNR was significantly higher for T1 Dixon than for T1 CHESS and for T2 Dixon than for STIR (p<0.0001). The SNR was significantly lower for T2 Dixon than for T2 CHESS (p<0.0001). ConclusionThe Dixon method yields more effective fat suppression and higher SNR than the CHESS technique at 2D T1-weighted MR imaging of the hands. At T2-weighted MR imaging, fat suppression is more effective with the Dixon method while SNR is higher with the CHESS technique.

Measurement of an oil–water flow using magnetic resonance imaging

In the oil and gas industry, the current standard that is used to quantify the fraction of water (so called “water-cut”) in an oil–water multiphase flow stipulates the oil–water mixture to be homogenised to ensure sampling is representative. Although there are devices that comply with the minimum requirements of the sindustry standards for custody transfer applications, our understanding of the homogenisation process is limited; where even small errors arising due to inhomogeneity could cost tens of millions of dollars annually per metering station. To that end, we have developed a flow loop and homogenisation process to study oil–water multiphase flow. Experimental investigations were carried out using magnetic resonance (MR) imaging and hence the entire flow loop has been designed to fit within a MR laboratory, with the homogenisation step itself performed within the bore of the magnet. Measurements were performed in a 2.5″ diameter Perspex pipe at stream velocities between 0.2ms−1 and 1.47ms−1, to mimic typical pipeline conditions. The size of the pipe diameter used in this study is unique compared to previous studies for oil–water flow applications using MR. To facilitate experimental investigation, we have developed MR techniques to quantify the water-cut and improve our understanding of mixing in liquid–liquid flows. Chemical shift selective (CHESS) MR was used to quantify the water-cut between 2.5% and 25% for static samples. These results show a linear relationship and demonstrate that the water cut is measured with an accuracy of ±0.2%. The CHESS sequence was combined with MR imaging sequences to enable visualisation of the water distribution in real time in one-dimension, or as a time-averaged measurement in two dimensions. MR measurements were also performed on an oil–water multiphase flow at a stream velocity of 0.2ms−1 and for water cuts between 1% and 7.5%. Local measurements of the water cut are performed with an error of less than 1%.

Selective missing pulse steady state free precession (MP-SSFP): inner volume and chemical shift selective imaging in a steady state sequence.

To examine new sequences that restrict acquisition of spins to those excited by both of the RF pulses in missing pulse steady state free precession (MP-SSFP) MRI. New MP-SSFP sequences were created by replacing one of the slice selective pulses (SSPs) with an orthogonal SSP for inner volume imaging, and with a chemical shift selective (CHESS) pulse for chemical shift imaging. The inner volume sequence was applied to a reduced field of view at the center of a resolution phantom; resulting images were evaluated for differences in the aliased signal. The CHESS sequence was applied to volunteers, as well as to and fat, water, and acetic acid phantoms. Results were evaluated with SNR measurements. The inner volume sequence eliminated the aliased signal, while nonselected fat and water levels were suppressed to that of noise by the CHESS sequence. Results suggest a novel steady state technique for rapid inner volume or chemical shift imaging.

Imaging Low-Concentration Metabolites in the Presence of a Large Background Signal

A pulse sequence (CD-CHESS) is described that addresses the challenge of imaging low-concentration metabolites whose chemical shifts are close to that of water. This sequence avoids the problems of the basic chemical- shift- selective (CHESS) imaging sequences, which produce an image contaminated by residual signal from the undesired component. Several signal suppression schemes are combined with the basic 2D CHESS imaging sequences and examined using a specially constructed chemical-shift phantom. The degree of suppression for the new enhanced CHESS sequences is compared with that of the basic CHESS sequences and the SUBMERGE-CHESS sequence. The most effective sequence incorporates cw irradiation and soft-pulse saturation with the basic CHESS sequence. The CDCHESS imaging sequence produces a suppression ratio of better than 1000 to 1 when the desired and undesired peaks are 1 ppm apart. The effectiveness of the CD-CHESS sequence is demonstrated by imaging the sugar protons in a phantom composed of 10% (w/v) sucrose in water. The CD-CHESS sequence is used for the selective imaging of sugars in peas, demonstrating that it can be extended to the broad lines normally encountered in biological specimens.

Cartilage disorders: comparison of spin-echo, CHESS, and FLASH sequence MR images.

Magnetic resonance (MR) imaging is known to be a suitable modality for the visualization of the hyaline cartilage and the fibrocartilage joint structures. To compare standard spin-echo (SE) images with water images obtained with the chemical shift selective (CHESS) sequence and with the fast low angle shot (FLASH) sequence, examinations were performed with all three sequences in eight volunteers and 28 patients with inflammatory degenerative and traumatic alterations of the knee, hip, and sacroiliac joints. Arthroscopic and/or surgical correlation were available in 16 patients; bone scanning and computed tomography of the sacroiliac joints were performed in four patients. CHESS-water and FLASH images proved superior to SE images in demonstrating hyaline cartilage disorders. There was no difference between SE, CHESS, and FLASH in the detection of fibrocartilage disorders. Short imaging times and satisfactory depiction of cartilage alterations make FLASH a promising method.