Fat Suppression Effect Research Articles

Comparison of different acceleration factors of artificial intelligence-compressed sensing for brachial plexus MRI imaging: scanning time and image quality.

3D brachial plexus MRI scanning is prone to examination failure due to the lengthy scan times, which can lead to patient discomfort and motion artifacts. Our purpose is to investigate the efficacy of artificial intelligence-assisted compressed sensing (ACS) in improving the acceleration efficiency and maintaining or enhancing the image quality of brachial plexus MR imaging. A total of 30 volunteers underwent 3D sampling perfection with application-optimized contrast using different flip angle evolution short time inversion recovery using a 3.0T MR scanner. The imaging protocol included parallel imaging (PI) and ACS employing acceleration factors of 4.37, 6.22, and 9.03. Radiologists evaluated the neural detail display, fat suppression effectiveness, presence of image artifacts, and overall image quality. Signal intensity and standard deviation of specific anatomical sites within the brachial plexus and background tissues were measured, with signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) subsequently calculated. Cohen's weighted kappa (κ), One-way ANOVA, Kruskal-Wallis and pairwise comparisons with Bonferroni-adjusted significance level. P < 0.05 was considered statistically significant. ACS significantly reduced scanning times compared to PI. Evaluations revealed differences in subjective scores and SNR across the sequences (P < 0.05), with no marked differences in CNR (P > 0.05). For subjective scores, ACS 9.03 were lower than the other three sequences in neural details display, image artifacts and overall image quality. There was no significant difference in fat suppression. For objective quantitative evaluation, SNR of right C6 root in ACS 6.22 and ACS 9.03 was higher than that in PI; SNR of left C6 root in ACS 4.37, ACS 6.22 and ACS 9.03 was higher than that in PI; SNR of medial cord in ACS 6.22, ACS 9.03 was higher than that in PI. Compared with PI, ACS can shorten scanning time while ensuring good image quality.

Carotid and aortic plaque imaging using 3D gradient-echo imaging and the three-point Dixon method with improved motion-sensitized driven-equilibrium (iMSDE)

BackgroundWe devised a method that combines the 3D-Dixon-gradientecho (GRE) method with an improved motion-sensitized driven-equilibrium (iMSDE) to suppress blood flow signals. PurposeThe purpose of this study was to evaluate the effectiveness of the new method we developed plaque imaging method (3D-Dixon-GRE with the iMSDE method). Study typeRetrospective cohort. PopulationThirty-nine patients who underwent cervical plaque imaging.FIELD STRENGTH/SEQUENCE:3.0 T/3D-GRE. AssessmentSignal intensities of the common carotid artery, aorta, plaque, muscle, and subcutaneous fat were measured through the VISTA and the 3D-Dixon-GRE with iMSDE methods, and each contrast was calculated. Statistical testUsed the Mann Whitney U test. P-values below 0.05 were considered statistically significant. ResultsPlaque and muscle contrast estimated through the VISTA method and 3D-Dixon-GRE with iMSDE method was 1.60 ± 0.96 and 2.04 ± 1.06, respectively, (P < 0.05). The contrast between the flow (common carotid artery and Aorta) and muscle according to the VISTA method and 3D-Dixon-GRE with iMSDE method was 0.24 ± 0.11 and 0.40 ± 0.12, respectively (P < 0.001). Finally, the mean contrast for subcutaneous fat and muscle at six locations was 3.05 ± 1.25 and 0.81 ± 0.23 for the VISTA method and 3D-Dixon-GRE with the iMSDE method, respectively (P < 0.001). Data conclusionCompared to the conventional method (VISTA), the 3D-Dixon-GRE with iMSDE method is preferable in relation to the fat suppression effect, but it is disadvantageous regarding blood flow signal suppression. Therefore, the 3D-Dixon-GRE with the iMSDE method could be considered useful for plaque imaging.

Basic MRI Study in the Imaging Direction of a Diffusion-weighted Whole Body Imaging with Background Body Signal Suppression

A diffusion-weighted whole body imaging with background body signal suppression (DWIBS) is usually imaged as a whole body with Transverse (Tra). However, Tra has a large number of stations and a larger number than Coronal (Cor), so the scan time is longer. There are also drawbacks, such as signal unevenness between series. It is known that the effect of distortion is large in Cor. There is no report on it in Sagittal (Sag). Therefore, in this study, we focused on Sag and examined the imaging time, image distortion, fat suppression effect, and continuity between stations. In the examination by the phantom, the scan time was the shortest for Cor and the longest for Sag. In the strain evaluation, the effect of strain could be suppressed compared to Cor by using a rectangle field of view (FOV) in the anterior to posterior (AP) direction in Tra and Sag. There was no difference in the fat suppression effect depending on the imaging direction. Similar results were obtained in a study of 10 healthy volunteers, with Sag having the best continuity between stations.

Assessment of ultrashort echo time (UTE) T2* mapping at 3T for the whole knee: repeatability, the effects of fat suppression, and knee position.

Knee tissues such as tendon, ligament and meniscus have short T2* relaxation times and tend to show little to no signal in conventional magnetic resonance acquisitions. An ultrashort echo time (UTE) technique offers a unique tool to probe fast-decaying signals in these tissues. Clinically relevant factors should be evaluated to quantify the sensitivity needed to distinguish diseased from control tissues. Therefore, the objectives of this study were to (I) quantify the repeatability of UTE-T2* relaxation time values, and (II) evaluate the effects of fat suppression and (III) knee positioning on UTE-T2* relaxation time quantification. A dual-echo, three-dimensional center-out radially sampling UTE and conventional gradient echo sequences were utilized to image gadolinium phantoms, one ex-vivo specimen, and five in-vivo subjects on a clinical 3T scanner. Scan-rescan images from the phantom and in-vivo experiments were used to evaluate the repeatability of T2* relaxation time values. Fat suppressed and non-suppressed images were acquired for phantoms and the ex-vivo specimen to evaluate the effect of fat suppression on T2* relaxation time quantifications. The effect of knee positioning was evaluated by imaging in-vivo subjects in extended and flexed positions within the knee coil and comparing T2* relaxation times quantified from tissues in each position. Phantom and in-vivo measurements demonstrated repeatable T2* mapping, where the percent difference between T2* relaxation time quantified from scan-rescan images was less than 8% for the phantom and knee tissues. The coefficient of variation across fat suppressed and non-suppressed images was less than 5% for the phantoms and ex-vivo knee tissues, showing that fat suppression had a minimal effect on T2* relaxation time quantification. Knee position introduced variability to T2* quantification of the anterior cruciate ligament, posterior cruciate ligament, and patellar tendon, with percent differences exceeding 20%, but the meniscus showed a percent difference less than 10%. The 3D radial UTE sequence presented in this study could potentially be used to detect clinically relevant changes in mean T2* relaxation time, however, reproducibility of these values is impacted by knee position consistency between scans.

Water excitation with LIBRE pulses in three-dimensional variable flip angle fast spin echo for fat-free and large field of view imaging at 3 tesla

PurposeTo develop and evaluate a sequence in which water excitation with lipid insensitive binomial off-resonant radio frequency excitation (LIBRE) pulses is incorporated into three-dimensional (3D) variable flip angle fast spin echo (LIBRE-vf-FSE) for fat-free and large field of view imaging at 3 Tesla (T). Materials and methodsNumerical simulation was conducted to optimize the parameters of LIBRE pulses, including the flip angle, pulse duration, and frequency offset, for maximizing the fat suppression effect of the proposed LIBRE-vf-FSE sequence. The sequence was then implemented at 3 T and assessed in phantoms, lower extremity imaging of 8 healthy volunteers, and head/neck imaging of 5 healthy volunteers. Conventional water excitation (WE) and fat saturation (FatSat) were also performed for comparison. Signal-to-noise ratio (SNR) of fat and contrast-to-noise ratio (CNR) between fat and water were used to evaluate the level of fat suppression. Standard deviation (SD) of SNR was used to evaluate the uniformity of fat suppression. ResultsThe numerical simulation demonstrated that LIBRE-vf-FSE enables large volume imaging with uniform fat suppression, which was further confirmed by phantom and healthy volunteer experiments. LIBRE provided the lowest fat SNR and offered more uniform fat suppression compared with the WE and FatSat. Specifically, average oil SNRs obtained by LIBRE (1.10 ms, 360 Hz, and 60°), WE, and FatSat were (180.1 vs. 280.2 vs. 811.2) in phantom experiments, and average fat SNRs and SDs in legs obtained by LIBRE (1.10 ms, 360 Hz, and 60°), WE, and FatSat were (85.1 vs. 105.0 vs. 105.1) and (22.4 vs. 27.4 vs. 56.4) in vivo experiments, respectively. ConclusionThe proposed LIBRE-vf-FSE sequence allows for fat suppression and large field of view imaging at 3 T. It could be an alternative approach for fat-free vf-FSE scan.

Feasibility of salt pads to improve fat suppression in low-field MRI systems

IntroductionFat-suppressed images are essential in clinical practice but are often affected by magnetic field inhomogeneity, resulting in poor image quality. We hypothesized that salt (99% sodium chloride [NaCl]) could be used as a magnetic field uniformity assist pad and verified whether salt pads improve magnetic field uniformity and the fat suppression effect in low-field magnetic resonance imaging (MRI) systems. MethodsWe conducted a small clinical study where coronal 2D fast spin-echo T2-weighted MRI with fat suppression was performed. The subjects were 10 healthy volunteers (six men and four women) with no surgical history, with a mean age of 20.5 years (range, 20–30 years). In the clinical study, we performed physical and visual evaluation by imaging a subject's knee with and without salt pads. ResultsThe results of the clinical study indicated that the use of salt pads improved the magnetic field uniformity, thus increasing the fat suppression effect. ConclusionsSalt pads improved the homogeneity of the magnetic field and the fat suppression effect in low-field MRI systems. Implications for practiceThe use of salt pads in low-field MRI systems could provide more accurate fat suppression images.

T2 Mapping with and without Fat-Suppression to Predict Treatment Response to Intravenous Glucocorticoid Therapy for Thyroid-Associated Ophthalmopathy.

ObjectiveTo evaluate the performance of baseline clinical characteristics and pretherapeutic histogram parameters derived from T2 mapping of the extraocular muscles (EOMs) in the prediction of treatment response to intravenous glucocorticoid (IVGC) therapy for active and moderate-to-severe thyroid-associated ophthalmopathy (TAO) and to investigate the effect of fat-suppression (FS) in T2 mapping in this prediction.Materials and MethodsA total of 79 patients clinically diagnosed with active, moderate-to-severe TAO (47 female, 32 male; mean age ± standard deviation, 46.1 ± 10 years), including 43 patients with a total of 86 orbits in the responsive group and 36 patients with a total of 72 orbits in the unresponsive group, were enrolled. Baseline clinical characteristics and pretherapeutic histogram parameters derived from T2 mapping with FS (i.e., FS T2 mapping) or without FS (i.e., conventional T2 mapping) of EOMs were compared between the two groups. Independent predictors of treatment response to IVGC were identified using multivariable analysis. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the predictive performance of the prediction models. Differences between the models were examined using the DeLong test.ResultsCompared to the unresponsive group, the responsive group had a shorter disease duration, lower kurtosis (FS-kurtosis), lower standard deviation, larger 75th, 90th, and 95th (FS-95th) T2 relaxation times in FS mapping and lower kurtosis in conventional T2 mapping. Multivariable analysis revealed that disease duration, FS-95th percentile, and FS-kurtosis were independent predictors of treatment response. The combined model, integrating all identified predictors, had an optimized area under the ROC curve of 0.797, 88.4% sensitivity, and 62.5% specificity, which were significantly superior to those of the imaging model (p = 0.013).ConclusionAn integrated combination of disease duration, FS-95th percentile, and FS-kurtosis was a potential predictor of treatment response to IVGC in patients with active and moderate-to-severe TAO. FS T2 mapping was superior to conventional T2 mapping in terms of prediction.

Evaluation of Fat Suppression Effect and SNR Using Pixel Shift Method of Fat Suppression Images with CHESS and IDEAL in Head and Neck MR Imaging

This study aims to evaluate the fat suppression effect on images of the head and neck region using chemical shift selective (CHESS), and iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL). A self-made phantom containing oil around the simulated bone marrow and muscle was scanned. The signal-to-noise ratio (SNR) was calculated using the National Electrical Manufacturers Association (NEMA) subtraction and pixel shift methods. Thereafter, the fat suppression effect and SNR were calculated in clinical images using the pixel shift method. In both phantom and clinical images, the fat suppression effect was higher using IDEAL. In addition, the SNR of the NEMA subtraction method and the pixel shift method in phantom images was higher in the simulated bone marrow than in the simulated muscle. The SNR of the vertebral body was higher than that of the tongue in the clinical images using IDEAL, and the same tendency was observed in the phantom image evaluation. However, there was a difference in SNR between the phantom and clinical images. In the head and neck region, fat-suppressed images using IDEAL showed the same higher fat-suppressing effect as that in a previous study. The SNR for the phantom and the clinical images was different. The SNR calculated using the pixel shift method for the phantom images with IDEAL and the clinical images showed the same tendency. Although there is a difference between the SNRs of phantom and clinical images calculated by the pixel shift method, it is suggested that the method can be used to compare the SNR between tissues such as the vertebral body and the tongue.

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.

Confounding factors in multi-parametric q-MRI protocol: A study of bone marrow biomarkers at 1.5 T

ObjectThe MRI tissue characterization of vertebral bone marrow includes the measurement of proton density fat fraction (PDFF), T1 and T2* relaxation times of the water and fat components (T1W, T1F, T2*W, T2*F), IVIM diffusion D, perfusion fraction f and pseudo-diffusion coefficient D*.However, the measurement of these vertebral bone marrow biomarkers (VBMBs) is affected with several confounding factors.In the current study, we investigated these confounding factors including the regional variation taking the example of variation between the anterior and posterior area in lumbar vertebrae, B1 inhomogeneity and the effect of fat suppression on f. Materials and methodsA fat suppressed diffusion-weighted sequence and two 3D gradient multi-echo sequences were used for the measurements of the seven VBMBs. A turbo flash B1 map sequence was used to estimate B1 inhomogeneities and thus, to correct flip angle for T1 quantification. We introduced a correction to perfusion fraction f measured with fat suppression, namely fPDFF. ResultsA significant difference in the values of PDFF, f and fPDFF, T1F, T2*W and D was observed between the anterior and posterior region. Although, little variations of flip angle were observed in this anterior-posterior direction in one vertebra but larger variations were observed in head-feet direction from L1 to L5 vertebrae. DiscussionThe regional difference in PDFF, fPDFF and T2*W can be ascribed to differences in the trabecular bone density and vascular network within vertebrae.The regional variation of VBMBs shows that care should be taken in reproducing the same region-of-interest location along a longitudinal study. The same attention should be taken while measuring f in fatty environment, and measuring T1. Furthermore, the MRI-protocol presented here allows for measurements of seven VBMBs in less than 6 min and is of interest for longitudinal studies of bone marrow diseases.

Diffusion processes modeling in magnetic resonance imaging

BackgroundThe paper covers modern approaches to the evaluation of neoplastic processes with diffusion-weighted imaging (DWI) and proposes a physical model for monitoring the primary quantitative parameters of DWI and quality assurance. Models of hindered and restricted diffusion are studied.Material and methodTo simulate hindered diffusion, we used aqueous solutions of polyvinylpyrrolidone with concentrations of 0 to 70%. We created siloxane-based water-in-oil emulsions that simulate restricted diffusion in the intracellular space. To obtain a high signal on DWI in the broadest range of b values, we used silicon oil with high T2: cyclomethicone and caprylyl methicone. For quantitative assessment of our phantom, we performed DWI on 1.5T magnetic resonance scanner with various fat suppression techniques. We assessed water-in-oil emulsion as an extracorporeal source signal by simultaneously scanning a patient in whole-body DWI sequence.ResultsWe developed phantom with control substances for apparent diffusion coefficient (ADC) measurements ranging from normal tissue to benign and malignant lesions: from 2.29 to 0.28 mm2/s. The ADC values of polymer solutions are well relevant to the mono-exponential equation with the mean relative difference of 0.91%.ConclusionThe phantom can be used to assess the accuracy of the ADC measurements, as well as the effectiveness of fat suppression. The control substances (emulsions) can be used as a body marker for quality assurance in whole-body DWI with a wide range of b values.

A mask method to assess the uniformity of fat suppression in phantom studies.

Fat suppression is a technique used to suppress the signals from adipose tissues, during clinical evaluation of the tissues near the fat-tissue boundary. However, in cases where the scan area has a complicated shape, the effect of fat suppression may demonstrate poor uniformity, resulting in diagnosis-related difficulties. To improve the uniformity of fat suppression, phantom studies are more suitable than volunteer studies. In this study, we evaluated the reliability of the region of interest (ROI) dependency using an unevenness phantom, to develop a method to assess the uniformity of fat suppression while using whole magnetic resonance imaging by masking the surrounding phantom. We modulated different ROI sizes, which were eroded from 100% to approximately 50%, and observed that the normalized absolute average deviation and error increased with decreased ROI. Using our method, more objective, concrete, and accurate data could be obtained by including the whole-body phantom (whole poor uniformity area).

Fat suppression for ultrashort echo time imaging using a novel soft-hard composite radiofrequency pulse.

To design a soft-hard composite pulse for fat suppression and water excitation in ultrashort echo time (UTE) imaging with minimal short T2 signal attenuation. The composite pulse contains a narrow bandwidth soft pulse centered on the fat peak with a small negative flip angle (-α) and a short rectangular pulse with a small positive flip angle (α). The fat magnetization experiences both tipping-down and -back with an identical flip angle and thus returns to the equilibrium state, leaving only the excited water magnetization. Bloch simulations, as well as knee, tibia, and ankle UTE imaging studies, were performed to investigate the effectiveness of fat suppression and corresponding water signal attenuation. A conventional fat saturation (FatSat) module was used for comparison. Signal suppression ratio (SSR), defined as the ratio of signal difference between non-fat-suppression and fat-suppression images over the non-fat-suppression signal, was introduced to evaluate the efficiency of the composite pulse. Numerical simulations demonstrate that the soft-hard pulse has little saturation effect on short T2 water signals. Knee, tibia, and ankle UTE imaging results suggest that comparable fat suppression can be achieved with the soft-hard pulse and the FatSat module. However, much less water saturation is induced by the soft-hard pulse, especially for short T2 tissues, with SSRs reduced from 71.8 ± 6.9% to 5.8 ± 4.4% for meniscus, from 68.7 ± 5.5% to 7.7 ± 7.6% for bone, and from 62.9 ± 12.0% to 4.8 ± 3.2% for the Achilles tendon. The soft-hard composite pulse can suppress fat signals in UTE imaging with little signal attenuation on short T2 tissues.

An investigation of the effect of fat suppression and dimensionality on the accuracy of breast MRI segmentation using U-nets.

Accurate segmentation of the breast is required for breast density estimation and the assessment of background parenchymal enhancement, both of which have been shown to be related to breast cancer risk. The MRI breast segmentation task is challenging, and recent work has demonstrated that convolutional neural networks perform well for this task. In this study, we have investigated the performance of several two-dimensional (2D) U-Net and three-dimensional (3D) U-Net configurations using both fat-suppressed and nonfat-suppressed images. We have also assessed the effect of changing the number and quality of the ground truth segmentations. We designed eight studies to investigate the effect of input types and the dimensionality of the U-Net operations for the breast MRI segmentation. Our training data contained 70 whole breast volumes of T1-weighted sequences without fat suppression (WOFS) and with fat suppression (FS). For each subject, we registered the WOFS and FS volumes together before manually segmenting the breast to generate ground truth. We compared four different input types to the U-nets: WOFS, FS, MIXED (WOFS and FS images treated as separate samples), and MULTI (WOFS and FS images combined into a single multichannel image). We trained 2D U-Nets and 3D U-Nets with these data, which resulted in our eight studies (2D-WOFS, 3D-WOFS, 2D-FS, 3D-FS, 2D-MIXED, 3D-MIXED, 2D-MULTI, and 3D-MULT). For each of these studies, we performed a systematic grid search to tune the hyperparameters of the U-Nets. A separate validation set with 15 whole breast volumes was used for hyperparameter tuning. We performed Kruskal-Walis test on the results of our hyperparameter tuning and did not find a statistically significant difference in the ten top models of each study. For this reason, we chose the best model as the model with the highest mean dice similarity coefficient (DSC) value on the validation set. The reported test results are the results of the top model of each study on our test set which contained 19 whole breast volumes annotated by three readers fused with the STAPLE algorithm. We also investigated the effect of the quality of the training annotations and the number of training samples for this task. The study with the highest average DSC result was 3D-MULTI with 0.96±0.02. The second highest average is 2D WOFS (0.96±0.03), and the third is 2D MULTI (0.96±0.03). We performed the Kruskal-Wallis one-way ANOVA test with Dunn's multiple comparison tests using Bonferroni P-value correction on the results of the selected model of each study and found that 3D-MULTI, 2D-MULTI, 3D-WOFS, 2D-WOFS, 2D-FS, and 3D-FS were not statistically different in their distributions, which indicates that comparable results could be obtained in fat-suppressed and nonfat-suppressed volumes and that there is no significant difference between the 3D and 2D approach. Our results also suggested that the networks trained on single sequence images or multiple sequence images organized in multichannel images perform better than the models trained on a mixture of volumes from different sequences. Our investigation of the size of the training set revealed that training a U-Net in this domain only requires a modest amount of training data and results obtained with 49 and 70 training datasets were not significantly different. To summarize, we investigated the use of 2D U-Nets and 3D U-Nets for breast volume segmentation in T1 fat-suppressed and without fat-suppressed volumes. Although our highest score was obtained in the 3D MULTI study, when we took advantage of information in both fat-suppressed and nonfat-suppressed volumes and their 3D structure, all of the methods we explored gave accurate segmentations with an average DSC on >94% demonstrating that the U-Net is a robust segmentation method for breast MRI volumes.

Improvement of Fat Suppressing Effect for Finger and Neck MRI by Using Small Glass Beads

The defectiveness of the fat suppression becomes the factor of the decrease of the quality of the diagnosis of magnetic resonance imaging. It is reported that the use of magnetic field uniformity adjuvant pad is effective for reduce poor fat suppression. The ball bullets, polystyrene balls, and polished rice are used for pad packing material, in recently, it was reported that fat suppression effect was good by the use of the small glass beads. Therefore, we tested the utility of small glass beads pad in the neck and fingers in this study. Neck and the fingers of subjects were imaged with T1-weighted image with fat suppression and T1-high resolution isotropic volume excitation image. The fat suppression effect of each image was compared with the polished rice and glass beads as material of pad used by physical, observation, and contact evaluation. In the result, satisfactory results were obtained by using glass beads, and it is suggested that fat suppression effect is improved by using glass beads as a filling material of pad in clinical study as a conclusion.

Optimization of Fat Suppression Technique and Imaging Parameters for MR Neurography Using 3D Turbo Spin Echo with Variable Refocusing Flip Angle at 3.0 T: Visualization of Brachial Plexus

Magnetic resonance neurography (MRN) has been used to evaluate abnormal conditions of entire nerves and nerve bundles. A fat-suppressed 3D turbo spin echo (TSE) sequence is one of the imaging techniques for MRN, which has been widely adopted at 1.5 T. However, MRN of the brachial plexus using a 3D TSE sequence with short-term inversion recovery (STIR) reduces the effect of fat suppression at 3.0 T. Moreover, the use of spectral pre-saturation with inversion recovery (SPIR) does not result in uniform fat suppression due to the inhomogeneity of the static magnetic field. On the other hand, it is well known that the visibility of the brachial plexus using a 3D TSE sequence greatly changes with the equivalent echo time (TEequiv). Therefore, we optimized the fat suppression technique and TEequiv so that the 3D TSE sequence, using a combination of STIR with SPIR and an optimal TEequiv (from 73 to 110 ms), achieved better visualization of the brachial plexus without residual fat.

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.

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.

Investigation of the Possibility to Reduce Susceptibility Artifacts in MRI Knee Examination

The aim of this present study is to evaluate the reduction of susceptibility artifacts by increasing bandwidth (BW) and echo train length (ETL) in proton density turbo spin echo (PD TSE) sequences with and without fat saturation (FS) and in turbo inversion recovery magnitude (TIRM) sequences. We compared: (1) TIRM coronal (COR) with TIRM COR with high (H) BW and Long ETL; (2) PD TSE sagittal (SAG) FS with the PD TSE SAG FS with (H) BW; (3) PD TSE SAG with PD TSE SAG with (H) BW; (4) PD TSE SAG with PD TSE SAG with (H) BW and Long ETL. A quantitative analysis measured the extent of the susceptibility artifacts. A qualitative analysis evaluated the susceptibility artifacts, image distortion and effectiveness of fat suppression. The depiction of cartilage, menisci, muscles, tendons and bone marrow were also qualitatively analyzed. In the quantitative analysis, modified TIRM appears superior. In the qualitative analysis, the modified TIRM appears superior in 8/10 characteristics. The modified PD TSE FS is superior to the conventional regarding the susceptibility artifacts, image distortion and the depiction of bone marrow and cartilage and fat saturation. The modified PD TSE with (H) BW is found to be superior to the conventional PD TSE only in cartilage. In these sequences, when ETL was increased there were significant differences in four characteristics (ghost artifacts, cartilage, menisci and muscles). TIRM sequences with an increased BW and ETL are proposed to be used in daily clinical practice.

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.