Usefulness of IDEAL T2 imaging for homogeneous fat suppression and reducing susceptibility artefacts in brachial plexus MRI at 3.0 T

Value of High-Resolution MRI in the Diagnosis of Brachial Plexus Injury in Infants and Young Children

Purpose

To investigate the value of high-resolution MRI based on 3D-short inversion time inversion recovery sampling perfection with application-optimized contrasts (3D-STIR SPACE) sequence for the diagnosis of brachial plexus injury in infants and young children.

Methods

Physical examination, electromyography (EMG) and MRI data of 26 children with brachial plexus injury were retrospectively analyzed. Sensitivity, specificity, and accuracy were calculated for the three tests. The agreement among these examinations was analyzed with the Kappa test. P<0.05 was considered statistically significant.

Results

Of the 26 children, 3 cases had normal MRIs, 23 cases had unilateral brachial plexus injury diagnosed with MRI, and a total of 73 nerve roots and/or sheaths were involved. Among the 23 cases with aberrant MRI findings, there were 19 cases of nerve root thickening (42 nerve roots), 4 cases of nerve root sleeve expansion (5 nerve roots), 17 cases of pseudomeningeal cysts (34 nerve roots), 2 cases of nerve root loosening (2 nerve roots), 8 cases of nerve root dissection (11 nerve roots), 19 cases with increased nerve signal (43 nerve roots), and 9 cases with an increased signal of the muscles on the affected side. As for the diagnosis of brachial plexus injury, the sensitivity and the accuracy of physical examination, EMG and MRI were 0.92, 0.86, and 0.88, respectively. The agreement between MRI and physical examination was substantial (κ=0.780, P=0.000), as did the agreement between MRI and EMG (κ=0.611, P=0.005).

Conclusion

High-resolution MRI based on 3D-STIR SPACE sequence plays a role in the diagnosis and evaluation of brachial plexus injury in infants and young children. It can accurately identify the injured nerve and characterize related pathological alterations. Besides EMG and physical examination, it can be used as a valuable tool for screening and monitoring of brachial plexus injury in infants and children.

MRI of Hands with Early Rheumatoid Arthritis: Usefulness of Three-Point Dixon Sequences to Quantitatively Assess Disease Activity

The use of efficient treatment with a treat-to-target strategy combined with early detection of the disease completely changed the imaging presentation and outcome of newly diagnosed rheumatoid arthritis (RA) patients. Magnetic Resonance Imaging (MRI) has become the reference technique in clinical research to detect and quantify inflammatory involvement of the soft tissues (synovitis and tenosynovitis) and bone marrow (osteitis) along with structural damages of the bone (erosions) in hands of patients with RA. Three-point Dixon MRI may be a valuable alternative to the currently recommended sequences as it yields effective fat signal suppression, high imaging quality and reproducible assessment of disease activity.

MR Neurography of Peripheral Nerve Injury in the Presence of Orthopedic Hardware: Technical Considerations

As the frequency of orthopedic procedures performed each year in the United States continues to increase, evaluation of peripheral nerve injury (PNI) in the presence of pre-existing metallic hardware is in higher demand. Advances in metal artifact reduction techniques have substantially improved the capability to reduce the susceptibility effect at MRI, but few reports have documented the use of MR neurography in the evaluation of peripheral nerves in the presence of orthopedic hardware. This report delineates the challenges of MR neurography around metal given the high spatial resolution often required to adequately depict small peripheral nerves. It offers practical tips, including strategies for prescan assessment and protocol optimization, including use of more conventional two-dimensional proton density and T2-weighted fat-suppressed sequences and specialized three-dimensional techniques, such as reversed free-induction steady-state precession and multispectral imaging, which enable vascular suppression and metal artifact reduction, respectively. Finally, this article emphasizes the importance of real-time monitoring by radiologists to optimize the diagnostic yield of MR neurography in the presence of orthopedic hardware. © RSNA, 2021.

The effects of three different contrast agents (Gd-BOPTA, Gd-DTPA, and Gd-DOTA) on brachial plexus magnetic resonance imaging

Background

MRI is very important for guiding the diagnosis and treatment of brachial plexus diseases. The most used type of MRI brachial plexus imaging is the 3D Short Term Inversion Recovery (STIR) sequence with contrast agent. This study aimed to investigate the effect of three contrast agents; gadobenate dimeglumine (Gd-BOPTA), gadopentetate dimeglumine (Gd-DTPA), and Gadoteric Acid Meglumine (Gd-DOTA) on brachial plexus magnetic resonance imaging (MRI).

Methods

We recruited 60 patients with suspected brachial plexus injury randomly into three groups. MRI images were obtained from each patient. Prior to scanning, the first group was injected with GD-BOPTA, the second group with Gd-DTPA, and the third with Gd-DOTA. The amount of contrast agent was 0.1 mmol/kg according to the weight of each patient, the injection rate was 1.5 mL/s, and 20 mL saline was injected at the same rate with a high-pressure injector. Immediately after the injection of contrast agent and saline, a 3D Sampling perfection with application optimized contrasts using different flip angle evolutions (SPACE) STIR sequence was used for scanning. The Signal Intensity (SI) and Standard Deviation (SD) of Maximal intensity projection (MIP) images for regions outside the anatomy (ROI background) with area of 17 mm² on both sides of the C6 peripheral nerves (ROI nerve), and tissue adjacent to the peripheral nerves (ROI tissue) were obtained. Signal to noise ratio (SNR) and contrast to noise ratio (CNR) were then calculated.

Results

The SNR was 40.66±25.27, 34.65±14.86, and 44.63±30.79 for Gd-BOPTA, Gd-DTPA, and Gd-DOTA, respectively and the CNR was 20.24±15.17, 16.07±7.50, and 20.84±15.53 for Gd-BOPTA, Gd-DTPA, and Gd-DOTA, respectively. In addition, there was no statistical difference in the SNR or CNR of brachial plexus nerves using the three contrast agents to enhance the 3D SPACE sequence χ²=1.877, P=0.391>0.05 and χ²=1.717, P=0.424, respectively.

Conclusions

There were no significant differences in the efficacy of three contrast agents in imaging the brachial plexus.

Two-point Dixon fat-water swapping artifact: lesion mimicker at musculoskeletal T2-weighted MRI

Fat-water swapping is an artifact specific to chemical shift encoded MRI and so-called Dixon methods. It is more frequent using the 2-point than the multi-point (> 2) Dixon method. Actually, fat-water swapping on the 2-point Dixon sequences partly triggered the development of the multi-point techniques. Fat-water swapping occurs on post-processing calculated fat- and water-only images, but not on the directly acquired in-phase and out-of-phase source images. It originates from a natural ambiguity between fat and water peaks that may cause inverted calculation between fat- and water-only voxels. Fat-water swapping artifact over large areas encompassing multiple tissues can easily be recognized, but it may be confusing when the calculation errors are limited to a single anatomic structure or a small area, especially on T2-weighted images. We report four cases with 2-point Dixon fat-water swapping artifacts mimicking musculoskeletal lesions at T2-weighted MRI and propose hints to avoid misinterpretation.

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

PURPOSE

To 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).

METHOD

Both 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).

RESULTS

Fat 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).

CONCLUSIONS

Dixon sequences yield more effective fat suppression and more reproducible RAMRIS scoring than CHESS sequences in hands with suspicion of early RA.

MR neurography of the brachial plexus in adult and pediatric age groups: evolution, recent advances, and future directions

Introduction: MR neurography (MRN) of the brachial plexus has emerged in recent years as a safe and accurate modality for the identification of brachial plexopathies in pediatric and adult populations. While clinical differentiation of brachial plexopathy from cervical spine-related radiculopathy or nerve injury has long relied upon nonspecific physical exam and electrodiagnostic testing modalities, MRN now permits detailed interrogation of peripheral nerve anatomy and pathology, as well as assessment of surrounding soft tissues and musculature, thereby facilitating accurate diagnosis. The reader will learn about the current state of brachial plexus MRN, including recent advances and future directions, and gain knowledge about the adult and pediatric brachial plexopathies that can be characterized using these techniques.Areas Covered: The review details recent developments in brachial plexus MRN, including increasing availability of 3.0-T MR scanners at both private and academic diagnostic imaging centers, as well as the advent of multiple new vascular and fat signal suppression techniques. A literature search of PubMed and SCOPUS was used as the principal source of information gathered for this review.Expert Opinion: Refinement of fat-suppression, 3D techniques and diffusion MR imaging modalities has improved the accuracy of MRN, rendering it as a useful adjunct to clinical findings during the evaluation of suspected brachial plexus lesions.

Frequency Offset Corrected Inversion Pulse for B0 and B1 Insensitive Fat Suppression at 3T: Application to MR Neurography of Brachial Plexus

BACKGROUND

The 3D short tau inversion recovery (STIR) sequence is routinely used in clinical MRI to achieve robust fat suppression. However, the performance of the commonly used adiabatic inversion pulse, hyperbolic secant (HS), is compromised in challenging areas with increased B₀ and B₁ inhomogeneities, such as brachial plexus at 3T.

PURPOSE

To demonstrate the frequency offset corrected inversion (FOCI) pulse as an efficient fat suppression STIR pulse with increased robustness to B₀ and B₁ inhomogeneities at 3T, compared to the HS pulse.

STUDY TYPE

Prospective.

SUBJECTS/PHANTOM

Initial evaluation was performed in phantoms and one healthy volunteer by varying the B₁ field, while subsequent comparison was performed in three healthy volunteers and five patients without varying the B₁ .

FIELD STRENGTH/SEQUENCE

3T; 3D TSE-STIR with HS and FOCI pulses.

ASSESSMENT

Brachial plexus images were qualitatively evaluated by two musculoskeletal radiologists independently using a four-point grading scale for fat suppression, shading artifacts, and nerve visualization.

STATISTICAL TEST

The Wilcoxon signed-rank test with P < 0.05 was considered statistically significant.

RESULTS

Simulations and phantom experiments demonstrated broader bandwidth (2.5 kHz vs. 0.83 kHz, increased B₀ robustness) at the same adiabatic threshold and lower adiabatic threshold (5 μT vs. 7 μT at 3.5 ppm, increased B₁ robustness) at the same bandwidth with the FOCI pulse compared to the HS pulse With increased bandwidth, the FOCI pulse achieved robust fat suppression even at 50% of maximum B₁ strength, while the HS pulse required >75% of maximum B₁ strength. Compared to the standard 3D TSE-STIR with HS pulse, the FOCI pulse achieved uniform fat suppression (P < 0.05), better nerve visualization (P < 0.05), and minimal shading artifacts (P < 0.01) in brachial plexus at 3T.

DATA CONCLUSION

The FOCI pulse has increased robustness to B₀ and B₁ inhomogeneities, compared to the HS pulse, and enables uniform fat suppression in brachial plexus at 3T.

LEVEL OF EVIDENCE

1 Techinical Efficacy: Stage 1 J. Magn. Reson. Imaging 2018;48:1104-1111.

A subjective and objective comparison of tissue contrast and imaging artifacts present in routine spin echoes and in iterative decomposition of asymmetric spin echoes for soft tissue neck MRI

OBJECTIVE

FSE sequences play key roles in neck MRI despite the susceptibility issues in neck region. Iterative decomposition of asymmetric echoes (IDEAL, GE) is a promising method that separates fat and water images resulting in high SNR and improved fat suppression. We tested how neck tissue contrasts, image artifacts and fat separation as opposed to fat suppression in terms of image quality compare between routine and IDEAL FSE.

METHODS

IDEAL based and routine T₁ and T₂-weighted FSE sequences were applied for neck MRI at 1.5T and 3T. Overall image quality including fat suppression, tissue contrast, image artifacts and lesion conspicuity were subjectively assessed for 20 patients clinically indicated for neck MRI. Quantitative tissue contrast estimates from parotid area were compared between IDEAL and routine FSE for 7 patients. Four patients with oncocytoma were also reviewed to assess benefits of separately reconstructed fat specific image sets.

RESULTS

Subjective tissue contrast and overall image quality including image sharpness, fat suppression and image artifacts were superior for IDEAL sequences. For oncocytoma fat specific IDEAL images provided additional information. Objective CNR estimates from a central slice were equivalent for IDEAL and routine FSE at both field strengths.

CONCLUSIONS

We demonstrated that high SNR inherent in IDEAL FSE consistently translates into high tissue contrast with image quality advantages in neck anatomy where large susceptibility variation and physiological motions reduce image quality for conventional FSE T₁ and T₂. However, the objective contrast estimates for parotid gland at isocenter were statistically equivalent for IDEAL and conventional FSE perhaps because at or near isocenter routine FSE works well. Additionally, fat specific IDEAL image sets add to diagnostic specificity for fat deficient lesions.