Fracture of ankle: MRI using opposed-phase imaging obtained from turbo spin echo modified Dixon image shows improved sensitivity

MRI in Acute Ankle Sprains: Should We Be More Aggressive with Indications?

Acute ankle sprains are common sports injuries. MRI is the most accurate test for assessing the integrity and severity of ligament injuries in acute ankle sprains. However, MRI may not detect syndesmotic and hindfoot instability, and many ankle sprains are treated conservatively, questioning the value of MRI. In our practice, MRI adds value in confirming the absence or presence of ankle sprain-associated hindfoot and midfoot injuries, especially when clinical examinations are challenging, radiographs are inconclusive, and subtle instability is suspected. This article reviews and illustrates the MRI appearances of the spectrum of ankle sprains and associated hindfoot and midfoot injuries.

Does Chemical Shift Magnetic Resonance Imaging Improve Visualization of Pars Interarticularis Defect?

Introduction A unilateral or bilateral pars interarticularis defect (spondylolysis) is a leading cause of axial back pain in adolescent athletes. Currently, a spectrum of imaging modalities is used for assessment of pars interarticularis defects.

Objectives The aim of this study is to compare the accuracy of chemical shift sequence (magnetic resonance imaging [MRI]) technique to conventional MRI sequences in the detection of pars defects.

Patients and Methods Conventional T1, T2, and short tau inversion recovery sagittal and axial, as well as “in-” and “out-” phase chemical shift sagittal MRI sequences of 70 consecutive patients referred for low back pain were reviewed. Demographic details, clinical indication, and presence/diagnosis of pars defects using a 5-point Likert scale on both conventional and chemical shift MRI sequences. Spearman's correlation was used for statistical analysis. Intraclass correlation coefficient analysis was evaluated to assess the intraclass reliability between observers. Data were analyzed using DATAtab web-based statistics software (2022).

Results A total of 70 patients with an average age of 54.34 years with a female predominance were included. There were 11 pars defects in the cohort. Both in and out phases of chemical shift imaging were able to identify pars defect and intact pars. However, out phase was relatively better in delineating pars defects, while the in phase was superior in identifying an intact pars, though this was not statistically significant. There was good intra- and interobserver reliabilities.

Conclusion Chemical shift MRI sequence is a quicker, complementary technique to assess and analyze pars interarticularis confidently than conventionally utilized MRI sequences in patients being evaluated for axial back pain.

Advances in Bone Marrow Imaging: Strengths and Limitations from a Clinical Perspective

Conventional magnetic resonance imaging (MRI) remains the modality of choice to image bone marrow. However, the last few decades have witnessed the emergence and development of novel MRI techniques, such as chemical shift imaging, diffusion-weighted imaging, dynamic contrast-enhanced MRI, and whole-body MRI, as well as spectral computed tomography and nuclear medicine techniques. We summarize the technical bases behind these methods, in relation to the common physiologic and pathologic processes involving the bone marrow. We present the strengths and limitations of these imaging methods and consider their added value compared with conventional imaging in assessing non-neoplastic disorders like septic, rheumatologic, traumatic, and metabolic conditions. The potential usefulness of these methods to differentiate between benign and malignant bone marrow lesions is discussed. Finally, we consider the limitations hampering a more widespread use of these techniques in clinical practice.

Chemical shift encoding using asymmetric readout waveforms

Purpose

To describe a new method for encoding chemical shift using asymmetric readout waveforms that enables more SNR‐efficient fat/water imaging.

Methods

Chemical shift was encoded using asymmetric readout waveforms, rather than conventional shifted trapezoid readouts. Two asymmetric waveforms are described: a triangle and a spline. The concept was applied to a fat/water separated RARE sequence to increase sampling efficiency. The benefits were investigated through comparisons to shifted trapezoid readouts. Using asymmetric readout waveforms, the scan time was either shortened or maintained to increase SNR. A matched in‐phase waveform is also described that aims to improve the SNR transfer function of the fat and water estimates. The sequence was demonstrated for cervical spine, musculoskeletal (MSK), and optic nerve applications at 3T and compared with conventional shifted readouts.

Results

By removing sequence dead times, scan times were shortened by 30% with maintained SNR. The shorter echo spacing also reduced T2 blurring. Maintaining the scan times and using asymmetric readout waveforms achieved an SNR improvement in agreement with the prolonged sampling duration.

Conclusions

Asymmetric readout waveforms offer an additional degree of freedom in pulse sequence designs where chemical shift encoding is desired. This can be used to significantly shorten scan times or to increase SNR with maintained scan time.

The added value of postmortem magnetic resonance imaging in cases of hanging compared to postmortem computed tomography and autopsy

The purpose of this study was to evaluate the added value of postmortem magnetic resonance imaging (MRI) compared to postmortem computed tomography (CT) and autopsy in cases of fatal hanging. In addition, the study analyzed the strengths of each examination method regarding typical injuries in these cases. We investigated a cohort of 25 decedents who underwent CT, MRI and autopsy. Two radiologists assessed all MR images of the head and neck as well as the corresponding CT images. The results were compared to autopsy findings by retrospectively analyzing the autopsy reports. Postmortem MRI revealed intramuscular hemorrhages in a large number of cases, however, autopsy did not confirm all of the detected hemorrhages. CT and autopsy detected fractures in several cases, whereas MRI showed a fracture in just one single case. Other previously described vital signs and relevant findings, such as fracture-related gas bubbles, soft tissue emphysema or pneumomediastinum, were observed in only a few individual cases. MRI provided added diagnostic value in the detection of soft tissue injuries and lymph node swelling in fatal hangings. As an adjunct to autopsy, postmortem MRI may reveal additional hemorrhages, which might be missed at autopsy. Since standard MRI demonstrated low sensitivity for the detection of fractures, an additional imaging modality or autopsy is required to overcome this limitation.

MRI of non-specific low back pain and/or lumbar radiculopathy: do we need T1 when using a sagittal T2-weighted Dixon sequence?

OBJECTIVE

To show that for the MRI workup of non-specific low back pain and/or lumbar radiculopathy, the acquisition of T1-weighted sequences in the sagittal plane could be waived when using an FSE T2-weighted Dixon sequence.

MATERIALS AND METHODS

Three musculoskeletal radiologists retrospectively reviewed fifty lumbar spine MRI examinations performed for non-specific low back pain and/or lumbar radiculopathy. Two protocols were separately analyzed in the sagittal plane: a standard protocol (T1-weighted, in-phase, and water-only images of an FSE T2-weighted Dixon sequence) and a simplified protocol (fat-only, in-phase, and water-only images of an FSE T2-weighted Dixon sequence). Eight items usually assessed on T1-weighted sequences were analyzed for each of the vertebrae (n = 250), vertebral endplates (n = 500), vertebral corners (n = 1000), foramina (n = 500), lamina (n = 500), and facet joints (n = 500). Interchangeability of these protocols was tested using the individual equivalence index. A decrease in interobserver agreement of ≥ 5% when one reader used the simplified protocol compared with when both readers used the standard protocol was considered clinically significant. Interreader and intrareader agreement were assessed using kappa statistics. Rates of findings with each protocol were compared using odd ratios.

RESULTS

The standard and simplified protocols were interchangeable (range of upper bound of the 95%CI of individual equivalence index = 0.25 to 1.38%). Intraprotocol and interprotocol interreader kappa values were similar (0.253-0.671 vs. 0.236-0.723, respectively). Rates of findings were not statistically significantly different (p ≥ 0.074), or were higher with the simplified protocol (p ≤ 0.036).

CONCLUSION

In our target population, a single sagittal T2-weighted Dixon sequence may replace the recommended combination of T1-, T2-, and fat-suppressed T2-weighted sequences.

KEY POINTS

• In patients with non-specific low back pain or lumbar radiculopathy, spine MRI in the sagittal plane could be limited to a single FSE T2-weighted Dixon sequence, hereby reducing the acquisition time. • A simplified protocol of spine MRI in the sagittal plane combining FSE T2-weighted Dixon sequence provides the same information as a standard protocol including T1-, T2-, and fat-suppressed T2-weighted sequences for the workup of degenerative lumbar spine lesions. • For some findings shown on the simplified protocol, such as focal bone marrow replacement lesions or signs of infection, additional sequences including pre- and post-contrast T1-weighted sequences may be required, as is currently the case when using the standard protocol.