Anomalous signal intensity increase on out-of-phase chemical shift imaging: a manifestation of marrow mineralisation?

In-phase and opposed-phase Dixon chemical shift imaging for the assessment of skeletal marrow lesions: comparison of measurements from longitudinal sequences to those from axial sequences

OBJECTIVE

In-phase and opposed-phase chemical shift imaging (CSI) is a useful technique for assessing skeletal lesions. This study determined the frequency of significant differences in measurements obtained from longitudinal (coronal or sagittal) sequences to those obtained from axial sequences.

METHODS

Chemical shift imaging was undertaken in 96 consecutive patients referred from the Musculoskeletal Sarcoma and Spinal Oncology services for assessment of possible bone tumours as part of a standard tumour protocol, which included turbo spin echo and inversion recovery sequences. For spinal lesions, CSI was obtained in the sagittal and axial planes, while for all other sites, it was obtained in the coronal and axial planes.

RESULTS

The study included 49 (51.0%) males and 47 (49.0%) females with mean age 42.4 years (range 2-91 years). In 4 cases, 2 individual lesions were assessed, making a total of 100 lesions. Based on typical imaging features (n = 57) or histology (n = 43), 22 lesions (22%) were classified as non-neoplastic, 44 (44%) as benign neoplasms, 6 (6%) as intermediate-grade neoplasms, and 28 (28%) as malignant neoplasms. A significant discrepancy, wherein a lesion was classified as fat-containing (% SI drop >20%-25%) in the longitudinal plane, while in the axial plane it was classified as fat-replacing (% SI drop <20%-25%), or vice versa, occurred in 9%-14% of cases. However, this discrepancy had no appreciable effect on overall diagnostic accuracy, which was calculated at 79% for the longitudinal plane and 75%-80% for the axial plane.

CONCLUSIONS

Significant differences in CSI measurements occur in 9%-14% of cases based on imaging plane, but with no significant effect on diagnostic accuracy.

ADVANCES IN KNOWLEDGE

Radiologists should be aware that CSI measurements in different planes appear to have significant differences in up to 14% of lesions. However, diagnostic accuracy does not seem to be significantly affected.

Imaging of bone marrow pitfalls with emphasis on MRI

Normal marrow contains both hematopoietic/red and fatty/yellow marrow with a predictable pattern of conversion and skeletal distribution on MRI. Many variations in normal bone marrow signal and appearances are apparent and the reporting radiologist must differentiate these from other non-neoplastic, benign or neoplastic processes. The advent of chemical shift imaging has helped in characterising and differentiating more focal heterogeneous areas of red marrow from marrow infiltration. This review aims to cover the MRI appearances of normal marrow, its evolution with age, marrow reconversion, variations of normal marrow signal, causes of oedema-like marrow signal, and some common non-neoplastic entities, which may mimic marrow neoplasms.

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.

Comparison of in-phase and opposed-phase T1W gradient echo and T2W fast spin echo dixon chemical shift imaging for the assessment of non-neoplastic, benign neoplastic and malignant marrow lesions

OBJECTIVE

The objective of this study is to compare T1-weighted gradient echo (T1W GrE: control technique) chemical shift imaging (CSI) with T2-weighted fast spin echo (T2W FSE: experimental technique) CSI for differentiating non-neoplastic and neoplastic marrow lesions.

MATERIALS AND METHODS

Patients undergoing MRI for various marrow lesions were investigated with T1W GrE and T2W FSE Dixon CSI. Signal intensity (SI) change between in-phase (IP) and opposed-phase (OP) sequences was calculated, and SI drop > 20% considered to represent non-neoplastic lesions while SI drop < 20% considered to represent neoplastic lesions. Final diagnosis was based on imaging features (n = 42) or histology (n = 43) and classified as non-neoplastic, benign neoplastic, and malignant neoplastic. Inter-observer and inter-technique agreement between 2 readers was calculated.

RESULTS

The study included 85 patients (44 males and 41 females; mean age 41.1 years, range 2-83 years). Final diagnosis included 19 (22.4%) non-neoplastic lesions, 27 (31.8%) benign neoplasms, and 39 (45.9%) malignant neoplasms. On T1W GrE CSI, 19-21 lesions were classed as non-neoplastic and 64-66 as neoplastic, while on T2W FSE Dixon CSI, 22-24 lesions were classed as non-neoplastic and 61-64 as neoplastic. Lesion classification matched between the 2 techniques in 91.8-96.5% of cases. Sensitivity, specificity, positive predictive value, negative predictive value, and accuracy of T1W GrE CSI for differentiating non-neoplastic and neoplastic marrow lesions were 66.7-72.2%, 88.1-89.6%, 61.9-63.2%, 90.9-92.2%, and 84.7%, and of T2W FSE Dixon CSI were 72.2-77.8%, 85.1-86.6%, 58.3-59.1%, 92.1-93.4%, and 83.5%.

CONCLUSIONS

T1W GrE CSI and T2W FSE Dixon CSI produce similar results in the assessment of non-neoplastic and neoplastic marrow lesions.

Differentiation between benign and malignant vertebral compression fractures using qualitative and quantitative analysis of a single fast spin echo T2-weighted Dixon sequence

Objectives

To determine and compare the qualitative and quantitative diagnostic performance of a single sagittal fast spin echo (FSE) T2-weighted Dixon sequence in differentiating benign and malignant vertebral compression fractures (VCF), using multiple readers and different quantitative methods.

Methods

From July 2014 to June 2020, 95 consecutive patients with spine MRI performed prior to cementoplasty for acute VCFs were retrospectively included. VCFs were categorized as benign (n = 63, mean age = 76 ± 12 years) or malignant (n = 32, mean age = 63 ± 12 years) with a best valuable comparator as a reference. Qualitative analysis was independently performed by four radiologists by categorizing each VCF as either benign or malignant using only the image sets provided by FSE T2-weighted Dixon sequences. Quantitative analysis was performed using two different regions of interest (ROI1-2) and three methods (signal drop, fat fraction (FF) from ROIs, FF maps). Diagnostic performance was compared using ROC curves analyses. Interobserver agreement was assessed using kappa statistics and intraclass correlation coefficients (ICC).

Results

The qualitative diagnostic performance ranged from area under the curve (AUC) = 0.97 (95% CI: 0.91–1.00) to AUC = 0.99 (95% CI: 0.95–1.0). The quantitative diagnostic performance ranged from AUC = 0.82 (95% CI: 0.73–0.89) to AUC = 0.97 (95% CI: 0.91–0.99). Pairwise comparisons showed no statistical difference in diagnostic performance (all p > 0.0013, Bonferroni-corrected p < 0.0011). All five cases with disagreement among the readers were correctly diagnosed at quantitative analysis using ROI2. Interobserver agreement was excellent for both qualitative and quantitative analyses.

Conclusions

A single FSE T2-weighted Dixon sequence can be used to differentiate benign and malignant VCF with high diagnostic performance using both qualitative and quantitative analyses, which can provide complementary information.

Key Points

• Qualitative analysis of a single FSE T2-weighted Dixon sequence yields high diagnostic performance and excellent observer agreement for differentiating benign and malignant compression fractures.

• The same FSE T2-weighted Dixon sequence allows quantitative assessment with high diagnostic performance.

• Quantitative data can readily be extracted from the FSE T2-weighted Dixon sequence and may provide complementary information to the qualitative analysis, which may be useful in doubtful cases.

Spinal collision lesions

Collision lesions are rare neoplasms often described in the hepatobiliary system, genitourinary system and adrenal glands. Vertebral haemangiomas (VH) are the most common lesions involving the vertebral bodies. VHs are usually asymptomatic and considered as "Do not touch" lesions. Rarely they can be symptomatic. Imaging findings of typical and atypical haemangiomas, variant forms of haemangioma such as aggressive haemangiomas are well known. Collision lesions involving VHs are extremely rare. This article presents a series of cases with collision lesions of the vertebral body involving VHs.

ADVANCES IN KNOWLEDGE

This Case series demonstrates the various collision lesions in spinal haemangioma.

Focal nodular marrow hyperplasia: Imaging features of 53 cases

OBJECTIVE

To describe the characteristic imaging features of focal nodular marrow hyperplasia (FNMH).

METHODS AND MATERIALS

Retrospective review of all patients with a diagnosis of FNMH between January 2007 and September 2019.

RESULTS

The study included 53 patients, 7 males and 46 females with a mean age of 58 years (range 12-95 years). All had MRI with conventional spin echo sequences showing a poorly defined round/oval lesion with mild T₁W iso/hyperintensity compared to skeletal muscle, low T₂W turbo spin echo (TSE) signal intensity (SI) compared to marrow fat and variable SI on STIR, but never associated with reactive marrow oedema. All 53 patients had follow-up MRI, with all lesions remaining stable or partially resolving. In-phase (IP) and out-of-phase (OP) chemical shift imaging (CSI) was obtained in 31 of these, with 28 (90.3%) showing >20% SI drop on the OP sequence, while 3 (9.7%) demonstrated <20% SI drop. CT was available in 26 cases, 17 (65.4%) showing mild medullary sclerosis. Single-photon emission computed tomography CT (SPECT-CT) was available in four cases and Flourodeoxyglucose positron emission tomography CT (FDG PET-CT) in 2, all showing increased uptake. Focal uptake was also seen in three of eight patients who had undergone whole body bone scintigraphy. Only one lesion was biopsied, confirming FNMH.

CONCLUSION

The imaging appearances of FNMH have been described on various modalities, particularly MRI with emphasis on the role of IP and OP CSI typically demonstrating >20% SI reduction. FNMH should be recognised and treated as a 'do not touch' lesion which does not require biopsy or prolonged follow-up.

ADVANCES IN KNOWLEDGE

We describe and clarify the imaging characteristics of FNMH on MRI, including CSI, CT and various nuclear medicine modalities. An imaging algorithm is suggested for allowing a non-invasive diagnosis.