Diffusion imaging of the vertebral bone marrow

Predicting cytogenetic risk in multiple myeloma using conventional whole-body MRI, spinal dynamic contrast-enhanced MRI, and spinal diffusion-weighted imaging

OBJECTIVES

Cytogenetic abnormalities are predictors of poor prognosis in multiple myeloma (MM). This paper aims to build and validate a multiparametric conventional and functional whole-body MRI-based prediction model for cytogenetic risk classification in newly diagnosed MM.

METHODS

Patients with newly diagnosed MM who underwent multiparametric conventional whole-body MRI, spinal dynamic contrast-enhanced (DCE-)MRI, spinal diffusion-weighted MRI (DWI) and had genetic analysis were retrospectively included (2011-2020/Ghent University Hospital/Belgium). Patients were stratified into standard versus intermediate/high cytogenetic risk groups. After segmentation, 303 MRI features were extracted. Univariate and model-based methods were evaluated for feature and model selection. Testing was performed using receiver operating characteristic (ROC) and precision-recall curves. Models comparing the performance for genetic risk classification of the entire MRI protocol and of all MRI sequences separately were evaluated, including all features. Four final models, including only the top three most predictive features, were evaluated.

RESULTS

Thirty-one patients were enrolled (mean age 66 ± 7 years, 15 men, 13 intermediate-/high-risk genetics). None of the univariate models and none of the models with all features included achieved good performance. The best performing model with only the three most predictive features and including all MRI sequences reached a ROC-area-under-the-curve of 0.80 and precision-recall-area-under-the-curve of 0.79. The highest statistical performance was reached when all three MRI sequences were combined (conventional whole-body MRI + DCE-MRI + DWI). Conventional MRI always outperformed the other sequences. DCE-MRI always outperformed DWI, except for specificity.

CONCLUSIONS

A multiparametric MRI-based model has a better performance in the noninvasive prediction of high-risk cytogenetics in newly diagnosed MM than conventional MRI alone.

CRITICAL RELEVANCE STATEMENT

An elaborate multiparametric MRI-based model performs better than conventional MRI alone for the noninvasive prediction of high-risk cytogenetics in newly diagnosed multiple myeloma; this opens opportunities to assess genetic heterogeneity thus overcoming sampling bias.

KEY POINTS

• Standard genetic techniques in multiple myeloma patients suffer from sampling bias due to tumoral heterogeneity. • Multiparametric MRI noninvasively predicts genetic risk in multiple myeloma. • Combined conventional anatomical MRI, DCE-MRI, and DWI had the highest statistical performance to predict genetic risk. • Conventional MRI alone always outperformed DCE-MRI and DWI separately to predict genetic risk. DCE-MRI alone always outperformed DWI separately, except for the parameter specificity to predict genetic risk. • This multiparametric MRI-based genetic risk prediction model opens opportunities to noninvasively assess genetic heterogeneity thereby overcoming sampling bias in predicting genetic risk in multiple myeloma.

Magnetic Resonance Imaging Biomarkers of Bone and Soft Tissue Tumors

Magnetic resonance imaging (MRI) is essential in the management of musculoskeletal (MSK) tumors. This review delves into the diverse MRI modalities, focusing on anatomical, functional, and metabolic sequences that provide essential biomarkers for tumor detection, characterization, disease extent determination, and assessment of treatment response. MRI's multimodal capabilities offer a range of biomarkers that enhance MSK tumor evaluation, aiding in better patient management.

Applications of Diffusion-Weighted MRI to the Musculoskeletal System

Diffusion-weighted imaging (DWI) is an established MRI technique that can investigate tissue microstructure at the scale of a few micrometers. Musculoskeletal tissues typically have a highly ordered structure to fulfill their functions and therefore represent an optimal application of DWI. Even more since disruption of tissue organization affects its biomechanical properties and may indicate irreversible damage. The application of DWI to the musculoskeletal system faces application-specific challenges on data acquisition including susceptibility effects, the low T2 relaxation time of most musculoskeletal tissues (2-70 msec) and the need for sub-millimetric resolution. Thus, musculoskeletal applications have been an area of development of new DWI methods. In this review, we provide an overview of the technical aspects of DWI acquisition including diffusion-weighting, MRI pulse sequences and different diffusion regimes to study tissue microstructure. For each tissue type (growth plate, articular cartilage, muscle, bone marrow, intervertebral discs, ligaments, tendons, menisci, and synovium), the rationale for the use of DWI and clinical studies in support of its use as a biomarker are presented. The review describes studies showing that DTI of the growth plate has predictive value for child growth and that DTI of articular cartilage has potential to predict the radiographic progression of joint damage in early stages of osteoarthritis. DTI has been used extensively in skeletal muscle where it has shown potential to detect microstructural and functional changes in a wide range of muscle pathologies. DWI of bone marrow showed to be a valuable tool for the diagnosis of benign and malignant acute vertebral fractures and bone metastases. DTI and diffusion kurtosis have been investigated as markers of early intervertebral disc degeneration and lower back pain. Finally, promising new applications of DTI to anterior cruciate ligament grafts and synovium are presented. The review ends with an overview of the use of DWI in clinical routine. EVIDENCE LEVEL: 5 TECHNICAL EFFICACY: Stage 3.

Comparison of reduced field-of-view DWI and conventional DWI techniques for the assessment of lumbar bone marrow infiltration in patients with acute leukemia

Objectives

To compare the imaging quality, apparent diffusion coefficient (ADC), and the value of assessing bone marrow infiltration between reduced field-of-view diffusion-weighted imaging (r-FOV DWI) and conventional DWI in the lumbar spine of acute leukemia (AL).

Methods

Patients with newly diagnosed AL were recruited and underwent both r-FOV DWI and conventional DWI in the lumbar spine. Two radiologists evaluated image quality scores using 5-Likert-type scales qualitatively and measured signal-to-noise ratio (SNR), contrast-to-noise (CNR), signal intensity ratio (SIR), and ADC quantitatively. Patients were divided into hypo- and normocellular group, moderately hypercellular group, and severely hypercellular group according to bone marrow cellularity (BMC) obtained from bone marrow biopsies. The image quality parameters and ADC value between the two sequences were compared. One-way analysis of variance followed by LSD post hoc test was used for the comparisons of the ADC values among the three groups. The performance of ADC obtained with r-FOV DWI (ADCr) and conventional DWI(ADCc) in evaluating BMC and their correlations with BMC and white blood cells (WBC) were analyzed and compared.

Results

71 AL patients (hypo- and normocellular: n=20; moderately hypercellular: n=19; severely hypercellular: n=32) were evaluated. The image quality scores, CNR, SIR, and ADC value of r-FOV DWI were significantly higher than those of conventional DWI (all p<0.05), and the SNR of r-FOV DWI was significantly lower (p<0.001). ADCr showed statistical differences in all pairwise comparisons among the three groups (all p<0.05), while ADCc showed significant difference only between hypo- and normocellular group and severely hypercellular group (p=0.014). The performance of ADCr in evaluating BMC (Z=2.380, p=0.017) and its correlations with BMC (Z=-2.008, p = 0.045) and WBC (Z=-2.022, p = 0.043) were significantly higher than those of ADCc.

Conclusion

Compared with conventional DWI, r-FOV DWI provides superior image quality of the lumbar spine in AL patients, thus yielding better performance in assessing bone marrow infiltration.

Deep learning-based k-space-to-image reconstruction and super resolution for diffusion-weighted imaging in whole-spine MRI

PURPOSE

To assess the feasibility of deep learning (DL)-based k-space-to-image reconstruction and super resolution for whole-spine diffusion-weighted imaging (DWI).

METHOD

This retrospective study included 97 consecutive patients with hematologic and/or oncologic diseases who underwent DL-processed whole-spine MRI from July 2022 to March 2023. For each patient, conventional (CONV) axial single-shot echo-planar DWI (b = 50, 800 s/mm2) was performed, followed by DL reconstruction and super resolution processing. The presence of malignant lesions and qualitative (overall image quality and diagnostic confidence) and quantitative (nonuniformity [NU], lesion contrast, signal-to-noise ratio [SNR], contrast-to-noise ratio [CNR], and ADC values) parameters were assessed for DL and CONV DWI.

RESULTS

Ultimately, 67 patients (mean age, 63.0 years; 35 females) were analyzed. The proportions of vertebrae with malignant lesions for both protocols were not significantly different (P: [0.55-0.99]). The overall image quality and diagnostic confidence scores were higher for DL DWI (all P ≤ 0.002) than CONV DWI. The NU, lesion contrast, SNR, and CNR of each vertebral segment (P ≤ 0.04) but not the NU of the sacral segment (P = 0.51) showed significant differences between protocols. For DL DWI, the NU was lower, and lesion contrast, SNR, and CNR were higher than those of CONV DWI (median values of all segments; 19.8 vs. 22.2, 5.4 vs. 4.3, 7.3 vs. 5.5, and 0.8 vs. 0.7). Mean ADC values of the lesions did not significantly differ between the protocols (P: [0.16-0.89]).

CONCLUSIONS

DL reconstruction can improve the image quality of whole-spine diffusion imaging.

Estimation of intravoxel incoherent motion (IVIM) parameters in vertebral bone marrow: a comparative study of five algorithms

OBJECTIVES

To access the performances of different algorithms for quantification of Intravoxel incoherent motion (IVIM) parameters D, f, [Formula: see text] in Vertebral Bone Marrow (VBM).

MATERIALS AND METHODS

Five algorithms were studied: four deterministic algorithms (the One-Step and three segmented methods: Two-Step, Three-Step, and Fixed-[Formula: see text] algorithm) based on the least-squares (LSQ) method and a Bayesian probabilistic algorithm. Numerical simulations and quantification of IVIM parameters D, f, [Formula: see text] in vivo in vertebral bone marrow, were done on six healthy volunteers. The One-way repeated-measures analysis of variance (ANOVA) followed by Bonferroni's multiple comparison test (p value = 0.05) was applied.

RESULTS

In numerical simulations, the Bayesian algorithm provided the best estimation of D, f, [Formula: see text] compared to the deterministic algorithms. In vivo VBM-IVIM, the values of D and f estimated by the Bayesian algorithm were close to those of the One-Step method, in contrast to the three segmented methods.

DISCUSSION

The comparison of the five algorithms indicates that the Bayesian algorithm provides the best estimation of VBM-IVIM parameters, in both numerical simulations and in vivo data.

Diffusion Weighted Imaging in Spine Tumors

Diffusion weighted imaging (DWI) has developed into a powerful tool for the evaluation of spine tumors, particularly for the assessment of vertebral marrow lesions and intramedullary tumors. Advances in magnetic resonance techniques have improved the quality of spine DWI and diffusion tensor imaging (DTI) in recent years, with increased reproducibility and utilization. DTI, with quantitative parameters such as fractional anisotropy and qualitative visual assessment of nerve fiber tracts, can play a valuable role in the evaluation and surgical planning of spinal cord tumors. These widely available techniques can be used to enhance the diagnostic evaluation of spinal tumors.

Imaging of low-energy vertebral fractures

Low-energy vertebral fractures pose a diagnostic challenge for the radiologist due to their often-inadvertent nature and often subtle imaging semiology. However, the diagnosis of this type of fractures can be decisive, not only because it allows targeted treatment to prevent complications, but also because of the possibility of diagnosing systemic pathologies such as osteoporosis or metastatic disease. Pharmacological treatment in the first case has been shown to prevent the development of other fractures and complications, while percutaneous treatments and various oncological therapies can be an alternative in the second case. Therefore, it is necessary to know the epidemiology and typical imaging findings of this type of fractures. The objective of this work is to review the imaging diagnosis of low-energy fractures, with special emphasis on the characteristics that should be outlined in the radiological report to guide a specific diagnosis that favours and optimizes the treatment of patients suffering of low energy fractures.

Prostate and metastasis diffusion volume based on apparent diffusion coefficient as a prognostic factor in Hormone-naïve prostate Cancer

In this study, to assess the utility of whole-body DWI (WB-DWI) as an imaging biomarker for metastatic hormone-naïve prostate cancer (mHNPC), we evaluated tumor diffusion volume based on apparent diffusion coefficient (ADC) values. WB-DWI results obtained from 62 mHNPC patients were evaluated in this retrospective analysis. The association with castration resistant-free survival (CFS) was evaluated for both prostate and metastatic tumor diffusion volume (pDV and mDV, respectively) based on WB-DWI. The usefulness of pDV and mDV based on ADC values to predict CFS was also examined. During the follow-up period, 22 patients progressed to castration-resistant prostate cancer, and the median CFS was 42.6 months. The median mDV and pDV were 6.7 and 12.6 mL, respectively. mDV was a significant predictor of CFS (hazard ratio [HR]: 2.75; p = 0.022), while pDV was not significant. When DV was divided into groups by ADC values (× 10^- 3 mm²/s) of 0.4-1.0 and 1.0-1.8 (× 10^- 3 mm²/s), mDV with ADC values (× 10^- 3 mm²/s) of 0.4-1.0 (mDV_0.4-1.0) showed a more favorable association with CFS compared to total mDV. On multivariate analysis, mDV_0.4-1.0 and Gleason grade group had a statistically significant association with CFS (HR: 4.0; p = 0.004, and HR: 3.4; p = 0.006, respectively), while pDV with ADC values (× 10^- 3 mm²/s) of 0.4-1.0 did not have a significant association. mDV is useful for predicting CFS in mHNPC patients. mDV may be a better imaging biomarker when based on ADC values.

Quantitative magnetic resonance imaging (qMRI) in axial spondyloarthritis

Imaging, and particularly MRI, plays a crucial role in the assessment of inflammation in rheumatic disease, and forms a core component of the diagnostic pathway in axial spondyloarthritis. However, conventional imaging techniques are limited by image contrast being non-specific to inflammation and a reliance on subjective, qualitative reader interpretation. Quantitative MRI methods offer scope to address these limitations and improve our ability to accurately and precisely detect and characterise inflammation, potentially facilitating a more personalised approach to management. Here, we review quantitative MRI methods and emerging quantitative imaging biomarkers for imaging inflammation in axial spondyloarthritis. We discuss the potential benefits as well as the practical considerations that must be addressed in the movement toward clinical translation of quantitative imaging biomarkers.

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.

Diffusion-weighted magnetic resonance imaging in differentiation between different vertebral lesions using ADC mapping as a quantitative assessment tool

Background

Diffusion-weighted imaging is one of the most useful clinical MRI techniques. Including this technique with other sequences used for routine spine scanning improves sensitivity and the capacity to characterize lesions. This study aims to evaluate the utility of apparent diffusion coefficient obtained from diffusion-weighted MR imaging in differentiating between benign and malignant vertebral lesions according to the optimal cutoff ADC value.

Results

This study included 30 patients at Ain Shams University hospitals; all of them were subjected to full clinical assessment and magnetic resonance imaging. Patients were classified into 4 groups: inflammatory lesions (12 cases) followed by malignant lesions (7 cases), then benign neoplastic lesions (6 cases), then traumatic lesions (3 cases) and osteoporosis (two cases). Inflammatory lesions revealed restricted diffusion. Benign neoplastic lesions/hemangioma showed low signal at DWIs due to free diffusion, while malignant/metastatic lesions showed restricted diffusion. Traumatic lesions showed restricted diffusion. The osteoporotic lesions showed iso- to hyper-intense signal at DWIs. The mean ADC value of the benign lesions was 1.8 ± 0.43 mm2/s, while metastatic tumors was 0.96 ± 0.5 × 10–3 mm2/s; however, overlapping values may be present.

Conclusions

Compared with benign tumors, malignant tumors have lower ADC values; nevertheless, some lesions, such as tuberculosis, have low ADC values that are like those of malignant tumors. Diffusion MRI and ADC values should always be analyzed in conjunction with standard MRI sequences as well as a thorough clinical history and examination.

Determination of Sr2+ mobility in viscous bovine bone marrow by cryo-time-of-flight secondary ion mass spectrometry

RATIONALE

In osteoporosis research, strontium ions (Sr²⁺ ) have emerged as promising therapeutic agent in modified bone cements for better fracture healing. Modeling of Sr²⁺ dispersion in bone could be used as a predictive tool for the evaluation of functionalized biomaterials in future. Therefore, determination of experimental parameters for Sr²⁺ transport in bone is essential. In this study, we focus on the determination of Sr²⁺ diffusion in viscous bovine bone marrow by time-of-flight secondary ion mass spectrometry (ToF-SIMS).

METHODS

For this comparatively fast diffusion (FD) experiment, a specific experimental protocol of ToF-SIMS depth profiling under cryogenic conditions was developed. The validity of our experimental approach is proven by a time-dependent experimental series. Furthermore, 2D and 3D mass spectrometric imaging analysis was used to study Sr²⁺ surface and bulk distribution within bovine bone marrow.

RESULTS

Detailed 2D and 3D mass spectrometric imaging analysis revealed that Sr²⁺ diffusion is slower in bone marrow areas with high intensity of lipid and fatty acid signals than in areas with less lipid content. The Sr²⁺ transport within this passive model can be described by Fickian diffusion. Average diffusion coefficients of Sr²⁺ in bovine bone marrow were obtained from diffusion profiles in FD areas (D_bovine,FD  = [2.09 ± 2.39]·10^-9 cm² s^-1 ), slow diffusion areas (D_bovine,SD  = [1.52 ± 1.80]·10^-10 cm² s^-1 ), and total area diffusion (D_bovine,TA  = [1.94 ± 2.40]·10^-9 cm² s^-1 ).

CONCLUSIONS

We were able to show that cryo-ToF-SIMS is a useful tool for the characterization of rapid diffusion in water-containing highly viscous media. To the best of our knowledge, this is the first reported experimental approach for the investigation of the distribution of low concentrated therapeutic agents in bone marrow. Overall, our results provide important insights about Sr²⁺ diffusion in bovine bone marrow.

Benefits of diffusion-weighted imaging in pediatric acute osteoarticular infections

BACKGROUND

Contrast-enhanced magnetic resonance imaging (MRI) is recommended for the diagnosis of acute osteoarticular infections in children. Diffusion-weighted imaging (DWI) may be an alternative to the injection of gadolinium.

OBJECTIVE

To evaluate unenhanced MRI with DWI in comparison to contrast-enhanced MRI for the diagnostic work-up of acute osteoarticular infections in children.

MATERIALS AND METHODS

This retrospective study included 36 children (age range: 7 months-12 years) with extra-spinal osteoarticular infections and MRI performed within 24 h of admission. MRI protocol included short tau inversion recovery (STIR), water-only T2 Dixon, T1, DWI, and gadolinium-enhanced T1 sequences. Two readers reviewed three sets of images: 1) unenhanced sequences, 2) unenhanced sequences with DWI and 3) unenhanced followed by contrast-enhanced sequences (reference standard). Sensitivity and specificity of sets 1 and 2 were compared to set 3 and assessed to identify osteoarticular infections: osteomyelitis (long bones, metaphyseal equivalents), septic arthritis and abscess (soft tissues, bone).

RESULTS

All 14 cases of osteomyelitis in the metaphyses and diaphyses of long bones and all 27 cases of septic arthritis were identified by unenhanced sequences, but 4/16 abscesses were missed. For the diagnosis of abscess, DWI increased sensitivity to 100%. Among the 18 osteomyelitis in metaphyseal equivalents, 4 femoral head chondroepiphyses were identified by contrast-enhanced sequences only.

CONCLUSION

MRI for suspected pediatric acute osteoarticular infections is the best diagnostic modality to guide patient management. An unenhanced protocol with DWI may be an alternative to a contrast-based protocol, even in the presence of an abscess. However, gadolinium remains necessary to assess for chondroepiphyseal involvement of the femoral head.

Engineered Tissue Models to Replicate Dynamic Interactions within the Hematopoietic Stem Cell Niche

Hematopoietic stem cells are the progenitors of the blood and immune system and represent the most widely used regenerative therapy. However, their rarity and limited donor base necessitate the design of ex vivo systems that support HSC expansion without the loss of long-term stem cell activity. This review describes recent advances in biomaterials systems to replicate features of the hematopoietic niche. Inspired by the native bone marrow, these instructive biomaterials provide stimuli and cues from cocultured niche-associated cells to support HSC encapsulation and expansion. Engineered systems increasingly enable study of the dynamic nature of the matrix and biomolecular environment as well as the role of cell-cell signaling (e.g., autocrine feedback vs paracrine signaling between dissimilar cells). The inherent coupling of material properties, biotransport of cell-secreted factors, and cell-mediated remodeling motivate dynamic biomaterial systems as well as characterization and modeling tools capable of evaluating a temporally evolving tissue microenvironment. Recent advances in HSC identification and tracking, model-based experimental design, and single-cell culture platforms facilitate the study of the effect of constellations of matrix, cell, and soluble factor signals on HSC fate. While inspired by the HSC niche, these tools are amenable to the broader stem cell engineering community.

Correlation among alveolar bone assessments provided by CBCT, micro-CT, and 14 T MRI

Objectives:

The aim of this study was to evaluate bone mineral adipose tissue (BMAT) volume in 21 alveolar bone specimens, as determined by 14 T magnetic resonance imaging (MRI), and correlate them to the radiodensity values obtained preoperatively of regions of interest by cone beam computed tomography (CBCT), and to the BV/TV ratio values obtained by micro-CT, the gold-standard for morphometric data collection.

Methods:

Partially edentulous patients were submitted to a CBCT scan, and the radiographic bone densities in each ROI were automatically calculated using coDiagnostiX software. Based on the CBCT surgical planning, a CAD/CAM stereolithographic surgical guide was fabricated to retrieve a bone biopsy from the same ROIs scanned preoperatively, and then to orientate the subsequent implant placement. The alveolar bone biopsies were then collected and scanned using the micro-CT and 14 T MRI techniques. Pearson’s correlation test was performed to correlate the results obtained using the three different techniques.

Results:

In the 21 eligible bone specimens (6 females, 15 males), age (mean age 52.9 years), micro-CT, and 14 T MRI variables were found to be normally distributed (p > 0.05). The strongest—and only statistically significant (p < 0.05)—correlation was found between micro-CT and 14 T MRI values (r = 0.943), and the weakest, between 14 T MRI and CBCT values (r = –0.068).

Conclusions:

The findings suggest that 14 T MRI can be used to evaluate BMAT as an indirect marker for bone volume, and that CBCT is not a reliable technique to provide accurate bone density values.

Characterisation of Sr2+ mobility in osteoporotic rat bone marrow by cryo-ToF-SIMS and cryo-OrbiSIMS

Mass spectrometric imaging approach for ex vivo monitoring of drug transport in bone sections. Cryo-ToF-SIMS depth profiling and high-resolution imaging as well as OrbiSIMS analysis revealed inhomogeneous Sr2+ transport in rat bone marrow.

Review of diffusion-weighted imaging and dynamic contrast-enhanced MRI for multiple myeloma and its precursors (monoclonal gammopathy of undetermined significance and smouldering myeloma)

The last decades, increasing research has been conducted on dynamic contrast-enhanced and diffusion-weighted MRI techniques in multiple myeloma and its precursors. Apart from anatomical sequences which are prone to interpretation errors due to anatomical variants, other pathologies and subjective evaluation of signal intensities, dynamic contrast-enhanced and diffusion-weighted MRI provide additional information on microenvironmental changes in bone marrow and are helpful in the diagnosis, staging and follow-up of plasma cell dyscrasias. Diffusion-weighted imaging provides information on diffusion (restriction) of water molecules in bone marrow and in malignant infiltration. Qualitative evaluation by visually assessing images with different diffusion sensitising gradients and quantitative evaluation of the apparent diffusion coefficient are studied extensively. Dynamic contrast-enhanced imaging provides information on bone marrow vascularisation, perfusion, capillary resistance, vascular permeability and interstitial space, which are systematically altered in different disease stages and can be evaluated in a qualitative and a (semi-)quantitative manner. Both diffusion restriction and abnormal dynamic contrast-enhanced MRI parameters are early biomarkers of malignancy or disease progression in focal lesions or in regions with diffuse abnormal signal intensities. The added value for both techniques lies in better detection and/or characterisation of abnormal bone marrow otherwise missed or misdiagnosed on anatomical MRI sequences. Increased detection rates of focal lesions or diffuse bone marrow infiltration upstage patients to higher disease stages, provide earlier access to therapy and slower disease progression and allow closer monitoring of high-risk patients. Despite promising results, variations in imaging protocols, scanner types and post-processing methods are large, thus hampering universal applicability and reproducibility of quantitative imaging parameters. The myeloma response assessment and diagnosis system and the international myeloma working group provide a systematic multicentre approach on imaging and propose which parameters to use in multiple myeloma and its precursors in an attempt to overcome the pitfalls of dynamic contrast-enhanced and diffusion-weighted imaging.Single sentence summary statementDiffusion-weighted imaging and dynamic contrast-enhanced MRI provide important additional information to standard anatomical MRI techniques for diagnosis, staging and follow-up of patients with plasma cell dyscrasias, although some precautions should be taken on standardisation of imaging protocols to improve reproducibility and application in multiple centres.

Effects of Sex and Age on Fat Fraction, Diffusion-Weighted Image Signal Intensity and Apparent Diffusion Coefficient in the Bone Marrow of Asymptomatic Individuals: A Cross-Sectional Whole-Body MRI Study

We aimed to describe the relationships between the relative fat fraction (%FF), muscle-normalized diffusion-weighted (DW) image signal intensity and water apparent diffusion coefficient (ADC), sex and age for normal bone marrow, in the normal population. Our retrospective cohort consisted of 100 asymptomatic individuals, equally divided by sex and 10-year age groups, who underwent whole-body MRI at 1.5 T for early cancer detection. Semi-automated segmentation of global bone marrow volume was performed using the DW images and the resulting segmentation masks were projected onto the ADC and %FF maps for extraction of parameter values. Differences in the parameter values between sexes at age ranges were assessed using the Mann–Whitney and Kruskal–Wallis tests. The Spearman correlation coefficient r was used to assess the relationship of each imaging parameter with age, and of %FF with ADC and normalized DW signal intensity values. The average %FF of normal bone marrow was 65.6 ± 7.2%, while nSI_b50, nSI_b900 and ADC were 1.7 ± 0.5, 3.2 ± 0.9 and 422 ± 67 μm²/s, respectively. The bone marrow %FF values increased with age in both sexes (r = 0.63 and r = 0.64, respectively, p < 0.001). Values of nSI_b50 and nSI_b900 were higher in younger women compared to men of the same age groups (p < 0.017), but this difference decreased with age. In our cohort of asymptomatic individuals, the values of bone marrow relative %FF, normalized DW image signal intensity and ADC indicate higher cellularity in premenopausal women, with increasing bone marrow fat with aging in both sexes.

Assessment of diffusion tensor imaging in differentiation between pyogenic and tuberculous spondylitis

PURPOSE

to assess diffusion tensor imaging (DTI); an emerging technique for differentiation between pyogenic and tuberculous spondylitis.

PATIENTS AND METHODS

The study was carried out on 33 patients with infective spondylitis performing conventional MRI and DTI. The mean diffusivity (MD) and fractional anisotropy (FA) of the affected vertebral body were calculated by two readers.

RESULTS

The MD of pyogenic spondylitis of both readers (1.48 ± 0.09 and 1.47 ± 0.08 × 10^-3 mm²/s) were significantly higher values (P = 0.001) than tuberculous spondylitis (1.11 ± 0.15 and 1.18 ± 0.08 × 10^-3 mm²/s). The FA of pyogenic spondylitis of both readers (0.18 ± 0.09 and 0.20 ± 0.08) were significantly lower values (P = 0.001) than tuberculous spondylitis (0.30 ± 0.05 and 0.32 ± 0.03). There was a strong inter-reader agreement between both readers using MD (K = 0.963) and FA (K = 0.858). The thresholds MD and FA used for differentiating pyogenic and tuberculous spondylitis of both readers were 1.37 and 1.33 × 10^-3 mm²/s and 0.21 and 0.25 with the area under the curve (AUC) of 0.927 and 0.831 respectively. Combined MD and FA revealed increased AUC to 0.97 and 0.98 of both readers respectively.

CONCLUSION

DTI with its parameters can be considered a noninvasive beneficial quantitative method that can help in differentiation between pyogenic and tuberculous spondylitis.

Edema-like marrow signal intensity: a narrative review with a pictorial essay

The term edema-like marrow signal intensity (ELMSI) represents a general term describing an area of abnormal signal intensity at MRI. Its appearance includes absence of clear margins and the possibility of exceeding well-defined anatomical borders (for example, physeal scars). We can define "ELMSI with unknown cause" an entity where the characteristic MR appearance is associated with the absence of specific signs of an underlying condition. However, it is more often an important finding indicating the presence of an underlying disease, and we describe this case as "ELMSI with known cause." It presents a dynamic behavior and its evolution can largely vary. It initially corresponds to an acute inflammatory response with edema, before being variably replaced by more permanent marrow remodeling changes such as fibrosis or myxomatous connective tissue that can occur over time. It is important to study ELMSI variations over time in order to evaluate the activity state and therapeutic response of an inflammatory chronic joint disease, the resolution of a trauma, and the severity of an osteoarthritis. We propose a narrative review of the literature dealing with various subjects about this challenging topic that is imaging, temporal evolution, etiology, differential diagnoses, and possible organization, together with a pictorial essay.

Diagnostic Accuracy of Quantitative Imaging Biomarkers in the Differentiation of Benign and Malignant Vertebral Lesions : Combination of Diffusion-Weighted and Proton Density Fat Fraction Spine MRI

Purpose

To compare and combine the diagnostic performance of the apparent diffusion coefficient (ADC) derived from diffusion-weighted imaging (DWI) and proton density fat fraction (PDFF) derived from chemical-shift encoding (CSE)-based water-fat magnetic resonance imaging (MRI) for distinguishing benign and malignant vertebral bone marrow lesions (VBML).

Methods

A total of 55 consecutive patients with 53 benign (traumatic, inflammatory and primary) and 36 malignant (metastatic and hematologic) previously untreated VBMLs were prospectively enrolled in this IRB-approved study and underwent sagittal DWI (single-shot spin-echo echo-planar with multi-slice short TI inversion recovery fat suppression) and CSE-based MRI (gradient-echo 6‑point modified Dixon) in addition to routine clinical spine MRI at 1.5 T or 3.0 T. Diagnostic reference standard was established according to histopathology or imaging follow-up. The ADC = ADC (0, 800) and PDFF = fat / (water + fat) were calculated voxel-wise and examined for differences between benign and malignant lesions.

Results

The ADC and PDFF values of malignant lesions were significantly lower compared to benign lesions (mean ADC 861 × 10⁻⁶ mm²/s vs. 1323 × 10⁻⁶ mm²/s, p < 0.001; mean PDFF 3.1% vs. 28.2%, p < 0.001). The areas under the curve (AUC) and diagnostic accuracies were 0.847 (p < 0.001) and 85.4% (cut-off at 1084.4 × 10⁻⁶ mm²/s) for ADC and 0.940 (p < 0.001) and 89.9% for PDFF (cut-off at 7.8%), respectively. The combined use of ADC and PDFF improved the diagnostic accuracy to 96.6% (malignancy if ADC ≤ 1118.2 × 10⁻⁶ mm²/s and PDFF ≤ 20.0%, otherwise benign).

Conclusion

Quantitative evaluation of both ADC and PDFF was useful in differentiating benign VBMLs from malignancy. The combination of ADC and PDFF improved the diagnostic performance and yielded high diagnostic accuracy for the differentiation of benign and malignant VBMLs.

Metastatic Diffusion Volume Based on Apparent Diffusion Coefficient as a Prognostic Factor in Castration-Resistant Prostate Cancer

BACKGROUND

Whole-body diffusion-weighted MRI (WB-DWI) is useful for assessing disease activity in castration-resistant prostate cancer (CRPC). MET-RADS-P is a subjective assessment-based reporting system proposed to standardize the interpretation of WB-DWI. However, a quantitative evaluation of WB-DWI has not been fully investigated.

PURPOSE

To investigate the validity, and analyze the prognostic value, of quantitative evaluation of WB-DWI based on apparent diffusion coefficient (ADC) values for CRPC.

STUDY TYPE

Retrospective.

POPULATION

Sixty-six patients with CRPC. The median age was 75 years. During the median follow-up period of 25.2 months, 23 of 66 patients (34.8%) died of prostate cancer.

FIELD STRENGTH/SEQUENCE

A 1.5 T WB-DWI was used with two b-values (0 s/mm² -1000 s/mm² ). A single-shot echo-planar imaging sequence was used.

ASSESSMENT

WB-DWI were evaluated by three readers according to MET-RADS-P scoring system. Using imaging software, Attractive BDScore, tumor diffusion volume (mDV) and ADC value of metastatic lesion (mADC) was calculated by two readers. The mDV was calculated with ADC values (×10^-3  mm² /sec) of 0.4-0.9 (mDV_0.4-0.9 ), 0.9-1.4 (mDV_0.9-1.4 ), and 1.4-1.8 (mDV_1.4-1.8 ), respectively.

STATISTICAL TESTS

Spearman's rank correlation coefficient was used to assess the correlation. The relationships between the variables with cancer-specific survival (CSS) were evaluated. Multivariate analysis was performed using the Cox proportional hazards model.

RESULTS

mDVs showed a strong positive correlation with MET-RADS-P scores (r = 0.90/0.87, P < 0.05 for both). mDV showed a statistically significant association with CSS (hazard ratio [HR]: 1.01, P < 0.05). When the mDVs calculated based on the ADC values were included, mDV_0.4-0.9 (HR: 1.02, P < 0.05) and the number of therapeutic lines (HR: 1.35, P < 0.05) were significant independent indicators of CSS shortening.

CONCLUSION

Assessment of metastatic tumor volume based on ADC values can be used in the prognostic evaluation of patients with CRPC. WB-DWI might be a potential prognostic imaging biomarker for CRPC.

EVIDENCE LEVEL

4 TECHNICAL EFFICACY: Stage 2.

Semi-Automated Segmentation of Bone Metastases from Whole-Body MRI: Reproducibility of Apparent Diffusion Coefficient Measurements

Using semi-automated software simplifies quantitative analysis of the visible burden of disease on whole-body MRI diffusion-weighted images. To establish the intra- and inter-observer reproducibility of apparent diffusion coefficient (ADC) measures, we retrospectively analyzed data from 20 patients with bone metastases from breast (BCa; n = 10; aged 62.3 ± 14.8) or prostate cancer (PCa; n = 10; aged 67.4 ± 9.0) who had undergone examinations at two timepoints, before and after hormone-therapy. Four independent observers processed all images twice, first segmenting the entire skeleton on diffusion-weighted images, and then isolating bone metastases via ADC histogram thresholding (ADC: 650–1400 µm²/s). Dice Similarity, Bland-Altman method, and Intraclass Correlation Coefficient were used to assess reproducibility. Inter-observer Dice similarity was moderate (0.71) for women with BCa and poor (0.40) for men with PCa. Nonetheless, the limits of agreement of the mean ADC were just ±6% for women with BCa and ±10% for men with PCa (mean ADCs: 941 and 999 µm²/s, respectively). Inter-observer Intraclass Correlation Coefficients of the ADC histogram parameters were consistently greater in women with BCa than in men with PCa. While scope remains for improving consistency of the volume segmented, the observer-dependent variability measured in this study was appropriate to distinguish the clinically meaningful changes of ADC observed in patients responding to therapy, as changes of at least 25% are of interest.

Clinical suspicion of spondylodiscitis with equivocal MRI findings: does diffusion-weighted imaging prove helpful here?

BACKGROUND

Despite the high sensitivity of magnetic resonance imaging (MRI), early detection of spondylodiscitis (SpD) remains challenging due to its low specificity.

PURPOSE

To assess the diagnostic value of diffusion-weighted imaging (DWI) in suspected cases of SpD with ambiguous early MRI findings in the differentiation of degenerative disorders (DD).

MATERIAL AND METHODS

In this prospective study, 52 patients suspected of having SpD underwent a whole-spine 3-T MRI scan comprising sagittal DWI. Of 58 conspicuous, T2-weighted, signal increased discs, 39 were successfully evaluated using DWI. Apparent diffusion coefficient (ADC) values and ADC maps were blindly analyzed using the region of interest of the conspicuous disc and a normal adjacent reference disc. Intraindividual ratios (conspicuous disc: reference disc) were calculated.

RESULTS

All conspicuous discs showed increased absolute ADC values, which did not differ significantly between SpD (n = 22) and DD (n = 17). However, ADC ratio was significantly higher in SpD vs. DD (P < 0.05). In receiver operating characteristic curve analysis, an ADC ratio threshold of 1.6 resulted in 45% sensitivity and 88% specificity (area under the curve = 0.69) for SpD diagnosis.

CONCLUSION

The absolute ADC value does not provide a reliable diagnosis of SpD. Increased diffusivity can be an indication of infection but should always be discussed in the context of existing disc degeneration.

Differentiation of Vertebral Metastases From Focal Hematopoietic Marrow Depositions on MRI: Added Value of Proton Density Fat Fraction

OBJECTIVE. The purpose of this study was to evaluate the added value of proton density fat fraction (PDFF) in differentiating vertebral metastases from focal hematopoietic marrow depositions. MATERIALS AND METHODS. The study included 44 patients with 30 vertebral metastases and 14 focal hematopoietic marrow depositions who underwent spinal MRI. The final diagnoses were based on histologic confirmation, follow-up MRI, or PET/CT. Two musculoskeletal radiologists with 1 and 15 years of experience independently interpreted both image sets (i.e., images from conventional MRI alone versus images from conventional MRI and PDFF combined). Using a 5-point scale, the readers scored their confidence in the malignancy of the vertebral lesions. The diagnostic performance (AUC) of the two image sets was assessed via ROC curve analyses. Sensitivities, specificities, and accuracies (for both image sets) were compared using the McNemar test. Kappa coefficients were calculated to assess interobserver agreement. RESULTS. Both readers showed improved diagnostic performance after PDFF was added (AUC, 0.840-0.912 and 0.805-0.895 for readers 1 and 2, respectively). However, adding PDFF did not significantly improve the sensitivity and specificity of either reader (p > .05). Interobserver agreement significantly improved from moderate (κ = 0.563) to excellent (κ = 0.947) after PDFF was added. CONCLUSION. The addition of PDFF to a conventional MRI protocol improved the diagnostic performance for differentiating vertebral metastases from focal hematopoietic marrow depositions but without resulting in significant improvement in sensitivity and specificity.

Whole-body magnetic resonance imaging for prostate cancer assessment: Current status and future directions

Over the past decade, updated definitions for the different stages of prostate cancer and risk for distant disease, along with the advent of new therapies, have remarkably changed the management of patients. The two expectations from imaging are accurate staging and appropriate assessment of disease response to therapies. Modern, next-generation imaging (NGI) modalities, including whole-body magnetic resonance imaging (WB-MRI) and nuclear medicine (most often prostate-specific membrane antigen [PSMA] positron emission tomography [PET]/computed tomography [CT]) bring added value to these imaging tasks. WB-MRI has proven its superiority over bone scintigraphy (BS) and CT for the detection of distant metastasis, also providing reliable evaluations of disease response to treatment. Comparison of the effectiveness of WB-MRI and molecular nuclear imaging techniques with regard to indications and the definition of their respective/complementary roles in clinical practice is ongoing. This paper illustrates the evolution of WB-MRI imaging protocols, defines the current state-of-the art, and highlights the latest developments and future challenges. The paper presents and discusses WB-MRI indications in the care pathway of men with prostate cancer in specific key situations: response assessment of metastatic disease, "all in one" cancer staging, and oligometastatic disease.

Differentiating atypical hemangiomas and vertebral metastases: a field-of-view (FOV) and FOCUS intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) study

PURPOSE

Some atypical vertebral hemangiomas (VHs) may mimic metastases on routine MRI and can result in misdiagnosis and ultimately to additional imaging, biopsy and unnecessary costs. The purpose of this study is to assess the utility of intravoxel incoherent motion (IVIM) diffusion-weighted imaging (DWI) on account of field-of-view optimized and constrained undistorted single shot (FOCUS) in distinguishing atypical VHs and vertebral metastases.

METHODS

A total of 25 patients with vertebral metastases and 25 patients with atypical VHs were confirmed by clinical follow-up or pathology. IVIM-DWI imaging was performed at different b values (0, 30, 50, 100, 150, 200, 400, 600, 800, 1000 mm²/s). IVIM parameters [the true diffusion coefficient (D), pseudodiffusion coefficient (D*), standard apparent diffusion coefficient (ADC), and perfusion fraction (f)] were calculated and compared between two groups by using Student's t test. A receiver operating characteristic analysis was performed.

RESULTS

Quantitative analysis of standard ADC and D parameters showed significantly lower values in vertebral metastases when compared to atypical hemangiomas [ADC value: (0.70 ± 0.12) × 10^-3 mm²/s vs (1.14 ± 0.28) × 10^-3 mm²/s; D value: (0.47 ± 0.07) × 10^-3 mm²/s vs (0.76 ± 0.14) × 10^-3 mm²/s, all P < 0.01]. The sensitivity and specificity of D value were 93.8% and 92.3%, respectively.

CONCLUSION

The standard ADC value and D value may be used as an indicator to distinguish vertebral metastases from atypical VHs. FOCUS IVIM-derived parameters provide potential value in the quantitatively differentiating vertebral metastases from vertebral atypical hemangiomas.

Variation of the apparent diffusion coefficient of skull bone marrow by age group, pubertal status, and gender in a pediatric population

BACKGROUND

Bone marrow composition varies with stage of development.

PURPOSE

To assess differences in apparent diffusion coefficient (ADC) derived from clivus bone marrow in healthy children by age, pubertal status, and gender as a benchmark when monitoring local and systemic treatment-induced effects.

MATERIAL AND METHODS

Non-oncological pediatric patients (30 pre-pubertal [15 girls, 15 boys] and 30 post-pubertal [15 girls, 15 boys]) with previous normal magnetic resonance imaging (MRI) of the brain including diffusion-weighted magnetic resonance imaging (DW-MRI; 1.5-T Philips Achieva-Ingenia, b-values 0 and 1000s/mm2) were studied. A 4-6 mm diameter region of interest (ROI), drawn within the clivus on two or three DW-MRI slices, yielded mean and centile ADC values. Pubertal status was recognized from imaging appearances of the pituitary gland and from fusion of the spheno-occipital synchondrosis. Correlations between ADC and age were assessed (Pearson's coefficient). Mann-Whitney U tests compared ADC by age, pubertal status, and gender.

RESULTS

Age and ADC were significantly negatively correlated (median ADC r=-0.48, mean ADC r=-0.42, P=0.0001 and 0.0008, respectively) which held true when divided by gender. Mean and median ADC differed significantly before and after puberty for the whole population (P=0.0001 and 0.0001, respectively). There was a left shift of the ADC histogram after puberty with significant differences in centile values. ADC differences before and after puberty remained when divided by gender (girls: P=0.04 and 0.009, respectively; boys: P=0.005 and 0.0002, respectively).

CONCLUSION

ADC of clivus bone marrow correlates with age in children. ADC decreases significantly after puberty, likely due to replacement of hypercellular marrow with fat. There are no gender-related differences in clivus bone-marrow ADC before or after puberty.

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

OBJECT

The 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 (T_1W, T_1F, 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 METHODS

A 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 f_PDFF.

RESULTS

A significant difference in the values of PDFF, f and f_PDFF, T_1F, 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.

DISCUSSION

The regional difference in PDFF, f_PDFF 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.

Role of diffusion-weighted magnetic resonance imaging in the evaluation of vertebral bone marrow lesions

Purpose

To evaluate the role of diffusion-weighted magnetic resonance imaging (DW-MRI) in differentiating vertebral marrow pathologies. To determine the sensitivity, specificity, and threshold apparent diffusion coefficient (ADC) values that can aid in the differentiation of malignant from benign bone marrow lesions.

Material and methods

This observational study included 100 patients, who underwent MRI examination with a 1.5 Tesla scanner. The ADC values of normal and pathological vertebrae were estimated, and the threshold ADC values were computed by receiver operating characteristic (ROC) analysis. The results were correlated with histopathological diagnosis, clinical follow-up, and other investigations. Statistical analysis was done by employing unpaired two-tailed Student’s t-test and the p-value of < 0.05 was deemed as statistically significant.

Results

Vertebral bone marrow lesions had a male predominance and there was a predilection towards thoracic and lumbar vertebrae, with L4 being the commonest. Metastasis was the commonest lesion, followed by spondylodiscitis. The mean ADC value of benign pathologies was significantly greater than malignant pathologies (p < 0.05). The threshold value for the demarcation between benign and malignant pathologies was computed to be 1.21 × 10^-3 mm²/s. DW imaging had sensitivity of 100%, specificity of 92.31%, positive predictive value of 87.5%, and negative predictive value of 100%.

Conclusions

Vertebral marrow lesions can be differentiated as benign or malignant with good sensitivity and specificity with the help of DW-ADC maps.

Imaging diagnosis of metastatic breast cancer

Numerous imaging modalities may be used for the staging of women with advanced breast cancer. Although bone scintigraphy and multiplanar-CT are the most frequently used tests, others including PET, MRI and hybrid scans are also utilised, with no specific recommendations of which test should be preferentially used. We review the evidence behind the imaging modalities that characterise metastases in breast cancer and to update the evidence on comparative imaging accuracy.

Histographic analysis of oedema and fat in inflamed bone marrow based on quantitative MRI

Objective

To demonstrate proof-of-concept for a quantitative MRI method using histographic analysis to assess bone marrow oedema and fat metaplasia in the sacroiliac joints.

Materials and methods

Fifty-three adolescents aged 12–23 with known or suspected sacroiliitis were prospectively recruited and underwent quantitative MRI (qMRI) scans, consisting of chemical shift-encoded (at 3 T) and diffusion-weighted imaging (at 1.5 T), plus conventional MRI (at 1.5 T) and clinical assessment. qMRI scans produced proton-density fat fraction (PDFF) and apparent diffusion coefficient (ADC) maps of the sacroiliac joints (SIJs), which were analysed using an in-house software tool enabling partially automated ROI definition and histographic analysis. Logistic regression and receiver operating characteristic (ROC) analyses assessed the predictive performance of ADC- and PDFF-based parameters in identifying active inflammation (oedema) and structural damage (fat metaplasia).

Results

ADC-based parameters were associated with increased odds of oedema (all p < 0.05); ROC-AUC was higher for histographic parameters representing the upper end of the ADC distribution than for simple averages. Similarly, PDFF-based parameters were associated with increased odds of fat metaplasia (all p < 0.05); ROC area-under-the-curve was higher for histographic parameters representing the upper end of the PDFF distribution than for simple averages. Both ADC- and PDFF-based histographic parameters demonstrated excellent inter- and intra-observer agreement (ICC > 0.9).

Conclusions

ADC-based parameters can differentiate patients with bone marrow oedema from those without, whilst PDFF-based parameters can differentiate patients with fat metaplasia from those without. Histographic analysis might improve performance compared with simple averages such as the mean and median and offers excellent agreement within and between observers.

Key Points

• Quantitative MRI with histographic analysis can identify bone marrow oedema (an active inflammatory lesion) and fat metaplasia (a ‘chronic’ inflammatory lesion) in patients with spondyloarthritis.

• The use of histographic analysis might improve the performance of quantitative MRI for detecting bone marrow oedema and fat metaplasia compared with simple averages such as the mean and median.

• Bone marrow oedema and fat metaplasia are known to be of diagnostic and prognostic significance, and the proposed method could support clinical decisions around biologic (and other) therapies in spondyloarthritis.

Electronic supplementary material

The online version of this article (10.1007/s00330-020-06785-x) contains supplementary material, which is available to authorized users.

Diffusion MRI for Assessment of Bone Quality; A Review of Findings in Healthy Aging and Osteoporosis

Diffusion MRI (dMRI) is a growing imaging technique with the potential to provide biomarkers of tissue variation, such as cellular density, tissue anisotropy, and microvascular perfusion. However, the role of dMRI in characterizing different aspects of bone quality, especially in aging and osteoporosis, has not yet been fully established, particularly in clinical applications. The reason lies in the complications accompanied with implementation of dMRI in assessment of human bone structure, in terms of acquisition and quantification. Bone is a composite tissue comprising different elements, each contributing to the overall quality and functional competence of bone. As diffusion is a critical biophysical process in biological tissues, early changes of tissue microstructure and function can affect diffusive properties of the tissue. While there are multiple MRI methods to detect variations of individual properties of bone quality due to aging and osteoporosis, dMRI has potential to serve as a superior method for characterizing different aspects of bone quality within the same framework but with higher sensitivity to early alterations. This is mainly because several properties of the tissue including directionality and anisotropy of trabecular bone and cell density can be collected using only dMRI. In this review article, we first describe components of human bone that can be potentially detected by their diffusivity properties and contribute to variations in bone quality during aging and osteoporosis. Then we discuss considerations and challenges of dMRI in bone imaging, current status, and suggestions for development of dMRI in research studies and clinics to segregate different contributing components of bone quality in an integrated acquisition. Level of Evidence: 5 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2020;51:975-992.

MRI Assessment of Bone Marrow Composition in Osteoporosis

PURPOSE OF REVIEW

To provide an overview on recent technical development for quantifying marrow composition using magnetic resonance imaging (MRI) and spectroscopy (MRS) techniques, as well as a summary on recent findings of interrelationship between marrow adipose tissue (MAT) and skeletal health in the context of osteoporosis.

RECENT FINDINGS

There have been significant technical advances in reliable quantification of marrow composition using MR techniques. Cross-sectional studies have demonstrated a negative correlation between MAT and bone, with trabecular bone associating more strongly with MAT than cortical bone. However, longitudinal studies of MAT and bone are limited. MAT contents and composition have been associated with prevalent vertebral fracture. The evidence between MAT and clinical fracture is more limited, and, to date, no studies have reported on the relationship between MAT and incident fracture. Increasing evidence suggests a dynamic role of marrow fat in skeletal health. Reliable non-invasive quantification of marrow composition will facilitate developing novel treatment strategies for osteoporosis.

Diffusion-Weighted Magnetic Resonance Imaging of Spine

척추영상에 사용되는 확산강조영상의 기술적 측면, 양성과 악성 척추체 압박골절의 구분, 다발성골수종이나 전이암의 발견과 감별진단, 그리고 항암화학요법이나 방사선치료 후 반응 평가에 대해 기술하고자 한다.

Emerging quantitative MR imaging biomarkers in inflammatory arthritides

PURPOSE

To review quantitative magnetic resonance imaging (qMRI) methods for imaging inflammation in connective tissues and the skeleton in inflammatory arthritis. This review is designed for a broad audience including radiologists, imaging technologists, rheumatologists and other healthcare professionals.

METHODS

We discuss the use of qMRI for imaging skeletal inflammation from both technical and clinical perspectives. We consider how qMRI can be targeted to specific aspects of the pathological process in synovium, cartilage, bone, tendons and entheses. Evidence for the various techniques from studies of both adults and children with inflammatory arthritis is reviewed and critically appraised.

RESULTS

qMRI has the potential to objectively identify, characterize and quantify inflammation of the connective tissues and skeleton in both adult and pediatric patients. Measurements of tissue properties derived using qMRI methods can serve as imaging biomarkers, which are potentially more reproducible and informative than conventional MRI methods. Several qMRI methods are nearing transition into clinical practice and may inform diagnosis and treatment decisions, with the potential to improve patient outcomes.

CONCLUSIONS

qMRI enables specific assessment of inflammation in synovium, cartilage, bone, tendons and entheses, and can facilitate a more consistent, personalized approach to diagnosis, characterisation and monitoring of disease.

Intravoxel incoherent motion MR imaging for differentiating malignant lesions in spine: A pilot study

PURPOSE

To determine the diagnostic potential of Intravoxel Incoherent Motion (IVIM) MRI for differentiating malignant spinal tumours from acute vertebral compression fractures and tuberculous spondylitis, and to compare IVIM with diffusion-weighted imaging (DWI) and chemical shift imaging (CSI).

METHODS

The Institutional Review Board approved this prospective study, and informed consent was obtained. IVIM MRI, DWI, and CSI at 1.5 T were performed in 25 patients with 12 acute compression fractures, 14 tuberculous spondylitis, and 18 malignant spinal tumours. The parameters of these techniques were assessed using the Kruskal-Wallis test. The diagnostic performance of the parameters was evaluated using receiver operating characteristic (ROC) analysis.

RESULTS

ADC, SIR, D_slow, D_fast, and f values of malignant tumours were significantly different from those of acute compression fracture (for all, p < 0.05). The mean D_slow and D_fast values of malignant spinal tumours had significant differences compared with those of tuberculous spondylitis (for all, p < 0.05). However, no significant differences were observed in any quantitative parameters between the acute compression fracture and the tuberculous spondylitis (p > 0.05). D_slow•f showed the highest AUC value of 0.980 (95%CI: 0.942-1.000) in differentiating acute compression fracture and malignant spinal tumours. D_slow showed the highest AUC value of 0.877 (95%CI: 0.713-0.966) in differentiating tuberculous spondylitis and malignant spinal tumours.

CONCLUSIONS

IVIM MR imaging may be helpful for differentiating malignant spinal tumours from acute vertebral compression fractures and tuberculous spondylitis.

MR Imaging of Pediatric Musculoskeletal Tumors:: Recent Advances and Clinical Applications

Pediatric musculoskeletal tumors comprise approximately 10% of childhood neoplasms, and MR imaging has been used as the imaging evaluation standard for these tumors. The role of MR imaging in these cases includes identification of tumor origin, tissue characterization, and definition of tumor extent and relationship to adjacent structures as well as therapeutic response in posttreatment surveillance. Technical advances have enabled quantitative evaluation of biochemical changes in tumors. This article reviews recent updates to MR imaging of pediatric musculoskeletal tumors, focusing on advanced MR imaging techniques and providing information on the relevant physics of these techniques, clinical applications, and pitfalls.

Multiparametric Magnetic Resonance Imaging of Prostate Cancer Bone Disease: Correlation With Bone Biopsy Histological and Molecular Features

OBJECTIVES

The aim of this study was to correlate magnetic resonance imaging (MRI) of castration-resistant prostate cancer (CRPC) bone metastases with histological and molecular features of bone metastases.

MATERIALS AND METHODS

Forty-three bone marrow biopsies from 33 metastatic CRPC (mCRPC) patients with multiparametric MRI and documented bone metastases were evaluated. A second cohort included 10 CRPC patients with no bone metastases. Associations of apparent diffusion coefficient (ADC), normalized b900 diffusion-weighted imaging (nDWI) signal, and signal-weighted fat fraction (swFF) with bone marrow biopsy histological parameters were evaluated using Mann-Whitney U test and Spearman correlations. Univariate and multivariate logistic regression models were analyzed.

RESULTS

Median ADC and nDWI signal was significantly higher, and median swFF was significantly lower, in bone metastases than nonmetastatic bone (P < 0.001). In the metastatic cohort, 31 (72.1%) of 43 biopsies had detectable cancer cells. Median ADC and swFF were significantly lower and median nDWI signal was significantly higher in biopsies with tumor cells versus nondetectable tumor cells (898 × 10 mm/s vs 1617 × 10 mm/s; 11.5% vs 62%; 5.3 vs 2.3, respectively; P < 0.001). Tumor cellularity inversely correlated with ADC and swFF, and positively correlated with nDWI signal (P < 0.001). In serial biopsies, taken before and after treatment, changes in multiparametric MRI parameters paralleled histological changes.

CONCLUSIONS

Multiparametric MRI provides valuable information about mCRPC bone metastases. These data further clinically qualify DWI as a response biomarker in mCRPC.

Magnetic Resonance Imaging correlates of benign and malignant alterations of the spinal bone marrow

BACKGROUND AND AIM OF THE WORK

Bone marrow (BM) abnormalities in the spine are a common, sometimes unexpected, finding on Magnetic Resonance Imaging (MRI), which is the most sensitive imaging modality to evaluate the marrow, and their interpretation can be difficult for the unexperienced radiologist. In this review, the MRI appearance of normal age-related BM changes, as well as the imaging features of benign and malignant diseases, are presented.

DISCUSSION

A large variety of BM signal alterations has been identified and described, including normal variants, BM reconversion,  degenerative changes, infections, spondyloarthritis and osteonecrosis, trauma, neoplastic lesions (both primary or metastatic), post-radiation and chemotherapy sequelae.

CONCLUSIONS

Knowledge of normal age-related BM appearance, normal variants and patterns of involvement in focal and diffuse bone diseases is essential, together with clinical and laboratory data, to narrow the list of the possible differential diagnoses. The radiologist should be familiar with these signal changes, as they can sometimes be discovered incidentally. In this context, it is equally important not to attribute pathological significance to benign alterations and to promptly detect signs of malignant diseases.

Review of the Imaging Features of Benign Osteoporotic and Malignant Vertebral Compression Fractures

Vertebral compression fractures are very common, especially in the elderly. Benign osteoporotic and malignant vertebral compression fractures have extremely different management and prognostic implications. Although there is an overlap in appearances, characteristic imaging features can aid in the distinction between these 2 types of compression fractures. The aim of this review is to characterize the imaging features of benign and malignant vertebral compression fractures seen with CT, PET, SPECT, and MR imaging.

Quantitative MRI and spectroscopy of bone marrow

Bone marrow is one of the largest organs in the human body, enclosing adipocytes, hematopoietic stem cells, which are responsible for blood cell production, and mesenchymal stem cells, which are responsible for the production of adipocytes and bone cells. Magnetic resonance imaging (MRI) is the ideal imaging modality to monitor bone marrow changes in healthy and pathological states, thanks to its inherent rich soft‐tissue contrast. Quantitative bone marrow MRI and magnetic resonance spectroscopy (MRS) techniques have been also developed in order to quantify changes in bone marrow water–fat composition, cellularity and perfusion in different pathologies, and to assist in understanding the role of bone marrow in the pathophysiology of systemic diseases (e.g. osteoporosis). The present review summarizes a large selection of studies published until March 2017 in proton‐based quantitative MRI and MRS of bone marrow. Some basic knowledge about bone marrow anatomy and physiology is first reviewed. The most important technical aspects of quantitative MR methods measuring bone marrow water–fat composition, fatty acid composition, perfusion, and diffusion are then described. Finally, previous MR studies are reviewed on the application of quantitative MR techniques in both healthy aging and diseased bone marrow affected by osteoporosis, fractures, metabolic diseases, multiple myeloma, and bone metastases.

Level of Evidence: 3

Technical Efficacy: Stage 2

J. Magn. Reson. Imaging 2018;47:332–353.