Diffusion-weighted imaging in musculoskeletal radiology-clinical applications and future directions

Comparison between ZOOMit DWI and conventional DWI in the assessment of foot and ankle infection: a prospective study

OBJECTIVE

The study aimed to compare ZOOMit diffusion-weighted imaging (DWI) MRI with conventional DWI MRI for visualizing small bones in the foot, soft tissue abscesses, and osteomyelitis.

MATERIALS AND METHODS

The cohort consisted of a consecutive series of patients with potential foot and ankle infections referred for MR imaging. Patients were imaged using both conventional and ZOOMit DWI in the same setting. Blinded reads were then conducted in separate settings and independent of known clinical diagnosis by two expert radiologists. The results from the reads were compared statistically using paired t-tests and with biopsy specimen analysis, both anatomopathological and microbiological.

RESULTS

There was improvement in fat suppression using ZOOMit sequence compared to conventional DWI (p = .001) with no significant difference in motion artifacts (p = .278). ZOOMit had a higher rate of concordance with pathology findings for osteomyelitis (72%, 31/43 cases) compared with conventional DWI (60%, 26/43 cases). ZOOMit also identified 46 additional small bones of the foot and ankle (405/596, 68.0%) than conventional DWI (359/596, 60.2%). Conventional DWI however exhibited a more negative contrast-to-noise ratio (CNR) than ZOOMit (p = 0.001).

CONCLUSION

ZOOMit DWI improves distal extremity proton diffusion assessment and helps visualize more bones in the foot, with less image distortion and improved fat saturation at the expense of reduced CNR. This makes it a viable option for assessing lower extremity infections.

CLINICAL RELEVANCE STATEMENT

This study highlights the novel utilization of ZOOMit diffusion-weighted imaging (DWI) for the assessment of lower extremity lesions compared to conventional DWI.

KEY POINTS

• Distal extremity diffusion-weighted imaging (DWI) is often limited. • ZOOMit DWI displayed improved fat suppression with less motion artifacts and better visualization of the lower extremity bones than conventional DWI. • ZOOMit shows decreased contrast-to-noise ratio than conventional DWI.

Bone tumors: state-of-the-art imaging

Imaging plays a central role in the management of patients with bone tumors. A number of imaging modalities are available, with different techniques having unique applications that render their use advantageous for various clinical purposes. Coupled with detailed clinical assessment, radiological imaging can assist clinicians in reaching a proper diagnosis, determining appropriate management, evaluating response to treatment, and monitoring for tumor recurrence. Although radiography is still the initial imaging test of choice for a patient presenting with a suspected bone tumor, technological innovations in the last decades have advanced the role of other imaging modalities for assessing bone tumors, including advances in computed tomography, magnetic resonance imaging, scintigraphy, and hybrid imaging techniques that combine two existing modalities, providing clinicians with diverse tools for bone tumor imaging applications. Determining the most suitable modality to use for a particular application requires familiarity with the modality in question, its advancements, and its limitations. This review highlights the various imaging techniques currently available and emphasizes the latest developments in imaging, offering a framework that can help guide the imaging of patients with bone tumors.

Quantitative Skeletal Imaging and Image-Based Modeling in Pediatric Orthopaedics

PURPOSE OF REVIEW

Musculoskeletal imaging serves a critical role in clinical care and orthopaedic research. Image-based modeling is also gaining traction as a useful tool in understanding skeletal morphology and mechanics. However, there are fewer studies on advanced imaging and modeling in pediatric populations. The purpose of this review is to provide an overview of recent literature on skeletal imaging modalities and modeling techniques with a special emphasis on current and future uses in pediatric research and clinical care.

RECENT FINDINGS

While many principles of imaging and 3D modeling are relevant across the lifespan, there are special considerations for pediatric musculoskeletal imaging and fewer studies of 3D skeletal modeling in pediatric populations. Improved understanding of bone morphology and growth during childhood in healthy and pathologic patients may provide new insight into the pathophysiology of pediatric-onset skeletal diseases and the biomechanics of bone development. Clinical translation of 3D modeling tools developed in orthopaedic research is limited by the requirement for manual image segmentation and the resources needed for segmentation, modeling, and analysis. This paper highlights the current and future uses of common musculoskeletal imaging modalities and 3D modeling techniques in pediatric orthopaedic clinical care and research.

Characteristic of Apparent Diffusion Coefficient and Time Intensity Curve Analysis of Dynamic Contrast Enhanced MRI in Osteosarcoma Histopathologic Subtypes

Background: According to WHO criteria, osteosarcoma (OS) consists of various histopathological subtypes. Thus, contrast-enhanced MRI is a very useful modality in the diagnosis and evaluation of osteosarcoma. Magnetic resonance imaging with dynamic contrast enhancement (DCE-MRI) studies was used to determine the apparent diffusion coefficient (ADC) value and the slope of the time-intensity curve (TIC). This study aimed to determine the correlation between ADC and TIC analysis using %Slope and maximum enhancement (ME) of histopathological osteosarcoma subtypes. Methods: This was a retrospective study with observational analysis on OS patients. The obtained data were 43 samples. Moreover, the interpretation was conducted by placing three regions of interest (ROI) in determining ADC value. It was observed by two radiologist observers with more than 10 years of experience. In this case, as many as six obtained ROIs were averaged. The inter-observer agreement was evaluated by Kappa test. TIC curve was analyzed and slope value was obtained afterward. Through SPSS 21 software, the data was analyzed. Results: The mean of ADC values of OS was (1.031x10^-3±0.31mm²/s), where the highest value was found in chondroblastic subtype (1.470 x10^-3±0.31mm²/s). However, the mean of TIC %slope of OS was (45.3%/s), where the highest result was found in the osteoblastic subtype (70.8%/s) followed by small cell subtype (60.8%/s) and the mean of ME of OS was 100.55% with the highest values was in osteoblastic subtype 172.72% followed by chondroblastic subtype (144.92%). This study found a significant correlation between the mean of ADC value and the OS histopathologic results as well as the correlation between the mean of ADC value and ME. Conclusion: The various types of osteosarcoma have a characteristic of radiological appearances which may similar to some bone tumor entities. The analysis of ADC values and TIC curves using % slope and ME of osteosarcoma subtypes can improve the accuracy of diagnosis as well as the monitoring of the treatment response and the disease progression.

Correcting B0 inhomogeneity-induced distortions in whole-body diffusion MRI of bone

Diffusion-weighted magnetic resonance imaging (DWI) of the musculoskeletal system has various applications, including visualization of bone tumors. However, DWI acquired with echo-planar imaging is susceptible to distortions due to static magnetic field inhomogeneities. This study aimed to estimate spatial displacements of bone and to examine whether distortion corrected DWI images more accurately reflect underlying anatomy. Whole-body MRI data from 127 prostate cancer patients were analyzed. The reverse polarity gradient (RPG) technique was applied to DWI data to estimate voxel-level distortions and to produce a distortion corrected DWI dataset. First, an anatomic landmark analysis was conducted, in which corresponding vertebral landmarks on DWI and anatomic T₂-weighted images were annotated. Changes in distance between DWI- and T₂-defined landmarks (i.e., changes in error) after distortion correction were calculated. In secondary analyses, distortion estimates from RPG were used to assess spatial displacements of bone metastases. Lastly, changes in mutual information between DWI and T₂-weighted images of bone metastases after distortion correction were calculated. Distortion correction reduced anatomic error of vertebral DWI up to 29 mm. Error reductions were consistent across subjects (Wilcoxon signed-rank p < 10^-20). On average (± SD), participants' largest error reduction was 11.8 mm (± 3.6). Mean (95% CI) displacement of bone lesions was 6.0 mm (95% CI 5.0-7.2); maximum displacement was 17.1 mm. Corrected diffusion images were more similar to structural MRI, as evidenced by consistent increases in mutual information (Wilcoxon signed-rank p < 10^-12). These findings support the use of distortion correction techniques to improve localization of bone on DWI.

Pediatric skeletal diffusion-weighted magnetic resonance imaging, part 2: current and emerging applications

Diffusion-weighted imaging (DWI) complements the more established T1, fluid-sensitive and gadolinium-enhanced magnetic resonance pulse sequences used to assess several pediatric skeletal pathologies. There is optimism that the technique might not just be complementary but could serve as an alternative to gadolinium and radiopharmaceuticals for several indications. As a non-contrast, free-breathing and noninvasive technique, DWI is especially valuable in children and is readily incorporated into existing MRI protocols. The indications for skeletal DWI in children include distinguishing between benign and malignant skeletal processes, initial assessment and treatment response assessment for osseous sarcomas, and assessment of inflammatory arthropathies and femoral head ischemia, among others. A notable challenge of diffusion MRI is the dynamic nature of the growing pediatric skeleton. It is important to consider the child's age when placing DWI findings in context with potential marrow pathology. This review article summarizes the current and evolving applications of DWI for assessing the pediatric skeleton, rounding off the discussion with evolving directions for further research in this realm.

An update in musculoskeletal tumors: from quantitative imaging to radiomics

In the last two decades, relevant progress has been made in the diagnosis of musculoskeletal tumors due to the development of new imaging tools, such as diffusion-weighted imaging, diffusion kurtosis imaging, magnetic resonance spectroscopy, and diffusion tensor imaging. Another important role has been played by the development of artificial intelligence software based on complex algorithms, which employ computing power in the detection of specific tumor types. The aim of this article is to report the most advanced imaging techniques focusing on their advantages in clinical practice.

Associations between apparent diffusion coefficient values and histopathological tissue alterations in myopathies

OBJECTIVES

Diffusion-weighted imaging (DWI) can reflect histopathologic changes in muscle disorders. The present study sought to elucidate possible associations between histopathology derived from muscle biopsies and DWI in myositis and other myopathies.

METHODS

Nineteen patients (10 women, 52.6%) with a mean age 51.43 ± 19 years were included in this retrospective study. Apparent diffusion coefficients (ADC) were evaluated with a histogram approach of the biopsied muscle. The histopathology analysis included the scoring systems proposed by Tateyama et al., Fanin et al., Allenbach et al. and immunhistochemical stainings for MHC, CD68, CD8, and CD4.

RESULTS

There was a tendency that skewness was lowered with increasing Tateyama score, but it did not reach statistical significance (p = .14). No statistical differences for the other scores were identified. There was a tendency that kurtosis was higher in MHC negative stained patient compared to positive patients, but statistically significance was not reached (p = .07). ADC histogram parameters did not correlate with CD68 and CD8 positive stained cells. There was a trend for skewness to correlate with the amount of CD4-positive cells (r = .57, p = .07).

CONCLUSION

The present study could not identify statistical significant associations between DWI and histopathology in muscle diseases based upon a small patient sample. Presumably, the investigated histopathology scores are more specific for certain disease aspects, whereas ADC values reflect the whole cellularity of the investigated muscle, which might cause the negative results.

Near-Silent and Distortion-Free Diffusion MRI in Pediatric Musculoskeletal Disorders: Comparison With Echo Planar Imaging Diffusion

BACKGROUND

Diffusion-weighted imaging (DWI) is common for evaluating pediatric musculoskeletal lesions, but suffers from geometric distortion and intense acoustic noise.

PURPOSE

To investigate the performance of a near-silent and distortion-free DWI sequence (DW-SD) relative to standard echo-planar DWI (DW-EPI) in pediatric extremity MRI.

STUDY TYPE

Prospective validation study.

SUBJECTS

Thirty-nine children referred for extremity MRI.

FIELD STRENGTH/SEQUENCE

DW-EPI and DW-SD, based on a rotating ultrafast sequence modified with sinusoidal diffusion preparation gradients, at 3T.

ASSESSMENT

DW-SD image quality (S_anat ) was assessed from 0 (nondiagnostic) to 5 (outstanding) and comparative image quality (S_comp ) (from -2 = DW-EPI more delineated to +2 = DW-SD more delineated, 0 = same). ADC measured by DW-SD and DW-EPI were compared in bone marrow, muscle, and lesions.

STATISTICAL TESTS

Wilcoxon rank-sum test and confidence interval of proportions (CIOP) were calculated for S_comp , Student's t-test, coefficient of variation (COV), and Bland-Altman analysis for ADC values, and intraclass correlation coefficient (ICC) for interreader agreement.

RESULTS

DW-SD and DW-EPI ADC values for bone marrow, muscle, and lesions were not significantly different (P = 0.3, P = 0.2, and P = 0.27, respectively) and had an overall ADC COV of 14.8% (95% confidence interval: 12.3%, 16.9%) and no significant proportional bias on Bland-Altman analysis. S_anat CIOP was rated diagnostic or better (score of 3, 4, or 5) in 72-98% of cases for bone marrow, muscle, and soft tissues. DW-SD was equivalent to or preferred over DW-EPI in muscles and soft tissues, with CIOP 86-93% and 93%, respectively. Lesions were equally visualized on DW-SD and DW-EPI in 40-51%, with DW-SD preferred in 44-56% of cases. DW-SD was rated significantly better than DW-EPI across all comparative variables that included bone marrow, muscle, soft tissue, cartilage, and lesions (P < 0.05). Readers had moderate to near-perfect (ICC range = 0.45-0.85).

DATA CONCLUSION

DW-SD of the extremities provided similar ADC values and improved image quality compared with conventional DW-EPI. Level of Evidence 2 Technical Efficacy Stage 2 J. MAGN. RESON. IMAGING 2021;53:504-513.

[Postoperative and posttherapeutic changes after primary bone tumors : What's important for radiologists?]

Posttreatment imaging of primary bone tumours represents a diagnostic challenge for radiologists. Depending on the primary bone tumour common radiological procedures, such as radiography, computed tomography (CT), and magnetic resonance imaging (MRI), are employed. Radiography and CT are particularly useful in benign bone tumours and in matrix-forming bone tumours. MRI comes into consideration with malignant tumour recurrence and tumoral soft tissue infiltration. Bone scintigraphy is of superior importance if a primarily multifocal manifestation of bone tumour or metastasizing tumour disease is suspected. Molecular imaging (FDG-PET and hybrid imaging, using CT) are gaining increasing importance in light of monitoring neoadjuvant chemotherapy and detecting recurrent tumour appearance. The current literature shows sensitivity and specificity values for recurrent detection of up to 92% and 93%. Diagnostic accuracy is as high as 95%, thus, exceeding accuracy values for CT (67%) and MRI (86%) by far. Likewise, this is also applicable for the assessment of the neoadjuvant chemotherapy. Moreover, PET-based modalities are able to establish prognostic statements using SUV-threshold values at baseline (especially for Ewing sarcomas). Advanced imaging techniques have made a great diagnostic step forward and have proven to be relevant and reproducible with respect to both relapse detection and treatment assessment. Furthermore, it is not clear whether a higher detection rate of early tumour recurrence will inevitably lead to better outcome and survival.

New Techniques in MR Imaging of the Ankle and Foot

Foot and ankle disorders are common in everyday clinical practice. MR imaging is frequently required for diagnosis given the variety and complexity of foot and ankle anatomy. Although conventional MR imaging plays a significant role in diagnosis, contemporary management increasingly relies on advanced imaging for monitoring therapeutic response. There is an expanding need for identification of biomarkers for musculoskeletal tissues. Advanced imaging techniques capable of imaging these tissue substrates will be increasingly used in routine clinical practice. Radiologists should therefore become familiar with these innovative MR techniques. Many such techniques are already widely used in other organ systems.

Quantitative imaging methods in osteoporosis

Osteoporosis is characterized by a decreased bone mass and quality resulting in an increased fracture risk. Quantitative imaging methods are critical in the diagnosis and follow-up of treatment effects in osteoporosis. Prior radiographic vertebral fractures and bone mineral density (BMD) as a quantitative parameter derived from dual-energy X-ray absorptiometry (DXA) are among the strongest known predictors of future osteoporotic fractures. Therefore, current clinical decision making relies heavily on accurate assessment of these imaging features. Further, novel quantitative techniques are being developed to appraise additional characteristics of osteoporosis including three-dimensional bone architecture with quantitative computed tomography (QCT). Dedicated high-resolution (HR) CT equipment is available to enhance image quality. At the other end of the spectrum, by utilizing post-processing techniques such as the trabecular bone score (TBS) information on three-dimensional architecture can be derived from DXA images. Further developments in magnetic resonance imaging (MRI) seem promising to not only capture bone micro-architecture but also characterize processes at the molecular level. This review provides an overview of various quantitative imaging techniques based on different radiological modalities utilized in clinical osteoporosis care and research.