Zero echo time pediatric musculoskeletal magnetic resonance imaging: initial experience

Comparison of short TE CT-like MRI sequences and UHR-CT in cadaveric wrist study

RATIONALE AND OBJECTIVES

To evaluate the performance of CT-like MRI sequences (gradient echo with radial k-space filling (GRE), pointwise encoding time reduction with radial acquisition (PETRA), radial Ultrashort Echo Time (UTE)) versus ultra-high-resolution CT (UHR-CT) in assessing carpal bones and soft tissue calcifications in cadaveric wrists.

MATERIALS AND METHODS

Five anonymized cadaveric forearm specimens were imaged using a 3 T MRI system with GRE, PETRA, and radial UTE sequences, alongside UHR-CT. Evaluated parameters included bone contours, carpal bone dimensions, cortical thickness, lesion size and soft tissue calcifications. Detection and diagnostic confidence of soft tissue calcifications were graded, and Contrast-to-Noise Ratio (CNR) was assessed for various tissues.

RESULTS

GRE provided the clearest bone contour visualization, closely matching UHR-CT, with a mean difference of less than 1 mm (p = 0.9). Geode sizes were underestimated by 16.1 % on GRE, 15.6 % on PETRA, and 22.5 % on radial UTE. GRE showed the highest CNR for bone (33.6 ± 15.4), outperforming PETRA (15.8 ± 8.5) and radial UTE (11.4 ± 8.1). Cortical thickness was overestimated significantly by PETRA (p = 0.05) and radial UTE (p = 0.009), but not by GRE (p = 0.5). GRE detected the most calcifications, but over 75 % of hypodense calcifications remained undetected. Overall, GRE offered the best bone contour visualization and CNR, while PETRA and radial UTE were better at distinguishing calcified tissue from tendons.

CONCLUSION

CT-like MRI sequences accurately assess bone morphology, with GRE offering the best bone contour visualization and CNR.

Assessment of sacroiliitis using zero echo time magnetic resonance imaging: a comprehensive evaluation

BACKGROUND

Enthesitis-related arthritis (ERA), a subset of juvenile idiopathic arthritis (JIA), is characterized by frequent involvement of the sacroiliac (SI) joints.

OBJECTIVE

The aim of this study was to assess the effectiveness of zero echo time (ZTE) magnetic resonance imaging (MRI) in identifying structural lesions in patients with ERA. Conventional MRI pulse sequences often struggle to adequately visualize osseous and calcified tissues.

MATERIALS AND METHODS

All MRI examinations were conducted using a 1.5-T (T) scanner. The MRI protocol included standard sequences such as fat-suppressed axial T2-weighted, axial T1-weighted, coronal short tau inversion recovery (STIR), and axial T2-weighted sequences. In addition to conventional MRI, a ZTE sequence was employed. Low-dose computed tomography (CT) served as the reference standard and was performed using a 640-multislice CT device. Structural lesions, including erosions, sclerosis, and changes in joint space, were compared between imaging modalities.

RESULTS

A total of 20 patients were included in the study (12 boys, 8 girls), with a median age at diagnosis of 14 years. ZTE-MRI demonstrated similar sensitivity to low-dose CT in detecting erosion (7 vs 8, P = 0.707). The interclass correlation coefficient (ICC) between low-dose CT and ZTE-MRI was 0.993 (P < 0.001), indicating excellent agreement. Moreover, ZTE-MRI showed strong agreement with low-dose CT in detecting sclerosis (ICC = 0.954, P < 0.001) and changes in joint space (ICC = 0.998, P < 0.001).

CONCLUSIONS

Zero echo time imaging shows promise in providing sacroiliac joint visualization comparable to low-dose CT scans, thereby improving the detection of subtle erosion and sclerosis in these joints.

Mineralized tissue visualization with MRI: Practical insights and recommendations for optimized clinical applications

Magnetic resonance imaging (MRI) techniques that enhance the visualization of mineralized tissues (hereafter referred to as MT-MRI) are increasingly being incorporated into clinical practice, particularly in musculoskeletal imaging. These techniques aim to mimic the contrast provided by computed tomography (CT), while taking advantage of MRI's superior soft tissue contrast and lack of ionizing radiation. However, the variety of MT-MRI techniques, including three-dimensional gradient-echo, ultra-short and zero-echo time, susceptibility-weighted imaging, and artificial intelligence-generated synthetic CT, each offer different technical characteristics, advantages, and limitations. Understanding these differences is critical to optimizing clinical application. This review provides a comprehensive overview of the most commonly used MT-MRI techniques, categorizing them based on their technical principles and clinical utility. The advantages and disadvantages of each approach, including their performance in bone morphology assessment, fracture detection, arthropathy-related findings, and soft tissue calcification evaluation are discussed. Additionally, technical limitations and artifacts that may affect image quality and diagnostic accuracy, such as susceptibility effects, signal-to-noise ratio issues, and motion artifacts are addressed. Despite promising developments, MT-MRI remains inferior to conventional CT for evaluating subtle bone abnormalities and soft tissue calcification due to spatial resolution limitations. However, advances in deep learning and hardware innovations, such as artificial intelligence-generated synthetic CT and ultrahigh-field MRI, may bridge this gap in the future.

Bone assessment of the sacroiliac joint in ankylosing spondylitis: Comparison between computed tomography and zero echo time MRI

PURPOSE

To demonstrate the clinical applicability of zero echo time magnetic resonance imaging (ZTE MRI) in bone assessment of the sacroiliac joint in ankylosing spondylitis.

METHOD

Between January 2021 and November 2021, twenty-one ankylosing spondylitis patients underwent clinically indicated MRI including ZTE sequence, in addition, all patients underwent a CT scan covering the sacroiliac joints within 6 months of the MRI examination. The sensitivity, specificity, and accuracy of ZTE MRI were calculated using CT as the reference standard. Cohen's κappa tests were applied to assess the agreement of positive imaging findings (including erosions, osteosclerosis, bony cystic changes, and joint space changes) between MRI and CT as well as the inter-reader agreement for the grading of sacroiliitis in AS patients.

RESULTS

There was no statistical significance between ZTE MRI and CT in detecting of ankylosing spondylitis(p＞0.05). The consistency of the diagnosis of positive imaging findings between ZTE MRI and CT was moderate to excellent (ranging from 0.611 to 0.889), and the consistency of the scores of positive imaging was good to excellent (ranging from 0.857 to 0.979).

CONCLUSIONS

ZTE MRI provides "CT-like" contrast for bony changes of the sacroiliac joint in ankylosing spondylitis and could simplify and reduce costs for some AS patients when both MRI and CT are typically required.

Pediatric Wrist

Pediatric wrist injuries pose unique diagnostic challenges due to distinct bone characteristics in children and their diverse injury patterns. The dynamic development of the wrist, marked by changes in bone age and emerging ossification centers, is crucial to evaluate growth and identify potential pathologies. The skeletal composition, rich in cartilage, renders bones relatively weaker yet more elastic, impacting their susceptibility to fracture. Forearm fractures display diverse patterns influenced by torsional forces. Scaphoid fractures, less common in children, differ from those in adults. Conditions like Madelung's deformity and ulnar variance are more common wrist disorders in the pediatric population. In addition, the scarcity and nonspecificity of symptoms in those with tendon injuries and triangular fibrocartilage complex lesions can be diagnostically challenging. This article reviews pediatric wrist injuries, emphasizing ossification patterns, common fracture types, and developmental variants. Grasping these complexities in pediatric wrist development and associated pathologies is essential for precise diagnosis and treatment.

Bone injury imaging in knee and ankle joints using fast-field-echo resembling a CT using restricted echo-spacing MRI: a feasibility study

Purpose

To explore the consistency of FRACTURE (Fast-field-echo Resembling A CT Using Restricted Echo-spacing) MRI and X-Ray/computerized tomography (CT) in the evaluation of bone injuries in knee and ankle joints.

Methods

From Nov. 2020 to Jul. 2023, 42 patients with knee joint or ankle joint injuries who underwent FRACTURE MRI examinations were retrospectively collected. 11 patients were examined by both X-Ray and FRACTURE examinations. 31 patients were examined by both CT and FRACTURE examinations. The fracture, osteophyte, and bone destruction of the joints were evaluated by two radiologists using X-Ray/CT and FRACTURE images, respectively. Kappa test was used for consistency analysis.

Results

The evaluation consistency of fracture, osteophyte and bone destruction via X-Ray and FRACTURE images by radiologist 1 were 0.879, 0.867 and 0.847 respectively, and for radiologist 2 were 0.899, 0.930, and 0.879, respectively. The evaluation consistency of fracture, osteophyte and bone destruction via CT and FRACTURE images by radiologist 1 were 0.938, 0.937 and 0.868 respectively, and for radiologist 2 were 0.961, 0.930, and 0.818, respectively.

Conclusion

For fracture, osteophyte, and bone destruction of knee and ankle joints. FRACTURE MRI showed a high consistency with X-Ray/CT examinations.

Molecular Imaging with PET-CT and PET-MRI in Pediatric Musculoskeletal Diseases

Molecular imaging has emerged as an integral part of oncologic imaging. Given the physiologic changes that precede anatomic changes, molecular imaging can enable early detection of disease and monitoring of response. [18F] Fluorodeoxyglucose (FDG) Positron emission tomography (PET) is the predominant molecular imaging modality used in oncologic assessment and can be performed using PET/CT or PET/MR. In pediatric patients, PET/MRI imaging is generally preferred due to low radiation exposure and PET/MRI is particularly advantageous for imaging musculoskeletal (MSK) diseases, as MRI provides superior characterization of tissue changes as compared to CT. In this article, we provide an overview of the typical role of PET CT/MRI in assessment of some common pediatric malignancies and benign MSK diseases with case examples. We also discuss the relative advantages of PET/MRI compared to PET/CT, and review published data with a primary focus on the use of PET/MR.

Zero Echo Time Magnetic Resonance Imaging; Techniques and Clinical Utility in Musculoskeletal System

Zero echo time (ZTE) sequence is recent advanced magnetic resonance technique that utilizes ultrafast readouts to capture signals from short-T2 tissues. This sequence enables T2- and T2* weighted imaging of tissues with short intrinsic relaxation times by using an extremely short TE, and are increasingly used in the musculoskeletal system. We review the imaging physics of these sequences, practical limitations, and image reconstruction, and then discuss the clinical utilities in various disorders of the musculoskeletal system. ZTE can be readily incorporated into the clinical workflow, and is a promising technique to avoid unnecessary radiation exposure, cost, and time-consuming by computed tomography in some cases. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY: Stage 1.

Magnetic resonance bone imaging: applications to vertebral lesions

MR bone imaging is a recently introduced technique, that allows visualization of bony structures in good contrast against adjacent structures, like CT. Although CT has long been considered the modality of choice for bone imaging, MR bone imaging allows visualization of the bone without radiation exposure while simultaneously allowing conventional MR images to be obtained. Accordingly, MR bone imaging is expected as a new imaging technique for the diagnosis of miscellaneous spinal diseases. This review presents several sequences used in MR bone imaging including black bone imaging, ultrashort/zero echo time (UTE/ZTE) sequences, and T1-weighted 3D gradient-echo sequence. We also illustrate clinical cases in which spinal lesions could be effectively demonstrated on MR bone imaging, performed in most cases using a 3D gradient-echo sequence at our institution. The lesions presented herein include degenerative diseases, tumors and similar diseases, fractures, infectious diseases, and hemangioma. Finally, we discuss the differences between MR bone imaging and previously reported techniques, and the limitations and future perspectives of MR bone imaging.

Zero Echo Time vs. T1-Weighted MRI for Assessment of Cortical and Medullary Bone Morphology Abnormalities Using CT as the Reference Standard

BACKGROUND

Conventional MR pulse sequences result in poor signal from low T2 cortical bone because the minimum achievable echo time is limited. A sequence resulting in improved bone contrast is desirable.

PURPOSE

To evaluate the image quality and diagnostic performance of grayscale inversion zero echo time imaging (GI-ZTE) and grayscale inversion T1-weighted imaging (GI-T1WI) compared with computed tomography (CT).

STUDY TYPE

Prospective.

SUBJECTS

A total of 50 patients with musculoskeletal tumors or tumor-like diseases of the lower extremities having MRI and CT studies.

FIELD STRENGTH/SEQUENCE

GI-T1WI and GI-ZTE sequences at 1.5 T.

ASSESSMENT

Assessed cortical and medullary bone morphology abnormalities using CT as the reference standard. Three radiologists scored the images quality and recorded nine metrics to assess the diagnostic performance.

STATISTICAL TESTS

Differences in image quality were calculated using the Wilcoxon signed-rank test. The intraclass correlation coefficient (ICC) was used to analyze the agreement of quantitative lesion parameters between CT and MR sequences, as well as the interobserver reliability. A P value <0.05 was considered statistically significant.

RESULTS

Image quality score was significantly higher for CT images than GI-TIWI images. Except for radiologist 3 [4(0) vs 4 (1)], there was no significant difference in scores between CT and GI-ZTE [radiologist 1: 4 (0) vs 4 (0), P = 0.133; radiologist 2: 4 (0) vs 4 (0), P = 0.085]. There was good-excellent agreement between both MR sequences and CT for size, lesion number, location, sclerotic rim, expanded shell, destruction pattern, and matrix mineralization for all radiologists (ICC: 0.636-1.000). The consistency of periosteal reaction and penetration of the cortex was fair to good (0.481-0.729) between GI-T1WI and CT and good to excellent between GI-ZTE and CT (0.682-0.852).

DATA CONCLUSIONS

GI-ZTE images had superior intermodality agreement with CT images and allowed visualization of more cortical bone detail than GI-T1WI images.

EVIDENCE LEVEL

1.

TECHNICAL EFFICACY

Stage 2.

Ankle Sprains in Athletes: Current Epidemiological, Clinical and Imaging Trends

Purpose

Ankle injuries are frequent sports injuries. Despite optimizing treatment strategies during recent years, the percentage of chronification following an ankle sprain remains high. The purpose of this review article is, to highlight current epidemiological, clinical and novel advanced cross-sectional imaging trends that may help to evaluate ankle sprain injuries.

Methods

Systematic PubMed literature research. Identification and review of studies (i) analyzing and describing ankle sprain and (ii) focusing on advanced cross-sectional imaging techniques at the ankle.

Results

The ankle is one of the most frequently injured body parts in sports. During the COVID-19 pandemic, there was a change in sporting behavior and sports injuries. Ankle sprains account for about 16-40% of the sports-related injuries. Novel cross-sectional imaging techniques, including Compressed Sensing MRI, 3D MRI, ankle MRI with traction or plantarflexion-supination, quantitative MRI, CT-like MRI, CT arthrography, weight-bearing cone beam CT, dual-energy CT, photon-counting CT, and projection-based metal artifact reduction CT may be introduced for detection and evaluation of specific pathologies after ankle injury. While simple ankle sprains are generally treated conservatively, unstable syndesmotic injuries may undergo stabilization using suture-button-fixation. Minced cartilage implantation is a novel cartilage repair technique for osteochondral defects at the ankle.

Conclusion

Applications and advantages of different cross-sectional imaging techniques at the ankle are highlighted. In a personalized approach, optimal imaging techniques may be chosen that best detect and delineate structural ankle injuries in athletes.

Synthetic CT in Musculoskeletal Disorders: A Systematic Review

ABSTRACT

Repeated computed tomography (CT) examinations increase patients' ionizing radiation exposure and health costs, making an alternative method desirable. Cortical and trabecular bone, however, have short T2 relaxation times, causing low signal intensity on conventional magnetic resonance (MR) sequences. Different techniques are available to create a "CT-like" contrast of bone, such as ultrashort echo time, zero echo time, gradient-echo, and susceptibility-weighted image MR sequences, and artificial intelligence. This systematic review summarizes the essential technical background and developments of ultrashort echo time, zero echo time, gradient-echo, susceptibility-weighted image MR imaging sequences and artificial intelligence; presents studies on research and clinical applications of "CT-like" MR imaging; and describes their main advantages and limitations. We also discuss future opportunities in research, which patients would benefit the most, the most appropriate situations for using the technique, and the potential to replace CT in the clinical workflow.

Zero-TE MRI: principles and applications in the head and neck

Zero echo-time (ZTE) MRI is a novel imaging technique that utilizes ultrafast readouts to capture signal from short-T2 tissues. Additional sequence advantages include rapid imaging times, silent scanning, and artifact resistance. A robust application of this technology is imaging of cortical bone without the use of ionizing radiation, thus representing a viable alternative to CT for both rapid screening and "one-stop-shop" MRI. Although ZTE is increasingly used in musculoskeletal and body imaging, neuroimaging applications have historically been limited by complex anatomy and pathology. In this article, we review the imaging physics of ZTE including pulse sequence options, practical limitations, and image reconstruction. We then discuss optimization of settings for ZTE bone neuroimaging including acquisition, processing, segmentation, synthetic CT generation, and artifacts. Finally, we examine clinical utility of ZTE in the head and neck with imaging examples including malformations, trauma, tumors, and interventional procedures.

Zero Echo Time Musculoskeletal MRI: Technique, Optimization, Applications, and Pitfalls

Zero echo time (ZTE) imaging is an MRI technique that produces images similar to those obtained with radiography or CT. In ZTE MRI, the very short T2 signal from the mineralized trabecular bone matrix and especially cortical bone-both of which have a low proton density (PD)-is sampled in a unique sequence setup. Additionally, the PD weighting of the ZTE sequence results in less contrast between soft tissues. Therefore, along with gray-scale inversion from black to white and vice versa, ZTE imaging provides excellent contrast between cortical bone and soft tissues similar to that of radiography and CT. However, despite isotropic or near-isotropic three-dimensional (3D) imaging capabilities of the ZTE sequence, spatial resolution in this technique is still inferior to that of radiography and CT, and 3D volume renderings are currently time-consuming and require postprocessing software that features segmentation and manual contouring. Optimization of ZTE MRI mostly entails adjustments of bandwidth, flip angle, field of view, and image matrix. A wide range of structural abnormalities and disease or healing processes in the musculoskeletal system are well delineated with ZTE MRI, including conditions that involve bone-based morphometric analyses (which aid diagnosis, help prognostication, and guide surgery), impaction, avulsion and stress fractures, loose bodies or erosions in and around joints, soft-tissue calcifications and ossifications, and bone tumors (including treatment response). The pitfalls of ZTE imaging include mimics of foci of calcification or ossification such as intra-articular gas and susceptibility artifacts from surgical materials and hemosiderin deposition, which can be avoided in many instances by cross-referencing images obtained with other MRI sequences. Online supplemental material is available for this article. ^©RSNA, 2022.

Pediatric cardiothoracic vasculitis: multimodality imaging review

The pediatric vasculitides are a relatively uncommon and heterogeneous group of disorders characterized by vessel inflammation, often with cardiothoracic involvement. Diagnosis and monitoring are often clinically challenging because of the nonspecific symptoms and laboratory markers. Thus, imaging has assumed increasing importance for early detection of disease activity, extent and complications as well as long-term monitoring pre- and post-treatment. Herein, we review the major pediatric vasculitides with frequent chest manifestations, including Takayasu arteritis, Kawasaki disease, granulomatosis with polyangiitis, eosinophilic granulomatosis with polyangiitis, microscopic polyangiitis, Behçet disease and potential mimics. We highlight key clinical features and management considerations, emphasizing the central role of imaging.