Comparison of magnetic resonance imaging and computed tomography for bone assessment of neurogenic heterotopic ossification of the hip: a preliminary study

Neurogenic heterotopic ossification of the hip: Magnetic resonance imaging versus computed tomography for pre-surgical assessment

PURPOSE

Neurogenic heterotopic ossification (NHO) of the hip is a frequent complication of spinal cord injuries, often requiring surgical management. Pre-surgical imaging assessment is essential, usually with computed tomography (CT)-scan. We aimed to compare magnetic resonance imaging (MRI) and CT for pre-surgical imaging assessment of the NHO, particularly for their relationships with vessels and nerves.

METHOD

This prospective study included consecutive patients who underwent surgery for NHO from July 2019 to April 2022. All patients had CT angiography and MRI including Zero Echo Time and TRICKS sequences. Radiologists used standardized reports for CT and MRI to evaluate NHO and their features, bone mineralization, and relation to the arteries, veins and nerves. Agreement between pre-surgical CT and MRI was evaluated.

RESULTS

Twenty-four patients (mean age: 53.5 ± 12.2 years) were included, among which 7 had bilateral NHO (31 hips). NHO were anterior in 15/31 hips (48 %), multifragmented in 25/31 hips (81 %). Mild and significant demineralization was most frequent. Gutter and tunnel were reported in 11.1 % of the arteries. Nerves were more often identified in MRI than in CT-scan. Agreement coefficients between CT and MRI were excellent for NHO location (0.95) and implantation (0.92), good for fragmentation (0.70), contact with joint capsule (0.66), bone mineralization (0.74), and relation to arteries (0.85), veins (0.76), sciatic nerve (0.7) and moderate for femoral nerve (0.47).

CONCLUSION

MRI exhibited a good agreement with CT for pre-surgical assessment of NHO of the hip, especially to evaluate their relationships with the arteries, veins and sciatic nerve. Femoral nerves were more often identified in MRI than in CT-scan.

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.

Zero echo time MRI in shoulder MRI protocols for the diagnosis of rotator cuff calcific tendinopathy improves identification of calcific deposits compared to conventional MR sequences but remains sub-optimal compared to radiographs

OBJECTIVE

To compare the diagnostic performance of standard MRI and standard MRI + ZTE images for the detection of rotator cuff calcific tendinopathy (RCCT) and to describe the artifacts encountered with ZTE images, using computed radiography (CR) as a reference.

METHODS

In a retrospective study, patients with suspicion of rotator cuff tendinopathy who underwent standard MRI + ZTE images after radiography were enrolled between June 2021 and June 2022. Images were independently analyzed for calcific deposit presence and ZTE images artifacts, by two radiologists. Diagnostic performance was calculated individually with MRI + CR as the reference standard.

RESULTS

A total of 46 RCCT subjects (27 women; mean age, 55.3 years ± 12.4) and 51 control subjects (27 men; mean age, 45.5 ± 12.9) were evaluated. For both readers, there was an increase in the sensitivity for the identification of calcific deposits of MRI + ZTE compared to MRI (77% (95% CI: 64.5-86.8) and 75.4% (95% CI: 62.7-85.5) versus 57.4% (95% IC: 44.1-70) and 47.5% (95% IC: 34.6-60.7), for R1 and R2, respectively). Specificity was quite similar for both readers and both imaging techniques and ranged from 96.6% (95% IC: 93.3-98.5) to 98.7% (95% IC: 96.3-99.7). Hyperintense joint fluid (62.8% of patients), long head of the biceps tendon (in 60.8%), and subacromial bursa (in 27.8%) on ZTE were considered artifactual.

CONCLUSION

The addition of ZTE images to a standard MRI protocol improved MRI diagnostic performance of RCCT, but with a suboptimal detection rate and a relatively high frequency of artifactual soft tissue signal hyperintensity.

KEY POINTS

• Adding ZTE images to standard shoulder MRI improves the MR-based detection of rotator cuff calcific tendinopathy, but half of the calcification unseen with standard MRI remained unseen with ZTE MRI. On ZTE images, joint fluid and long head biceps tendon were hyperintense in about 60% of the shoulders, as well as the subacromial bursa in about 30%, without calcific deposit on conventional radiographs. • The detection rate of calcific deposits using ZTE images was dependent on the disease phase. In the calcific stage, it reached 100% in this study but remained at a maximum of 80.7% in the resorptive phase.

Bone Tissue in Magnetic Resonance Imaging: Contribution of New Zero Echo Time Sequences

The introduction of new ultrashort and zero echo time (ZTE) sequences is revolutionizing magnetic resonance imaging (MRI) and optimizing patient management. These sequences acquire signals in tissues with very short T2: mineralized bone, cortical bone, and calcium deposits. They can be added to a classic MRI protocol. ZTE MRI provides computed tomography-like contrast for bone.

Early diagnosis of heterotopic ossification with a NIR fluorescent probe by targeting type II collagen

Heterotopic ossification (HO) is a devastating sequela in which the pathologic extracellular matrix of the cartilage and bone forms abnormally in soft tissues following traumatic injuries or orthopaedic surgeries. Early treatment is essential for inhibiting the progression of HO but is currently limited by the absence of sensitive and specific early diagnosis. Herein, this study exploits the enrichment of type II collagen (Col2a1) in the HO cartilage formation stage towards developing a near-infrared (NIR) probe for early HO diagnosis, namely WL-808 by conjugating a Col2a1-binding peptide (WYRGRL) and a cyanine dye (IR-808). WL-808 exhibits high specificity for targeting the cartilage in vitro and in vivo with no apparent cytotoxicity. The NIR signal of WL-808 can be detected in the HO cartilage lesions as early as 1 week after injury when micro-CT cannot show any ectopic bone formation. Moreover, the probe is rarely distributed in the normal knee articular cartilage in vivo via the intravenous administration method. Taken together, WL-808 demonstrates great potential in early HO diagnosis under NIR imaging, facilitating early HO prophylaxis and treatment in the clinic.

Idiopathic Spontaneous Occurrence of Heterotrophic Occurrence During Pregnancy

Heterotopic ossification (HO) typically presents in the hip, knee, and elbow joints in the setting of trauma or postsurgical intervention. Less commonly, it may occur secondary to neurologic dysfunction or underlying genetic conditions, but idiopathic HO is rare. Most cases of HO are managed nonoperatively with surgical resection remaining a controversy due to high recurrence rates. We describe a case of idiopathic HO of the shoulder that occurred in the absence of trauma, neurologic dysfunction, or underlying genetic disorder that was treated with surgical excision.

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 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.

Heterotopic ossification and COVID 19: Imaging analysis of ten consecutive cases

PURPOSE

Heterotopic ossification (HO) is defined by the formation of mature lamellar bone in periarticular soft tissue due to prolonged immobility. This study aimed to explore the imaging features of HOs in immobilized COVID-19 patients compared to other causes previously described in the literature.

METHOD

This retrospective single centre study included patients with severe COVID-19 hospitalized in intensive care unit (ICU) with mechanical ventilation and affected by HOs between March 2020 and December 2021. Two radiologists reviewed imaging features of biphasic CT-scans using a standardized template including morphological findings and anatomical relationship of the HO with the joint, vessels and nerves.

RESULTS

10 COVID-19 patients with 19 analyzed HOs following ICU hospitalization were including. Biphasic CT imaging characteristics were analyzed. The hips were the most commonly affected joint (n = 14/19; 74%). The distribution was mainly posterior (n = 7/19; 38%). HOs were located away from main arteries. No case of severe demineralization was observed. Capsular disruption was observed for three HOs (n = 3/19; 16%). One patient presented concomitant venous thrombosis ipsilateral to the HO. CT-scan demonstrated neural involvement of the sciatic nerve in 3 patients with HO (n = 3/19; 16%).

CONCLUSION

Severe COVID-19 patients with a biphasic CT imaging presented HO mainly located around the hips, with rare vessel and nerve invasion and no severe demineralization. Some features such as a lower level of local invasion differ from HOs related to other disorders as described in the literature whereas morphological aspects are similar.