Naveen Subhas

Background: The United States Food and Drug Administration (FDA) recently published a model observer‐based framework for the objective performance assessment of computed tomography (CT) metal artifact reduction (MAR) algorithms and demonstrated the framework's feasibility in the low‐contrast detectability (LCD) task‐based assessment of MAR performance in a mathematical phantom. Purpose: This study investigates the feasibility of the model observer‐based framework in LCD task‐based assessment of MAR performance using a physical arthroplasty phantom, results of which were then compared with the performance of human observers. Methods: A phantom simulating a unilateral hip prosthesis was designed with a rotatable insert containing a metal implant (cobalt‐chromium spheres attached to titanium rods) and 16 unique low‐contrast spherical lesions. Each lesion was scanned 100 times on a CT scanner (Somatom Force, Siemens Healthineers) with standard full‐dose and half‐dose protocols (140 kVp, 300 and 150 quality reference mAs) in each of four different insert rotations to supply 100 pairs of signal‐present (lesion) and signal‐absent (background) images needed for model observer analyses. Lesion detectability (d′) using channelized Hotelling observers (CHO) was optimized by testing different image transformation techniques and channel selection (Gabor and Laguerre–Gauss [LG]) and calculated for each lesion reconstructed with and without iterative MAR (iMAR, Siemens Healthineers). Linear regression was used to assess the d′ in each image set. Spearman's correlation was used to compare d′ results to human detectability and confidence scores from a previously published human observer study involving the same phantom. Results: CHO d′ measurements using LG channels were less sensitive to artifacts than those using Gabor channels and were therefore selected for the LCD assessment. Image masking and thresholding provided more accurate d′ by isolating the signal and minimizing background differences. For all lesions, d′ values of full‐dose iMAR images were significantly greater than those of filtered back projection (FBP) images at full dose ( p < 0.001) and half dose ( p < 0.001). Additionally, d′ values of half‐dose iMAR images were significantly greater than those of FBP images at full dose ( p = 0.010) and half dose ( p < 0.001). The d′ values were not significantly different between full‐dose and half‐dose FBP ( p = 0.620) or between full‐dose and half‐dose iMAR ( p = 0.358). Pooling across all lesions, d′ measurements were positively correlated with human detection rate (Spearman correlation coefficient = 0.723; p < 0.001) and confidence scores (Spearman correlation coefficient = 0.727; p < 0.001). Conclusions: The use of CHO in the LCD assessment of MAR performance can be feasibly performed on a physical phantom, and results using this method correlated well with findings from human observers.

Bone marrow edema-like lesions (BMEL) in the knee have been linked to the symptoms and progression of osteoarthritis (OA), a highly prevalent disease with profound public health implications. Manual and semi-automatic segmentations of BMELs in magnetic resonance images (MRI) have been used to quantify the significance of BMELs. However, their utilization is hampered by the labor-intensive and time-consuming nature of the process as well as by annotator bias, especially since BMELs exhibit various sizes and irregular shapes with diffuse signal that lead to poor intra- and inter-rater reliability. In this study, we propose a novel unsupervised method for fully automated segmentation of BMELs that leverages conditional diffusion models, multiple MRI sequences that have different contrast of BMELs, and anomaly detection that do not rely on costly and error-prone annotations. We also analyze BMEL segmentation annotations from multiple experts, reporting intra-/inter-rater variability and setting better benchmarks for BMEL segmentation performance.

Objective To determine the cost-effectiveness of rotator cuff hydroxyapatite deposition disease (HADD) treatments. Method A 1-year time horizon decision analytic model was created from the US healthcare system perspective for a 52-year-old female with shoulder HADD failing conservative management. The model evaluated the incremental cost-effectiveness ratio (ICER) and net monetary benefit (NMB) of standard strategies, including conservative management, ultrasound-guided barbotage (UGB), high- and low-energy extracorporeal shock wave therapy (ECSW), and surgery. The primary effectiveness outcome was quality-adjusted life years (QALY). Costs were estimated in 2022 US dollars. The willingness-to-pay (WTP) threshold was $100,000. Results For the base case, UGB was the preferred strategy (0.9725 QALY, total cost, $2199.35, NMB, $95,048.45, and ICER, $33,992.99), with conservative management (0.9670 QALY, NMB $94,688.83) a reasonable alternative. High-energy ECSW (0.9837 QALY, NMB $94,805.72), though most effective, had an ICER of $121, 558.90, surpassing the WTP threshold. Surgery (0.9532 QALY, NMB $92,092.46) and low-energy ECSW (0.9287 QALY, NMB $87,881.20) were each dominated. Sensitivity analysis demonstrated that high-energy ECSW would become the favored strategy when its cost was < $2905.66, and conservative management was favored when the cost was < $990.34. Probabilistic sensitivity analysis supported the base case results, with UGB preferred in 43% of simulations, high-energy ECSW in 36%, conservative management in 20%, and low-energy ECSW and surgery in < 1%. Conclusion UGB appears to be the most cost-effective strategy for patients with HADD, while surgery and low-energy ECSW are the least cost-effective. Conservative management may be considered a reasonable alternative treatment strategy in the appropriate clinical setting.

This Editorial Comment discusses the following AJR article: Image Quality and Diagnostic Performance of Accelerated Shoulder MRI With Deep Learning-Based Reconstruction.

Glenoid component loosening remains a common complication following anatomic total shoulder arthroplasty (TSA); however, plain radiographs are unable to accurately detect early implant migration. The purpose of this study was to validate the accuracy of a method of postoperative, three‐dimensional (3D) computed tomography (CT) imaging with metal artifact reduction (MAR) to detect glenoid component migration following anatomic TSA. Tantalum bead markers were inserted into polyethylene glenoid components for implant detection on 3D CT. In‐vitro validation was performed using a glenoid component placed into a scapula sawbone and incrementally translated and rotated, with MAR 3D CT acquired at each test position. Accuracy was evaluated by root mean square error (RMSE). In‐vivo validation was performed on six patients who underwent anatomic TSA, with two postoperative CT scans acquired in each patient and marker‐based radiostereometric analysis (RSA) performed on the same days. Glenoid component migration was calculated relative to a scapular coordinate system for both MAR 3D CT and RSA. Accuracy was evaluated by RMSE and paired Student's t‐tests. The largest RMSE on in‐vitro testing was 0.24 mm in translation and 0.11° in rotation, and on in‐vivo testing was 0.47 mm in translation and 1.04° in rotation. There were no significant differences between MAR 3D CT and RSA measurement methods. MAR 3D CT imaging is capable of quantifying glenoid component migration with a high level of accuracy. MAR 3D CT imaging is advantageous over RSA because it is readily available clinically and can also be used to evaluate the implant‐bone interface.

Three-dimensional (3D) magnetic resonance imaging (MRI) of the knee is widely used in musculoskeletal (MSK) imaging. Currently, 3D sequences are most commonly used for morphological imaging. Isotropic 3D MRI provides higher out-of-plane resolution than standard two-dimensional (2D) MRI, leading to reduced partial volume averaging artifacts and allowing for multiplanar reconstructions in any plane with any thickness from a single high-resolution isotropic acquisition. Specifically, isotropic 3D fast spin-echo imaging, with options for tissue weighting similar to those used in multiplanar 2D FSE imaging, is of particular interest to MSK radiologists. New applications for 3D spatially encoded sequences are also increasingly available for clinical use. These applications offer advantages over standard 2D techniques for metal artifact reduction, quantitative cartilage imaging, nerve imaging, and bone shape analysis. Emerging fast imaging techniques can be used to overcome the long acquisition times that have limited the adoption of 3D imaging in clinical protocols.

Objective To determine whether a simulated low-dose metal artifact reduction (MAR) CT technique is comparable with a clinical dose MAR technique for shoulder arthroplasty evaluation. Materials and methods Two shoulder arthroplasties in cadavers and 25 shoulder arthroplasties in patients were scanned using a clinical dose (140 kVp, 300 qrmAs); cadavers were also scanned at half dose (140 kVp, 150 qrmAs). Images were reconstructed using a MAR CT algorithm at full dose and a noise-insertion algorithm simulating 50% dose reduction. For the actual and simulated half-dose cadaver scans, differences in SD for regions of interest were assessed, and streak artifact near the arthroplasty was graded by 3 blinded readers. Simulated half-dose scans were compared with full-dose scans in patients by measuring differences in implant position and by comparing readers’ grades of periprosthetic osteolysis and muscle atrophy. Results The mean difference in SD between actual and simulated half-dose methods was 2.42 HU (95% CI [1.4, 3.4]). No differences in streak artifact grades were seen in 13/18 (72.2%) comparisons in cadavers. In patients, differences in implant position measurements were within 1° or 1 mm in 149/150 (99.3%) measurements. The inter-reader agreement rates were nearly identical when readers were using full-dose (77.3% [232/300] for osteolysis and 76.9% [173/225] for muscle atrophy) and simulated half-dose (76.7% [920/1200] for osteolysis and 74.0% [666/900] for muscle atrophy) scans. Conclusion A simulated half-dose MAR CT technique is comparable both quantitatively and qualitatively with a standard-dose technique for shoulder arthroplasty evaluation, demonstrating that this technique could be used to reduce dose in arthroplasty imaging.

Objective To evaluate the feasibility of producing 2-dimensional (2D) virtual noncontrast images and 3-dimensional (3D) bone models from dual-energy computed tomography (DECT) arthrograms and to determine whether this is best accomplished using 190 keV virtual monoenergetic images (VMI) or virtual unenhanced (VUE) images. Materials and methods VMI and VUE images were retrospectively reconstructed from patients with internal derangement of the shoulder or knee joint who underwent DECT arthrography between September 2017 and August 2019. A region of interest was placed in the area of brightest contrast, and the mean attenuation (in Hounsfield units [HUs]) was recorded. Two blinded musculoskeletal radiologists qualitatively graded the 2D images and 3D models using scores ranging from 0 to 3 (0 considered optimal). Results Twenty-six patients (mean age ± SD, 57.5 ± 16.8 years; 6 women) were included in the study. The contrast attenuation on VUE images (overall mean ± SD, 10.5 ± 16.4 HU; knee, 19.3 ± 10.7 HU; shoulder, 5.0 ± 17.2 HU) was significantly lower (p < 0.001 for all comparisons) than on VMI (overall mean ± SD, 107.7 ± 43.8 HU; knee, 104.6 ± 31.1 HU; shoulder, 109.6 ± 51.0 HU). The proportion of cases with optimal scores (0 or 1) was significantly higher with VUE than with VMI for both 2D and 3D images (p < 0.001). Conclusions DECT arthrography can be used to produce 2D virtual noncontrast images and to generate 3D bone models. The VUE technique is superior to VMI in producing virtual noncontrast images.