Ultrashort time to echo magnetic resonance techniques for the musculoskeletal system

Magnetic resonance (MR) imaging has been widely implemented as a non-invasive modality to investigate musculoskeletal (MSK) tissue disease, injury, and pathology. Advancements in MR sequences provide not only enhanced morphologic contrast for soft tissues, but also quantitative biochemical evaluation. Ultrashort time to echo (UTE) sequence, in particular, enables novel morphologic and quantitative evaluation of previously unseen MSK tissues. By using short minimum echo times (TE) below 1 msec, the UTE sequence can unveil short T2 properties of tissues including the deepest layers of the articular cartilage, cartilaginous endplate at the discovertebral junction, the meniscus, and the cortical bone. This article will discuss the application of UTE to evaluate these MSK tissues, starting with tissue structure, MR imaging appearance on standard versus short and ultrashort TE sequences, and provide the range of quantitative MR values found in literature

Ultrashort Time to Echo Magnetic Resonance Evaluation of Calcium Pyrophosphate Crystal Deposition in Human Menisci.

OBJECTIVES In human menisci, we aimed to investigate whether calcium pyrophosphate crystal deposition (CPPD) affects biomechanical and quantitative MR properties, and their zonal distribution. MATERIALS AND METHODS From 9 cadaveric knees, sectioned triangular meniscus pieces were harvested. Samples were classified into "normal" or "CPPD" groups based upon visual inspection. Micro computed tomography scan verified CPPD. Using magnetic resonance imaging, ultrashort echo time (UTE) T2* and spin echo (SE) T2, quantitative values in 3 zones (red, red-white, and white) were determined. Using biomechanical test, indentation forces in the same zones were determined. Effects of CPPD and meniscal zone on indentation force and quantitative MR values were compared. RESULTS On UTE MRI scans, CPPD-affected menisci exhibited punctate dark regions, found mostly (92%) in avascular white and red-white zones. Indentation forces were significantly higher for CPPD samples in the red-white (all P 0.2). Similarly, UTE T2* red zone values were similar between both groups (~6.6 milliseconds, P = 0.8), whereas in the red-white and white zones, CPPD samples had significantly lower values (~5.1 milliseconds, P = 0.005 to 0.007). In contrast, SE T2 values showed no difference with CPPD (P = 0.12 to 0.16). UTE T2*, but not SE T2, correlated significantly with indentation force (R = -0.29, P = 0.009). CONCLUSIONS Dark CPP deposits were detectable on UTE images featuring high signal intensity from surrounding meniscal tissue. Preliminary results indicate that CPP deposits were almost exclusively found in the avascular zones. Compared with normal, CPPD menisci featured higher indentation stiffness and lower UTE T2* values in the affected zones

The Calcaneal Crescent in Patients With and Without Plantar Fasciitis: An Ankle MRI Study

OBJECTIVE The bundled, crescent-shaped trabeculae within the calcaneal tuberosity-which we term and refer to here as the "calcaneal crescent"-may represent a structural adaption to the prevailing forces. Given Wolff law, we hypothesized that the calcaneal crescent would be more robust in patients with plantar fasciitis, a syndrome in part characterized by overload of the Achilles tendon-calcaneal crescent-plantar fascia system, than in patients without plantar fasciitis. MATERIALS AND METHODS MR images of 37 patients (27 women and 10 men; mean age ± SD, 51 ± 13 years; mean body mass index [BMI, weight in kilograms divided by the square of height in meters], 26.8 ± 6.3) referred for workup of foot or ankle pain were retrospectively evaluated by two blinded readers in this study. Patients were assigned to two groups: group A, which was composed of 15 subjects without clinical signs or MRI findings of Achilles tendon-calcaneal crescent-plantar fascia system abnormalities, or group B, which was composed of 22 patients with findings of plantar fasciitis. The thickness and cross-sectional area (CSA) of the Achilles tendon, calcaneal crescent, and plantar fascia were measured on proton density (PD)-weighted MR images. The entire crescent volume was manually measured using OsiriX software on consecutive sagittal PD-weighted images. Additionally, contrast-to-noise ratio (CNR) as a surrogate marker for trabecular density and the mean thickness of the calcaneal crescent were determined on PD-weighted MR images. The groupwise difference in the morphologic measurements were evaluated using ANOVA with BMI as a covariate. Partial correlation was used to assess the relationships of measurements for the group with plantar fasciitis (group B). Intraclass correlation coefficient (ICC) statistics were performed. RESULTS Patients with plantar fasciitis had a greater CSA and volume of the calcaneal crescent and had lower CNR (i.e., denser trabeculae) than those without Achilles tendon-calcaneal crescent-plantar fascia system abnormalities (CSA, 100.2 vs 73.7 mm, p = 0.019; volume, 3.06 vs 1.99 cm, p = 0.006; CNR, -28.40 vs -38.10, p = 0.009). Interreader agreement was excellent (ICC = 0.85-0.99). CONCLUSION In patients with plantar fasciitis, the calcaneal crescent is enlarged compared with those without abnormalities of the Achilles tendon-calcaneal crescent-plantar fascia system. An enlarged and trabeculae-rich calcaneal crescent may potentially indicate that abnormally increased forces are being exerted onto the Achilles tendon-calcaneal crescent-plantar fascia system

Ultrashort Time-to-Echo Magnetic Resonance Imaging at 3 T for the Detection of Spondylolysis in Cadaveric Spines

ObjectivesThe objective of this study was to compare the diagnostic performance and confidence of conventional, optimized, and ultrashort time to echo (UTE) magnetic resonance (MR) protocols for detection of simulated lumbar spondylolysis in human cadavers. In addition, we sought to demonstrate the feasibility of the UTE technique in subjects with and without spondylolysis.Materials and methodsFour human lumbar spine specimens with 46 individual pars interarticularis were randomly left intact (n = 26) or received experimental osteotomy (n = 20) using a microsurgical saw to simulate spondylolysis. The specimens were imaged using a computed tomography (CT) scan along with 3 "Tiers" of MR protocols at 3 T: Tier 1, conventional lumbar MR protocol; Tier 2, optimized conventional protocol consisting of a sagittal oblique spoiled gradient recall echo and axial oblique T1 and short tau inversion recovery sequences; and Tier 3, a sagittal UTE MR sequence. Two blinded readers evaluated the images using a 4-point scale (1 = spondylolysis certainly absent, 2 = probably absent, 3 = probably present, 4 = certainly present) at each individual pars. For each imaging protocol, diagnostic performance (sensitivity, specificity, and area under the receiver operating characteristic curve, using the surgical osteotomy as the reference) and confidence were assessed and compared using the McNemar test. Furthermore, 2 human subjects were imaged with the conventional and UTE MR protocols to demonstrate feasibility in vivo.ResultsDiagnostic performance was moderate for Tiers 1 and 2, with a moderate sensitivity (0.70 to 0.75) and high (1.00) specificity. In contrast, CT and Tier 3 UTE MR imaging had both high sensitivity (1.00) and specificity (1.00). The sensitivities of CT or Tier 3 were statistically greater than Tier 1 sensitivity (P = 0.041) and neared statistical significance when compared with Tier 2 sensitivity (P = 0.074). Area under the receiver operating characteristic curve was also significantly greater for CT and Tier 3 (each area = 1.00), compared with the areas for Tier 1 (0.89, P = 0.037) or Tier 2 (0.873, P = 0.024). Diagnostic confidences of CT or Tier 3 were much greater than other Tiers: Both Tiers 1 and 2 had a large percentage of uncertain (>60%, P < 0.001) or wrong interpretations (>10%, P < 0.001), unlike CT or Tier 3 (0% uncertain or wrong interpretations). Preliminary in vivo UTE images clearly depicted intact and fractured pars.ConclusionsOur study demonstrated that the detection of pars fractures using a single sagittal UTE MR sequence is superior in performance and confidence to conventional and optimized MR protocols at 3 T, whereas matching those from CT evaluation. Furthermore, we demonstrated the feasibility of in vivo application of the UTE sequence in subjects with and without spondylolysis

Robustness of Radiomic Features: Two-Dimensional versus Three-Dimensional MRI-Based Feature Reproducibility in Lipomatous Soft-Tissue Tumors

This retrospective study aimed to compare the intra- and inter-observer manual-segmentation variability in the feature reproducibility between two-dimensional (2D) and three-dimensional (3D) magnetic-resonance imaging (MRI)-based radiomic features. The study included patients with lipomatous soft-tissue tumors that were diagnosed with histopathology and underwent MRI scans. Tumor segmentation based on the 2D and 3D MRI images was performed by two observers to assess the intra- and inter-observer variability. In both the 2D and the 3D segmentations, the radiomic features were extracted from the normalized images. Regarding the stability of the features, the intraclass correlation coefficient (ICC) was used to evaluate the intra- and inter-observer segmentation variability. Features with ICC > 0.75 were considered reproducible. The degree of feature robustness was classified as low, moderate, or high. Additionally, we compared the efficacy of 2D and 3D contour-focused segmentation in terms of the effects of the stable feature rate, sensitivity, specificity, and diagnostic accuracy of machine learning on the reproducible features. In total, 93 and 107 features were extracted from the 2D and 3D images, respectively. Only 35 features from the 2D images and 63 features from the 3D images were reproducible. The stable feature rate for the 3D segmentation was more significant than for the 2D segmentation (58.9% vs. 37.6%, p = 0.002). The majority of the features for the 3D segmentation had moderate-to-high robustness, while 40.9% of the features for the 2D segmentation had low robustness. The diagnostic accuracy of the machine-learning model for the 2D segmentation was close to that for the 3D segmentation (88% vs. 90%). In both the 2D and the 3D segmentation, the specificity values were equal to 100%. However, the sensitivity for the 2D segmentation was lower than for the 3D segmentation (75% vs. 83%). For the 2D + 3D radiomic features, the model achieved a diagnostic accuracy of 87% (sensitivity, 100%, and specificity, 80%). Both 2D and 3D MRI-based radiomic features of lipomatous soft-tissue tumors are reproducible. With a higher stable feature rate, 3D contour-focused segmentation should be selected for the feature-extraction process

Tumor-to-bone distance and radiomic features on MRI distinguish intramuscular lipomas from well-differentiated liposarcomas

Abstract Background To develop a machine learning model based on tumor-to-bone distance and radiomic features derived from preoperative MRI images to distinguish intramuscular (IM) lipomas and atypical lipomatous tumors/well-differentiated liposarcomas (ALTs/WDLSs) and compared with radiologists. Methods The study included patients with IM lipomas and ALTs/WDLSs diagnosed between 2010 and 2022, and with MRI scans (sequence/field strength: T1-weighted (T1W) imaging at 1.5 or 3.0 Tesla MRI). Manual segmentation of tumors based on the three-dimensional T1W images was performed by two observers to appraise the intra- and interobserver variability. After radiomic features and tumor-to-bone distance were extracted, it was used to train a machine learning model to distinguish IM lipomas and ALTs/WDLSs. Both feature selection and classification steps were performed using Least Absolute Shrinkage and Selection Operator logistic regression. The performance of the classification model was assessed using a tenfold cross-validation strategy and subsequently evaluated using the receiver operating characteristic curve (ROC) analysis. The classification agreement of two experienced musculoskeletal (MSK) radiologists was assessed using the kappa statistics. The diagnosis accuracy of each radiologist was evaluated using the final pathological results as the gold standard. Additionally, we compared the performance of the model and two radiologists in terms of the area under the receiver operator characteristic curves (AUCs) using the Delong’s test. Results There were 68 tumors (38 IM lipomas and 30 ALTs/WDLSs). The AUC of the machine learning model was 0.88 [95% CI 0.72–1] (sensitivity, 91.6%; specificity, 85.7%; and accuracy, 89.0%). For Radiologist 1, the AUC was 0.94 [95% CI 0.87–1] (sensitivity, 97.4%; specificity, 90.9%; and accuracy, 95.0%), and as to Radiologist 2, the AUC was 0.91 [95% CI 0.83–0.99] (sensitivity, 100%; specificity, 81.8%; and accuracy, 93.3%). The classification agreement of the radiologists was 0.89 of kappa value (95% CI 0.76–1). Although the AUC of the model was lower than of two experienced MSK radiologists, there was no statistically significant difference between the model and two radiologists (all P > 0.05). Conclusions The novel machine learning model based on tumor-to-bone distance and radiomic features is a noninvasive procedure that has the potential for distinguishing IM lipomas from ALTs/WDLSs. The predictive features that suggested malignancy were size, shape, depth, texture, histogram, and tumor-to-bone distance

Patterns of cartilage degeneration in knees with medial tibiofemoral offset

OBJECTIVE To determine if radiographic medial tibiofemoral offset (MTFO) is associated with: (1) magnetic resonance imaging (MRI) pathology of cartilage, meniscus, and ligament; and (2) a distinct pattern of lateral cartilage degeneration on MRI. MATERIALS AND METHODS Three hundred consecutive adult knee MRIs with anteroposterior (AP) radiographs were retrospectively reviewed, and 145 studies were included. MTFO was defined as a medial extension of the medial femoral condyle beyond the articular surface of the medial tibial plateau on weight-bearing AP radiographs. The patients were then divided into the MTFO (n = 61) or no-offset (n = 84) groups. On MRI data obtained on a 1.5-Tesla system, articular cartilage of the femoral condyle and tibial plateau were graded using a modified Outerbridge classification (36 sub-regions similar to whole-organ MRI Score (WORMS) system). In addition, MR pathology of the ACL, MCL, LCL, medial and lateral menisci, were determined. RESULTS Significantly increased (ANOVA p < 0.007) MR grade of the ligaments, menisci, and cartilage in the MTFO group (ranging from 0.3 to 2.5) compared to the control group (0.2 to 1.1). Color maps of the cartilage grades suggested a marked difference in both severity of degeneration and regional variations between the groups. MTFO group exhibited focally increased cartilage grades in the central, non-weight regions of lateral compartment (region p = 0.07 to 0.12, interaction p = 0.05 to 0.1). CONCLUSIONS MTFO is associated with overall degeneration of the knee and features a distinct lateral cartilage degeneration pattern, which may reflect non-physiologic contact of the cartilage between the lateral tibial eminence and lateral central femoral condyle

Patterns of cartilage degeneration in knees with medial tibiofemoral offset

ObjectiveTo determine if radiographic medial tibiofemoral offset (MTFO) is associated with: (1) magnetic resonance imaging (MRI) pathology of cartilage, meniscus, and ligament; and (2) a distinct pattern of lateral cartilage degeneration on MRI.Materials and methodsThree hundred consecutive adult knee MRIs with anteroposterior (AP) radiographs were retrospectively reviewed, and 145 studies were included. MTFO was defined as a medial extension of the medial femoral condyle beyond the articular surface of the medial tibial plateau on weight-bearing AP radiographs. The patients were then divided into the MTFO (n = 61) or no-offset (n = 84) groups. On MRI data obtained on a 1.5-Tesla system, articular cartilage of the femoral condyle and tibial plateau were graded using a modified Outerbridge classification (36 sub-regions similar to whole-organ MRI Score (WORMS) system). In addition, MR pathology of the ACL, MCL, LCL, medial and lateral menisci, were determined.ResultsSignificantly increased (ANOVA p &lt; 0.007) MR grade of the ligaments, menisci, and cartilage in the MTFO group (ranging from 0.3 to 2.5) compared to the control group (0.2 to 1.1). Color maps of the cartilage grades suggested a marked difference in both severity of degeneration and regional variations between the groups. MTFO group exhibited focally increased cartilage grades in the central, non-weight regions of lateral compartment (region p = 0.07 to 0.12, interaction p = 0.05 to 0.1).ConclusionsMTFO is associated with overall degeneration of the knee and features a distinct lateral cartilage degeneration pattern, which may reflect non-physiologic contact of the cartilage between the lateral tibial eminence and lateral central femoral condyle

Advanced MRI Techniques for the Ankle

Ankle injury is common in both the athletic and general population, with magnetic resonance imaging (MRI) the established non-invasive means of evaluation. This manuscript provides consideration for a state-of-the-art routine MR protocol of the ankle. It provides problem-solving tools based upon specific clinical indications. Further it introduces principles and implementation of novel Ultrashort Echo Time (UTE) MRI in the ankle, including morphologic and quantitative assessment