Faculty Bibliography

PURPOSE/OBJECTIVE:To investigate whether liver stiffness measured by acoustic radiation force impulse (ARFI) sonoelastography always correlates with the liver perfusion parameters quantified by perfusion CT in patients with known liver cirrhosis. METHODS:Sonoelastography and perfusion CT were performed in 50 patients (mean age 65.5; range 45-87 years) with liver cirrhosis, who were classified according to Child-Pugh into class A (30/50, 60%), B (17/50, 34%), and C (3/50, 6%). For standardized ARFI measurements in the left liver lobe at a depth of 4 cm, a convex 6-MHz probe was used. CT examinations were performed using 80 kV, 100 mAs, and 50 ml of iodinated contrast agent injected at 5 ml/s. Using standardized region-of-interest measurements, we quantified arterial, portal venous, and total liver perfusion. RESULTS:There was a significant linear correlation between tissue stiffness and arterial liver perfusion (p = 0.015), and also when limiting the analysis to patients with histology (p = 0.019). In addition, there was a positive correlation between the total blood supply (arterial + portal-venous liver perfusion) to the liver and tissue stiffness (p = 0.001; with histology, p = 0.027). Shear wave velocity increased with higher Child-Pugh stages (p = 0.013). CONCLUSION/CONCLUSIONS:The degree of tissue stiffness in cirrhotic livers correlates expectedly-even if only moderately-with the magnitude of arterial liver perfusion and total liver perfusion. As such, liver elastography remains the leading imaging tool in assessing liver fibrosis.

The Segond fracture is a tibial avulsion injury of the insertion of the middle third of the lateral capsular ligament that is typically associated with anterior cruciate ligament and meniscal tears. The classically assigned mechanism of injury is a combination of internal rotation and varus stress. We report two cases of Segond fractures that presented with a variant pattern including osseous avulsion injuries of the medial collateral ligament at the femoral origin, anterior cruciate ligament tear, and pivot shift-type osseous contusion pattern, suggesting an alternative mechanism of injury that includes dominant valgus stress and external rotation components. Awareness of this pattern may aid radiologists, surgeons, and sport medicine physicians in the accurate diagnosis of this injury complex and initiation of appropriate treatment in a timely fashion.

OBJECTIVE:The aim of this study was to compare the effects of combined virtual monoenergetic extrapolation (VME) of dual-energy computed tomography data and iterative metal artifact reduction (iMAR) at higher photon energies on low- and high-density metal artifacts and overall image quality of the ankle arthroplasty implants with iMAR, weighted filtered back projection (WFBP), and WFBP-based VME. MATERIALS AND METHODS:Total ankle arthroplasty implants in 6 human cadaver ankles served as surrogates for arthroplasty implants. All specimens underwent computed tomography with a 2 × 192-slice dual-source computed tomography scanner at tube voltages of 80 and tin-filtered 150 kVp to produce mixed 120 kVp equivalent polychromatic and virtual monoenergetic extrapolated images at 150 and 190 keV (VME 150 and VME 190, respectively). By implementing the WFBP and iMAR reconstruction algorithms on polychromatic, VME 150 and VME 190 data, 6 image datasets were created: WFBP-Polychromatic, iMAR-Polychromatic, WFBP-VME 150, WFBP-VME 190, iMAR-VME 150, and iMAR-VME 190. High-density and low-density artifacts were separately quantified with a threshold-based computer algorithm. After anonymization and randomization, 2 observers independently ranked the datasets for overall image quality. Repeated measures analysis of variance, Friedman, and Cohen weighted κ tests were applied for statistical analysis. A conservative P value of less than 0.001 was considered statistically significant. RESULTS:iMAR-VME 190 keV and iMAR-VME 150 keV created the least amount of high-density artifacts (all P < 0.001), whereas iMAR-Polychromatic was the most effective method to mitigate low-density streaks (P < 0.001). For low- and high-density artifacts, polychromatic iMAR acquisition was superior to WFBP-VME 150 keV and WFBP-VME 190 keV (all P < 0.001). On sharp kernel reconstructions, readers ranked the overall image quality of iMAR-Polychromatic images highest (all P < 0.001). Similarly, on soft tissue kernel reconstructions, readers ranked iMAR-Polychromatic images highest with a statistically significant difference over other techniques (all P < 0.001), except for iMAR-VME 150 keV (P = 0.356). CONCLUSIONS:In computed tomography imaging of ankle arthroplasty implants, iMAR reconstruction results in fewer metal artifacts and better image quality than WFBP reconstruction for both polychromatic and virtual monoenergetic data. The combination of iMAR and VME at higher photon energies results in mixed effects on implant-induced metal artifacts, including decreased high-density and increased low-density artifacts, which in combination does not improve image quality over iMAR reconstruction of the polychromatic data. Our results suggest that, for ankle arthroplasty implants, the highest image quality is obtained by iMAR reconstruction of the polychromatic data without the need to implement VME at high-energy levels.

OBJECTIVES:The aim of this study was to test the hypothesis that magnetic resonance imaging (MRI) of the knee with 10-minute 3-dimensional (3D) controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) sampling perfection with application optimized contrast using different flip angle evolutions (SPACE) turbo spin echo (TSE) protocols can replace 20-minute 2-dimensional (2D) TSE standard-of-reference protocols for the diagnosis of internal derangement. MATERIALS AND METHODS:After internal review board approval and prospective informed consent, 100 symptomatic subjects underwent MRI of the knee at 3 T and 50 symptomatic subjects at 1.5 T, consisting of 10-minute 3D CAIPIRINHA SPACE TSE and 20-minute standard-of-reference 2D TSE protocols. Two fellowship-trained musculoskeletal radiologists assessed the studies in an anonymized and randomized fashion for structural abnormalities. Descriptive statistics, interreader reliability, intermethod concordance, diagnostic definitiveness, and interchangeability tests were applied. P values equal to or smaller than 0.01 were considered significant. RESULTS:The interchangeability analysis showed that the 3D MRI can replace the 2D MRI protocols, whereas a superiority of 3D MRI was suggested statistically for the detection of medial and lateral meniscal tears, cartilage defects, and bone marrow edema by significantly higher common pair exact match proportions of readers (P < 0.01, respectively).The overall interreader reliabilities were 89% of exact matches for 2D TSE (κ, 0.842) and 96% of exact matches for 3D TSE (κ, 0.941) (P < 0.01). There was good intermethod concordance (κ, 0.736; range, 0.579-1.000). The interreader reliability (2D TSE: κ, 0.748 [0.603-1.000]; 3D TSE: κ, 0.901 [0.797-1.000]) and diagnostic definitiveness were significantly higher for the 3D than 2D MRI (P < 0.01). CONCLUSIONS:10-minute 3D CAIPIRINHA SPACE TSE MRI protocols can replace 20-minute 2D TSE standard-of-reference MRI protocols for the evaluation of internal derangement of the knee by producing similar results in individual patient diagnoses, whereas interpretations of 3D CAIPIRINHA SPACE TSE MRI examinations resulted in an overall higher interreader reliability, intermethod concordance, and reader definitiveness.

Purpose To test the hypothesis that synthetic MRI of the knee generates accurate and repeatable quantitative maps and produces morphologic MR images with similar quality and detection rates of structural abnormalities than does conventional MRI. Materials and Methods Data were collected prospectively between January 2017 and April 2018 and were retrospectively analyzed. An International Society for Magnetic Resonance in Medicine-National Institute of Standards and Technology phantom was used to determine the accuracy of T1, T2, and proton density (PD) quantification. Statistical models were applied for correction. Fifty-four participants (24 men, 30 women; mean age, 40 years; range, 18-62 years) underwent synthetic and conventional 3-T MRI twice on the same day. Fifteen of 54 participants (28%) repeated the protocol within 9 days. The intra- and interday agreements of quantitative cartilage measurements were assessed. Contrast-to-noise (CNR) ratios, image quality, and structural abnormalities were assessed on corresponding synthetic and conventional images. Statistical analyses included the Wilcoxon test, χ² test, and Cohen Kappa. P values less than or equal to .01 were considered to indicate a statistically significant difference. Results Synthetic MRI quantification of T1, T2, and PD values had an overall model-corrected error margin of 0.8%. The synthetic MRI interday repeatability of articular cartilage quantification had native and model-corrected error margins of 3.3% and 3.5%, respectively. The cartilage-to-fluid CNR and menisci-to-fluid CNR was higher on synthetic than conventional MR images (P ≤ .001, respectively). Synthetic MRI improved short-tau inversion recovery fat suppression (P Ë‚ .01). Intermethod agreements of structural abnormalities were good (kappa, 0.621-0.739). Conclusion Synthetic MRI of the knee is accurate for T1, T2, and proton density quantification, and simultaneously generated morphologic MR images have detection rates of structural abnormalities similar to those of conventional MR images, with similar acquisition time. © RSNA, 2018.

Purpose To determine the diagnostic performance of three-dimensional (3D) MRI for the depiction and characterization of cartilage defects within the knee joint by using arthroscopy and/or open surgery as the standard of reference. Materials and Methods A systematic literature search was performed to extract diagnostic studies published between January 1985 and October 2017. Two independent investigators assessed the methodologic quality of each study by using Quality Assessment of Diagnostic Accuracy Studies 2. Bivariate random-effects model was used to compare the diagnostic odds ratio (DOR) of 3D and two-dimensional (2D) MRI for helping to detect knee cartilage defects and to assess the effect of relevant covariates on diagnostic performance of 3D MRI. Meta-regression analysis was performed to assess DOR of 3D MRI during the last 3 decades. Results Twenty-seven studies (composed of 1710 MRI examinations) were included. Of those, 16 (59%) studies compared the diagnostic performance of 3D and 2D MRI. The diagnostic performance of 3D MRI statistically significantly improved over the last 3 decades (P = .003). Three-dimensional MRI obtained by using 3.0-T field strength had higher DOR relative to 1.5-T or lower field strength (relative DOR, 4.05; P = .01). Three-dimensional multiplanar reformation was associated with higher specificity (P = .001) compared with conventional axial, sagittal, and coronal 2D MRI planes. Three-dimensional fast-spin-echo sequences provided higher sensitivity and specificity (P < .05) than did 2D MRI. Conclusion Three-dimensional MRI currently provides comparable diagnostic performance to two-dimensional MRI, with improvement in diagnostic performance achieved by using 3.0-T field strength, three-dimensional fast-spin-echo sequences, and multiplanar reformation. © RSNA, 2018 Online supplemental material is available for this article.

PURPOSE/OBJECTIVE:To evaluate CT patterns and textural features of soft tissue sarcomas following trabectedin therapy as well as their suitability for predicting therapeutic response. MATERIAL AND METHODS/METHODS:A total of 31 patients (18 female, 13 male; mean age, 58.0years; range, 38-79years) with sarcoma under trabectedin as a third-line therapy between October 2008 and July 2017 underwent baseline and follow-up contrast-enhanced CT. Response evaluation was based on modifiedCHOI-criteria and RECIST1.1, classified as partial response(PR), stable disease(SD), progressive disease(PD). For CT-texture analysis (CTTA), mean, entropy and uniformity of intensity/skewness/entropy of co-occurrence matrix (COM) and contrast of neighboring-grey-level-dependence-matrix (NGLDM) were calculated. RESULTS:Following CHOI-criteria, 9 patients achieved PR, 10 SD and 12 PD. RECIST1.1. classified patients into 5 PR, 15 SD and 11 PD. A frequent (n = 6/31; 19.3%) pattern of response was tumor liquefaction. In responders differences in entropy of entropy-NGLDM(p = 0.028) and uniformity-NGLDM(p = 0.021), in non-responders entropy of average(p = 0.039), deviation(p = 0.04) and uniformity of deviation(p = 0.013) occured between baseline and follow-up. Mean intensity and average were higher when liquefication occured(p = 0.03; p = 0.02), whereas mean deviation was lower(p = 0.02) at baseline compared to other response patterns. Differences in mean(p = 0.023), entropy(p = 0.049) and uniformity(p = 0.023) of entropy-NGLDM were found between responders and non-responders at follow-up. For the mean of heterogeneity a cut-off value was calculated for prediction of response in baseline CTTA (0.12; sensitivity 89%; specificity 77%). CONCLUSION/CONCLUSIONS:A frequent pattern of response to trabectedin was tumor liquefication being responsible for pseudoprogression, therefore modifiedCHOI should be preferred. Single CT-textural features can be used complementarily for prediction and monitoring response to trabectedin.

Advances in surgical techniques, orthopaedic implant design, and higher demands for improved functionality of the aging population have resulted in a high prevalence of patients with metallic implants about the knee. Total knee arthroplasty, knee-replacing tumor prostheses, and osteosynthesis implants create various imaging artifacts and pose special challenges for the imaging evaluation with computed tomography (CT) and magnetic resonance imaging (MRI). CT artifacts can be effectively mitigated with metal artifact reduction reconstruction algorithms, dual-energy data acquisition with virtual monoenergetic extrapolation, and three-dimensional postprocessing techniques, such as volume and cinematic rendering. Artifacts related to metal implants on MRI can be reduced via optimization of the scan parameters and using advanced techniques such as multi-acquisition variable-resonance image combination, and slice encoding for metal artifact correction.