Faculty Bibliography

OBJECTIVES/OBJECTIVE:To test the hypothesis that an accelerated, T1-weighted 3D CAIPIRINHA SPACE sequence with isotropic voxel size offers a similar performance to conventional T1-weighted 2D TSE (turbo spin echo) for the evaluation of bone tumor extent and characteristics. METHODS:Thirty-four patients who underwent 3-T MRI with 3DT1 (CAIPIRINHA SPACE TSE) and 2DT1 (TSE) were included. Sequence acquisition time was reported. Two radiologists independently evaluated each technique for tumor location, size/length, tumor-to-joint distance, signal intensity, margin/extraosseous extension, and signal-to-noise (SNR) and contrast-to-noise (CNR) ratios. RESULTS:Tumors were located in long (20/36, 55.5%) and pelvic (16/36, 44.4%) bones. 3DT1 sequence required an average acquisition time of 235 s (± 42 s, range 156-372), while two plane 2DT1 sequences combined (coronal and axial) had an average acquisition time of 381 s (± 73 s, range 312-523). There was no difference in the measurements of tumor length and tumor-to-joint distance (p = 0.95) between 3DT1 and 2DT1 images. Tumors were hypointense (17/36, 47.2% vs 17/36, 47.2%), isointense (12/36, 33.3% vs 12/36, 33.3%), or hyperintense (7/36, 19.4% vs 7/36, 19.4%) on 3DT1 vs 2DT1, respectively. Assessment of tumor margins and extraosseous extension was similar, and there was no difference in tumor SNR or CNR (p > 0.05). CONCLUSIONS:An accelerated 3D CAIPIRINHA SPACE T1 sequence provides comparable assessments of intramedullary bone tumor extent and similar tumor characteristics to conventional 2DT1 MRI. For the assessment of bone tumors, the isotropic volume acquisition and multiplanar reformation capability of the 3DT1 datasets can obviate the need for 2DT1 acquisitions in multiple planes. KEY POINTS/CONCLUSIONS:• 3DT1 offers an equivalent performance to 2DT1 for the assessment of bone tumor characteristics, with faster and higher resolution capability, obviating the need for acquiring 2DT1 in multiple planes. • There was no difference in the measurements of tumor length and tumor-to-joint distance obtained on 3DT1 and 2DT1 images. • There was no difference in signal-to-noise ratio (SNR) or contrast-to-noise ratio (CNR) measures between 3DT1 and 2DT1.

OBJECTIVE:field on metal implant-induced artifacts of titanium (Ti) and cobalt-chromium (CoCr) hip arthroplasty implants at 1.5-T and 3.0-T field strengths. MATERIAL AND METHODS/METHODS:field as the system default, as well as 3.0-T, which permitted CP and EP. Manual segmentation quantified the size of the metal artifacts at the level of the acetabular cup, femoral neck, and femoral shaft. RESULTS:In the acetabular cup and femoral neck, 1.5-T CP achieved smaller artifact sizes than 3.0-T CP (28-29% on HBW-TSE, p = 0.002-0.005; 17-34% on SEMAC, p = 0.019-0.102) and 3.0-T EP (25-28% on HBW-TSE, p = 0.010-0.011; 14-36% on SEMAC, p = 0.058-0.135) techniques. In the femoral stem region, 3.0-T EP achieved more efficient artifact suppression than 3.0-T CP (HBW-TSE 44-45%, p < 0.001-0.022; SEMAC 76-104%, p < 0.001-0.022) and 1.5-T CP (HBW-TSE 76-96%, p < 0.001-0.003; SEMAC 138-173%, p = 0.003-0.005) techniques. CONCLUSION/CONCLUSIONS:Despite slightly superior metal reduction ability of the 1.5-T in the region of the acetabular cup and prosthesis neck, 3.0-T MRI of hip arthroplasty implants using elliptically polarized RF pulses may overall be more effective in reducing metal artifacts than the current standard 1.5-T MRI techniques, which by default implements circularly polarized RF pulses.

Background Dual-energy CT (DECT) shows promising performance in detecting bone marrow edema (BME) associated with vertebral body fractures. However, the optimal technical and image interpretation parameters are not well described. Purpose To conduct a systematic review and meta-analysis to determine the diagnostic performance of DECT in detecting BME associated with vertebral fractures (VFs), using different technical and image interpretation parameters, compared with MRI as the reference standard. Materials and Methods A systematic literature search was performed on July 9, 2020, to identify studies evaluating DECT performance for in vivo detection of vertebral BME. A random-effects model was used to derive estimates of the diagnostic accuracy parameters of DECT. The impact of relevant covariates in technical, image interpretation, and study design parameters on the diagnostic performance of DECT was investigated using subgroup analyses. Results Seventeen studies (with 742 of 2468 vertebrae with BME at MRI) met inclusion criteria. Pooled estimates of sensitivity, specificity, and area under the curve of DECT for vertebral body BME were 89% (95% CI: 84%, 92%), 96% (95% CI: 92%, 98%), and 96% (95% CI: 94%, 97%), respectively. Single-source consecutive scanning showed poor specificity (78%) compared with the dual-source technique (98%, P < .001). Specificity was higher using bone and soft-tissue kernels (98%) compared with using only soft-tissue kernels (90%, P = .001). Qualitative assessment had a better specificity (97%) versus quantitative assessment (90%) of DECT images (P = .01). Experienced readers showed considerably higher specificity (96%) compared with trainees (79%, P = .01). DECT sensitivity improved using a higher difference between low- and high-energy spectra (90% vs 83%, P = .04). Conclusion Given its high specificity, the detection of vertebral bone marrow edema with dual-energy CT (DECT) associated with vertebral fracture may obviate confirmatory MRI in an emergency setting. Technical parameters, such as the dual-source technique, both bone and soft-tissue kernels, and qualitative assessment by experienced readers, can ensure the high specificity of DECT. © RSNA, 2021 Online supplemental material is available for this article.

Background Rapid knee MRI using combined simultaneous multislice (SMS) technique and parallel imaging (PI) acceleration can add value through reduced acquisition time but requires validation of clinical efficacy. Purpose To evaluate the performance of clinical fourfold SMS-PI-accelerated, 5-minute, five-sequence, multicontrast knee MRI protocols compared with standard twofold PI-accelerated, 10-minute knee MRI protocols. Materials and Methods Adults with painful knee conditions were prospectively enrolled from April 2018 to October 2019. Participants underwent fourfold SMS-PI-accelerated, 5-minute, turbo spin-echo (TSE) knee MRI and standard-of-care twofold PI-accelerated, 10-minute, TSE knee MRI at either 1.5 T or 3.0 T. Three radiologists independently evaluated the knee MRI studies for meniscal, tendinous, ligamentous, and osseocartilaginous injuries. Statistical analyses included k-based intermethod agreements and diagnostic performance testing. P < .05 was considered indicative of a statistically significant difference. Results A total of 252 adults were evaluated (mean age ± standard deviation, 47 years ± 17; 134 men). Among the participants, 104 (mean age, 42 years 5 18; 57 women) were in the 1.5-T arm and 148 (mean age, 46 years 5 17; 87 men) were in the 3.0-T arm. Twenty-nine participants (mean age, 38 years 5 12; 15 men) in the 1.5-T arm and 42 (mean age, 41 years 5 16; 24 men) in the 3.0-T arm underwent arthroscopy a mean of 45 days 5 31 and 45 days 5 22 after MRI, respectively. Intermethod agreements were good at 1.5 T (κ >0.71 [95% CI: 0.56, 0.83]) and very good at 3.0 T (κ >0.85 [95% CI: 0.69, 0.96]). The diagnostic performances of corresponding 5-minute and 10-minute MRI protocols were similar for 1.5 T, with areas under the receiver operating characteristic curve (AUCs) greater than 0.78 (95% CI: 0.71, 0.84) (P > .32), and 3.0 T, with AUCs greater than 0.83 (95% CI: 0.78, 0.88) (P > .32). Conclusion Comparisons of 5-minute five-sequence simultaneous multislice- and parallel imaging (PI)-accelerated and 10-minute five-sequence PI-accelerated turbo spin-echo MRI of the knee suggest similar performances at 1.5 and 3.0 T. © RSNA, 2021 Online supplemental material is available for this article. See also the editorial by Subhas in this issue.

OBJECTIVES/OBJECTIVE:The aim of this study was to quantify the spatial temperature rises that occur during 1.5- and 3.0-T magnetic resonance imaging (MRI) of different types of hip arthroplasty implants using different metal artifact reduction techniques. MATERIALS AND METHODS/METHODS:Using a prospective in vitro study design, we evaluated the spatial temperature rises of 4 different total hip arthroplasty constructs using clinical metal artifact reduction techniques including high-bandwidth turbo spin echo (HBW-TSE), slice encoding for metal artifact correction (SEMAC), and compressed sensing SEMAC at 1.5 and 3.0 T. Each MRI protocol included 6 pulse sequences, with imaging planes, parameters, and coverage identical to those in patients. Implants were immersed in standard American Society for Testing and Materials phantoms, and fiber optic sensors were used for temperature measurement. Effects of field strength, radiofrequency pulse polarization at 3.0 T, pulse protocol, and gradient coil switching on heating were assessed using nonparametric Friedman and Wilcoxon signed-rank tests. RESULTS:Across all implant constructs and MRI protocols, the maximum heating at any single point reached 13.1°C at 1.5 T and 1.9°C at 3.0 T. The temperature rises at 3.0 T were similar to that of background in the absence of implants (P = 1). Higher temperature rises occurred at 1.5 T compared with 3.0 T (P < 0.0001), and circular compared with elliptical radiofrequency pulse polarization (P < 0.0001). Compressed sensing SEMAC generated equal or lower degrees of heating compared with HBW-TSE at both field strengths (P < 0.0001). CONCLUSIONS:Magnetic resonance imaging of commonly used total hip arthroplasty implants is associated with variable degrees of periprosthetic tissue heating. In the absence of any perfusion effects, the maximum temperature rises fall within the physiological range at 3.0 T and within the supraphysiologic range at 1.5 T. However, with the simulation of tissue perfusion effects, the heating at 1.5 T also reduces to the upper physiologic range. Compressed sensing SEMAC metal artifact reduction MRI is not associated with higher degrees of heating than the HBW-TSE technique.

OBJECTIVE. The purpose of this article is to provide a practice-focused review of the clinical application of advanced acceleration techniques for rapid musculoskeletal MRI examinations. CONCLUSION. Parallel imaging, simultaneous multislice acquisition, compressed sensing-based sampling, and synthetic MRI techniques provide unprecedented opportunities for rapid musculoskeletal MRI examinations. For 2D and 3D fast spin-echo and turbo spin-echo pulse sequences, acceleration factors between 3 and 8 can be realized in clinical practice, amounting to a time savings of 66-85% when compared with unaccelerated acquisitions.

OBJECTIVE. The purpose of this article is to provide a practice-focused review of accelerating musculoskeletal MRI with the use of widely accessible techniques and to assess the effects of such acceleration on the value of musculoskeletal MRI. CONCLUSION. Echo-train compaction with fast radiofrequency pulses, high gradient performance modes, and high receiver bandwidth, as well as basic phase undersampling techniques, affords at least twofold acceleration of musculoskeletal MRI examinations while retaining image quality, comprehensiveness, and diagnostic performance. Optimized efficiency is a cornerstone for adding value to musculoskeletal MRI.