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:To prospectively assess the evolution of postoperative MRI findings in asymptomatic patients after total hip arthroplasty (THA) over 24 months (mo). METHODS:This prospective cohort study included 9 asymptomatic patients (56.7 ± 15.0 years) after THA. Metal artifact-reduced 1.5-T MRI was performed at 3, 6, 12, and 24 mo after surgery. The femoral stem and acetabular cup were assessed by two readers for bone marrow edema (BME), periprosthetic bone resorption, and periosteal edema in addition to periarticular soft tissue edema and joint effusion. RESULTS:BME was common around the femoral stem in all Gruen zones after 3 mo (range: 50-100%) and 6 mo (range: 33-100%) and in the acetabulum in DeLee and Charnley zone II after 3 mo (100%) and 6 mo (33%). BME decreased substantially after 12 mo (range: 0-78%) and 24 mo (range: 0-50%), may however persist in particular in Gruen zones 1 + 7. Periosteal edema along the stem was common 3 mo postoperatively (range: 63-75%) and rare after 24 mo: 13% only in Gruen zones 2 and 5. Twelve months and 24 mo postoperatively, periprosthetic bone resorption was occasionally present around the femoral stem (range: 11-33% and 13-38%, respectively). Soft tissue edema occurred exclusively along the surgical access route after 3 mo (100%) and 6 mo (89%) and never at 12 mo or 24 mo (0%). CONCLUSION/CONCLUSIONS:Around the femoral stem, BME (33-100%) and periosteal edema (0-75%) are common until 6 mo after THA, decreasing substantially in the following period, may however persist up to 24 mo (BME: 0-50%; periosteal edema: 0-13%) in few non-adjoining Gruen zones. Soft tissue edema along the surgical access route should have disappeared 12 mo after surgery.

OBJECTIVE:To describe and illustrate the magnetic resonance imaging (MRI) anatomy of the anterior femoral cutaneous nerve (AFCN) and a new technique for cryoanalgesia of the AFCN for long-term analgesic treatment of recalcitrant AFCN-mediated neuropathic pain. MATERIALS AND METHODS/METHODS:Using a procedural high-resolution MRI technique, we describe the MRI anatomy of the AFCN. Three patients (mean age, 48 years; range, 41-67 years) with selective nerve block-verified recalcitrant AFCN-mediated anterior thigh pain were enrolled to undergo cryoanalgesia of the AFCN. Procedures were performed under MRI guidance using clinical wide-bore MR imaging systems and commercially available cryoablation system with MR-conditional probes. Outcome variables included technical success, clinical effectiveness including symptom relief measured on an 11-point visual analog scale, frequency of complications, and procedure time. RESULTS:Procedural MRI allowed to successfully demonstrate the course of the AFCN, accurate cryoprobe placement, and monitoring of the ice ball, which resulted in technically successful iceball growth around the AFCN in all cases. All procedures were clinically effective, with median pain intensity decreasing from 8 (7-9) before the procedure to 1 (0-2) after the procedure. The cryoanalgesia effect persisted during a 12-month follow-up period in all three patients. No major complications occurred. The average total procedure time was 98 min (range, 85-125 min). CONCLUSION/CONCLUSIONS:We describe the MRI anatomy of the AFCN and a new technique for cryoanalgesia of the AFCN using MRI guidance, which permits identification of the AFCN, selective targeting, and iceball monitoring to achieve long-term AFCN-mediated neuropathic pain relief.

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: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.

Purpose: To investigate the heating effect of clinical metal artifact reduction MRI protocols at 1.5 and 3T on different types of hip arthroplasty implants.
Material(s) and Method(s): Two standard ASTM MRI phantoms were placed head-to-head on the scanner table to simulate the upper and lower portions of a human torso. The phantoms were filled with gelled saline medium, which had the electrical and thermal properties of human muscle. Four different total hip arthroplasty implant configurations, including a metal-on-polyethylene construct with cobalt chromium (CoCr) femoral stem, a metal-on-metal construct with CoCr femoral stem, and two metalon-ceramic constructs with titanium (Ti) femoral stems at two lengths were tested. Fiber optic temperature sensors were used to measure the temperature at seven points along the implants. Temperature changes of three clinical pulse sequence type protocols, including high-bandwidth turbo spin echo (HBW-TSE), Slice Encoding for Metal Artifact Correction (SEMAC), and compressed sensing SEMAC (CS-SEMAC) were measured. Each protocol contained 6 pulse sequences, which were obtained in coronal, sagittal and axial orientations as intermediateweighted and short tau inversion recovery (STIR) varieties with image coverage identical to that in patients. Non-parametric Friedman and Wilcoxon signed-rank tests were implemented for multi-group comparisons.
Result(s): In 1.5T experiments, the maximum heating consistently occurred at the tip of the femoral stem for all implant types (p < 0.01). The maximum heating at any single point reached to 13.1degreeC at 1.5T which was at the tip of the shorter Ti stem. Across all 3T MRI protocols and all implant constructs, the maximum heating at any single point was 1.9 degreeC. Maximum temperature rises at 3T occurred at the tip of the femoral stem and medial aspect of the acetabular cup in most cases; however, there was no significant heating difference among various points along the implant periphery (p > 0.05). The degree of heating was not different between different implant types at 1.5 or 3T (p > 0.05).
Conclusion(s): Metal artifact reduction MRI at 1.5T may result in supraphysiological heating of the implant which can be mitigated with proper adjustment of scan protocol. However, 3T MRI poses no risk of thermal injury, and can be considered safe clinically

Musculoskeletal (MSK) image-guided oncologic intervention is an established field within radiology. Numerous studies have described its clinical benefits, safety, cost effectiveness, patient satisfaction, and improved quality of life, thereby establishing image-guided oncologic intervention as a preferred pathway in treating patients presenting with specific benign MSK tumors. But there is a paradigm shift on the horizon because these techniques may also support established pillars (surgery, systemic treatment, radiotherapy) in the treatment of malignant MSK tumors. Unlike benign tumors, where they are used as primary therapy lines with curative intent, such interventions can be selected for malignant tumors as adjuvant treatment in painful or unstable bone or soft tissue lesions or as more palliative therapy strategies. Using examples from our clinical practices, we elaborate on the benefits of applying a multidisciplinary approach (traditionally involving MSK radiologists, oncologists, orthopaedic surgeons, microbiologists, pathologists, physiotherapists, and pain management experts), ideally within a sarcoma treatment center to deliver a patient-specific therapy plan and illustrate methods to assess the benefits of this model of care.In this article, we review the current repertoire of ablation techniques, demonstrate why such procedures offer value-based alternatives to conventional treatments of specific tumors, and reflect on future directions. Additionally, we review the advantages and limitations of each technique and offer guidance to improve outcomes.

OBJECTIVES/OBJECTIVE:Longitudinal assessment of changes in apparent diffusion coefficient (ADC)-values in multiple myeloma (MM) patients and their potential role for classifying disease activity. METHODS:Retrospective analysis of whole-body-MRI data in 73 stage III MM patients undergoing systemic treatment. Bone marrow involvement was evaluated using a standardized unenhanced 4-sequences whole-body-MRI protocol. We measured ADC-values in focal lesions (FL) and diffusely involved bone marrow (DIBM) areas. Response to treatment was based on the course of hematologic parameters. The time points of MRI-examinations were baseline, 1st (mean, 3 months), 2nd (mean, 10 months), and 3rd (mean, 18 months) follow up (FU). RESULTS:/s for diagnosing inactive disease at follow-up proved unreliable. CONCLUSIONS:In myeloma-patients with lower tumor burden, the longitudinal course of ADC-values is predictable only for FL whereas for DIBM ADC-changes considerably overlap between responders and non-responders and are not indicative for assessment of the disease activity.