Synthetic MRI is not yet ready for morphologic and functional assessment of patellar cartilage at 1.5Tesla.

PURPOSE: The purpose of this study was to compare morphologic assessment and relaxometry of patellar hyaline cartilage between conventional sequences (fast spin-echo [FSE] T2-weighted fat-saturated and T2-mapping) and synthetic T2 short-TI inversion recovery (STIR) and T2 maps at 1.5T magnetic resonance imaging (MRI). METHOD: The MRI examinations of the knee obtained at 1.5T in 49 consecutive patients were retrospectively studied. There were 21 men and 28 women with a mean age of 45±17.7 (SD) years (range: 18-88 years). Conventional and synthetic acquisitions were performed, including T2-weighted fat-saturated and T2-mapping sequences. Two radiologists independently compared patellar cartilage T2-relaxation time on conventional T2-mapping and synthetic T2-mapping images. A third radiologist evaluated the patellar cartilage morphology on conventional and synthetic T2-weighted images. The presence of artifacts was also assessed. Interobserver agreement for quantitative variables was assessed using intraclass correlation coefficient (ICC). RESULTS: In vitro, conventional and synthetic T2 maps yielded similar mean T2 values 58.5±2.3 (SD) ms and 58.8±2.6 (SD) ms, respectively (P=0.414) and 6% lower than the expected experimental values (P=0.038). Synthetic images allowed for a 15% reduction in examination time compared to conventional images. On conventional sequences, patellar chondropathy was identified in 35 patients (35/49; 71%) with a mean chondropathy grade of 4.8±4.8 (SD). On synthetic images, 28 patients (28/49; 57%) were diagnosed with patellar chondropathy, with a significant 14% difference (P=0.009) and lower chondropathy scores (3.7±4.9 [SD]) compared to conventional images. Motion artifacts were more frequently observed on synthetic images (18%) than on conventional ones (6%). The interobserver agreement was excellent for both conventional and synthetic T2 maps (ICC>0.83). Mean cartilage T2 values were significantly greater on synthetic images (36.2±3.8 [SD] ms; range: 29-46ms) relative to conventional T2 maps (31.8±4.1 [SD] ms; range: 26-49ms) (P<0.0001). CONCLUSION: Despite a decrease in examination duration, synthetic images convey lower diagnostic performance for chondropathy, greater prevalence of motion artifacts, and an overestimation of T2 values compared to conventional MRI sequences.

Evidence-based MR imaging follow-up strategy for desmoid-type fibromatosis.

OBJECTIVES: To propose a follow-up strategy for desmoid-type fibromatosis (DF) based on tumor growth behavior and the signal on T2-weighted MRI. METHODS: We retrospectively reviewed 296 MRI studies of 34 patients with histologically proven DF. In each study, tumor volume and T2 signal relatively normal striated muscle were assessed. Volume variation and monthly growth rates were analyzed to determine lesion growth behavior (progressing versus stable/regressing lesions). Growth behavior was correlated with T2 signal, tumor location, ß-catenin status, treatment strategy, and follow-up duration. Interobserver variability of volume measurements and interobserver measurement variation ratio were assessed. RESULTS: There were 25 women and 9 men with a mean age of 39.9 ± 19 (4-73) years. Mean follow-up time in the patients included was 55 ± 41 (12-148) months. In progressing lesions, the mean average monthly growth ratio was 10.9 ± 9.2 (1.1-42.5) %. Interobserver variability of volume measurements was excellent (ICC = 0.96). Mean interobserver measurement variation ratio was 20.4 ± 23.6%. The only factor correlated with tumor growth behavior was T2 signal ratio (p < 0.0001). Seventeen out of 34 (50%) patients presented a signal change over the threshold of 1 during follow-up. There were five occurrences of secondary growth after a period of stability with a mean delay until growth of 38.2 ± 44.2 (17-116) months. CONCLUSION: DF growth rate was quantitatively assessed. A threshold for volume variation detection was established. DF growth behavior was significantly related to T2 signal. An evidence-based follow-up strategy is proposed. KEY POINTS: • In progressing desmoid fibromatosis, the mean average monthly growth ratio was 10.9 ± 9.2%. • Lesions with muscle/tumor T2 signal ratios lower than 1 tended to be stable or regress over time. • Given the interobserver measurement variability and MRI in-plane spatial resolution, a variation higher than 42.6% in tumor volume is required to confirm punctual progression.

Intravoxel incoherent motion MRI for the initial characterization of non-fatty non-vascular soft tissue tumors.

PURPOSE: To compare the capabilities of intravoxel incoherent motion (IVIM) to those of monoexponential diffusion-weighted imaging for differentiating benign from malignant non-vascular, non-fatty soft tissue tumors (NVSFSTT). MATERIAL AND METHODS: A total of 64 patients with 64 histologically confirmed soft-tissue tumors were retrospectively included. There were 23 men and 41 women with a mean age of 52±17 (SD) (range: 18-92 years). IVIM parameters, including molecular diffusion restriction coefficient (ADCtrue), perfusion fraction, and tissue perfusion related coefficient were compared to mean monoexponential ADC (ADCstd) values. Two readers calculated all parameters, which were compared to histopathological findings that were used as standard of reference. RESULTS: The overall performance of ADCtrue and ADCstd was similar for the benign-malignant differentiation of NFNVSTT with accuracies ranging from 73% to 75% for both readers (P=0.3). Interobserver reproducibility was considered excellent for both ADCstd and all IVIM parameters (ICC=0.81-0.96). When myxoid tumors were excluded from morphological analysis, an increase in sensitivity of 16-21% of ADCtrue was observed, with no changes in specificity values. The use of perfusion related IVIM parameters in association with ADCtrue did not improve tumor characterization. CONCLUSION: The use of IVIM parameters does not improve the characterization of NVNFSTT by comparison with conventional monoexponential ADC calculation.

Metal artifact reduction for intracranial projectiles on post mortem computed tomography.

PURPOSE: To compare the image quality of cranial post-mortem computed tomography (CT) obtained with and without projection-based single-energy metal artifact reduction (SEMAR) in cadavers with intracranial metallic ballistic projectiles. MATERIALS AND METHODS: From January 2017 to January 2018, cadavers with ballistic projectile head wounds with metal fragments and without massive head destruction were investigated using post-mortem CT. All subjects underwent CT using a conventional iterative reconstruction (IR) and SEMAR. To evaluate the impact of metallic artifacts, the total intracranial area (TA), non-interpretable zone (NIZ), disturbed interpretation zone (DZ), and artifact total surface (ATS) were delineated. Two independent readers identified extra-axial hemorrhage (EAH) and subarachnoid hemorrhage (SAH). Autopsy reports were used as the standard of reference. RESULTS: Eleven corpses (10 males, 1 female; mean age, 62.8±17.9 [SD] years) were evaluated. SEMAR showed a significant decrease in the ATS ratio with respect to conventional IR (72.1±26.1 [SD] % [range: 26.8-99.1] vs. 86.4±17.8 [SD] % [range: 37.2-100]; P<0.001) and NIZ/TA ratios (11.6±8.26% [range: 0.95-33.4] versus 42.5±30.5% [range: 3.86-100]; P<0.001). The interobserver reproducibility in diagnosing EAH and SAH was excellent with conventional IR (0.82) and good with SEMAR (0.75). SEMAR reduced uncertain diagnoses of EAH in 7 subjects for Reader 1 and in 6 for Reader 2, but did not influence the diagnosis of SAH for either reader. CONCLUSION: SEMAR reduces the influence of metallic artifacts and increases the confidence with which the diagnosis of EAH can be made on post-mortem CT.

Correlation between tumor growth and hormonal therapy with MR signal characteristics of desmoid-type fibromatosis: A preliminary study.

PURPOSE: To evaluate the impact of hormonal therapy on MRI characteristics of desmoid-type fibromatosis on T1-weighted, T2-weighted fat-saturated and post-contrast sequences. MATERIALS AND METHODS: Nineteen patients with histologically-proven desmoid-type fibromatosis were prospectively followed up on MR imaging. Eight patients underwent hormonal therapy and 11 were only surveyed. Change in tumor size during follow-up was analyzed according to RECIST. Signal intensity on T1-weighted, T2-weighted fat-saturated and T1-weighted fat-saturated post-contrast images was graded from 0 to 5 using adjacent normal muscle as reference. Findings were compared with tumor growth and treatment option. RESULTS: There were seven men and 12 women with a mean age of 42.2±16.4 (SD) years (range: 18 - 64 years) yielding twenty-six follow-up periods: eight of tumor progression and 18 of tumor stability/regression (some tumors exhibited more than one behavior type). Hormonal therapy was associated with tumor stability or regression (P=0.0207). There was a significant reduction in enhancement among treated patients with stable/regressing disease (P=0.049). The mean variation in enhancement grade was -1.3±1.2 in these patients. All successfully treated patients presented a reduction in enhancement. Lesions with marked low enhancement or very low signal on T2-weighted images were rare in progressing lesions (0% and 13%). CONCLUSION: Hormonal therapy has an impact on desmoid-type fibromatosis signal characteristics reducing lesion enhancement.

Perfusion MR imaging at 3-Tesla: Can it predict tumor grade and histologic necrosis rate of musculoskeletal sarcoma?

PURPOSE: To identify quantitative perfusion parameters that are best associated with tumor grade and tumor necrosis at magnetic resonance (MR) imaging at 3-Tesla. METHODS: MR perfusion studies of 31 patients with a musculoskeletal sarcoma were retrospectively evaluated by two readers. There were 18 men and 13 women with a mean age of 34.9±24.4 (standard deviation [SD] years) (range: 6-87 years). All patients underwent carcinologic tumor resection less than 3 months after MR imaging. For all patients six perfusion parameters (three semi-quantitative and three permeability parameters) were analyzed. The percentage of tumor necrosis was estimated using MR imaging. Perfusion data were compared between groups of tumors with different grades and necrosis ratios. Interobserver variability was calculated using intraclass correlation coefficient (ICC). RESULTS: Interobserver variability among the perfusion parameters was good to excellent (ICC: 0.72-0.9). The area under the curve and maximum slope values showed a significant association with the degree of tumor necrosis (P=0.02-0.04). When tumors with low necrosis ratios were compared to those with high ratios the former parameter was 80% lower. In the same groups, the imaging necrosis index was 56.9-59.8% higher in patients with grade 2 necrosis (P=0.01). Extracellular space volume (Ve) was 31.4% to 55.8% lower in tumors with high grade while the backflow constant (Kep) was 33.6% to 40.1%% higher in tumors with high grade. CONCLUSION: Semi-quantitative MR perfusion parameters have an excellent reproducibility and are associated with the degree of histologic tumor necrosis in musculoskeletal sarcomas. The utility of permeability parameters for determining tumor grade needs further investigations.

Protocol optimization of sacroiliac joint MR Imaging at 3 Tesla: Impact of coil design and motion resistant sequences on image quality.

PURPOSE: To evaluate the impact of coil design and motion-resistant sequences on the quality of sacroiliac magnetic resonance imaging (MRI) examination in patients with spondyloarthropathy. PATIENTS AND METHODS: One hundred and twenty-one patients with suspected sacroiliitis and referred for MRI of the sacroiliac joints were retrospectively evaluated with MRI at 3-Tesla. There were 78 women and 43 men with a mean age of 36.7±11.5 (SD) years (range: 15.8-78.4 years). Conventional and motion-resistant fat-saturated fast-spin echo T2-weighted sequences were performed with two different coils. Image quality was subjectively evaluated by two independent readers (R1 and R2) using a four-point scale. Confidence in the identification of bone marrow edema pattern (BMEP) was also evaluated subjectively using a three-point scale. RESULTS: Phased array body coil yielded improved image quality compared to surface coil (14.1 to 30.4% for R1 and 14.6 to 25.7% for R2; P<0.0001). The impact of the sequence type on quality was also statistically significant (P=0.0046). BMEP was identified in 40 patients and best inter-reader agreement was obtained using the combination of phased-array body coil with motion-resistant T2-weighted sequence (kappa 0.990). The smallest number of indeterminate BMEP zones was seen on MRI set acquired with the phased-array body coil and motion-resistant T2-weighted sequence. CONCLUSION: Phased array body coil and motion-resistant T2-weighted sequences perform better than surface coil and conventional T2-weighted sequences for the evaluation of sacroiliac joints, increasing confidence in the identification of BMEP.

Subchondral linear hyperintensity of the femoral head: MR imaging findings and associations with femoro-acetabular joint pathology.

PURPOSE: The goal of this study was to evaluate the associations between linear hyperintensity in the subchondral bone of the femoral head on T2-weighted MR imaging and structural bone lesions. MATERIAL AND METHODS: The MR imaging examinations of 63 patients (66 hips) that showed a bone marrow edema pattern (BMEP) of the hip were retrospectively evaluated (study group). The study group comprised 43 men and 20 women, with a mean age of 55.3 years±16.9 (SD) (range: 19-84 years). A control group of 61 patients (77 hips) without BMEP of the hip on MR imaging was created. The control group comprised 30 men and 31 women, with a mean age of 53.1 years±15.6 (SD) (range: 25-83 years). The presence of linear abnormalities of the subchondral bone on T2-weighted fat-saturated sequences (TR/TE=4220-4340/42-45ms) was evaluated and MR imaging findings were correlated with structural femoro-acetabular pathology (advanced chondropathy, osteonecrosis, subchondral insufficiency fractures and macroscopic fractures) and with pain duration. RESULTS: A linear hyperintensity in the subchondral bone on T2-weighted MR imaging was found in 43/66 hips with areas of BMEP (65.1%) and in 3/77 hips without BMEP (3.8%). Subchondral linear hyperintensity was seen in 15/16 (93.7%) hips with a subchondral insufficiency fracture. Among the 16 hips with an ARCO stage III osteonecrosis, 13 (76.9%) presented BMEP associated with a subchondral linear hyperintensity. BMEP was present in 6/8 hips with ARCO stage IV osteonecrosis; however, only two hips (25%) exhibited subchondral linear hyperintensities. Finally, 77.7% of patients with subchondral linear hyperintensities presented with acute or subacute hip pain (P<0.0001). CONCLUSION: Femoral head subchondral linear hyperintensity on T2-weighted MR imaging is common and is associated with acute subchondral bone damage.

Wide area detector CT perfusion: can it differentiate osteoid osteomas from other lytic bone lesions?

PURPOSE: To compare the enhancement dynamics of osteoid osteomas with other benign and malignant lytic bone lesions using CT perfusion. PATIENTS AND METHODS: CT perfusion parameters of 15 patients with a final diagnosis of osteoid osteoma, 15 patients with lesions that mimic osteoid osteomas and 26 patients with other bone lytic lesions were compared. RESULTS: Enhancement curve morphology of the osteoid osteomas was significantly different from its mimickers. All osteoid osteomas had an early enhancement with a delay between nidus and arterial peak below 30 seconds. Eighty percent of the mimickers demonstrated a slow and progressive enhancement. The perfusion parameters of the other lytic bone lesions were similar to those of the osteoid osteomas in 46.1% of the patients. CONCLUSION: Early enhancement is suggestive but not pathognomonic of osteoid osteomas. Absent or delayed enhancement in similar lesions should evoke an alternative diagnosis. The same contrast enhancement dynamics of osteoid osteomas can be seen in other bone lesions, both malignant and benign.