Faculty Bibliography

RATIONALE AND OBJECTIVES:This study aimed to determine the diagnostic aid of computed tomography (CT) features for the differentiation of active alveolitis and fibrosis using a CT texture analysis (CTTA) prototype and CT densitometry in patients with systemic sclerosis (SSc) using ancillary high-resolution computed tomography (HRCT) features and their longitudinal course as standard of reference. MATERIALS AND METHODS:We retrospectively analyzed thin-slice noncontrast chest CT image data of 43 patients with SSc (18 men, mean age 51.55 ± 15.52 years; range 23-71 years). All of them had repeated noncontrast enhanced HRCT of the lung. Classification into active alveolitis or fibrosis was done on HRCT based on classical HRCT findings (active alveolitis [19; 44.2%] and fibrosis [24; 55.8%]) and their course at midterm. Results were compared to pulmonary functional tests and were followed up by CT. Ground glass opacity was considered suggestive of alveolitis, whereas coarse reticulation with parenchymal distortion, traction bronchiectasis, and honeycombing were assigned to fibrosis. RESULTS:Statistically significant differences in CTTA were found for first-order textural features (mean intensity, average, deviation, skewness) and second-order statistics (entropy of co-occurrence matrix, mean number of nonuniformity (NGLDM), entropy of NGLDM, entropy of heterogeneity, intensity, and average). Cut-off value for the prediction of fibrosis at baseline was significant for entropy of intensity (P value < .001) and for mean deviation (P value < .001), and for prediction of alveolitis was significant for uniformity of intensity (P value < .001) and for NGLDM (P value < .001). At pulmonary functional tests, forced expiratory volume in 1 second and single-breath diffusion capacity for carbon monoxide were significantly lower in fibrosis than in alveolitis 2.03 ± 0.78 vs. 2.61 ± 0.83, P < .016 and 4.51 ± 1.61 vs. 6.04 ± 1.75, P < .009, respectively. Differences in CT densitometry between alveolitis and fibrosis were not significant. CONCLUSIONS:CTTA parameters are significantly different in active alveolitis vs. fibrosis in patients with SSc and may be helpful for differentiation of these two entities.

OBJECTIVES:Long echo train length (ETL) is an often recommended but unproven technique to decrease metal artifacts on magnetic resonance imaging (MRI) scans. Therefore, we quantitatively and qualitatively assessed the effects of ETL on metal artifact on MRI scans using a cobalt-chromium-containing arthroplasty implant system. MATERIALS AND METHODS:Using a total ankle arthroplasty system implanted into a human cadaver ankle and a clinical 1.5 T MRI system, turbo spin echo (TSE) pulse sequences were acquired with ETL ranging from 3 to 23 and receiver bandwidth (BW) from 100 to 750 Hz/pixel, whereas effective echo time and spatial resolution were controlled. A compressed sensing slice encoding for metal artifact correction TSE prototype pulse sequence was used as reference standard. End points included the total implant-related artifact area and implant-related signal void areas. Two raters evaluated the overall image quality and preference across varying BW and ETL. Two-factor analysis of variance, Friedman test, Kruskal-Wallis test, and Pearson correlation were used. P values of less than 0.05 were considered statistically significant. RESULTS:The total implant-related artifact area ranged from 0.119 for compressed sensing slice encoding for metal artifact correction (BW, 600 Hz/pixel; ETL, 3) to 0.265 for TSE (BW, 100 Hz/pixel; ETL, 23). Longer ETL significantly increases the total implant-related artifact area (P = 0.0004), whereas it decreased with increasing BW (P < 0.0001). Implant-related signal void areas were not significantly affected by larger echo train length, but reduced with higher BW (P < 0.0001). Readers had a significant preference for images with high BW and short ETL (P < 0.0001). CONCLUSIONS:High receiver BW is the most effective parameter for reduction of arthroplasty implant-induced metal artifact on MRI scans, whereas in contradiction to prevalent notions, long echo trains fail to reduce implant-related metal artifacts, but in fact cause degradation of image quality around the implant with resultant larger appearing total metal artifacts.

PURPOSE:The aim of this study was to prospectively test the hypothesis that 6-fold acceleration of a 3-dimensional (3D) turbo spin echo (TSE) magnetic resonance imaging (MRI) pulse sequence with k-space undersampling and iterative reconstruction is feasible for fast high spatial resolution MRI of the knee, while yielding similar image quality and diagnostic performance when compared with a conventional 2-dimensional (2D) TSE MRI standard. MATERIALS AND METHODS:The study was approved by the institutional review board. A 10-minute isotropic 3D TSE knee protocol consisting of accelerated intermediate-weighted (repetition time, 900 milliseconds; echo time, 29 milliseconds; voxel size, 0.5 × 0.5 × 0.5 mm; acquisition time, 4:45 minutes) and fat-saturated T2-weighted (repetition time, 900 milliseconds; echo time, 92 milliseconds; voxel size, 0.5 × 0.5 × 0.5 mm; acquisition time, 5:10 minutes) SPACE (sampling perfection with application optimized contrast using different flip angle evolutions) sequence prototypes was compared against a 20-minute 2D TSE standard protocol. The accelerated SPACE sequences were equipped with an optional variable-density poisson-disc pattern as an undersampling mask. An undersampling factor of 0.17 was chosen (6-fold acceleration compared with an acquisition with full sampling). An iterative, sensitivity encoding-type reconstruction with L1 norm-based regularization term was used. The study was performed on a 3 T MRI system using a 15-channel transmit/receive knee coil. The study groups included 15 asymptomatic volunteers and 15 patient volunteers. Quantitative and qualitative assessments were performed by 2 observers. Outcome variables included signal and contrast-to-noise ratio, image quality, and diagnostic accuracy. Qualitative and quantitative measurements were statistically analyzed using nonparametric tests. P values of less than 0.01 were considered significant. RESULTS:The signal-to-noise ratios of 2D and 3D MRI were similar with the exception of fluid, which was brighter on 2D MRI. Relevant contrast-to-noise ratios of 2D MRI were higher than 3D MRI; however, observer ratings for satisfaction, image quality, and visibility of anatomic structures were similar for 2D and 3D MRI. There was moderate to excellent interobserver (κ = 0.54-1.00) and intermethod (κ = 0.54-1.00) agreement for assessing menisci, cartilage, ligaments, cartilage, and bone. Two-dimensional and 3D MRI had similar sensitivity (100%/100%, respectively) and specificity (87%/75%, respectively) for detecting 9 meniscal tears (P = 1.00). CONCLUSIONS:We demonstrate the successful clinical implementation of 3D TSE MRI with incoherent k-space undersampling and iterative reconstruction for 6-fold accelerated high spatial resolution isotropic 3D MRI data acquisition. Our preliminary assessments suggest similar image quality and diagnostic performance of a comprehensive 10-minute 3D TSE MRI prototype protocol and 20-minute TSE MRI standard protocol.

Hereditary multiple exostoses (HME) is an autosomal dominant disorder characterized by the formation of multiple osteochondromas. Because of its superior soft tissue contrast and absence of ionizing radiation, magnetic resonance imaging is the first choice imaging technique for the evaluation of complex lesions and complications related to HME. However, multidetector computed tomography (MDCT) also can be of value in the evaluation of patients with HME, which is reviewed in this article. Topics outlined are low-dose MDCT technique, 3-dimensional visualization techniques, typical MDCT appearances, differential diagnostic considerations, and the usefulness of MDCT in the assessment of emergent and non-emergent complications related to HME, among which spinal cord compression, pneumothorax and hematothorax, pseudoaneurysms, fractures, growth disturbances, chondrosarcoma transformation, and muscular and peripheral nerve involvement.

OBJECTIVE:Perineural ganglion impar injections are used in the management of pelvic pain syndromes; however, there is no consensus regarding the optimal image guidance. Magnetic resonance imaging (MRI) provides high soft tissue contrast and the potential to directly visualize and target the ganglion. The purpose of this study was to assess the feasibility of MR-guided percutaneous perineural ganglion impar injections. MATERIALS AND METHODS/METHODS:Six MR-guided ganglion impar injections were performed in six human cadavers. Procedures were performed with a clinical 1.5-Tesla MRI system through a far lateral transgluteus approach. Ganglion impar visibility, distance from the sacrococcygeal joint, number of intermittent MRI control steps required to place the needle, target error between the intended and final needle tip location, inadvertent punctures of non-targeted vulnerable structures, injectant distribution, and procedure time were determined. RESULTS:The ganglion impar was seen on MRI in 4/6 (66 %) of cases and located 0.8 mm cephalad to 16.3 mm caudad (average 1.2 mm caudad) to the midpoint of the sacrococcygeal joint. Needle placement required an average of three MRI control steps (range, 2-6). The average target error was 2.2 ± 2.1 mm. In 6/6 cases (100 %), there was appropriate periganglionic distribution and filling of the presacrococcygeal space. No punctures of non-targeted structures occurred. The median procedure time was 20 min (range, 12-29 min). CONCLUSION/CONCLUSIONS:Interventional MRI can visualize and directly target the ganglion impar for accurate needle placement and successful periganglionic injection with the additional benefit of no ionizing radiation exposure to patient and staff. Our results support clinical evaluation.

Gout is a true crystal deposition arthropathy caused by the precipitation of monosodium urate into joints and periarticular soft tissues. It is the most common inflammatory arthropathy in men and women of older age with a male-to-female ratio of 3 to 8:1. The disease may progress from asymptomatic hyperuricemia through symptomatic acute gout attacks with asymptomatic periods into chronic symptomatic tophaceous gout. Although invasive arthrocentesis and demonstration of monosodium urate crystals on polarized light microscopy is definitive for the diagnosis of gout, dual-energy computed tomography (CT) allows for noninvasive visualization and reproducible volume quantification of monosodium urate crystals. Based on the high diagnostic performance, dual-energy CT has been included in the 2015 American College of Rheumatology/European League Against Rheumatism Collaborative Initiative Classification Criteria for Gout. Increasing evidence indicates the usefulness of dual-energy CT to guide the management of patients with suspected gout and monitor the effectiveness of urate-lowering medical therapy.

OBJECTIVE:The aim of this study was to prospectively test the hypothesis that a 2-dimensional (2D) CAIPIRINHA (controlled aliasing in parallel imaging results in higher acceleration) sampling pattern facilitates 5-minute high spatial resolution 3-dimensional (3D) sampling perfection with application optimized contrast using different flip angle evolutions (SPACE) magnetic resonance imaging (MRI) of the knee with image quality similar or better than current 2D turbo spin echo (TSE) and 3D SPACE standards. MATERIALS AND METHODS:The study was approved by our institutional review board. Twenty asymptomatic subjects (12 men, 8 women; mean age, 42 years; age range, 24-65 years) underwent 3 T MRI of the knee. A 4-fold accelerated 3D SPACE TSE prototype with 2D CAIPIRINHA sampling pattern and 5-minute acquisition time was compared with commercially available 2-fold and 4-fold accelerated 3D SPACE and 2D TSE pulse sequences with acquisition times of 11 minutes and 15 seconds, 6 minutes and 30 seconds, as well as 9 minutes and 48 seconds, respectively. Outcome variables included image quality, anatomic visibility, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Statistical analysis included Friedman, repeated measures analysis of variances, and Cohen's weighted κ tests. Bonferroni-corrected P values of 0.005 and less were considered statistically significant. RESULTS:Overall, image quality, visibility of anatomic structures, SNR, and CNR of 3D CAIPIRINHA SPACE were statistically similar to 2-fold accelerated 3D SPACE and significantly better than 4-fold accelerated 3D SPACE, which exhibited degrading parallel imaging artifacts. Compared with 2.5-mm 2D TSE images, 0.5-mm 3D CAIPIRINHA SPACE images showed statistically similar good edge sharpness and very good contrast resolution, and significantly less partial volume as well as absent chemical shift and pulsatile flow artifacts. Visibility of menisci, anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament, and lateral collateral ligament was good to very good on 0.5-mm 3D CAIPIRINHA SPACE images as compared with good on 2.5-mm 2D TSE image (P < 0.005). The SNR of fat, fluid, and cartilage as well as CNR between cartilage, fluid, fat, posterior cruciate ligament, and menisci were minimally higher on 2.5-mm 2D TSE image (P < 0.005). Image quality, visibility of anatomic structures, SNR, and CNR of 2.5-mm 3D CAIPIRINHA SPACE and 2.5-mm 2D TSE images were good to very good without significant differences. CONCLUSIONS:Three-dimensional SPACE with 2D CAIPIRINHA sampling pattern enables high-quality 3D TSE MRI of the knee at an acquisition time of 5 minutes and image quality, visibility of anatomic structures, SNR, and CNR similar to conventional 3D SPACE and 2D TSE, both of which require approximately 10-minute acquisition times.

OBJECTIVE:Compressed sensing (CS) acceleration has been theorized for slice encoding for metal artifact correction (SEMAC), but has not been shown to be feasible. Therefore, we tested the hypothesis that CS-SEMAC is feasible for MRI of metal-on-metal hip resurfacing implants. MATERIALS AND METHODS/METHODS:Following prospective institutional review board approval, 22 subjects with metal-on-metal hip resurfacing implants underwent 1.5 T MRI. We compared CS-SEMAC prototype, high-bandwidth TSE, and SEMAC sequences with acquisition times of 4-5, 4-5 and 10-12 min, respectively. Outcome measures included bone-implant interfaces, image quality, periprosthetic structures, artifact size, and signal- and contrast-to-noise ratios (SNR and CNR). Using Friedman, repeated measures analysis of variances, and Cohen's weighted kappa tests, Bonferroni-corrected p-values of 0.005 and less were considered statistically significant. RESULTS:There was no statistical difference of outcomes measures of SEMAC and CS-SEMAC images. Visibility of implant-bone interfaces and pseudocapsule as well as fat suppression and metal reduction were "adequate" to "good" on CS-SEMAC and "non-diagnostic" to "adequate" on high-BW TSE (p < 0.001, respectively). SEMAC and CS-SEMAC showed mild blur and ripple artifacts. The metal artifact size was 63 % larger for high-BW TSE as compared to SEMAC and CS-SEMAC (p < 0.0001, respectively). CNRs were sufficiently high and statistically similar, with the exception of CNR of fluid and muscle and CNR of fluid and tendon, which were higher on intermediate-weighted high-BW TSE (p < 0.005, respectively). CONCLUSION/CONCLUSIONS:Compressed sensing acceleration enables the time-neutral use of SEMAC for MRI of metal-on-metal hip resurfacing implants when compared to high-BW TSE and image quality similar to conventional SEMAC.