Cationic tantalum oxide nanoparticle contrast agent for micro computed tomography reveals articular cartilage proteoglycan distribution and collagen architecture alterations.

OBJECTIVE: Cationic tantalum oxide nanoparticles (Ta2O5-cNPs), as a newly introduced contrast agent for computed tomography of cartilage, offer quantitative evaluation of proteoglycan (PG) content and biomechanical properties. However, knowledge on the depth-wise impact of cartilage constituents on nanoparticle diffusion, particularly the influence of the collagen network, is lacking. In this study, we aim to establish the depth-dependent relationship between Ta2O5-cNP diffusion and cartilage constituents (PG content, collagen content and network architecture). METHODS: Osteochondral samples (n = 30) were harvested from healthy equine stifle joints (N = 15) and the diffusion of 2.55 nm diameter cationic Ta2O5-cNPs into the cartilage was followed with micro computed tomography (µCT) imaging for up to 96 hours. The diffusion-related parameters, Ta2O5-cNP maximum partition (Pmax) and diffusion time constant, were compared against biomechanical and depth-wise structural properties. Biomechanics were assessed using stress-relaxation and sinusoidal loading protocols, whereas PG content, collagen content and collagen network architecture were determined using digital densitometry, Fourier-transform infrared spectroscopy and polarized light microscopy, respectively. RESULTS: The Pmax correlates with the depth-wise distribution of PGs (bulk Spearman's ρ = 0.87, p < 0.001). More open collagen network architecture at the superficial zone enhances intake of Ta2O5-cNPs, but collagen content overall decreases the intake. The Pmax values correlate with the equilibrium modulus (ρ = 0.80, p < 0.001) of articular cartilage. CONCLUSION: This study establishes the feasibility of Ta2O5-cNPs for the precise and comprehensive identification of biomechanical and structural changes in articular cartilage via contrast-enhanced µCT.

Radiation exposure to fetus from extremity CBCT examinations.

PURPOSE: To evaluate fetal doses from extremity CBCT examinations at different stages of pregnancy and to investigate different methods of fetal dose optimization. METHOD: Fetal doses were measured in an anthropomorphic phantom for two CBCT examination protocols - knee and elbow. The measurements were made at three different heights representing the three trimesters during pregnancy and three different depths in the phantom. The effect of soft tissue layer, tube voltage, add-on device shield and body angulation on fetal dose were investigated. RESULTS: The fetal doses in clinical examination protocols were in the range of 3.4 to 6.0 µGy during knee examinations and 2.9 to 7.7 µGy during elbow examinations depending on the depth of the fetus and the stage of pregnancy. A soft tissue layer representing variative body composition above abdomen region decreased the fetal dose up to 19 % in knee and up to 21 % in elbow examinations. Using lower tube voltage decreased the fetal doses up to 45 % (knee) and 51 % (elbow). An add-on device shield decreased the fetal doses up to 91 % (knee) and up to 75 % (elbow). Turning the body away from the device bore reduced the fetal doses up to 62 %. The conversion factor to convert an entrance surface dose to the fetal dose ranged from 0.4 to 0.6. CONCLUSIONS: The fetal doses from CBCT examinations of extremities are low and do not produce a concern about radiation detriment to the fetus. The most efficient way found to reduce the fetal dose was to use the add-on device shielding.

Wall Shear Stress Predicts Media Degeneration and Biomechanical Changes in Thoracic Aorta.

Objectives: In thoracic aortic aneurysm (TAA) of the ascending aorta (AA), AA is progressively dilating due to the weakening of the aortic wall. Predicting and preventing aortic dissections and ruptures in TAA continues to be challenging, and more accurate assessment of the AA dilatation, identification of high-risk patients, and timing of repair surgery are required. We investigated whether wall shear stress (WSS) predicts pathological and biomechanical changes in the aortic wall in TAA. Methods: The study included 12 patients with bicuspid (BAV) and 20 patients with the tricuspid aortic valve (TAV). 4D flow magnetic resonance imaging (MRI) was performed a day before aortic replacement surgery. Biomechanical and histological parameters, including assessing of wall strength, media degeneration, elastin, and cell content were analyzed from the resected AA samples. Results: WSSs were greater in the outer curves of the AA compared to the inner curves in all TAA patients. WSSs correlated with media degeneration of the aortic wall (ρ = -0.48, p < 0.01), elastin content (ρ = 0.47, p < 0.01), and aortic wall strength (ρ = -0.49, p = 0.029). Subsequently, the media of the outer curves was thinner, more rigid, and tolerated lower failure strains. Failure values were shown to correlate with smooth muscle cell (SMC) density (ρ = -0.45, p < 0.02), and indicated the more MYH10+ SMCs the lower the strength of the aortic wall structure. More macrophages were detected in patients with severe media degeneration and the areas with lower WSSs. Conclusion: The findings indicate that MRI-derived WSS predicts pathological and biomechanical changes in the aortic wall in patients with TAA and could be used for identification of high-risk patients.

Effect of MOSFET dosimeters' calibration method on calibration factors and radiation doses measured with the dosimeters in radiology.

MOSFET dosimeters have widely been used to measure radiation doses caused by x-rays. When using the MOSFET dosimeters, calibration factors (CFs) have a direct effect on reliability of dose measurements. The aim of this paper was to study the effect of various calibration methods on the CFs of the MOSFET dosimeters. The CFs were measured on clinical digital x-ray angiography (XA) and computed tomography (CT) devices using a calibrated CT ionization chamber and a standard polymethyl methacrylate (PMMA) phantom. The measurements were conducted by having the dosimeters (1) in air, (2) on the surface of the PMMA phantom and (3) inside the phantom. A statistically significant difference was seen between the CFs measured on the XA and CT devices. The CFs measured on the CT device were 20%-165% higher than those measured with the XA device (p < 0.001) in every calibration geometry. Furthermore, the calibration geometry had a notable effect on the CFs on CT. The CFs on the surface of the phantom were 18%-25% higher than in air (p < 0.05), and the CFs inside the phantom were 32%-39% smaller than in air (p < 0.05). These results suggest that the calibration of the MOSFET dosimeters should be conducted with the same device that is used in actual dose measurements. Also, the scattering conditions and the calibration geometry should be similar in the calibration and subsequent dose measurements.

A dose-neutral image quality comparison of different CBCT and CT systems using paranasal sinus imaging protocols and phantoms.

PURPOSE: To compare the image quality produced by equivalent low-dose and default sinus imaging protocols of a conventional dental cone-beam computed tomography (CBCT) scanner, an extremity CBCT scanner and a clinical multidetector computed tomography (MDCT) scanner. METHODS: Three different phantoms were scanned using dose-neutral ultra-low-dose and low-dose sinus imaging protocols, as well as default sinus protocols of each device. Quantified parameters of image quality included modulation transfer function (MTF) to characterize the spatial response of the imaging system, contrast-to-noise ratio, low contrast visibility, image uniformity and Hounsfield unit accuracy. MTF was calculated using the line spread and edge spread functions (LSF and ESF). RESULTS: The dental CBCT had superior performance over the extremity CBCT in each studied parameter at similar dose levels. The MDCT had better contrast-to-noise ratio, low contrast visibility and image uniformity than the CBCT scanners. However, the CBCT scanners had better resolution compared to the MDCT. Accuracy of HU values for different materials was on the same level between the dental CBCT and MDCT, but substantially poorer performance was observed with the extremity CBCT. CONCLUSIONS: The studied dental CBCT scanner showed superior performance over the studied extremity CBCT scanner when using dose-neutral imaging protocols. In case a dental CBCT is not available, the given extremity CBCT is still a viable option as it provides the benefit of high resolution over a conventional MDCT.

Effect of different thresholds for CT perfusion volumetric analysis on estimated ischemic core and penumbral volumes.

PURPOSE: This single-center study compared three threshold settings for automated analysis of the ischemic core (IC) and penumbral volumes using computed tomographic perfusion, and their accuracy for predicting final infarct volume (FIV) in patients with anterior circulation acute ischemic stroke (AIS). METHODS: Fifty-two consecutive AIS patients undergoing mechanical thrombectomy (November 2015-March 2018) were included. Perfusion images were retrospectively analyzed using a single CT Neuro perfusion application (syngo.via 4.1, Siemens Healthcare GmbH). Three threshold values (S1-S3) were derived from another commercial package (RAPID; iSchema View) (S1), up-to-date syngo.via default values (S2), and adapted values for syngo.via from a reference study (S3). The results were compared with FIV determined by non-contrast CT. RESULTS: The median IC volume (mL) was 24.6 (interquartile range: 13.7-58.1) with S1 and 30.1 (20.1-53.1) with S2/S3. After removing the contralateral hemisphere from the analysis, the median IC volume decreased by 1.33(0-3.14) with S1 versus 9.13 (6.24-14.82) with S2/S3. The median penumbral volume (mL) was 74.52 (49.64-131.91), 77.86 (46.56-99.23), and 173.23 (125.86-200.64) for S1, S2, and S3, respectively. Limiting analysis to the affected hemisphere, the penumbral volume decreased by 1.6 (0.13-9.02), 19.29 (12.59-26.52), and 58.33 mL (45.53-74.84) for S1, S2, and S3, respectively. The correlation between IC and FIV was highest in patients with successful recanalization (n = 34, r = 0.784 for S1; r = 0.797 for S2/S3). CONCLUSION: Optimizing thresholds significantly improves the accuracy of estimated IC and penumbral volumes. Current recommended values produce diversified results. International guidelines based on larger multicenter studies should be established to support the standardization of volumetric analysis in clinical decision-making.

Operator's eye lens dose in computed tomography-guided interventions.

OBJECTIVES: To survey (1) operator's eye lens doses in typical computed tomography (CT)-guided interventions, (2) correlation between dose length product (DLP) and the operator's dose, and (3) different ways for estimating the eye lens dose in clinical settings. METHODS: Doses of 16 radiologists in 164 CT-guided interventional procedures were prospectively measured during a 6-month time period upon radioprotective garments and descriptive statistical outcomes were calculated. The correlations between DLP and measured doses were surveyed. RESULTS: On average, the operator's dose at the eye level (DEL, Hp(0.07)) was 22 µSv per procedure and the personal equivalent dose Hp(10) at the collar level was 21 µSv per procedure. The mean DLP of a procedure was 320 mGy cm, where 54% resulted from the fluoroscopy, the mean exposure time being 18 s. Based on the results, the operator's DEL could be estimated from DLP using the equation DEL (µSv) = 0.10 µSv/mGy cm × patient fluoro DLP (mGycm) (p < 0.001), and the dose at the collar level (DCL) using the equation DCL (µSv) = 0.12 µSv/mGy cm × patient fluoro DLP (mGy cm) (p < 0.001). In addition, DEL (µSv) = 0.7 × DCL (µSv). CONCLUSIONS: The eye lens doses in CT-guided interventions are generally low even without protective equipment, and it is unlikely that the recommended annual equivalent dose limit of 20 mSv for the lens of the eye will be exceeded by conducting CT-guided interventions solely. Eye lens dose can be roughly estimated based on either DLP of the procedure or dose measured at the operator's collar level. KEY POINTS: • Eye lens doses in CT-guided operations are generally low. • It is unlikely that the ICRP recommendation of the yearly equivalent dose limit of 20 mSv will be exceeded by conducting CT-guided interventions solely. • Magnitude of eye lens dose can be estimated based on either DLP of the procedure or dose measured at the operator's collar level.

CONTEMPORARY RADIATION DOSES IN INTERVENTIONAL CARDIOLOGY: A NATIONWIDE STUDY OF PATIENT SKIN DOSES IN FINLAND.

In contemporary interventional cardiology, for typical elderly patients, the most severe radiation-related harm to patients can be considered to come from skin exposures. In this paper, maximum local skin doses in cardiological procedures are explored with Gafchromic film dosimetry. Film and reader calibrations and reading were performed at the Secondary Standards Dosimetry Laboratory of the Radiation and Nuclear Safety Authority (STUK), and data were gathered from seven hospitals in Finland. As alert levels for early transient erythema, 200 Gycm2 kerma area product (KAP) and 2000 mGy air kerma levels for transcatheter aortic valve implantations (TAVI) procedures are proposed. The largest doses were measured in TAVI (4158.8 mGy) and percutaneous coronary interventions (PCI) (941.68 mGy). Accuracies of the GE DoseWatch and Siemens CareMonitor skin dose estimates were reasonable, but more results are needed to reliably assess and validate the tools' capabilities and reliabilities. Uncertainty of the Gafchromic dosimetry was estimated as 9.1% for a calibration with seven data points and 19.3% for a calibration with five data points.

Automated segmentation of cortical and trabecular bone to generate finite element models for femoral bone mechanics.

Finite element (FE) models based on quantitative computed tomography (CT) images are better predictors of bone strength than conventional areal bone mineral density measurements. However, FE models require manual segmentation of the femur, which is not clinically applicable. This study developed a method for automated FE analyses from clinical CT images. Clinical in-vivo CT images of 13 elderly female subjects were collected to evaluate the method. Secondly, proximal cadaver femurs were harvested and imaged with clinical CT (N = 17). Of these femurs, 14 were imaged with µCT and three had earlier been tested experimentally in stance-loading, while collecting surface deformations with digital image correlation. Femurs were segmented from clinical CT images using an automated method, based on the segmentation tool Stradwin. The method automatically distinguishes trabecular and cortical bone, corrects partial volume effect and generates input for FE analysis. The manual and automatic segmentations agreed within about one voxel for in-vivo subjects (0.99 ±â€¯0.23 mm) and cadaver femurs (0.21 ±â€¯0.07 mm). The strains from the FE predictions closely matched with the experimentally measured strains (R2 = 0.89). The method can automatically generate meshes suitable for FE analysis. The method may bring us one step closer to enable clinical usage of patient-specific FE analyses.

CONTEMPORARY RADIATION DOSES IN INTERVENTIONAL CARDIOLOGY: A NATIONWIDE STUDY OF PATIENT DOSES IN FINLAND.

The amount of interventional procedures such as percutaneous coronary intervention (PCI), transcatheter aortic valve implantation (TAVI), pacemaker implantation (PI) and ablations has increased within the previous decade. Simultaneously, novel fluoroscopy mainframes enable lower radiation doses for patients and operators. Therefore, there is a need to update the existing diagnostic reference levels (DRLs) and propose new ones for common or recently introduced procedures. We sought to assess patient radiation doses in interventional cardiology in a large sample from seven hospitals across Finland between 2014 and 2016. Data were used to set updated national DRLs for coronary angiographies (kerma-air product (KAP) 30 Gycm2) and PCIs (KAP 75 cm2), and novel levels for PIs (KAP 3.5 Gycm2), atrial fibrillation ablation procedures (KAP 25 Gycm2) and TAVI (KAP 90 Gycm2). Tentative KAP values were set for implantations of cardiac resynchronization therapy devices (CRT, KAP 22 Gycm2), electrophysiological treatment of atrioventricular nodal re-entry tachycardia (6 Gycm2) and atrial flutter procedures (KAP 16 Gycm2). The values for TAVI and CRT device implantation are published for the first time on national level. Dose from image acquisition (cine) constitutes the major part of the total dose in coronary and atrial fibrillation ablation procedures. For TAVI, patient weight is a good predictor of patient dose.

Imaging of proteoglycan and water contents in human articular cartilage with full-body CT using dual contrast technique.

Assessment of cartilage composition via tomographic imaging is critical after cartilage injury to prevent post-traumatic osteoarthritis. Diffusion of cationic contrast agents in cartilage is affected by proteoglycan loss and elevated water content. These changes have opposite effects on diffusion and, thereby, reduce the diagnostic accuracy of cationic agents. Here, we apply, for the first time, a clinical full-body CT for dual contrast imaging of articular cartilage. We hypothesize that full-body CT can simultaneously determine the diffusion and partitioning of cationic and non-ionic contrast agents and that normalization of the cationic agent partition with that of the non-ionic agent minimizes the effect of water content and tissue permeability, especially at early diffusion time points. Cylindrical (d = 8 mm) human osteochondral samples (n = 45; four cadavers) of a variable degenerative state were immersed in a mixture of cationic iodinated CA4+ and non-charged gadoteridol contrast agents and imaged with a full-body CT scanner at various time points. Determination of contrast agents' distributions within cartilage was possible at all phases of diffusion. At early time points, gadoteridol, and CA4+ distributed throughout cartilage with lower concentrations in the deep cartilage. At ≥24 h, the gadoteridol concentration remained nearly constant, while the CA4+ concentration increased toward deep cartilage. Normalization of the CA4+ partition with that of gadoteridol significantly (p < 0.05) enhanced correlation with proteoglycan content and Mankin score at the early time points. To conclude, the dual contrast technique was found advantageous over single contrast imaging enabling more sensitive diagnosis of cartilage degeneration. © 2019 The Authors. Journal of Orthopaedic Research Published by Wiley Periodicals, Inc. J Orthop Res 9999:1-12, 2019.

Cochlear Implantation With a Novel Long Straight Electrode: the Insertion Results Evaluated by Imaging and Histology in Human Temporal Bones.

HYPOTHESIS: To evaluate the insertion results of a novel straight array (EVO) by detailed imaging and subsequent histology in human temporal bones (TB). BACKGROUND: The main focuses of modern cochlear implant surgery are to prevent damage to the intracochlear structures and to preserve residual hearing. This is often achievable with new atraumatic electrode arrays in combination with meticulous surgical techniques. METHODS: Twenty fresh-frozen TBs were implanted with the EVO. Pre- and postoperative cone beam computed tomography scans were reconstructed and fused for an artifact-free representation of the electrode. The array's vertical position was quantified in relation to the basilar membrane on basis of which trauma was classified (Grades 0-4). The basilar membrane location was modeled from previous histologic data. The TBs underwent subsequent histologic examination. RESULTS: The EVOs were successfully inserted in all TBs. Atraumatic insertion (Grades 0-1) were accomplished in 14 of 20 TBs (70%). There were three apical translocations, and two basal translocations due to electrode bulging. One TB had multiple translocations. The sensitivity and specificity of imaging for detecting insertion trauma (Grades 2-4) was 87.5% and 97.3.0%, respectively. CONCLUSION: Comparable insertion results as reported for other arrays were also found for the EVO. Insertion trauma can be mostly avoided with meticulous insertion techniques to prevent bulging and by limiting the insertion depth angle to 360 degrees. The image fusion technique is a reliable tool for evaluating electrode placement and is feasible for trauma grading.

A New Slim Modiolar Electrode Array for Cochlear Implantation: A Radiological and Histological Study.

HYPOTHESIS: To explore the results of a new slim modiolar electrode array (SMA) with respect to intracochlear placement and trauma evaluated by detailed radiologic imaging and histology. BACKGROUND: Hearing and structure preservation is the goal of cochlear implantation for advanced hearing outcomes. Currently, this is most consistently achieved with thin lateral wall electrodes. Modiolar electrodes are located nearer the modiolus and may provide some electrophysiological advantages, but have a greater tendency for causing insertion trauma. METHODS: The SMA was implanted in 20 fresh-frozen human temporal bones (TB). All TBs were scanned pre- and postoperatively with cone beam computed tomography. For atraumatic insertion, the round window approach was preferred. Scalar localization and trauma were analyzed by three-dimensional image fusion reconstructions of the pre- and postimplant scans. The TBs underwent histologic examination to validate the radiologic findings. RESULTS: Insertion through the round window was performed in 19 TBs and through a cochleostomy in one TB. In one TB trauma in the form of scala translocation was identified radiologically and histologically. In the remaining TBs there was no insertion trauma. Adequate modiolar localization of the SMA was found in 19 of 20 TBs. The mean angular insertion depth was 400 degrees without correlation to cochlea size. There was no significant statistical difference between the radiological and histological measurements of electrode localization. CONCLUSION: The SMA showed consistent and atraumatic insertion results in TBs. Pre- and postimplant cone beam computed tomography with image fusion was shown to be very accurate for the assessment of electrode position and insertion trauma.

Comprehensive MR Urography Protocol: Equally Good Diagnostic Performance and Enhanced Visibility of the Upper Urinary Tract Compared to Triple-Phase CT Urography.

OBJECTIVES: To prospectively compare the diagnostic performance and the visualization of the upper urinary tract (UUT) using a comprehensive 3.0T- magnetic resonance urography (MRU) protocol versus triple-phase computed tomography urography (CTU). METHODS: During the study period (January-2014 through December-2015), all consecutive patients in our tertiary university hospital scheduled by a urologist for CTU to exclude UUT malignancy were invited to participate. Diagnostic performance and visualization scores of 3.0T-MRU were compared to CTU using Wilcoxon matched-pairs test. RESULTS: Twenty patients (39 UUT excreting units) were evaluated. 3.0T-MRU and CTU achieved equal diagnostic performances. The benign etiology of seven UUT obstructions was clarified equally with both methods. Another two urinary tract malignant tumors and one benign extraurinary tumor were detected and confirmed. Diagnostic visualization was slightly better in the intrarenal cavity areas with CTU but worsened towards distal ureter. MRU showed consistently slightly better visualization of the ureter. In the comparison, full 100% visualizations were detected in all areas in 93.6% (with 3.0T-MRU) and 87.2% (with CTU) and >75% visualization in 100% (3.0T-MRU) and 93.6% (CTU). Mean CTU effective radiation dose was 9.2 mSv. CONCLUSIONS: Comprehensive 3.0T-MRU is an accurate imaging modality achieving comparable performance with CTU; since it does not entail exposure to radiation, it has the potential to become the primary investigation technique in selected patients. TRIAL REGISTRATION: ClinicalTrials.gov NCT02606513.