ToScA North America (6 – 8 June 2017, The University of Texas, Austin, TX) Program

ToScA North America will address key areas of science, including Multi-modal Imaging, Geosciences, Forensics, Increasing Contrast, Educational Outreach, Data, Materials Science and Medical and Biological Science.University of Texas High-Resolution X-ray CT Facility (UTCT); Jackson School of Geosciences, The University of Texas at Austin; Natural History Museum (London); Royal Microscopical Society (Oxford, UK)Geological Science

Technical Note: Phantom study to evaluate the dose and image quality effects of a computed tomography Organ-based Tube Current Modulation Technique

Purpose This technical note quantifies the dose and image quality performance of a clinically available organ-dose-based tube current modulation (ODM) technique, using experimental and simulation phantom studies. The investigated ODM implementation reduces the tube current for the anterior source positions, without increasing current for posterior positions, although such an approach was also evaluated for comparison. Methods Axial CT scans at 120 kV were performed on head and chest phantoms on an ODM-equipped scanner (Optima CT660, GE Healthcare, Chalfont St. Giles, England). Dosimeters quantified dose to breast, lung, heart, spine, eye lens, and brain regions for ODM and 3D-modulation (SmartmA) settings. Monte Carlo simulations, validated with experimental data, were performed on 28 voxelized head phantoms and 10 chest phantoms to quantify organ dose and noise standard deviation. The dose and noise effects of increasing the posterior tube current were also investigated. Results ODM reduced the dose for all experimental dosimeters with respect to SmartmA, with average dose reductions across dosimeters of 31% (breast), 21% (lung), 24% (heart), 6% (spine), 19% (eye lens), and 11% (brain), with similar results for the simulation validation study. In the phantom library study, the average dose reduction across all phantoms was 34% (breast), 20% (lung), 8% (spine), 20% (eye lens), and 8% (brain). ODM increased the noise standard deviation in reconstructed images by 6%–20%, with generally greater noise increases in anterior regions. Increasing the posterior tube current provided similar dose reduction as ODM for breast and eye lens, increased dose to the spine, with noise effects ranging from 2% noise reduction to 16% noise increase. At noise equal to SmartmA, ODM increased the estimated effective dose by 4% and 8% for chest and head scans, respectively. Increasing the posterior tube current further increased the effective dose by 15% (chest) and 18% (head) relative to SmartmA. Conclusions ODM reduced dose in all experimental and simulation studies over a range of phantoms, while increasing noise. The results suggest a net dose/noise benefit for breast and eye lens for all studied phantoms, negligible lung dose effects for two phantoms, increased lung dose and/or noise for eight phantoms, and increased dose and/or noise for brain and spine for all studied phantoms compared to the reference protocol

Quantitative Computed Tomography Based Finite Element Modeling of Normal and Osteoarthritic Knees: In vivo Precision and Preliminary Comparisons

Osteoarthritis (OA) is a debilitating joint disease which affects nearly 85% of the Canadian population over 75 years of age. OA not only affects cartilage, but it also alters subchondral bone (bone underlying cartilage). Altered subchondral bone could be related to OA initiation, progression, and OA-related pain. To help clarify the role of subchondral bone in OA, accurate in vivo methods are needed to monitor subchondral bone mechanical property variations in people living with OA. Subject-specific finite element (FE) modeling has potential to investigate the role of mechanical properties of subchondral bone in OA. However, associated precision errors of FE-derived mechanical properties are not known. The objectives of this study were to 1) develop a subject-specific FE modeling methodology for OA and normal knees, 2) determine the in vivo precision of FE-derived stress/strain distributions and stiffness of the proximal tibia, and 3) determine whether FE-derived metrics discriminate normal and OA knees. Subject-specific FE models were developed for 14 participants (7 OA, 7 normal) with three repeated CT images of knee joint. Von-Mises stress and strain, minimum principal stress and strain, plus structural stiffness outcomes were acquired for each proximal tibia image. Root mean square coefficient of variations (CV%) were used to assess in vivo precision of the FE-based outcomes. Comparisons between OA and normal groups were performed using unpaired t-tests for normally distributed outcomes, and Mann-Whitney U-tests for not normally distributed outcomes. For all the outcomes the average CV% was less than 6.1%. On average, von-Mises stress and minimum principal stress were respectively 65% and 70% higher in OA versus normal knees whereas strain values did not differ. No difference was observed in stiffness values. Thesis results indicate that FE modeling could be used to precisely quantify and differentiate mechanical property variations in normal and OA knees, in vivo. Results suggest that OA and normal bone exhibit dissimilar stress levels but similar strain levels, likely indicating adaptation of bone in response to altered joint mechanics with OA

2D-3D reconstruction of the proximal femur from DXA scans: Evaluation of the 3D-Shaper software.

Introduction: Osteoporosis is currently diagnosed based on areal bone mineral density (aBMD) computed from 2D DXA scans. However, aBMD is a limited surrogate for femoral strength since it does not account for 3D bone geometry and density distribution. QCT scans combined with finite element (FE) analysis can deliver improved femoral strength predictions. However, non-negligible radiation dose and high costs prevent a systematic usage of this technique for screening purposes. As an alternative, the 3D-Shaper software (3D-Shaper Medical, Spain) reconstructs the 3D shape and density distribution of the femur from 2D DXA scans. This approach could deliver a more accurate estimation of femoral strength than aBMD by using FE analysis on the reconstructed 3D DXA. Methods: Here we present the first independent evaluation of the software, using a dataset of 77 ex vivo femora. We extend a prior evaluation by including the density distribution differences, the spatial correlation of density values and an FE analysis. Yet, cortical thickness is left out of this evaluation, since the cortex is not resolved in our FE models. Results: We found an average surface distance of 1.16 mm between 3D DXA and QCT images, which shows a good reconstruction of the bone geometry. Although BMD values obtained from 3D DXA and QCT correlated well (r 2 = 0.92), the 3D DXA BMD were systematically lower. The average BMD difference amounted to 64 mg/cm3, more than one-third of the 3D DXA BMD. Furthermore, the low correlation (r 2 = 0.48) between density values of both images indicates a limited reconstruction of the 3D density distribution. FE results were in good agreement between QCT and 3D DXA images, with a high coefficient of determination (r 2 = 0.88). However, this correlation was not statistically different from a direct prediction by aBMD. Moreover, we found differences in the fracture patterns between the two image types. QCT-based FE analysis resulted mostly in femoral neck fractures and 3D DXA-based FE in subcapital or pertrochanteric fractures. Discussion: In conclusion, 3D-Shaper generates an altered BMD distribution compared to QCT but, after careful density calibration, shows an interesting potential for deriving a standardized femoral strength from a DXA scan

Uncertainties analysis of Digital Volume Correlation measurements for synchrotron-based tomographic images of bone

La valutazione dell'eterogeneità delle deformazioni all'interno del tessuto osseo è importante per stabilire l'effetto delle patologie e degli interventi che riguardano il sistema scheletrico, così come per validare modelli computazionali. La Digital Volume Correlation (DVC) ha dimostrato essere una tecnica potente per misurare il campo di spostamento e deformazione all'interno dell’osso. Recenti studi hanno mostrato come la micro tomografia computerizzata a radiazione di sincrotrone (SR-microCT) può migliorare l'accuratezza della DVC. Tuttavia, in quei lavori, solamente test su scansioni ripetute (zero-strain) o spostamenti virtuali sono stati utilizzati per quantificare le incertezze della DVC, portando ad una potenziale sottostima degli errori. In questo studio, per la prima volta, le incertezze di un approccio DVC globale sono state valutate su immagini ripetute e virtualmente deformate per tenere conto sia del rumore dell'immagine che della deformazione applicata. A partire da scansioni SR-microCT di provini di osso corticale bovino, con una risoluzione nominale di 1.6 μm, sono stati simulati diversi livelli e direzioni di deformazione. Successivamente, con un software di registrazione dell’Università di Sheffield (Sheffield Image Registration Toolkit, ShIRT), combinato con un pacchetto software ad elementi finiti, sono stati calcolati i campi di deformazione. La quantificazione e la distribuzione degli errori è stata effettuata per ogni componente di deformazione. I risultati provenienti da questo lavoro di tesi hanno permesso di integrare gli studi precedenti e di ampliare le conoscenze sull'utilizzo di questa tecnica. Rimangono da testare campi di deformazione più eterogenei, come per esempio quelli provenienti da modelli agli elementi finiti, per completare la valutazione delle incertezze associate alle misure della DVC

Validation of Subject Specific Computed Tomography-based Finite Element Models of the Human Proximal Tibia using Full-field Experimental Displacement Measurements from Digital Volume Correlation

Quantitative computed tomography-based finite element (QCT-FE) modeling is a computational tool for predicting bone’s response to applied load, and is used by musculoskeletal researchers to better understand bone mechanics and their role in joint health. Decisions made at the modeling stage, such as the method for assigning material properties, can dictate model accuracy. Predictions of surface strains/stiffness from QCT-FE models of the proximal tibia have been validated against experiment, yet it is unclear whether these models accurately predict internal bone mechanics (displacement). Digital volume correlation (DVC) can measure internal bone displacements and has been used to validate FE models of bone; though, its use has been limited to small specimens. The objectives of this study were to 1) establish a methodology for high-resolution peripheral QCT (HR-pQCT) scan acquisition and image processing resulting in low DVC displacement measurement error in long human bones, and 2) apply different density-modulus relationships and material models from the literature to QCT-FE models of the proximal tibia and identify those approaches which best predicted experimentally measured internal bone displacements and related external reaction forces, with highest explained variance and least error. Using a modified protocol for HR-pQCT, DVC displacement errors for large scan volumes were less than 19μm (0.5 voxels). Specific trabecular and cortical models from the literature were identified which resulted in the most accurate QCT-FE predictions of internal displacements (RMSE%=3.9%, R2>0.98) and reaction forces (RMSE%=12.2%, R2=0.78). This study is the first study to quantify experimental displacements inside a long human bone using DVC. It is also the first study to assess the accuracy of QCT-FE predicted internal displacements in the tibia. Our results indicate that QCT-FE models of the tibia offer reasonably accurate predictions of internal bone displacements and reaction forces for use in studying bone mechanics and joint health

Three-dimensional-printed patient-specific instrumentation is an accurate tool to reproduce femoral bone tunnels in multiple-ligament knee injuries

Altres ajuts: acords transformatius de la UABMultiple-ligament knee reconstruction techniques often involve the creation of several bone tunnels for various reconstruction grafts. A critical step in this procedure is to avoid short tunnels or convergences among them. Currently, no specific template guide to reproduce these angulations has been reported in the literature, and the success of the technique still depends on the experience of the surgeon. The aim of this study is to analyze the accuracy and reliability of 3D-printed patient-specific instrumentation (PSI) for lateral and medial anatomical knee reconstructions. Ten cadaveric knees were scanned by computed tomography (CT). Using specific computer software, anatomical femoral attachments were identified: (1) on the lateral side the lateral collateral ligament (LCL) and the popliteal tendon (PT) and (2) on the medial side the medial collateral ligament (MCL) and the posterior oblique ligament (POL). Four bone tunnels were planned for each knee, and PSI with different directions were designed as templates to reproduce the planned tunnels during surgery. Twenty 3D-printed PSI were used: ten were tailored to the medial side for reconstructing MCL and POL tunnels, and the other ten were tailored to the lateral side for reconstructing LCL and PT tunnels. Postoperative CT scans were made for each cadaveric knee. The accuracy of the use of 3D-printed PSI was assessed by superimposing post-operative CT images onto pre-operative images and analyzing the deviation of tunnels performed based on the planning, specifically the entry point and the angular deviations. The median entry point deviations for the tunnels were as follows: LCL tunnel, 1.88 mm (interquartile range (IQR) 2.2 mm); PT tunnel, 2.93 mm (IQR 1.17 mm); MCL tunnel, 1.93 mm (IQR 4.26 mm); and POL tunnel, 2.16 mm (IQR 2.39). The median angular deviations for the tunnels were as follows: LCL tunnel, 2.42° (IQR 6.49°); PT tunnel, 4.15° (IQR 6.68); MCL tunnel, 4.50° (IQR 6.34°); and POL tunnel, 4.69° (IQR 3.1°). No statistically significant differences were found in either the entry point or the angular deviation among the different bone tunnels. The use of 3D-printed PSI for lateral and medial anatomical knee reconstructions provides accurate and reproducible results and may be a promising tool for use in clinical practice