Regional trabecular bone quality estimation for purposes of femoral bone strength prediction is important for improving the clinical assessment of osteoporotic fracture risk. In this study, we explore the ability of 3D Minkowski Functionals derived from multi-detector computed tomography (MDCT) images of proximal femur specimens in predicting their corresponding biomechanical strength. MDCT scans were acquired for 50 proximal femur specimens harvested from human cadavers. An automated volume of interest (VOI)-fitting algorithm was used to define a consistent volume in the femoral head of each specimen. In these VOIs, the trabecular bone micro-architecture was characterized by statistical moments of its BMD distribution and by topological features derived from Minkowski Functionals. A linear multiregression analysis and a support vector regression (SVR) algorithm with a linear kernel were used to predict the failure load (FL) from the feature sets; the predicted FL was compared to the true FL determined through biomechanical testing. The prediction performance was measured by the root mean square error (RMSE) for each feature set. The best prediction result was obtained from the Minkowski Functional surface used in combination with SVR, which had the lowest prediction error (RMSE = 0.939 ± 0.345) and which was significantly lower than mean BMD (RMSE = 1.075 ± 0.279, p<0.005). Our results indicate that the biomechanical strength prediction can be significantly improved in proximal femur specimens with Minkowski Functionals extracted from on MDCT images used in conjunction with support vector regression.
Breast conserving therapy (BCT) of breast cancer is now widely accepted due to improved cosmetic outcome and improved patients’ quality of life. One of the critical issues in performing breast-conserving surgery is trying to achieve microscopically clear surgical margins while maintaining excellent cosmesis. Unfortunately, unacceptably close or positive surgical margins occur in at least 20-25% of all patients undergoing BCT requiring repeat surgical excision days or weeks later, as permanent histopathology routinely takes days to complete. Our aim is to develop a better method for intraoperative imaging of non-palpable breast malignancies excised by wire or needle localization. Providing non-deformed three dimensional imaging of the excised breast tissue should allow more accurate assessment of tumor margins and consequently allow further excision at the time of initial surgery thus limiting the enormous financial and emotional burden of additional surgery. We have designed and constructed a device that allows preservation of the excised breast tissue in its natural anatomic position relative to the breast as it is imaged to assess adequate excision. We performed initial tests with needle-guided lumpectomy specimens using micro-CT and digital breast tomosynthesis (DBT). Our device consists of a plastic sphere inside a cylindrical holder. The surgeon inserts a freshly excised piece of breast tissue into the sphere and matches its anatomic orientation with the fiducial markers on the sphere. A custom-shaped foam is placed inside the sphere to prevent specimen deformation due to gravity. DBT followed by micro-CT images of the specimen were obtained. We confirmed that our device preserved spatial orientation of the excised breast tissue and that the location error was lower than 10mm and 10 degrees. The initial obtained results indicate that breast lesions containing microcalcifications allow a good 3D imaging of margins providing immediate intraoperative feedback for further excision as needed at the initial operation.
We investigate the use of different trabecular bone descriptors and advanced machine learning techniques to complement standard bone mineral density (BMD) measures derived from dual-energy x-ray absorptiometry (DXA) for improving clinical assessment of osteoporotic fracture risk. For this purpose, volumes of interest were extracted from the head, neck, and trochanter of 146 ex vivo proximal femur specimens on multidetector computer tomography. The trabecular bone captured was characterized with (1) statistical moments of the BMD distribution, (2) geometrical features derived from the scaling index method (SIM), and (3) morphometric parameters, such as bone fraction, trabecular thickness, etc. Feature sets comprising DXA BMD and such supplemental features were used to predict the failure load (FL) of the specimens, previously determined through biomechanical testing, with multiregression and support vector regression. Prediction performance was measured by the root mean square error (RMSE); correlation with measured FL was evaluated using the coefficient of determination R 2 . The best prediction performance was achieved by a combination of DXA BMD and SIM-derived geometric features derived from the femoral head (RMSE: 0.869±0.121 , R 2 : 0.68±0.079 ), which was significantly better than DXA BMD alone (RMSE: 0.948±0.119 , R 2 : 0.61±0.101 ) (p<10 −4 ). For multivariate feature sets, SVR outperformed multiregression (p<0.05 ). These results suggest that supplementing standard DXA BMD measurements with sophisticated femoral trabecular bone characterization and supervised learning techniques can significantly improve biomechanical strength prediction in proximal femur specimens.
Estimating local trabecular bone quality for purposes of femoral bone strength prediction is important for improving
the clinical assessment of osteoporotic hip fracture risk. In this study, we explore the ability of geometric features
derived from the Scaling Index Method (SIM) in predicting the biomechanical strength of proximal femur specimens
as visualized on multi-detector computed tomography (MDCT) images. MDCT scans were acquired for 50 proximal
femur specimens harvested from human cadavers. An automated volume of interest (VOI)-fitting algorithm was
used to define a consistent volume in the femoral head of each specimen. In these VOIs, the non-linear micro-structure of the trabecular bone was characterized by statistical moments of its BMD distribution and by local scaling properties derived from SIM. Linear multi-regression analysis and support vector regression with a linear kernel (SVRlin) were used to predict the failure load (FL) from the feature sets; the predicted FL was compared to the FL values determined through biomechanical testing. The prediction performance was measured by the root mean square error (RMSE) for each image feature on independent test set. The best prediction result was obtained from the SIM feature set with SVRlin, which had the lowest prediction error (RMSE = 0.842 ± 0.209) and which
was significantly lower than the conventionally used mean BMD (RMSE = 1.103 ± 0.262, , p<0.005). Our results indicate that the biomechanical strength prediction can be significantly improved in proximal femur specimens on MDCT images by using high-dimensional geometric features derived from SIM with support vector regression.
The current approach to evaluating cartilage degeneration at the knee joint requires visualization of the joint space on
radiographic images where indirect cues such as joint space narrowing serve as markers for osteoarthritis. A recent novel
approach to visualizing the knee cartilage matrix using phase contrast CT imaging (PCI-CT) was shown to allow direct
examination of chondrocyte cell patterns and their subsequent correlation to osteoarthritis. This study aims to
characterize chondrocyte cell patterns in the radial zone of the knee cartilage matrix in the presence and absence of
osteoarthritic damage through both gray-level co-occurrence matrix (GLCM) derived texture features as well as
Minkowski Functionals (MF). Thirteen GLCM and three MF texture features were extracted from 404 regions of interest
(ROI) annotated on PCI images of healthy and osteoarthritic specimens of knee cartilage. These texture features were
then used in a machine learning task to classify ROIs as healthy or osteoarthritic. A fuzzy k-nearest neighbor classifier
was used and its performance was evaluated using the area under the ROC curve (AUC). The best classification
performance was observed with the MF features 'perimeter' and 'Euler characteristic' and with GLCM correlation
features (f3 and f13). With the experimental conditions used in this study, both Minkowski Functionals and GLCM
achieved a high classification performance (AUC value of 0.97) in the task of distinguishing between health and
osteoarthritic ROIs. These results show that such quantitative analysis of chondrocyte patterns in the knee cartilage
matrix can distinguish between healthy and osteoarthritic tissue with high accuracy.
To improve the clinical assessment of osteoporotic hip fracture risk, recent computer-aided diagnosis systems
explore new approaches to estimate the local trabecular bone quality beyond bone density alone to predict femoral
bone strength. In this context, statistical bone mineral density (BMD) features extracted from multi-detector
computed tomography (MDCT) images of proximal femur specimens and different function approximations
methods were compared in their ability to predict the biomechanical strength. MDCT scans were acquired in
146 proximal femur specimens harvested from human cadavers. The femurs' failure load (FL) was determined
through biomechanical testing. An automated volume of interest (VOI)-fitting algorithm was used to define a
consistent volume in the femoral head of each specimen. In these VOIs, the trabecular bone was represented
by statistical moments of the BMD distribution and by pairwise spatial occurrence of BMD values using the
gray-level co-occurrence (GLCM) approach. A linear multi-regression analysis (MultiReg) and a support vector
regression algorithm with a linear kernel (SVRlin) were used to predict the FL from the image feature sets.
The prediction performance was measured by the root mean square error (RMSE) for each image feature on
independent test sets; in addition the coefficient of determination R2 was calculated. The best prediction
result was obtained with a GLCM feature set using SVRlin, which had the lowest prediction error (RSME =
1.040±0.143, R2 = 0.544) and which was significantly lower that the standard approach of using BMD.mean and
MultiReg (RSME = 1.093±0.133, R2 = 0.490, p<0.0001). The combined sets including BMD.mean and GLCM
features had a similar or slightly lower performance than using only GLCM features. The results indicate that the
performance of high-dimensional BMD features extracted from MDCT images in predicting the biomechanical
strength of proximal femur specimens can be significantly improved by using support vector regression.
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