Phase contrast X-ray computed tomography (PCI-CT) has recently emerged as a novel imaging technique that allows visualization of cartilage soft tissue, subsequent examination of chondrocyte patterns, and their correlation to osteoarthritis. Previous studies have shown that 2D texture features are effective at distinguishing between healthy and osteoarthritic regions of interest annotated in the radial zone of cartilage matrix on PCI-CT images. In this study, we further extend the texture analysis to 3D and investigate the ability of volumetric texture features at characterizing chondrocyte patterns in the cartilage matrix for purposes of classification. Here, we extracted volumetric texture features derived from Minkowski Functionals and gray-level co-occurrence matrices (GLCM) from 496 volumes of interest (VOI) annotated on PCI-CT images of human patellar cartilage specimens. The extracted features were then used in a machine-learning task involving support vector regression to classify ROIs as healthy or osteoarthritic. Classification performance was evaluated using the area under the receiver operating characteristic (ROC) curve (AUC). The best classification performance was observed with GLCM features correlation (AUC = 0.83 ± 0.06) and homogeneity (AUC = 0.82 ± 0.07), which significantly outperformed all Minkowski Functionals (p < 0.05). These results suggest that such quantitative analysis of chondrocyte patterns in human patellar cartilage matrix involving GLCM-derived statistical features can distinguish between healthy and osteoarthritic tissue with high accuracy.
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.
Current assessment of cartilage is primarily based on identification of indirect markers such as joint space narrowing and increased subchondral bone density on x-ray images. In this context, phase contrast CT imaging (PCI-CT) has recently emerged as a novel imaging technique that allows a direct examination of chondrocyte patterns and their correlation to osteoarthritis through visualization of cartilage soft tissue. This study investigates the use of topological and geometrical approaches for characterizing chondrocyte patterns in the radial zone of the knee cartilage matrix in the presence and absence of osteoarthritic damage. For this purpose, topological features derived from Minkowski Functionals and geometric features derived from the Scaling Index Method (SIM) were extracted from 842 regions of interest (ROI) annotated on PCI-CT images of healthy and osteoarthritic specimens of human patellar cartilage. The extracted features were then used in a machine learning task involving support vector regression to classify ROIs as healthy or osteoarthritic. Classification performance was evaluated using the area under the receiver operating characteristic (ROC) curve (AUC). The best classification performance was observed with high-dimensional geometrical feature vectors derived from SIM (0.95 ± 0.06) which outperformed all Minkowski Functionals (p < 0.001). These results suggest that such quantitative analysis of chondrocyte patterns in human patellar cartilage matrix involving SIM-derived geometrical features can distinguish between healthy and osteoarthritic tissue with high accuracy.
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 imaging (PCI) with computed tomography (CT) was shown to allow direct examination of chondrocyte 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 texture analysis. Statistical features derived from gray-level co-occurrence matrices (GLCM) and geometric features derived from the Scaling Index Method (SIM) 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 Receiver Operating Characteristic (ROC) curve (AUC). The best classification performance was observed with high-dimensional
geometrical feature vectors derived from SIM and GLCM correlation features. With the experimental conditions used in
this study, both SIM and GLCM achieved a high classification performance (AUC value of 0.98) in the task of distinguishing between healthy 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.
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.
The tumor extracellular matrix has been focused on by newer approaches to cancer therapy owing to its important
functions in the process of drug delivery and cellular metastasis. This study aims to characterize tumor extracellular
matrix structures in the presence and absence of therapy, as observed on second harmonic generation (SHG) images
through both gray-level co-occurrence matrix (GLCM) derived texture features as well as Minkowski Functionals (MF)
that focus on the underlying gray-level topology and geometry of the texture patterns. Thirteen GLCM texture features
and three MF texture features were extracted from 119 regions of interest (ROI) annotated on SHG images of treated and
control samples of tumor extracellular matrix. These texture features were then used in a machine learning task to
classify ROIs as belonging to treated or control samples. A fuzzy k-nearest neighbor classifier was optimized using
random sub-sampling cross-validation for each texture feature and the classification performance was calculated on an
independent test set using the area under the ROC curve (AUC); AUC distributions of different features were compared
using a Mann-Whitney U-test. Two GLCM features f3 and f13 exhibited a significantly higher classification
performance when compared to other GLCM features (p < 0.05). The MF feature Area exhibited the best classification
performance among the MF features while also being comparable to that obtained with the best GLCM features. These
results show that both statistical and topological texture features can be used as quantitative measures is evaluating the
effects of therapy on the tumor extracellular matrix.
Local scaling properties of texture regions were compared in their ability to classify morphological patterns
known as 'honeycombing' that are considered indicative for the presence of fibrotic interstitial lung diseases
in high-resolution computed tomography (HRCT) images. For 14 patients with known occurrence of honeycombing,
a stack of 70 axial, lung kernel reconstructed images were acquired from HRCT chest exams. 241
regions of interest of both healthy and pathological (89) lung tissue were identified by an experienced radiologist.
Texture features were extracted using six properties calculated from gray-level co-occurrence matrices (GLCM),
Minkowski Dimensions (MDs), and the estimation of local scaling properties with Scaling Index Method (SIM).
A k-nearest-neighbor (k-NN) classifier and a Multilayer Radial Basis Functions Network (RBFN) were optimized
in a 10-fold cross-validation for each texture vector, and the classification accuracy was calculated on independent
test sets as a quantitative measure of automated tissue characterization. A Wilcoxon signed-rank test was used
to compare two accuracy distributions including the Bonferroni correction. The best classification results were
obtained by the set of SIM features, which performed significantly better than all the standard GLCM and
MD features (p < 0.005) for both classifiers with the highest accuracy (94.1%, 93.7%; for the k-NN and RBFN
classifier, respectively). The best standard texture features were the GLCM features 'homogeneity' (91.8%,
87.2%) and 'absolute value' (90.2%, 88.5%). The results indicate that advanced texture features using local
scaling properties can provide superior classification performance in computer-assisted diagnosis of interstitial
lung diseases when compared to standard texture analysis methods.
Morphological characterization of lesions on dynamic breast MRI exams through texture analysis has typically involved
the computation of gray-level co-occurrence matrices (GLCM), which serve as the basis for second order statistical
texture features. This study aims to characterize lesion morphology through the underlying topology and geometry with
Minkowski Functionals (MF) and investigate the impact of using such texture features extracted dynamically over a time
series in classifying benign and malignant lesions. 60 lesions (28 malignant & 32 benign) were identified and annotated
by experienced radiologists on 54 breast MRI exams of female patients where histopathological reports were available
prior to this investigation. 13 GLCM-derived texture features and 3 MF features were then extracted from lesion ROIs
on all five post-contrast images. These texture features were combined into high dimensional texture feature vectors and
used in a lesion classification task. A fuzzy k-nearest neighbor classifier was optimized using random sub-sampling
cross-validation for each texture feature and the classification performance was calculated on an independent test set
using the area under the ROC curve (AUC); AUC distributions of different features were compared using a Mann-
Whitney U-test. The MF feature 'Area' exhibited significantly improvements in classification performance (p<0.05)
when compared to all GLCM-derived features while the MF feature 'Perimeter' significantly outperformed 12 out of 13
GLCM features (p<0.05) in the lesion classification task. These results show that dynamic texture tracking of
morphological characterization that relies on topological texture features can contribute to better lesion character
classification.
The Generalized Matrix Learning Vector Quantization (GMLVQ) is used to estimate the relevance of texture
features in their ability to classify interstitial lung disease patterns in high-resolution computed tomography
(HRCT) images. After a stochastic gradient descent, the GMLVQ algorithm provides a discriminative distance
measure of relevance factors, which can account for pairwise correlations between different texture features and
their importance for the classification of healthy and diseased patterns. Texture features were extracted from
gray-level co-occurrence matrices (GLCMs), and were ranked and selected according to their relevance obtained
by GMLVQ and, for comparison, to a mutual information (MI) criteria. A k-nearest-neighbor (kNN) classifier
and a Support Vector Machine with a radial basis function kernel (SVMrbf) were optimized in a 10-fold crossvalidation
for different texture feature sets. In our experiment with real-world data, the feature sets selected by
the GMLVQ approach had a significantly better classification performance compared with feature sets selected
by a MI ranking.
Haralick texture features derived from gray-level co-occurrence matrices (GLCM) were used to classify the character of
suspicious breast lesions as benign or malignant on dynamic contrast-enhanced MRI studies. Lesions were identified and
annotated by an experienced radiologist on 54 MRI exams of female patients where histopathological reports were
available prior to this investigation. GLCMs were then extracted from these 2D regions of interest (ROI) for four
principal directions (0°, 45°, 90° & 135°) and used to compute Haralick texture features. A fuzzy k-nearest neighbor (k-
NN) classifier was optimized in ten-fold cross-validation for each texture feature and the classification performance was
calculated on an independent test set as a function of area under the ROC curve. The lesion ROIs were characterized by
texture feature vectors containing the Haralick feature values computed from each directional-GLCM; and the classifier
results obtained were compared to a previously used approach where the directional-GLCMs were summed to a nondirectional
GLCM which could further yield a set of texture feature values. The impact of varying the inter-pixel
distance while generating the GLCMs on the classifier's performance was also investigated. Classifier's AUC was found
to significantly increase when the high-dimensional texture feature vector approach was pursued, and when features
derived from GLCMs generated using different inter-pixel distances were incorporated into the classification task. These
results indicate that lesion character classification accuracy could be improved by retaining the texture features derived
from the different directional GLCMs rather than combining these to yield a set of scalar feature values instead.
Trabecular bone parameters extracted from magnetic resonance (MR) images are compared in their ability to
predict biomechanical properties determined through mechanical testing. Trabecular bone density and structural
changes throughout the proximal tibia are indicative of several musculoskeletal disorders of the knee joint involving
changes in the bone quality and the surrounding soft tissue. Recent studies have shown that MR imaging,
most frequently applied in soft tissue imaging, also allows non-invasive 3-dimensional characterization of bone
microstructure. Sophisticated MR image features that estimate local structural and geometric properties of the
trabecular bone may improve the ability of MR imaging to determine local bone quality in vivo. The purpose
of the current study is to use whole joint MR images to compare the performance of trabecular bone features
extracted from the images in predicting biomechanical strength properties measured on the corresponding ex
vivo specimens. The regional apparent bone volume fraction (appBVF) and scaling index method (SIM) derived
features were calculated; a Multilayer Radial Basis Functions Network was then optimized to calculate the prediction
accuracy as measured by the root mean square error (RSME) for each bone feature. The best prediction
result was obtained with a SIM feature with the lowest prediction error (RSME=0.246) and the highest coefficient
of determination (R2 = 0.769). The current study demonstrates that the combination of sophisticated
bone structure features and supervised learning techniques can improve MR imaging as an in vivo imaging tool
in determining local trabecular bone quality.
Topological texture features were compared in their ability to classify morphological patterns known as 'honeycombing'
that are considered indicative for the presence of fibrotic interstitial lung diseases in high-resolution
computed tomography (HRCT) images. For 14 patients with known occurrence of honey-combing, a stack of 70
axial, lung kernel reconstructed images were acquired from HRCT chest exams. A set of 241 regions of interest
of both healthy and pathological (89) lung tissue were identified by an experienced radiologist. Texture features
were extracted using six properties calculated from gray-level co-occurrence matrices (GLCM), Minkowski Dimensions
(MDs), and three Minkowski Functionals (MFs, e.g. MF.euler). A k-nearest-neighbor (k-NN) classifier
and a Multilayer Radial Basis Functions Network (RBFN) were optimized in a 10-fold cross-validation for each
texture vector, and the classification accuracy was calculated on independent test sets as a quantitative measure
of automated tissue characterization. A Wilcoxon signed-rank test was used to compare two accuracy distributions
and the significance thresholds were adjusted for multiple comparisons by the Bonferroni correction.
The best classification results were obtained by the MF features, which performed significantly better than all
the standard GLCM and MD features (p < 0.005) for both classifiers. The highest accuracy was found for
MF.euler (97.5%, 96.6%; for the k-NN and RBFN classifier, respectively). The best standard texture features
were the GLCM features 'homogeneity' (91.8%, 87.2%) and 'absolute value' (90.2%, 88.5%). The results indicate
that advanced topological texture features can provide superior classification performance in computer-assisted
diagnosis of interstitial lung diseases when compared to standard texture analysis methods.
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