KEYWORDS: Image segmentation, 3D modeling, Prostate, Magnetic resonance imaging, Machine learning, 3D image processing, Pattern recognition, Image analysis, Data modeling, Principal component analysis, Statistical modeling, Cancer
Prostate segmentation on 3D MR images is a challenging task due to image artifacts, large inter-patient prostate shape and texture variability, and lack of a clear prostate boundary specifically at apex and base levels. We propose a supervised machine learning model that combines atlas based Active Appearance Model (AAM) with a Deep Learning model to segment the prostate on MR images. The performance of the segmentation method is evaluated on 20 unseen MR image datasets. The proposed method combining AAM and Deep Learning achieves a mean Dice Similarity Coefficient (DSC) of 0.925 for whole 3D MR images of the prostate using axial cross-sections. The proposed model utilizes the adaptive atlas-based AAM model and Deep Learning to achieve significant segmentation accuracy.
In computer-aided diagnosis (CAD) systems for prostate cancer, dynamic contrast enhanced (DCE) magnetic resonance imaging is useful for distinguishing cancerous and benign tissue. The Tofts physiological model is a commonly used representation of the DCE image data, but the parameters require extensive computation. Hence, we developed an alternative representation based on the Hilbert transform of the DCE images. The time maximum of the Hilbert transform, a binary metric of early enhancement, and a pre-DCE value was assigned to each voxel and appended to a standard feature set derived from T2-weighted images and apparent diffusion coefficient maps. A cohort of 40 patients was used for training the classifier, and 20 patients were used for testing. The AUC was calculated by pooling the voxel-wise prediction values and comparing with the ground truth. The resulting AUC of 0.92 (95% CI [0.87 0.97]) is not significantly different from an AUC calculated using Tofts physiological models of 0.92 (95% CI [0.87 0.97]), as validated by a Wilcoxon signed rank test on each patient’s AUC (p = 0.19). The time required for calculation and feature extraction is 11.39 seconds (95% CI [10.95 11.82]) per patient using the Hilbert-based feature set, two orders of magnitude faster than the 1319 seconds (95% CI [1233 1404]) required for the Tofts parameter-based feature set (p<0.001). Hence, the features proposed herein appear useful for CAD systems integrated into clinical workflows where efficiency is important.
Accurate segmentation of ovarian cancer metastases is clinically useful to evaluate tumor growth and determine follow-up treatment. We present a region-based level set algorithm with localization constraints to segment ovarian cancer metastases. Our approach is established on a representative region-based level set, Chan-Vese model, in which an active contour is driven by region competition. To reduce over-segmentation, we constrain the level set propagation within a narrow image band by embedding a dynamic localization function. The metastasis intensity prior is also estimated from image regions within the level set initialization. The localization function and intensity prior force the level set to stop at the desired metastasis boundaries. Our approach was validated on 19 ovarian cancer metastases with radiologist-labeled ground-truth on contrast-enhanced CT scans from 15 patients. The comparison between our algorithm and geodesic active contour indicated that the volume overlap was 75±10% vs. 56±6%, the Dice coefficient was 83±8% vs. 63±8%, and the average surface distance was 2.2±0.6mm vs. 4.4±0.9mm. Experimental results demonstrated that our algorithm outperformed traditional level set algorithms.
We propose a new method for detecting abdominal lymphadenopathy by utilizing a random forest statistical classifier to create voxel-level lymph node predictions, i.e. initial detection of enlarged lymph nodes. The framework permits the combination of multiple statistical lymph node descriptors and appropriate feature selection in order to improve lesion detection beyond traditional enhancement filters. We show that Hessian blobness measurements alone are inadequate for detecting lymph nodes in the abdominal cavity. Of the features tested here, intensity proved to be the most important predictor for lymph node classification. For initial detection, candidate lesions were extracted from the 3D prediction map generated by random forest. Statistical features describing intensity distribution, shape, and texture were calculated from each enlarged lymph node candidate. In the last step, a support vector machine (SVM) was trained and tested based on the calculated features from candidates and labels determined by two experienced radiologists. The computer-aided detection (CAD) system was tested on a dataset containing 30 patients with 119 enlarged lymph nodes. Our method achieved an AUC of 0.762±0.022 and a sensitivity of 79.8% with 15 false positives suggesting it can aid radiologists in finding enlarged lymph nodes.
Lymph nodes play an important role in clinical practice but detection is challenging due to low contrast surrounding structures and variable size and shape. We propose a fully automatic method for mediastinal lymph node detection on thoracic CT scans. First, lungs are automatically segmented to locate the mediastinum region. Shape features by Hessian analysis, local scale, and circular transformation are computed at each voxel. Spatial prior distribution is determined based on the identification of multiple anatomical structures (esophagus, aortic arch, heart, etc.) by using multi-atlas label fusion. Shape features and spatial prior are then integrated for lymph node detection. The detected candidates are segmented by curve evolution. Characteristic features are calculated on the segmented lymph nodes and support vector machine is utilized for classification and false positive reduction. We applied our method to 20 patients with 62 enlarged mediastinal lymph nodes. The system achieved a significant improvement with 80% sensitivity at 8 false positives per patient with spatial prior compared to 45% sensitivity at 8 false positives per patient without a spatial prior.
Renal calculi are one of the most painful urologic disorders causing 3 million treatments per year in the United States.
The objective of this paper is the automated detection of renal calculi from CT colonography (CTC) images on which
they are one of the major extracolonic findings. However, the primary purpose of the CTC protocols is not for the
detection of renal calculi, but for screening of colon cancer. The kidneys are imaged with significant amounts of noise in the non-contrast CTC images, which makes the detection of renal calculi extremely challenging. We propose a
computer-aided diagnosis method to detect renal calculi in CTC images. It is built on three novel techniques: 1) total
variation (TV) flow to reduce image noise while keeping calculi, 2) maximally stable extremal region (MSER) features
to find calculus candidates, 3) salient feature descriptors based on intensity properties to train a support vector machine classifier and filter false positives. We selected 23 CTC cases with 36 renal calculi to analyze the detection algorithm. The calculus size ranged from 1.0mm to 6.8mm. Fifteen cases were selected as the training dataset, and the remaining eight cases were used for the testing dataset. The area under the receiver operating characteristic curve (AUC) values were 0.92 in the training datasets and 0.93 in the testing datasets. The testing dataset confidence interval for AUC reported by ROCKIT was [0.8799, 0.9591] and the training dataset was [0.8974, 0.9642]. These encouraging results demonstrated that our detection algorithm can robustly and accurately identify renal calculi from CTC images.
CT colonography (CTC) can increase the chance of detecting high-risk lesions not only within the colon but anywhere in the abdomen with a low cost. Extracolonic findings such as calculi and masses are frequently found in the kidneys on CTC. Accurate kidney segmentation is an important step to detect extracolonic findings in the kidneys. However, noncontrast CTC images make the task of kidney segmentation substantially challenging because the intensity values of kidney parenchyma are similar to those of adjacent structures. In this paper, we present a fully automatic kidney
segmentation algorithm to support extracolonic diagnosis from CTC data. It is built upon three major contributions: 1)
localize kidney search regions by exploiting the segmented liver and spleen as well as body symmetry; 2) construct a
probabilistic shape prior handling the issue of kidney touching other organs; 3) employ efficient belief propagation on the shape prior to extract the kidneys. We evaluated the accuracy of our algorithm on five non-contrast CTC datasets with manual kidney segmentation as the ground-truth. The Dice volume overlaps were 88%/89%, the root-mean-squared errors were 3.4 mm/2.8 mm, and the average surface distances were 2.1 mm/1.9 mm for the left/right kidney respectively. We also validated the robustness on 27 additional CTC cases, and 23 datasets were successfully segmented. In four problematic cases, the segmentation of the left kidney failed due to problems with the spleen segmentation. The results demonstrated that the proposed algorithm could automatically and accurately segment kidneys from CTC images, given the prior correct segmentation of the liver and spleen.
We propose a new method for prostate cancer classification based on supervised statistical learning methods by
integrating T2-weighted, diffusion-weighted, and dynamic contrast-enhanced MRI images with targeted prostate biopsy results. In the first step of the method, all three imaging modalities are registered based on the image coordinates encoded in the DICOM images. In the second step, local statistical features are extracted in each imaging modality to capture intensity, shape, and texture information at every biopsy target. Finally, using support vector machines, supervised learning is conducted with the biopsy results to train a classification system that predicts the pathology of suspicious cancer lesions. The algorithm was tested with a dataset of 54 patients that underwent 164 targeted biopsies (58 positive, 106 negative). The proposed tri-modal MRI algorithm shows significant improvement over a similar approach that utilizes only T2-weighted MRI images (p= 0.048). The areas under the ROC curve for these methods were 0.82 (95% CI: [0.71, 0.93]) and 0.73 (95% CI: [0.55, 0.84]), respectively.
The manuscript presents the automated detection and segmentation of hepatic tumors from abdominal CT
images with variable acquisition parameters. After obtaining an initial segmentation of the liver, optimized
graph cuts segment the liver tumor candidates using shape and enhancement constraints. One hundred and
fifty-seven features are computed for the tumor candidates and support vector machines are used to select
features and separate true and false detections. Training and testing are performed using leave-one-patientout
on 14 patients with a total of 79 tumors. After selection, the feature space is reduced to eight. The
resulting sensitivity for tumor detection was 100% at 2.3 false positives/case. For the true tumors, 74.1%
overlap and 1.6mm average surface distance were recorded between the ground truth and the results of the
automated method. Results from test data demonstrate the method's robustness to analyze livers from
difficult clinical cases to allow the diagnoses and temporal monitoring of patients with hepatic cancer.
Computed tomographic colonography (CTC) is a minimally invasive technique for colonic polyps and cancer
screening. The marginal artery of the colon, also known as the marginal artery of Drummond, is the blood
vessel that connects the inferior mesenteric artery with the superior mesenteric artery. The marginal artery
runs parallel to the colon for its entire length, providing the blood supply to the colon. Detecting the marginal
artery may benefit computer-aided detection (CAD) of colonic polyp. It can be used to identify teniae coli
based on their anatomic spatial relationship. It can also serve as an alternative marker for colon localization,
in case of colon collapse and inability to directly compute the endoluminal centerline. This paper proposes an
automatic method for marginal artery detection on CTC. To the best of our knowledge, this is the first work
presented for this purpose. Our method includes two stages. The first stage extracts the blood vessels in the
abdominal region. The eigenvalue of Hessian matrix is used to detect line-like structures in the images. The
second stage is to reduce the false positives in the first step. We used two different masks to exclude the false
positive vessel regions. One is a dilated colon mask which is obtained by colon segmentation. The other is an
eroded visceral fat mask which is obtained by fat segmentation in the abdominal region. We tested our
method on a CTC dataset with 6 cases. Using ratio-of-overlap with manual labeling of the marginal artery as
the standard-of-reference, our method yielded true positive, false positive and false negative fractions of 89%,
33%, 11%, respectively.
In this paper, we present evaluation results for a novel colonic polyp classification method for use as part of a computed
tomographic colonography (CTC) computer-aided detection (CAD) algorithm. Inspired by the interpretative
methodology of radiologists using 3D fly-through mode in CTC reading, we have developed an algorithm which utilizes
sequences of images (referred to here as videos) for classification of CAD marks. First, we generated an initial list of
polyp candidates using an existing CAD system. For each of these candidates, we created a video composed of a series
of intraluminal, volume-rendered images focusing on the candidate from multiple viewpoints. These videos illustrated
the shape of the polyp candidate and gathered contextual information of diagnostic importance. We calculated the
histogram of oriented gradients (HOG) feature on each frame of the video and utilized a support vector machine for
classification. We tested our method by analyzing a CTC data set of 50 patients from three medical centers. Our
proposed video analysis method for polyp classification showed significantly better performance than an approach using
only the 2D CT slice data. The areas under the ROC curve for these methods were 0.88 (95% CI: [0.84, 0.91]) and 0.80
(95% CI: [0.75, 0.84]) respectively (p=0.0005).
Computed tomographic colonography (CTC) is a minimally invasive technique for colonic polyps and cancer screening.
Teniae coli are three bands of longitudinal smooth muscle on the colon surface. They are parallel, equally distributed on
the colon wall, and form a triple helix structure from the appendix to the sigmoid colon. Because of their characteristics,
teniae coli are important anatomical meaningful landmarks on human colon. This paper proposes a novel method for
teniae coli detection on CT colonography. We first unfold the three-dimensional (3D) colon using a reversible projection
technique and compute the two-dimensional (2D) height map of the unfolded colon. The height map records the
elevation of colon surface relative to the unfolding plane, where haustral folds corresponding to high elevation points and
teniae to low elevation points. The teniae coli are detected on the height map and then projected back to the 3D colon.
Since teniae are located where the haustral folds meet, we break down the problem by first detecting haustral folds. We
apply 2D Gabor filter banks to extract fold features. The maximum response of the filter banks is then selected as the
feature image. The fold centers are then identified based on piecewise thresholding on the feature image. Connecting the
fold centers yields a path of the folds. Teniae coli are finally extracted as lines running between the fold paths.
Experiments were carried out on 7 cases. The proposed method yielded a promising result with an average normalized
RMSE of 5.66% and standard deviation of 4.79% of the circumference of the colon.
In this paper, we propose a new registration method for supine and prone computed tomographic colonography scans
based on graph matching. We first formulated 3D colon registration as a graph matching problem and utilized a graph
matching algorithm based on mean field theory. During the iterative optimization process, one-to-one matching
constraints were added to the system step-by-step. Prominent matching pairs found in previous iterations are used to
guide subsequent mean field calculations. The advantage of the proposed method is that it does not require a colon
centerline for registration. We tested the algorithm on a CTC dataset of 19 patients with 19 polyps. The average
registration error of the proposed method was 4.0cm (std. 2.1cm). The 95% confidence intervals were [3.0cm, 5.0mm].
There was no significant difference between the proposed method and our previous method based on the normalized
distance along the colon centerline (p=0.1).
Computed tomographic colonography (CTC) combined with a computer aided detection system has the potential for
improving colonic polyp detection and increasing the use of CTC for colon cancer screening. In the clinical use of CTC,
a true colonic polyp will be confirmed with high confidence if a radiologist can find it on both the supine and prone
scans. To assist radiologists in CTC reading, we propose a new method for matching polyp findings on the supine and
prone scans. The method performs a colon registration using four automatically identified anatomical salient points and
correlation optimized warping (COW) of colon centerline features. We first exclude false positive detections using
prediction information from a support vector machine (SVM) classifier committee to reduce initial false positive pairs.
Then each remaining CAD detection is mapped to the other scan using COW technique applied to the distance along the
centerline in each colon. In the last step, a new SVM classifier is applied to the candidate pair dataset to find true polyp
pairs between supine and prone scans. Experimental results show that our method can improve the sensitivity to 0.87 at 4
false positive pairs per patient compared with 0.72 for a competing method that uses the normalized distance along the
colon centerline (p<0.01).
CT colonography (CTC) is a feasible and minimally invasive method for the detection of colorectal polyps and cancer
screening. Computer-aided detection (CAD) of polyps has improved consistency and sensitivity of virtual colonoscopy
interpretation and reduced interpretation burden. A CAD system typically consists of four stages: (1) image preprocessing
including colon segmentation; (2) initial detection generation; (3) feature selection; and (4) detection
classification. In our experience, three existing problems limit the performance of our current CAD system. First, highdensity
orally administered contrast agents in fecal-tagging CTC have scatter effects on neighboring tissues. The
scattering manifests itself as an artificial elevation in the observed CT attenuation values of the neighboring tissues. This
pseudo-enhancement phenomenon presents a problem for the application of computer-aided polyp detection, especially
when polyps are submerged in the contrast agents. Second, general kernel approach for surface curvature computation in
the second stage of our CAD system could yield erroneous results for thin structures such as small (6-9 mm) polyps and
for touching structures such as polyps that lie on haustral folds. Those erroneous curvatures will reduce the sensitivity of
polyp detection. The third problem is that more than 150 features are selected from each polyp candidate in the third
stage of our CAD system. These high dimensional features make it difficult to learn a good decision boundary for
detection classification and reduce the accuracy of predictions. Therefore, an improved CAD system for polyp detection
in CTC data is proposed by introducing three new techniques. First, a scale-based scatter correction algorithm is applied
to reduce pseudo-enhancement effects in the image pre-processing stage. Second, a cubic spline interpolation method is
utilized to accurately estimate curvatures for initial detection generation. Third, a new dimensionality reduction
classifier, diffusion map and local linear embedding (DMLLE), is developed for classification and false positives (FP)
reduction. Performance of the improved CAD system is evaluated and compared with our existing CAD system (without
applying those techniques) using CT scans of 1186 patients. These scans are divided into a training set and a test set. The
sensitivity of the improved CAD system increased 18% on training data at a rate of 5 FPs per patient and 15% on test
data at a rate of 5 FPs per patient. Our results indicated that the improved CAD system achieved significantly better
performance on medium-sized colonic adenomas with higher sensitivity and lower FP rate in CTC.
Colon cancer is the second leading cause of cancer-related deaths in the United States. Computed tomographic colonography (CTC) combined with a computer aided detection system provides a feasible combination for improving colonic polyps detection and increasing the use of CTC for colon cancer screening. To distinguish true polyps from false positives, various features extracted from polyp candidates have been proposed. Most of these features try to capture the shape information of polyp candidates or neighborhood knowledge about the surrounding structures (fold, colon wall, etc.). In this paper, we propose a new set of shape descriptors for polyp candidates based on statistical curvature information. These features, called histogram of curvature features, are rotation, translation and scale invariant and can be treated as complementing our existing feature set. Then in order to make full use of the traditional features (defined as group A) and the new features (group B) which are highly heterogeneous, we employed a multiple kernel learning method based on semi-definite programming to identify an optimized classification kernel based on the combined set of features. We did leave-one-patient-out test on a CTC dataset which contained scans from 50 patients (with 90 6-9mm polyp detections). Experimental results show that a support vector machine (SVM) based on the combined feature set
and the semi-definite optimization kernel achieved higher FROC performance compared to SVMs using the two groups of features separately. At a false positive per patient rate of 7, the sensitivity on 6-9mm polyps using the combined features improved from 0.78 (Group A) and 0.73 (Group B) to 0.82 (p<=0.01).
Computed tomographic colonography (CTC) is a feasible and minimally invasive method for the detection of colorectal polyps and cancer screening. In current practice, a patient will be scanned twice during the CTC examination - once supine and once prone. In order to assist the radiologists in evaluating colon polyp candidates in both scans, we expect the computer aided detection (CAD) system can provide not only the locations of suspicious polyps, but also the possible matched pairs of polyps in two scans. In this paper, we propose a new automated matching method based on the extracted features of polyps by using principal component analysis (PCA) and Support Vector Machines (SVMs). Our dataset comes from the 104 CT scans of 52 patients with supine and prone positions collected from three medical centers. From it we constructed two groups of matched polyp candidates according to the size of true polyps: group A contains 12 true polyp pairs (> 9 mm) and 454 false pairs; group B contains 24 true polyp pairs (6-9 mm) and 514 false pairs. By using PCA, we reduced the dimensions of original data (with 157 attributes) to 30 dimensions. We did leave-one-patient-out test on the two groups of data. ROC analysis shows that it is easier to match bigger polyps than that of smaller polyps. On group A data, when false alarm probability is 0.18, the sensitivity of SVM achieves 0.83 which shows that automated matching of polyp candidates is practicable for clinical applications.
Computer-aided diagnosis systems have been shown to be feasible for polyp detection on computed tomography (CT) scans. After 3-D image segmentation and feature extraction, the dataset of colonic polyp candidates has large-scale and high dimension characteristics. In this paper, we propose a large-scale dimensionality reduction method based on Diffusion Map and Locally Linear Embedding for detection of polyps in CT colonography. By selecting partial data as landmarks, we first map the landmarks into a low dimensional embedding space using Diffusion Map. Then by using Locally Linear Embedding algorithm, non-landmark samples are embedded into the same low dimensional space according to their nearest landmark samples. The local geometry of samples is preserved in both the original space and the embedding space. We applied the proposed method called DMLLE to a colonic polyp dataset which contains 58336 candidates (including 85 6-9mm true polyps) with 155 features. Visual inspection shows that true polyps with similar shapes are mapped to close vicinity in the low dimensional space. FROC analysis shows that SVM with DMLLE achieves higher sensitivity with lower false positives per patient than that of SVM using all features. At the false positives of 8 per patient, SVM with DMLLE improves the average sensitivity from 64% to 75% for polyps whose sizes are in the range from 6 mm to 9 mm (p < 0.05). This higher sensitivity is comparable to unaided readings by trained
radiologists.
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