We introduce a Markov random field (MRF)-driven region-based active contour model (MaRACel) for histological image segmentation. This Bayesian segmentation method combines a region-based active contour (RAC) with an MRF. State-of-the-art RAC models assume that every spatial location in the image is statistically independent, thereby ignoring valuable contextual information among spatial locations. To address this shortcoming, we incorporate an MRF prior into energy term of the RAC. This requires a formulation of the Markov prior consistent with the continuous variational framework characteristic of active contours; consequently, we introduce a continuous analog to the discrete Potts model. Based on the automated segmentation boundary of glands by MaRACel model, explicit shape descriptors are then employed to distinguish prostate glands belonging to Gleason patterns 3 (G3) and 4 (G4). To demonstrate the effectiveness of MaRACel, we compare its performance to the popular models proposed by Chan and Vese (CV) and Rousson and Deriche (RD) with respect to the following tasks: (1) the segmentation of prostatic acini (glands) and (2) the differentiation of G3 and G4 glands. On almost 600 prostate biopsy needle images, MaRACel was shown to have higher average dice coefficients, overlap ratios, sensitivities, specificities, and positive predictive values both in terms of segmentation accuracy and ability to discriminate between G3 and G4 glands compared to the CV and RD models.
Markov Random Fields (MRFs) provide a tractable means for incorporating contextual information into a Bayesian framework.
This contextual information is modeled using multiple local conditional probability density functions (LCPDFs)
which the MRF framework implicitly combines into a single joint probability density function (JPDF) that describes the
entire system. However, only LCPDFs of certain functional forms are consistent, meaning they reconstitute a valid JPDF.
These forms are specified by the Gibbs-Markov equivalence theorem which indicates that the JPDF, and hence the LCPDFs,
should be representable as a product of potential functions (i.e. Gibbs distributions). Unfortunately, potential functions
are mathematical abstractions that lack intuition; and consequently, constructing LCPDFs through their selection becomes
an ad hoc procedure, usually resulting in generic and/or heuristic models. In this paper we demonstrate that under certain
conditions the LCDPFs can be formulated in terms of quantities that are both meaningful and descriptive: probability distributions.
Using probability distributions instead of potential functions enables us to construct consistent LCPDFs whose
modeling capabilities are both more intuitive and expansive than typical MRF models. As an example, we compare the efficacy
of our so-called probabilistic pairwise Markov models (PPMMs) to the prevalent Potts model by incorporating both
into a novel computer aided diagnosis (CAD) system for detecting prostate cancer in whole-mount histological sections.
Using the Potts model the CAD system is able to detection cancerous glands with a specificity of 0.82 and sensitivity of
0.71; its area under the receiver operator characteristic (AUC) curve is 0.83. If instead the PPMM model is employed the
sensitivity (specificity is held fixed) and AUC increase to 0.77 and 0.87.
Computer-aided diagnosis (CAD) systems for the detection of cancer in medical images require precise labeling
of training data. For magnetic resonance (MR) imaging (MRI) of the prostate, training labels define the spatial
extent of prostate cancer (CaP); the most common source for these labels is expert segmentations. When
ancillary data such as whole mount histology (WMH) sections, which provide the gold standard for cancer
ground truth, are available, the manual labeling of CaP can be improved by referencing WMH. However, manual
segmentation is error prone, time consuming and not reproducible. Therefore, we present the use of multimodal
image registration to automatically and accurately transcribe CaP from histology onto MRI following alignment
of the two modalities, in order to improve the quality of training data and hence classifier performance. We
quantitatively demonstrate the superiority of this registration-based methodology by comparing its results to
the manual CaP annotation of expert radiologists. Five supervised CAD classifiers were trained using the labels
for CaP extent on MRI obtained by the expert and 4 different registration techniques. Two of the registration
methods were affi;ne schemes; one based on maximization of mutual information (MI) and the other method
that we previously developed, Combined Feature Ensemble Mutual Information (COFEMI), which incorporates
high-order statistical features for robust multimodal registration. Two non-rigid schemes were obtained by
succeeding the two affine registration methods with an elastic deformation step using thin-plate splines (TPS).
In the absence of definitive ground truth for CaP extent on MRI, classifier accuracy was evaluated against 7
ground truth surrogates obtained by different combinations of the expert and registration segmentations. For
26 multimodal MRI-WMH image pairs, all four registration methods produced a higher area under the receiver
operating characteristic curve compared to that obtained from expert annotation. These results suggest that in
the presence of additional multimodal image information one can obtain more accurate object annotations than
achievable via expert delineation despite vast differences between modalities that hinder image registration.
Conference Committee Involvement (14)
Digital and Computational Pathology
18 February 2025 | San Diego, California, United States
Digital and Computational Pathology
19 February 2024 | San Diego, California, United States
Digital and Computational Pathology
20 February 2023 | San Diego, California, United States
Digital and Computational Pathology
20 February 2022 | San Diego, California, United States
Digital and Computational Pathology
15 February 2021 | Online Only, California, United States
Digital Pathology
19 February 2020 | Houston, Texas, United States
Digital Pathology
20 February 2019 | San Diego, California, United States
Digital Pathology
11 February 2018 | Houston, Texas, United States
Digital Pathology
12 February 2017 | Orlando, Florida, United States
Digital Pathology Posters
12 February 2017 | Orlando, FL, United States
Digital Pathology
2 March 2016 | San Diego, California, United States
Digital Pathology
25 February 2015 | Orlando, Florida, United States
Digital Pathology
16 February 2014 | San Diego, California, United States
Digital Pathology
10 February 2013 | Lake Buena Vista (Orlando Area), Florida, United States
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