Assessment of the extent of cerebral damage on admission in patients with acute ischemic stroke could play an important role in treatment decision making. Computed tomography perfusion (CTP) imaging can be used to determine the extent of damage. However, clinical application is hindered by differences among vendors and used methodology. As a result, threshold based methods and visual assessment of CTP images has not yet shown to be useful in treatment decision making and predicting clinical outcome. Preliminary results in MR studies have shown the benefit of using supervised classifiers for predicting tissue outcome, but this has not been demonstrated for CTP. We present a novel method for the automatic prediction of tissue outcome by combining multi-parametric CTP images into a tissue outcome probability map. A supervised classification scheme was developed to extract absolute and relative perfusion values from processed CTP images that are summarized by a trained classifier into a likelihood of infarction. Training was performed using follow-up CT scans of 20 acute stroke patients with complete recanalization of the vessel that was occluded on admission. Infarcted regions were annotated by expert neuroradiologists. Multiple classifiers were evaluated in a leave-one-patient-out strategy for their discriminating performance using receiver operating characteristic (ROC) statistics. Results showed that a RandomForest classifier performed optimally with an area under the ROC of 0.90 for discriminating infarct tissue. The obtained results are an improvement over existing thresholding methods and are in line with results found in literature where MR perfusion was used.
Stroke is the third most common cause of death in developed countries. Clinical trials are currently investigating whether advanced Computed Tomography can be of benefit for diagnosing stroke at the acute phase. These trials are based on large patients cohorts that need to be manually annotated to obtain a reference standard of tissue loss at follow-up, resulting in extensive workload for the radiologists. Therefore, there is a demand for accurate and reliable automatic lesion segmentation methods. This paper presents a novel method for the automatic detection and segmentation of ischemic lesions in CT images. The method consists of multiple sequential stages. In the initial stage, pixel classification is performed using a naive Bayes classifier in combination with a tissue homogeneity algorithm in order to localize ischemic lesion candidates. In the next stage, the candidates are segmented using a marching cubes algorithm. Regional statistical analysis is used to extract features based on local information as well as contextual information from the contra-lateral hemisphere. Finally, the extracted features are summarized into a likelihood of ischemia by a supervised classifier. An area under the Receiver Operating Characteristic curve of 0.91 was obtained for the identification of ischemic lesions. The method performance on lesion segmentation reached a Dice similarity coeficient (DSC) of 0.74±0.09, whereas an independent human observer obtained a DSC of 0.79±0.11 in the same dataset. The experiments showed that it is feasible to automatically detect and segment ischemic lesions in CT images, obtaining a comparable performance as human observers.
Accurate segmentation of the brain ventricular system in Computed Tomography (CT) images is useful in neurodiagnosis,
providing quantitative measures on changes in ventricular size due to stroke. Manual segmentation,
however, is a time-consuming, tedious task and is prone to large inter-observer variability. This study presents an
automatic ventricle system segmentation method by combining the results of supervised pixel classification based
on intensities with spatial information obtained from a multi-atlas-based segmentation method. The method is
applied to follow-up brain CT images which were collected from a cohort of 20 patients with proven ischemic
stroke. The automatic segmentation performance was evaluated in a leave-one-out strategy by comparing with
manual segmentations. The results show that combining information obtained from pixel classification and multi-atlas-based segmentation significantly outperforms each method independently with a mean Dice coefficient index
of 0.810.07.±
The presence of collateral blood flow is found to be a strong predictor of patient outcome after acute ischemic stroke. Collateral blood flow is defined as an alternative way to provide oxygenated blood to ischemic cerebral tissue. Assessment of collateral blood supply is currently performed by visual inspection of a Computed Tomography Angiogram (CTA) which introduces inter-observer variability and depends on the grading scale. Furthermore, variations in the arterial contrast arrival time may lead to underestimation of collateral blood supply in a CTA which exerts a negative influence on the prediction of patient outcome. In this study, the feasibility of a Computer-aided Diagnosis system is investigated capable of objectively predicting patient outcome. We present a novel automatic method for quantitative assessment of cerebral hypoperfusion in timing-invariant (i.e. delay insensitive) CTA (TI-CTA). The proposed Vessel Density Symmetry algorithm automatically generates descriptive maps based on hemispheric asymmetry of blood vessels. Intensity and symmetry based features are extracted from these descriptive maps and subjected to a best-first-search feature selection. Linear Discriminant Analysis is performed to combine selected features into a likelihood of good patient outcome. Receiver operating characteristic (ROC) analysis is conducted to evaluate the diagnostic performance of the CAD by leave-one- patient-out cross validation. A Positive Predicting Value of 1 was obtained at a sensitivity of 25% with an area under the ROC-curve of 0.86. The results show that the CAD is feasible to objectively predict patient outcome. The presented CAD could make an important contribution to acute ischemic stroke diagnosis and treatment.
Development of CAD systems for detection of prostate cancer has been a recent topic of research. A multi-stage
computer aided detection scheme is proposed to help reduce perception and oversight errors in multi-parametric
prostate cancer screening MRI. In addition, important features for development of computer aided detection
systems for prostate cancer screening MRI are identified. A fast, robust prostate segmentation routine is used
to segment the prostate, based on coupled appearance and anatomy models. Subsequently a voxel classification
is performed using a support vector machine to compute an abnormality likelihood map of the prostate. This
classification step is based on quantitative voxel features like the apparent diffusion coefficient (ADC) and
pharmacokinetic parameters. Local maxima in the likelihood map are found using a local maxima detector, after
which regions around the local maxima are segmented. Region features are computed to represent statistical
properties of the voxel features within the regions. Region classification is performed using these features, which
results in a likelihood of abnormality per region. Performance was validated using a 188 patient dataset in
a leave-one-patient-out manner. Ground truth was annotated by two expert radiologists. The results were
evaluated using FROC analysis. The FROC curves show that inclusion of ADC and pharmacokinetic parameter
features increases the performance of an automatic detection system. In addition it shows the potential of such
an automated system in aiding radiologists diagnosing prostate MR, obtaining a sensitivity of respectively 74.7%
and 83.4% at 7 and 9 false positives per patient.
For pharmacokinetic (PK) analysis of Dynamic Contrast Enhanced (DCE) MRI the arterial input function
needs to be estimated. Previously, we demonstrated that PK parameters have a significant better discriminative
performance when per patient reference tissue was used, but required manual annotation of reference tissue. In
this study we propose a fully automated reference tissue segmentation method that tackles this limitation. The
method was tested with our Computer Aided Diagnosis (CADx) system to study the effect on the discriminating
performance for differentiating prostate cancer from benign areas in the peripheral zone (PZ).
The proposed method automatically segments normal PZ tissue from DCE derived data. First, the bladder
is segmented in the start-to-enhance map using the Otsu histogram threshold selection method. Second, the
prostate is detected by applying a multi-scale Hessian filter to the relative enhancement map. Third, normal
PZ tissue was segmented by threshold and morphological operators. The resulting segmentation was used as
reference tissue to estimate the PK parameters. In 39 consecutive patients carcinoma, benign and normal tissue
were annotated on MR images by a radiologist and a researcher using whole mount step-section histopathology
as reference. PK parameters were computed for each ROI. Features were extracted from the set of ROIs using
percentiles to train a support vector machine that was used as classifier. Prospective performance was estimated
by means of leave-one-patient-out cross validation. A bootstrap resampling approach with 10,000 iterations was
used for estimating the bootstrap mean AUCs and 95% confidence intervals.
In total 42 malignant, 29 benign and 37 normal regions were annotated. For all patients, normal PZ was
successfully segmented. The diagnostic accuracy obtained for differentiating malignant from benign lesions using
a conventional general patient plasma profile showed an accuracy of 0.64 (0.53-0.74). Using the automated
per-patient calibration method the diagnostic performance improved significantly to 0.76 (0.67-0.86, p=0.017) ,
whereas the manual per-patient calibration showed a diagnostic performance of 0.79 (0.70-0.89, p=0.01).
In conclusion, the results show that an automated per-patient reference tissue PK model is feasible. A
significantly better discriminating performance compared to the conventional general calibration was obtained
and the diagnostic accuracy is similar to using manual per-patient calibration.
In this study, we investigate the diagnostic performance of our CAD system when discriminating prostate cancer
from benign lesions and normal peripheral zone using registered multi-modal images. We have developed a
method that automatically extracts quantitative T2 values out of acquired T2-w images and evaluated its additional
value to the discriminating performance of our CAD system. This study addresses 2 issues when using
both T2-w and dynamic MR images for the characterization of prostate lesions. Firstly, T2-w images do not
provide quantitative values, and secondly, images can be misaligned due to patient movements. To compensate,
a mutual information registration strategy is performed after which T2 values are estimated using the acquired
proton density images. From the resulted quantitative T2 maps as well as the dynamic images relevant features
were extracted for training a support vector machine as classfier. The output of the classifier was used as a
measure of likelihood of malignancy. General performance of the scheme was evaluated using the area under the
ROC curve.
We conclude that it is feasible to automatically extract diagnostic T2 values out of acquired T2-w images.
Furthermore, a discriminating performance of 0.75 (0.66-0.85) was obtained when only using T2-values as feature.
Combining the T2 values with pharmacokinetic parameters did not increase diagnostic performance in a pilot
study.
In this study, we investigated the effect of different patient calibration methods on the performance of our CAD
system when discriminating prostate cancer from non-malignant suspicious enhancing areas in the peripheral
zone and the normal peripheral zone.
Our database consisted of 34 consecutive patients with histologically proven adenocarcinoma of the prostate.
Both carcinoma and normal tissue were annotated on MR images by a radiologist and a researcher using whole
mount step-section histopathology as standard of reference. The annotated regions were used as regions of interest
in the contrast enhanced MRI images. A feature set comprising pharmacokinetic parametes was extracted from
the ROIs to train a support vector machine as classifier. The output of the classifier was used as a measure of
likelihood of malignancy. General performance of the scheme was evaluated using the area under the ROC curve.
The diagnostic accuracy obtained for differentiating normal peripheral zone and non-malignant suspicious
enhancing areas from malignant lesions was 0.88 (0.81-0.95) when per patient calibration was performed, whereas
fixed calibration resulted in a diagnostic accuracy of 0.77 (0.69-0.85). These preliminary results indicate that
when per patient calibration is used, the performance is improved with statistical significance (p=0.026).
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