Automated axial right ventricle to left ventricle diameter ratio computation in computed tomography pulmonary angiography - PubMed (original) (raw)
Automated axial right ventricle to left ventricle diameter ratio computation in computed tomography pulmonary angiography
Germán González et al. PLoS One. 2015.
Abstract
Background and purpose: Right Ventricular to Left Ventricular (RV/LV) diameter ratio has been shown to be a prognostic biomarker for patients suffering from acute Pulmonary Embolism (PE). While Computed Tomography Pulmonary Angiography (CTPA) images used to confirm a clinical suspicion of PE do include information of the heart, a numerical RV/LV diameter ratio is not universally reported, likely because of lack in training, inter-reader variability in the measurements, and additional effort by the radiologist. This study designs and validates a completely automated Computer Aided Detection (CAD) system to compute the axial RV/LV diameter ratio from CTPA images so that the RV/LV diameter ratio can be a more objective metric that is consistently reported in patients for whom CTPA diagnoses PE.
Materials and methods: The CAD system was designed specifically for RV/LV measurements. The system was tested in 198 consecutive CTPA patients with acute PE. Its accuracy was evaluated using reference standard RV/LV radiologist measurements and its prognostic value was established for 30-day PE-specific mortality and a composite outcome of 30-day PE-specific mortality or the need for intensive therapies. The study was Institutional Review Board (IRB) approved and HIPAA compliant.
Results: The CAD system analyzed correctly 92.4% (183/198) of CTPA studies. The mean difference between automated and manually computed axial RV/LV ratios was 0.03±0.22. The correlation between the RV/LV diameter ratio obtained by the CAD system and that obtained by the radiologist was high (r=0.81). Compared to the radiologist, the CAD system equally achieved high accuracy for the composite outcome, with areas under the receiver operating characteristic curves of 0.75 vs. 0.78. Similar results were found for 30-days PE-specific mortality, with areas under the curve of 0.72 vs. 0.75.
Conclusions: An automated CAD system for determining the CT derived RV/LV diameter ratio in patients with acute PE has high accuracy when compared to manual measurements and similar prognostic significance for two clinical outcomes.
Conflict of interest statement
Competing Interests: Dr. Rybicki receives research support from Toshiba Medical Systems Corporation that is unrelated to this work. This does not alter the authors' adherence to PLOS ONE policies on sharing data and materials. All other authors have declared that no competing interests exist.
Figures
Fig 1. Algorithm description.
First, the right ventricle and the left ventricle are detected on each axial slice. The detections are clustered to position seeds for further segmentation. The seeds are used to detect the septum. Using the seeds and the septum, the ventricles are segmented and the calipers positioned. Finally the right ventricular to left ventricular axial diameter ratio is estimated.
Fig 2. Axial images of a computed tomography pulmonary angiography of a 27 years old female with acute pulmonary embolism.
Top row: manually estimated axial ventricular diameters. Bottom row: automatically estimated axial ventricular diameters and depiction of the different steps followed to compute them: ventricle detection (red boxes), seed positioning (green dots), interventricular septum estimation (blue line), ventricle segmentation (blue areas) and ventricular diameter estimation (yellow lines).
Fig 3. Interface designed to visualize the automatically computed axial ventricular diameters.
The system automatically locates the diameters and adjusts the viewing window to maximize contrast. The RV/LV diameter ratio is shown between the two images.
Fig 4. Tukey outlier box plot of manually and automated extracted ventricular diameters and diameter ratios.
The box is placed at the median of the distribution. Top and bottom limits of the boxes represent 1st and 3rd quartiles of the data respectively. Whiskers length is 1.5 inter-quartile distances. Individual dots are considered outliers. While both RV and LV are underestimated by the automated method, the manually and automated estimated ratios are not significantly different, as shown in Table 1.
Fig 5. Comparison of automated and manually computed RV/LV diameter ratios.
A) Correlation plot. A linear model is fitted to the data. The intercept’s value is -0.16, the slope is 1.11, Person’s correlation coefficient is R = 0.81, 95% CI [0.76–0.86]. B) Bland-Altman comparison. The mean difference is -0.023 (95% CI [-0.061 0.003], p = 0.08), is depicted with a red line and its 95% CI as dotted red lines. Dot-dashed blue line: 95% limits of agreement of manual vs. automated measurement. Dashed green line: 95% CI limits of agreement between two expert readers. 72.1% (132/183) cases are within the limits of inter-reader variability.
Fig 6. Prediction of clinical outcome.
ROCs curve for the manual (dashed blue line) and automated (red line) logistic regression models when used to predict: A) 30 days PE-related mortality and B) 30 days PE-related mortality or the need for intensive therapies. Areas under the curve are 0.75 for the manual method and 0.72 for the automated method for Fig 6A and 0.78 for the manual method and 0.75 for the automated method in Fig 6B.
References
- Torbicki A, Perrier A, Konstantinides S, Agnelli G, Galiè N, Pruszczyk P, et al. Guidelines on the diagnosis and management of acute pulmonary embolism: the Task Force for the Diagnosis and Management of Acute Pulmonary Embolism of the European Society of Cardiology (ESC). Eur Heart J. 2008;29: 2276–2315. 10.1093/eurheartj/ehn310 -DOI -PubMed
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