Bhargav Raman

Fully Automated System for Three-Dimensional Bronchial Morphology Analysis Using Volumetric Multidetector Computed Tomography of the Chest

Recent advancements in computed tomography (CT) have enabled quantitative assessment of severity and progression of large airway damage in chronic pulmonary disease. The advent of fast multidetector computed tomography scanning has allowed the acquisition of rapid, low-dose 3D volumetric pulmonary scans that depict the bronchial tree in great detail. Volumetric CT allows quantitative indices of bronchial airway morphology to be calculated, including airway diameters, wall thicknesses, wall area, airway segment lengths, airway taper indices, and airway branching patterns. However, the complexity and size of the bronchial tree render manual measurement methods impractical and inaccurate. We have developed an integrated software package utilizing a new measurement algorithm termed mirror-image Gaussian fit that enables the user to perform automated bronchial segmentation, measurement, and database archiving of the bronchial morphology in high resolution and volumetric CT scans and also allows 3D localization, visualization, and registration.

Impact of Quantitatively Determined Native Thoracic Aortic Tortuosity on Endoleak Development After Thoracic Endovascular Aortic Repair

OBJECTIVE The objective of our study was to assess whether there is an association between native thoracic aortic curvature and the development of endoleaks after thoracic endovascular aortic repair. MATERIALS AND METHODS Quantitative analysis of the native aortic lumen was performed on preprocedural CT angiograms of 40 patients with thoracic aortic aneurysm treated by thoracic endovascular aortic repair. The curvature of the median centerline was measured. Tortuosity indexes were calculated on the basis of the sum of the curvature values within the diseased segment and in the proximal and distal fixation zones. The association between the tortuosity index and endoleak was analyzed. RESULTS Compared with patients without endoleaks, the tortuosity index of the proximal fixation zone was higher in patients with type Ia endoleak (9.5 vs 1.5 cm(-1), p < 0.01); the tortuosity index of the distal fixation zone was higher in type Ib endoleak patients (6.6 vs 0.5 cm(-1), p < 0.05); and the tortuosity indexes of the proximal fixation zone and of the diseased segment were higher in type III endoleak patients (11.0 vs 1.5 cm(-1), p < 0.01; and 15.8 vs 7.2 cm(-1), p < 0.01, respectively). Patients with a type III endoleak had longer diseased segments and larger mean diameters of the aneurysm than patients without endoleaks (148.6 vs 87.1 mm, p < 0.01; and 75.4 vs 63.2 mm, p < 0.05, respectively). Logistic regression analysis revealed that the risk of a type I or type III endoleak increased as the tortuosity index increased, with a 90% risk of endoleak at a tortuosity index of 10 cm(-1) in the proximal fixation zone. CONCLUSION Quantification of aortic tortuosity using CT angiograms may help to predict whether an endoleak will develop after thoracic endovascular aortic repair, and this quantification method may become an important tool for risk stratification before thoracic endovascular aortic repair.

Discriminant Analysis of Native Thoracic Aortic Curvature: Risk Prediction for Endoleak Formation After Thoracic Endovascular Aortic Repair

PURPOSE To determine the association of native thoracic aortic curvature measured from computed tomographic (CT) angiography categorized by discriminant analysis with the development of endoleaks after thoracic endovascular aortic repair (EVAR). MATERIALS AND METHODS Forty patients (28 men, 12 women; mean age, 74 y; range, 40-89 y) with aortic diseases treated with thoracic EVAR were evaluated. Diseases treated included atherosclerotic aneurysm (n = 27), penetrating atherosclerotic ulcer (n = 4), intramural hematoma (n = 3), mycotic aneurysm (n = 3), and anastomotic pseudoaneurysm (n = 3). Quantitative analysis of native aortic morphology was performed on preprocedural CT angiograms with an original customized computer program, and regional curvature indices in each anatomic segment of the aorta were calculated. Patterns of native thoracic aortic morphology were analyzed by discriminant analysis. The association between the morphologic pattern of the aorta and the presence and type of endoleak was assessed. RESULTS After leave-one-out cross-validation methods had been applied, the sensitivity, specificity, and accuracy to detect endoleak formation in a new population group by discriminant analysis of the patterns of native aortic curvature were estimated as 84.0%, 58.8%, and 73.8%, respectively. Compared with the no-endoleak group, the type Ia endoleak group had greater curvature at the aortic arch, the type Ib endoleak group had greater curvature at the thoracoabdominal junction, and the type III endoleak group had greater curvature in the midportion of the descending aorta. CONCLUSIONS Discriminant analysis of native thoracic aortic morphology measured from CT angiography is a useful tool to predict the risk of endoleak formation after thoracic EVAR and should be implemented during treatment planning and follow-up.

Semiautomated Quantification of the Mass and Distribution of Vascular Calcification with Multidetector CT: Method and Evaluation

Institutional review board approval was obtained for this HIPAA-compliant study. Informed consent was obtained for prospective evaluation in 21 asymptomatic volunteers (10 women, 11 men; mean age, 60 years) but waived for retrospective (10 patients with and five patients without disease) evaluation. Prospective validation was in phantoms. Quantification of mass and calcium distribution was performed with fast semiautomated method, without calibration. For actual versus measured mass in phantoms, R(2) was 0.98; absolute and percentage errors were 1.2 mg and 9.1%, respectively. In asymptomatic volunteers, mean interscan variability for calcium mass quantification in extracoronary arteries was 24.9 mg; mean was 991 units for Agatston scoring. In coronary arteries, mean variability was 5.5 mg; mean Agatston variability was 27.7 units. At retrospective computed tomography, mean total calcified mass was 321.3 mg. Accurate quantification of mass and distribution of calcification in simulated arteries with this method can be applied in vivo, with low interscan variability.

Automated Quantification of Aortoaortic and Aortoiliac Angulation for Computed Tomographic Angiography of Abdominal Aortic Aneurysms before Endovascular Repair: Preliminary Study

The degree of angulation of abdominal aortic aneurysms (AAAs) has emerged as an important factor in assessing eligibility for endovascular aneurysm repair (EVAR). The authors developed an automatic algorithm that reduces variability of measurement of aortoiliac angulation. For highly structured manual methods, intraobserver variability was 8.2 degrees ± 5.0 (31% ± 20) and interobserver variability was 5.6 degrees ± 2.5 (20% ± 9.1) compared with 0.6 degrees ± 0.8 (2.2% ± 3.6) (intraobserver) and 0.4 degrees ± 0.4 (1.4% ± 1.9) (interobserver) for the automatic algorithm (P < .01). In phantoms, the automatically measured angles were equivalent to reference values (P < .05). This algorithm was also faster than manual methods and has the potential to enhance the clinical utility and reliability of computed tomographic angiography for preoperative assessment for EVAR.

Development and Validation of Automated 2D–3D Bronchial Airway Matching to Track Changes in Regional Bronchial Morphology Using Serial Low-Dose Chest CT Scans in Children with Chronic Lung Disease

To address potential concern for cumulative radiation exposure with serial spiral chest computed tomography (CT) scans in children with chronic lung disease, we developed an approach to match bronchial airways on low-dose spiral and low-dose high-resolution CT (HRCT) chest images to allow serial comparisons. An automated algorithm matches the position and orientation of bronchial airways obtained from HRCT slices with those in the spiral CT scan. To validate this algorithm, we compared manual matching vs automatic matching of bronchial airways in three pediatric patients. The mean absolute percentage difference between the manually matched spiral CT airway and the index HRCT airways were 9.4 ± 8.5% for the internal diameter measurements, 6.0 ± 4.1% for the outer diameter measurements, and 10.1 ± 9.3% for the wall thickness measurements. The mean absolute percentage difference between the automatically matched spiral CT airway measurements and index HRCT airway measurements were 9.2 ± 8.6% for the inner diameter, 5.8 ± 4.5% for the outer diameter, and 9.9 ± 9.5% for the wall thickness. The overall difference between manual and automated methods was 2.1 ± 1.2%, which was significantly less than the interuser variability of 5.1 ± 4.6% (p < 0.05). Tests of equivalence had p < 0.05, demonstrating no significant difference between the two methods. The time required for matching was significantly reduced in the automated method (p < 0.01) and was as accurate as manual matching, allowing efficient comparison of airways obtained on low-dose spiral CT imaging with low-dose HRCT scans.

Improved speed of bone removal in computed tomographic angiography using automated targeted morphological separation: method and evaluation in computed tomographic angiography of lower extremity occlusive disease.

We developed an automated algorithm for bone removal in computed tomographic angiographic images that identifies and deletes connections between bone and vessels. Our automated algorithm is significantly faster than manual methods (2.45 minutes vs 73 minutes) and only generates about 2 small artifactual deletions per patient, mostly in the region of the ankle. Image quality was equivalent to manual methods. It shows promise as a tool for fast and accurate postprocessing of computed tomographic angiograms.

Breast Angiosarcoma: Case Series and Expression of Vascular Endothelial Growth Factor.

Purpose: Angiosarcoma of the breast is a rare, malignant tumor for which little is known regarding prognostic indicators and optimal therapeutic regimens. To address this issue, we performed a retrospective analysis of breast angiosarcoma cases seen at Stanford University along with immunohistochemical analysis for markers of angiogenesis. Methods: Breast angiosarcoma cases seen between 1980 and 2008 were examined. Viable tissue blocks were analyzed for expression of vascular endothelial growth factor and its receptors. Results: A total of 16 cases were identified. Data was collected regarding epidemiology, treatment, response rates, disease-free survival, and the use of various imaging modalities. Five tissue blocks remained viable for immunohistochemical analysis. Vascular endothelial growth factor-A was positively expressed in 3 of these samples. Conclusion: Angiosarcoma of the breast is an aggressive malignancy with a propensity for both local recurrence and distant metastases. Angiogenesis inhibition may represent a novel therapeutic modality in this rare, vascular malignancy.

Automated creation of radiology teaching modules: demonstration of PACS integration and distribution

The creation of radiology teaching modules has historically required manual offline authoring. Our system can integrate with commercial PACS to allow clinicians to author teaching modules at their clinical PACS workstations without further manual input. Our system provides a DICOM interface and an automated teaching file database. We tested our system with the PACS deployed at our institution (GE Medical Systems, Milwaukee, WI). We used a networked Windows workstation (Microsoft, Redmond, WA) running SQL Server 2000, registered on our PACS system as a DICOM receiver. Teaching files were created at clinical workstations and any desired annotation and cataloguing instructions were added using standard annotation tools. The files were pushed using DICOM network transfer. Anonymizing, annotation and cataloguing were done automatically using DICOM header information. Additional information from our HIS/RIS system was transmitted using private DICOM header fields. Teaching files were then added to the web - accessible teaching module database. We present a system that integrates the creation of teaching files into the daily clinical workflow, allowing clinicians to immediately publish interesting cases from their clinical workstation. Our system uses standard protocols and requires minimal configuration to integrate with existing PACS systems, enabling a low-cost, expandable and vendor independent solution.

Assessment of the Relationship Between Native Thoracic Aortic Curvature and Endoleak Formation After TEVAR Based on Linear Discriminant Analysis

In the field of surgery treatment, thoracic endovascular aortic repair has recently gained popularity, but this treatment often causes an adverse clinical side effect called endoleak. The risk prediction of endoleak is essential for pre-operative planning (Nakatamari et al., J Vasc Interv Radiol 22(7):974–979, 2011). In this study, we focus on a quantitative curvature in the morphology of a patient’s aorta, and predict the risk of endoleak formation through linear discriminant analysis. Here, we objectively evaluate the relationship between the side effect after stent-graft treatment for thoracic aneurysm and a patient’s native thoracic aortic curvature. In addition, based on the sample influence function for the average of discriminant scores in linear discriminant analysis, we also perform statistical diagnostics on the result of the analysis. We detected the influential training samples to be deleted to realize improved prediction accuracy, and made subsets of all of their possible combinations. Furthermore, by considering the minimum misclassification rate based on leave-one-out cross-validation in Hastie et al. (The elements of statistical learning. Springer, New York, 2001, pp. 214–216) and the minimum number of training samples to be deleted, we deduced the subset to be excluded from training data when we develop the target classifier. From this study, we detected an important part of the native thoracic aorta in terms of risk prediction of endoleak occurrence, and identified influential patients for the result of the discrimination.