G Parraga

Publications (4)5.66 Total impact

• Conference Proceeding: Three-dimensional ultrasound imaging of carotid atherosclerosis

  E. Ukwatta, D. Buchanan, G. Parraga, Aaron Fenster
  IEEE International Conference on Intelligent Computation and Bio-Medical Instrumentation, Wuhan, China; 12/2011
• Article: Three-dimensional ultrasound of carotid atherosclerosis: semiautomated segmentation using a level set-based method.

  E Ukwatta, J Awad, A D Ward, D Buchanan, J Samarabandu, G Parraga, A Fenster
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  ABSTRACT: Three-dimensional ultrasound (3D US) of the carotid artery provides measurements of arterial wall and plaque [vessel wall volume (VWV)] that are complementary to the one-dimensional measurement of the carotid artery intima-media thickness. 3D US VWV requires an observer to delineate the media-adventitia boundary (MAB) and lumen-intima boundary (LIB) of the carotid artery. The main purpose of this work was to develop and evaluate a semiautomated segmentation algorithm for delineating the MAB and LIB of the carotid artery from 3D US images. To segment the MAB and LIB, the authors used a level set method and combined several low-level image cues with high-level domain knowledge and limited user interaction. First, the operator initialized the algorithm by choosing anchor points on the boundaries, identified in the images. The MAB was segmented using local region- and edge-based energies and an energy that encourages the boundary to pass through anchor points from the preprocessed images. For the LIB segmentation, the authors used local and global region-based energies, the anchor point-based energy, as well as a constraint promoting a boundary separation between the MAB and LIB. The data set consisted of 231 2D images (11 2D images per each of 21 subjects) extracted from 3D US images. The image slices were segmented five times each by a single observer using the algorithm and the manual method. Volume-based, region-based, and boundary distance-based metrics were used to evaluate accuracy. Moreover, repeated measures analysis was used to evaluate precision. The algorithm yielded an absolute VWV difference of 5.0% +/- 4.3% with a segmentation bias of -0.9% +/- 6.6%. For the MAB and LIB segmentations, the method gave absolute volume differences of 2.5% +/- 1.8% and 5.6% +/- 3.0%, Dice coefficients of 95.4% +/- 1.6% and 93.1% +/- 3.1%, mean absolute distances of 0.2 +/- 0.1 and 0.2 +/- 0.1 mm, and maximum absolute distances of 0.6 +/- 0.3 and 0.7 +/- 0.6 mm, respectively. The coefficients of variation of the algorithm (5.1%) and manual methods (3.9%) were not significantly different, but the average time saved using the algorithm (2.8 min versus 8.3 min) was substantial. The authors generated and tested a semiautomated carotid artery VWV measurement tool to provide measurements with reduced operator time and interaction, with high Dice coefficients, and with necessary required precision.
  Medical Physics 05/2011; 38(5):2479-93. · 2.83 Impact Factor
• Conference Proceeding: Quantification of progression and regression of carotid vessel atherosclerosis using 3D ultrasound images

  B. Chiu, M. Egger, J.D. Spence, G. Parraga, A. Fenster
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  ABSTRACT: Atherosclerosis is an inflammatory process similar to scar formation in the inner wall of the artery. It is the underlying cause of heart attacks and some strokes. Atherosclerotic lesions in the artery wall are called plaques. 3D ultrasound (US) has been used to monitor the progression of carotid vessel plaques in symptomatic and asymptomatic patients. Different ways of measuring various ultrasound phenotypes of atherosclerosis have been developed. Here, we report on the development and application of a method used to analyze changes in carotid plaque morphology from 3D US. In an effort to extend our previous work in plaque thickness analysis, we developed a procedure that facilitates the visualization and comparison of the distribution of plaque thickness by mapping the 3D arterial structure into a 2D plane
  Engineering in Medicine and Biology Society, 2006. EMBS '06. 28th Annual International Conference of the IEEE; 10/2006
• Article: Po‐Thur Eve General‐24: Non‐Invasive Imaging Phenotypes of Carotid Atherosclerosis in Subjects: MRI, B‐mode and 3D Ultrasound Measurements

  M Egger, C Blake, A Vidal, J Kost, JD Spence, B Rutt, A Fenster, A House, G Parraga
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  ABSTRACT: Atherosclerosis is a chronic inflammatory disease, characterized by the accumulation of lipids and fibrous elements within the inner‐most layer of the artery wall. Vulnerable atherosclerotic plaques may eventually rupture, resulting in emboli that can obstruct blood flow and result in stroke or myocardial infarction. Direct measurements of atherosclerosis include non‐invasive imaging phenotypes such as MRI and 3DUS derived plaque and wall volume measurements and B‐mode US measurements of the intima media thickness (IMT). Here we report the first comparison of IMT with 3D Ultrasound and MRI‐derived atherosclerosis phenotypes measured in five subjects with moderate carotid atherosclerosis. Five research subjects with carotid plaque area ⩾ 0.5 cm2 were studied and all subjects were undergoing treatment for hyperlipidemia. Mean age was 66 yrs with no significant difference between males and females. Subjects underwent MRI, 3DUS and 2D B‐mode US of the left and right carotid arteries. A single observer carried out 3DUS vessel wall volume measurements (VWV) in 10 subject images at both time points, a second observer measured MRI vessel wall volume; a third observer measured IMT. Both 3DUS VWV and MRI VWV measurements were repeated five times to determine intra‐observer variability and variability between time points. At baseline 3DUS and MRI VWV measurements were not significantly different. No significant differences was observed for mean 3DUS VWV and MRI VWV at test and retest. No significant difference between mean IMT at test and retest was found. IMT measurements had the highest intra‐class correlation coefficients and the lowest coefficient of variation values.
  Medical Physics 06/2006; 33(7):2664-2664. · 2.83 Impact Factor