0
Research Papers

The Direct Incorporation of Perfusion Defect Information to Define Ischemia and Infarction in a Finite Element Model of the Left Ventricle

[+] Author and Article Information
Alexander I. Veress

Department of Mechanical Engineering,
University of Washington,
Stevens Way,
Box 352600,
Seattle, WA 98195
e-mail: averess@uw.edu

George S. K. Fung

Department of Radiology,
The Johns Hopkins University,
601 North Caroline Street,
JHOC Room 4263,
Baltimore, MD 21287-0859
e-mail: gfung2@jhmi.edu

Taek-Soo Lee

Department of Radiology,
The Johns Hopkins University,
601 North Caroline Street,
JHOC Room 4263,
Baltimore, MD 21287-0859
e-mail: tslee@jhmi.edu

Benjamin M. W. Tsui

Department of Radiology,
The Johns Hopkins University,
601 North Caroline Street,
JHOC Room 4263,
Baltimore, MD 21287-0859
e-mail: btsui@jhmi.edu

Gregory A. Kicska

Department of Radiology,
University of Washington,
1959 NE Pacific Street,
Seattle, WA 98195
e-mail: gkicska@gmail.com

W. Paul Segars

Carl E. Ravin Advanced Imaging Laboratories,
Duke University,
Duke University Hock Plaza,
2424 Suite 302, Erwin Road,
Durham, NC 27705
e-mail: paul.segars@duke.edu

Grant T. Gullberg

Structural Biology and Imaging Department,
Ernest Orlando Lawrence
Berkeley National Laboratory,
One Cyclotron Road, MS 55R0121,
Berkeley, CA 94720
e-mail: gtgullberg@lbl.gov

Manuscript received May 13, 2014; final manuscript received October 22, 2014; published online February 25, 2015. Assoc. Editor: Dalin Tang.

J Biomech Eng 137(5), 051004 (May 01, 2015) (10 pages) Paper No: BIO-14-1209; doi: 10.1115/1.4028989 History: Received May 13, 2014; Revised October 22, 2014; Online February 25, 2015

This paper describes the process in which complex lesion geometries (specified by computer generated perfusion defects) are incorporated in the description of nonlinear finite element (FE) mechanical models used for specifying the motion of the left ventricle (LV) in the 4D extended cardiac torso (XCAT) phantom to simulate gated cardiac image data. An image interrogation process was developed to define the elements in the LV mesh as ischemic or infarcted based upon the values of sampled intensity levels of the perfusion maps. The intensity values were determined for each of the interior integration points of every element of the FE mesh. The average element intensity levels were then determined. The elements with average intensity values below a user-controlled threshold were defined as ischemic or infarcted depending upon the model being defined. For the infarction model cases, the thresholding and interrogation process were repeated in order to define a border zone (BZ) surrounding the infarction. This methodology was evaluated using perfusion maps created by the perfusion cardiac-torso (PCAT) phantom an extension of the 4D XCAT phantom. The PCAT was used to create 3D perfusion maps representing 90% occlusions at four locations (left anterior descending (LAD) segments 6 and 9, left circumflex (LCX) segment 11, right coronary artery (RCA) segment 1) in the coronary tree. The volumes and shapes of the defects defined in the FE mechanical models were compared with perfusion maps produced by the PCAT. The models were incorporated into the XCAT phantom. The ischemia models had reduced stroke volume (SV) by 18–59 ml. and ejection fraction (EF) values by 14–50% points compared to the normal models. The infarction models, had less reductions in SV and EF, 17–54 ml. and 14–45% points, respectively. The volumes of the ischemic/infarcted regions of the models were nearly identical to those volumes obtained from the perfusion images and were highly correlated (R2= 0.99).

FIGURES IN THIS ARTICLE
<>
Copyright © 2015 by ASME
Your Session has timed out. Please sign back in to continue.

References

Figures

Grahic Jump Location
Fig. 1

Infarct model with simplified infarct region (black) surrounded by a one element thick BZ (white). This type of model was demonstrated in our previous work [2].

Grahic Jump Location
Fig. 2

The location of the occlusions (top) used to define the perfusion maps in the PCAT. Arrows indicate the location of the vessel occlusions. The resulting bull's eye maps (bottom) showing the extent of the perfusion defects.

Grahic Jump Location
Fig. 3

Thresholding was used to isolate the ischemic/infarcted regions of the myocardium. A midventricular, short axis slice of the 3D perfusion map for the proximal LAD with a 90% occlusion is shown on the left. The ischemic/infarcted region is shown on the right with threshold values of 6% (lower cutoff) and 90% (upper cutoff) of the maximum intesity.

Grahic Jump Location
Fig. 4

The locations of the integration points within a hexahedral element

Grahic Jump Location
Fig. 5

A 5 voxel Gaussian blur was applied to the thresholded image (left) to increase the size of the lesions (middle). This image was processed in order to define the BZ (right) which is the region with normal perfusion that borders the infarcted region.

Grahic Jump Location
Fig. 6

The ischemic/infarcted regions of the FE models show similar size and shape compared with the renderings of the perfusion maps. The ischemic/infarcted regions are defined as the blue interior regions for the models. The BZ is the continuous region surrounding the infarct. RCA segment 1 has had the RV removed from the rendered images.

Grahic Jump Location
Fig. 7

The comparison of the ischemic and infarcted volumes given in Table 2 shows a slight tendency toward underestimation

Grahic Jump Location
Fig. 8

Positive fiber strain result from the aneurysmic deformations associated with the ischemic (left column) and infarcted (right column) regions (positive fiber strains—elongation) as demonstrated in these midventricular short axis slices. This is in contrast to the deformations of the normal model (right column—top) which shows fiber contraction (negative fiber strains).

Grahic Jump Location
Fig. 9

This demonstrates how the ischemia mechanical model was defined from the PCAT perfusion data. The deformations predicted by this mechanical model were then used to define the LV within the XCAT phantom. This was used to create simulated SPECT images, in this case noise-free, which can reproduce the dyskinetic (aneurysmic) deformations of acute ischemia.

Grahic Jump Location
Fig. 10

Short axis cine reconstructed images corresponding to each perfusion defect. PCAT derived perfusion images (left), 4D XCAT reconstructed using FBP (center) and OS–EM reconstruction.

Grahic Jump Location
Fig. 11

Thresholding was used to isolate the enhanced region of the myocardium. (a) The delayed enhanced MRI image with an anterior defect. (b) A thresholding value of 185 (lower threshold) was used to isolate the enhanced perfusion region. (c) A 3 voxel Gaussian blur was applied to the thresholded image to smooth the boundary of the enhanced region. (d) The image theresholded to isolate the enhanced region.

Grahic Jump Location
Fig. 12

Thresholding was used to isolate the no-reflow zone of the myocardium in this (a) perfusion MRI image. (b) A 5 voxel Gaussian blur was applied to the image. (c) The contrast was enhanced and (d) a thresholding value of 190 was used to isolate the no reflow region. The underlying cause of no reflow is microvascular obstruction, which is confined to the irreversibly damaged necrotic zone of the infarct [54].

Tables

Errata

Discussions

Some tools below are only available to our subscribers or users with an online account.

Related Content

Customize your page view by dragging and repositioning the boxes below.

Related Journal Articles
Related eBook Content
Topic Collections

Sorry! You do not have access to this content. For assistance or to subscribe, please contact us:

  • TELEPHONE: 1-800-843-2763 (Toll-free in the USA)
  • EMAIL: asmedigitalcollection@asme.org
Sign In