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Research Papers

# Patient-Specific MRI-Based 3D FSI RV/LV/Patch Models for Pulmonary Valve Replacement Surgery and Patch Optimization

[+] Author and Article Information
Dalin Tang1

Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609dtang@wpi.edu

Chun Yang

Mathematical Sciences Department, Worcester Polytechnic Institute, Worcester, MA 01609; Mathematics Department, Beijing Normal University, Beijing, P.R.C.

Tal Geva

Department of Cardiology, Children’s Hospital, Boston, MA 02115; Department of Pediatric, Harvard Medical School, Boston, MA 02115

Pedro J. del Nido

Department of Cardiac Surgery, Children’s Hospital, Harvard Medical School, Boston, MA 02115

1

Corresponding author.

J Biomech Eng 130(4), 041010 (Jun 03, 2008) (10 pages) doi:10.1115/1.2913339 History: Received May 19, 2007; Revised September 08, 2007; Published June 03, 2008

## Abstract

A patient-specific right/left ventricle and patch (RV/LV/patch) combination model with fluid-structure interactions (FSIs) was introduced to evaluate and optimize human pulmonary valve replacement/insertion (PVR) surgical procedure and patch design. Cardiac magnetic resonance (CMR) imaging studies were performed to acquire ventricle geometry, flow velocity, and flow rate for healthy volunteers and patients needing RV remodeling and PVR before and after scheduled surgeries. CMR-based RV/LV/patch FSI models were constructed to perform mechanical analysis and assess RV cardiac functions. Both pre- and postoperation CMR data were used to adjust and validate the model so that predicted RV volumes reached good agreement with CMR measurements (error $<3%$). Two RV/LV/patch models were made based on preoperation data to evaluate and compare two PVR surgical procedures: (i) conventional patch with little or no scar tissue trimming, and (ii) small patch with aggressive scar trimming and RV volume reduction. Our modeling results indicated that (a) patient-specific CMR-based computational modeling can provide accurate assessment of RV cardiac functions, and (b) PVR with a smaller patch and more aggressive scar removal led to reduced stress/strain conditions in the patch area and may lead to improved recovery of RV functions. More patient studies are needed to validate our findings.

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## Figures

Figure 6

Recorded ((a) and (b)) and prescribed (c) pressure conditions at the tricuspid (inlet) and pulmonary (outlet) valves (35). Prescribed numerical pressure conditions and valve close/open times were modified from the recorded data so that pressure conditions were as consistent with the recorded data as possible. The vertical bars in (c) indicate valve open/close switch time.

Figure 7

Stress-P1 and Strain-P1 distributions in the RV may provide useful information for mechanical analysis and disease state assessment. (a) 3D view of Stress-P1 under maximum pressure and position of the cut, (b) Stress-P1 on the inner surface of RV under maximum pressure (horizontal flipped for better view), (c) Strain-P1 on the inner surface of RV under maximum pressure, and (d) Strain-P1 on the out-surface of the whole model.

Figure 8

Velocity plots at different phases showing interesting flow patterns: (a) beginning of the filling phase, (b) flow patterns just before the ending of filling phase, (c) beginning of the ejection phase, and (d) ejection continues

Figure 1

Right ventricle late after repair of tetralogy showing area of transannular patch plus thinning and scarring on the anterior surface of the RV (lighter gray area). (a) A diseased RV with old patch and scar tissue, (b) RV after pulmonary valve insertion (PVR) surgery with conventional patch, and (c) RV after PVR with scar removal and a smaller patch.

Figure 2

Basic plots showing the modeling procedure. (a) A human heart sketch showing left and right ventricles with valve positions, (b) segmented RV MRI contour plots, (c) RV/LV geometry from MRI, and (d) the reconstructed 3D geometry of the RV/LV combination model.

Figure 9

Adjusted patient-specific material stress-stretch curves from Mooney–Rivlin models for ventricle tissue, scar and patch materials, specified pressure conditions, and computed RV volume compared with CMR recorded data showing good agreement (error margin <3%)

Figure 10

Selected cut surface and Stress-P1/Strain-P1 at maximum and minimum pressure conditions

Figure 11

Sketch of models with different patch designs. (a) Preoperation model with the old patch and scar tissues, (b) Patch Model 1 with a conventional patch and minimum scar tissue trimming, and (c) Patch Model 2 with a small patch and aggressive trimming.

Figure 12

(a) Overlapping contours of the preoperation model and Patch Model 2 showing RV reduction at contour level, and (b) overlapping contours of one slice from the three models M1, M2, and M3 showing the model modification process and differences

Figure 3

Preoperation CMR images (end systole) acquired from a patient and segmented contours

Figure 4

Reconstructed 3D geometry of RV and LV showing valve and patch positions

Figure 13

Stress-P1/Strain-P1 variations tracked at selected locations for the three cases show that stress/strain levels (around the patches) are considerably lower (50% for stress and 40% for strain) from Patch Model 2 than that from the other two models. ((a)–(c)) Strain-P1 distributions from the three models are used to show locations of tracking sites. Selected tracking points and marking symbols in the plots: X1: *, just below the patch (or scar for M2); X2: x, just next to the left of the patch; X3: o, just above the patch; X4: +, just next to the right of the patch; X5: v, at the center of the patch; and X6: ̂, just below the patch (this is for the preoperation model only).

Figure 14

Validation by postoperation data. (a) Computational pre- and postoperation pressure conditions in RV, and (b) comparison between measured RV volume and two computational predictions. Blue line: pressure and volume from Patch Model 2 prior to postoperative data (CMR max volume 188.3ml, predicted volume 205.97ml, and error margin 9.4%); black line: adjust pressure condition and improved RV volume prediction using postoperation data (new predicted volume 190.2ml and error <3%).

Figure 15

CMR-measured averaged flow rate and accumulated outflow volume at the pulmonary valve for the preoperation model. “ *” marks CMR data points.

Figure 5

(a) Experimental data for RV material properties and the stress-stretch curve derived from the Mooney–Rivlin model with parameters selected to fit experimental data. Parameter values used for the Mooney-Rivlin model: c1=3600dyn∕cm2, D1=818dyn∕cm2, c2=0, and D2=12. (b) Adjusted patient-specific material stress-stretch curves from Mooney–Rivlin models fitting CMR data. RV tissue: c1=92,000dyn∕cm2, D1=36,000dyn∕cm2, c2=0, and D2=2.0; scar: c1=920,000dyn∕cm2, D1=360,000dyn∕cm2, c2=0, and D2=2.0; patch: c1=1,840,000dyn∕cm2, D1=720,000dyn∕cm2, c2=0, and D2=2.0.

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