Created by Tina Morrison
Updated April 2010
Updated April 2010
Purpose
Relatively little is known about the wall dynamics of the human
thoracic aorta, in particular the longitudinal motion. Previous
studies have reported circumferential strain using an Eulerian
frame, but no studies heretofore have quantified longitudinal strain,
nor have any implemented a Lagrangian frame. It is vital to
understand the dynamics of this region because it affects stents
and other medical implants. The aim of this study is to characterize
the longitudinal strain, and to compare the diameter and
circumferential strain of the proximal and distal descending thoracic
aorta (DTA) over the cardiac cycle.
Materials and Methods
The DTA of seven patients (6M, 1F, 46±5 yrs) with no aortic
pathology were studied using 4D cardiac gated-CT. Each data set
contained ten 3D volumes of the vasculature, each volume
representing 1/10th of the cardiac cycle. Because it has been
shown that strain and pressure peak nearly simultaneously in the
cardiac cycle, all measurements were made at peak-systole and
diastole1. Using SimVascular2, a center-line path of the DTA was
created, and the location and centroid of the ostia of the two most
proximal and distal intercostal arteries were marked. The ostia
serve as the Lagrangian reference frame, versus the previously
used3 Eulerian frame. The centroids were then projected to the
center-line. We defined the length of the DTA as the arc length
between the most proximal and distal projected centroids. We
computed the length of the DTA at diastole Dzd and peak-systole
Dzs, and the effective diameter of each cross-section just below the
ostia at diastole Dcd and peak-systole Dcs. We calculated the
longitudinal and circumferential strain by (Dzs-Dzd)/Dzd and
(Dcs-Dcd)/Dcd.
Relatively little is known about the wall dynamics of the human
thoracic aorta, in particular the longitudinal motion. Previous
studies have reported circumferential strain using an Eulerian
frame, but no studies heretofore have quantified longitudinal strain,
nor have any implemented a Lagrangian frame. It is vital to
understand the dynamics of this region because it affects stents
and other medical implants. The aim of this study is to characterize
the longitudinal strain, and to compare the diameter and
circumferential strain of the proximal and distal descending thoracic
aorta (DTA) over the cardiac cycle.
Materials and Methods
The DTA of seven patients (6M, 1F, 46±5 yrs) with no aortic
pathology were studied using 4D cardiac gated-CT. Each data set
contained ten 3D volumes of the vasculature, each volume
representing 1/10th of the cardiac cycle. Because it has been
shown that strain and pressure peak nearly simultaneously in the
cardiac cycle, all measurements were made at peak-systole and
diastole1. Using SimVascular2, a center-line path of the DTA was
created, and the location and centroid of the ostia of the two most
proximal and distal intercostal arteries were marked. The ostia
serve as the Lagrangian reference frame, versus the previously
used3 Eulerian frame. The centroids were then projected to the
center-line. We defined the length of the DTA as the arc length
between the most proximal and distal projected centroids. We
computed the length of the DTA at diastole Dzd and peak-systole
Dzs, and the effective diameter of each cross-section just below the
ostia at diastole Dcd and peak-systole Dcs. We calculated the
longitudinal and circumferential strain by (Dzs-Dzd)/Dzd and
(Dcs-Dcd)/Dcd.
Accepted Abstract for BCATS Symposium. You will also find my poster at the Life in Motion Symposium.
Cardiac gated-CT (4D) image of a
descending thoracic aorta. You can see its
wall motion and the heart beating over the
cardiac cycle.
descending thoracic aorta. You can see its
wall motion and the heart beating over the
cardiac cycle.
Tina M. Morrison, PhD, Polina Segalova
Christopher K. Zarins, MD, and Charles A. Taylor, PhD
Christopher K. Zarins, MD, and Charles A. Taylor, PhD
Quantification of in vivo wall motion of the descending thoracic aorta using 4D-CT
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Cardiovascular Biomechanics Research Laboratory
My research in the CVBRL involved developing and applying methods to quantify in vivo
deformations of normal and diseased thoracic aortas using cardiac-gated CT imaging data, which
enables us to understand the biomechanical environment and progression of disease in the aorta.
The group has extended those methods to quantify in vivo deformations of, and loads on,
cardiovascular stent-grafts from medical imaging data. Finally, research was conducted to validated
fluid-structure-interaction computer simulations of thoracic aortic wall motion with cardiac-gated CT
imaging data.
Below are 3D volume rendered images of different thoracic aortas generated from CT data. Starting from the
left is a healthy straight aorta, a curved healthy aorta, a tortuous aorta, an aorta with an ascending aortic
aneurysm, and an aorta with a descending aortic aneurysm. My research involves examining the
biomechanical environment and quantifying wall motion using 4D-CT data and SimVascular software.
deformations of normal and diseased thoracic aortas using cardiac-gated CT imaging data, which
enables us to understand the biomechanical environment and progression of disease in the aorta.
The group has extended those methods to quantify in vivo deformations of, and loads on,
cardiovascular stent-grafts from medical imaging data. Finally, research was conducted to validated
fluid-structure-interaction computer simulations of thoracic aortic wall motion with cardiac-gated CT
imaging data.
Below are 3D volume rendered images of different thoracic aortas generated from CT data. Starting from the
left is a healthy straight aorta, a curved healthy aorta, a tortuous aorta, an aorta with an ascending aortic
aneurysm, and an aorta with a descending aortic aneurysm. My research involves examining the
biomechanical environment and quantifying wall motion using 4D-CT data and SimVascular software.
Accepted abstract to the Society of Experimental Mechanics
SEM XI International Congress & Exposition on Experimental & Applied Mechanics
SEM XI International Congress & Exposition on Experimental & Applied Mechanics
Tina M. Morrison, PhD and Charles A. Taylor, PhD
Quantification of the in vivo wall thickness and material
properties of the descending thoracic aorta using 4D-CT
properties of the descending thoracic aorta using 4D-CT
Relatively little is known about the wall dynamics of the human thoracic aorta, in particular the variability in wall
thickness and material properties of the descending thoracic aorta (DTA). Recently, we quantified, for the first time,
the longitudinal and circumferential strain of the DTA using 4D cardiac-gated CT image data. We extended those
techniques, and using Simvascular software, to quantify the wall thickness and material properties of the DTA , and
were compared simulated deformation patterns to the in vivo measured data. Previously, a direct correlation was
determined between cyclic aortic wall strain and wall thickness at one level of a thoracic aorta in a pig. The similarity
in the deformation patterns between porcine and human descending thoracic aorta suggests that the human aorta
also exhibits circumferential variation in wall structure. To capture this, we solved an inverse-elasticity problem.
This involved minimizing the difference between the measured deformation from the 4D-CT data and the simulated
deformation using Simvascular, in concert with the incremental elastic modulus (defined as function of the systolic
and diastolic pressure and radius, measured cyclic strain, and a nominal thickness), by systematically varying the
wall thickness until the simulated deformation matches the measured nonuniform deformation. Results and a
description of the method will be presented.
thickness and material properties of the descending thoracic aorta (DTA). Recently, we quantified, for the first time,
the longitudinal and circumferential strain of the DTA using 4D cardiac-gated CT image data. We extended those
techniques, and using Simvascular software, to quantify the wall thickness and material properties of the DTA , and
were compared simulated deformation patterns to the in vivo measured data. Previously, a direct correlation was
determined between cyclic aortic wall strain and wall thickness at one level of a thoracic aorta in a pig. The similarity
in the deformation patterns between porcine and human descending thoracic aorta suggests that the human aorta
also exhibits circumferential variation in wall structure. To capture this, we solved an inverse-elasticity problem.
This involved minimizing the difference between the measured deformation from the 4D-CT data and the simulated
deformation using Simvascular, in concert with the incremental elastic modulus (defined as function of the systolic
and diastolic pressure and radius, measured cyclic strain, and a nominal thickness), by systematically varying the
wall thickness until the simulated deformation matches the measured nonuniform deformation. Results and a
description of the method will be presented.
Accepted abstract to the International Society of Endovascular Specialist
9th Annual Endovascular Research Competition
9th Annual Endovascular Research Competition
Tina M. Morrison, PhD, Christopher K. Zarins, MD, and Charles A. Taylor, PhD
Quantification and comparison of the in vivo wall dynamics of the descending thoracic aorta in
younger and older patients using 4D-CT
younger and older patients using 4D-CT
Results
The length of the DTA at systole was 12.0±1.3cm, larger than the
length at diastole 11.8±1.3cm (p < 0.0001), with a longitudinal
strain of 1.9±0.7%. The effective proximal and distal diameters at
systole were 23.4±1.3 and 21.8±1.1mm (p < 0.005), and the
effective proximal and distal diameters at diastole were 21.8±1.2
and 20.1±1.0mm (p < 0.0001). The proximal and distal
circumferential strains were 7.4±3.5 and 8.7±2.2% but not
statistically different.
Conclusions
Reported for the first time is the in vivo longitudinal strain of the
human DTA (≈2%), which is about 1/4 of the circumferential strain
(≈8%). Also, the proximal diameter of the DTA is larger than the
distal diameter over the cardiac cycle. These results may prove
useful in clinical and engineering applications. Future work lies in
extending this study to patients with disease of the DTA.
References
[1] Draney et al, Magn Reson Med, 52:286-295 (2004)
[2] Wilson et al, Lec Notes Com Sci, 2208:449-456 (2001) => Website
[3] Draney et al, 2005 Proc Ann Mtg Soc Vasc Surg (2005)
Presented a poster at the Cardiovascular Institute Retreat at Stanford University
Tina M. Morrison, PhD, Gilwoo Choi, Polina Segalove, Christopher K. Zarins, MD, and Charles A. Taylor, PhD
Age-related changes in the biomechanical cyclic strain of the human thoracic aorta using 4D-CT
Tina M. Morrison, PhD, Gilwoo Choi, Polina Segalove, Christopher K. Zarins, MD, and Charles A. Taylor, PhD
Age-related changes in the longitudinal and circumferential cyclic strain of the human thoracic aorta
Podium Presenter at the Design of Biomechanical Devices Symposium ASME Summer
Bioengineering Conference in Marco, FL 25-29 June 2008
Bioengineering Conference in Marco, FL 25-29 June 2008
On 21 May 2008, I was awarded an American Heart Association Post Doctoral Fellowship for my
research on 'Understanding the Influence of Biomechanical Forces on Normal and Aneurysmal
Thoracic Aortic Function'
research on 'Understanding the Influence of Biomechanical Forces on Normal and Aneurysmal
Thoracic Aortic Function'
Solid model of a thoracic aorta created by
Tina Morrison using Simvascular software,
developed at Stanford, super-imposed with
CT image data.
Tina Morrison using Simvascular software,
developed at Stanford, super-imposed with
CT image data.
News Flash: On 2 September 2008, I will begin my new appointment in the Medical Device Fellowship
Program at the Food and Drug Administration in Rockville, MD. My new position is lead engineer on
pre-market approval of stent-grafts, and medical image consultant for the animal testing laboratory.
Program at the Food and Drug Administration in Rockville, MD. My new position is lead engineer on
pre-market approval of stent-grafts, and medical image consultant for the animal testing laboratory.
Presented a seminar for the Department of Biomedical Engineering at Texas A&M on 25
August 2008
August 2008
Dr. Morrison was cited in The Gray Sheet following my fill-in presentation for Dr. Taylor at
the Critical Paths Initiative meeting on 16 September 2008, sponsored by DIA.
the Critical Paths Initiative meeting on 16 September 2008, sponsored by DIA.
Cyclic strain, curvature and branch vessel angles of the human thoracic aorta: age-related changes
Invited to Present a seminar for the Office of Science and Engineering Laboratories at the
FDA at the Center for Devices and Radiological Health on 30 September 2008
FDA at the Center for Devices and Radiological Health on 30 September 2008
My recent submission to the Journal of Vascular Surgery has appeared in the April 2009
edition. Click here.
edition. Click here.