Synopsis
Estimating the stiffness of left ventricle and aorta provides important information in diagnosing various cardiovascular diseases. MR elastography (MRE) is a noninvasive technique to estimate the stiffness of soft tissues. This abstract will demonstrate the principle and application of MRE for diagnosing cardiovascular diseases.
Why estimating LV and aortic stifffness?
Cardiovascular disease is one of the leading causes of death worldwide.
Ventricular-vascular coupling i.e. functional properties of both the organs in
conjunction play an important role in different disease states including
hypertension, aortic stenosis etc. One of the mechanical properties i.e. myocardial
stiffness is a major determinant of cardiac function and is increased in many
diseases including the spectrum of ischemia [1], diastolic dysfunction [2], hypertension [3], and hypertrophic cardiomyopathy [4]. Similarly, aortic wall stiffness is a
fundamental biomechanical parameter that reflects the structural integrity
aortic tissue. Aortic compliance and distensibility reflect overall wall
stiffness, an extremely important and fundamental parameter altered in multiple
diseases including hypertension, coronary artery disease, and aortic aneurysm
formation [5]. Therefore, it is important to estimate the
stiffness of heart and aorta, noninvasively. Existing Methods to Estimate Stiffness
To date, myocardial
stiffness can only be measured with ex-vivo mechanical testing [6] or in-vivo by
indirectly inferring it from pressure-volume (P-V) relationships [7]. However, P-V
methods are: invasive; assess only global LV chamber, rather than the true
intrinsic properties of the myocardium [7]. A non-invasive method for
assessing true myocardial stiffness does not yet exist. Similarly, aortic stiffness
has been measured with catheter [8] or ultrasound-based
methods, such as pulse-wave velocity (PWV) [9] or pulse-wave
imaging (PWI) [10], or magnetic
resonance imaging (MRI)-based PWV [11]. Catheter-based
methods are invasive and provide only a global indirect measure of stiffness.
Non-invasive ultrasound methods provide only an indirect estimation based on
wave velocity in peripheral arteries [12], which is a poor
reflection of central aortic stiffness [13]. PWI is limited by
acoustic window, is one-dimensional, has limited imaging depth [14]. Similarly, MRI-based
measurement of PWV provides only an indirect global estimate of aortic wall
stiffness.Magnetic Resonance Elastography and its applications
Magnetic resonance
elastography (MRE) is a novel, noninvasive technique to estimate the stiffness
of soft tissues [5, 15]. In MRE, an external motion is
synchronized with the motion encoding gradients using a phase contrast MRI sequence
to encode the waves in the phase of an MR image. These wave images are
processed using a mathematical algorithm to obtain the stiffness maps. These
stiffness maps are spatially and temporally resolved. This abstract will
present the application of MRE and its validation against gold standard
techniques in the heart and aorta. First, the validation of MRE in animal
models such as diastolic dysfunction, myocardial infarction, hypertension,
aortic aneurysms will be presented and eventually its application in normal
subjects then in patients with disease conditions. Additionally, this abstract
will also present the future work. Acknowledgements
I would like to acknowledge NIH grant funding R01HL124096 and American Heart Association grant funding 13SDG14690027References
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