## 6 Applications to Cardiovascular Medicine
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**Section** & & \\ \hline \multirow{4}{*}{5.} & Early assessments of in vivo stiffness of blood vessels relied on measurements of luminal area changes. However, the predictive capabilities of these factors are inconsistent among different arterial locations and pathologies. In vivo medical imaging has evolved to provide not only anatomical geometric information but also detailed kinematic measurements. The accuracy and availability of these techniques are limited by image resolution, signal-to-noise ratio (SNR), the occurrence of artifacts, and practical obstacles related to testing costs and health hazards. & \\ \hline \multirow{4}{*}{5.1} & Ultrasound (US) uses high-frequency (2 to 15 MHz) acoustic waves to create real-time in vivo images of tissues, organs, and blood pools using piezoelectric transducers with lateral resolution of 1 mm /pixel. US is relatively inexpensive, portable, and safe, so it has become a customary tool in many clinical applications. However, the accuracy and reproducibility of US-derived measurements are limited in comparison to MRI-based measurements. Blood flow velocity can be assessed with echo and vector doppler technology. & \\ \cline{1-1}  & Tissue displacement can be measured using speckle tracking technology, which consists of image tracking the acoustic response of tissue fibers to ultrasound signals. & \\ \hline \multirow{4}{*}{5.2} & Magnetic resonance imaging (MRI) offers superior quantitative utility compared to ultrasound as it can offer higher resolution and accuracy of measurements of anatomical features. & \\ \cline{1-1}  & MRI generally poses minimal hazard to patients unless they have implanted medical devices/objects or suffer from clauestrophobia. However, the technique requires specialized equipment and trained staff, which limits availability compared to US. & \\ \cline{1-1}  & MRI-based techniques for assessment of tissue kinematics include tissue tagging and DENSE MRI. & \\ \cline{1-1}  & Tissue tagging is based on image tracking of magnetically induced markers, while DENSE MRI encodes the tissue displacement on the phase of the MR signal. & \\ \cline{1-1}  & Tissue tagging and DENSE MRI have been used to assess the kinematics of the myocardium. However, the superior resolution and accuracy of DENSE MRI allow the assessment of aortic kinematics. & \\ \cline{1-1}  & Phase-contrast (PC) MRI is a technique that allows the time-resolved quantification of blood flow velocity in or through a 2D plane by encoding the velocity in the phase of the MRI signal. & \\ \cline{1-1}  & PC MRI has been generalized to 3D spaces at the expense of decreased spatial and temporal resolution. The resulting technique is called 4D flow MRI. & \\ \cline{1-1}  & PC MRI and 4D flow MRI have been applied to the study of healthy and pathological hemodynamics of the heart and large arteries and are currently implemented in clinical practice for the assessment of aortic and pulmonary diseases. & \\ \cline{1-1}  & MRI can provide other complementary information relevant for inverse modeling analyses of the cardiovascular system. & \\ \cline{1-1}  & Diffusion-tensor MRI can resolve the orientation of tissue fibers based on the principle that the Brownian displacement of water molecules occurs preferentially in the direction of fibers. & \\ \cline{1-1}  & Gadolinium-enhanced (GE) MRI can be used to resolve the size and severity of cardiac lesions. Since healthy cell membranes are impermeable to gadolinium, this contrast agent occupies a larger volume in injured tissue where cell membrane integrity is compromised. & \\ \cline{1-1}  & Perfusion stress tests use contrast agents and MRI imaging to assess the severity of coronary artery insufficiency. This is performed by comparing the perfusion of contrast agents in the myocardium at rest and at a stress state (high heart rate). & \\ \hline \multirow{4}{*}{5.3} & Computerized tomography (CT) provides the best resolution among all the medical imaging techniques with pixel sizes around 0.5 mm. & \\ \cline{1-1}  & The high-resolution CT images can be used to assess cardiovascular kinematics through image tracking of anatomical features. & \\ \cline{1-1}  & However, this requires the introduction of assumptions of displacement modes. & \\ \cline{1-1}  & CT scans are based on X-ray technology with inherent ionizing radiation hazards. & \\ \hline \hline \end{tabular}
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