## 5 Medical Imaging-Based Kinematics
### Ultrasound Technology (US)  
Ultrasound (US) uses high frequency (2 to 15 MHz) acoustic waves to create real-time 2D in vivo images of tissues, organs, and blood pools using piezoelectric transducers. As in any wave, higher frequencies are associated with smaller wavelengths, higher penetration power, and improved image resolution [152; 153]. Volume rendering from ultrasound images has led to three-dimensional, time-resolved ultrasound (4D US), and real-time imag \begin{table}
\begin{tabular}{p{56.9 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt} p{113.8 pt}} \hline \hline
**Technology** & **Technique** & **Principle** & **Resolution** & **Applications** \\ \hline \multirow{4}{*}{US} & \multirow{4}{*}{Speckle Tracking} & Acoustic response to the interaction & Spatial and displacement & Identification of: septal defects, CHD, valve resolution \textless{}1 mm/pixel & Identification of: septal defects, CHD, valve structure. Assessment of cardiac and aortic function. \\  & & & tissue fibers. & Real-time temporal resolution. & Cardiac and aortic function. \\ \hline \multirow{4}{*}{MRI} & \multirow{4}{*}{Tissue tagging} & Local perturbation of myocardium magnetization with selective radiofrequency saturation sequences & Spatial and displacement resolution \textless{}1 mm & Assessment of cardiac function; motion and deformation of myocardium, skeletal muscle, lung tissue and tongue. \\  & & Applied magnetic field gradients produce a phase shift on proton spins proportional to its relative displacement. & Pixel size \textless{}2.5 mm for myocardial motion [149], \textless{}1.3 mm for aortic motion [150] & Assessment of myocardial and aortic motion, deformation, and function. \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \cline{1-1} \cline{2-5}  & & & & \\ \hline \end{tabular}
\end{table} 
Table 4: Image-based technique for assessment of tissue motion. ing [154]. US is relatively inexpensive, portable, and safe, so it has become a customary tool in many clinical applications such as anesthesia, critical care, prenatal care, and pain management. Its application to cardiology, commonly known as echocardiography, was introduced in the 1950s, and currently is the more ubiquitous diagnostic tool to assess cardiovascular structure and function. With an approximate lateral resolution of 1 mm/pixel, this technique allows the estimation of heart chamber size, valve structure, identification of structural abnormalities such as seen in congenital heart defects (CHD), and determination of systolic and diastolic function (Figure 7c) [155]. Nevertheless, echocardiography presents some intrinsic limitations regarding accuracy and repeatability, particularly in patients with complex flow patterns related to congenital heart disease, aortic regurgitation, or dissection, in which case it is recommended to complement the study with other imaging techniques [156]. Intravascular ultrasound technology (IVUS) was developed following the principle that accuracy and resolution are improved as the transducer is closer to the tissue of interest. This technology involves placing a miniature ultrasound probe at the end of a catheter and then introducing the catheter into the vessel of interest in order to resolve the surrounding structures with greater detail than allowed by standard external US. This invasive technique is mostly used to study the conditions and progression of atherosclerosis in patients with coronary and carotid artery disease [157]. US technology can also provide blood flow and tissue kinematic information through the use of echo-Doppler and speckle tracking techniques.