Evaluating the contribution of the different ventricular portions to the global ventricular performance is important in many cardiac diseases. The parameters used to study regional ventricular function are myocardial wall thickness, systolic wall thickening, and circumferential and longitudinal wall motion or shortening.

Preserved wall thickness is a good indicator of the presence of viable myocardium in the setting of a chronic infarction and wall thickening analysis is more sensitive in the detection of dysfunctional myocardium than wall motion analysis [6]. Some studies have shown that measuring regional contractility is a better prognostic indicator than left ventricular EF and that quantitative measurement of wall thickening provides a more precise indication of regional function than does visual estimation of wall motion [7, 8].

CMR short-axis acquisitions have proved their usefulness for the determination of left ventricular regional wall parameters [6]. In contrast to echocardiography, which only provide good visualization of the endocardial borders of the myocardium, CMR also provides excellent depiction of the epicardial borders of the myocardium. This allows assessment of not only wall motion but also wall thickening and thinning. Local wall thickness and thickening can be derived from manually or automatically defined endocardial and epicardial profile in end diastole and end systole of left and right ventricle.

The commonest way to assess wall thickness and thickening is based on the centerline method (Fig. 6.2). In short-axis images, myocardial thickness is divided by a line into two equal parts, equidistant to the endocardium and epicardium; multiple lines are drawn perpendicular to this line, covering the entire myocardium at defined intervals. The length of each line indicates parietal thickness, while the relationship between the length of each line at the end of systole and diastole defines systolic thickening [9].

Normal values for end-systolic wall thickening can be used for comparison to determine which myocardial regions are impaired. The most important clinical application of regional functional analysis is the assessment of reversibly injured yet viable myocardium in ischemic heart disease [10, 11].

Although, for daily clinical use, wall motion is often visually assessed, contouring of endo- and epicardial borders may be helpful to quantify motion (e.g., amount of centripetal motion of endocardial border during systole).

Accurate regional function analysis has become feasible with the introduction of CMR myocardial tagging (Fig. 6.3) allowing an highly reproducible quantitative assessment of mechanical properties such as myocardial strain deformation. It consists in applying, on a standard SSPF sequence, a radiofrequency prepulse perpendicular to the plane of the image, immediately following the ECG R-wave, appearing in the image as a grid of dark saturated lines. Dedicated computer algorithms have been developed to track the intersection points of the tagging lines over the cardiac cycle, to analyze the deformation of the saturation grid and sequent quantification of regional myocardial deformations. By applying this technique in multiple slices in both short-axis and long-axis directions, 3D-myocardial strain measurements can be performed, allowing an accurate quantification of circumferential and longitudinal shortening [12].

Cardiac-gated phase-contrast (PC) sequences with flow-encoding gradients are used to quantify velocity and blood flow in the heart and great vessels. 2D PC CMR sequences are the most commonly used in clinical practice and the flow quantification is based on the phase shift measurement induced in the protons in motion by the application of pulsed gradients.

PC can accurately quantify the regurgitant volume, either as an absolute value or as the regurgitant fraction. Each PC acquisition produced two sets of cine-images: a magnitude image, used for anatomic orientation, and a phase image in which the gray value of each pixel represents the velocity information in that voxel. For flow quantification, phase information acquired on a perpendicular plane through the jet of regurgitation, just near the valve, are required (Fig.6.4). Stationary spins are represented as mid-gray, while increasing velocities in either direction are shown in increasing grades of black or white. Black values show flow toward the viewer, whereas white values show flow away from the viewer. It is important to define the size of velocity encode window as close to the peak velocity as possible, to reduce aliasing of peak velocities and maintaining sensitivity for flow measurements. Measurement of the spatial mean velocity for all pixels in a region of interest of known area enables the calculation of the instantaneous flow volume at any point in the cardiac cycle. Calculation of the flow volume per heart beat can be made by integrating the instantaneous flow volumes for all frames throughout the cardiac cycle [13]. This technique has been validated in vitro and in vivo and is extremely accurate and reproducible [14]. The severity of regurgitation can be defined as mild (regurgitant fraction 15–20%), moderate (regurgitant fraction 20–40%), and severe (regurgitant fraction >40%) [15].

Application of PC to the proximal portion of the ascending aorta allows the assessment of left ventricular systolic function by evaluating the flow over a complete cardiac cycle. Such a study requires a PC acquisition in the oblique axial plane crossing the ascending aorta and the left ventricular stroke volume can be obtained tracing the lumen of the vessels in every phase of the cardiac cycle [16].

Quantification of the right ventricular and left ventricular outputs can be compared using through-plane flow measurements from the proximal ascending aorta and pulmonary trunk (Qp/Qs ratio = 1 in normal individuals), thus allowing quantification of shunts in patients with congenital heart disease [17].

In patients with known or suspected ischemic heart disease, diagnosis of an hemodynamically significant stenosis, and assessment of functional significance of an anatomical lesion, is of crucial importance in the evaluation and therapeutic decision-making.

The intrinsic mechanisms of coronary microvascular adaptation (coronary reserve) do not allow to appreciate myocardial perfusion defects at rest. To detect significant stenoses of the epicardial coronary arteries, it is helpful to stress the patient so that a measure of the coronary flow reserve, or similar measures such as the myocardial perfusion reserve index, can be obtained [18]. Stress conditions are induced by physical exercise or pharmacological agents such as dipyridamole, adenosine, or dobutamine.

Compared with the radionuclide techniques, myocardial MR perfusion imaging has several advantages, including its lack of ionizing radiation, higher spatial resolution to allow analysis of transmural differences in myocardial blood flow (MBF), no attenuation problem related to overlying breast shadow or obesity [19].