Black blood imaging provides clear depiction of the cardiac anatomy. The electrocardiographically triggered multislice spinecho acquisition is performed during breath-holds. The black blood appearance is caused by a double-inversion pulse with an appropriate delay, creating a signal void for flowing blood (black) with high tissue-to-blood contrast. It provides twodimensional (2D) images in three different directions (sagittal, transverse, and coronal) and in any other direction tailored to the morphology (1). Thin-slice (3 to 5 mm) imaging is preferred to avoid partial volume effects. For example, the assessment of focal stenosis as in coarctation of the aorta is best accomplished with 3-mm slice thickness in double-oblique planes along the course of the vessel of interest.

Gradient-echo balanced fast-field echo techniques can be used to assess the function of both ventricles in a highly
reproducible way (2,3 and 4). A stack of consecutive slices can be applied in the transverse plane or in short-axis orientation, covering both ventricles. Endocardial and epicardial borders can then be traced by using a dedicated software package. Parameters like end-diastolic volume (EDV) and end-systolic volume (ESV), stroke volume (SV), cardiac output, ejection fraction (EF), and wall mass (the latter to assess the degree of myocardial hypertrophy) can be obtained. Wall motion abnormalities can be easily depicted when these images are displayed in movie-loop. Gradient-echo multislice multiphase MRI also allows identification of recurrent or residual septal defects by displaying a signal void at the site of turbulent and/or high-velocity flow through a defect. The signal void is caused by dephasing of the protons within a jet, resulting in a local loss of signal intensity observed (Fig. 30.1). Such flow voids can also indicate valvular regurgitation or stenosis.

So-called SENSE (SENSitivity Encoding) technology allows considerable scan-time reduction in most MRI techniques, including black blood spin-echo and balanced fast-field gradientecho imaging. Simultaneously operated coils are used to improve the signal-to-noise ratio. New techniques like the recently introduced k-t broad-use linear acquisition speed-up technique (k-t BLAST) will also provide increased spatial and temporal resolution, in which a complete stack of short-axis images can be obtained in a single breath-hold (5). These faster imaging sequences will especially be of benefit for the pediatric population, because small children often have difficulties with holding their breath.

Assessment of valvular and vascular function with phasecontrast MRI is another essential tool, allowing accurate measurement of regurgitation and/or stenosis at any level in the heart. With phase-contrast MRI the flow velocity of blood can be measured, based on velocity-induced phase shifts of moving protons in the presence of a magnetic field gradient. Across the area of interest, flow volumes of both the forward flow and any regurgitation can be assessed, whereas peak velocities can be used to estimate pressure gradients over stenotic segments, using the modified Bernoulli equation. The advent of three-dimensional (3D) flow mapping with retrospective valve tracking allows more detailed evaluation of valvular function. Valve tracking is especially important to study flow over the tricuspid en mitral valve, as they move up to 24 mm during ventricular contraction (6). Based on this technique flow mapping can also provide information on the diastolic filling pattern of the ventricle and allows the construction of a ventricular time-volume curve (Fig. 30.2) (7). In patients with corrected TOF and pulmonary regurgitation (PR), right ventricular (RV) inflow curves have been used to demonstrate impaired relaxation and restriction to filling as markers of abnormal RV diastolic function (7). Shunt quantification in the case of a left-to-right shunt is possible by comparing the aortic and pulmonary net forward flow (8,9 and 10). It can also be assessed by comparison of the RV and left ventricular (LV) SVs calculated from gradient-echo imaging, with the exception of the presence of a ventricular septal defect (VSD), because RV and LV SVs appear to be the same then. Furthermore, shunt quantification is complicated when multiple shunts are present or with coexisting valvular regurgitation. More recently phase-contrast MRI was used to assess myocardial velocity, providing information on regional systolic and diastolic peak velocities and differences in timing of these events within the left and right ventricle, which is of importance if resynchronization therapy is considered (Fig. 30.3) (11,12).

Detection of cardiac dysfunction at an early stage is important to allow timely (re-)intervention when necessary. Stress testing, either pharmacologic or physical, may reveal subtle abnormal ventricular function that may not be apparent at rest (18,19 and 20). Pharmacologic stress testing using MRI has successfully been applied in the evaluation of ischemic heart disease (21), and in CHD patients (22). Physical stress testing with MRI does not require infusion of inotropes and is feasible in children and
adults with CHD (18,19 and 20). Despite certain practical problems, especially related to space limitations in the scanner when performing bicycle exercise and the induction of motion-related artifacts that might degrade image quality, the use of an MRI-compatible bicycle ergometer and a dedicated exercise protocol allows measurement of large vessel flow and biventricular function in response to exercise. For example, in a study of TOF patients after correction exercise MRI revealed that although resting EF of the right ventricle (RV) was normal in 80% of patients, the majority of 93% showed an abnormal RV response to exercise. This is most likely to be caused by longstanding volume overload because of PR (19).