The most effective form of cardiac gating is ECG gating which requires a high-amplitude QRS complex. In case of inadequate QRS complex, we can use the peripheral pulse from fingertip pulse monitors. An arrhythmia may lead to inappropriate triggering and image blurring or artifacts. An arrhythmia rejection technique is useful but prolongs the acquisition time.

When the images are blurred and signal-to-noise ratio (SNR) is too weak due to the respiratory motion, increasing the number of image acquisitions helps to improve SNR and reduce respiratory motion artifacts [2]. There are different kinds of respiratory fixing methods used in the clinical settings.

The bolus injection of contrast medium is helpful to increase the signal of the blood or the targeted tissue. 3D MRA study is useful in the evaluation of blood vessels. The early phase of enhancement in the targeted tissue is related to the vascularity of the tissue and also reflects the fractional blood volume of the tissue and the extravascular microcirculation of the contrast medium. The inflammation of the targeted tissue or the higher vascularity of the tumors may represent prominent early enhancement. Differential distribution of contrast medium in early dynamic phases is helpful to differentiate between the normal myocardium and the pathologic myocardium in ischemic conditions.

The late phase of enhancement in the targeted tissue can be used to evaluate the abnormal stasis of the contrast medium which is useful to evaluate the areas of fibrosis. Stasis of contrast medium in the myocardium is made more prominent on the images by using the inversion recovery pulse which suppresses the normal myocardial signal.

The heart is positioned in the thoracic cage with a little oblique direction to the standard view of the thorax. Therefore, cardiac MR images are generally obtained along the long and short axes of the heart rather than those of the thorax. The long axis of the heart is the line from the cardiac base to the apex, and the short axis is the line perpendicular to the long axis of the heart. Although we can obtain all cardiac views through the freely positioned acquisition windows in any orientation, we usually obtain the dedicated views similar to echocardiography to allow assessment of cardiac chamber morphology or function and to communicate effectively among the clinicians.

MR signal intensity in many situations is too weak to provide an appropriate information from the targeted images. The preparation pulse plays a role to create a preexisting magnetization prior to the application of RF pulses destined for data readout. It was usually applied before the spin echo or gradient echo pulse sequences were performed. Major roles are enhancing tissue contrast and suppressing signal intensity from the targeted tissues. Preparation pulse may prolong the acquisition time.

MR signal intensities usually depend on the repetition time (TR) and the echo time (TE). The repetition time is the time between consecutive excitations, and the echo time is the time between the excitation and the detection of the signal which are applied for the spin echo or gradient echo. We need to select an appropriate TR or TE to characterize the tissue components.