Final answer:
Myocardial thickening on gated images is often due to cardiac hypertrophy, a compensatory response to increased workload or stress, such as from atherosclerotic coronary arteries or negative inotropic factors.
Step-by-step explanation:
The effect that causes myocardial thickening on gated images is primarily due to conditions such as cardiac hypertrophy, which is an abnormal enlargement or thickening of the heart muscle. The myocardium, the thickest layer of the heart, is composed of cardiac muscle cells supported by collagenous fibers and blood vessels. In response to increased workload or negative inotropic factors, the myocardium may thicken as a compensatory mechanism to maintain cardiac output.
In the context of MRI imaging, as seen in Figure 14.7.4, when patients are injected with a paramagnetic contrast agent, the magnetic properties of water in cells are altered, providing detailed images of soft tissues, including the myocardium. With a thicker myocardium, as seen in Figure 19.8, the left ventricle must generate greater pressure to overcome systemic resistance, which can be visualized on MRI as myocardial thickening. Prolonged conditions leading to myocardial thickening, like atherosclerotic coronary arteries, can eventually lead to myocardial infarction if untreated.