Imaging description

Inappropriate selection of the inversion time (TI) in late gadolinium enhancement (LGE) cardiac MRI (CMR) examinations results in incomplete suppression of the myocardium. Most frequently encountered is the selection of a TI that is slightly too short, resulting in a subendocardial “ring of hypointensity” and a mid-myocardial zone of hyperintensity (Figures 47.1 and 47.2). These artifacts may mimic true mid-myocardial delayed enhancement that can be seen in pathologic conditions such as sarcoidosis or dilated cardiomyopathy (Figure 47.3). In a less commonly encountered clinical scenario, suppression of abnormal myocardium (amyloidosis is the prototypical example) will cause hypointensity of abnormal myocardium. This will result in the poor quality of delayed enhancement images that is a hallmark of patients with amyloidosis (Figure 47.4).

Importance

Two potential pitfalls result from incorrect inversion time selection. First, incorrect nulling of the myocardium reduces the conspicuity of true myocardial delayed enhancement, potentially hiding underlying pathology, resulting in a falsenegative result. Second, incomplete nulling due to a short inversion time, if not recognized as artifact, can be erroneously interpreted as diffuse mid-myocardial LGE, leading to a falsepositive result. The interpreting radiologist must be familiar with the appearance of deviations of the TI selection, and be aware of underlying conditions, particularly amyloidosis, that can cause difficulty in selecting the correct TI time.

Typical clinical scenario

TI is selected to provide maximal contrast between normal and abnormal myocardium by completely nulling any signal from normal myocardium. TI selection determines the sensitivity for the detection of myocardial damage. The actual TI time needed for normal myocardial suppression depends on multiple factors, including the time after contrast injection, renal elimination of contrast, patient size, cardiac output, contrast dose and contrast agent. A typical approach for TI selection is the use of a “TI scout” sequence, which is typically an ECG-gated post-contrast sequence with images acquired at multiple delay times after an initial 180 degree inversion pulse, resulting in different TI contrasts throughout the cardiac cycle.