Imaging description

High-signal mimicking thrombus can occur in cardiac chambers on inversion recovery-based dark blood images due to slow flow. Double inversion recovery dark blood images use an initial non-slice-selective 180 degree inversion pulse followed immediately by a second slice-selective inversion pulse in the plane of interest. The net effect is to invert all protons outside of the imaging plane while leaving protons in the plane unaffected. Image acquisition begins when inverted blood protons cross the null point during T1 recovery, typically corresponding to mid-diastole. The sequence relies on flowing blood to replace non-inverted blood protons in the image plane with nulled blood from outside the plane. If there is slow moving blood in a cardiac chamber, there will be incomplete blood suppression. In patients with localized hypokinetic regions, artifactual high signal in these regions of stasis is common and can mimic thrombus (Figure 48.1). This is also common in the subendocardial region in patients with reduced ejection fraction due to slow flow in trabeculations (Figure 48.2).

Importance

Misdiagnosis of thrombus in cardiac chambers could lead to risks from anticoagulation and additional unnecessary followup imaging.

Typical clinical scenario

Artifactual signal from slow flow on dark blood images is common in the left ventricular apex, both in the setting of a global cardiomyopathy or prior apical myocardial infarction. However, artifactual high signal can be seen anywhere there is sluggish flow, including the right ventricle and atria.

Differential diagnosis

Pseudothrombus on dark blood images should be distinguished from a true thrombus. Both of these entities can occur in the setting of blood stasis. However, unlike dark blood artifacts, true thrombus should be present on all pulse sequences both pre- and post-contrast (Figure 48.1).