Long inversion delayed enhancement MRI: A useful sequence for thrombus identification in congenital heart disease (QF_TH_063)

A 30-year-old female with Tetralogy of Fallot/ Pulmonary atresia, and right aortic arch presented to the Adult Congenital Heart Disease Clinic with progressive dyspnea on exertion. She underwent staged biventricular palliation, with the most recent procedure being VSD closure with placement of a 20mm aortic homograft 25 years ago. The echocardiogram was challenging due to limited windows but revealed slowly progressing, now moderate conduit stenosis with mild regurgitation and evidence of RV dysfunction with dilation. Cardiac MRI was obtained to assess RV function, volumes, and homograft regurgitation fraction, specifically to focus on the timing of future interventions.

Diagnostic Techniques and Their Most Important Findings:

Cardiac magnetic resonance imaging (CMR) was performed on a 1.5T scanner (Magnetom Aera, Siemens), demonstrating a moderate stenosis within the RV-PA conduit, particularly at the level of the valve leaflets and extending to the supravalvular region, partly due to a mobile, homogeneous, hypointense supravalvular mass measuring 18 x 16 mm. The mass was adherent to the right side of the conduit just above the valve leaflets, causing narrowing of the conduit and turbulent blood flow (visible on the CINE RVOT sequences as a supravalvular dephasing jet.). Mild RV-PA conduit regurgitation with a fraction of 23% was also observed, although the right ventricular ejection fraction (RVEF) remained within normal limits. Standard Late Gadolinium Enhancement (LGE) imaging using Phase Sensitive Inversion Recovery (PSIR) at inversion times-Ti~260ms and Ti~300ms was positive for focal delayed enhancement at the right ventricular septal insertion, consistent with fibrotic scar tissue, while the mass remained hypointense. A review of prior imaging showed that the mass had remained similar in size and appearance over time, making differentiation between thrombus and other lesions challenging. By increasing the inversion time to be very long i.e., Ti~600ms, the mass continued to not enhance confirming an organized thrombus.

Learning Points from this Case:

This case emphasizes that the addition of a very long inversion time (TI ~600ms) to the standard PSIR sequence can be an effective tool for detecting organized thrombus or clot. This approach is particularly useful in patients with severe ventricular dysfunction where occult clots are a concern or in those with palliated congenital heart disease, where thrombus on prosthetic materials such as conduits can contribute to new or increased gradients. It is specifically advantageous in patients with a poor echo window.