The Roles of CMR and MSCT in Adult Congenital Heart Disease

Abstract

Both CMR and MSCT give almost unrestricted access to intra-thoracic structures, which is important as ultrasonic access may be limited in ACHD patients, many of whom have had previous cardiothoracic surgery. MSCT, generally using intra-vascular contrast, gives superior spatial resolution in much shorter study times than CMR, although the radiation dose is a concern in this relatively young patient group that may require repeated studies. CMR offers unrivaled versatility of acquisition methods without ionizing radiation, enabling biventricular functional assessment, flow measurements, myocardial viability assessment, angiography, and more. For these reasons, a dedicated CMR service should be regarded as a necessary facility in a centre specializing in ACHD care. However, the short acquisition time and high spatial resolution of contrast-enhanced MSCT is advantageous, notably for imaging the epicardial coronary arteries and other narrow structures. MSCT also shows conduit calcification or stent location clearly, and retrospective ECG-gated multi-phase reformatting allows measurements of biventricular size and function, providing an alternative to CMR in patients with a pacemaker or ICD. To realize their full potential and avoid pitfalls, CMR and MSCT of ACHD require training and experience. Appropriate understanding is needed for the evaluation of congenitally and surgically altered circulatory function as after Fontan operations, surgery for transposition of the great arteries, or tetralogy of Fallot (ToF) repair. For these and other more complex cases, CMR and MSCT should ideally be undertaken by experienced congenital cardiovascular imaging specialists committed to long-term collaboration with the cardiologists and surgeons managing ACHD patients in a tertiary referral centre.

The relatively unrestricted access provided by CMR and MSCT allows the assessment of clinically important regions that may lie beyond ultrasonic access. These include the pulmonary veins and the sinus venosus regions of the atrial septum, the right ventricular free wall and outflow tract, the pulmonary arteries, and the whole aorta and the para-mediastinal regions, which may be crossed by aorto-pulmonary collateral arteries.1, 2 Both CMR and MSCT allow 3D contrast-enhanced angiography and regional or global assessment of biventricular function with good blood-tissue differentiation. MSCT offers the better spatial resolution and does not require specific predetermination of imaging planes as there is a complete volume of data that can be rotated and cut to any desired plane. CMR offers the possibility of “dynamic” angiography, visualizing the sequential opacification of successive vascular regions. Besides freedom from radiation, the key additional strengths of CMR lie in its high temporal resolution, measurements of flow volumes, and characterization of tissues, if needed.