Cardiac morphology and function

Breath-hold SE imaging with multislice transaxial FSE followed by multislice SSFP in all three orthogonal planes (transaxial, coronal and sagittal) is useful for optimal planning of subsequent planes. Adequate anatomical coverage is preserved despite the temporal limitation imposed by breath-holding using staggered acquisition of contiguous slices and allowing breathing in-between, or additional software which speeds up the scan further at the expense of resolution. In the presence of significant metallic artefact FSE acquisitions are degraded to a lesser degree than GE sequences.

Subsequent cines are acquired in planes determined by the underlying diagnosis and provide higher resolution anatomical and functional information on parameters including biventricular size, function and mass. Assessment of the RV and pulmonary vasculature is of particular importance in ACHD along with extensive flow velocity mapping for measurement of peak velocities, regurgitant fractions and shunt performance (Figure 7.2). The Venc is set to account for low velocities in venous systems and higher velocities within shunts. Information from both the cines and velocity mapping is crucial for interpretation of the patterns of blood flow. Cine images also direct optimal positioning of velocity mapping sequences.

Figure 7.2 Preoperative CMR assessment of a 73-year-old woman with PS.

(a) Modified sagittal SSFP cine view showing the stenotic pulmonary valve (PV; black arrow), an aneurysmal LPA (maximal diameter 4.2 cm) and right ventricular hypertrophy (RVH). Turbulent blood flow above the valve is noted as signal loss within the otherwise high intensity blood signal. A perpendicular imaging plane was then acquired just above the valve, within the narrow part of the jet (black line). (b) Resulting SSFP cine showing the PV with restricted opening (solid white arrow). (c) Subsequent velocity mapping CMR in the same plane. Peak velocity was measured at 2.8 m/s within the area indicated (dashed white arrow).

Contrast use

MRA with gadolinium is useful for the assessment of pulmonary branch artery, aortic and major arterial anatomy. The LGE technique is being increasingly used to identify ischaemic or post-surgical scarring of ventricular myocardium.

Ventricular septal defect

VSDs are the most common congenital heart defects. They range from small haemodynamically insignificant and isolated lesions to large defects associated with multiple cardiac anomalies such as in TOF. CMR is complementary to echocardiography in the assessment of simple and complex VSDs. It allows multiplanar visualization of the spatial relationship of the defect to surrounding structures, can diagnose concurrent cardiac pathology and their functional sequelae, and quantify shunt size and effect on the RV and PAs. SE imaging en-face and parallel to the VSD provides anatomical information. SSFP cines show signal loss in the RV due to blood flow through the VSD and are useful in assessing the shape and dimensions of the defect (Figure 7.3). Shunt ratio can be calculated in two ways: firstly, comparison of pulmonary to systemic flow (Qp:Qs) obtained by velocity mapping CMR, and secondly, from the difference in ventricular SV obtained from the ventricular short-axis stack of cines (Figure 7.4).

Figure 7.3 Four-chamber SSFP GE cines from a 65-year-old man with a suspected Gerbode defect (VSD communicating directly between LV and RA).

(a) Small, basal, probably muscular VSD is identified (dashed white arrow). (b) Flow through this defect is into the RV (solid white arrow) and not the RA. Associated TR (black arrow) is in fact responsible for the dilated RA. Of note, the apparent interatrial defect seen on these images is a consequence of the imaging plane and not an ASD, and there is RVH.

Figure 7.4 Calculation of Qp:Qs for the VSD case presented in Figure 7.3 using velocity mapping CMR.

(a, b) Oblique sagittal views of the ascending aorta in cross section by (a) magnitude and (b) phase-subtracted components of velocity mapping CMR. This plane is obtained from the SSFP cine LVOT view by imaging perpendicularly and just distal to the AV. (c, d) Oblique transaxial views of the proximal MPA in cross section by (c) magnitude and (d) phase-subtracted components of velocity mapping CMR. This plane is obtained from the SSFP GE cine RVOT view by imaging perpendicularly and just distal to the PV. (b, d) Flow within the aorta (white circle) and MPA (black circle) is calculated throughout the cardiac cycle and was 5.0 and 9.2 L/min, respectively, giving a Qp:Qs of 1.8:1. Calculations of the Qp:Qs by comparison of SV will be overestimated in the presence of severe TR.

Specific reporting features in the CMR assessment of VSD are therefore:

Atrial septal defect

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