Heart valve disease: investigation by cardiovascular magnetic resonance

Abstract

Cardiovascular magnetic resonance (CMR) has become a valuable investigative tool in many areas of cardiac medicine. Its value in heart valve disease is less well appreciated however, particularly as echocardiography is a powerful and widely available technique in valve disease. This review highlights the added value that CMR can bring in valve disease, complementing echocardiography in many areas, but it has also become the first-line investigation in some, such as pulmonary valve disease and assessing the right ventricle. CMR has many advantages, including the ability to image in any plane, which allows full visualisation of valves and their inflow/outflow tracts, direct measurement of valve area (particularly for stenotic valves), and characterisation of the associated great vessel anatomy (e.g. the aortic root and arch in aortic valve disease). A particular strength is the ability to quantify flow, which allows accurate measurement of regurgitation, cardiac shunt volumes/ratios and differential flow volumes (e.g. left and right pulmonary arteries). Quantification of ventricular volumes and mass is vital for determining the impact of valve disease on the heart, and CMR is the 'Gold standard' for this. Limitations of the technique include partial volume effects due to image slice thickness, and a low ability to identify small, highly mobile objects (such as vegetations) due to the need to acquire images over several cardiac cycles. The review examines the advantages and disadvantages of each imaging aspect in detail, and considers how CMR can be used optimally for each valve lesion.

Figures

Figure 1

SSFP sequence in the LV outflow tract view in systole showing restricted aortic valve leaflets (black arrows) and a high velocity jet of aortic stenosis (white arrow), with high signal (white) from the more stable core surrounded by low signal (black) due to shear and turbulence. Parallel dashed lines indicate the slice position for imaging the valve tips for assessment of valve area (Figure 6).

Figure 2

LVOT view in diastole showing jet of eccentric aortic regurgitation (arrow) visualised by the low signal on SSFP sequences, due to spin-dephasing caused by shear and turbulence.

Figure 3

Through-plane phase contrast velocity mapping for flow quantification of aortic regurgitation at the valve tips. Left: magnitude (anatomical) images in systole (top) and diastole (bottom). Right: corresponding phase (velocity) images at the same phase; forward flow in white, regurgitant flow in black; dotted line represents region of interest for post-processing of velocity data. Resulting flow-time graph after integration of velocity in each voxel over one cardiac cycle, demonstrating forward flow above the line and regurgitant flow below the line. The area under the curve represents the volume of flow, and can be calculated by the software.

Figure 4

Example of in-plane phase contrast velocity mapping in the LV outflow tract in a patient with dynamic outflow tract obstruction. Left: cine image; right: corresponding phase image from in-plane velocity mapping. The highest velocities can be visualised in the outflow tract (arrowed), below the aortic valve. LV = left ventricle; Ao = aorta.

Figure 5

Aortic stenosis in a bicuspid aortic valve: standard left ventricular outflow tract (LVOT) view (top) and 'coronal' LVOT view (bottom), acquired perpendicular to the standard LVOT view through the valve tips. Note the domed leaflets with restricted tips typical for congenital stenosis (white arrows) and the high velocity jet (black arrows).

Figure 6

Through-plane SSFP image in systole through the valve tips in a patient with aortic stenosis. The tips are outlined by dark (low signal), partly due to signal loss from shear. The orifice area can in this case be measured directly by planimetry, but this should not be attempted if the outlines are unclear on the available cine images.

Figure 7

LVOT view in diastole showing turbulent jet of aortic regurgitation (arrow) and position for through-plane velocity mapping image (dashed lines) to quantify aortic flow.

Figure 8

(taken from the Oxford Handbook of CMR, OUP) Mechanism for potential underestimation of aortic regurgitation. The gap between the valve and the image plane for flow mapping expands in systole from a combination of movement of the aortic valve towards the apex and elastic expansion of the aortic sinuses and root. Blood entering this space in systole (grey stippled area) returns to the LV in diastole (via a regurgitant valve) without passing through the image plane (dashed lines), and thus may not be measured.

Figure 9

Imaging the mitral valve segments - a modified approach adapted from reference 47. A basal short axis slice through the mitral commissure is used (top left) to orientate the subsequent image slices for each of the segments. The left atrial appendage is identified by the asterisk (*). Cine sequences are then acquired perpendicular to the mitral commissure for each of the 3 scallops (parallel dashed lines). Systolic frames from the resulting images are shown here (top right and bottom images). In this patient, there is isolated prolapse of the posterior leaflet P2 segment (bottom right, black arrow), but other segments have normal coaption (top right and bottom left).

Figure 10

Location for direct assessment of mitral regurgitation flow using through-plane velocity mapping. Slice position indicated by dashed lines in LVOT view (top) and VLA view (bottom), perpendicular to the regurgitant jet (arrowed).

Figure 11

Assessing mitral stenosis by direct planimetry of the mitral tips. Top: diastolic frame from an LVOT view demonstrating slice position for subsequent imaging (dashed line). Bottom: resulting modified short axis view through the mitral tips in diastole, showing the easily visualized mitral orifice (arrow).

Figure 12

Right ventricular outflow tract view showing fore-shortened right ventricle (RV) and a pulmonary valve with moderate-severe stenosis. The high velocity jet of the stenosis can be seen (arrowed). PA = main pulmonary artery.

Figure 13

Left: RV outflow tract view in diastole in a patient with repaired Fallot's tetralogy and severe pulmonary regurgitation. There is almost no turbulence, due to the wide jet with mostly laminar flow. The flow can be visualized with in-plane flow imaging (right), where the wide regurgitant jet is seen in black (arrowed). The dashed lines on the cine image indicate the slice location for through-plane velocity mapping.

Figure 14

Severe tricuspid regurgitation seen in the HLA view. In the SSFP cine (top), there is little regurgitation seen due to the minimal turbulence from the jet. Bottom: in-plane velocity mapping sequence in the same position demonstrating the wide jet of torrential regurgitation (arrowed).

Figure 15

Tricuspid regurgitation; modified short axis cine view in systole, positioned through the tricuspid valve tips. The large regurgitant orifice is easily visualized in this case (arrowed). In some cases, through-plane velocity mapping may give clearer delineation of flow through the orifice.

Figure 16

Prosthetic valves with CMR. Top: Carbomedics bioprosthetic valve in the aortic position in systole (left) and diastole (right). Bottom: ATS bi-leaflet tilting disc valves in both aortic and mitral positions (arrowed).

Figure 17

Through-plane velocity mapping above a prosthetic aortic valve (bi-leaflet tilting disc type). The characteristic flow pattern of two crescents and a bridging 'strut' can be seen, reminiscent of a Star Wars™ TIE fighter viewed from the front.