Assessment of mitral regurgitation (MR) has traditionally been performed with echocardiography. However, echocardiography has known limitations including the lack of a single reliable parameter of severity, high inter- and intraobserver variability, and discordance between echocardiographic parameters in a given patient.¹ To quantify MR, echocardiography relies on either the mitral regurgitant Doppler jet characteristics or quantification of flow across the left ventricular (LV) outflow tract and mitral inflow. These methods lend themselves to poor reproducibility and geometric assumptions, and rely on the assumption that the relationship between the characteristics of the color Doppler jet and MR severity is linear.²

Cardiovascular magnetic resonance (CMR) offers an alternative method to quantify MR and has several advantages that lend itself to accurately quantify regurgitant lesions such as MR (Figure 1). CMR is the reference standard for noninvasive quantification of ventricular and atrial size and function. Advantages of CMR include the ability to image in any plane chosen by the operator, the lack of geometric assumptions, and low interobserver variability.

Figure 1: Role of CMR in Mitral Regurgitation

CMR is a robust technique to assess MR. Quantification of MRV and MRF as well as the hemodynamic consequences MR has on LA and LV size and function. CMR can also assess the etiology of MR such as functional versus degenerative, the presence of a prolapse or flail, and the leaflet segments involved. Scar quantification and assessment of ECV may also be useful in determining the health of the myocardium. Newer techniques such as 4D flow may prove useful in assessing MR.

CMR = cardiovascular magnetic resonance; ECV = extracellular volume; LA = left atrium; LGE = late gadolinium enhancement; LV = left ventricular; MRF = mitral regurgitant fraction; MRV = mitral regurgitant volume.

Single-shot steady-state free-precession (SSFP) imaging is used to acquire short- and long-axis views of the atria and ventricles. An advantage of SSFP imaging is the high contrast between the blood pool and myocardium allowing for accurate segmentation of the heart. Segmentation of the LV and right ventricle (RV) in the short-axis view is used to quantify LV and RV end-diastolic volumes, end-systolic volumes, and stroke volumes (Figure 2).

Figure 2: Short-Axis Segmentation of the Ventricles

Short-axis steady-state free-precession imaging is used to segment the LV and RV. Note the contrast between the myocardial blood pool and the myocardium allowing for segmentation of the ventricles without geometric assumptions. Segmentation allows quantification and calculation of LV and RV parameters used in the quantification of MR.

EDV = end-diastolic volume; ESV = end-systolic volume; LV = left ventricular; RV = right ventricular.

Using phase contrast (PC) imaging, CMR can quantify flow in the pulmonary artery (PA) and ascending aorta (Ao) allowing forward stroke volume (FSV) to be accurately quantified (Figure 3). Because accurate PC imaging relies on laminar flow, it is best to acquire these images in the Ao and PA 5 mm above the sinotubular junction. This will avoid turbulent flow that arises from the valve. This technique has been shown to have low variability.

Figure 3: Phase Contrast Imaging in the Pulmonary Artery and Ascending Aorta

Phase contrast imaging is used to quantify blood flow in the ascending aorta and the pulmonary artery. These parameters are used to quantify forward stroke volume in patients with mitral regurgitation.

The underlying principle of quantifying regurgitant lesions by means of CMR is to determine FSV, defined as the amount of blood that is ejected from the ventricle and does not return via a leaky valve. In a patient with lone MR, the FSV can be quantified by RV stroke volume (RVSV), Ao PC, and PA PC (Figure 4).

Figure 4: A Quantitative Approach to MR

Panel A: In patients with no valvular regurgitation and no cardiac shunt, both the LVSV and RVSV and the Ao PC and PA PC are equal. Panel B: In lone MR, FSV is quantified by Ao PC, RVSV, and PA PC. Panel C: In patients with MR and AR, FSV is quantified by Ao PC, RVSV, and PA PC. LVSV = FSV + MR + AR. AR can be quantified by the diastolic flow on the Ao PC.

Ao = ascending aorta; AR = aortic regurgitation; FSV = forward stroke volume; LVSV = left ventricular stroke volume; MR = mitral regurgitation; PA = pulmonary artery; PC = phase contrast; RVSV = right ventricular stroke volume; TSV = total stroke volume.

Having three independent measures of FSV allows the operator to ensure that the data are trustworthy and consistent, ensuring that technical errors or errors of quantification do not falsely increase or decrease FSV. In the presence of a stenotic valve such as aortic stenosis, the Ao PC may be unreliable, causing the operator to rely on the RVSV and PA PC. Additionally, it is best to acquire two Ao PCs and PA PCs to ensure that the PC data are reproducible. This is particularly important in patients with arrhythmias. In MR, the LV stroke volume (LVSV) or total stroke volume is comprised of the FSV and the MR volume. Thus, MR volume is simply LVSV – FSV. MR fraction can then be calculated as MR volume ÷ LVSV. As discussed previously, this method has been shown to be highly reproducible.

Studies that have compared echocardiography and CMR in MR have highlighted a high rate of discordance.³ This discordance is even more pronounced when patients are diagnosed with severe MR by CMR or echocardiography, with echocardiography diagnosing severe MR significantly more compared with CMR. These findings are concerning, given the centrality of diagnosing severe MR in the American College of Cardiology/American Heart Association valvular heart disease guideline when deciding on referral for mitral valve surgery.⁴ In head-to-head studies, CMR more accurately predicted clinical outcomes in addition to the hemodynamic response of the LV after surgery.^5-8 Two studies looked at need for surgery. These findings highlight the accuracy of CMR for quantifying MR.

In addition to quantifying MR, CMR can determine the mechanism of MR including differentiating primary versus secondary MR as well as identifying the mechanism of MR such as prolapse or flail. En face and long-axis views of the mitral valve can be used to determine the presence of a prolapse or flail and which portion of the leaflet is involved (Figure 5). This can allow for surgical planning without needing another test.

Figure 5: Assessment of MR Etiology

Patient with a P₂ prolapse. Panel A: Short-axis en face view of the mitral valve highlighting a prolapse of the P₂ scallop (arrows). Panel B: Long-axis view of the mitral valve highlighting the P₂ prolapse (arrow).

Tissue characterization is an important and valuable tool that can be performed with CMR. Late gadolinium enhancement can be used to identify and quantify myocardial scar of the LV. T1 mapping can be used to assess the extracellular volume (ECV) of the myocardial tissue and is an accurate technique to quantify the degree of fibrosis within the myocardial tissue. Active research is ongoing to assess the clinical utility of these techniques in MR.⁹ MR is a volume overload lesion, which commonly results in normal or supranormal LV ejection fraction. A challenge facing clinicians is knowing when LV dysfunction will occur. CMR techniques such as late gadolinium enhancement and ECV quantification may hold promise in early detection of LV failure.

One of the newest techniques CMR can use to assess MR is 4D flow.¹⁰ 4D flow allows single acquisition free breathing assessment of blood flow superimposed upon the cardiac anatomy. 4D flow can be analyzed retrospectively measuring blood flow in the ventricles, blood vessels, and through plane of the valves. Ongoing research is assessing the clinical usefulness of this technique in MR.

In summary, CMR is a useful imaging technique to accurately quantify MR volume and fraction, assess the etiology of the MR, quantify the size of the LV and RV, and quantify LV scar and fibrosis.

References

1. Connelly KA, Ho EC, Leong-Poi H. Controversies in quantification of mitral valve regurgitation: role of cardiac magnetic resonance imaging. Curr Opin Cardiol. 2017;32(2):152-160. doi:10.1097/HCO.0000000000000363
2. Biner S, Rafique A, Rafii F, et al. Reproducibility of proximal isovelocity surface area, vena contracta, and regurgitant jet area for assessment of mitral regurgitation severity. JACC Cardiovasc Imaging. 2010;3(3):235-243. doi:10.1016/j.jcmg.2009.09.029
3. Garg P, Pavon AG, Penicka M, Uretsky S. Cardiovascular magnetic resonance imaging in mitral valve disease. Eur Heart J. 2025;46(7):606-619. doi:10.1093/eurheartj/ehae801
4. Writing Committee Members, Otto CM, Nishimura RA, et al. 2020 ACC/AHA guideline for the management of patients with valvular heart disease: a report of the American College of Cardiology/American Heart Association Joint Committee on Clinical Practice Guidelines [published correction appears in J Am Coll Cardiol. 2021 Feb 2;77(4):509. doi: 10.1016/j.jacc.2020.12.040.] [published correction appears in J Am Coll Cardiol. 2021 Mar 9;77(9):1275. doi: 10.1016/j.jacc.2021.02.007.] [published correction appears in J Am Coll Cardiol. 2023 Aug 29;82(9):969. doi: 10.1016/j.jacc.2023.07.010.] [published correction appears in J Am Coll Cardiol. 2024 Oct 29;84(18):1772. doi: 10.1016/j.jacc.2024.09.025.]. J Am Coll Cardiol. 2021;77(4):e25-e197. doi:10.1016/j.jacc.2020.11.018
5. Myerson SG, d'Arcy J, Christiansen JP, et al. Determination of clinical outcome in mitral regurgitation with cardiovascular magnetic resonance quantification. Circulation. 2016;133(23):2287-2296. doi:10.1161/CIRCULATIONAHA.115.017888
6. Penicka M, Vecera J, Mirica DC, Kotrc M, Kockova R, Van Camp G. Prognostic implications of magnetic resonance-derived quantification in asymptomatic patients with organic mitral regurgitation: comparison with Doppler echocardiography-derived integrative approach. Circulation. 2018;137(13):1349-1360. doi:10.1161/CIRCULATIONAHA.117.029332
7. Uretsky S, Animashaun IB, Sakul S, et al. American Society of Echocardiography algorithm for degenerative mitral regurgitation: comparison with CMR. JACC Cardiovasc Imaging. 2022;15(5):747-760. doi:10.1016/j.jcmg.2021.10.006
8. Uretsky S, Gillam L, Lang R, et al. Discordance between echocardiography and MRI in the assessment of mitral regurgitation severity: a prospective multicenter trial. J Am Coll Cardiol. 2015;65(11):1078-1088. doi:10.1016/j.jacc.2014.12.047
9. Kitkungvan D, Yang EY, El Tallawi KC, et al. Extracellular volume in primary mitral regurgitation. JACC Cardiovasc Imaging. 2021;14(6):1146-1160. doi:10.1016/j.jcmg.2020.10.010
10. Gorecka M, Bissell MM, Higgins DM, Garg P, Plein S, Greenwood JP. Rationale and clinical applications of 4D flow cardiovascular magnetic resonance in assessment of valvular heart disease: a comprehensive review. J Cardiovasc Magn Reson. 2022;24(1):49. Published 2022 Aug 22. doi:10.1186/s12968-022-00882-0