Keywords

Introduction

Although there have been improvements in cardiac imaging, assessing the complex geometries of the right atrium (RA), tricuspid valve (TV), and right ventricle (RV) remains a challenge with strictly two-dimensional imaging. The substernal (anterior) position and complex morphology of these structures underlie much of this difficulty [1].

Transthoracic echocardiography, radionuclide ventriculography, and computed tomography are commonly used in clinical practice to qualitatively monitor RV size and systolic function. Given the complex shape, thin wall, and substernal location of the RV, echocardiography evaluation is limited. Computed tomography can circumnavigate some of these, though it exposes patients to ionizing radiation. CMR provides the most comprehensive evaluation of the RV. It is the gold standard for quantification of ventricular volume and ejection fraction with additional benefits of tissue characterization and accurate quantification of blood flow [2, 3]. CMR affords a reasonable compromise of high temporal, spatial, and contrast resolution with a wide field of view without radiation exposure. The interest in CMR is based on these features, as well as the reproducible nature of volumetric and flow measurements [2, 4]. The RV and TV can be evaluated from multiple planes using steady-state free precession (SSFP) sequences. SSFP techniques have been validated for the quantification of ventricular volumes and function and evaluating valvular structures [5]. Gradient echo (GRE) imaging allows for accurate visualization of stenotic and regurgitant flow [5]. Furthermore, quantification of flow across the TV and pulmonary valve can be evaluated using phase-contrast velocity-encoding [5]. RV systolic function is most commonly assessed by global metrics (e.g., ejection fraction, stroke volume, cavity volume, and myocardial thickness); however, regional assessment can also be obtained [3]. Recent research has shown regional changes in strain and strain rate were sensitive for detecting early manifestations of dysfunction and so may provide additional information when assessing RV systolic function [6, 7].

This chapter will provide a brief synopsis of the underlying principles of CMR assessment as it relates to RV function and the TV.

CMR Pulse Sequences and Strain: General Principles

There are a variety of CMR pulse sequences used in cardiac imaging. The most common pulse sequences for the assessment of ventricular function and heart valvular disease are summarized in Table 6.1 [8] and discussed in this section.

Table 6.1 CMR pulse sequences with utility in the evaluation of valvular heart disease
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Steady-State Free Precession

Steady-state free precession (SSFP) sequences are gradient echo sequences with a short repetition time in which a steady residual transverse magnetization is maintained between successive cycles [9]. SSFP provides a high signal-to-noise ratio and excellent contrast between the blood pool and myocardium. RV volumes are measured from the plane of the TV to the RV apex using either axial or short-axis stacks [10]. Endocardial and epicardial contours are drawn at both end-diastolic and end-systolic phases of the cardiac cycle throughout the stack, allowing for accurate calculation of RV volumes, ejection fraction, and myocardial mass (Fig. 6.1). Although there are advantages of SSFP imaging, among the limitations is the possibility of signal loss. Marked signal loss can occur in regions of flow turbulence or susceptibility artifacts due to magnetic field inhomogeneities. To minimize any signal loss, echo times for SSFP imaging are kept relatively short. Furthermore, it is imperative to properly align planes when more than one jet is present in order to identify the mechanism of regurgitation and the location of the regurgitant jets.

Fig. 6.1
figure 1

Steady-state free precession sequence in short-axis view. RV volume, ejection fraction, and mass are calculated using an SSFP short-axis stack. Endocardial and epicardial contours are drawn at both end-diastole and end-systole throughout the stack. SSFP steady-state free precession sequence

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GRE Imaging

GRE imaging uses increased spin dephasing, which improves the sensitivity of detecting abnormal flow, and is less subject to signal loss compared to SSFP imaging. GRE short-axis stacks can be used to measure valve orifice area. This can be performed by using slightly overlapped slices while giving attention to ensure there is complete visualization through the orifice. This technique is more accurate when the orifice has a simple shape, and the jet is coherent. Irregular regurgitant jet shapes with multiple components compromise the sensitivity of this technique.

Phase Contrast Mapping

Phase-contrast velocity mapping utilizes gradient velocity-encoding to generate a phase shift of moving protons within the magnetic field [11]. Velocity mapping imaging can be used to measure jet velocity and volume flow. The intensity of the phase images is directly proportional to the velocity of spins within each voxel, which allows for quantitative assessment of flow velocities. Directional components (X, Y, and Z planes) of velocity are encoded; however, the through plane (slice selection) is assigned to the Z-plane. Phase-contrast velocity mapping is susceptible to aliasing, which occurs when the maximum measurable encoding velocity (VENC) is set too low. In contrast, when the VENC is set too high, sensitivity is reduced. The optimal VENC is ~10% greater than the maximum velocity component in the image.

CMR-Derived Strain

Strain is defined as the deformation of an object in response to an applied force and is conventionally reported as a percent change. The speed at which the deformation occurs is termed as strain rate. Regional strain can be calculated using the Lagrangian formula: [e = (L − Lo)/Lo], where e is strain, Lo is original length, and L is the length of the object after the applied force resulting in deformation. A negative strain value occurs when L is shorter than Lo, and a positive strain value occurs when L exceeds Lo. Strain is a tensor and can be calculated in three principal directions (longitudinal, circumferential, and radial). There are several CMR acquisition techniques that can be used to analyze strain, including myocardial tagging, displacement-encoding (DENSE), strain encoding (SENC), and feature tracking (FT) [12]. While myocardial tagging MRI is the gold standard for myocardial deformation, this method is time-consuming. This spurred the development of FT-CMR, which is less time-consuming (Fig. 6.2), and analogous to speckle-tracking echocardiography. FT-CMR is a post-processing technique in which myocardial tissue signatures in cine images are tracked to measure heart deformation. Endocardial and epicardial borders are delineated and tracked using cine imaging from short-axis and three long-axis views (four-chamber, two-chamber, and three-chamber) throughout the cardiac cycle. FT-CMR has good intra- and inter-observer reproducibility [13,14,15]. An important advantage is that it can be applied to SSFP imaging, which is commonly part of routine CMR protocols, thus requiring no additional sequences.

Fig. 6.2
figure 2

Cardiovascular magnetic resonance-tissue tracking in the assessment of right ventricular function. Longitudinal strain in the apical four-chamber view with the strain curve demonstrated

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CMR Assessment in Tricuspid Valve and Right Heart Disease

Right Atrium Anatomy, Size, and Function

The RA is less uniform in thickness compared to the left atrium. The terminal crest demarcates the junction between the right atrial appendage and venous inflow. Pectinate muscles arise from the terminal crest and course in branched and often overlapping fashion toward the TV. The prominent RA musculature underlies the increased TV ring excursion compared to the mitral valve [16]. Atrial size and function, including atrial strain, can be measured by CMR. CMR offers advantages compared to echocardiography for evaluating the RA: wider field of view, greater signal-to-noise ratio with improved image quality, and border tracking for the RA [17]. Normal values for right atrial function are provided in Table 6.2. Similar to the assessment of ventricular deformation, the quantitative assessment of atrial deformation by feature tracking or tissue tracking is reproducible [18]. Regional deformation for both atria can be compared to measure inter-atrial dyssynchrony. In addition, assessment for late gadolinium enhancement as a measure of atrial wall fibrosis is possible by CMR, although improved sequences with very good spatial resolution are required for this to be adopted widely in clinical practice due to the thin atrial wall [19].

Table 6.2 Ventricular reference range for Caucasian adults
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Tricuspid Valve Anatomy and Function

When viewed using standard orthogonal body coordinates, the TV consists of the anterosuperior (often referred to as anterior), septal, and inferior (often referred to as posterior) leaflets [20]. For purposes of concordance with clinical literature, we will refer to the anterosuperior leaflet as “anterior” and inferior leaflet as “posterior.” The TV is the largest cardiac valve with a wide variability in the number and morphology of the leaflets [1, 21]. Compared to the mitral valve, the TV annulus is located slightly closer to the apex and has papillary muscle and direct chordal attachments to the interventricular septum. One of the most consistent features of the TV and its supporting apparatus are the multiple direct chordal attachments tethering the septal leaflet to the interventricular septum (Fig. 6.3). In contrast, there is marked variability in the morphology and location of the supporting papillary muscles. The anterior and septal leaflets are usually the largest, and the posterior leaflets are generally the smallest of the three [1]. The normal tricuspid annulus is a complex nonplanar structure, measuring approximately 4–6 cm2 in area in adults when fully open in diastole, with dynamic changes throughout the cardiac cycle and under varying loading conditions [22].

Fig. 6.3
figure 3

Normal right ventricle and tricuspid valve. This normal heart specimen is opened to view the right ventricular cavity and tricuspid valve. The three leaflets of the tricuspid valve are visualized (anterior, septal, and posterior leaflets) guarding the inlet of the right ventricle. The tripartite right ventricle consists of inlet, apical trabecular, and outlet components with the hashed white lines marking the boundaries between each

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CMR evaluation of TV leaflet morphology can be challenging because the normal leaflets are thin. Thin slice SSFP cine imaging is used to assess the anatomy and function of the TV. Common imaging planes include the four-chamber cine to assess the anterior and septal leaflets and the RV inflow or two-chamber and RV inflow/outflow cines, which can assess the anterior and posterior leaflets (Fig. 6.4). The short-axis cine stack slices through the TV en face. Conventional and time-resolved magnetic angiography allows for multiplanar reformatting and 3D CMR reconstruction, which can provide a detailed anatomical evaluation of the TV [23,24,25].

Fig. 6.4
figure 4

Cardiovascular magnetic resonance in the assessment of right ventricle and tricuspid valve. (a) Four-chamber view: evaluates the inflow and the apical trabecular portion of the RV, the septal and anterior leaflets of the tricuspid valve; (b) Short-axis view: a stack can be obtained through the entire tripartite RV, viewing the three leaflets of the tricuspid valve en face at the base of the heart; (c) RV inflow: evaluates the inflow and the apical trabecular portion of the RV, and the anterior and posterior leaflets of the tricuspid valve; (d) RV inflow/outflow: evaluates the entire tripartite RV from the inlet to apical trabecular to outlet components, viewing the anterior and posterior leaflets of the tricuspid valve. RV right ventricle, TR tricuspid valve, RA right atrium, PT pulmonary trunk, RVOT right ventricular outflow tract; (1), anterior wall; (2), inferior wall; (3), interventricular septum; (4), trabecular bands

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Right Ventricle Anatomy, Size, and Function

The normal RV is tripartite with an inlet, apical trabecular, and outlet component (see Fig. 6.4). The inlet of the RV extends from the TV annular plane to its chordal and papillary muscle attachments on the interventricular septum and RV free wall. The apical trabecular component has coarse trabeculations with the prominent and distinct moderator band coursing from the septum to RV free wall [26] (see Fig. 6.3). The normal RV outlet differs from the left ventricular outlet. In the RV, there is a free-standing muscular sleeve or infundibulum that lifts the pulmonary root away from the base of the heart resulting in fibrous discontinuity between the TV and pulmonary valve [27]. By two-dimensional imaging, the RV appears crescent shaped when viewed in its short axis and pyramidal shaped in its long axis.

Contraction of the RV consists of a peristalsis-like motion with synchronized contraction occurring from the inlet and apex toward the outlet [28]. This predominately longitudinal shortening with delay in contraction from inlet to outlet of approximately 20–50 ms results in indistinct isovolumetric periods, in contrast to the left ventricular contraction pattern [28, 29]. The end-diastolic volume of the normal RV is on average 10–15% larger than that of the LV, with approximately 20% of its volume accounted for by the infundibulum. The RV free wall is thinner than that of the LV and is one-sixth to one-third the mass of the LV [28].

There are several methods used to measure RV systolic function, including volumetric and tissue tracking techniques. Ventricular systolic function can be estimated by measuring the ejection fraction by CMR using the Simpson method. This method uses a stack of contiguous slices of the entire ventricle. The ventricular volume is the sum of the individual slice volumes (slice thickness × slice area). The RV stroke volume (SV) can be noninvasively calculated as the difference of end-diastolic volume (EDV) and end-systolic volume (ESV) (SV = EDV − ESV). The ejection fraction is the SV divided by EDV (SV/EDV). Normal reference values for RV function using CMR are provided in Table 6.2.

Right Atrial Pathology

Right Atrial Dysfunction

Right atrial dysfunction is now recognized as a distinct clinical entity [30]. RA dysfunction is important in pulmonary arterial hypertension, heart failure, and CHD. It has been shown to be a predictor of clinical outcomes in a variety of cardiovascular diseases [31,32,33,34]. CMR is the gold standard modality for the assessment of the RA function due to its excellent spatial resolution and endocardial border definition. CMR-derived RA strain allows identification of all phases of RA dynamics (reservoir, conduit, and booster function) [35], allowing for detection of subclinical dysfunction [36]. Whether or not RA function will be relevant to the success of individualized TV interventions remains to be determined.

Tricuspid Valve Pathology

Tricuspid Valve Regurgitation

Physiological TR , often termed trivial, is a common finding in healthy individuals, while pathological TR is commonly a consequence of annular dilation, increased RV pressure, or a leaflet abnormality. Left-sided heart failure resulting in RV hypertension is the most common cause of TR in adults. There are multiple congenital TV malformations, including leaflet dysplasia, annular hypoplasia, leaflet cleft, Ebstein anomaly, and leaflet prolapse. Annular dilation of the TV with resulting functional TR as a result of RV dilation is also common in many forms of congenital heart disease (CHD), such as repaired tetralogy of Fallot.

Velocity encoding can be used to directly quantify TR from a short-axis en face acquisition (Fig. 6.5). However, this technique is challenging due to the movement of tricuspid annulus. Dephasing allows for planimetry of a clearly delineated vena contracta, and >7 mm suggests the presence of severe TR [37]. There are quantitative techniques that allow for indirect quantification of TR. RV stroke volume (SV) can be compared to the pulmonary valve forward flow and can be used to calculate TR: TR fraction = (RV SV − pulmonary valve forward flow)/RV SV × 100%. It should be noted that this technique is susceptible to error in any situation where there is significant intracardiac shunting, beat-to-beat variability of SV, such as an arrhythmia or significant pericardial effusion, since the RV stroke volume and pulmonary valve phase-contrast sequences are acquired over multiple heartbeats. Alternatively, ventricular SVs can be compared (RV SV − left ventricular SV)/RV SV × 100% [25]. This technique becomes difficult to use in the setting of polyvalvular regurgitation and also becomes less reliable in the face of arrhythmia. Finally, in the absence of significant atrial level shunting, the TR regurgitant fraction can be calculated using tricuspid and mitral valve antegrade diastolic flow using the following formula: TR regurgitant flow = TV diastolic flow – mitral valve diastolic inflow. This technique becomes less useful if there is mitral regurgitation.

Fig. 6.5
figure 5

Tricuspid regurgitation on gradient recalled echo and phase-contrast velocity imaging. (a) Gradient recalled echo imaging demonstrating non-coaptation of the tricuspid valve (yellow arrow); (b) phase-contrast velocity encoded imaging demonstrating tricuspid valve regurgitation (yellow arrow) at the level of valve orifice in short-axis view

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CMR in Transcatheter Tricuspid Valve Interventions

Severe TR is associated with poor prognosis if left untreated. The current recommendations for TR intervention include (1) severe TR undergoing left-sided valve surgery, (2) mild or moderate functional TR at the time of left-sided valve surgery with tricuspid annular dilation or evidence of right heart failure, and (3) severe primary TR with symptoms unresponsive to medical therapy [38, 39]. The recent guidelines emphasize the importance of early treatment of TR [38]. Though still in clinical trials, transcatheter interventions have emerged as alternatives to conventional surgery in the management of TV disease because of the growing number of high surgical risk elderly patients [25]. Recently, 6-month outcomes have suggested the safety of the transcatheter interventions in patients with symptomatic and moderate to severe functional TR with a decrease of annular dimensions, a significant reduction in regurgitant severity, improvements in heart failure symptoms, improved quality of life, and increased exercise capacity [40]. The primary imaging modality for diagnosis and longitudinal evaluation of tricuspid regurgitation is two-dimensional echocardiography with supplemental three-dimensional echocardiography; however, CMR imaging can be used to inform the timing of TV surgery and assess potential hemodynamic improvements after intervention [25, 41].

Tricuspid Valve Stenosis

Tricuspid stenosis is decreasing in incidence and, when diagnosed, is commonly attributed to rheumatic heart disease [38, 42]. Other causes include infective endocarditis, carcinoid, endomyocardial fibrosis, systemic lupus erythematous, and congenital TV lesions [42]. Varying degrees of TV hypoplasia and resulting stenosis are also seen in forms of congenital heart disease (CHD), such as pulmonary atresia with an intact ventricular septum.

CMR use in the setting of tricuspid stenosis has not been well studied. However, tricuspid stenosis by CMR will typically demonstrate thickened leaflets with restricted excursion during diastole [42, 43]. Tricuspid stenosis is often visualized as a signal void during the diastolic phase extending into the RV. CMR short-axis images and phase velocity maps can be aligned to transect the stenotic lesion close to the orifice. A valve orifice measured in diastole from short-axis images of <1 cm2 is indicative of severe stenosis [42].

Right Ventricle Pathology

Ischemic Heart Disease

RV infarction has been reported in as many as 50% of cases involving inferior myocardial infarctions and 33% of all anterior myocardial infarctions [44,45,46]. RV systolic dysfunction resulting from concomitant left ventricular myocardial infarction is associated with higher rates of morbidity and mortality [47]. The RV ejection fraction and degree of regional wall motion abnormalities are important prognostic markers. RV infarction can be detected and evaluated by the use of late gadolinium enhancement (LGE) (Fig. 6.6) and T2-weighted imaging. Tissue characterization assessing myocardial edema and detection of LGE help differentiate reversible and irreversible injury.

Fig. 6.6
figure 6

Right ventricular myocardial infarction on late enhancement cardiovascular magnetic resonance imaging. (a) LGE is present in the anterior part of the RV free wall in a patient with anterior STEMI; (b, c) LGE is present in the inferior or both the inferior and the mid-part of RV free wall in patients with inferior STEMI. Yellow arrows indicate LGE in RV free wall, white arrows indicate LGE in left ventricular wall, and red arrows indicate microvascular obstruction. RV right ventricular, LGE late gadolinium enhancement, STEMI ST-segment elevation myocardial infarction. (Reprinted with permission from Miszalski-Jamka et al. [82])

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Pulmonary Hypertension and Left-Sided Heart Failure

Accurate quantitation of RV volumes and systolic function provides important prognostic information and can be used for risk-stratification in both RV and LV heart failure with reduced and preserved ejection fraction [48,49,50] and pulmonary artery hypertension [51, 52]. Increased RV to LV volume ratio has been associated with increased all-cause mortality in patients with pulmonary hypertension [51]. Furthermore, CMR RV functional assessment (RV EDV, ESV, and ejection fraction) has contributed to improved medical management of pulmonary hypertension. CMR-derived septal curvature is associated with mortality and can be used to monitor response to pulmonary hypertension therapy [53].

Congenital Heart Disease

The TV and RV are involved in various forms of CHD . CMR is used for both the diagnosis and follow-up of pediatric and adult CHD patients (Table 6.3) [54, 55]. For example, tetralogy of Fallot is the most common form of cyanotic CHD and affects approximately 1 in 3600 live births [56]. With improving care, there are now more adults living with repaired or palliated CHD than their pediatric counterparts, including those with repaired tetralogy of Fallot [57]. CMR is an important tool for follow-up of children and adults with repaired tetralogy of Fallot because the assessment of RV size and systolic function (Fig. 6.7) is important for guiding management and determining the need and timing of pulmonary valve replacement [58, 59]. In fact, both preoperative RV systolic dysfunction and RV-mass-to-volume ratio as determined by CMR relate to occurrence of death or sustained ventricular tachycardia following pulmonary valve replacement [60]. While there is no consensus on criteria for concomitant TV replacement at the time of PVR in repaired TOF [61], intervening on severe TR may be warranted, with CMR often being necessary for more objective quantification. Additionally, CMR affords assessment of the RV outflow tract, including the degree of stenosis and regurgitation, as well as the branch pulmonary artery anatomy and differential flow. Similar evaluation is often necessary in other forms of repaired CHD leading to RV dilation and systolic dysfunction, such as any patient prone to pulmonary artery or RV-to-pulmonary artery conduit stenosis or regurgitation. Such patients include those with tetralogy of Fallot with pulmonary atresia following complete repair utilizing an RV-to-pulmonary artery conduit, transposition of the great arteries status post arterial switch, or those undergoing a Ross procedure where the native pulmonary root is surgically placed into the aortic position necessitating an RV-to-pulmonary artery conduit [62].

Table 6.3 Right-heart CHD lesions commonly evaluated by CMR in alphabetical order
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Fig. 6.7
figure 7

Repaired tetralogy of Fallot with severe right ventricular dilation on cardiovascular magnetic resonance. This short-axis cine at the mid-ventricular level in a patient with repaired TOF demonstrates a severely dilated RV with diastolic flattening of the interventricular septum. TOF tetralogy of Fallot, RV right ventricular, LV left ventricle

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Ebstein’s anomaly of the TV involves apical displacement, or in its severe form better described as the rotation of the septal and posterior leaflets of the TV into the RV outflow tract (Fig. 6.8). Both the degree of displacement and extent of development of the posterior and septal leaflet should be interrogated. In fact, a simple measure of the valve rotation angle by CMR prior to the cone surgical reconstruction has been shown to be predictive of unsuccessful repair with subsequent dehiscence [63]. The anterior leaflet retains its normal attachment at the true annulus; however, it is often large and sail-like and can have fenestrations and excessive chordal attachments to the RV free wall limiting its mobility. These are important surgical considerations that need to be meticulously described [64]. While echocardiography plays an important role in delineating the anatomy of the malformed TV, CMR can add value via a more accurate assessment of the degree of tricuspid regurgitation and RV size and function [65]. Additionally, CMR is important in assessing the atrialized RV volume, which relates to exercise capacity [66]. Hemodynamically significant TV abnormalities occur in up to one-third of patients with congenitally corrected transposition of the great arteries, with valvular dysplasia being the most common, followed by Ebstenoid malformation of the TV. In this lesion, the RV is now the systemic ventricle and the TV is exposed to systemic pressures and largely impacted by the interventricular septal position. Competence of the TV now becomes even more important, with the vicious circle of worsening TR and depressed RV systolic function linked to poorer overall outcomes [67]. There are other less common forms of malformation of the TV and RV, which similarly benefit from CMR assessment.

Fig. 6.8
figure 8

Cardiovascular magnetic resonance imaging in Ebstein anomaly. (a) A four-chamber image in a patient with Ebstein’s anomaly of the tricuspid valve demonstrates the large and sail-like anterior leaflet retaining its normal hinge with severe displacement and rotation of the septal leaflet toward the right ventricular outflow tract resulting in a large atrialized RV and dilated RA. The LV is heavily trabeculated and meets the criteria for LV noncompaction, a common finding present in up to one-fifth of those with Ebstein’s anomaly. (b) This RV inflow–outflow cine image again demonstrates the normal hinge point of the anterior leaflet, with mild displacement of the posterior leaflet toward the RV apex. RV right ventricle, RA right atrium, LV left ventricle, AAo ascending aorta, AV atrioventricular, PT pulmonary trunk, LA left atrium

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Hypoplastic left heart syndrome (HLHS) is the most common form of CHD with single ventricle physiology [68]. In this disease, patients are born with atretic or severely hypoplastic mitral and aortic valves and undergo serial surgical palliations, ending with the Fontan operation, which connects the systemic veins directly to the branch pulmonary arteries [69]. The RV in this disease is the systemic ventricle, and thus accurate evaluation of ventricular function is crucial as heart failure is a leading cause for mortality in this patient population [70]. CMR provides functional evaluation of the single ventricle, assessment of TR, and evaluation of the Fontan pathway and branch pulmonary arteries, all of which are proven to have a prognostic value in this population [71, 72]. TR can result from structural abnormalities in the TR, and the most common is a small septal leaflet and anterior leaflet prolapse [73]. In addition, frequently encountered abnormalities are valve leaflet dysplasia and leaflet prolapse that alter TV geometry resulting in abnormal coaptation [74,75,76]. Leaflet tethering can result in restricted leaflet motion, deficient coaptation, and regurgitation. A higher tethering volume has been correlated with increased TR [77]. Tethering can also occur as a consequence of the lateral displacement of the anterior papillary muscle due to the abnormal geometry and dilation of a single RV [73, 77,78,79]. Abnormal chordae tendinae, including elongation, deficiency, or malattachment, are pathologic findings that result in AVVR. Finally, functional TR occurs in the absence of structural abnormalities of the valve apparatus secondary to ventricular and annular dilation. This results in a stretched annulus and deficient coaptation of valve leaflets. CMR is better suited to evaluate flow and quantify TR in HLHS [80]. Serial CMR exams can assess the progression of ventricular dilation or systolic dysfunction, each of which predisposes to mortality after TR intervention post-Fontan [76]. Other diseases with a systemic RV, including congenitally corrected transposition, as discussed above, and transposition of the great arteries after atrial baffle require serial evaluation of the RV and TR with CMR.

Limitations of MRI

There are limitations to the use of CMR. Implantable devices that are not MRI compatible dictate patient selection. In CHD, the presence of stainless steel or ferromagnetic vascular coils, stents, or occlusion devices may cause imaging artifacts and limit evaluation by CMR. Quantifying flow by two-dimensional imaging can be especially challenging given the fixed slice location and valvular movement relative to that slice results in through-plane motion. Additionally, image acquisition usually requires an appropriate breath-hold technique over multiple cardiac cycles. Contiguous stacks of cine images along with using a multiplanar approach to imaging the TV are essential to evaluate the anatomy in its entirety. Signal loss can occur when using phase velocity mapping secondary to partial volume averaging or when the size of the voxels (too large) in relation to the size and shape of a jet (narrow) do not match. Structural heterogeneity of the RV in the presence of CHD and arrhythmias can make volumetric analysis both challenging and time-consuming.