Dynamic MRI in Cardiovascular Diagnosis

### **Chapter 2**

## State of the Art and New Advances: Cardiac MRI

*Hunter Frederiksen, Corina Iorgoveanu and Mahi L. Ashwath*

### **Abstract**

Cardiac Magnetic Resonance Imaging (CMR) is an advanced imaging modality for better assessment of cardiac structure, function and tissue characterization. This is an essential imaging modality when indicated for assessment of a variety of cardiomyopathies, cardiac ischemia, myocardial viability, arrhythmias, cardiac masses, congenital heart disease, shunts, acute and constrictive pericardial diseases among others. CMR is sometimes referred to as the non-invasive biopsy given the significant information it provides. This chapter discusses the current state of the art of CMR with discussion about the indications, common sequences used, and the role of CMR in evaluation of ischemic and non-ischemic cardiac disease. This chapter also discusses new advances and the future of the field of CMR.

**Keywords:** CMR, ischemic cardiomyopathy, non-ischemic cardiomyopathy, cardiac masses, pericardial disease, arrhythmias, advances in CMR

### **1. Introduction**

Imaging the heart using magnetic resonance imaging (MRI) started for diagnostic utilization in the 1980s and has since contributed to significant advances in the fields of adult and pediatric cardiology and cardiothoracic surgery. Cardiac MRI (CMR) provides precise visualization of myocardial structure, function, perfusion, viability, and tissue characterization offering a comprehensive evaluation that remains unparalleled by any other imaging technique. Compared to other cardiac imaging modalities such as transthoracic echocardiogram (TTE), transesophageal echocardiogram (TEE), cardiac catheterization, or cardiac computed tomographic angiography (CTA), CMR has the advantages of reliable, high quality imaging with advanced tissue characterization which is not limited by body habitus, does not have radiation, is noninvasive, and has been shown to be sufficient for disease characterization and subsequent treatment strategies [1] aiding in tailoring specific treatment options and enhancing patient outcomes. Over the years, CMR with a continuing addition of several new techniques, has proven to be critically important for cardiovascular disease characterization and subsequent management and outcomes. We discuss the indications for CMR, common CMR scanning sequences, current state of the art of CMR followed by advances in CMR.

## **2. Indications for CMR**

CMR should be considered as part of the diagnostic imaging in patients with


### **3. Scanning protocol and sequences**

A regular CMR uses cine images for function and morphology followed by delayed enhancement (DE) images after administration of contrast for scar evaluation. While the scan as described provides significant information, additional information can be obtained, using additional sequences as desired. The study and the sequences are usually tailored for the indication to meet the needs appropriately. Commonly used sequences in CMR scanning include:


**Figure 1.** *Normal DE imaging with myocardium appearing uniformly black.*

a set time point post-contrast injection to evaluate how the contrast distributes into the extracellular space. LGE patterns on delayed enhancement imaging assist in the differentiation of ischemic and nonischemic cardiomyopathies. LGE in nonischemic cardiomyopathy is present in a noncoronary distribution and can have diffuse myocardial, mid myocardial or epicardial enhancement. Ischemic cardiomyopathy always has subendocardial involvement due to coronary blood flow pattern. Quantifying LGE and thereby assessing scar burden can provide prognostic and outcomes information. Studies have showed that presence of LGE in cardiomyopathy patients was associated with an increased risk of all-cause mortality, hospitalization for heart failure, and sudden cardiac death (SCD) [2].


**Figure 2.** *T1 mapping sequence.*


## **4. Current state of the art of CMR**

CMR has extensive role in the evaluation of various ischemic and non-ischemic etiologies. A few of the common pathologies are discussed below.

### **4.1 Evaluation of ischemic heart disease**

Coronary artery disease (CAD) is the leading cause of death in the United States. One person dies every 33 seconds from cardiovascular disease in the United States [4]. CMR has unique value in the evaluation of acute and chronic ischemic heart disease and in patients presenting with chest pain for the evaluation of ischemia.

### *4.1.1 Acute ischemic heart disease and CMR*

CMR provides many insights in the evaluation of patients presenting with acute MI. While TTE is easily accessible, CMR is superior to TTE in the evaluation wall

### *State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

motion abnormalities and LV ejection fraction (EF) with high quality imaging in cine sequences. CMR provides additional information about edema and the area at risk of infarction which can be evaluated by T1, T2 mapping and assessment of ECV. Resting myocardial perfusion imaging in patients presenting with chest pain can show areas of decreased resting myocardial perfusion, denoting significant coronary stenosis (greater than 80% stenosis) in the coronary arteries supplying those territories [5] (Video 5). Early gadolinium imaging shows areas of thrombus (**Figure 3**) and microvascular obstruction (**Figure 4**). Microvascular obstruction signifies areas with extensive ischemia with associated capillary cell death in addition to myocardial cell death. Presence of microvascular ischemia portends a worse prognosis compared to patients who do not have microvascular ischemia [6] LGE on DE imaging

**Figure 3.** *Early gadolinium imaging with a right atrial thrombus as hypointense lesion.*

#### **Figure 4.**

*Cine image (a) and DE imaging (b) in acute MI showing a significant dark zone of microvascular obstruction embedded within the infarcted area in the mid to apical inferolateral wall.*

#### **Figure 5.**

*Cine image (a) and DE imaging (b) in MI showing bright scar tissue in LAD territory, signifying lack of viable myocardium with superimposed thrombus in black.*

shows areas of myocardial scar [7] (**Figure 5**). Ischemic scar always involves the sub endocardium as shown on pathology studies. Studies have shown that myocardium with less than 50% involvement of the myocardial thickness with scar have improvement in function with revascularization, suggestive of viable myocardium, while segments with more than 50% wall thickness involvement with scar do not have functional recovery [7]. Assessment of viable myocardium can have value in deciding revascularization strategies. CMR also plays an important role in the evaluation of complications of acute MI such as pseudoaneurysm (Video 6), thrombus, rupture of the septum, myocardial free wall rupture or papillary muscle rupture. Above findings, especially LV EF, microvascular obstruction and degree of scar have been shown to have prognostic valve.

#### *4.1.2 Chronic ischemic heart disease and CMR*

In patients with chronic CAD, CMR provides information about EF with cine imaging, thrombus evaluation with cine, early gadolinium enhancement, LGE imaging as described in the above section along with the detection and quantification of scar. Despite its widespread availability, TTE can be diagnostically limited in evaluation of intracardiac thrombus. Studies comparing TTE, TEE and CMR have clearly demonstrated the superiority of CMR in diagnosing thrombi [8]. CMR imaging provides tissue characterization of thrombus and can identify structural risk factors for LV thrombus such as infarct size/distribution and contractile dysfunction [9]. Presence of scar in myocardial infarcts can be most accurately detected by CMR compared to any other imaging study [10]. Transmural scar shows non-viable myocardium and identifies patients who are less likely to improve function [11]. Studies in patients with non-Q wave MI and unstable angina demonstrated the importance of subendocardial scar detected in CMR and its prognostic value [12]. Other studies have shown how these subendocardial scars can be easily missed on single-photon emission computed tomography (SPECT) imaging. Above findings, especially LV EF, and degree of scar have been shown to have prognostic valve.

#### *4.1.3 Evaluation of ischemia in patients with chest pain and CMR*

CMR provides valuable information in the evaluation of chest pain or ischemia with stress testing. Perfusion CMR, a technique that uses contrast dynamics to

#### *State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

visualize saturations of blood flow into the myocardium is used in stress perfusion CMR. In stress CMR, Gadolinium based contrast agent is paired with a vasodilator such as adenosine or Regadenoson and images are obtained continuously over several cardiac cycles to visualize the myocardial uptake and fade-out of contrast. In healthy myocardium, the contrast distributes homogenously. Defects in perfusion are typically detected as areas of low contrast resulting in minimal signal and therefore representing hypoperfusion and must last for four or more consecutive cardiac cycles [13]. Studies such as CE MARC showed the non-inferiority of Stress CMR compared to SPECT [14]. The GadaCad trial which compared Stress CMR to invasive coronary angiography or coronary CTA as the reference standard showed that stress CMR had sensitivities of 79% and 87% and specificities of 87% and 73% for singleand multi-vessel CAD, respectively. Studies such as SPINS showed the prognostic value of Stress CMR with patients with normal Stress CMR—patients with normal myocardial perfusion and normal LGE have 99.3% event free survival for a median 5.5 years [15].

When compared to SPECT, stress CMR has several technical advantages. CMR has a larger field of view, superior spatial resolution, and better tissue differentiation. It is not limited by attenuation artifacts or contamination of the myocardium by other signal sources such as gut uptake as can be the case with SPECT. Stress CMR can also identify subendocardial ischemia, making it less susceptible to balanced ischemia than SPECT, where multivessel ischemia may be present but falsely appear normal on perfusion images [16]. Additionally, stress CMR does not expose patients to ionizing radiation, making it advantageous for younger patients and those who require multiple scans over time.

### **4.2 Evaluation of non-ischemic heart disease (NICM)**

The present classification system for cardiomyopathies, established by the American Heart Association distinguishes between primary ones that solely impact the heart and secondary ones that are part of a larger systemic disease affecting multiple organs. CMR has a distinct advantage in evaluation of these cardiomyopathies by providing insights into tissue composition and characteristics beyond structural imaging.

### *4.2.1 Primary cardiomyopathies*

### *4.2.1.1 Hypertrophic cardiomyopathy (HCM)*

HCM is a genetic cardiomyopathy, characterized by myocardial hypertrophy and disarray with an estimated prevalence of 1 in 500. CMR excels in identifying location and degree of hypertrophy, accurate maximal wall thickness, systolic anterior motion of the mitral valve and LV outflow tract obstruction, LV crypts, aneurysms and morphological variations involving the mitral valve apparatus and papillary muscles (Video 7). The classic scar pattern in HCM involves LGE at right ventricular (RV) insertion points [17] (**Figure 6**). A comprehensive multicenter study involving nearly 1300 patients diagnosed with HCM revealed that the extent of LGE can effectively identify individuals who are at an elevated risk of sudden death who would need to be considered for implantable cardioverter-defibrillator (ICD) placement. Extensive LGE, encompassing 15% or more of the LV mass, indicates a twofold higher risk of sudden death compared to the absence of LGE [18].

**Figure 6.** *Short axis cine (a) and DE (b) showing septal hypertrophy with LGE at RV insertion points in HCM.*

### *4.2.1.2 Arrhythmogenic right ventricular cardiomyopathy (ARVC)*

ARVC, the most prominent form of heritable arrhythmogenic cardiomyopathy (ACM), is a genetic disorder that is characterized by the loss of myocytes and the replacement of myocardial tissue with fibrofatty deposits, primarily affecting the RV. ARVC is associated with the occurrence of ventricular arrhythmias and an elevated risk of SCD and heart failure. Given the limitations of TTE in the visualization of the RV, CMR is the preferred diagnostic test for this lethal cardiomyopathy. CMR offers a comprehensive assessment of RV for enlargement of the RV outflow tract, dilation of the RV, fibrofatty replacement of the myocardium, as well as global or regional systolic dysfunction (Video 8). According to the 2010 Task Force Criteria, qualitative CMR identification of increased RV end-diastolic volumes, RV akinesia, dyskinesia, or dyssynchronous RV contraction is necessary to fulfill major or minor diagnostic criteria.

In the coming years, the analysis of tissue deformation and strain using CMR holds the potential to offer valuable diagnostic and prognostic insights. Strain imaging has shown promise in distinguishing individuals with ARVC and borderline ARVC from healthy volunteers, as well as differentiating it from other conditions like right ventricular outflow-tract ventricular tachycardia (RVOT-ventricular tachycardia) and Brugada syndrome. Impaired strain in both the LV and RV is indicative of ARVC. Emerging techniques, such as water and fat separation and high-resolution 3D LGE imaging hold potential for enhancing the identification of ARVC [19].

### *4.2.1.3 Left ventricular non-compaction (LVNC)*

LVNC refers to a structural configuration of the LV wall that is distinguished by prominent trabeculae within the LV, a thin layer of compacted myocardium, and deep recesses between the trabeculae. CMR cine images offer superior contrast resolution and improved differentiation between blood and muscle, enabling clearer visualization of ventricular trabeculation (**Figure 7**). Various CMR criteria have been proposed, with the criterion introduced by Petersen et al. being the most utilized. According to this criterion, a ratio of trabecular to compact myocardial thicknesses greater than 2.3 at end-diastole in long-axis views is consistent with noncompaction cardiomyopathy [20]. With the help of LGE in LVNC, regions of LGE in the

*State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

**Figure 8.** *Short axis cine (a) and DE (b) imaging showing the inferolateral epicardial scar in myocarditis.*

trabecular and subendocardial layers can be observed, indicating the presence of subendocardial and trabecular fibrosis as well as fibroelastosis. These fibrotic areas serve as the substrate for potentially life-threatening arrhythmias, which are the primary cause of sudden death in affected patients [21].

### *4.2.1.4 Myocarditis*

Myocarditis is an inflammatory condition of the myocardium, which can arise due to various causes, including a broad spectrum of infectious and noninfectious etiologies [22]. CMR detects several cardinal features of myocarditis such as inflammation, edema, necrosis, and contractile dysfunction (**Figure 6**) [23]. Cine images assist with assessment of wall motion abnormalities, T1 and T2 mapping with assessment for ECV and myocardial edema and DE imaging with assessment for focal scars. DE is typically observed in a mid-myocardial or sub-epicardial pattern primarily affecting

the basal to mid inferolateral and inferior segments [24] (**Figure 8**). The Lake Louise Criteria aid in the decision making by using CMR to detect myocarditis with high specificity and positive predictive value [3].

### *4.2.2 Secondary cardiomyopathies*

## *4.2.2.1 Cardiac amyloidosis*

Amyloidosis is a rare medical condition that arises due to the accumulation of insoluble proteinaceous material in the extracellular matrix. The likelihood of amyloidosis affecting the heart varies depending on the specific type, with primary/AL type having the highest incidence of cardiac involvement, affecting up to 50% of patients, followed by familial/ATTR type affecting 10–50% of patients, while the incidence is less than 5% for secondary/AA type [25]. CMR can detect key features of cardiac amyloid and can serve to rule in or rule out a diagnosis of cardiac amyloidosis [26]. The presence of the abnormal protein in the myocardium affects its T1 relaxation, making it challenging to null the myocardium and resulting in increased T1 values, which can be quantified using mapping techniques. ECV calculates the extracellular expansion due to amyloid and represents the closest, non-invasive quantification of cardiac amyloid burden. DE imaging shows a global subendocardial or transmural patchy enhancement (**Figure 9**). The presence and the degree of enhancement have been shown to have prognostic value in addition to the prognostic value provided by T1 and ECV values [27–29].

### *4.2.2.2 Sarcoidosis*

Sarcoidosis is a destructive granulomatous disease of the myocardium, which can lead to several cardiac pathologies including heart failure, heart blocks, ventricular arrythmias, and SCD. Diagnosing cardiac sarcoidosis is a challenge as symptoms often mimic other cardiac conditions. Autopsy studies have shown that isolated cardiac sarcoidosis can occur, and cardiac arrhythmias can be the first presentation [29]. Currently, the best imaging modalities for detecting sarcoid inflammation are cardiac positron emission tomography (CPET) and CMR [30]. CPET is useful for detecting active areas of inflammation and can provide good insight into disease burden. CMR on the other hand can show active areas of inflammation using T1 and

**Figure 9.** *Global subendocardial (a) and diffuse (b) enhancement in amyloidosis.*

**Figure 10.** *Short axis cine (a) and DE (b) imaging showing epicardial and septal scar in sarcoidosis.*

T2 mapping in addition to detecting areas of involved myocardium and scar tissue left over from active disease with DE imaging (**Figure 10**). The societal recommendation for imaging cardiac sarcoidosis involves obtaining cine, LGE, resting perfusion and T2-weighted sequences [31]. Regional wall motion abnormalities with cine imaging, focal perfusion abnormalities during perfusion imaging, signs of inflammation and edema during the acute phase of the disease on T1-weighted images [25], epicardial, midmyocardial DE and RV involvement with wall motion abnormalities and scarring have all been reported. Scar tissue serves as the epicenter for developing arrythmias. CMR locates and quantifies scar tissue burden and can aid in predicting risk for fatal arrythmias and patients that need treatment with an ICD [32].

### *4.2.2.3 Fabry cardiomyopathy*

Fabry disease (FD) is a lysosomal storage disorder that presents with a range of cardiac manifestations such as ventricular hypertrophy and fibrosis, valve thickening or regurgitation, heart failure, angina, dysrhythmias, cardiac conduction abnormalities, and SCD [33]. CMR has contributed significantly to our understanding of the underlying processes that lead to inflammation and fibrosis as a response to the accumulation of glycosphingolipids [34]. Earlier in the disease when the characteristic feature is fatty changes, decrease in native T1 time occurs [35]. This finding has the potential to identify individuals with early cardiac involvement and has been demonstrated to be predictive of disease progression [34]. As the disease progresses, the fatty changes are replaced with fibrosis, which leads to increase in T1 values along with patchy enhancement which is typically seen in the basal inferolateral wall [33] (**Figure 11**). These changes can occur concurrently with fatty changes in the septum and fibrosis in the inferolateral wall with rate of disease progression varying in different segments. These changes can also happen prior to the detection of LV hypertrophy, leading to early diagnosis.

### *4.2.2.4 Endomyocardial fibrosis (EMF)*

EMF is a type of restrictive cardiomyopathy, and although no exact cause has been fully understood, various factors have been described that contribute to an inflammatory response, leading to damage in the endomyocardial layers and the subsequent formation of fibrosis [36]. On CMR cine images shows apical

#### **Figure 11.**

*Short axis basal (a) and mid-level (b) DE imaging showing inferolateral patchy enhancement in Fabry cardiomyopathy.*

**Figure 12.** *Cine imaging in endomyocardial fibrosis showing apical hypertrophy.*

hypertrophic pattern, (**Figure 12**) however LGE serves as a dependable noninvasive approach for diagnosing EMF. The characteristic DE pattern observed in EMF is subendocardial, not limited to a specific coronary distribution with overlying thrombus. It primarily affects the apical walls of the LV and may extend continuously to the inflow tract. At the ventricular apex, a distinct imaging feature known as a "double V" sign can be observed. This sign exhibits a three-layered appearance comprising normal myocardium, enhanced endomyocardium and a layer of thrombus (**Figure 13**). CMR findings also have prognostic value. An increased deposition of apical fibrous tissue, indexed to body surface area (BSA) (>19 mL/m<sup>2</sup> ), has been directly associated with worse New York Heart Association (NYHA) functional class and elevated mortality rates [37].

**Figure 13.** *DE imaging in endomyocardial fibrosis showing apical to mid ventricular scar with superimposed thrombus.*

### **4.3 Valvular heart disease**

Over the last two decades CMR has emerged as a non-invasive and radiation-free alternative that can be used in individuals with valvular heart disease. CMR can provide images of valve anatomy and enables the quantitative evaluation of stenosis and regurgitation. Cine imaging assists with assessment the valvular structures in motion along with visualization of flows. Phase-contrast velocity encoded sequences help with quantification of peak velocities and regurgitant fractions. CMR can also detect the consequences of valvular lesions, such as changes in systolic function and the effects of ventricular volume or pressure overload [38]. Time-resolved 3D phasecontrast MRI, also known as 4D flow MRI, is a newer sequence, that possesses impressive capabilities in measuring blood flow velocities within a volume, noninvasively and in vivo, across the three primary directions, enabling the dynamic assessment of blood flow in both the heart and major vessels [38].

### **4.4 Cardiac masses**

Either of primary or secondary origin, cardiac masses can have various tissue compositions such as myxomas, rhabdomyomas, fibromas, angiosarcomas, and metastasis from extra-cardiac cancers. The characterization of cardiac masses is based on size, location, interaction with surrounding structures and mobility [39]. The first level of diagnostics remains to be an TTE as it is widely available, convenient, and of relatively minimal cost but has its own limitations. CMR can provide a multiplanar approach to assess the mass relative to surrounding intra- and extra-cardiac structures, tissue characterization, perfusion to assess for vascularity

#### **Figure 14.**

*T2 Stir image without (a) and with (b) fat saturation, showing a fatty mass in the right ventricular apex, likely lipoma.*

#### **Figure 15.**

*Four-chamber cine (a), perfusion (b) and DE (c) imaging in a large RV mass showing a large mass, which has partial perfusion, and a partial "etched appearance" on DE imaging consistent with a tumor with a large thrombus burden.*

and enhancement. CMR enables the evaluation of various characteristics including morphology, dimensions, location, extension, homogeneity, presence of infiltration in the surrounding tissues, and signal characteristics that aid in histopathological characterization. These signal characteristics encompass fatty infiltration, necrosis, hemorrhage, calcification, vascularity, among others. To achieve a comprehensive assessment, several imaging sequences are employed, such as double-inversion recovery fast spin-echo with triple inversion recovery to assess the amount of fat within the mass, (**Figure 14**) pre-contrast T2-weighted imaging, resting first-pass perfusion sequences, early gadolinium imaging, and late gadolinium DE imaging (**Figure 15**) [40]. CMR is considered a non-invasive biopsy in the assessment of cardiac masses.

#### **4.5 Pericardial evaluation**

CMR is a highly beneficial tool for evaluating and tracking various pericardial conditions, such as pericarditis, pericardial effusion, and constrictive pericarditis. Cine sequences evaluate function and effusion, free-breathing real time sequence assess ventricular interdependence in constriction, T2-STIR identifies edema, DE sequence detects LGE that indicates inflammation or fibrosis (**Figure 16**), and other T1- and T2-weighted and perfusion imaging techniques are used for tissue characterization of pericardial effusion and masses [41]. DE sequence plays a crucial role

**Figure 16.** *Short axis DE imaging showing diffuse circumferential pericardial enhancement, consistent with acute pericarditis.*

in diagnosing pericardial inflammation and monitoring the effectiveness of antiinflammatory treatments [42]. The degree of pericardial LGE observed in the initial MRI is significantly linked to recurring episodes of pericarditis and the need for intensified therapy. Recent research has introduced quantitative methods for measuring pericardial LGE, which may have potential clinical applications in the future [43]. Differentiating between active pericarditis and chronic inflammation leading to constrictive pericarditis is of utmost importance, as the treatment modalities are completely different (anti-inflammatory drugs vs. pericardiectomy).

### **4.6 Arrhythmias and application in electrophysiology**

CMR is widely used in electrophysiology (EP) for primary prevention of SCD and for secondary prevention in both brady and tachy arrhythmias. ICDs are used for primary prevention of SCD in patients with ischemic and NICM. A proportion of these patients do not have any lethal arrhythmias after implantation, prompting the need for better risk stratification of these patients. Scar quantification by DE imaging has been shown to have prognostic value in identifying patients more likely to benefit from ICD implantation for primary prevention. Further studies are underway to identify percent of scar and features of scar which denote increased arrhythmogenic substrate. CMR adds significantly to the management of patients presenting with bradyarrhythmia and heart block. Identification of scar involving the myocardium, predominantly the basal septum has been seen with cardiac sarcoidosis in addition to other etiologies.

Patients presenting with arrhythmias causing SCD from a variety of etiologies benefit from a CMR to identify and understand myocardial characteristics and abnormalities. In patients with arrhythmias, mapping techniques, such as T1/T2,

can identify edema, necrosis, and scarring contributing to arrhythmias [44] which is further enhanced by identification of LGE in DE imaging. Further characterization of these lesions and anatomical geometry with CMR also allows for stratifying patients most suitable for ablation [45], along with identifying focus of arrhythmia to assist with ablation procedures. These maps can be used alone or integrated with electroanatomic mapping to identify potential arrhythmogenic targets for ablation [46]. Post-ablation CMR images can also be used to determine prognostic factors contributing to the recurrence of arrhythmia.

Real-time CMR ablations have also been studied as an alternative to current ablation procedures utilizing radiation and iodinated contrast [47]; however, clinical implementation is limited by a lack of CMR-compatible devices and catheters required for these procedures.

### **4.7 Congenital heart disease (CHD)**

In CHD, CMR can aid in diagnostics as well as post-intervention follow up. CMR provides unrestricted evaluation of intracardiac and vascular structures pertinent to the altered anatomy present in CHD to assist with diagnosis. Assessment of LV and RV size and function by cine, shunt quantification and Qp/Qs calculations by flow hemodynamics assist in assessing the severity of congenital heart defect guiding medical and surgical management accordingly (**Figure 17**). The utilization of contrast enhanced MRA is highly advantageous in visualizing and defining vascular structures, which often exhibit abnormalities in cases of CHD [48]. CMR is considered the imaging modality of choice in the serial follow in CHD.

#### **Figure 17.**

*Four chamber cine showing defect in the atrial septum with dilated right atrium and ventricle in a patient with atrial septal defect.*

### **5. Advances in CMR**

Advances are being made in CMR in the scanning part and in post processing. This section discusses technologic developments and advances in CMR with a focus on improvements in data acquisition, and reconstruction, new technologies and new clinical applications of CMR, MR guided cardiac procedures, and the role of artificial intelligence and machine learning in further advancing the field.

### **5.1 Advances in data acquisition techniques**

### *5.1.1 Faster scanning*

One of the limitations for the widespread use of CMR has been the time needed for scanning and for post processing. Considerable efforts are underway to decrease these times with a focus on improving the speed and efficiency of image acquisition, resolution, and reconstruction. Parallel imaging (PI) is used currently to decrease acquisition times. PI reduces redundant phase coiling data and processing steps [49]. PI, however, has known limitations due to under-sampling, such as lowering the signal-to-noise ratio and thus contributing to image degradation [50]. A novel method has since been developed called compressed sensing (CS) that utilizes similar under-sampling from PI with the addition of a noise-reduction algorithm [51]. CS results in faster data acquisition times without compromising image quality [51]. Current research is directed at further optimizing these systems to improve image quality and reduce artifacts, such as combing CS and PI [52] and designing algorithms to separate cardiac and respiration motion artifacts [53]. In addition to developments with CS, there is an interest in implementing artificial intelligence (AI) to improve data acquisition and processing performance further. The use of deep learning (DL) has been shown to accurately reconstruct cardiac MRI images at a faster rate compared to the methods described previously [54].

### *5.1.2 Respiratory and cardiac gating*

Respiratory and cardiac gating techniques are well-established with CMR to reduce the physiologic motion of both systems and synchronize data acquisition throughout the cardiorespiratory cycle. These gating methods rely on ECGs, and image accuracy can be affected by arrhythmia and fluctuations in cardiac rhythm even in healthy subjects [55]. Novel techniques have been developed, such as non-ECG gated protocols, and have been found to improve spatial resolution and reduce cardiac motion artifacts without relying on ECG synchronization [56]. The same techniques have been implemented to reduce respiratory motion artifacts [57].

### *5.1.3 Whole heart spatial coverage*

One of the limitations of current CMR imaging protocols is the use of 2D mapping slices. This method limits image acquisition to focal areas of tissue due to the thicker slices that can only cover a portion of the heart and require multiple breath holds impractical for certain patient populations. Newer mapping techniques have now emerged that provide a comprehensive analysis and image of the entire heart to better detect fibrosis and edema that may have been missed on older scanning

modalities. This developing image acquisition technique provides whole heart spatial coverage with 3-dimensional (3D) data from one scan. The quicker scan times and improvements in motion artifacts have allowed for whole heart spatial coverage with 3D analysis to emerge as an effective alternative to more invasive diagnostic imaging techniques. While the image quality is currently a limitation, further efforts are in progress with potential in this area.

### *5.1.4 Cardiac mapping*

Myocardial mapping and CMR fingerprinting continue to expand. Data acquisition speed and accuracy improvements have expanded the clinical utility of T1 and T2 mapping. CMR fingerprinting has recently been developed to efficiently produce T1 and T2 maps from a single scan and single breath hold [58]. Additional uses have included measuring fat fraction to further characterize ischemic scars to better prognosticate cardiomyopathies [59]. Future progression is focused on applying fingerprinting to more advanced imaging sequences in 3-dimensional (3D) and 4-dimensional (4D) data sets.

### **5.2 Stress testing**

While stress testing is commonly used, the predominant form of stress is chemical. The difficulty with treadmill stress is the expense involved with MRI compatible treadmills along with the need to lay the patient down quickly on the MRI scanning table in the same position as images obtained prior to stress. Another limitation is excess motion whether whole body or during respiration with exercise. A novel stress testing technique is supine MRI-compatible exercise ergometer. With a better safety profile than pharmacological stressors, physical stress on the heart visualized via CMR can provide insight into tissue function and characteristics specific to ischemia [60]. For post processing of stress perfusion sequences, currently most centers use visual estimation for stress perfusion. Current quantitative perfusion post processing software is tedious and time consuming. Advances are being made in stress testing with faster post processing software for quantitative perfusion.

### **5.3 Artifact reduction**

Artifact reduction has become important to obtain CMR images in patients with pacemakers (PM) and ICDs. Despite developments in manufacturing MRIcompatible PM and ICDs, there remains difficulty in acquiring accurate CMR images of the myocardium due to the obscuring metal artifacts from these devices [61]. Inversion recovery sequences in LGE imaging have since been modified by adjusting the bandwidth and rate of pulsed radio frequencies to eliminate hyperintense artifacts [62]. These efforts have further expanded compatible patient populations who may benefit from CMR.

### **5.4 4-dimensional (4D) acquisition**

Four-dimensional (4D) data acquisition especially for flow analysis is an emerging advanced imaging sequence in CMR. The data from 4D image reconstruction provides 3D dynamic values over time, which can be useful in patients with complex anatomy and differing flow gradients [57]. While clinical application of 4D image acquisition

*State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

is limited by a lack of ubiquitous hardware and software, there is vast potential in developing imaging protocols to better diagnose and monitor valvular pathologies and CHD.

### **5.5 Myocardial strain**

While myocardial strain is being done by TTE currently, the use of CMR strain has significant potential (**Figure 18**). Myocardial strain assesses myocardial deformation and can serve as a precursor to myocardial dysfunction and cardiomyopathy [64] and has also been shown to predict cardiac mortality [65]. CMR is emerging as a diagnostic modality in determining myocardial strain due to several developing techniques. Displacement encoding with stimulated echocardiography (DENSE) is an acquisition method that measures myocardial tissue displacement to estimate strain. Feature tracking (FT) is another post-processing algorithm that calculates myocardial deformation [66]. Both DENSE and FT have been utilized to measure cardiac strain. However, a lack of inter-vendor standardization and clinical validity for cardiac strain remain salient limitations [66]. A new and developing technique called fast strainencoded CMR (fast-SENC) is another imaging technique that can determine cardiac contractility with comparable results to FT and DENSE [67]. The clinical implication

#### **Figure 18.**

*Example of colored strain analysis with a feature-tracking software (Circle CVI42®). From long-axis fourchamber SSFP cine image (a), longitudinal strain curve is derived (b) and short-axis SSFP image (c) is used for calculation of circumferential (d) and radial strain curves (e). Reproduced with permission from Scatteia et al. [63].*

is evaluating subclinical cardiomyopathies and adjusting treatment plans to prevent or monitor disease progression.

#### **5.6 Diffusion-weighted CMR**

Clinical utility and advances in diffusion-weighted imaging (DWI) of the heart is evolving. A subcategory of cardiac DWI with clinical potential is diffusion tensor imaging (DTI). DTI allows for 3-dimensional visualization and diffusion parameters of the cardiomyocyte microstructure without the need for exogenous contrast [68]. This modality measures water diffusion gradients within myocytes that are reconstructed to provide information about myofibers' orientation, rotation, and torsion [32]. One limitation of DWI and DTI in the heart is the signal loss inherent with cardiac motion which prevents the identification of true signal loss due to diffusion compared to signal loss due to cardiac motion. Recent advances have augmented preexisting algorithms to account for this motion discrepancy [69] and improvements in the DTI data acquisition process reduce the total imaging time [70]. While the clinical utility of DTI information continues to expand, multiple studies have investigated how the cardiac microstructure data is affected by various pathologies. Parameters such as myocyte fiber orientation, fractional anisotropy, mean diffusivity gradients, tractographic propagation angle, and helical angle are all novel approaches to better characterizing infarcted tissue [71].

#### **5.7 CMR guided interventions**

CMR-guided interventions are continuously developing. Procedures like percutaneous coronary intervention used for obstructive CAD can cause acute kidney injury from the iodinated contrast used, leading to an increase in all-cause mortality [72]. Additionally, fluoroscopy exposes patients and staff to ionized radiation, increasing the risk of future malignancy [73]. While fluoroscopic X-ray remains the gold standard for these procedures, there is growing interest in using cardiac MRI as a procedural aid to reduce the need for fluoroscopy. Transarterial valve replacements and stenting procedures using CMR have been utilized in animal studies, however, the feasibility of implementing these techniques in human subjects remains a challenge and is still experimental at this stage. Other interventional cardiac procedures have also utilized CMR to reduce their fluoroscopic footprint such as EP.

#### **5.8 Artificial intelligence and machine learning**

Artificial intelligence (AI) is quickly becoming one of the fastest-growing fields within CMR. Briefly, AI is the method of developing intelligent algorithms that can perform tasks and solve complex problems [74]. Machine learning (ML) is a subset of AI that continually improves pattern recognition and makes data inferences with the more data it processes [75]. Although the clinical applications of AI and ML are still being developed and validated, implementing these resources will drastically change the future of CMR. Most notably, AI will significantly contribute to data acquisition and reconstruction acceleration, expand CMR metrics for further diagnostic and therapeutic effects, and increase the accessibility of CMR [75]. The current ML systems that have been developed expand on CS data acquisition models to further reconstruct under-sampled data. These models learn from CMR data sets by further exploiting redundancies of the temporospatial relationships of tissue, thus resulting

### *State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

in quicker processing times and equivocal imaging resolution [75]. There have been numerous examples of ML-generated systems significantly accelerating processing times in CMR angiography [75], whole heart 3D LGE reconstruction [76], reduction of respiratory motion artifact [77], and T1 and T2 mapping [78]. Intracardiac volume measurements have also been generated from ML systems and have been used to risk stratify patients with severe AS [79]. There are instances where ML has been found to be more accurate in measuring certain parameters, such as ventricular volume, compared to human analyses [80]. Newer approaches are using ML to identify ischemic scars without utilizing LGE CMR and subjecting patients to contrast [81]. The clinical use of ML continues to expand within all fields of CMR in identifying fibrosis and scar with and without LGE, 3D and 4D flow reconstruction, and mapping techniques.

Several limitations exist regarding ML in CMR, given the field's novelty. For one, ML requires a fully sampled learning database to make inferences on testing samples, which is not widely available. Evidence suggests variations in image reconstruction based on certain parameters from the learning database, such as signal-to-noise ratios [82]. Additional improvements in central and graphical processing units are required to run these systems and models. Despite these restrictions, the use of AI and ML in CMR continues to improve and may have significant implications in imaging accessibility by providing automated analyses of cardiac disease.

### **6. Conclusion**

CMR is an excellent and comprehensive imaging modality, providing information about myocardial structure, function, tissue characterization, edema, infiltration, inflammation, scar, myocardial perfusion, congenital heart disease, shunts, flow quantification in addition to viability and any other cardiac abnormalities like masses. Currently being limited by the time involved in acquiring the scan and in the post processing of these scans, as seen above, there are a lot of advances and research happening in all areas. The clinical and research uses of CMR continue to grow and it continues to offer valuable insight into a variety of cardiac pathologies.

### **Acknowledgements**

All three authors had substantial contribution to the book chapter writing in drafting, revising the work and approval of the manuscript version to be published. The authors would like to acknowledge Michaela Kiel, Medical student for her assistance in the initial stages of the work.

*New Advances in Magnetic Resonance Imaging*

### **Author details**

Hunter Frederiksen, Corina Iorgoveanu and Mahi L. Ashwath\* University of Iowa Hospitals and Clinics, University of Iowa**,** Iowa City, USA

\*Address all correspondence to: mahi-ashwath@uiowa.edu

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*State of the Art and New Advances: Cardiac MRI DOI: http://dx.doi.org/10.5772/intechopen.112413*

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### **Chapter 3**

## New Advances in Cardiac Magnetic Resonance Imaging of Congenital Heart Disease

*Karima Hami*

### **Abstract**

Cardiac magnetic resonance (CMR) is an indispensable second-line tool, next to CT (computed tomography), in the evaluation and follow-up of congenital heart disease in adults and children, as a complement to echocardiography, without the inconvenience of X-rays. This imaging requires a long examination time and good cooperation from the patient to achieve good apnea, or the use of general anesthesia in children under 8 years of age. In this chapter, we summarize the recent advances in CMR sequences, notably the four-dimensional (4D) flow, in software and hardware technologies that allow a wider use, thanks to the simplification of the examination protocols and the decrease of the acquisition time.

**Keywords:** 4D flow, cardiovascular magnetic resonance, cardiac heart diseases, 3D printing, invasive CMR

### **1. Introduction**

Significant improvements in the diagnosis and management of patients with congenital heart disease (CHD) have led to increased number of patients surviving to adulthood [1]. These patients require lifelong noninvasive follow-up to detect longterm complications [2, 3].

Since 2020, the ACC/AH and the ESC published [4] the new guidelines for the management of adult CHD [5].

CMR is the only imaging modality offering in a single time an excellent anatomical and functional information of the heart [6, 7]. Long follow-up with repetitive CMR imaging is reasonable for its high reproducibility and safety compared to CT and catheterization, in the young population.

This imaging requires a long examination time and good cooperation from the patient to achieve good apnea, or the use of general anesthesia in young children. The use of advanced CMR sequences as such a 4D flow is a good option for improving this limitation.

Novel emerging techniques especially advanced flow evaluation and reduced acquisition and post-processing times [8] are a major step forward in the evaluation of CHD with flow perturbations [9].

### **2. 4D flow**

4D flow CMR refers to phase-contrast CMR with flow-encoding in all three spatial directions, in typical transverse, sagittal, and coronal planes and resolved to the three dimensions of space and the dimension of time along the cardiac cycle. It allows a velocity assessment in the whole heart and great vessels [10] with prospective or retrospective electrocardiogram (ECG) gating. The images obtained are displayed in a colored representation of the flow patterns.

The 4D flow enables a flow analysis in any vessel section in a single acquisition, which is especially relevant in complex CHD.

4D flow CMR requires a reliable ECG with detectable R-wave. To cover the entire aorta, it is important that the coils are positioned high enough to explore certain aortic pathologies. The scans can be relatively long and it is important to inform the patient before.

4D flow CMR employs spoiled gradient echo sequences with short TR for rapid imaging with the generation of PC angiograms without the need for an external contrast agent. According to the 4D flow cardiovascular magnetic resonance consensus statement 2023, the recommended spatial resolution in adult vessels is 2.5–3 mm3 , 2–2.5 mm3 in pediatric vessels, and 30–50 ms for temporal resolution. A flip angle of 7° is advised if non-contrast acquisition [11].

The advantage of 4D flow CMR is the retrospective analysis of the blood flow through any planes of interest across the 3D volume.

Moreover, the analysis of advanced hemodynamic parameters as kinetic energy (KE) and wall shear stress (WSS) has become possible [12, 13].

4d flow allows precise assessment in a variety of clinical situations, including evaluation of the QP/QS ratio, collateral flow, and valve regurgitation.

Retrospective cardiac gating is preferred, to analyze the flow in systole and diastole. Respiratory gating is used to avoid motion artifacts; respiratory motion compensation is a good alternative if it is available.

As with 2D, 4D flow requires a close value of real peak velocity to avoid aliasing. A VENC of 120–150 cm/s is sufficient in the absence of stenosis; otherwise it should be increased to the peak velocity expected by other methods, such as echocardiography, and using post-processing tools with anti-aliasing correction should be considered.

• Resolution: Acquired voxel size according to JCMR consensus document [11] for intracardiac flow is 3 mm or less. In small children, higher spatial resolution is recommended, because of the smaller FOV (field of view).

### **3. Application**

### **3.1 Fontan repair**

The Fontan operation is the last stage in the palliative treatment in univentricular heart [14].

The main goal of CMR is the assessment of the ventricle function, possible valvular regurgitation, the patency of the Fontan pathway, and the presence of collateral flow [15].

Various manifestations can occur such as protein-losing enteropathy, plastic bronchitis, interstitial pulmonary edema, pleuro-pericardial effusion, and ascites. *New Advances in Cardiac Magnetic Resonance Imaging of Congenital Heart Disease DOI: http://dx.doi.org/10.5772/intechopen.113148*

#### **Figure 1.**

*4D flow MRI in a total cavo-pulmonary connection with flow distribution 70% into the RPA and 30% in LPA. RPA: Right pulmonary artery, LPA: Left pulmonary artery.*

MR is able to characterize lymphatic perfusion abnormalities using static and dynamic sequences, which will not be detailed in this chapter.

Aortic forward flow should be equal to total systemic venous return and to total pulmonary venous return. The divergence in flows indicates the presence of regurgitant lesions, patent fenestration, or significant systemic-to-collateral [16].

Late gadolinium enhancement (LGE) imaging is indicated in cases of recent degradation in cardiac function, suspicion of thrombus formation, or new onset of complex arrhythmias to detect the presence and extension of myocardial fibrosis. Contrast-enhanced (CE-MRA) in the venous phase allows the assessment of the permeability of the Fontan circuit. Moreover, 4D flow imaging allows the quantification of any obstruction based on distribution patterns of caval or pulmonary artery flows (**Figure 1**) [16].

### **4. Tetralogy of Fallot (TOF)**

An accurate assessment of pulmonary valve regurgitation (PVR) is essential prior to pulmonary revalvulation (PR). This assessment is better performed using 4D flow CMR because of the possibility to correct for through-plane motion of the valve and flow angulation. Advanced flow parameters such as ventricular kinetic energy

(KE) represent a novel tool to assess cardiac function; KE represents the amount of energy present in the blood flow due to movement and is considered a good marker of ventricular efficiency; it is calculated using the following equation: KE = ½*mv*<sup>2</sup> where m represents the mass (the voxel volume multiplied by the density of blood) and v represents the velocity of each voxel, determined from the 4D flow. Jeong found that the KE was abnormal in TOF patients compared to in healthy controls [17].

According to the current CMR criteria, a large percentage of patients continue to experience symptoms of the classic complications observed in patients not undergoing PR, such us ventricular arrhythmias and heart failure [18].

4D flow provides a more accurate assessment of PV regurgitant flow, which may lead to better timing of revalvulation.

Several studies show that turbulent kinetic energy in the right ventricle was higher in patients with TOF than in healthy controls, mainly in the RVOT [17, 19, 20].

Jeong demonstrated that KE is an earlier indicator of cardiac dysfunction than classic parameters such us EDVI, ESVI, and EF.

Furthermore, patients with TOF may have pulmonary valve or branch stenosis. Consequently, analysis of PA flow based on 2D PC CMR plane is prone to error. Geiger and Francois [21] found that TOF patients present helical flow patterns in the pulmonary arteries [22].

These findings have been reported by Hu et al. [23]. They found that vortices were predominantly present in the main PA and helical flow patterns were predominantly present in the right PA, which was associated with systolic energy loss in the right PA and increased RV dimensions, suggesting impaired ventricular–arterial coupling.

### **5. Aortic diseases**

In the aorta, aortic flow was assessed in all three segments, on the ascending, transverse, and descending aorta, in a plane perpendicular to the aortic axis.

The advantage of the 4D flow is that the plans can be placed after the acquisition.

Vorticity and helicity are two parameters that provide information about the rotational movement of blood flow.

Vorticity describes the rotation of a fluid particle around the same axis as well as around its own axis, which describes a curved movement.

Helicity is determined from vorticity and the principal component of flow velocity, which determines the direction of flow.

In aorta, the flow has a helical pattern at the end of systole, in the upper aortic arch as has been described by Kilner [24]; (**Figure 2**) it allows the preservation of laminar flow in the aortic arch. In aortic pathological conditions such as aneurysms, aortic bicuspidi, coarctation, or dissection, rotational flow is abnormal.

### **6. Three-dimensional printing and virtual reality**

Three-dimensional (3D) printing technology has become an attractive tool for creating patient-specific anatomical models (**Figure 3**). Its role in clinical decision and patient management in complex CHD is increasing.

Numerous studies have demonstrated superior advantages of 3D-printed models over the traditional 2D and 3D image reconstructions, enhancing the perception of

*New Advances in Cardiac Magnetic Resonance Imaging of Congenital Heart Disease DOI: http://dx.doi.org/10.5772/intechopen.113148*

#### **Figure 2.**

*4D flow CMR of the normal aorta showing the direction of flow in all three phases of systole (early, peak, and end systole).*

distances and spatial configuration of the complex cardiac morphology and therefore facilitating the surgical planning [25–27].

A multicenter study [28] showed that the use of 3D-printed heart CHD models enabled surgical decisions to be modified in around 50% of cases.

In a similar way, other studies have confirmed the usefulness of 3D-printed cardiac models to guide surgical procedures in patients with CHD [20, 29–31].

#### **Figure 3.**

*3D-printed models of transposition of the great arteries and arterial switch operation. Ao, aorta; SVC, superior vena cava; PT, pulmonary trunk; LV, left ventricle; RA, right atrium; RV, right ventricle.*

Gomez-Ciriza et al. [32] reported their experience of 7 years in which 3D-printed heart models were able tomodify the surgical decision in 48% of cases.

However, the large application of 3D printing technology in pediatric cardiology practice is still limited by some barriers.

Geographic location: A recent international survey [33] has found that the ability to access 3D printing technology differs from region to region.

The cost of printing materials is another factor that limits its application in many practices, especially soft and elastic materials (high-cost 3D-printed models) with tissue properties similar to normal cardiovascular tissues.

Another limitation of this model is the long time required from image reconstruction to printing and cleaning of the models.

If 3D printing is unavailable, virtual reality (VR) could be a promising technique in clinical application and medical education for CHD. Raimondil and colleagues [34] noticed that the median time to elaborate VR models was only 5 min, which is interesting compared to 3D printing models, which required a long time (8 hours).

### **7. Interventional CMR**

Invasive cardiovascular magnetic resonance imaging (CMR) of cardiac catheterization is a better alternative to fluoroscopy, which has been the gold standard in the assessment of patients with congenital heart disease (CHD). It provides real-time anatomical visualization of the cardiovascular structures [35–37] and the guidance for hemodynamic data without the radiation exposure. The harmful effects of repeated use of X-rays in this population have been increasingly debated in recent years. Prolonged exposure to radiation would be associated with increased risk of cancer in adult patients followed for congenital heart disease [38, 39]. Then, interventional CMR catheterization is a good alternative without ionizing radiation in children, in whom a repetitive hemodynamic assessment would be necessary.

Conditioned catheters and guidewires with gadolinium-filled balloon have been used in CMR-guided cardiac catheterization [40–42].

A few centers reported their experiences with invasive CMR [35, 43–48] for diagnostic and interventional procedures under CMR guidance such as CoA, and Fontan fenestration test occlusion, and pulmonary vein access [49].

ICMR is currently performed in several centers [50], in patients with CHD patients before surgery or in the postoperative follow-up, for diagnostic purposes, in particular catheterization of the right heart in cases of pulmonary hypertension or a more detailed hemodynamic study in complex congenital heart disease (pre-Fontan study, or Fontan fenestration test occlusion, for example,) or for therapeutic purposes (closure of an intercavitary shunt).

The advantage of ICMR is its ability to measure cardiac output and the QP/QS ratio by phase contrast, which have proved to be more reliable than thermodilution, which can be distorted by the presence of a valve leak, or Fick's principle, which gives an estimated rather than measured VO2 value, and at rest rather than during exercise or stress.

In addition, MRI allows ventricular and atrial volumes, EF and functional analysis, and tissue characterization.

Reddy [49] demonstrates the potential of iCMR in diagnostic right and left heart catheterization, CoA diagnosis, and Fontan fenestration occlusion hemodynamic testing. *New Advances in Cardiac Magnetic Resonance Imaging of Congenital Heart Disease DOI: http://dx.doi.org/10.5772/intechopen.113148*

#### **Figure 4.**

*Series showing a MR-conditional guidewire (a–b solid white arrow) used to guide the gadolinium-filled balloon (dashed white arrow) for a RHC and LHC (c), Fontan fenestration test occlusion, and measure (D–G) of the pulmonary venous saturation in the LA. F: Gadolinium-filled balloon crossing a severe CoA with the assistance of an MR-conditional guidewire. Image courtesy of Surendranath R. Veeram Reddy and Yousef Arar, pediatric cardiology, Children's medical center Dallas, 1935 Medical District Dr., Dallas, TX, 75235, USA.*

The balloon attached to the tip of the catheter was filled with diluted gadolinium and guided using a conditioned guide toward the structures to be evaluated hemodynamically, using the real-time sequence (**Figure 4**).

Recently, use of fully insulated nitinol guidewires is feasible in low-SAR and lowfield imaging [51, 52].

In the electrophysiology field, CMR allows complete delineation of the atrial anatomy and detection of fibrosis of the left atrium and intra-atrial thrombosis. CMR-guided ablations in particular, cavotricuspid isthmus (CTI) ablation by realtime iCMR guidance is increasingly performed in different centers with similar results to conventional fluoroscopy-guided ablation [53].

### **8. Conclusion**

The new techniques developed over the last decade in cardiac MRI of CHD are promising, offering reduced acquisition and post-processing times while exploring multiple flows in the same examination, thanks to 4D flow, radiation-free diagnostic and therapeutic procedures with ICMR, and accurate anatomical description elaborated by 3D printing in complex CHD. These new tools are currently used in only a few centers and should be accessible in the coming years to the various magnetic resonance imaging centers.

*New Advances in Magnetic Resonance Imaging*

## **Author details**

Karima Hami Cheikh Zaid Hospital, University Aboulcassis, Rabat, Morocco

\*Address all correspondence to: hami7esp@yahoo.com

© 2023 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

*New Advances in Cardiac Magnetic Resonance Imaging of Congenital Heart Disease DOI: http://dx.doi.org/10.5772/intechopen.113148*

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Section 3
