[level-membership-for-cardiothoracic-surgery-category]Chapter 9

Cardiac Anatomy Using MR

Cardiac MR Axial 1

Normal Variant

This axial MR image shows a common vascular variation—an aberrant right subclavian artery. Thoracic CT Soft Tissue Axial Plates 1 to 5 show the normal origin and course of the right subclavian artery. The aberrant right subclavian artery is one of the most common congenital vascular anomalies affecting the aortic arch and great vessels. Normally the right subclavian artery arises from the right brachiocephalic artery and courses into the right upper extremity (see Thoracic CT Soft Tissue Axial Plates 1 to 5). In contrast, the aberrant right subclavian artery typically arises from the distal aspect of the aortic arch or proximal descending thoracic aorta and courses through the mediastinum, posterior to the esophagus, to reach the right upper extremity.

Cardiac MR Axial 2

Cardiac MR Axial 3

Cardiac MR Axial 4

Cardiac MR Axial 5

Technical Consideration

These two MR images illustrate two of the many MR techniques used to examine the thoracic and cardiovascular system: “black blood” and “white blood” imaging techniques, named for the appearance of flowing blood on the image. There are a number of ways in which “black blood” images may be created, but these techniques have in common the lack of significant signal associated with flowing blood—hence, the vessels and cardiac chambers appear black. “White blood” sequences are often used for functional analysis and, although the bright signal within the vessels and cardiac chambers gives the impression that intravenous contrast has been injected, these imaging sequences do not require the use of intravenous contrast to generate signal within the vascular system.

Cardiac MR Axial 6

Cardiac MR Axial 7

Diagnostic Consideration

A small amount of pericardial fluid is shown surrounding the ascending aorta. The normal pericardial sac is composed of an outer fibrous layer and an inner serous pericardial sac. The serous pericardium consists of an inner visceral layer (the epicardium), which is intimately adherent to the heart and epicardial fat, and an outer parietal layer, which lines the inner surface of the fibrous pericardium. The pericardial sac is divided into the pericardium proper and a number of sinuses and recesses. Up to 25 mL of fluid may be present within the pericardial sac under normal conditions. On MR and CT, normal pericardium is often seen, and the thickness of normal pericardium typically does not exceed 2 mm.

Cardiac MR Axial 8

Cardiac MR Axial 9

Cardiac MR Axial 10

Cardiac MR Axial 11

Cardiac MR Axial 12

Cardiac MR Axial 13

Cardiac MR Axial 14

Diagnostic Consideration

Right ventricular anatomy with MR is shown. Cardiac CT requires the injection of iodinated contrast material to opacify the cardiac chambers and vessels to allow adequate visualization of these structures, but dense contrast within the right atrium and ventricle can often obscure adjacent anatomy, such as the right coronary artery, on CT. For this reason, cardiac CT examinations are often conducted with an injection of saline or saline-contrast mixtures following the injection of undiluted iodinated contrast to clear the dense contrast from the right cardiac chambers. Although this technique results in excellent imaging for left-sided cardiac structures and the right coronary artery, it may result in suboptimal visualization of right chamber anatomy (see Cardiac CTA plates). However, note the excellent demonstration of right chamber anatomy on MR—the trabeculae carneae, papillary muscles, and moderator band of the right ventricle and the tricuspid valve are readily visible, and intravenous contrast administration is not required for MR to demonstrate such detail.

Cardiac MR Axial 15

Cardiac MR Axial 16

Cardiac MR Axial 17

Cardiac MR Axial 18

Cardiac MR Axial 19

Cardiac MR 2-Chamber 1

Technical Consideration

Cardiac imaging is often interpreted with images displayed in planes oriented with reference to the cardiac axis, as opposed to the axes of the body as is typical for most imaging applications (the axial, coronal, and sagittal planes). Cardiac imaging planes typically include “two-chamber,” “three-chamber,” “four-chamber,” and “short axis” planes, and are commonly used for cardiac CT, MRI, nuclear medicine, and echocardiography. This “two-chamber” or “vertical long axis” view of the heart is useful for assessing the left ventricular cavity, left ventricular inferior and anterior wall motion, the mitral valve, and the left atrial appendage.

Cardiac MR 3-Chamber 1

Technical Consideration

This is commonly referred to as a “three-chamber” view of the heart; it is useful for displaying the left ventricular outflow tract, left atrium, and mitral and aortic valves. The anteroseptal and inferolateral walls of the left ventricle are also well seen. Note how the continuity between the aortic root and anterior mitral valve are well shown in this view.

Cardiac MR 4-Chamber 1

Technical Consideration

This view, often referred to as a “four-chamber” or “horizontal long axis” view, is oriented through the mid portions of the right and left ventricles, along a plane extending through the mitral valve to the apex of the heart. This projection provides a more precise analysis of ventricular size and morphology than standard axial, coronal, or sagittal imaging and is useful for assessing the function of the mitral and tricuspid valves. Left ventricular septal and lateral wall motion is also evaluable in this view.

Cardiac MR Short Axis 1

Technical Consideration

This view, often referred to as a “short axis” view, is oriented orthogonal to the four-chamber view, perpendicular to the long axis of the left ventricle from the mitral valve to the apex of the heart. This view is used for calculation of ventricular volumes and ejection fraction as well as assessment of left ventricular wall motion.

[/level-membership-for-cardiothoracic-surgery-category][not-level-membership-for-cardiothoracic-surgery-category]Chapter 9

Cardiac Anatomy Using MR

Cardiac MR Axial 1

Normal Variant

This axial MR image shows a common vascular variation—an aberrant right subclavian artery. Thoracic CT Soft Tissue Axial Plates 1 to 5 show the normal origin and course of the right subclavian artery. The aberrant right subclavian artery is one of the most common congenital vascular anomalies affecting the aortic arch and great vessels. Normally the right subclavian artery arises from the right brachiocephalic artery and courses into the right upper extremity (see Thoracic CT Soft Tissue Axial Plates 1 to 5). In contrast, the aberrant right subclavian artery typically arises from the distal aspect of the aortic arch or proximal descending thoracic aorta and courses through the mediastinum, posterior to the esophagus, to reach the right upper extremity.

Cardiac MR Axial 2

Cardiac MR Axial 3

Cardiac MR Axial 4

Cardiac MR Axial 5

Technical Consideration

These two MR images illustrate two of the many MR techniques used to examine the thoracic and cardiovascular system: “black blood” and “white blood” imaging techniques, named for the appearance of flowing blood on the image. There are a number of ways in which “black blood” images may be created, but these techniques have in common the lack of significant signal associated with flowing blood—hence, the vessels and cardiac chambers appear black. “White blood” sequences are often used for functional analysis and, although the bright signal within the vessels and cardiac chambers gives the impression that intravenous contrast has been injected, these imaging sequences do not require the use of intravenous contrast to generate signal within the vascular system.

Cardiac MR Axial 6

Cardiac MR Axial 7

Diagnostic Consideration

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Netters Correlative Imaging Cardiothoracic Anatomy