Imaging Anatomy of the Heart and Thoracic Great Vessels

▪ Introduction

Various imaging techniques are used in the assessment of the normal anatomy and pathology of the heart and great vessels. Chest radiography is the most commonly used modality and is often the first imaging test used in the assessment of patients with suspected cardiovascular disorders. Advances in cross-sectional imaging, such as computed tomography (CT) and magnetic resonance imaging (MRI), have enabled dedicated and precise assessment of the morphology and function of the heart. The cardiac chambers, coronary vessels, and valves can all be comprehensively imaged with CT and MRI. With the routine use of retrospective electrocardiographic (ECG) gating or prospective triggering and advanced postprocessing techniques, cardiac structures can be assessed without motion artifacts in multiple planes.

Cardiac Anatomy on Conventional Radiography

The use of conventional posteroanterior and lateral chest radiographs enables the assessment of the normal and abnormal cardiovascular structures that have their interface with the lung. On the posteroanterior radiograph, the structures that form the right margin of the cardiomediastinal silhouette from superior to inferior are the right innominate vein, superior vena cava (SVC), right atrial appendage (RAA), right atrium (RA), and inferior vena cava (IVC; Fig. 3.1A ). The structures that form the left margin of the cardiomediastinal silhouette, from superior to inferior, are the left subclavian artery, aortic knob, aortopulmonary window, main pulmonary artery (MPA), left atrial appendage (LAA), and left ventricle (LV).

Figure 3.1, Chest radiograph. (A) Posteroanterior radiograph shows that the right border of the cardiomediastinal silhouette is formed by the right innominate vein, superior vena cava, right atrium (RA). and inferior vena cava, from top to bottom. Dilation of the RA (small arrows) and inferior vena cava can cause widening of the right cardiac silhouette. The left border of the cardiomediastinal silhouette is formed by the left subclavian artery, aortic knuckle (AO), aortopulmonary window, main pulmonary artery (MPA), left atrial appendage, and left ventricle (LV) (arrowheads) . Aortopulmonary (AP) window nodal enlargement and an enlarged MPA are common causes of the convex appearance of the AP window; LV enlargement results in leftward, inferior, or posterior displacement of the left heart border. (B) Lateral radiograph shows that the anterior margin of the cardiac silhouette is formed by the right ventricle (RV; thin white arrows ), right ventricular outflow tract (RVOT; white bold arrows ), and the MPA (arrowhead). An enlarged RVOT and RV cause obliteration of retrosternal space on lateral view. The upper half of the posterior border of the cardiac silhouette is formed by the left atrium, and the posterior wall of the LV forms the lower half. Left atrial enlargement causes posterior displacement of the left main bronchus on lateral chest x-ray and a convex appearance of the upper posterior cardiac silhouette.

On the lateral radiograph, the anterior margin of the cardiac silhouette is formed by the right ventricle (RV), right ventricular outflow tract (RVOT), and MPA. The upper half of the posterior border of the cardiac silhouette is formed by the left atrium (LA), and the lower half is formed by the posterior wall of the LV. On the lateral radiograph, the right pulmonary artery (RPA) is seen as an oval opacity located immediately anterior to the right upper lobe bronchus, whereas the left pulmonary artery (LPA) is seen above the left upper lobe bronchus (see Fig. 3.1B ).

Technical Factors for Cardiac Imaging and the Imaging Planes

Electrocardiographic Gated Scan

Cardiac motion leads to blurred image borders on CT and MRI. With the use of ECG gating, the image acquisition is timed to the specific phase of the cardiac cycle that provides relatively motionless imaging of the heart, coronary vessels, and proximal aorta. ECG gating can be done retrospectively or prospectively. Retrospective ECG gating is a look-back technique in which images are obtained during the entire cardiac cycle, and the best phases are reconstructed later. In prospective triggering, the data are obtained only during a specific phase of the cardiac cycle that typically is end-diastole, because it is the most motion-free phase of cardiac cycle. The radiation dose to the patient is lower with prospective ECG triggering but, if cine images are required for assessment of left ventricular (LV) wall motion or cardiac valves, retrospective ECG gating is preferred. The images can be reconstructed at specific points during the cardiac cycle for cine imaging. Cine imaging is also required for the assessment of LV wall thickening and determination of quantitative LV functional parameters (e.g., ventricular volumes, stroke volume, ejection fraction).

Cardiac Imaging Planes

Various imaging techniques such as echocardiography, single-photon emission computed tomography (SPECT), positron emission tomography (PET), CT, and MRI have been used to image the heart. To maintain standardization across various techniques, imaging of the heart is displayed along standard orientation planes—short axis, vertical long axis, two chamber, and horizontal long axis, four chamber. These orientation planes also help match various segments of myocardium with their coronary artery supply. The short-axis, horizontal, and vertical long-axis images are obtained at 90 degrees to the long axis of the LV (plane through the apex and center of the mitral valve [MV]).

Although CT images are obtained perpendicular to the long axis of body, four-chamber, three-chamber, and two-chamber planes can be reconstructed from volumetric data due to isotropic resolution of images obtained on newer scanners. The three-dimensional (3D) workstations with cardiac analysis capability can easily produce images in standard planes. These planes can be briefly summarized as below.

Two-Chamber View (Paraseptal View)

The two-chamber or vertical long axis view is an oblique sagittal plane along the LV cavity axis and is best suited for visualization of the left atrial (LA) and LV cavities, MV, and anterior and inferior walls of the LV ( Fig. 3.2A ).

Figure 3.2, Cardiac imaging views. (A) Two-chamber, steady-state free precession (SSFP) view showing the left ventricle (LV) , left atrium (LA) , and mitral valve (MV). This view helps assess the LV apex and anterior and inferior walls for pathologies, including infarcts and aneurysms. (B) Three-chamber SSFP view shows the LA, LV, and left ventricular outflow tract. The MV and aortic valve are also shown; this is a good view to assess for left atrial enlargement and systolic anterior motion of the MV in hypertrophic cardiomyopathy, in addition to anteroseptal and inferolateral wall abnormalities. (C) Four-chamber SSFP view shows all four cardiac chambers and the mitral and tricuspid valves and is a good view to assess abnormalities of the atrioventricular valves, cardiac chambers, and wall motion abnormalities, including right ventricular free wall dyskinesia in arrhythmogenic right ventricular dysplasia and LV aneurysm. RA, Right atrium; RV, right ventricle. (D) Short-axis SSFP view shows the LV and RV with the interventricular septum separating them and is a standard view in cine to assess for wall motion abnormalities and cardiac functions. (E) The 17-segment model for two-dimensional transthoracic echocardiography. The ventricle is divided into thirds from base to apex, and then the radial segments are assigned names and numbers at each level. The basal third extends from the mitral annulus to the tip of the papillary muscles at end-diastole, the middle third extends through the papillary muscles, and the apical third is composed of the remaining cavity, distally from the end of the papillary muscle; the true apex is a single segment. LAD, Left anterior descending artery; LCx, left circumflex artery; RCA, right coronary artery. (F) The 17-segmental model for the nuclear stress test.

Three-Chamber View

The three-chamber view is an oblique plane that is useful for the evaluation of the mitral and aortic valves, LA and LV cavities, and aortic root. This plane can be obtained manually on multiplanar images by including three points—the center of the MV, the LV apex, and the center of the aortic valve. Other structures that can be evaluated on this plane include the inferolateral and anteroseptal segments of the LV and the posteromedial papillary muscles, along with its chordae tendineae (see Fig. 3.2B ).

Four-Chamber View

The four-chamber view is an oblique plane that displays all four chambers of the heart. This plane can be manually reproduced on multiplanar images by including the center of the MV, the LV apex, and the center of the tricuspid valve (TV). This plane allows for the assessment of cardiac chamber sizes, evaluation of the MV and TV, and LV inferoseptal and anterolateral segments and LV apex (see Fig. 3.2C ).

Short-Axis Views

Short-axis views are a stack of oblique planes perpendicular to the long axis of the LV cavity on both the four-chamber and paraseptal long axis views (see Fig. 3.2D ). The LV myocardium can be divided into basal, mid, and apical segments in the short-axis planes. Short-axis views are useful for assessing the LV cavity, regional wall motion, and myocardial anatomy based on the 17-segment model (see Fig. 3.2E ).

Aortic Valve: Short-Axis View

This plane is used for the evaluation of aortic valvular morphology, stenosis, regurgitation, valve prostheses, or masses. The aortic valve short-axis view is a plane that is orthogonal to the long axis of the LV outflow tract (LVOT) and aortic root on the three-chamber view.

Right Ventricular Inflow-Outflow Plane

This plane is used for the evaluation of the right side chambers and tricuspid and pulmonic valves. It can be manually reconstructed by joining the center of the TV, RV apex, and center of the pulmonic valve ( Fig. 3.3A–C ).

Figure 3.3, Right cardiac chamber imaging views. (A) Right ventricle (RV) outflow steady-state free precession view shows the right ventricular outflow tract (RVOT), pulmonic valve (arrows) , and main pulmonary artery (MPA) . This is useful to assess for RVOT stenosis, pulmonic valve abnormalities, and pulmonary artery dilation and narrowing. (B) RV inflow shows the right atrium (RA), tricuspid valve (arrows), RV, pulmonic valve, and MPA. (C) RV, horizontal long-axis view, shows all four cardiac chambers and the RV free wall anteriorly. LA, Left atrium; LV, left ventricle. (D) Bicaval view shows both the superior vena cava (SVC) and inferior vena cava (IVC) draining into the RA and is useful to assess their drainage pattern and filling defects.

Bicaval View

The bicaval view is a standard view on echocardiography that helps visualize the SVC and IVC inflow and superior part of the interatrial septum (IAS), mostly needed for the evaluation and treatment planning of ostium secundum atrial septal defect (ASD; see Fig. 3.3D ). On CT, this view can be manually reconstructed using multiplanar techniques.

You're Reading a Preview

Become a Clinical Tree membership for Full access and enjoy Unlimited articles

Become membership

If you are a member. Log in here

▪

Introduction