The heart Modalities
Conventional radiology
The cardiac radiographic study consists of one frontal and one lateral film (Fig. 1 a, b). In addition, two oblique projections are taken in special cases, but these usually give little additional information beyond that obtained from frontal and lateral views.
The frontal film is exposed in full inspiration. The distance between the film and the x-ray tube should be standardized in order to permit measurement of cardiac dimensions. The normal focal-film distance is 1.80 metres. In the frontal view, the heart appears as a white shadow, where it is only possible to assess changes in shape and size.
The lateral view is often taken with contrast medium in the esophagus to facilitate assessment of the position of the posterior outline (left atrium). It is not possible on the lateral view to evaluate internal structures
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Figure 1.
a) PA view of heart of normal size. The right atrium makes the right, and the left ventricle makes the left outline. Cranially, the superior vena cava is seen on the right and the arch of the aorta on the left side.
b) Lateral view of a heart of normal size with contrast in the esophagus. In front, the right ventricle is next to the sternum, and the left atrium forms the upper part of the posterior heart outline and is next to the esophagus. The posterior border of the left ventricle makes the lower part of the heart's posterior outline.
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of the heart but rather the heart size and contour are evaluated. However, intracardiac and pericardial calcification can be readily assessed in a lateral view.
Fluoroscopy is used to localize intracardiac calcifications. This modality permits evaluation of motion of the calcification during the cardiac cycle. Fluoroscopy may also be useful to identify paradoxical movement of the left ventricle (with aneurysms of the left ventricle ), and to examine the relationship between the heart and mediastinal structures.
Computed tomography (CT)
Computed tomography (Fig. 2 a, b) is not used routinely in the radiological evaluation of the heart, but CT programs have been constructed
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Figure 2.
a) Computed tomography; section through the heart at the level of the ventricles. The picture shows the right and left ventricle and the course of the ventricular septum.
b) Cross section through the upper part of the heart; intravenous contrast medium. The left atrium is seen at the back, and the right atrium to the right as a tapering cleft-like space. The outlets of the right and left ventricles, respectively, are seen in the middle anteriorly.
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that can follow a contrast bolus through the heart from the right side through the pulmonary circulation to the left side. Special CT equipment (ultra fast CT, or cine CT -scanner) has also been constructed for dynamic CT studies of the heart. Cine CT has been shown to be very effective for demonstrating patency of coronary artery bypasses; quantifying ventricular volumes and function; evaluating pericardial diseases and complications of myocardial infarctions; and defining the morphology of congenital heart disease. Recently, some enthusiasm has been revived for using cine CT as a highly sensitive method for demonstrating coronary arterial calcification and using this to propose the relative risk of obstructive coronary arterial disease in specific populations.
Magnetic resonance imaging (MRI)
Magnetic resonance imaging (MRI) (Fig. 3) is used for the diagnosis of a few specific types of cardiac disease, and will be of great importance in the future, especially with the continued development of fast MR imaging techniques. The initial MRI technique, ECG gated spin echo imaging, provides striking depiction of cardiac morphology. Subsequently,
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Figure 3.
Transverse section through the heart (MRI). Large dilated left ventricle in a child. A small triangular right ventricle is seen at the front with the right atrium behind it. The left atrium is seen in front of the vertebral column, with the opening of one of the pulmonary veins on the left.
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Figure 4.
ECG gated spin echo (a) and cine MR (b) in the transaxial plane display a dissection of the descending aorta. The intimal flap (arrow)
separates the true (T) and false (F) channels. On the spin echo image, the signal in the false channel is caused by slow velocity of blood flow.
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cine MRI was introduced, which provides images corresponding to multiple phases of the cardiac cycle. This enabled evaluation of cardiac contraction and valvular motion. It is now possible to obtain a cine MRI acquisition during a breath hold period of 14 to 16 seconds. MR images can also be obtained at a rate of one per second or slightly longer in order to monitor contrast media distribution in the cardiac chambers and myocardium. Monitoring of the first pass dynamics of MR contrast media constitutes a new method for evaluating mycardial perfusion. Finally, nearly real time MR imaging of the heart is possible with echoplanar MRI.
The role of MRI of the heart is still evolving and consensus is not established regarding all the proposed uses of it for cardiovascular diagnosis. MRI can be considered for the evaluation of the following clinical situations:
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Figure 5.
ECG gated spin echo images in the transaxial (a) and coronal (b) planes in two patients with constrictive pericarditis. The thick pericardium is demonstrated in both patients.
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Figure 6.
ECG gated spin echo image in the transaxial plane demonstrates hemorrhagic (H) and nonhemorrhagic (E) pericardial collections.
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1. Thoracic aortic disease, including dissections and aneurysms (Fig. 4)
2. Some forms of pericardial disease, especially for the definitive diagnosis of constrictive pericarditis (Fig. 5); loculated pericardial effusions (Fig. 6) and pericardial hematoma (Fig. 6).
3. Intracardiac (Figs. 7, 8) and paracardiac masses (Fig. 9)
4. Complications of acute myocardial infarction such as true and false ventricular aneurysms and mural thrombus (Fig. 10).
5. Right ventricular dysplasia and outflow tachycardia
6. Several types of con genital heart disease such as coarctation (Fig. 11); arch anomalies;
pulmonary arterial and venous abnormalities; and postoperative
congenital heart disease.
The cine MRI technique can be used to evaluate dimensions and function of both ventricles. Cine MRI is also used to identify pathological (high velocity turbulent) flow caused by valvular regurgitation and stenosis (Fig. 12, 13). The velocity encoded cine MRI technique provides measurement of blood flow and velocity in the heart and great vessels. It has been used for quantifying the volume of valvular regurgitation and the gradient across valvular stenosis. It can also be used to measure the volume of left to right shunts and differential flow in the right and left pulmonary arteries.
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| Figure 11.
ECG gated spin echo images in the transaxial (a) and sagittal (b) planes in a patient with a severe juxtaductal coarctation (arrow) of the aorta. Large paravertebral collateral arteries are demonstrated(arrows). |
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Coronal cine MR images in a patient with aortic regurgitation. Images in the upper panels are during systole and those in lower panels are in diastole. The signal void emanating from the aortic valve in diastole represents the jet of aortic regurgitation. |
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Cine MR image in a patient with aortic stenosis. Systolic phase. The signal void emanating from the aortic valve into the ascending aorta is caused by aortic stenosis.
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Angiocardiography/coronary angiographyAngiography (Fig. 14 a-d) is used to examine the heart chambers and the coronary arteries. Under the guidance of fluoroscopy, a catheter is inserted, usually via the femoral artery, to the left ventricle, where contrast is injected. This permits measurement of the volume of the left ventricle and parameters of left ventricular function. The movement and competency of the cardiac valves can also be evaluated. The catheter is then routinely withdrawn to immediately above the aortic valves so that this portion of the ascending aorta and the aortic valves can be examined. In addition, selective catheterization of the left and right coronary arteries is carried out, and films are acquired in several projections to assess pathological changes such as stenosis or occlusion. When the right side of the heart is examined (cardiac catheterization), the catheter is inserted from either the femoral vein, or an antecubital vein, to selected sites in the right half of the heart or superior vena cava, depending on the problem under investigation. At the same time, pressure is registered, and the oxygen content of the blood is measured. Since injection of contrast agents into the heart itself necessitates large volumes injected very rapidly (45 ml injection volume, 15 to 25 ml per second with injection into the left ventricle ), an automatic high pressure syringe is needed for these injections. Injection into the coronary arteries is usually carried out by manual injection of from 5 to 8 ml of contrast medium per injection. The films in angiocardiography and coronary angiography are usually recorded on cine film (35 mm film). In order to obtain continuous, sharply defined images of the movements of the heart, a minimum of 24 frames per second is often used during these examinations, which can also be carried out using digital format instead of ordinary cine film. Ultrasound scanning of the heart can either be performed as M-mode or two-dimensional (2-D) echocardiography (Fig. 15 a, b). M-mode echocardiography gives a one-dimensional image of the structures of the heart. Since the different parts of the heart move synchronously in relation to each other during the cardiac cycle, the echo from these structures will move coordinate with each other in relation to the ultrasonic transducer on the chest wall. These echoes are recorded on an oscillograph or on videotape as a continuous one-dimensional representation.
 a  b |  c  d | Figure 14.
a) Angiocardiography - catheter from the femoral artery down into the left ventricle. b) Thoracic aortography with injection of contrast medium into the thoracic ascending aorta immediately above the aortic orifice. Normal right and left coronary arteries are visible.
c) Selective injection of contrast medium into the left coronary artery with normal arteries to the anterior and posterior walls of the heart.
d) Selective injection of contrast medium into a normal right coronary artery. |
In two-dimensional echocardiography, the sonic waves travel in one plane through the heart, and the echoes received by the transducer are shown on a monitor in real time. This provides a tomographic image of the plane under examination. Most of the heart can be visualized in this way. The major limiting factors for attaining an acoustic window for recording are interposition of bony structures of the chest wall or lung. It has recently become customary to use Doppler echocardiography when examining the heart. The direction and velocity of blood flow can be determined using Doppler echocardiography. The Doppler technique
is very well suite d for detecting pathological changes in the flow of blood, which may occur with atrial septal defect, ventricular septal defect, and pathological changes in the heart waves (pulmonary, mitral and aortic orifices ).
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| Figure 17.
a) PA view - normal heart
b) Lateral view - normal heart
c) Photo of a heart model - PA projection. |  b |  c
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lsotope scanning of the heart (Fig. 16 a, b) is a noninvasive examination which provides not only pure pictorial information, but also details of physiological conditions. This examination can provide information on function of the left ventricle; myocardial perfusion; presence of myocardial infarcts; and presence and volume of intracardiac shunts. Several radioactive isotopes are used in cardiac scintigraphic diagnosis. The most frequently used are technetium 99m (99m Tc), thallium 201TI, and 99mTc sestamibi. |
Arnulf Skjennald and Charles B. Higgins