Collection of multiple articles in one palce....

Noninvasive Cardiac Imaging: Echocardiography, Nuclear Cardiology, and MRI/CT Imaging:

Cardiovascular imaging has significantly enhanced the practice of cardiology over the past few decades. Two

(2D) echocardiography is able to visualize the heart directly in real time using ultrasound, providing instantaneous

assessment of the myocardium, cardiac chambers, valves, pericardium, and great vessels. Doppler echocardiography

measures the velocity of moving red blood cells and has become a noninvasive alternative to cardiac catheterization for assessment of hemodynamics. Transesophageal echocardiography (TEE) provides a unique window for high
imaging of posterior structures of the heart, particularly the left atrium, mitral valve, and aorta. Nuclear cardiology uses isotopes to assess myocardial perfusion and ventricular function and has contributed greatly to the evaluation of patient with ischemic heart disease. Cardiac MRI and CT can delineate cardiac structure and function with high resolution. They particularly useful in the examination of cardiac masses, the pericardium, and the great vessels. MRI stress testing is no possible examining both ventricular function and perfusion. Detection of coronary calcification by CT as well as direct
visualization of coronary arteries by CT angiography (CTA) are of growing utility in patients with suspected coronary art disease (CAD). This chapter provides an overview of the basic concepts of these cardiac imaging modalities, as well as t clinical indications for each procedure. The illustrations in this chapter are supplemented by "real time" and other static images in Chap. e20, "The Atlas of Noninvasive Cardiac Imaging."

Two-Dimensional Echocardiography

BASIC PRINCIPLES

2D echocardiography uses the principle of ultrasound reflection off cardiac structures to produce images of the heart (T 222-1). For a transthoracic echocardiogram (TTE), the imaging is performed with a handheld transducer placed directly the chest wall. In selected patients, a TEE may be performed, in which an ultrasound transducer is mounted on the tip o endoscope placed in the esophagus and directed toward the cardiac structures.

Table 1 Clinical Uses of Echocardiography

Two-Dimensional Echocardiography                Doppler Echocardiography

Cardiac chambers                                                 Valve stenosis

Chamber size                                                         Gradient

Left ventricular                                                         Valve area

Hypertrophy                                                       Valve regurgitation

Regional wall motion abnormalities                  Semiquantitation

Valve                                                                         Intracardiac pressures

Morphology and motion                                  Volumetric flow

Pericardium                                                             Diastolic filling

Effusion                                                             Intracardiac shunts

Tamponade                                                      Transesophageal Echocardiography

Masses                                                                    Inadequate transthoracic images

Great vessels                                                          Aortic disease

Stress Echocardiography                                     Infective endocarditis

Two-dimensional                                                   Source of embolism

Myocardial ischemia                                       Valve prosthesis

Viable myocardium                                         Intraoperative

Doppler

Valve disease

Current echocardiographic machines are portable and can be wheeled directly to the patient's bedside. Thus, a major

advantage of echocardiography over other imaging modalities is the ability to obtain instantaneous images of the cardia structures for immediate interpretation. Handheld echocardiographic units weighing 6 lb (<2.7 kg) have now become available, further enhancing the ease and portability of echocardiography. They are becoming an essential initial diagno modality for the critically ill patient in the emergency room and critical care setting.

A limitation of TTE is the inability to obtain high-quality images in all patients, especially those with a thick chest wall o severe lung disease, as ultrasound waves are poorly transmitted through lung parenchyma. New technology such as harmonic imaging and IV contrast agents (which traverse the pulmonary circulation) can now be used to enhance
endocardial borders in patients with poor acoustic windows.

CHAMBER SIZE AND FUNCTION

2D echocardiography is an ideal imaging modality for assessing left ventricular (LV) size and function (Fig. 1

qualitative assessment of the cavity sizes of the ventricles and systolic function can be made directly from the 2D imag experienced observers. 2D echocardiography is useful in the diagnosis of LV hypertrophy and is the imaging modality o choice for the diagnosis of hypertrophic cardiomyopathy. Other chamber sizes are assessed by visual analysis, including left atrium and right-sided chambers.

Figure 1

Two-dimensional echocardiographic still-frame images from a normal patient with a normal heart. Top: Parasternal l axis view during systole and diastole (left) and systole (right). During systole, there is thickening of the myocardium and reducti the size of the left ventricle (LV). The valve leaflets are thin and open widely. Bottom: Parasternal short axis view during diastol (left) and systole (right) demonstrating a decrease in the left ventricular cavity size during systole as well as an increase in wall thickening. LA, left atrium; RV, right ventricle; Ao, aorta.