ULTRASONIC EXAMINATION Ultrasonic examination is a very method in the clinical diagnosis of diseases. Recently, Ultrasound, isotopic scanner, and X-ray (including computerized tomography) comprise the three important imaging diagnostic techniques in modern medicine. Ultrasound has many advantages, it is a non-invasive diagnostic technique which can be used in the detection of many human organs, operated easily, not dangerous and not harmful to the patients. It can be repeated many times in the short period, and obtain the results very soon. Moreover, it is the most cheap among the three techniques. Section Ⅰ.Basic physics of ultrasound The nature of sound waves

1. Basic conceptionSound is a mechanical vibration that is propagated through matter which is also

called medium. It cannot travel through a vacuum. Sound waves are produced by vibrating sources that are calls “sound source”. One of the simplest example of the sources is a tuning fork vibrating in the air. The ultrasound is one kind of the sound.2. The formula about the sound

There are three elementary parameters about the sound:Velocity(C) frequency (f), and wavelength( ).These three parameters of sound are related in the following equation:C=f*For and given material, the velocity of sound is constant. Therefore, if the

frequency is increased, the wavelength must decrease proportionally.3. Types of waves

1) Longitudinal wave. It is the predominant type in the human body.2) Transverse wave. Only solid can support transverse wave. With the

exception of compact bone, the longitudinal waves are the only type observe within the body.

4. Sound velocityTable 1. acoustic velocity in various tissues

Tissues of material Acoustic velocity(m/sec)Air 331Fat 1450

Water 1495Soft tissue (mean value) 1540

Kidney 1561Muscle 1585Bone 4085

The average sound velocity for soft tissues is 1540 meters per second, and this value is uses in the calibration of clinical ultrasonic instruments.

5. Wavelength The wavelength of a sound eave is the distance from one wave peak to the successive peak. Wavelength ranging from 0.1 to 1.5mm is utilized in medical applications. The wavelength is important because it determines the theoretical limit of resolution. Under on circumstances are structures that are closer together than one wavelength identifiable as two distinct entities.

6. Frequency The frequency of a sound wave is defined as the number of the associated pressure wave that pass a given point in one second. The unit of frequency is the hertz (Hz). One Hz means 1 cycle per second. One Kilohertz (KHz) equals 1000 Hz and 1 megahertz (MHz) equals 1,000,000Hz.

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Table 2. Categories of soundCategory Frequency range (Hz)

Ultrasound >20,000Audible sound 16-20,000

Infra-sound <16The human ear is sensitive to sonic frequencies from 20 to 20,000 Hz. This

provides a convenient classification of sound into three categories as listed in Table 2.Sound frequency employed in medical applications ranges from 1 to 15 MHz

and therefore they are in the ultrasonic range.The choice of frequency used in any medical application is a compromise

between resolving capability and penetration. The higher the frequency, the more rapidly sound is absorbed, and the smaller the distance it can penetrate into tissue. The lower the frequency, the poorer is the resolving capability.

II. Production of ultrasoundThe ultrasound comes from the probe, which is made of piezoelectric crystals.

The piezoelectric effect is the generation of an electric voltage when a crystal is compressed. The voltage generated is proportional to the amount of compressing. According to the principle of the reverse piezoelectric effect the crystal, which is in the high frequency alternative electric field, induces the successive composing and stretch in the certain direction, in other words, it induces the vibration. If the frequency of the alternative electric field is higher than 20,000 Hz the ultrasound is produced. Meanwhile, the crystal possesses also the direct piezoelectric effect. It is able to receive the echo signals and convert sonic energy into the electric signals, then through the detective instruments the echo signals are showed on the screen in different forms. That is called “ultrasonogram”.

III. The properties of the ultrasonic waves1.Directional property to the ultrasonic wavesThe directional property of ultrasound is related to the diameter of the crystal of the

probe and its vibrating frequency. It is according to the ratio of the probe diameter and the wavelength. While the probe diameter is more large than the wavelength, the ultrasonic waves, produce by the probe, possess the property that they are propagated through a special direction. We can use the ultrasound to correctly detect the certain tissue, organ, and lesion in the body, because the ultrasound has the perfect directional property. Sound beams are classified as divergent, sollimated or focused. At the near part to the soundsource (probe), which is called “near field”, the diameter of the sound beam is same, but through the narrowest part of the sound beam it becomes a divergent one that likes a circular cone. The latter part is called “far field”. In the near field besides the main lobe (main sound beam) there are some additional lobes in the different directions that are called side lobes. If the side lobes meet the reflecting interface the echoes are produced. These echoes are the “pseudo” echoes and they often induce the difficult problem to the diagnostic analysis. Ultrasound width different frequencies has different wavelength in the soft tissues.

Table 3. The wavelength in the soft tissuesFrequency (MHz) 1.00 2.25 2.50 3.50 5.00Wavelength (mm) 1.54 0.68 0.60 0.44 0.31

1.Reflection, refraction and scatterAcoustic impedance. The product of density of a material and the speed of sound in

that material is a quantity alwwed the characteristic acoustic impedance. The significance of this quantity is its role in determing the amplitude of reflected and transmitted ways at an interface.(see table 4). There is a fomula : Z=P*C Not Z is the

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impedance, P is the density of the medium and C is the speed of sound.Reflection.Whenever an ultrasound beam is incident on an interface formed by two materials

having different acousicic impedances, in general, some of the energy in the beam will be reflected and the remainder transmitted. The amplitude of the reflected wave depends on the difference between the acoustic impedances of the two materials forming the interface, and the intensity of the incident ultrasound. According to the Snell law, the reflecting direction to the Snell law, the reflecting direction of incident ultrasound from the interface is related to the incident angle. When the incident angle is 0 degree, the reflecting echoes return to the probe, and the ultrasonogram is showed on the screen. If the ultrasonic beams are not perpendicular to the interface, there are part or whole reflecting echoes that cannot reach to the probe. So the screen does not show the Table 4. The acoustic velocity and impedance of human normal organs.

Tissue or organ Velocity (m/sec) Impedance/square 5 (cmec*10)Fat 1,450 1.38

Soft tissue (mean) 1,540 1.63Liver 1,549 1.65

Kidney 1,561 1.62Spleen 1,566 1.63Blood 1,570 1.61Muscle 1,585 1.70Bone 4,080 7.80Air 331 0.0004

Water 1,498 1.48Sonogram. When the interface is not smooth or its diameter is less than the diameter of ultrasonic beam, the incident ultrasound ontl induce the nonspecular reflection or scatter. These echo signals are difficult to be received by probe. The acoustic impedance of the air is biggest and its reflecting coefficient is 1. When the ultrasound propagates from air to another medium, it will induce “whole reflection” that is the ultrasound cannot transmit the air.

3.Absorption and attenuation Absorption is the transfer of energy from the sound beam to the tissue. It is proportional to frequency. In addition to frequency, the amount of absorption depends on the viscosity of the tissue through which the sound travels. In general, the more rigid the tissue, the greater the absorption.

Attenuation. The intensity a sound beam constantly decreases as it travels through tissue. This decrease in intensity is called attenuation. It is due to three factors: (a) divergence of the sound beam, (b )absrption of sound energy by the tissue, and (c) reflection of sound out of the beam.

4.Resolution and penetrabilityResolution is the ability ultrasound can distinct and show two different interfaces

which intervals the least. There are two kinds of resolution: longitudinal and transverse resolution. The higher the frequency, the better the resolution, but the less the penetrability.

5. Doppler effectDr any sound beam, whenever there is relative motion between the source and the

listener, the frequency heard by the listener will differ from that produced by the source. The perceived frequency will be either greater or less than that transmitted by the source depending on whether the source and the listener are moving toward or away from one another. Such a shift in the perceived frece ency relative to the transmitted frequency is called a Doppler shift. A Doppler frequency shift can occur

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for a moving source and ctatinary listener., a moving listener and stationary source, or a moving source and listener. The ultrasound Doppler effect is employed in detection of the heart and its movement of the valves, fetal heart sound, fetal movement and blood flow.

Ⅳ.The principles of ultrasonic diagnosis1.Measurement of the echo distance2.Identification of property of the tissue, organ and lesions.Solid organ: homogeneous or non-honogeneousLiquid organ: sonolucent, liquid dark areaHollow organ with gas: full reflectionAcoustic shadowConstrast echogram3.Absorption by the tissue and attenuation4.Dynamic and functional examination of the organsSection Ⅱ. Mode and properties of ultrasonic DiagnosisA-mode:echogramIt is mostly used to measure the distance, e.g. the brain midline.B-mode: sonogram or echotomogramBright spot imaging,Static B-mode imaging,Real time B-mode imaging,Gray scale display,Across sectional echocardiography or two dimentional echocardiographyM-mode: echocardiogramTime-space curveIt is uses to observe time change of the movable interface.D-mode: Doppler effectSection Ⅲ. Clinical Application of Ultrasonic ExaminationⅠ. Brain Midline echoⅡ. Obstetrics and gynecology1.Uterus. Normal and myoma.

2.Pregnancy.3.Hydatideform mole.Ⅲ. Abdominal mass1. PropertiesTable 5. Mass lesions: +sonograghic characterization

Cystic Complex SclidFeatures

Internal echoes No Yes YesWall sharpness Yes Yes Yes

Beam attenuation No No YesTypical causes Symple Infected Solid

cyst cyst tumorAbscesstumor

2.Site (Location)3.Benigh or malignantⅣ.Hydrops in the body cavity1.Hodrothorax2.Ascites3.Hydropericardium

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Ⅴ. Liver and spleen1.Normal liver and spleen2.Measurement of liver and spleen and normal values.Liver: left libe, the up-down length is 4-8cm;The oblique thickness of right lobe is less than 14.6cm.Spleen: the thickness at the hilus of spleen is 1.7-3.6cm.Portal vein: diameter of main PV is less than 1.6cm.3.Liver cancerA. High reflecting type, local giant bright lump, non-homogeneous distribution, “bull’s eye sign”B. Lower reflecting typeC. Mixed reflecting typeD. Enlargement of liver with irregular contour; other signs: necrosis and liquefaction, cancer embolus4.Liver abscess5.Liver cirrhosis Surface of liver uneven, intrahepatic echoes increase, non-homogeneous distribution, dilated portal and splenic veinsⅥ.Gallbladder1.sonolucent Iblong structureA-P diameter is 2-4cmLong diameter is 4-9cmThickness of GB wall is less than 3.5cm2.abnormal gallbladderacute cholecystitischronic chloecystitisgall stone: (a) stone reflection(b) shift with position changes(c) acoustic shadowgallbladder tumor3.Billiary system and its diseasesCommon bile duct, left and right hepatic ducts, intrahepatic bile ducts, stone in the CBD4.Differentiation of obtructice jaundice intrahepatic bile stasis,Obstruction of extrahepatic bile ductⅦ. Limitation1.Ultrasound is a non-specific method. On many conditions, it cannot give an etiologic diagnosis.2.Ultrasound beam cannot penetrate gas and bome. When the sound beam transverses tissue interface of widely different acoustic impedance most of the beam is reflected back and racorede as useless noise. At a bone-tissue boundary a 70% reflected occurs a gas-tissue interface reflects 99% of the beam. Thus, sonography through aerated lungs or the bony pelvis are not feasible to detected, and it has been estimated up 25% of abdominal examinations are unsatisfactory because of intestinal gas.3.It is difficult to the early diagnosis, if the lesion is less than 1-2cm or the impedance difference is too small.4.It is interfered by many factors, for instance, the type and property of the machine, the experience and skill of examiner, the condition of the patient. In addition, there may be some false positive or negative results.

Echocardiography

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The term echocardiography refers to a group of tests that utilize ultrasound to examine the heart and record information in the form of echoes. It is composed of M-mode echocardiography, two-dimensional echocardiography, Doppler echocardiography, Doppler color flow mapping, contrast echocardiography etc. Echocardiography can be used in the following respects: (1) to diagnose the valvular heart diseases. (2) to diagnose cardiac masses, vegetations, thrombosis and pericardial effusion. (3) to detect constrictive pericarditis, dilated and hypertrophic cardiomyopathy and coronary heart disease. (4) a useful method to differentiate most congenital heart diseases, such as atrial septal defect, ventricular septal defect, patent ductus arteriosus, tetralogy of Fallot, etc. (5) to follow up the functional status of prosthetic valves. (6) to measure the dimensions of cardiac chamber and detect ventricular performance. (7) to explain and differentiate the origin of abnormal heart sound and cardiac murmurs.

Examination Of The Normal Heart M-Mode Echocardiography An M-mode recording is sometimes called a one-dimensional or an “ice pick” view

of the heart. However, since time is the second dimension on M-mode tracings, this display is not truly one-dimensional. The M-mode presentation permits recording of amplitude and of the rate of motion of moving objects with great accuracy. The sampling rate is essentially 1000 pulses/sec. With the transducer placed along the left sternal border in approximately the third or fourth intercostal space, the ultrasonic beam can be swept in a sector between the apex and the base of the heart:

1.When the transducer is pointed toward the apex of the heart, the ultrasonic beam traverses the left ventricular cavity at the level of the papillary muscles and passes through a small portion of the right ventricular cavity (position 1).

2.Tilting the transducer superiorly and medially causes the ultrasonic beam to traverse the left ventricular cavity at the level of the chordae tendae(position 2a) or at the edges of the mitral valve leaflets (position 2b). The beam again passes through a small portion of the right ventricle. In this position the distance between the left side of the interventricular septum and the posterior left ventricular endocardium is largest, so the diastolic and systolic dimensions of the left ventricle can be measured in this position. Septal and posterior wall thickness can also be measured.

3.By directing the transducer more superiorly and medially, more of the anterior leaflet of the mitral valve can be recorded and the beam may traverse part of the left atrial cavity (position 3).

The curve of the anterior mitral valve leaflet can be traced in position 2b and position 3. At the onset of left ventricular diastole, the anterior mitral valve leaflet moves abruptly forward (toward the transducer) as the valve opens. The E point is the maximum opening of the very early diastole—rapid filling stage. At the end of this stage, the anterior mitral leaflet moves rapidly backward to a semiclosed position to form the descending part of the E wave. The later diastolic phase is related to atrial systole, which produces a rapid forward motion of the anterior leaflet as the valve is reopened at the A point. Following atrial systole, the mitral valve begins to close before ventricular systole. The point of complete mitral valve closure is the C point. The D point is the end systolic point. It is common to see segment CD gradually move forward during the whole systolic stage. The characteristic M-shaped configuration of the anterior mitral leaflet is made by the large E point and the relatively smaller A point. The echogram of the posterior mitral leaflet is the approximate mirror image of

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anterior leaflet and has a W-shaped configuration.4.Further tilting of the transducer superiorly and medially directs the beam through

the root of the aorta, the leaflets of the aortic valve, and the body of the left atrium(position 4). The curve of the aortic root can be traced in this position: The anterior and posterior aortic walls are seen moving synchronously with each heart beat in two parallel echoes. Both wall of the aorta move forward during systole and backward during diastole. The aortic valve leaflets are recognized by a thin echogram midway between the two parallel aortic walls during diastole and by their abrupt opening motion at the onset of ventricular ejection. Normally, the two commonly visualized cusps (right coronary cusp and non-coronary cusp) open to the periphery in systole, producing a boxlike pattern with opening and closing of the valve leaflets during each cardiac cycle. Left atrial measurements are also commonly made in this position.

Two-Dimensional Echocardiography The ultrasonic beam now moves in a sector so that a pie-shaped slice of the heart is

interrogated. Most commercial 2-D echocardiographs move the ultrasonic beam so that approximately 30 slices/sec are obtained. The ultrasonic beam can be moved mechanically by oscillating a single transducer or by rotating a series of transducers. The ultrasound can also be steered electronically using the so-called phased array principles. An infinite number of slices of the heart can theoretically be obtained using 2-D echocardiography. Three standard planes are the long-axis, short-axis, and four-chamber views.

1.The long-axis plane is the imaging plane that transects the heart perpendicular to the dorsal and ventral surfaces of the body and parallel to the long axis of the heart. The parasternal long axis view can be obtained with the transducer in the third or fourth intercostal space adjacent to the left sternal border. The leaflets of mitral valve can be seen to open in their full excursion during diastole. The left atrium is posterior to the posterior wall of the aorta. The cusps of the aortic valve can be seen to co apt in a single line during diastole. The right ventricular outflow tract is anterior to the aorta. The left ventricular cavity is seen in its long axis. The interventricular septum and right ventricle are located anteriorly, and the left ventricular posterior wall and posterior papillary muscle are located posteriorly. The apex of the left ventricle is identified as the round tip at the left of the image, but it may not be easily visualized in this view. This picture is the most fundamental view in 2D echocardiographic examination. 2.The plane transecting the heart perpendicular to the dorsal and ventral surfaces of the body, but perpendicular to the long axis of the heart, is defined as the short-axis plane. Such an examination can be obtained with the transducer in the parasternal position or in the subcostal (subxiphoid) position. Various short-axis examinations are commonly obtained at the level of the apex, the papillary muscles, the mitral valve, and the base of the heart. Short-axis views cut across the heart so that the left ventricle resembles a circle. The right ventricle can be seen curving around the left ventricle. The short-axis view at the base of the heart can examine aortic valve, the pulmonary valve, the atrial and the pulmonary artery with its bifurcation. It is also possible to record the origins of the coronary arteries and the left atrial appendage.

3.The plane that transects the heart approximately parallel to the dorsal and ventral surfaces of the body is referred to as the four-chamber plan. Such a view permits the examination of all four cardiac chambers simultaneously. This type of examination can be obtained with the transducer over the cardiac apex or with the transducer in the subcostal position. Doppler Echocardiography

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M-mode and 2-D echocardiography essentially create ultrasonic images of the heart. Doppler echocardiography utilizes ultrasound to record blood flow within the cardiovascular system. Doppler technique can also provide useful information concerning intracardiac pressure and pressure gradients across the stenotic orifice. The principle of the Doppler effect is represented by Doppler equations that relate Doppler frequency (fd) and the velocity of the moving target (v):

fd = 2f·v·cosθ/cfd is the Doppler shift or Doppler frequency represents the difference between the

reflected and transmitted frequencies. If the ultrasonic beam is reflected by a stationary object, the fd equals to zero. However, if the target reflecting the ultrasonic energy is moving toward the transducer, the reflected frequency is greater than the transmitted frequency, fd is positive. When the target is moving away from the transducer, the reflected frequency is less than the transmitted frequency, fd is negative. f is the transmitted frequency; θ is the angle between the paths of the ultrasonic beam and moving target; c is the velocity of sound in the medium being examined; in Doppler echocardiography the targets are the red blood cells. By this equation, one can calculate the velocity(v) of the moving target.

There are two kinds of Doppler waves: the continuous-wave Doppler and the pulsed Doppler. Significant differences exist between continuous wave and pulsed Doppler. The velocity that can be recorded using pulsed Doppler is limited. Thus, if the blood is moving very rapidly, as might occur when it is passing through a stenotic valve, continuous-wave Doppler is necessary for recording very high velocities. Although the pulsed Doppler can not be used to quantitate the high velocity, it is useful to locate the sampling volume where the stenosis occurs.

The Doppler recording is a spectral display using fast Fourier analysis of the audible Doppler signal. The recording is usually on strip chart paper or videotape and is commonly referred to as spectral Doppler. There are two kinds of flow pattern: The laminar flow is supposed to be normal blood flow, it has a totally different quality in spectrum than that which originates from stenotic orifice, named disturbed or turbulent flow.

Normal spectral Doppler recordings are basically of three types. There is the venous, ventricular inflow and ventricular outflow pattern of Doppler flow. Venous flow has both systolic and diastolic components. There will be some slight variation whether the recording is from systemic or pulmonary veins. Ventricular inflow is totally diastolic. There is an early component that peaks at the E wave and a late component following atrial contraction that peaks with an A wave. Ventricular outflow is entirely systolic in nature. The systolic flow moving away from the transducer during systole. Doppler flow patterns on the right side of the heart are essentially the same except the velocities are lower. The peak mitral velocity is about 100 cm/sec, and the aortic velocity is about 120 cm/sec. Color Doppler Doppler information from the cardiovascular system can also be recorded in a spatially correct format superimposed on an M-mode or 2-D echocardiogram. The direction of the blood is displayed in color. With this particular instrument blood moving toward the transducer is depicted in shades of yellow and red, whereas blood moving away from the transducer is in shades of blue. Turbulent flow can be displayed as green or as a mosaic of colors. Abnormal Echocardiogram Mitral Stenosis

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The detection of mitral stenosis (MS) was the first clinical application of echocardiography. It remains an important technique in the evaluation of suspected mitral valve disease because echocardiography can allow visualization of the mitral valve in a manner not possible with any other procedure. The M-mode examination provides a sensitive assessment of the motion and thickness of the valve leaflets, while the 2-D technique provides a spatial image of the valve and allows direct measurement of the valve orifice. Doppler echocardiography provides hemodynamic assessment of the stenotic orifice.

M-mode echocardiogram of a patient with calcific MS shows the motion of the mitral valve is considerably altered from the normal pattern. The normal M-shaped configuration during diastole is no longer present, since the presence of a holodiastolic atrioventricular pressure gradient (diastasis) prevents rapid closure of the valve in mid-diastole. Although sinus rhythm was present, there was no reopening of the valve with atrial contraction and no A wave. Thus, the M-mode echocardiographic hallmark of MS is the absence of valve closure in mid-diastole and of reopening in late diastole.

In addition to the change in motion of the valve, the number of echoes originating from the valve is increased when it is fibrotic or calcified, and another echocardiographic sign of MS is increased thickness of the valve leaflets. Inadequate separation of the anterior and posterior leaflets of the valve occurs during diastole. Normally the two leaflets move in opposite directions during diastole, but when fused, as in MS, they do not separate widely and may actually appear to move in the same direction. The M-mode findings of reduced diastolic slope, increased thickness, and decreased separation of the valve leaflets provide a sensitive and accurate method for detection of MS---Great Wall-like picture.

The diagnosis of MS by 2-D echocardiography is made by noting thickening, doming, and restricted motion of the leaflets. In long-axis view, doming of any valve on 2-D echocardiography is a characteristic sign of stenosis. This distortion in shape indicates that the tips of the leaflets are restricted in their ability to open, whereas the bodies of the leaflets still wish to accommodate more blood flow; thus the leaflets are curved, or domed. The presence of doming distinguishes a valve that is truly stenotic from one that opens poorly because of low flow. Two-dimensional echocardiography in short-axis view provides an opportunity to measure the flow-restricting orifice of the stenotic mitral valve directly, which assumes the shape of a funnel.

Two-dimensional echocardiography is also the procedure of choice for assessing the fibrosis, the degree of calcification and pliability of the mitral valve apparatus, especially when subvalvular adhesions are present.

Doppler echocardiography provides another means of quantitating the degree of MS. Pulsed Doppler recording of a patient with MS and atrial fibrillation demonstrates there is no A wave. The peak velocities are increased, and the fall in velocity in early diastole is decreased. The technique for quantitating the degree of MS depends on the rate of velocity decrease in early diastole. The time interval required for the peak velocity to reach half of its initial level is related directly to the severity of the obstruction of the mitral orifice. This pressure half-time correlates reasonably well with the mitral valve area.

Secondary effects of mitral stenosis, such as left atrial, right ventricular dilatation and pulmonary hypertension, can be detected with various echocardiographic examinations. Mitral Valve Prolapse With Mitral Regurgitation

Echocardiography is particularly useful in the diagnosis of this condition. The principal M-mode finding is a fairly abrupt posterior (downward) motion of the mitral

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valve apparatus in mid or late systole. This motion often commences simultaneously with the mid or late systolic click, a typical auscultatory and phonocardiographic finding in this condition.

Several findings on 2-D echocardiography have been suggested for the diagnosis of mitral valve prolapse, including the recording of buckling or herniating of one or both mitral leaflets into the left atrium during systole.

Other echocardiographic findings in patients with mitral valve prolapse include excessive amplitude of motion of the valve during diastole that can be appreciated in both M-mode and 2-D examinations. Thickening of the leaflets is common and is presumably due to myxomatous degeneration. The leaflets may also be redundant and seem to fold on themselves in diastole. Doppler echocardiography is the specific procedure of choice for detection of mitral regurgitation in mitral prolapse patient. Pulsed Doppler echocardiography can detect mitral regurgitation spectrum in systole that is high velocity and marked broadening. Color flow Doppler can detect the regurgitant blood flows into the left atrium during ventricular systole. The velocity is very high, and a mosaic multicolored pattern is recorded because of aliasing. Echocardiography is also helpful in assessing the hemodynamic consequences of the MR. The left atrium is invariably dilated, and left ventricular stroke volume increases with frequent left ventricular dilatation.

Aortic Stenosis

M-mode and 2-D echocardiography have always provided an excellent qualitative diagnosis of AS. Doppler echocardiography now provides an opportunity for the quantitative diagnosis. The M-mode echocardiographic diagnosis of a stenotic aortic valve include thickening of the valve leaflets as demonstrated by multiple echoes coming from the leaflets. If one measured the distance between the leaflets, it would be below normal, which is approximately 1.5 to 2.5cm in adults. The 2-D echocardiographic diagnosis of valvular aortic stenosis is doming, thickening, and restricted motion of the leaflets. The valve may be heavily calcified and immobile.

The best ultrasonic technique for quantifying AS utilizes continuous-wave Doppler. Using the modified Bernoulli equation, it is possible to measure the pressure gradient across the aortic valve. The higher the pressure gradient, the more severe the stenosis.

There are secondary signs of AS that can be noted on the echocardiogram. Both M-mode and 2-D echocardiography can detect left ventricular hypertrophy with increased thickness of the left ventricular walls.

Left Aatrial Myxoma Left atrial myxoma is by far the most common cardiac tumor, and echocardiography has proved to be an extremely important diagnostic technique for its recognition. M-mode echocardiography was the first technique utilized to detect left atrial myxomas. One sees a cloud of tumor echoes behind the anterior leaflet of the mitral valve, the echo-producing mass almost completely fills the mitral valve throughout diastole. Directing the ultrasonic beam into the left atrium, one can follow the echo-producing mass into the left atrium and see how it practically fills the entire left atrial cavity. The spatial 2D examination provides additional useful information, and the size and shape of the mass are apparent. In addition, the site of attachment of the mass to the cardiac structure can frequently be detected.

Pericardial EffusionSince the acoustic properties of fluid differ significantly from those of cardiac

muscle, the effusion surrounding the heart is less echogenic than is the myocardium.

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Accordingly, the detection of effusion was one of the first and has remained one of the most useful applications of echocardiography.

The size of the effusion is estimated by the amount of echo-free space surrounding the heart. Frequently with small effusions one sees only a posterior echo-free space and very little fluid anteriorly. As the fluid increases it distributes both anteriorly and posteriorly. With large effusions, one usually sees more anterior fluid than posterior fluid as the heart tends to sink posteriorly.

There are several echocardiographic signs for cardiac tamponade. One of the most frequent findings is collapse of the anterior right ventricular free wall. Right atrial collapse is slightly more sensitive but less specific than right ventricular collapse.

With very large effusions one can detect excessive motion of the heart within the pericardial sac. This excessive motion has been noted as a “swinging heart.” If the motion is such that the heart does not resume its original position before the next electric depolarization occurs, then the axis of the QRS is altered and one notes electrical alternans on the electrocardiogram.

CARDIOMYOPATHIES

Hypertrophic Cardiomyopathy(HCM) Echocardiography is an important diagnostic tool in patients with HCM. An early

echocardiographic abnormality to be noted was systolic anterior motion of the mitral valve (termed SAM), which appeared to be related to and was correlated with the presence of obstruction to left ventricular outflow. The shorter the distance between the septum and the leaflet and the longer the duration of apposition between these two structures, the more severe the obstruction.

A second echocardiographic finding in patients with obstructive HCM is midsystolic closure of the aortic valve. However, as noted earlier, this sign is not specific for HCM and is also present in patients with discrete subaortic stenosis.

The basic abnormalities of HCM, and a key echocardiographic finding is disproportionate hypertrophy of the septum in relation to the posterior wall of the left ventricle, so that the ratio of thickness of the septum to the free wall exceeds 1.3:1.0 and the motion of the hypertrophied septum is reduced. There are patients with asymmetrical septal hypertrophy who do not show SAM and therefore do not have obstruction to left ventricular outflow. These patients may be considered to have HCM without obstruction.

Two-dimensional echocardiography provides additional information by indicating the shape and location of the hypertrophied myocardium in patients with known or suspected HCM. Some patients have hypertrophied septum limited to the basal two-thirds of the septum, while the apex is virtually free of muscular hypertrophy. Other patients exhibit an apical form of hypertrophy with the proximal septum being relatively thin. Concentric hypertrophy is also a fairly common form of hypertrophic myopathy. Cavity obliteration with ventricular systole is almost always present with this type of disease. An intriguing observation is that the echoes from the diseased septum in HCM are more reflective or “speckled”than those from the free posterior wall.

Doppler echocardiography may also be helpful in evaluating hypertrophic cardiomyopathy. The Doppler recording of the left ventricular outflow may show an abnormal pattern with the abnormally high velocity occurring in late systole. The systolic gradient can be estimated using the Doppler technique. The left ventricular hypertrophy and reduced left ventricular compliance alter the Doppler recording of mitral valve flow. The early diastolic velocity or E point is reduced, and the late

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velocity with atrial systole is increased. Color Doppler provides spatial visualization of the altered blood flow in patients with obstructive HCM. Congestive (Dilated) Cardiomyopathy The echocardiogram characteristically reveals a dilated poorly contracting left ventricle in patients with congestive cardiomyopathy. Signs of reduced cardiac output include a poorly moving aorta, slow closure of the aortic valve, and reduced opening of the mitral valve. In M-mode tracing, the size of the opening of the mitral valve is so small compared to dilated left ventricle that it is like the shape of a “diamond”. The left atrium is dilated, and the abnormal closure of the mitral valve indicative of elevated left diastolic pressure is frequently noted. Incomplete closure of the mitral valve or papillary muscle dysfunction and subsequent mitral regurgitation are common. Left ventricular filling on Doppler echograms changes as the disease progresses.

CONGENITAL HEART DISEASE

Atrial Septal DefectEchocardiography is an accurate means of detecting atrial septal defects of all

types. Atrial septal defects are classified according to the involved region of the atrial septum. The most common type is the secundum defect, comprises approximately 70% of atrial septal defects. Abort 15% of atrial septal defects are of the ostium primum type, and 15% are of the sinus venosus type.

The M-mode echocardiographic abnormality associated with an atrial septal defect is that of a right ventricular volume overload. The two components of this echocardiographic finding are a dilated right ventricle and abnormal septal motion.

The 2-D echocardiographic examination, especially from the subcostal position, provides an opportunity for direct examination of the interarterial septum. In a patient with an ostium secundum atrial septal defect, a remnant of the interatrial septum can be seen attached to the ventricular septum. In contrast, in a patient with an ostium primum defect, there is no residual septum attached to the ventricular septum. Thus, the 2-D technique not only helps to identify the presence of an atrial septal defect, but it is also an excellent means of differentiating a secundum from a primum type of abnormality.

Color flow Doppler can be used to demonstrate atrial septal defects. One can see the red-encoded blood passing from the left atrium to the right atrium through the defect. Pulsed Doppler can detect diastolic turbulent flow with upward spectrum.

Tetralogy of Fallot The Tetralogy of Fallot consists of a combination of a perimembranous ventricular septal defect, overriding of the aorta over the ventricular septal defect, pulmonic stenosis and right ventricular hypertrophy/dilation. The M-mode detects the discontinuity of the anterior aortic root and ventricular septum. The narrowed right ventricular outflow tract can also be detected with M-mode echocardiography. Because of right ventricular overload, the septal motion was abnormal. Two-dimensional echocardiography allows direct visualization of the intracardiac anatomy and documentation of the presence of a perimembranous ventricular septal defect and degree of aortic overriding. Additionally the degree of narrowing of the right ventricular outflow tract can be determined accurately. Doppler echocardiography can detect turbulent flows at the sites of the ventricular septal defect and pulmonic stenosis.

Infective EndocarditisEchocardiography provides a means for visualizing the vegetations of infective

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valvular endocarditis, which appear as echo-producing masses attached to the infected valve. They are usually asymmetrical, commonly involving one leaflet more than another, but may be present on more than one valve. If the vegetation is associated with destruction of the valve or if it is on a long “stalk,”it can be readily imaged; its excessive motion can be appreciated on both M-mode and 2-D echocardiography. Transesophageal echocardiography is proving to be much more sensitive than transthoracic echocardiography in detecting valvular vegetations.

One of the major applications of echocardiography in patients with endocarditis is in the identification of complications. When the valve is damaged to the point that it is grossly incompetent, echocardiography can both detect and assess the hemodynamic importance of the valvular regurgitation.

Special Echocardiography

Transesophageal Echocardiography

Transesophageal echocardiography has been available for many years. With the technical advances in placing a 2-D transducer at the end of a flexible endoscope, it is now possible to obtain high-quality 2-D images via the esophagus in multiple planes

Transesophageal echocardiography is useful in patients in whom the examination from the usual transthoracic approach is technically difficult or impossible. This approach is particularly helpful in assessing prosthetic valves, vegetations, aortic disease, and intracardiac masses. Another major application for esophageal echocardiography is in the patient undergoing surgery. The esophageal ultrasonic probe can be used to monitor cardiac left ventricular function throughout the surgical procedure and into the postoperative state. Transesophageal echocardiography is being used in the operating room during open-heart surgery and to monitor myocardial ischemia during noncardiac surgery. Cardiac surgeons are finding echocardiography helpful in assessing cardiac morphology and function before, during, and after surgical repair of valvular or congenital conditions.

Intravascular Ultrasound The ultrasonic transducer can be placed in a small catheter so that a vessel can be

imaged via the lumen to provide an intravascular echocardiogram, a technique known as intravascular ultrasound. Several intravascular ultrasonic devices are currently being used. The techniques utilize a rotating transducer, rotating ultrasonic mirror, or phased array multielement systems. These devices are generating considerable interest, especially for the ability to evaluate atherosclerosis from within the arteries. Slightly larger intravascular ultrasonic devices are being used to visualize the heart from within the cardiac chambers. Contrast Echocardiography Ultrasound is an extremely sensitive detector of intravascular bubbles. The injection of almost any liquid into the intravascular spaces will introduce many microbubbles that appear as a cloud of echoes on the echocardiogram. Contrast echocardiography is a very sensitive technique for detecting right-to-left shunts. The contrast agents that have been used include the patient’s blood, saline, indocyanine green dye, agitated or sonicated angiographic contrast agents, and sonicated albumen. In all cases the contrast effect originates from suspended microbubbles in the fluid. Commercially manufactured microbubbles that traverse the pulmonary capillaries are now available. The potential clinical uses for contrast echocardiography are numerous.

Three-dimensional Echocardiography

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A variety of approaches to recording echocardiograms that are oriented in three-dimensional (3-D) space have been proposed. One technique orients a 2-D transducer in 3-D space using spark gap sensors. Most investigators are creating 3-D images of the heart using gated, reconstructed 2-D examinations.

Stress EchocardiographyAlthough echocardiography has been used primarily for evaluating the cardiac chambers at rest, there is increasing interest in performing the ultrasonic examination during or immediately after some form of stress. These studies have utilized supineor upright bicycle exercise, immediate post-treadmill exercise, pharmacological stress, and atrial pacing. This type of examination is being done primarily for detecting exercise-induced regional wall motion abnormalities in patients with coronary artery disease. Exercise studies using Doppler measurements during exercise have also been used to assess global changes in left ventricular function and hemodynamics in patients with valvular heart disease or congenital heart disease.

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