Post on 07-Apr-2018
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 1/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 1
1How to Obtain a Good
Echocardiography
Examination: UltrasoundPhysics, Technique,
and Medical Knowledge
The burgeoning technologic revolution of the past two
decades hasproduced a continuousevolutionin thedefini-
tion of a complete and comprehensive echocardiographic
evaluation (Fig. 1-1). Echocardiography is now a fully FIG1.1
grown tree. It has numerous clinical applications, with var-
iousforms of ultrasoundtechnologybeing usedthroughout
the entire field of cardiovascular medicine. This mature ul-
trasound tree has grown from a seed planted more than
50 years ago. Since then, the tree has been trimmed and
nourished carefully by many pioneers to serve the needs of
patients and clinicians.
In 1954, Edler and Hertz (1) of Sweden were the first
to record movements of cardiac structures, in particular,
the mitral valve, with ultrasound. In the early 1960s in
the United States, Joyner and Reid (2) at the University of
Pennsylvania were the first to use ultrasound to examine
the heart. Shortly afterward, in 1965, Feigenbaum and
colleagues (3) at Indiana University reported the first
detection of pericardial effusion with ultrasound and
were responsible for introducing echocardiography into
the clinical practice of cardiology. However, M-mode
echocardiography produced only an ‘‘ice pick’’ view of the
heart;two-dimensional (2D) sector scanning, developed in
the mid-1970s, allowed real-time tomographic images of
cardiacmorphologyand function(4). Thefirstphased array
2Dsector scan atMayo Clinicwasmade onMarch17, 1977.
Although the development of Doppler echocardiography
paralleled that of M-mode and 2D echocardiography from
the early 1950s, it was not used clinically until the late
1970s. Pressure gradients across a fixed orifice could
be obtained reliably with blood-flow velocities recorded
by Doppler echocardiography. Two groups, Holen and
colleagues (5) and Hatle and colleagues (6), should be
credited for introducing Doppler echocardiography into
clinical practice.
Numerous validation studies subsequently confirmed
the accuracy of Doppler echocardiography in the assess-
mentof cardiac pressures.Therefore, theDoppler technique
made echocardiography not only an imaging but also a
hemodynamictechnique. On thebasisof theDoppler con-
cept,colorflowimaging wasdeveloped inthe early1980sso
that blood flow could also be visualized noninvasively (7).
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 2/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 2
2 Chapter 1
Figure 1-1 Echocardiography has become a mature tree thathas numerous branches and is still growing. CFI, color flowimaging; ICUS , intracardiac ultrasonography; I-Op, intraoperativeechocardiography, IVUS , intravascular ultrasonography;TEE , trans-esophagealechocardiography;3D/4D, three- and four-dimensionalechocardiography.
Another ingenious modification of Doppler echocardio-
graphy was tissue Doppler imaging (TDI), which allows
echocardiographers to record myocardial tissue velocity
and to measure the extent of myocardial deformation as
strain(8,9). Thesemeasurements providea sensitive assess-
ment of systolic and diastolic function and are becoming a
standard componentof a comprehensive echocardiography
examination. Widespread clinical use of transesophageal
echocardiography (TEE) began in 1987 (10), and the
subsequent development of intravascular and intracardiac high-frequency transducers has permitted extraordinarily
detailed imaging and hemodynamic assessment of the car-
diovascular system. Most recently, three-dimensional (3D)
echocardiography has become a reality. It provides a more
realistic depiction of cardiovascular structures and more
accurate volumetric quantitation (11,12).
With these technologic advances, the application of
echocardiography has been spreading into numerous clin-
ical areas, including the evaluation of diastolic function,
stress echocardiography, intraoperative echocardiography,
fetal echocardiography, contrast echocardiography, intrac-
ardiac imaging, and vascular imaging. The size of the
ultrasound unit is becoming smaller, and some units
can be hand-carried to the patient’s bedside (13,14). We
are fortunate to have this versatile diagnostic modality to
provide reliable structural, functional, and hemodynamic
information about the cardiovascular system of our pa-tients.
ULTRASOUND AND TRANSDUCER
Echocardiography uses ultrasound to create real-time
images of the cardiovascular system in action. Ultrasound
represents sound waves with a frequency of 20,000 Hz or
A Time
Period
Figure 1-2 Diagram of a sound wave. A, amplitude.
more. All sound waves (Fig. 1-2) are characterized by the FIG1.2
following seven variables (15): frequency ( f ), wavelength
(λ), period (p), speed (s), amplitude (A), power, and
intensity.
f = the number of cycles per second; 1 cps is 1 Hz.
λ = the length of one complete cycle of the sound; its
usual unit of measure is millimeters (mm).
s = the speed or velocity of sound waves through a
medium is equal to the product of f and λ (s = f • λ)
and is determined by the characteristics of the
medium. Speed is not affected by the frequency of
sound. The average speed of sound in soft tissue is
1,540 m/s.
p = the time duration of 1 cycle; hence, 1 s/ f = p or
f • p = 1.
A = the magnitude of a sound wave, the maximum
change from the baseline.
Power is the rate at which energy is transferred from a
sound beam, in watts (W), and is proportional to the
amplitude squared (15).
Intensityis theconcentration of energyin a sound beam
and equals power divided by its cross-sectional area.
Sound waves canbe combined to createone wave. Thus,twoin-phase (orsuperimposed) waves createa wavewith a
larger amplitude, and two out-of-phase (or mirror-image)
waves create a wave with a smaller amplitude or the two
waves cancel each other if they have the same amplitude.
This phenomenon is called interference (15). It is used
in pulse-inversion and pulse-modulation techniques for
harmonic imaging and contrast echocardiography.
At the start of an echocardiography examination, the
appropriate transducer is selected according to the type of
examinationand patient’s bodyhabitus. A higherfrequency
transducerprovidesbetter resolution, butit hasa shallower
depth of penetration. For the pediatric population, the
transducer frequency is usually 5 to 7.5 MHz (1 MHz =
1million cps), but for adults the transducer frequency at
the start of an examination is usually 2 to 2.5 MHz and
occasionally 5 MHz for patients with a thin chest wall.
The transducer consists of piezoelectric elements that convert electrical energy to ultrasound and vice versa.
Electrical energy is applied to the transducer in pulses
with a defined pulse repetition frequency (PRF in kilohertz
[kHz]), producing ultrasound waves at defined, regular
intervals of pulsed repetition period. The wavelength of
the ultrasound generated is related to the thickness of
the piezoelectric elements. The thinner the elements, the
shorter the wavelength. Because the product of wavelength
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 3/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 3
How to Obtain a Good Echocardiography Examination: Ultrasound Physics, Technique, and Medical Knowledge 3
(λ) and sound frequency ( f ) is the speed of the sound in
the tissue (λ • f = 1, 540 m/s), sound frequency is related
inversely to the thickness of the piezoelectric elements.
These transducer elements need to move to generate
multidirectional ultrasound beams. This movement can
be achieved mechanically or electronically. Although a
mechanical transducer can produce multiple imaging lines
from a small transducerarea,the ultrasoundbeam diverges
more the deeper it penetrates tissue. In an electronic
transducer, multiple piezoelectric elements are arranged
in a straight line and sound beams are steered and
focused electronically. Most of the current ultrasound units
have electronic steering, with phased stimulation of the
piezoelectric elements. Because image resolution is better with shorter wavelengths, a higher frequency transducer
produces an image with better resolution but shallower
penetration. Technology has advanced to the point that a
transducer contains 3,000 piezoelectric elements to create
a matrix transducer, which allows real-time 3D imaging.
In fundamental imaging, echocardiographic images are
created when the transducer receives reflected beams of the
same frequency as the transmitted beam, but the interface
between tissue and blood can be delineated better with
the reception of harmonic frequencies. Harmonic imaging
has developed directly from arduous attempts to improve
the ultrasound imaging of contrast microbubbles. When
contrast microbubbles are imaged, the bubbles resonate
and produce harmonic frequencies(i.e.,equivalent to mul-
tiple of thetransmittedfrequency).When theonly reflected
frequency received to create the ultrasound image is equal
to a multiple (2 f , 3 f , . . .) of the transmitted frequency,
images of contrast microbubbles are preferentially pro-duced (contrast harmonic imaging). Like microbubbles,
myocardial tissues are able to generate harmonic frequen-
cies, and harmonic imaging improves the delineation of
the endocardial border (tissue harmonic imaging). As a
result, harmonic imaging is usually the imaging modality
of choice not only for contrast echocardiography but also
for a standard echocardiography examination. Additional
modificationsof harmonic imaginginclude pulseinversion
and power modulation imaging, which improved resolu-
tion in contrast imaging.A limitation of harmonic imaging
in routine 2D echocardiography is the increased sparkling
qualityto theultrasound image andthe increasedthickness
of the endocardial border. If the image quality is not opti-
mal in spite of all measures, including harmonic imaging,
then a contrast agent should be injected intravenously to
improve the definition of the endocardial border. Because
intravenous accessis required,a qualified memberof an in-travenous team should be available to start an intravenous
line as soon as contrast echocardiography is needed.
SCREEN DISPLAY AND KNOB SETTINGS
How best to display echocardiographic images on the
screen is a personal choice and should be choreographed
Figure 1-3 Still frame of a typical echocardiography monitorscreen. It is essential for the screen to display the patient’sidentification, blood pressure (BP ), and cardiac rhythm. The typeof transducer, field depth, color map, and other machine settingsare also displayed. In the example here, the BP was 120/52 mmHg, with a wide pulse pressure. Aortic valve shows doming (arrow )during systole (a break in the ECG at the bottom indicates thetiming of the image on the screen), with moderately severe aorticregurgitation that explains the wide pulse pressure. ‘‘H3.5 MHz’’indicates harmonic imaging with a 3.5-MHz transducer. Field depthis 160 mm (this information is important in stress echocardiographyand other quantitative studies for which the same depth isdesired for all images). ‘‘MI’’ indicates mechanical index, whichis an essential function in contrast echocardiography. ‘‘Store inprogress’’ indicates that the echocardiographic images are storeddigitally while the phrase is shown on the screen; thus, desiredimages need to be maintained during this period. HR , heart rate.
according to the clinical objectives of the examiner.
The following should be shown on the screen: the
patient’s identification, blood pressure at the time of theexamination, and a sharp electrocardiographic tracing with
prominent R and A waves (Fig. 1-3 and 1-4). Depth, size,
FIG1.3
FIG1.4
and gain settings of the ultrasound images need to be
adjusted frequently during the examination. To develop
an initial impression of the overall cardiac structure and
Figure 1-4 Initial parasternal long-axis view with an imagingdepth of 24 cm (240 mm on screen) demonstrating a large pleuraleffusion (PL) andpericardialeffusion(PE ). Lesionsin thedescendingaorta (*) can also be appreciated with a long imaging depth. LA,left atrium; LV , left ventricle; RV , right ventricle.
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 4/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 4
4 Chapter 1
function, theexaminationof an adultpatient usuallybegins
with a depth of 20 to 25cm and a widesector (90 degrees).
This also gives an idea about any unusual extracardiac
structures (Fig. 1-4). After the initial view, adjust the field
depth to use the entire screen to demonstrate the intended
cardiovascular images. A zoom or regional expansion
selection (RES) function should be used frequently to
visualize a region of interest in more detail. The zoomed
image is also betterfor making quantitative measurements,
with less intraobserver and interobserver variability. When
quantitative measurements are made, review the acquired
image in a cine loop format to identify a frame at a specific
timing of a cardiaccycle. Examples area mid-systolicframe
to measurethe diameter of theleftventricularoutflowtract,an end-systolic frame to measure the size of the left atrium,
and an end-diastolic frame to measure thewall thickness of
theleftventricle. Afteran overview,specificareasneedto be
imaged and it may be necessary to decrease the sector size,
which will improve temporal resolution by increasing the
frame rate. The gain of the image is controlled by overall
gainand regional gain(by time gaincompensation [TGC]).
As sound waves travel through a medium (e.g., tissue
or blood), the intensity weakens or attenuates. The degree
of attenuation is expressed in decibels (dB). Absorption
represents a conversion of sound energy to anotherform of
energy and is the major reason for attenuation. Therefore,
attenuation is determined by ultrasound frequency and
tissue depth. Attenuation is also greater for high-frequency
sounds, which result in higher absorption and more
scatter. Total attenuation is calculated by multiplying the
attenuation coefficient by the length of imaged tissue. TGC
allows amplification of ultrasound beams from deeper depths because different amplitudes of ultrasound signals
are produced when received from different depths. More
TGC is required for higher frequency transducers, which
create more attenuation. Compression also reduces the
differences between the smallest and largest amplitudes
of ultrasound images by reducing the total range without
altering the signal ratio.
Once 2D images are optimized, color flow imaging
is turned on to visualize the intracardiac blood flow
characteristics and to identify any turbulent flow within
the heart. Occasionally, color flow imaging demonstrates
hemodynamic or structural abnormalities that are not
readily apparent with 2D echocardiography alone. When
color flow imaging is used to show a regurgitant jet,
the color map aliasing velocity should be set as high
as possible (by moving the velocity scale up as far as
possible). The color gain should be increased to the point that it just begins to create background noise and then
decreased to the level that optimizes color flow imaging
of blood flow. The size of the color flow sector should be
optimized because the frame rate for color flow imaging
is inversely proportional to the area of imaging. The
location and size of color flow imaging can be adjusted
according to the objectives of the examination. If 2D
or color flow imaging (or both) identifies an area of
concern, a further quantitative assessment is made, such as
measuring the size of the lesion, calculating the area of the
stenotic or regurgitant orifice, or calculating the pressure
gradient. Even without the presence of obvious structural
or functional abnormalities, several areas of the heart need
to be interrogated to assess systolic and diastolic function.
Therefore, a pulsed wave Doppler examination follows
and complements color flow imaging. A pulsed wave
Doppler examination of the left ventricular outflow tract
andthe mitralleaflettipsis routinelyperformedto calculate
strokevolume and to assess diastolic function, respectively.
Other relatively routine pulsed Doppler examinations
includethe right ventricular outflow tract, pulmonary vein,
hepaticvein, upperdescending aorta,and abdominal aorta. A comprehensive echocardiography examination should
include a continuous wave Doppler examination of the
descending aorta to assess for the presence of coarctation,
especially in patients who have hypertension or a bicuspid
aortic valve. Another important area of a pulsed wave
Doppler examination is the mitral anulus, but the Doppler
mode needs to be changed to TDI.
Pulsed wave Doppler has been modified to record
velocityfrom thetissues which is lower in absolute velocity
but higher in amplitude. When TDI or myocardial imaging
is selected, higher tissue velocities are filtered out and
only lower tissue velocities, usually 5 to 20 cm/s, are
recorded. Because of the higher amplitude, the gain needs
to be decreased when the examination is switched from
regular pulsed wave Doppler imaging to TDI. TDI has
numerous applications (see Chapter 4). It is essential in
evaluating cardiac function (systolic and diastolic) and
the timing of cardiac events, and it is useful in assessing mechanical dyssynchrony among different regions of the
left ventricle (16,17). Myocardial strain and strain rate
can be derived from TDI (18). Tissue tracking and tissue
synchronization imaging (TSI) have been developed to
allow echocardiographers to assess the pattern and timing
of myocardial contraction readily with color imaging of
tissue Doppler velocities.
Duringa Doppler examination, therecording of velocity
is optimized by selecting or adjusting the velocity scale,
gain, baseline position, sweep speed, sample volume size,
and respiratory cycle. Recording space should be used fully
by selecting the highest velocity to be about 25% higher
than the obtained velocity. For example, if aortic stenosis
velocityis 4 m/s, it isbetter to havethehighestvelocity scale
setat 5 m/sinsteadof 7 m/s. Ifpulmonaryveinpeakvelocity
is 80 cm/s, it is better to have the Nyquist limit or aliasing
velocity at 120 cm/s instead of 200 cm/s. The baseline canbe shifted accordingly to demonstrate fully the obtained
or desired recorded velocity. Initial Doppler gain should
be increased to the point of background noise and then
decreased to produce optimal contrast with the recorded
signal.Colorization of the Doppler signalfrequentlymakes
the velocity sharper and is available on most machines by
pushing or selecting that option. The smallest possible
sample volume size (1–2 mm) usually is selected to record
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 5/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 5
How to Obtain a Good Echocardiography Examination: Ultrasound Physics, Technique, and Medical Knowledge 5
the pure velocity signal from the region of interest when
a slight variation in sample volume location can produce
different velocities, as in the left ventricular outflow tract
or mitral leaflet tips. However, a larger sample volume size
(3–5 mm)may benecessary toobtaina goodvelocity signal
from an area of interest that is small, as in a pulmonary
vein, or hepatic vein, or during tissue Doppler imaging of
the mitral anulus. Color flow imaging is helpful as a guide
for locating the ideal site for placing a sample volume.
When the region of interest moves with the cardiac cycle or
with respiration, a signal may be obtained by instructing
thepatient to hold hisor her breathor by slightly changing
the location of the sample volume during several attempts
to obtain the signal. The sweep speed is usually set at 50 mm/s for recording Doppler velocities, but when time
intervals are measured, it may be increased to 100 mm/s.
When multiple cardiaccycles need to be recorded together,
the sweep speed is reduced to 25 mm/s, especially when
the respiratory variation of Doppler velocity is assessed.
Because contrast can dramatically enhance weak Doppler
signals, it should be considered for improving the accuracy
of the examination of patients who have weak tricuspid
regurgitation or an aortic stenosis jet.
GOAL-DIRECTED AND COMPREHENSIVEEXAMINATION BY WELL-TRAINEDPERSONNEL
To perform a clinically pertinent echocardiography exam-
ination, it is important to have a strategy to determine
which of the numerous echocardiographic views and pa-
rameters will providethe optimalinformationfor assessing
the patient being examined. A strategy is best formulated
after the examiner (sonographer or physician) has a clear
understanding of the clinical problem or problems to
be evaluated. An echocardiography examination is highly
useful clinically and cost-effective when sound medical
knowledge is combined with sound technical skills, in-
cluding an understanding of ultrasound physics (15,19)
and the instrumentation, and interpretive skills. Some
start echocardiographic training by developing technical
expertise, and others approach this training after medical
school or residency. The miniaturization and portability
of echocardiographic machines may provide a strong
incentive for physicians to learn technical and interpre-
tive skills of ultrasonography during medical school (13)
or residency, akin to learning about heart sounds by us-
ing a stethoscope. Sonographers take a different road to
sonography, approaching echocardiography by learning
and perfecting technical skills. When a sonographer under-
stands which echocardiographic parameters are important
for a specific clinical diagnosis or for thepatient’ssymptoms
and why, he or sheis truly an accomplished echocardiogra-
pher. Therefore, the echocardiography examination shouldintegrate the medical and sonographic skills to produce
clinically relevant and visually attractive echocardiograms.
Physician training requirements for the performance
and interpretation of adult transthoracic echocardiography
examinations have been developed by the ACC/AHA Task
Force on competence in collaboration with the American
Society of Echocardiography, the Society of Cardiovascular
Anesthesiologists, and the Society of Pediatric Echocardio-
graphy (Table 1-1) (20). There are three levels of physician TAB1.1
training:
Level 1 training is defined as the minimal introduc-
tory training that must be achieved by all trainees
in adult cardiovascular medicine. This includes a ba-
sic understanding of the physics of ultrasound, the
fundamental technical aspects of the examination, car-
diovascular anatomy and physiology related to echocar-
diographic and Doppler imaging, and recognition of
simple and complex cardiac abnormalities and their
pathophysiology.
Level 2 training is the minimum recommended training
for a physician to perform echocardiography and to
interpret echocardiograms independently.
Level 3 training requires at least 12 months of training
that provides a level of expertise sufficient to enable a
physician to serve as director of an echocardiography
laboratory and to be directly responsible for quality
TABLE 1-1TRAINING REQUIREMENTS FOR THE PERFORMANCEAND INTERPRETATION OF ADULT TRANSTHORACIC
ECHOCARDIOGRAPHY EXAMINATIONS
Cumulative durationof training, mo
Minimum total numberof examinationsperformed
Minimum numberof examinationsinterpreted
Level 1 3 75 150
Level 2 6 150 (75 additional) 300 (150 additional)
Level 3 12 300 (150 additional) 750 (450 additional)
8/6/2019 Obtaining Good Echo
http://slidepdf.com/reader/full/obtaining-good-echo 6/6
Oh-Echo ch01.tex V1 - July 20, 2006 6:14 P.M. Page 6
6 Chapter 1
control and for training sonographersand physicians in
echocardiography.
DIGITAL ECHOCARDIOGRAPHY
Digital echocardiography has profoundly changed and
improved the practice of echocardiography (21). It is
extremely convenient to acquire, transmit, and review
echocardiographic imagesdigitally. However, because only
a limited number of cardiac cycles usually are acquired, it
is essential for examiners to capture the most representa-
tive cardiac cycles. The number of cardiac cycles for image
acquisition can be adjusted. One cycle is most economicalfor storage space, but it may not be representative, espe-
cially if the underlying rhythm is not regular. Acquisition
of more cardiac cycles increases the time and storage space
of thestudy.If thepatient hasnormalsinusrhythm, a good
compromise is to capture two or three cardiac cycles. How-
ever, one cardiac cycle is better for stress echocardiography
because each view is compared with other images simul-
taneously side by side. If the patient has atrial fibrillation,
three to five cardiac cycles should be acquired.
Digitalimaging exposes theultrasoundsystem to therisk
of viruses, worms, and parasites of the electronic system.
To maintain the function of the machine and the security
of patient information, the ultrasound unit needs to be
protected against these electronic hazards.
ECHOCARDIOGRAPHY REPORT
Ideally, the echocardiographic reporting system should
be integrated with the digital imaging system. With this
integrated system, measured echocardiographic data are
transferred automatically to the echocardiographic report
and a still frame or even small clip of a real-time image can
be included.
The echocardiography report is the medium through
which an echocardiographer conveys not only the descrip-
tive findings of echocardiography but, more importantly,
the clinical implications and diagnostic considerations in
the context of the patient’s clinical presentation. A report
should do the following three things: 1) answer referral
questions; even if echocardiography does not demonstrate
any abnormality to explain the patient’s symptoms, the
absence of positive findings should be stated; 2) describe
unsuspected,but clinicallyimportant, findings; and 3) pro-
vide basic data for all patients. The basic data include thefollowing: left ventricular systolic and diastolic function,
left ventricular cavity size, wall thickness, right ventricular
size andfunction,valvular structureand function, left atrial
volume, anatomyof thegreatvessels, andpulmonaryartery
systolic pressure. Typical echocardiography reports from
the Mayo Clinic laboratory are shown in the Appendix.
REFERENCES1. Edler I, Hertz CH. The use of ultrasonic reflectoscope for the continuous
recording of the movements of heart walls. 1954. Clinical Physiology andFunctional Imaging, 2004;24:118–136.
2. Joyner CR Jr, Reid JM. Applications of ultrasound in cardiology and car-diovascular physiology. Progress in Cardiovascular Diseases, 1963;5:482–497.
3. Feigenbaum H, Waldhausen JA, Hyde LP. Ultrasound diagnosis of pericar-dialeffusion. JAMA: theJournalof theAmerican MedicalAssociation,1965;191:711–714.
4. Tajik AJ, Seward JB, Hagler DJ, et al. Two-dimensional real-time ultra-sonic imaging of the heart and great vessels: Technique, image orien-tation, structure identification, and validation. Mayo Clinic Proceedings,1978;53:271–303.
5. Holen J, Aaslid R, Landmark K, et al. Determination of pressure gradient in mitral stenosis with a non-invasive ultrasound Doppler technique. ActaMedica Scandinavica, 1976;199:455–460.
6. Hatle L, Brubakk A, Tromsdal A, et al. Noninvasive assessment of pressuredrop in mitral stenosis by Doppler ultrasound. British Heart Journal, 1978;40:131–140.
7. Omoto R, Kasai C. Physics and instrumentation of Doppler color flowmapping. Echocardiography, 1987;4:467–483.
8. McDicken WN, Sutherland GR, Moran CM, et al. Colour Doppler velocity imaging of the myocardium. Ultrasound in Medicine and Biology,1992;18:651–654.
9. Heimdal A, Stoylen A, Torp H, et al. Real-time strain rate imaging of the left ventricle by ultrasound. Journal of the American Society of Echocardiogra-phy, 1998;11:1013–1019.
10. Seward JB, Khandheria BK, Oh JK, et al. Transesophageal echocardio-graphy: Technique, anatomic correlations, implementation, and clinicalapplications. Mayo Clinic Proceedings, 1988;63:649–680.
11. Zamorano J, Cordeiro P, Sugeng L, et al. Real-time three-dimensionalechocardiography for rheumatic mitral valve stenosis evaluation: Anaccurateand novelapproach.Journalofthe American Collegeof Cardiology,2004;43:2091–2096.
12. Kuhl HP, Schreckenberg M, Rulands D, et al. High-resolution transthoracic real-time three-dimensional echocardiography: Quantitation of cardiac vol-umes and function using semi-automatic border detection and comparison with cardiac magnetic resonance imaging. Journal of the American Collegeof Cardiology, 2004;43:2083–2090.
13. Wittich CM, Montgomery SC, Neben MA, et al. Teaching cardiovascular
anatomy to medical students by using a handheld ultrasound device.JAMA: the Journal of the American Medical Association, 2002;288:1062–1063.
14. Seward JB, Douglas PS, Erbel R, et al. Hand-carried cardiac ultrasound(HCU) device: Recommendations regarding new technology: A report fromthe Echocardiography Task Force on New Technology of the Nomenclatureand Standards Committee of the American Society of Echocardiography.Journal of the American Society of Echocardiography, 2002;15:369–373.
15. Edelman SK, ed. Understanding Ultrasound Physics: Fundamentals andExam Review, 2nd ed. Woodlands, TX: ESP, 1994.
16. Ommen SR, Nishimura RA, Appleton CP, et al. Clinical utility of Doppler echocardiography and tissue Doppler imaging in the estimation of left ventricular filling pressures: A comparative simultaneous Doppler-catheterization study. Circulation, 2000;102:1788–1794.
17. Oh JK, Tajik J. The return of cardiac time intervals: The phoenix is rising.Journal of the American College of Cardiology, 2003;42:1471–1474.
18. UrheimS, EdvardsenT, TorpH, et al. Myocardialstrainby Doppler echocar-diography: Validation of a new method to quantify regional myocardialfunction. Circulation, 2000;102:1158–1164.
19. Kremkau FW, ed. Diagnostic Ultrasound: Principles and Instruments, 6thed. Philadelphia: W.B. Saunders, 2002.
20. Quinones MA, Douglas PS, Foster E, et al. American College of Cardiology, American Heart Association, American College of Physicians-AmericanSocietyof Internal Medicine,AmericanSocietyof Echocardiography,Society of Cardiovascular Anesthesiologists, Society of Pediatric Echocardiography. ACC/AHA clinical competence statement on echocardiography: A report of
the American College of Cardiology/American Heart Association/AmericanCollege of Physicians-American Society of Internal Medicine Task Forceon Clinical Competence. Journal of the American College of Cardiology,2003;41:687–708.
21. Hansen WH, Gilman G, Finnesgard SJ, et al. The transition from an analog to a digital echocardiography laboratory: The Mayo experience. Journal of the American Society of Echocardiography, 2004;17:1214–1224.