This document provides an overview of echocardiography, including the basics of trans-thoracic echocardiography, normal doppler echocardiography, and evaluation of cardiac chambers and structures. It discusses the standard scanning planes used in echocardiography including parasternal, apical, subcostal, and suprasternal. It also covers doppler modalities for assessing blood flow through structures like the valves and vessels. The implications of echocardiography are evaluating cardiac size, function, valves, hemodynamics, and diseases.

1. ECHOCARDIOGRAPHY
Dr. Gobardhan Thapa
Resident, MD Radiodiagnosis
NAMS, Bir Hospital
Kathmandu, Nepal

2. Presentation outlines:
• Trans-thoracic echocardiography basics
– Scanning planes
• Normal doppler echocardiography
• Myocardial Doppler Tissue Imaging
• Evaluation of cardiac chambers -
morphometry
• Newer trans-echocardiographic modalities
• Trans-esophageal echocardiography

3. Implications:
• Chamber size, thickness
and function
• Assess all cardiac valves
• Assess hemodynamics
• Cardiac disease including
the valvular and
congenital heart diseases
• Pericardial disease
• Its an ultrasound of the heart using an echo
machine equipped with a range of probes, each
has a spectrum of frequencies

4. Two-Dimensional Trans-thoracic
Examination
• ultrasound directed through a
number of selected planes of the
heart to record a set of standardized
views of the cardiac structures for
subsequent analysis.
• Views designated by
– the position of the transducer,
– the orientation of the viewing plane
relative to the primary axis of the
heart, and
– the structures included in the image
Typical 1-5 MHz adult
trans-thoracic echo
trasducer

5. Imaging planes:
A. Left parasternal
B. Apical
C. Subcostal
D. Suprasternal

6. A. Left parasternal:
I. Long axis left ventricle
II. Short axis aortic valve level
III. Short axis mitral valve level
IV. Short axis papillary muscle level
V. Short axis apical level

7. B. Apical:
I. Four chamber
II.Five chamber
III.Apical long axis of left ventricle
IV.Two chamber

8. C. subcostal
I. Four chamber

9. D. Suprasternal:
aortic arch

10. Left Parasternal
Imaging Planes
• transducer positioned along the left
parasternal intercostal spaces (2nd - 4th ).
• long- and short-axis images of the heart are
obtained.
• long-axis view - mitral leaflets and chordal
apparatus, right ventricular outflow tract,
aortic valve, left atrium, long axis of the left
ventricle, and aorta.
• Rightward angulations allow more complete
imaging of the right ventricle. The right
ventricular inflow view allows assessment of
the right atrium, the proximal portion of the
inferior vena cava, and the entry of the
coronary sinus, the tricuspid valve, and the
base of the right ventricle.

11. Fig. Parasternal long axis view of left
ventricle; in this diastolic image, the mitral
valve leaflets are open and the aortic valve
leaflets are closed. The descending aorta
can be seen in cross section as it passes
beneath the left atrium. AV, aortic valve;
dAo, descending aorta; LA, left atrium;
AMVL, anterior mitral valve leaflet; LV, left
ventricle; RV, right ventricular outflow tract.
Fig. parasternal view of the long axis of
the right heart. The tricuspid valve leaflets
(arrowheads) are seen closing in systole.
RA, right atrium; RV, right ventricle; TV,
tricuspid valve.

12. Fig. parasternal short-axis view at the base of the
heart. The aortic root with its three aortic sinuses is
shown in the center with the left atrium directly
posterior to it. A prominent left atrial appendage is
present (long arrow), and the left upper pulmonary
vein can be seen entering the left atrium. The right
ventricular outflow tract lies anterior to the aorta,
with the posterior cusp of the pulmonic valve
depicted by the short arrow. LA, left atrium; LAA, left
atrial appendage; PV, pulmonic valve; pv, pulmonary
vein; RA, right atrium.
• Parasternal short-axis images of the
heart – transducer rotated 90 degrees
from the long-axis plane and swept
from a cranial to a caudal position.
• The most cranial view – aortic valve
level
visualization of the aortic valve, atria,
right ventricular outflow tract, and
proximal pulmonary arteries. The three
normal coronary cusps of the aortic
valve can be viewed with possible
imaging of the proximal right coronary
artery arising from the right coronary
cusp at the 10 o’clock position, and the
left main coronary artery originating
from the left coronary cusp at the 3
o’clock position.
• The right ventricle appears as a
crescentic structure along the right
anterior surface of the left ventricle.

13. Fig. Parasternal short-axis view of the left
ventricle at the level of the mitral valve. In
diastole, the mitral valve leaflets are open
in a “fish mouth” pattern. The left ventricle
appears circular and the right ventricle is
crescentic in shape. IVS, interventricular
septum; MV, mitral valve; RV, right
ventricle.
• At the basal level, the fish-
mouthed appearance of the
mitral valve is apparent.
• At the mid-ventricular level,
the anterolateral and
posteromedial papillary
muscles are seen.
• The most caudal angulation
allows visualization of the left
ventricular apex.

14. Fig. Parasternal short-axis view of the left
ventricle at the level of the papillary muscles.
Both papillary muscles can be seen projecting
into the lumen of the left ventricle. LV, left
ventricle; PM, papillary muscles; RV, right
ventricle.
Fig. Parasternal short-axis view of the left
ventricle at the level of the apex. LV, left
ventricle; RV, right ventricle.

15. Apical Imaging Planes
• Transducer placed at the
cardiac apex and orienting
the imaging sector toward the
base of the heart - obtain the
apical views of the heart;
visualization of all chambers
of the heart and the tricuspid
and mitral valves.
• With the transducer oriented
in a mediolateral plane at 0
degrees, an apical four-
chamber view of the heart is
obtained.
Fig. Apical four-chamber view of the heart.
LA, left atrium; LV, left ventricle; RA, right atrium; RV,
right ventricle.

16. •Superficial angulation of the
scanning plane from the apical
four-chamber view brings the left
ventricular outflow tract and
aortic valve into view, producing
the five-chamber view.
Fig. Apical five-chamber view of
the heart.
Includes left ventricular outflow
tract and aortic valve.

17. Fig. Apical long-axis view of the heart. To
obtain this view, the transducer is rotated
so that the index marker is pointed toward
the suprasternal notch. AV, aortic valve;
LA, left atrium; LV, left ventricle.
• As the transducer is rotated
45 degrees clockwise to this
plane, the apical long-axis
view of the heart is obtained.

18. •Further clockwise rotation of
the transducer to a full 90
degrees produces the apical
two-chamber view.
The apical two-chamber view -
direct visualization of the true
inferior and anterior wall of the
ventricle.
Fig. Apical two-chamber view of the heart.
To obtain this view, the transducer is rotated
45 degree clockwise from
the long-axis view. This image plane lies
between long-axis view and
four-chamber view.
anterior (Ant) and inferior (Inf)
walls ; LA, left atrium; LV, left ventricle.

19. Subcostal Imaging Planes
• Access to the heart through the solid tissue of the liver,
which readily transmits sound waves - better visualization
of the atrial and ventricular septae because the sound
beam strikes these structures in a perpendicular direction.
• A series of long- and short-axis images are usually obtained
from this window. The inferior vena cava and hepatic veins,
the liver, and the abdominal aorta can also be evaluated
subcostally.
• In the ICU setting, it may be the only viewpoint to image
the heart in the patient with chest wall injury, hyperinflated
lungs, or pneumothorax.
• In infants and small children, the subcostal window
provides excellent images of all cardiac structures.

20. Fig. Subcostal view
LA, left atrium; LV, left ventricle; RA, right atrium; RV, right ventricle.

21. Suprasternal Imaging
Planes
• by placing the transducer in the suprasternal notch.
• Both longitudinal and transverse planes of the great
vessels can be imaged.
• The longitudinal plane orients through the long axis of
the aorta and includes the origins of the innominate,
left common carotid, and left subclavian arteries.
• The transverse plane includes a cross section through
the ascending aorta, with the right pulmonary artery
crossing behind. Portions of the innominate vein and
superior vena cava are visible anterior to the aorta. The
left atrium and pulmonary veins are posterior to the
right pulmonary artery.

22. Fig. suprasternal long-axis view of the aortic arch.
The proximal portions of the brachiocephalic vessels
are demonstrated arising from the aortic arch: (1)
right brachiocephalic artery, (2) left common carotid
artery, and (3) left subclavian artery. The right
pulmonary artery (RPA) can be seen in cross section
as it passes beneath the ascending aorta (Ao). DAo,
descending aorta; LA, left atrium.
Fig. Suprasternal short-axis view of the aortic arch.
The right pulmonary artery (RPA) crosses beneath the
aorta (Ao) and the pulmonary veins enter the left
atrium with a “crablike” appearance. LA, left atrium;
LIPV, left inferior pulmonary vein; LSPV, left superior
pulmonary vein; RIPV, right inferior pulmonary vein;
RSPV, right superior pulmonary vein

23. Other views:
Right Parasternal View
• particularly helpful with medially positioned
hearts, right ventricular enlargement, and
rightward orientation of the ascending aorta.
• By allowing direct visualization of the right
atrium, both venae cavae, and the interatrial
septum, this view is also of particular value in the
assessment of interatrial shunt flow, and in the
detection of anomalous pulmonary venous
drainage.

24. The Normal Doppler Examination
• Frequency shift of ultrasound waves reflected from
moving red blood cells can be used to determine the
velocity and direction of blood flow.
• Done with either pulsed Doppler or continuous wave
Doppler.
• Pulsed Doppler (uses PRF) - analysis of the velocity
and direction of blood flow at a specific site.
• Continuous wave Doppler (uses continuous USG
signals) - resolution and analysis of high-velocity flow
along the entire length of the Doppler beam.

25. Fig. Continuous wave Doppler spectral tracing of
flow across the mitral valve from the apical
window. In diastole, flow is recorded above the
baseline as blood moves toward the transducer
at the apex across the mitral valve into the left
ventricle. In systole, mitral regurgitant flow is
shown below the baseline as it passes away
from the apex and into the left atrium. This
patient with rheumatic mitral stenosis has high
velocity mitral inflow (1.8 m/sec) and mitral
regurgitation (5 m/sec).
• The data can be displayed
graphically (Figure 2-16).
• By convention, flow toward
the interrogating transducer
is represented as a
deflection above, and flow
away from the transducer
appears as a deflection
below the baseline. The x-
axis represents time and the
y-axis represents velocity.

26. Fig. parasternal long-axis view of the mitral
valve in systole. A large stream of mitral
regurgitation (MR) (arrowhead) is seen
emerging from the leaflet coaptation point
and spreading into the left atrium (LA). The jet
is blue (indicating flow away from the
transducer) with mosaic of color to reflect
turbulent flow. LV, left ventricle.
• Parasternal Long-Axis View
• In this view, mitral regurgitation is seen
as a discrete blue jet in the left atrium
during systole. Small jets can be seen
with normal valves.
• Aortic regurgitation is seen as blue or
red jet emanating from a closed aortic
valve. The jet is located in the left
ventricular outflow tract and occurs in
diastole. The presence of this jet
represents an abnormal aortic valve.

27. • Right Ventricular Inflow View
• Inferior vena cava inflow is seen as a red jet seen at the
inferior margin of the right atrium. It has both systole and
diastole phases and flow velocity is normally less than 1.0
m/sec by pulsed Doppler.
• Tricuspid inflow is seen as red jet crossing the tricuspid
valve. It occurs in diastole with velocities less than 0.6
m/sec.
• Tricuspid regurgitation is a blue jet in the right atrium which
occurs in systole. Small jets are normal. The peak velocity of
regurgitant flow can be quantified by continuous wave
Doppler.

28. • Parasternal Short Axis
• Inferior vena cava inflow is a continuous low-velocity
red jet that enters through the right atrial floor
adjacent to the interatrial septum.
• Vigorous caval flow such as seen in children may be
confused with left to right interatrial shunt flow.
• Pulmonary outflow is a systolic blue jet in the
pulmonary artery. The normal velocity across the
pulmonary outflow tract is 0.6 to 0.9 m/sec in adults
and 0.7-1.2 m/sec in children.

29. • Apical Views
• Transmitral and tricuspid flow are best evaluated in the four
chamber view as a result of the parallel position of the
doppler beam to the direction of blood flow.
• Likewise, transaortic flow can be assessed in the apical long
axis or five-chamber view.

30. • The flows detected in this view are:
• Mitral inflow occurs in diastole and can be quantified
by pulsed Doppler with the sample volume placed at
the mitral leaflet tips in the ventricular cavity.
• The initial positive deflection (E wave) represents
early passive ventricular filling and the subsequent
deflection (A wave) reflects the late phase of
ventricular filling that is as a result of atrial contraction.
• The normal E wave velocity is less than 1.2 m/sec and
A wave velocity is less than 0.8 m/sec.

31. Fig. Pulsed Doppler spectral profile of mitral inflow obtained from
an apical window. Flow toward the transducer is shown above the
baseline in diastole during left ventricular filling. The typical mitral
biphasic-filling pattern is seen, with a prominent early filling wave
(E wave) and smaller late diastolic filling wave (A wave).

32. • Aortic and left ventricular outflow is seen as blue
flow detected in systole. The Doppler profile
appears as a negative single uniform systolic
profile.
• Pulmonary vein inflow from the right upper
pulmonary vein is seen as a red jet entering the
left atrium in proximity of the interatrial septum.
It can be quantified by pulsed Doppler with
sample volume placed 1 to 2 cm into the
pulmonary vein. There is biphasic flow in systole
and diastole.

33. Fig. Pulsed Doppler spectral profile of aortic outflow obtained
from an apical window. Flow velocities are plotted below the
baseline to indicate that the direction of flow is away from the
apically positioned transducer. The typical aortic flow profile is a
systolic flow with rapid upstroke to a peak velocity in mid-systole
and rapid decline in velocity during late systole.

34. • Other Views
Subcostal views are useful for assessing flow
within the inferior vena cava, hepatic veins,
and abdominal aorta. The suprasternal
window is used for recording flow in the
ascending and descending aorta and in the
superior vena cava.

35. Myocardial Doppler Tissue Imaging
• myocardium (low velocity) as the target of
ultrasound reflection rather than blood cells
(high velocity).
• Similar Doppler principles can be applied with
color saturation of the tissue to indicate
direction and velocity of the myocardium.

36. • sample volume (similar to pulsed Doppler)
placed within the myocardium or valvular
annulus to obtain a quantitative spectral
profile of myocardial motion.
• Doppler derived tissue velocity, strain and
strain rate have been demonstrated to
improve evaluation of myocardial mechanics
when compared to previous measures such as
wall thickening or motion.

37. Fig. Tissue Doppler imaging shows
myocardial velocity in a target sample
region. In this case the sample volume
is placed at the septal mitral annulus.
The systolic motion of the annulus (s′)
and the diastolic motion (e′ and a′) are
shown.
Fig. Tissue velocity derived radial strain of
the left ventricle shown from the
midventricular short axis. The two areas of
interest are shown by ovals superimposed
on the myocardium. The peak strain value
for normal myocardium (anteroseptum,
yellow curve) has a higher positive strain
(myocardial lengthening) than
dysfunctional myocardium (inferior wall,
green curve) during systole.

38. Evaluation of Cardiac Chambers
Aortic root—end diastole 24-39 mm
Left atrium—end systole 25-38 mm
Left ventricle—end diastole 37-53 mm
Interventricular septal thickness—end diastole 7-11 mm
Left ventricular posterior wall thickness—end diastole 7-11 mm
*Obtained from para-sternal long-axis view.
Normal Linear Dimensions
• By convention, most laboratories report the size of the left
atrium, aortic root, and left ventricle from the measurement of
the linear dimensions of each structure in the para-sternal
long-axis view of the heart.
• All linear dimensions - bear a direct linear relation to body
height.

39. Left Ventricular Volume
• The ellipsoid formula
– requires measuring the length of the ventricle and its
diameter at the base. This volume estimation is valid
in normal (symmetric) left ventricles, but it is less
reliable when there is a distortion of ventricular shape
(e.g., following myocardial infarction).
• Simpson’s rule
– requires measuring the length of the ventricle from
apical views and then determining the volume of a
predefined number of disk-like cross-sectional
segments from base to apex.

40. • Three-dimensional volume
measurement makes no
geometric assumptions
and thus can determine
the volume of both normal
and distorted ventricles.
Fig. A three-dimensional left ventricular volume
assessment allows all regions of the ventricular
myocardium to be incorporated into the
volume assessment. Each region is depicted by
the different color code representing the 17-
segment model. The image is from a patient
with dilated cardiomyopathy and thus the
ventricular shape is more globular in structure.

41. Left Ventricular Systolic Function from Two-
dimensional Images
• Real-time echocardiographic assessment of
endocardial motion and the degree of wall
thickening during systole allows excellent
qualitative assessment of global and regional
ventricular function.
• Using this method, systolic function can be
described as either normal or depressed, and
regional function is either normal, hyperkinetic,
hypokinetic, akinetic, or dyskinetic.

42. • Left Ventricular Systolic Function from Doppler
Echocardiography
• Doppler echocardiography makes it possible to
estimate stroke volume and cardiac output by
measuring volumetric flow through the heart.
• Stroke volume is calculated by measuring the cross-
sectional area of a vessel or valve (e.g. aortic valve
diameter and flow velocities ) and then integrating the
flow velocities across that specific region in the vessel
or valve throughout the period of flow.
• The product of stroke volume and heart rate then gives
an estimate of cardiac output.

43. Left Atrium
• anteroposterior dimension measured at end systole in the
parasternal long-axis view from a line drawn through the
plane of the aortic valve.
• Atrial enlargement may occur as a consequence of
– either an increase in atrial pressure (resulting from mitral
stenosis or elevated left ventricular end-diastolic pressure), an
increase in volume (as in mitral regurgitation), or as a
consequence of primary atrial dysfunction (as in atrial
fibrillation).
• The left atrial appendage is a “dog ear”-shaped extension
of the atrium situated along the lateral aspect of the
chamber near the mitral annulus. - trabeculated
structurecan be confused with thrombus, which may form
within the appendage

44. Fig. A two-dimensional transesophageal echocardiogram showing
the left ventricle (LV), left atrium (LA), left atrial appendage (LAA),
and large thrombus (arrowheads).

45. Right Ventricle
• Morphologically, divided into
an inflow portion: heavily trabeculated body of the
ventricle, and an outflow portion: infundibulum.
• The inflow portion extends from the tricuspid valve to the
apex.
• The lateral or free wall of the right ventricle normally has a
radius of curvature approximately equal to the left
ventricular free wall.
• complex shape of the right ventricle, so is less amenable to
geometric modeling than the left ventricle.Thus, newer
three-dimensional echocardiographic techniques are more
reliable in assessing right ventricular volume.

46. • Right ventricular enlargement may be due to
– right ventricular volume loading, right ventricular infarction, or as part
of a generalized cardiomyopathic process. In each instance, as
dilatation progresses, the anteroposterior dimension of the ventricle
increases and interventricular septal motion becomes increasingly
abnormal.
• Specifically, in diastole the septum may appear to flatten, especially
at the base, and in early systole the septum may move rightward
(paradoxically) rather than leftward.
• Pressure loading results in progressive hypertrophy.
• free wall thickness of greater than 5 mm is a quantitative criterion
for right ventricular hypertrophy.
• Marked pressure overloading typically produces systolic flattening
of the interventricular septum.

47. Fig. Apical four-chamber view of a patient with severe primary pulmonary
hypertension. The right ventricle (RV) is enlarged. There is hypertrophy of the
free wall (RVH). The right atrium (RA) is enlarged and high right atrial
pressures cause displacement of the interatrial septum (IAS) to the left. The
left atrium (LA) and left ventricle (LV) are under filled as a result of the
reduced output from the right heart and are thus small.

48. Right Atrium
• Assessed qualitatively by comparing it to the left atrium in the
apical four-chamber view and quantitatively by measuring the
maximal mediolateral and supero-inferior dimensions in this view.
• Normal structures within the right atrium include
– Eustachian valve (or valve of IVC), which crosses from the inferior
vena cava to the region of the foramen ovale, and
– Crista terminalis; apical four chamber view - a ridge of tissue that
separates the smooth-walled portion of the right atrium from its
trabeculated anterior portion, often noted as a small mass of echoes
located adjacent to the superior border of the right atrium.
– right atrial appendage: a broad-based triangular structure anterior to
the atrial chamber near the ascending aorta; most visible in the
parasternal views of the right atrium and readily visualized by TEE.

49. Novel Echocardiographic Tools:
Contrast Echocardiography
• Contrast echocardiography uses intravenous agents that result
in increased echogenicity of blood or myocardium with
ultrasound imaging.
• Contrast agents form small microbubbles, which at low
ultrasound power, output disperse ultrasound at the gas and
liquid interface, thus increasing the signal detected by the
transducer.
• Contrast echocardiography improves analysis of regional wall
abnormalities. Real-time myocardial contrast
echocardiography is being investigated as a tool for
quantitative analysis of myocardial perfusion.

50. Fig. Apical four-chamber view recorded of a
patient with left ventricular apical
pseudoaneurysm (PSA) following left
ventricular contrast agent injection showing
complete cavity opacification and delineation
of all left ventricular walls. IVS,
interventricular septum; LV, left ventricle; RV,
right ventricle.
Fig. Apical four-chamber view recorded after the
injection of contrast into an upper limb vein. Contrast
is seen to fill the right atrium (RA) and right ventricle
(RV) before entering the left atrium (LA) and left
ventricle (LV). The image is acquired after a Valsalva
maneuver that transiently increases the right atrial
pressure. This is reflected in the leftward
displacement of the interatrial septum (IAS) resulting
in increased right to left flow through the patent
foramen ovale.

51. Three-Dimensional Echocardiography
• Volumetric imaging using a complex multi-array
transducer
• Three-dimensional pyramidal volume data used to
obtain images of the cardiac structures in three spatial
dimensions.
• Post-acquisition processing allows different views of
the interior structures of the heart to be displayed.
• The structure studied can be manipulated so that it is
viewed from multiple angles such as the surgical
enface view of the mitral valve from the left atrium.

52. Fig. A 3-D enface view of the mitral valve from the left atrial perspective -
prolapse of the middle scallop of the anterior mitral leaflet (pAMVL).

53. • Real-time 3-D transesophageal
echocardiography (TEE) - to assist with device
implantation in the catheter laboratory.
• current limitations: image quality, ultrasound
artifact, and temporal resolution.

54. Fig. A three-dimensional left ventricular volume
assessment allows all regions of the ventricular
myocardium to be incorporated into the
volume assessment. Each region is depicted by
the different color code representing the 17-
segment model. The image is from a patient
with dilated cardiomyopathy and thus the
ventricular shape is more globular in structure.
Fig. A 3-D study recorded during an ASD closure
procedure. The image is recorded from the left
atrial aspect showing the catheter traversing
the atrial septal defect (ASD). The Atrial Septal
Closure device (AMP) is seen at the tip of the
catheter (CATH) as it is being positioned along
the interatrial septum.

55. Transesophageal Imaging
• visualize the heart and great vessels in
patients with suboptimal transthoracic
imaging windows.
• This may occur as a result of body habitus,
lung disease, or operative room or
intensive care environment where access
to the chest wall and optimal positioning
is prohibitive.
• uses a specially designed ultrasound probe
incorporated within a standard
gastroscope - semi-invasive procedure
requiring blind esophageal intubation.

56. • High-frequency transducers (5.0 to 7.5 MHz)
are routinely used because of close proximity
of the heart to the transducer - better
definition of small structures than the lower
frequencies used transthoracically (2.5 to 3.5
MHz).
• So, particularly valuable in the routine clinical
setting for the detection of atrial thrombi,
small vegetations, diseases of the aorta,
atrial septal defects, patent foramen ovale,
and the assessment of prosthetic valve
function.

57. • In operating or catheter suites to monitor and assess
the repair of cardiac structures.
• Current instrumentation allows imaging of multiple
planes through the heart with multiplane
transesophageal probes in which the ultrasound plane
is electronically steered through an arc of 180 degrees.
• The anteroposterior orientation of images from the
esophagus is the reverse of images from the
transthoracic window because the ultrasound beam
first encounters the more posterior structures closest
to the esophagus.

58. Fig. Diagrammatic representation of the standard imaging planes obtained with multiplane
transesophageal echocardiography. Views from the upper esophageal, midesophageal, and
transgastric probe orientations are demonstrated. The icon adjacent to each view indicates the
approximate multiplane angle. AV, aortic valve; LAX, long axis; ME, midesophageal; RV, right
ventricle; SAX, short axis; TG, transgastric; UE, upper esophageal.

59. References:
1. Cardiac imaging : the requisites / Stephen
Wilmot Miller, Lawrence M. Boxt, Suhny
Abbara. — 3rd ed.
2. Normal Echocardiographic Parameters of
Healthy Adult Individuals working in National
Heart Centre; Prajapati D et al, Nepalese heart
journal, vol. 9, no. 1: nov 2012
3. http://www.wikiecho.org