medicine is the key

1. By CHU Emmanuel NDZE
B.Sc in Medical Imaging Technology
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3.  Introduction
 Physics
 Instrumentation
 Terminology
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4. At the end of this course, the student should be able to;
 Explain how ultrasound works
 Explain the principles of a transducer
 Name the different Scanning plains
 State the advantages and disadvantages of ultrasound
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5.  Sound is a mechanical, longitudinal wave that travels in
a straight line and measured by cycle per second by
Hertz(Hz) unit. Audible Sound is 20-20,000Hz.
 Sound requires a material medium through which to
travel
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6.  Ultrasonography (ultrasound) is an imaging technique using
high frequency sound waves of 2-20MHz to produce images
of structure within the body.
 A frequency of 1MHz is 1,000,000 cycles per second. The
pulse are repeated about 1000times per second.
 The ultrasound waves passes at different speeds through
different tissues and are altered in different ways.
 Some tissues reflect back directly while others scatter the
waves before they are returned back to the crystal.
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7.  The ultrasound frequency is expressed in MEGAHERZ(MHz).
Sound waves are audible up to a frequency(f) of 20KHz i.e.
20,000 cycles per second. The longer the wavelength of the
sound beam, the smaller the frequency. The shorter the
wavelength, the higher the frequency(f).
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9.  A wave is a disturbance with a regularly repeating pattern,
which travels from one point to another.
 Types; transverse
 Longitudinal
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10.  Audible sound waves lie between 20 and 20,000 Hz.
 Ultrasound uses sound waves with far greater frequency
 i.e 1 – 30MHz
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11.  Sound waves do not exist in a vacuum
 Propagation in gas is poor because the molecules are widely
separated
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12.  Speed
 Frequency
 Wavelength
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13.  Frequency is inversely proportional to wavelength
 High frequency beams are more sensitive and show greater details
but are less penetrating and vice versa
 This means that, the HIGHER the frequency, the BETTER the
resolution
 The LOWER the frequency, the LESSER the resolution
 A 12 MHz transducer has very good resolution, but cannot penetrate
very deep into the body
 A 3 MHz transducer can penetrate deep into the body, but the
resolution is not as good as the 12 MHz.
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14.  Piezoelectric crystal
 Entire probe
 Monitor
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15.  Also called a probe
 Houses the piezoelectric crystal
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 The basic component in medical ultrasound sound is the
piezoelectric crystal. Excitation of this crystal by a small
electric current causes it to vibrate and emit high frequency
sound waves. These waves are reflected back to the crystal,
which also acts as receiver, at interfaces within the body.
These reflected waves are then converted into small electrical
signal by the crystal and stored and analyzed by the
computer.
 An image in 2 dimensions, corresponding to the structures in
the part of the body examined is displayed on a TV monitor.

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19. Image Formation
 Strong echoes are displayed as bright or white dots while
echoes of lesser intensity are displayed as lighter or darker
shades of grey.
 If no echoes are received the area will be displayed as black.
 Very strong bright echoes are said to be of high intensity
while darker echoes are said to be of low intensity.
 Brightness of the dots is proportional to the strength of the
returning echoes; Location of the dots is determined by travel
time. The velocity in tissue is assumed constant at
1540m/sec
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20.  Echoes reaching the transducer are amplified by a computer.
Echoes from the deeper parts of the body needs more
enhancement than those from superficial structures.
 Based on the length of time it takes for the sound waves to return
to the transducer, the depth of the interface can be estimated.
Distance = Velocity/Time
 There are controls the ultrasound machine, which can be adjusted
as necessary, to increase echoes from different depths in the each
patient.
 There is also a control button, GAIN control, which allows the
operator to increase all the echoes( overall sensitivity). These
increases the overall whitening of the image.
 The controls should be adjusted until a balanced image is
obtained otherwise serious errors can be made during image
interpretation
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22.  Used for the breast, musculoskeletal work, thyroid and
Doppler imaging of vessels
 Linear array of crystals
 Image produced is rectangular in shape
 5 – 13 MHz
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24.  Also called convex probe
 the pregnant uterus in the first, second and third trimester,
and Every part of the body except the heart
 Frequency range is 1 – 8 MHz
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26.  Also called a Sector probe
 Originates from a point source
 Dissects between the two other types
 Frequency between 2-8MHz
 Cardiac imaging, imaging between the ribs and small places.
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28.  The endocavitary probe has a curvilinear footprint with a wide
view but has a much higher frequency (8-13 MHz) than a
curvilinear ultrasound probe.
 The image resolution of the endocavitary probe is
exceptional, but like the linear probe, it must be adjacent to
the structure of interest since it has such a high
frequency/resolution, but poor penetration.
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29.  The most common FOCUS applications for the endocavitary
ultrasound probe are for intraoral (peritonsillar abscess) and
transvaginal applications (early pregnancy, ovarian torsion,
ovarian cyst, fibroids, ectopic pregnancy, etc). Make sure to
always place a sterile endocavitary probe cover (condom or
glove) prior to scanning.
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32.  Reflection
 Refraction
 Scattering
 Attenuation
 Absorption
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33.  Ultrasound is reflected, refracted, scattered, or attenuated
or absorbed on meeting the various interfaces in the body
between different structures.
 With reflection the waves are returned directly to the
transducer whereas with refraction the waves are bent and
changes direction.
 Some will reach the transducer at different angle of
incidence and some will be lost.
 Waves which are eventually reflected back to the
transducer, produces the ultrasound image.
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34.  There are several methods for recording ultrasound
images.
 The most commonly used is the B-mode. Here the
intensity of the reflected echoes to the probe is
proportional to the whitening of the image.
 Rapid viewing of the multiple images on the monitor
permits motion of the internal structures in the body to be
viewed in real time.
 Different body tissues produce different degree of sound
reflection and said to be of different echogenicity.
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35.  Body Tissues which have no internal echoes are refers to
as Anechoeic structures, and they appears black.
 Structures containing internal echoes are said to be
echogenic and appear as an area of white on the screen.
 A tissue of high echogenicity reflects more sound than a
tissue of low echogenicity and is said to be echogenic
(hyperechogenic) or hyperechoeic.
 These tissues are seen as white or light grey structures.
E.g Calcifications such as gallstones, certain metastases
and haemangiomas
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36.  A tissues reflecting less sound back to the transducer and
of lower echogenicity is said to be hypoechoeic or
hypoechogenic
 These structures are seen as white dark grey or almost
black. Eg lymphoma and certain metastases.
 N/B; Pure fluid reflects no sound at all and is said to be
Anechoeic because it contain no internal echoes. Fluid
therefore is seen as black and because there is better
transmission of sound waves through it the tissues
behind it are brighter in appearance.
 E.g. Bile and urine in the bladder as well as a simple cyst
will be anechoeic.
 The increased brightness behind cystic structures is
Acoustic enhancement
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37.  As a result of the absence of sound reflection or
absorption in an anechoeic structure, a strong sound wave
reaches the deeper tissues causing them to appear more
echogenic than adjacent tissues where sound beam has
been attenuated before reaching them.
 This is also called back wall effect, bright up or increased
through transmission.
 NB: A dark structure that does not show acoustic
enhancement is probably not cystic.
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40.  It is the opposite of effect and occurs when few echoes
pass beyond a structure.
 The structure has sharply increased echogenicity, causing
most of the sound waves to be reflected back and the
distal tissues receiving little sound.
 This tissues distal to the structure appears black like a
shadow. Example of such structures are gallstones, renal
stones, other calcifications and some dense tumors
especially in the breast.
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42.  Acoustic enhancement and shadowing are very important
in ultrasound scanning.
 Bone and gas behave very differently to other structures
and reflect or refract the beam very strongly.
 This prevents visualization of any structure lying behind
them.
 Therefore, it is not possible to image the adult brain,
lungs or abdominal structures lying behind a lot of bowel
gas.
 However, pleural disease can be imaged as it lies against
the chest wall and the baby`s brain can be image
through the fontanelles before closure.
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43.  If two structures within the body are of very different
echogenicity( impedance value) then more of the beam
will be reflected back to transducer.
 If the structure being imaged has a very wide reflecting
boundary it acts like a mirror and will be seen clearly as a
thin white structure e.g. the diaphragm, the foetal skull,
the walls of the vessels and soft tissues
interfaces(connective tissue).
 Because of these boundary effect a coupling agent is
necessary to exclude all the air from the gap between the
skin and transducer.
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44.  If ultrasound is directed towards a moving structure the
reflected beam will be at a greater or lesser frequency
depending on whether the structure is moving towards or
away from the transducer.
 If moving towards the transducer the frequency will be
greater.
 The different in frequency will also be proportional to the
speed of movement.
 The difference b/w the two frequencies is called Doppler
shift and this made use of in Doppler imaging.
 Doppler ultrasound is can be use to detect and measure
blood flow.
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45. In continuous wave Doppler: the wave is very continuous
and measures high velocities very accurately.
However there is no depth resolution so individual vessels
cannot be image separately and all the movement along
the beam is image together.
Pulsed Doppler: transmits the sound beam intermittently
(in pluses). It can be aimed directly at a particular vessel
but cannot measure very high velocities accurately.
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46. Colour Doppler: the movement is shown in colour and the
direction of flow shown by different colours. By convention
, movement towards the transducer is shown as red while
movement away shows as blue but this can be altered.
Duplex Doppler: this allows the velocity of flow to be
measure along with imaging. A particular vessel can be
seen and the cursor placed more accurately over the
lumen of the vessel at the site interest.
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48.  A-Mode
 B-Mode
 M-Mode
 Doppler
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49.  Simplest form of ultrasound which is based on the pulse-
echo principle
 A scan can be used to measure distances.
 A-mode scans only give one dimension information
 Not so useful for imaging.
 Used for echo-encephalography and echo-ophthalmoscopy
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50.  B stands for brightness
 2 dimensional information
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51.  M stands for motion
 It is a way of displaying motion where it is displayed as
wavy line.
 Represents movement of structures over time.
 It is most commonly used for cardiac imaging, the
different heart valves producing different but
characteristic appearances in their wave pattern.
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53.  This is a feature seen on the image not
corresponding to actual structure within the body.
 It is a missing, distorted or additional image.
 Most artefacts are miss leading and an
understanding of them is necessary to avoid errors
in image interpretation.
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54.  Enhancement
 Shadowing
 Reverberation
 Edge artifact
 Side lobes
 Mirror-image
 Speckles
 Slice thickness
 Equipment generated
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55.  Reverberation is one form of the artefact, which occurs
due to reflection of back and forth echoes at two
strong interfaces almost parallel to each other.
 This often results in duplication or triplication the
image. E.g. the anterior wall of distended bladder.
 Appearance: multiple equidistantly spaced linear
reflection, bladder
 Physics: Parallel highly reflective surfaces, the echoes
generated from a primary US beam may be repeatedly
reflected back and forth before returning to the
transducer for detection
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57.  Appearance – shadow occurring at the edge of a curved
surface.
 Physics – sound waves encountering a cyst wall or a
curved surface at a tangential angle are scattered and
refracted
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58.  Appearance – hyperechoeic rounded object within an
anechoic or hypoechoeic structure e.g urinary bladder or
gall bladder.
 Physics – multiple other low-amplitude beams project
radically at different angles away from the main beam axis.
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59.  Occur due to the specular
reflection of the beam at large
smooth interface.
 An area close to a specular
reflector will be imaged twice,
once by the original ultrasound
beam and once by the beam after
it has reflected off the specular
reflector.
 Most commonly seen where there
is acoustic mismatch such as air-
fluid levels.
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60.  Appearance – the random granular texture that obscures
anatomy in ultrasound images (noise).
 Physics – complex interference of ultrasound echoes made by
reflectors spaced closer together than ultrasound system’s
resolution limit.
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61.  Misuse of controls such as the Gain or TGC can result in echoes being recorded
as too dark or too bright.
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62.  These artifacts will typically be seen in transverse views of the
urinary bladder when structures adjacent to the slice through the
bladder being scanned will be incorporated into the image.
 These echoes are then displayed as if they were arising from within
the bladder.
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63.  Biliary tract diseases
 Pregnancy
 Abdominal masses and other intra-abdominal pathologies
 Pelvic or gynaecological pathology(uterus, ovaries,
prostate, bladder)
 Venography and arteriography
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64.  Relatively cheap
 Readily available
 Non invasive
 No ionizing radiations
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65.  It is very operator dependent
 Cannot penetrate bone or gas. Hence not use for the lung
or the brain(except the brain in infants).
 Fats degrades the waves making it less efficient for
fat/obese patients
 Patient preparation is important
 Better no scan at all than a scan badly performed. The
ready availability of U/S makes this one of its major
drawbacks at the present time. It is not possible to train
someone to be competent in ultrasound in 2 months,
never mind 2 weeks.
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66.  Indicated on the probe and on the screen
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67. Longitudinal (sagittal) plane
 This is vertical cut through the body , along the
long axis, dividing the it into right and left.
 A longitudinal scan be obtained in patient lying
supine, standing erect, lying prone, or lying on
ones side.
 Caudal structures appear to the left of the screen.
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68.  The image is displayed with the left side of the patient on the
right hand side of the screen.
 This is the cut via the body at right angles to the longitudinal
scan dividing it into a head section and foot section
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70.  The left side organs are displayed on the right side of the
screen.
 This plane divides the body into anterior and posterior
sections.
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71.  In addition to 2D imaging, ultrasound provides
anatomic distance and volume measurements, motion
studies, blood velocity measurements, 3D and most
recently, the 4D imaging.
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74.  Ability to distinguish between two different structures
 It is the detail an image holds.
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75.  There are three aspects;
 Spatial (detail)
 Contrast
 temporal
 Contrast and temporal resolutions relate more
directly to instruments.
 Spatial resolution relates more directly to
transducers.
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76.  Also called linear, range, longitudinal, or depth
resolution
 Ability to separate structures parallel to the ultrasound
beam.
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77.  Also known as angular or transverse resolution
 Ability to differentiate between structures
perpendicular to the ultrasound beam.
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78.  It is the ability of a gray-scale display to distinguish
between echoes of slightly different intensities
 An image with many shades of gray has better contrast
resolution.
 An image with less shades of gray degrades contrast
resolution.
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79.  The ability of an ultrasound machine to distinguish
closely spaced events in time.
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80.  Piezoelectric effect: effects caused by crystals changing
shape when in an electrical field or when mechanically
stressed so that an electric impulse can generate a sound
wave or vice versa
 Beam: directed acoustic field produced by a transducer
 Attenuation: progressive weakening of the sound beam as it
travels through body tissue, caused by scatter, absorption,
and reflection
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