1. Medical Imaging By
Prof. M.M. Mohamed

2. DIAGNOSTIC ULTRASOUND
WHAT IS
SOUND?
Audible Sound
Up to 20 kHz
ULTRA
Ultrasound
2-10 MHz
DIAGNOSTIC ULTRASOUND
MHz

3. < 20 Hz Infrasound 20 Hz - 20 kHz Audible Sound > 20 kHz
Frequency Range
Name
< 20 Hz
Infrasound
20 Hz - 20 kHz
Audible Sound
> 20 kHz
Ultrasound

4. WHY ULTRASOUND ? X-RAYs NUCLEAR MRI ULTRASOUND NONINVASIVE
NON-TRAUMATIC
LESS EXPENSIVE

5. Because of High Impedance Mismatch
Cannot penetrate mature adult bone (brain).
BUT……………...
Cannot penetrate any substantial gas-layer.
Because of High Impedance Mismatch

6. Historical Overview 1880... Piezoelectric effect
1887… Waves which are used in ultrasonic devices
1917… Transmit sound waves under the see water
1920… Study the interaction between ultrasound and living systems.
… Slow evolutionary period.
1960’s… Increasing number of physicians accept ultrasound in the clinic.
1970’s - until now… Widespread use of
ultrasound, as well as the development of new techniques.

7. Ultrasound Applications
Ultrasound is used in a variety of applications and devices.
We see it used in everything from toothbrushes and TV remotes to that Ultrasound equipment that we most commonly see in the Medical environment.
Of the this equipment the most commonly confused are Therapeutic and Medical Imaging. That is to say Ultrasound equipment used to stimulate tissue repair and that equipment that is used for Diagnostic Imaging have more differences than similarities.

8. One hertz simply means "one per second“.
Frequency is the measurement of the number of times that a repeated event occurs per unit time. It is also defined as the rate of change of phase of a sinusoidal waveform.
Phase describes the current state of something that changes cyclically (oscillates).

9. TASK: What are the units of Z?
Acoustic Impedance, Z
As stated earlier, when an ultrasound wave meets a boundary between two different materials some of it is refracted and some is reflected. The reflected wave is detected by the ultrasound scanner and forms the image. The proportion of the incident wave that is reflected depends on
the change in the acoustic impedance, Z.
Acoustic Impedance, Z of a medium is defined as:
Z = c
Where  = the density of the material, kgm-3
c = speed of sound in that material, ms-1
TASK: What are the units of Z?
See page 201/203 of textbook for typical values

10. Characterization of Acoustic Wave

11. Acoustic energy and intensity

12. Acoustic Properties of Common Material

13. Acoustic properties of tissues Tissue / Ultrasound waves Interaction
Absorption.
Scattering.
Attenuation.

14. Reflection and Refraction: Geometric Characteristics

15. 1) Absorption 2) Scattering
Absorption mechanisms converts the energy of an acoustic wave to heat as the wave propagates through a medium. A plane ultrasonic wave in an absorbing medium will lose intensity as
2) Scattering
The scattering of a wave on an obstacle is a very complicated process, where it depends on its cross-section.

16. 3) Attenuation
The term attenuation refers to loss in energy from the ultrasonic beam passing through a length of tissue.
db/cm for f > 0
Where,
f is the frequency,
a(f) is the frequency dependent attenuation coefficient,
b is the attenuation coefficient slope with frequency, and
n is the non linearity frequency attenuation parameter.

17. Ultrasound System
Ultrasound systems must contain some form of the five system blocks.
Display - The system will have some way of displaying the data it acquires.
User Interface - It must have a user interface, this may be mechanical or voice activated.
Transducer – Your ultrasound system will have a transducer to convert electrical impulses to sound and back.
Image Processing - The ultrasound machine will have some sort of image processing. This may be analog or digital.
Power Supply - Finally it will have a power supply, again analog or digital.
Peripherals ( may include cameras, or printers).

18. Transducer Linear Array Sector Phased Array Vector Phased Array
Linear Phased Array
Curved Phased Array
Mechanical Endo Cavity
Phased Endo Cavity
Mechanical, rotating wheel
Mechanical, wobblers
Mechanical, acoustic mirror

20. Ultrasonic transducer
In the case of ultrasound two transducer function are recognized:
conversion of ac electric oscillation into acoustic vibration, and
Conversion of acoustic vibrations into ac oscillations of the same frequency.
These two functions are the transmitter and receiver transducers.

21. Piezoelectric materials
Natural quartz,
Barium titanate,
Rochelle salts,and
Lead zirconate titanate

22. Piezoelectric effect - + (A) (B) (C) + + + + + + + + +
(A)
(B)
(C)

23. Piezoelectric element (a) at rest, (b) defect left, (c) defect right

39. Intensity reflection coefficient, 
At a boundary between mediums, the ratio of the intensity reflected, Ir to the intensity incident, I0 is known as the intensity reflection coefficient, .
 = Ir I0
The intensity of both the reflected and incident ultrasound waves depend on the acoustic impedance, Z of the two mediums. Therefore the fraction of the wave intensity reflected can be calculated for an ultrasound wave travelling from medium 1, (acoustic impedance Z1) to medium 2 (acoustic impedance Z2).
 = Ir = Z2 - Z1
I0 Z2 + Z1
If 2 mediums have a large difference in impedance, then most of the wave is reflected. If they have a similar impedance then none is reflected. 2

40. Impedance Matching / Gel
When ultrasound passes through two very different materials the majority of it is reflected. This happens between air and the body, meaning that most ultrasound waves never enter the body. To prevent this large difference in impedance a coupling medium (gel) is used between the air and the skin. The need to match up similar impedances to ensure the waves pass through the body is known as impedance matching.

41. A-Scan A-Scan (Amplitude scan) Gives no photo image
Pulses of ultrasound sent into the body, reflected ultrasound is detected and appear as vertical spikes on a CRO screen.
The horizontal positions of the ‘spikes’ indicate the time it took for the wave to be reflected.
Commonly used to measure size of foetal head.

42. B-Scan B-Scan (Brightness scan)
An array of transducers are used and the ultrasound beam is spread out across the body.
Returning waves are detected and appear as spots of varying brightness.
These spots of brightness are used to build up a picture.

43. The Doppler Effect
The apparent frequency of a wave increases when the source of a wave is moving towards you.
The Doppler effect can be used to measure blood flow in adults, children and developing babies.
Both the time for the reflected ultrasound wave and the ‘new’ frequency of the reflected wave are measured. This enables the speed of blood flow to be calculated. The greater the difference between the original frequency and the reflected frequency, the greater the speed. Computers then display this info as ‘moving images’ by updating data several times per second.

44. Linear Array probes have a distinctive format.
Sector phased array have a characteristic point to the image.
Vector phased array images are similar but have flattened tops.
Linear phased arrays have a rectangular image.
Curved arrays are arched at the top.
There are many other configuration, some very exotic

48. This is a simplistic view of a transducer but it contains all the basic elements.
The cable provide the electrical connection.
The strain relief supports the very fine coaxial cables in the cable.
The case protects the internal crystal connections.
The damping material isolates the crystal element from mechanical noise and provides mechanical support.
The piezoelectric element convert electrical impulses to mechanical motion and back.
The filler or lens provides mechanical isolation for the crystal element, impedance matching and it’s shape provides focus.

49. Array construction Array construction contains the same basic parts.
The main difference is in the Piezoelectric Material. Instead of a single crystal the array is sliced transversely to create a large number of small elements.
Arrays of linear or phased construction are similar but differ when it comes to system construction.
The filler material does more than protect the array, it is a specifically designed acoustic lens.

51. Ultrasound Modes
A Mode presents reflected ultrasound energy on a single line display. The strength of the reflected energy at nay particular depth is visualized as the amplitude of the waveform.
B Mode converts A Mode information into a two dimensional grayscale display.
C Mode is a color representation of blood flow velocity and direction.
D Mode is a spectral representation of blood flow velocity and direction.
P Mode is used to visualize very low blood flows in color. Unlike C Mode, this mode does not show the operator flow direction.
Triplex is the simultaneous operation of B Mode, C Mode and D Mode.
M Mode is a scrolling display allowing the operator to view and record organ motion.

53. Axial Resolution Another concern is Resolution.
Axial resolution is corresponds directly to the wave length characteristics of the Ultrasound wave. As frequency increases wave length shortens allowing for greater resolution. What we loose is penetration. Again as frequency increases penetration decreases. Higher frequencies also provide finer tissue grain or smoothness. A less grainy look.

55. Lateral resolution
In simple ultrasound systems Lateral resolution is attributed to physical focus characteristics of the crystal element. The concaved shape of the element provides focus to the beam and the width of the beam at any particular point effects the ability of the ultrasound system to resolve small objects that are side by side.

57. Transverse resolution
Transverse resolution is unique to the phase array probe. It is the ability of the probe to resolve objects side by side, as in lateral resolution, but in this case it is measured transverse to what would be considered the normal imaging plane. Again this is assuming simplest probe construction.

59. Contrast Resolution
The ability of the system to resolve adjacent bright reflectors is called contrast resolution. This is in small part due to the cumulative effects of axial and lateral resolution. The systems scan converter plays a large role is this characteristic.

61. Diagnostic Ultrasonography
Displaying Monitor
Transducer / Probe
Keyboard
Probe Connector
Printer (B/W & Color)

62. Piezoelectric property
TRANSDUCERS
Device that can change one form of energy into another.
Piezoelectric property
Electrical excitation into motion and pressure.
Piezoelectric material
The necessary element for generating acoustic waves.

63. Piezoelectric effect + - (A) (B) (C) + + + + + + + + +
(A)
(B)
(C)

64. Transducer Design

69. Echoes from Two Interfaces

70. Echoes from Internal Organ

71. DISPLAY TECHNIQUES
A- mode
M- mode
B- mode
Doppler
Pulsed
Continuos

72. Saw tooth voltage sweep
1) A- mode
Amp H. V
CRT
Transducer
Organ
Body
T/R
switch
Trigger
Pulser
Time variable gain
Saw tooth voltage sweep
Block diagram of an A-scan instrument. A pulser circuit triggers the transducer, and the saw-tooth generator. The T/R switch isolates the receiver amplifier during transmission. Amplitudes of the received echo signals are presented on the vertical axis of the CRT.

73. 2) B-mode
Brightness modulation
CRT
Time variable gain
Vert.
Amp
Horiz.
Pulser circuit
Beam steering control unit
T/R
switch
Saw tooth voltage sweep
A pulser circuit triggers the transducer, and the saw tooth generator. The T/R switch isolates the receiver amplifier during transmission. For each scanning line, the amplitudes of the received echo signals are modulated to brightness. Steering unit is controlling the synchronization process.

74. Sawtooth voltage sweep
3) M- mode
Slow voltage ramp
CRT B
Time variable gain
Vert.
Amp
Horiz.
Pulser circuit
Sawtooth voltage sweep
T/R
switch
Trigger
Body B A
Fixed organ
Transducer
Moving Organ

75. TRANSDUCER MODES
TRANSMITTER
RECEIVER
PULSED
CONTINUES

76. TRANSDUCERS TYPES
1) Linear array

77. TRANSDUCERS TYPES
2) Sector
3) Convex

80. Linear Probe Image

81. Sector (Phased array) Probe

82. Convex Probe Image

83. Real Time 3D

84. Fetal Spine

85. Reconstructional 3-D
Obstetrics

86. Ultrasound Machines

87. Ultrasound Machines Function
Diagnostic ultrasound machines are used to give images of structures within the body. This chapter does not deal with other kinds of machine (e.g. therapeutic and lithotripsy). The diagnostic machine probes, which produce the ultrasound, come in a variety of sizes and styles, each type being produced for a particular special use. Some require a large trolley for all the parts of the unit, while the smallest come in a small box with only a audio loudspeaker as output. They may be found in cardiology, maternity, outpatients and radiology departments and will often have a printer attached for recording images. Unlike X-rays, ultrasound poses no danger to the human body.
How it works
The ultrasound probe contains a crystal that sends out bursts of high frequency vibrations that pass through gel and on through the body. Soft tissue and bone reflect echoes back to the probe, while pockets of liquid pass the ultrasound straight through. The echoes are picked up and arranged into an image displayed on a screen. The machine offers a number of processing options for the signal and image and also allows the user to measure physical features displayed on the screen. This requires the machine to incorporate a computer.

93. How TO CHOOSE TRANSDUCER
1) FREQUENCY
2) SCANNING ANGLE
3) RADIUS or LENGTH

94. WHAT TYPES OF EXAMINATION ARE TO BE CARRIED OUT ?
WHAT WE HAVE TO KNOW BEFORE PURCHASING A G.P.U.S
WHAT TYPES OF EXAMINATION ARE TO BE CARRIED OUT ?

95. 1. TRANSDUCER
* Curvilinear or combination of linear and sector.
2. FREQUENCY
* Standard transducer should have central frequency of 3.5 MHz.
3. ANGLE for Sector probe should be 40 or more, linear array should be cm long.
4. FRAM RATE… Hz for linear array,
Hz for sector array.
5. FRAM FREEZE DENSITY… at least 512*512*4 bits to provide 16 gray levels

96. 6. ELECTRONIC CALIPERS… one pair at least, with Quantitative readout.
7. ADD DATA IS POSSIBLE… patient identification, hospital name, date of examination… etc.
8. HARD COPY… should be possible.
9. MONITOR… at least 13 cm * 10 cm (preferably larger)
10. STABILIZING… should be able to stabilize voltage variation of +/- 10%.
11. Biometric tables… (it may not be universal and should be adjusted for local standards.

97. WHEN WE RECEIVE THE SCANER
WHAT WE HAVE TO CHECK
WHEN WE RECEIVE THE SCANER
SERVICE MANUAL
USER’S MANUAL

98. Checking every instruction in the manual may takes time.
But if you do so,
you will save time, money, and frustration.

99. CHECK LIST
1. Voltage setting should be compatible with the electrical supply.
2. Interference on the screen/ whit sparks.
3. Transducer and cables test.
4. Check the cursor / measuring length, …
5. Check the accessibility of the biometrics or measurement tables.

100. IMAGE ARTIFACTS
Any missing or distorted image that does not match the real image of the part being examined

101. Acoustic characteristics of the tissues. Scanner’s settings.
ARTIFACT'S CAUSES
Acoustic characteristics of the tissues.
Scanner’s settings.
Lack of user’s experience.
Defected part within the scanner.

102. To confirm any suspected abnormality,
Use multiple projections at different angles
COMMON ARTIFACTS:
Cyst’s artifact (strong back-wall effect).
Abdominal wall artifact.
Gas artifact.
Reverberation artifact.
Incomplete imaging artifact.
Gain artifact.
Shadows artifact.

103. DAILY CHECKS "visual" Visually inspects all transducers.
“Cable, cracked surface, punctured, discolored casing”
Visually inspect the power cords.
Verify that the trackball and DGC controls appears clean and free from gel or other contaminants.
Once the system is powered on:
Verify that the monitor displays CORRECTLY the connected transducer’s identification, current date, time.

104. DAILY ADJUSTMENT FOCUS. DEPTH GAIN COMPENSATION. OVERALL GAIN. ZOOM.
MONITOR (B/C).

105. CLEANING AND DISINFECTING
TRANSDUCERS
Linear, convex, …..
Endocavity, interoperative, …
MAIN UNIT
Surface of the system.
DGC slides control.
Trackball.
Unit filters.