Physics Safety

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PhysicsSafety Infection ControlSetting Up The
Machine

• H. Gee MD, FRCOG
• (teaching materials provided by David Cole,
  Lecturer at City University, Birmingham)

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Sound
WAVELENGTH ?

HIGH PRESSURE REGION
LOW PRESSURE REGION
ONE CYCLE
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A sound wave
wavelength
Excess pressure
amplitude
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Amplitude Frequency

• Frequency
• Pitch
• Amplitude
• Loudness
• the strength of the sound.
• The maximum change in pressure due to the
  soundwave

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Ultrasound
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Ultrasound

• High Frequency Sound
• gt 20 KHz (above the audible range)
• Short Wavelength
• Resolution ? Wavelength
• 3.5 MHz - Wavelength .44 mm
• Frequency ? Penetration ?

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Spatial Resolution

• The ability to display two small structures
  situated close together as separate images

objects
Image resolved
Image unresolved
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Piezo-electric effect

• Sound ? Electricity

Piezo-electric crystal
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Inverse piezo-electric effect

• Electricity ? Sound

Piezo-electric crystal
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Ultrasound transducer
PULSE
CONVERTS ELECTRICITY INTO SOUND
PIEZO ELECTRIC CRYSTAL
ECHO
CONVERTS SOUND INTO ELECTRICITY
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Pulse echo techniquemultiple reflectors
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Imaging Principles
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Imaging Principles
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How the image is produced
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Summary

• Sound
• Ultrasound
• Piezo-electric effect
• Pulse-echo technique
• Imaging principles
• Resolution

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Infection Control
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Setting up the Machine

• Two Parts
• Monitor (may be done automatically)
• Contrast
• Brightness
• Grey Scale on Screen ALL GRADATIONS
• Imaging System

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(No Transcript)
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Equipment Controls

• Probe selection
• Mode selection 2D, Doppler, Colour
• Gain, TGC, Power
• Depth and Zoom Scan angle (field size)
• Focus
• Measurement, freeze
• (Examination selection post processing)

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Probe selection

• This control is used to select from the probes
  available
• For example
• Curvilinear general
• Transvaginal
• Linear array for small parts

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Mode selection 2D, Doppler, Colour

• 2D is normally selected automatically for all
  examinations and the other modalities are
  selected when required during the examination.

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Making the image darker or brighter

• Power
• Gain,
• Time Gain Compensation

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Safety

• Cavitation
• Heating

• Frequency
• Duration
• Intensity
• Power

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Power (Output) increased
Safety implications Set power to 35 Use gain to
control brightness
BRIGHTER IMAGE
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Power reduced
DARKER IMAGE
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Gain

• Controls image brightness by amplifying echo
  signals
• Completely safe

• Increased image noise

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Gain
INCREASE IN GAIN MORE NOISE
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Time gain compensation (TGC)
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Time gain compensation (TGC)
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Time gain compensation (TGC)
TGC correct
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Changing the field size

• The following controls change the size of the
  field of view
• Depth
• Zoom
• (Scan angle)

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Freeze

• Measurement
• Image recording

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Measurement

• Electronic callipers
• Linear
• Circumference / area
• Ellipse / trace
• Volume measurement
• Organ specific
• Embedded charts

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Summary

• Probe selection
• Mode selection 2D, Doppler, Colour
• Depth and Zoom Scan angle (field size)
• Gain, TGC, Power
• Focus
• Measurement, freeze ( cine loop)
• (Examination selection post processing)

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Important Controls

• Power (output, acoustic)
• Gain
• Time gain compensation (TGC)
• Freeze
• Electronic calipers