Pulse Echo Imaging

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Pulse Echo Imaging
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Pulse Definition

• A collection of ultrasound waves emitted by the
  transducer as a single unit that travel
  together

Schlerien Photography
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Range Equation
Formula

• D VT

where d distance v velocity t time
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Range equation
Calculate the depth of a reflector that requires
13 ?s for round trip travel in the body.
D VT V 1540 m/sec, (.00154 m/?sec) T 13 ?s
  D (.00154 m/?s) x 13 ?s D .02 m D 2
cm (round trip time) ? 2 D 1 cm
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Range equation
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Pulse Wave Parameters

• Pulse duration
• Spatial pulse length
• Pulse repetition period
• Pulse repetition frequency
• Duty factor

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Pulse Duration

• The amount of time from the beginning to the end
  of a single pulse of ultrasound.
• The amount of emission or sound ON time and
  varies with the number of cycles emitted and the
  period of each cycle

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Pulse Duration
Formula
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Spatial Pulse Length

• Spatial pulse length is the length of a single
  pulse in space.
• Determined by the wavelength (?) of a single
  wave, which is a distance measurement, and the
  number of cycles per pulse

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Spatial Pulse Length
Formula
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Pulse repetition frequency (PRF)

• The rate at which the system will pulse the
  transducer.
• Defined as the number of pulses that occur in a
  single second

? IMAGING DEPTH ? ?PRF ? IMAGING DEPTH ? ? PRF
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Pulse repetition period (PRP)

• The amount of time from the start of one pulse to
  the start of the next pulse.
• Includes both the sound ON time and the sound
  OFF time

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Pulse repetition period (PRP)
Formula
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Duty Factor

• The proportion of time that the ultrasound
  transducer is actually producing sound energy.
• It is the ratio between pulse duration (sound ON
  time) and PRP (sound ON and sound OFF time).
• In most sonographic imaging systems it averages
  between 1 and 2.

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Duty factor
? PRP ? ? DUTY FACTOR ? PRP ? ? DUTY FACTOR
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Real-time Scanning Basics
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Definition

• An automated B-scan imaging process that permits
  the display of echo information as it is received
  by the transducer.
• The rapid display of a series of single, static
  images that produce the illusion of motion

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General considerations
Differences over static imaging techniques
include

• Demonstration of motion
• Anatomical surveying
• Optimizing imaging windows

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Demonstration of Motion

• Respiratory motion
• Vascular motion
• Bowel motion
• Fetal motion
• Cardiac motion (echocardiography)

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Anatomical Surveying

• Large areas rapidly surveyed
• Lay of the land
• Reduce overall examination time
• Optimize imaging parameters
• Tailor study for each patient

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Optimize Imaging Windows

• Optimal image quality depends on angle of
  insonation.
• Optimize specular reflections
• Allow free and subtle adjusment of imaging angle
  and orientation
• Operator mastery of transducer movements is
  essential.

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Real-time probes - transducers
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Real-time transducers

• Mechanical sectors
• Electronic probes
• Sequential linear array
• Phased array
• Linear
• Convex
• Sector

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Mechanical Sector

• Single crystal
• Use motor to move crystal or other probe parts.

Oscillating crystal
Oscillating mirror
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Mechanical Sector
ATL c.1980
Toshiba 1974
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Mechanical Sector
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Mechanical sector
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Electronic (phased) probes

• Multiple crystals (elements)
• Electronic timing of crystal firing produces a
  sweep of the beam

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Electronic probes
SEQUENTIAL LINEAR ARRAY
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Electronic probes
SEGMENTAL LINEAR ARRAY
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Electronic probes
CONVEX SWITCHED ARRAY
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Annular Array
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Phased Array

• Beam geometry and field of view vary based on
  timing sequence of crystal excitation

Linear array
Convex array
Sector
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Dynamic Focusing
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Beam steering
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Beam steering
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Image creation

• Each image consists of many lines of sight

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Image formation

• Each line of sight consists of many pixels

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Pulse listen time
PLT pulse listen time FOV field of view
(depth in cm)
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Frame time
PLT pulse listen time n number of lines
of site
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Frame rate
FT frame time
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Image formation

• Many single images are displayed in 1 second to
  produce motion
• Frame rate frames /second
• Flicker fusion rate (minimum 25 fps)