This document discusses the basic physics and settings of endoscopic ultrasound (EUS) systems. It covers the properties of ultrasound waves, how they propagate and are affected in different media like tissues. It describes transducer characteristics, imaging principles including resolution, scanning, Doppler and common artifacts. Key points are that EUS uses high frequency sound waves (5-30 MHz) for detailed imaging, linear array transducers allow electronic focusing, and imaging is affected by factors like impedance and scattering in tissues.

1. BASIC PHYSICS & SETTING OF
EUS SYSTEM
MR.PRIYARANJAN DAS (OLYMPUS)

2. Basic Properties Of Ultrasound Waves
• Ultrasound- a form of
mechanical energy,
• Propagation occurs in the
form of vibrations in a
medium.i.e displacement &
oscillations of atomic
particles.
• A sinusoidal wave.
• Medical applications-1to
50MHz but in EUS (5MHz –
30MHz)

3. Basic Properties Of Ultrasound Waves
• Velocity=wavelengthx frequency
• Velocity depends on physical
properties of the medium-density &
compressibility.
• Acoustic waves of different
frequencies propagate with the same
velocity in a single medium

4. Properties Of Medium
• Density
• Compressibility
• Bulk Modulus
• As Density increases,
compressibility decreases &
bulk modulus increases

5. What happens to ultrasound in
tissues
• Short pulses of US are
transmitted into the tissue &
reflected tissues are received.
Undergoes:
Reflection.
Refraction
Scattering
Absorption
• Acoustic Impedance: resistance
to sound propagation.
• Impedance=density x velocity

6. SCATTERING
• Scattering: occurs when US wave
interacts with small components in
tissue that are smaller than the
wavelength than incident waves and
different impedance values.
• Eg: individual cells, fat, collagen
• Responsible for different echotextures
of organs.
• Fat: high scattering; appears brighter,
due to multiple reflections

7. THE EUS MACHINE & EQUIPMENT
• Transducer:A device which
converts electrical energy into
mechanical energy and sends as
ultrsound pulses into tissue
• The back received signals are
picked up by the receiver built
in the transducer and sent to
processor which generates real
time images.

8. Linear Array Transducers
• Multiple single element transducers
can be combined to form an array
which gives focussing at different
depths,
• they can be fired individually or in
groups.
• Allows electronic focussing at
different depths

9. Processor Characteristics
• Depth of interface(D)=
VxT/2
• Amplification of output can
be adjusted by
1. GAIN-increasing the
overall gain which
increases the amplitude
of all received echoes but
at the expense of
resolution.
2. TGC: allows selective
amplifictaion of weaker
echoes from deeper
structures

10. IMAGING PRINCIPLES
RESOLUTION
• SPATIAL (X-axis -Axial, Y-axis - Lateral & Azimuthal Angle – Z-axis which is
Manufacturer dependent and fixed)
• TEMPORAL (Depends on FR, FW, Depth) – Function of time.
• CONTRAST
8-Bit Processor(256 shades of grey viz. as Dynamic Range.
CT has 10-Bit processing so gives higher resolution of B-Mode Imaging.

11. IMAGING PRINCIPLES
• RESOLUTION:
• Axial: smallest seperation
distance between two
objects that can be detected
along the beam.
• Determined by spatial pulse
length(SPL)-the length of
time the ultrasound pulse
occupies in space
• SPL =velocity/frequency x n.
• The limit of axial resolution is
SPL/2.

12. High Vs Low Frequency

13. IMAGING PRINCIPLES
• RESOLUTION:
• Lateral:
• Ability to discriminate
between two objects in a
perpendicular plane to that
of beam
• Depends on focusing of the
transducer;highly focused
transducer has narrow beam
width

14. Scanning
• A Mode Scan: Amplitude
Mode gives radiofrequency
wave patterns.
• Rarely used clinically.
• Forms the basis for other
modes.
• B Mode:-Brightness mode.
• Created by processing a
series of A mode signals-
resulting in a compound B
mode image.

15. DOPPLER
• Is used to identify objects that are
in motion relative to transducer.
• An object in motion will reflect a
wave that is of different
frequency; this is called doppler
shift.;this depends on velocity of
moving object.
• Greatest shifts detected when
transducer is aligned to flow
direction(Cos0 or Cos180)

16. Doppler
• Continuous doppler is used for recording high
velocities
• Pulse doppler is used for depth acuity
• Color doppler is like pulse doppler.
• Blood flow towards the transducer-Red.
• Flow away from the transducer-Blue.
• High velocities-turblant flow-green hue-mosaic
pattern
• Power doppler: determines the strength of doppler
signal discards info on velocity or direction.
• H-Flow : most sensitive for detecting blood flow
(Minute blood vessels visualization possible near
pancreatic region for better ROI targeting to collect
FNB/FNAC through EUS needle)

17. Imaging Artifacts
• Reverberation: Single transmitted
pulse undergoes multiple reflections
from a strong reflector,received by
transducer-reflected back.
• Identified by equal spacing between
hyperechoic bands

18. Reverberation Artifact

19. Acoustic Shadowing
• Large impedance encounter
• Majority is reflected and no
echo is detected beyond the
interface.
• Useful in detecting
calcifications.

20. Acoustic Shadowing
• Also seen due to refraction at a
boundary between tissue with
different velocities.-tumor or
cyst.
• Because of bending of the beam
some amount of tissue is not
visible-

21. Reflection-Mirror Imaging
• Occurs when imaging
near an airwater
interface such as
lumen partially filled
with water.
• Becuz of significant
impedance mismatch
the transmitted pulse
is reflected multiple
times.
• can be avoided by
removing air

22. Through Transmission
• Enhancement of a structure
beyond a fluid filled structure
such as cyst.
• Due to less attenuation of the
wave as it passes through the
cyst.
• Seen with cyst or blood vessel.

23. Tangential Scanning
• To accurately measure the
thickness of a strucure the
transducer should be
perpendicular to the structure.
• Tangential scanning results in over
estimation of thickness.
• Importance lies in staging of GI
cancers
• On radial EUS this can be
identified.
• Tip maneuvering should be done

24. Side Lobe Artifacts
• Off axis secondary projections of US
beam.
• They are of low intensities but still can
produce weak echoes but usually are
obscured by on axis high intensity beam.
• But while viewing anechoic structures
these atrifacts become manifest.
• Disappears with repositioning the
transducer.
Harmonics utility is helpful to eliminate
the side lobe artifacts or reverberation
by increasing SNR which results in
increasing resolution of B-Mode imaging
drastically.