Transcript Development of an Ultrasound Lab

Development of an Ultrasound
Lab
Laura Wade
April 4th 2012
3970Z
Introduction
• Piezoelectric – an alternating voltage across
the crystal causes it to flex and contract,
emitting sound.
• Piezoelectrics also generates alternating
voltage in response to a returning sound
wave.
• It emits sound waves and receives them.
• Speed of sound depends on compressibility of
a material
• Acoustic Impedance (Z) is a measure of
resistance to sound waves.
• Large differences in Z create strong refections
(signals)
• B Mode Imaging
• Produces a 2D grayscale
Image.
• Brightness is proportional to amplitude of the
reflected sound waves.
•The time at which the
signals are received
indicates depth.
c= 2D/t
• Colour Doppler
• Velocity information is represented by colour and is
overlaid onto a 2D B-Mode image.
• Velocity is determined using the Doppler effect:
Δf = 2f0 (v/c) cosα
• Pulse Wave Doppler:
velocity is measured at a specific depth, which
can be adjusted
• Continuous Wave Doppler:
measures all velocities along the ultrasound
beam. It provides no information about depth
of the signal.
Colour Power Doppler:
• Displays the amplitude of the frequency shift.
• Amplitude is a function
of the number of reflectors
(RBCs) with that velocity.
• Colour is still used to
determine direction
Objectives
• Develop an experiment using sonography to
measure blood flow in the carotid artery.
• Develop a complete set of instructions for the
operation of the equipment as it applies to
this lab.
• Determine a way to analyze the data acquired
from the sonographs.
Approach
• Research the theory behind ultrasound
• Master the technical systems to be used in the
lab
• Research possible parameters and treatments
to use in the lab
• Develop appropriate protocol
Hypotheses
• Sonography can be used to verify continuity of
flow in the carotid artery.
• Increasing both physical and mental activity
will increase blood flow in the carotid arteries.
Methods
• Carotid Ultrasound
Carotid is located at a depth of
3-4cm beneath the surface of
the skin.
•Remember to calibrate the
system to the angle the
transducer is held at.
• Sonosite 180
•A 38-element
linear array
transducer is
used
•Uses frequency
of 5MHz
Measurements and Calculations
• Flow in the right carotid before and after the
carotid bifurcation using PWD.
• A1v1 = A2v2
• Cardiac Output (CO)
•Measure peak systolic
velocity and end diastolic
velocity.
•Calculate Volume Flow Rate
(CBF)
•Use known relationship to
calculate CO
• Cerebral Blood Flow (CBF) before and after
exercise and/or mental activity
• Volume Flow = Area * Velocity
Results
• CBF = ~750mL/min at rest
• Flow in the carotid before and after the
bifurcation is equal.
• CO = 5 – 5.5 L/min at rest
• Flow in the carotid is increased during both
exercise and increased mental activity.
• Paired t – test results in significance with
p<0.05.
Discussion
• Why should we incorporate this lab into the
3970Z curriculum?
– Ultrasound is covered in both 3rd and 4th year
courses
– Noninvasive, inexpensive, and therefore common
imaging technique
• Sources of Error
• Inaccurate measurement of cross
sectional area.
• Inaccurate angle correction.
• Noise
• Questions for Discussion:
– Would the effectiveness of sonography be
different for an obese patient? Why?
– Would ultrasound be effective for imaging blood
vessels in the torso?
– How could an occluded blood vessel be detected?
– What would be the effect of not using lubrication
between the skin and transducer?
Acknowledgements
I would like to thank:
• Dr. Ian MacDonald, Supervisor
• Michelle Belton, Lab Manager
Thank you for your time.
Any Questions?