Development of an Ultrasound Lab

Laura WadeApril 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?