Development of an Ultrasound Lab

1. Development of an Ultrasound Lab Laura Wade April 4th 2012 3970Z

2. 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.

3. 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)

4. 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

5. 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

6. PulseWave 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.

7. 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

8. 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.

9. 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

10. 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.

11. 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.

12. A 38-element linear array transducer is used • Uses frequency of 5MHz • Sonosite 180

13. Measurements and Calculations • Flow in the right carotid before and after the carotid bifurcation using PWD. • A1v1 = A2v2

14. Cardiac Output (CO) • Measure peak systolic velocity and end diastolic velocity. • Calculate Volume Flow Rate (CBF) • Use known relationship to calculate CO

15. Cerebral Blood Flow (CBF) before and after exercise and/or mental activity • Volume Flow = Area * Velocity

16. 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.

17. 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

18. Sources of Error • Inaccurate measurement of cross sectional area. • Inaccurate angle correction. • Noise

19. 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?

20. Acknowledgements I would like to thank: • Dr. Ian MacDonald, Supervisor • Michelle Belton, Lab Manager

21. Thank you for your time. Any Questions?