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?