ECE 501 Introduction to BME Dr. Hang

Part VI Medical Imaging Diagnostic Ultrasound Imaging ECE 501 Dr. Hang

Introduction Ultrasound Imaging System Physics of Ultrasound Dr. Hang ECE 501 Dr. Hang

Physics of Ultrasound What is Sound? Sound is a wave, i.e. traveling variations of pressure. It involves mechanical motion in the medium through which it travels Pressure variations cause particles of the medium to vibrate due to increase and decrease of density. ECE 501 Dr. Hang

Physics of Ultrasound What is Ultrasound? Pressure waves with frequencies higher than 20 KHz, higher than audible range of human beings. Harmless unless very high intensities are used. ECE 501 Dr. Hang

Physics of Ultrasound Pulsed Ultrasound Emitted from transducer ECE 501 Dr. Hang

Physics of Ultrasound Resolution of Typical Ultrasound Scanner Center frequency f0: 2-10 MHz Speed of sound in tissue C: 1540m/s Wavelength λ = C/f0 ECE 501 Dr. Hang

Physics of Ultrasound How to Get Positional Information? Range equation: ECE 501 Dr. Hang

Physics of Ultrasound Wave Propagation Absorption: main factor that contributes to attenuation Reflection & Scattering: essential to create an image but contribute little to attenuation. Refraction ECE 501 Dr. Hang

Physics of Ultrasound Acoustic Impendence Density of medium Speed of sound in the medium ECE 501 Dr. Hang

Physics of Ultrasound Reflection Reflection Factor: Transmission Factor: ECE 501 Dr. Hang

Physics of Ultrasound Oblique Incidence ECE 501 Dr. Hang

Physics of Ultrasound Scattering Specular scattering Diffractive scattering Diffusive scattering ECE 501 Dr. Hang

Physics of Ultrasound Attenuation Scattering 20% Absorption (conversion of wave energy into heat) 80% Linear function of frequency: high frequencies are more attenuated than low frequencies ECE 501 Dr. Hang

Physics of Ultrasound Doppler Effect fD: Doppler shift frequency f0: transducer frequency v: blood moving velocity c: sound speed ECE 501 Dr. Hang

Ultrasound Imaging System Transducer An array of Piezoelectric crystal/ceramic Deforms when a voltage is applied and transmits acoustic waves Electrical charge is created by the mechanical of deformation ECE 501 Dr. Hang

Ultrasound Imaging System Transducer Appropriately delayed pulses are transmitted from an array of piezoelectric elements to achieve steering and focusing at the point of interest. The echoes returning are likewise delayed before they are summed together to form a strong echo signal from the region of interest. ECE 501 Dr. Hang

Ultrasound Imaging System Transducer ECE 501 Dr. Hang

Ultrasound Imaging System System Diagram ECE 501 Dr. Hang

Ultrasound Imaging System TGC (Time Gain Compensation): amplifies the returned signal in proportion to depth or the time required for the signal to return ECE 501 Dr. Hang

Ultrasound Imaging System Demodulator: Removes the carrier frequency Hilbert transform (for our project) ECE 501 Dr. Hang

Ultrasound Imaging System Echo processing: Magnitude: Envelope detection LOG Compress: reduce the range from 12 bit to 8 bit ECE 501 Dr. Hang

Ultrasound Imaging System Scan conversion: Interpolation ECE 501 Dr. Hang

Ultrasound Imaging System Spectral Doppler: Short Time Fourier Transform (spectrogram) ECE 501 Dr. Hang