生医工程实验期报告Ultrasound.pptVIP

生醫工程實驗 期中報告 Ultrasound Apr. 2’ 2007 第一組： 郭昱昇 溫仁揚 溫昌懌 Outline History Principles Characteristic Applications History Principle – Transducer Piezoelectric Principle – Focusing Lateral Resolution = D = depth, W = wavelength, A = Aperture F number, F# = Ex: f=5Mhz, A = 2cm, V = 1500 m/s In depth 4 cm, resolution = Principle – Focusing (cont’d) Improve larger aperture higher frequency (shorter wavelength) multiple focusing dynamic focusing Principle – Focusing (cont’d) Improve larger aperture higher frequency (shorter wavelength) multiple focusing dynamic focusing Principle – Focusing (cont’d) Improve larger aperture higher frequency (shorter wavelength) multiple focusing dynamic focusing Principle – Effects : Attenuation The loss of energy in tissue: f : frequency, z: depth , a0 :attenuation coefficient of medium , typically n=1 Non-linearity Assuming p was only a tiny disturbance of static pressure With increasing acoustic pressure , the wave changes shape Principle – Speckle Coherent Imaging system Interference of scatterers Principle – Speckle Scatter size (radius a) Wavelength (λ) Wave number K=2π/λ Optical : ka1 Rayleigh : ka1 Oscillatory : between Principle – Speckle Principle – Speckle Soft tissue : less than 100μm Independent of scattering structures Dependent of imaging system、distance Principle – Speckle Let A be signal received from scatterer with phase θi , we have: If N→∞ , Re{ A } and Im{ A } are asymptotically Gaussian. Joint probability density function: Principle – Speckle Intensity I≡ Re{ A }2 +Im{ A } 2 Principle – Speckle Define: I0 is an arbitrary reference signal Expand f: Ignoring R , we have Characteristic Modes A mode B mode M mode Color Doppler mode Acoustic impedance Characteristic – Modes A mode B mode M mode CPD Applications Diagnostics Therapy 3D 4D Strengths of Ultrasound It images muscles and soft tissues well It’s “Live” Non-invasive It has no known long-term s