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Lecture 20 US_imaging_diagnostic_BME100

Lecture 20 US_imaging_diagnostic_BME100 - Quantitative...

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Quantitative Imaging Ultrasound for Characterization of Bone Quality Yi-Xian Qin, Ph.D. Orthopaedic Bioengineering Research Laboratory Department of Biomedical Engineering Stony Brook University BME 100 Lecture, 2011 Electromagnetic Spectrum 1 eV = 1.602 x 10 -19 J Ultrasound EM spectrum Radio microwave Visible, and UV X-ray, and Gamma Basic Engineering: What is sound (ultrasound)? Ultrasound is classified as sound waves possessing high frequency. Sound (ultrasound) is a mechanical vibration propagating in a fluid or a solid medium. Can ultrasound travel through vacuum? Electromagnetic wave propagation Wave propagation Wave velocity c Vibrations of particles—elastic wave or pressure wave Wave propagation (2) Compression/longitudinal waves Shear wave Tissue/cell interactions Attenuations in longitudinal and shear waves
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Frequency – period - wavelength Wave motion is defined by o Frequency f o Period T o Wavelength λ λ = c / f = c T Ultimate resolution capability Ultimate resolution of tissue (c = 1500 m/s) R mm = 1.5 / f MHz Soft tissue : 0.70 mm at 2.25 MHz 75 micron at 20 MHz Cortical bone : ~3 mm at 1 MHz (c ~ 3000 m/s) Cancellous bone : ~1.5 mm at 1 MHz (c ~ 1400 m/s) Velocity of ultrasound Wave propagation velocity c (speed of sound) Elastic modulus M Unperturbed density ρ In a longitudinal elastic wave in an infinite isotropic homogenous solid body (E: Young’s modulus, σ : poisson ratio) V = (M / ρ ) 1/2 V = {E(1- σ ) / [ ρ (1+ σ )(1-2 σ )]} 1/2 Osteoporosis -- Extent of the Health Problem U.S.: 15 million with osteoporosis, and 34 million with osteopenia [1] A woman’s risk of hip fracture = breast + uterine + ovarian cancer National direct expenditures = $18 billion/year (2001) After age 50: 50% of women, and 25% of men will have a fragility fracture 24% 1-year mortality post fracture 25% require long-term care Clinical consequences [2] : Increased kyphosis Loss of height Difficulty ambulating Chronic pain – Depression Increased risk of future fractures [1] NOF.org (2003); [2] osteofound.org (2003); Image from osteofound.org.
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