Medical Imaging Physics Spring Quarter Week 3-2

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1 Medical Imaging Physics Spring Quarter Week 3-2 Ultrasound Daor Balzar

2 Outline Ultrasound Light, Eyes and Vision Reading assignment: CSG 12; D 15 Homework D 12: 5,6 and Add. problems Due Tuesday, Apr 15 CSG 12: 1,2,11,14,15; D 15: 8 Due Tuesday, Apr 22

3 Sound in Animal World Bats -- different species. The Vespertilionidae family: Short chirps (3 ms in duration with a spacing of 70 ms) As a bat gets closer to an object, both time interals gradually shortened down to 0.3 ms and 5 ms Frequency aries during single chirp (100,000 Hz-30,000 Hz) Most bats can detect wires as thin as 0.1 mm Sounds produced by other animals Sea mammals => sonars What about insects or the rattlesnake?

Ultrasound We hear only certain frequencies: 16-20 Hz 20 khz Ultrasound: aboe 20 khz 2-20 MHz used in medicine for diagnostic purposes Imaging of the body, examining

4 Ultrasound We hear only certain frequencies: Hz 20 khz Ultrasound: aboe 20 khz 2-20 MHz used in medicine for diagnostic purposes Imaging of the body, examining the fetus,... Technique: Pulse-echo (sonar) Transducer Imaging of reflecting surfaces Normally interfaces between different tissues Fluid moement (blood) Doppler effect

5 Resolution Resolution (leel of anatomical detail) Depends on frequency High frequency short waelength Short waelength => short pulses

6 Ultrasound Pulse Pulse elocity Depends on the medium Material Fat Water Soft tissue (aerage) Bone Velocity (m/sec) Measured distances An assumed elocity of 1540 m/sec Distances not always accurate!

Intensity Intensity has to be considered with respect to biological effects and safety About few mw/cm 2 Relatie intensity Relatie Intensity (ratio) = I2 / I1 Relatie Intensity (db) = 10 log / ( I I

7 Intensity Intensity has to be considered with respect to biological effects and safety About few mw/cm 2 Relatie intensity Relatie Intensity (ratio) = I2 / I1 Relatie Intensity (db) = 10 log / ( I I ) 2 1 Sound pulse has to be aeraged both oer time and space if the aerage (as opposed to peak) intensity is considered Thermal effects: Depend on spatial-peak and temporalaerage intensity Mechanical effects (ibrations): Depend on spatial-peak and pulseaerage intensity

$conerted into heat Scattering and refraction Attenuation α I fx = I 0 e$

8 Interactions of Ultrasound with Matter Ultrasound pulse interacts with tissues Absorption causes attenuation Implies loss of ultrasonic energy Some energy conerted into heat Scattering and refraction Attenuation α I fx = I 0 e Attenuation (db) = α fx α attenuation coefficient (db/cm at 1 MHz) f frequency x tissue thickness

9 Attenuation Water Good conductor of ultrasound Bones High attenuation rate shields from looking at some parts of the body Lungs High attenuation rate Air in aleoli scatter ultrasound waes Muscle Range of alues depending on the direction relatie to the muscle fibers

10 Reflection Interaction that creates the image Occurs at the interface between dissimilar materials Acoustic impedance is important Z = ρ Only a portion of the pulse is reflected Reflection loss (db) = 20 log (Z2 - Z1 )/(Z2 + Z1 )

11 What Do You See?

12 Similar To

13 What s Important?

14 The Doppler Effect We are familiar with the fact that a frequency of a moing sound depends on the direction of moement. Approaching ehicle s (train, car, ) siren changes frequency after passing by Applies not only to sound waes The Doppler effect Stationary source, moing obserer Speed of sound Obserer s speed D D Obserer Relatie elocity = + D Normal source Pressure maxima are spaced by λ

15 The Doppler Effect/2 Frequency is different for the obserer f + = = D λ λ f = λ f = f + D If obserer is moing away f = f D General solution f ± = f D + toward; - away D = 0 f = f

16 The Doppler Effect/3 Source moing, stationary detector Speed of sound Source speed S S Relatie elocity = S Apparent waelength changes f f = S Obserer λ = = S f = f f λ Moing source Pressure maxima are not spaced by λ D

17 The Doppler Effect/4 If source is moing away f f = + General solution f = f General Doppler-effect equation Both source and detector are moing ± f = f D S S S - toward; + away = 0 f = f S Choose the sign to increase the frequency if moing toward and ice ersa

18 Human Body

19 Other Ultrasound Uses Potential problems with ultrasound uses for diagnostics: Vibrations? Oerheating? Other uses: Local heating of tissues Relieing pain and promoting healing Destroying kidney and gall stones

20 Light, Eyes, and Vision

10 22 f 10 21 10 20 10 19 10 18 10 17 10 16 10 15 10 14 10 13 10 12 10 11 10 10 10 9 10 8

Electromagnetic Spectrum X-rays Ultra Violet ~ 380 nm - 0.

21 10 22 f gamma rays TV, FM Other Bands λ 1 Å 1nm 1μm 1mm 1cm 1m 1km Electromagnetic Spectrum X-rays Ultra Violet ~ 380 nm nm Visible Light ~ 400 nm 700 nm Infrared ~ 700 nm - 1mm Microwaes Radio Waes c = λ f Energy: E = hf Photons (particles) of energy E

22 Electromagnetic Wae Electromagnetic wae speed 1 c = = με EM wae propagates ia: m/s Changing electric field generates magnetic field and ice ersa Two fields are perpendicular E = E sin kz ωt x 0x ( ) ( ) By = B0 ysin kz ωt Wae propagates in z-direction E c B = 1 c μ0ε 0 ω = = λ f = c k Speed of light E B c Transerse Wae E B direction

23 Vision The sense of ision: Eyes focusing light on the retina Optical neres Visual cortex The eyes can operate oer a range of light intensity of :1 Eye focusing: Cornea and lens The retina: Conerts light images into electrical nere impulses Most ision restricted to the foea centralis within the yellow spot

24 Eye Accommodation The focusing is controlled by the ciliary muscle Muscle relaxed => the lens flat => parallel beam focused at the retina Eye is focused for distant objects (about 6 m and beyond) Closer objects require stronger focusing => the lens is cured The near point of the eye (the minimum distance of sharp focus) Depends on age (7 cm at 10 years -> 100 cm at 60) Aperture and Depth of Field Iris controls the aperture The smallest aperture gies best image quality Imperfections around the lens edges Image disk for poorly focused objects smaller Depth of Field better» The range of object distances with good image for gien focus

25 Next Time Finish Eyes and Vision

Structure of Biological Materials

ELEC ENG 3BA3: Structure of Biological Materials Notes for Lecture #19 Monday, November 22, 2010 6.5 Nuclear medicine imaging Nuclear imaging produces images of the distribution of radiopharmaceuticals