intro radiation atom-2013!01!31a
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khfhTRANSCRIPT
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UW and Brent K. Stewart PhD, DABMP 1
Introduction to Medical Imaging Chapter 1*Radiation and the Atom Chapter 2*
Brent K. Stewart, PhD, DABMPProfessor, Radiology
Director, Diagnostic Physics
a copy of this lecture may be found at:http://courses.washington.edu/radxphys/r2.html
* refers to The Essential Physics of Medical Imaging, 3rd ed., Bushberg, et al. 2012
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UW and Brent K. Stewart PhD, DABMP 2
Chapters 1 & 2 Lecture Objectives
Intro to Medical Imaging what are we after technically? Contrast Spatial Resolution
Generally describe what processes are involved in the diagnostic radiology imaging chain
Describe the basic characteristics of electromagnetic (EM) radiation and how they are mathematically related
Describe how atomic electronic structure determines the characteristics of emitted EM radiation
Particulate radiation and the atomic nucleus whats the matter?
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UW and Brent K. Stewart PhD, DABMP 3
What a Nobel Path you Tread
Roentgen (1901, physics): discovery of x-radiation Rabi (1944, physics): nuclear magnetic resonance
(NMR) methodology Bloch and Purcell (1952, physics): NMR precision
measurements Cormack and Hounsfield (1979, medicine): computed
assisted tomography (CT) Ernst (1991, chemistry): high-resolution NMR
spectroscopy Laterbur and Mansfield (2003, medicine): discoveries
concerning magnetic resonance imaging (MRI)
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UW and Brent K. Stewart PhD, DABMP 4
Introduction to Medical Imaging
Medical imaging requires some form of radiation capable of penetrating tissues
This radiation must interact with the bodys various tissues in some differential manner to provide contrast
The diagnostic utility of a medical image relates to both technical image quality and acquisition conditions
Image quality results from many trade-offs Patient safety levels of radiation utilized (ALARA) Spatial resolution Temporal resolution Noise properties
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UW and Brent K. Stewart PhD, DABMP 5
MRI
Transparency of Human Body to EM Radiation
c.f. Macovski, A. Medical Imaging Systems, p. 3.
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UW and Brent K. Stewart PhD, DABMP 6
X-rays the Basic Radiological Tool
Roentgens experimental apparatus (Crookes tube) that led to the discovery of the new radiation on 8 Nov. 1895 he demonstrated that the radiation was not due to charged particles, but due to an as yet unknown source, hence x radiation or x-rays
Known as the radiograph of Bera Roentgens hand taken 22 Dec. 1895
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UW and Brent K. Stewart PhD, DABMP 7
NMR T1 for Tumor and Normal Tissue
c.f. Damadian, R, et al. PNAS 1974; 71: 1471-3.
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UW and Brent K. Stewart PhD, DABMP 8
A Systematic Approach to Medical Imaging
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X-ray Computed Tomography
XX--ray Tuberay Tube
DetectorsDetectors
CT TableCT Table
XX--ray Beamray Beam
XX--ray Tuberay Tube
DetectorsDetectors
CT TableCT Table
XX--ray Beamray Beam
9Figure from M. Mahesh, Johns Hopkins
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Other X-ray Modalities
Plane-projection radiography Fluoroscopy Mammography
UW & Brent K Stewart, Ph.D., DABMP 10c.f. http://emedicine.medscape.com/article/353833-media
c.f. http://jlgh.org/assetMgmt/getImage.aspx?AssetID=46
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Magnetic Resonance Imaging
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., pp. 426, 429 & 461. UW & Brent K Stewart, Ph.D., DABMP 11
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Ultrasound
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 501.
c.f. http://www.cs.adelaide.edu.au/~evan/project/prog1.htm 12
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Nuclear Medicine/Positron Emission Tomography
c.f. http://www.griffwason.com/gw_images/MRI_scanner/glw-pet_scanner1.jpg
c.f. http://www.medscape.com/content/2003/00/45/79/457982/art-ar457982.fig10.jpg 13
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UW and Brent K. Stewart PhD, DABMP 14
Spatial Resolution What are the limits?
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 15.
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UW and Brent K. Stewart PhD, DABMP 15
Contrast What does it depend on?
Radiation must interact with the bodys various tissues in some differential manner to provide contrast
X-ray/CT: differences in e- density (e-/cm3 = e-/gr) Ultrasound: differences in acoustic impedance (Z = c) MRI: endogenous and exogenous differences
endogenous: T1, T2, H, flow, perfusion, diffusion exogenous: TR, TE, and TI
NM: concentration () of radionuclide or + emitter Contrast agents exaggerate natural contrast levels
Iodinated (x-ray/CT) Paramagnetic (MRI) Microspheres (US)
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UW and Brent K. Stewart PhD, DABMP 16
Radiation and the Physics of Medical Imaging
Without radiation, life itself would be impossible Prof. Stewart
Radiation is all around us. From natural sources like the Sun to man made sources that provide life saving medical benefits, smoke detectors, etc... - nuclearactive.com
Youre soaking in it Madge, Palmolive spokeswoman
10 Gy/day keeps the Dr. away "Its not the volts thatll get ya, its
the amps. Billy Crystal, Running Scared
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UW and Brent K. Stewart PhD, DABMP 17
Radiation
The propagation of energy through: Space Matter
Can be thought of as either: Corpuscular (particles, e.g., electron) Electromagnetic (EM) Acoustic
Acoustic radiation awaits the ultrasound sessions later on in the course
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UW and Brent K. Stewart PhD, DABMP 18
Characterization of Waves
Amplitude: intensity of the wave Wavelength (): distance between identical points on adjacent
cycles [m, nm] (1 nm = 10-9 m) Period (): time required to complete one cycle () of a wave [sec] Frequency (): number of periods per second = (1/) [Hz or sec-1] Speed of radiation: c = [m/sec]
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.18.
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UW and Brent K. Stewart PhD, DABMP 19
Electromagnetic (EM) Radiation
EM radiation consists of the transport of energy through space as a combination of an electric (E) and magnetic (M) field, both of which vary sinusoidally as a function of space and time, e.g., E(t) = E0 sin(2ct/), where is the wavelength of oscillation and c is the speed of light
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.19.
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UW and Brent K. Stewart PhD, DABMP 20
The Electromagnetic (EM) Spectrum
Physical manifestations are classified in the EM spectrum based on energy (E) and wavelength () and comprise the following general categories: Radiant heat, radio waves, microwaves Light infrared, visible and ultraviolet X-rays and gamma-rays (high energy EM emitted from the nucleus)
c.f. http://www.uic.com.au/ral.htm
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UW and Brent K. Stewart PhD, DABMP 21
EM Radiation Share the Following
Velocity in vacuum (c) = 3 x 108 m/sec Highly directional travel, esp. for shorter Interaction with matter via either absorption or scattering Unaffected by external E or M fields Characterized by , frequency (), and energy (E) So-called wave-particle duality, the manifestation
depending on E and relative dimensions of the detector to . All EM radiation has zero mass.
*X-rays are ionizing radiation, removing bound electrons - can cause either immediate or latent biological damage
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UW and Brent K. Stewart PhD, DABMP 22
EM Wave and Particle Characteristics
Wave characteristics used to explain interference and diffraction phenomena: c [m/sec] = [m] [1/sec] As c is essentially constant, then 1/ (inversely proportional) Wavelength often measured in nanometers (nm = 10-9 m) Frequency measured in Hertz (Hz): Hz = 1/sec or sec-1
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.18.
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UW and Brent K. Stewart PhD, DABMP 23
EM Wave and Particle Characteristics
Particle characteristics when interacting with matter, high energy EM radiation act as energy quanta: photons
E [Joule] = h = hc/, where h = Plancks constant (6.62x10-34 Joule-sec = 4.13x10-18 keV-sec)
If E expressed in keV and in nm: E [keV] = 1.24/ [nm]
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.18.
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UW and Brent K. Stewart PhD, DABMP 24
Transparency of Human Body to EM Radiation
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.18. c.f. Macovski, A. Medical Imaging Systems, p. 3.
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UW and Brent K. Stewart PhD, DABMP 25
Raphex 2000 Question: EM Radiation
G46. Regarding electromagnetic radiation: A. Wavelength is directly proportional to frequency. B. Velocity is directly proportional to frequency. C. Energy is directly proportional to frequency. D. Energy is directly proportional to wavelength. E. Energy is inversely proportional to frequency.
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UW and Brent K. Stewart PhD, DABMP 26
Raphex 2001 Question: EM Radiation
G51. Which of the following has the highest photon energy? A. Radio waves B. Visible light C. Ultrasound D. X-rays E. Ultraviolet
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UW and Brent K. Stewart PhD, DABMP 27
Raphex 2001 Question: EM Radiation
G52. Which of the following has the longest wavelength? A. Radio waves B. Visible light C. Ultraviolet D. X-rays E. Gamma rays
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UW and Brent K. Stewart PhD, DABMP 28
Raphex 2002 Question: EM Radiation
G51. Visible light has a wavelength of about 6 x 10-7 m. 60Co gammas have a wavelength of 10-12 m and an energy of 1.2 MeV. The approximate energy of visible light is: A. 720 MeV B. 72 keV C. 2 eV D. 7.2 x 10-4 eV E. 2 x 10-6 eV
E1 = hc/1 and E2 = hc/2, so E11 = hc = E22 E2 = E11/2 = (12 x 105 eV)(10-12 m)/(6 x 10-7 m) = 2 eV
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UW and Brent K. Stewart PhD, DABMP 29
Cartoon of the Day
c.f. www.physics.utah.edu/~mohit/Physics_Cartoons.html.
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UW and Brent K. Stewart PhD, DABMP 30
Particulate Radiation
Corpuscular radiations are comprised of moving particles of matter the energy of which is based on the mass and velocity of the particles
Kinetic energy (KE) = m0v2 (for non-relativistic velocities)
Simplified Einstein mass-energy relationship: E = m0c2
The most significant particulate radiations of interest are:
Alpha particles 2+
Electrons e-
Positron +
Negatrons -
Protons p+
Neutrons n0
Interactions with matter are collisional in nature and are governed by the conservation of energy (E) and momentum(p = mv).
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UW and Brent K. Stewart PhD, DABMP 31c.f. http://www.ktf-split.hr/periodni/en/index.html
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UW and Brent K. Stewart PhD, DABMP 32
Electronic Structure Electron Orbits
Pauli exclusion principle No two electrons in an atom may
have identical quantum numbers
max. 2n2 electrons per shell Quantum Numbers
n: principal q.n. which e- shell : azimuthal angular momentum
q.n. ( = 0, 1, ... , n-1) m: magnetic q.n. orientation of
the e- magnetic moment in a magnetic field (m = -, -+1, ..., 0, ... -1, )
ms: spin q.n. direction of the e-
spin (ms = + or -)
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.21.
For a more detailed discussion, see - http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/eleorb.html
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UW and Brent K. Stewart PhD, DABMP 33
Electronic Structure Electron Orbits (2)
c.f. Hendee, et al. Medical Imaging Physics, 4th ed., p.13.
c.f. Hendee, et al. Medical Imaging Physics, 2nd ed., p.4.
s, p, d, f, g, h,
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UW and Brent K. Stewart PhD, DABMP 34c.f. http://www.ktf-split.hr/periodni/en/index.html
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Electron Configuration Table
UW and Brent K. Stewart PhD, DABMP 35c.f. http://en.wikipedia.org/wiki/Periodic_table c.f. http://en.wikipedia.org/wiki/Electron_configuration
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UW and Brent K. Stewart PhD, DABMP 36
Electronic Structure Electron Binding Energy
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.22.
Eb Z2
c.f. http://astro.u-strasbg.fr/~koppen/discharge/
Highly suggested, very nice detailed description - http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html
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Tungsten Bremsstrahlung Characteristic X-rays
UW and Brent K. Stewart PhD, DABMP 37c.f.: Bushberg, et al., The Essential Physics of Medical Imaging, 2nd ed., p. 101.
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UW and Brent K. Stewart PhD, DABMP 38
Radiation from Electron Transitions
Characteristic X-rays Auger Electrons and Fluorescent Yield (K):
(characteristic x-rays/total) Preference for Auger e- at low Z
c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p.23.
c.f. Sorenson, et al. Physics in Nuclear Medicine, 1st ed., p.8.
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UW and Brent K. Stewart PhD, DABMP 39
The Atomic Nucleus
Covered in later Nuclear Medicine sessions Composition of the Nucleus
Protons and Neutron Number of protons = Z (same Z: isotopes) Number of neutrons = N (same N: isotones) Mass number = A = Z + N (same A: isobars) Chemical symbol = X Notation: AZXN, but AX uniquely defines an isotope (also written
as X-A) as X implies Z and N = A - Z For example 131I or I-131, rather than 13153X78
Isomers: nuclides with same N and Z) but different energies, e.g., 99Tc and its metastable state 99mTc
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UW and Brent K. Stewart PhD, DABMP 40
Raphex 2000 Question: Atomic Structure
G10-G14. Give the charge carried by each of the following: A. +4 B. +2 C. +1 D. 0 E. -1
G10. Alpha particle G11. Neutron G12. Electron G13. Positron G14. Photon
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UW and Brent K. Stewart PhD, DABMP 41
Raphex 2002 Question: Atomic Structure
G17. Tungsten has a K-shell binding energy of 69.5 keV. Which of the following is true? A. The L-shell has a higher binding energy. B. Carbon has a higher K-shell binding energy. C. Two successive 35 keV photons could remove an electron
from the K-shell. D. A 69 keV photon could not remove the K-shell electron, but
could remove an L-shell electron.
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UW and Brent K. Stewart PhD, DABMP 42
Raphex 2001 Question: Atomic Structure
G18. How many of the following elements have 8 electrons in their outer shell? Element: Sulfur Chlorine Argon Potassium Z: 16 17 18 19 A. None B. 1 C. 2 D. 3 E. 4
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UW and Brent K. Stewart PhD, DABMP 43
Raphex 2001 Question: Atomic Structure
G18. B The nth shell can contain a maximumof 2n2 electrons, but no shell can contain more than 8 if it is the outer shell. The shell filling is as follows:
Z K shell L shell M shell N shell Sulfur 16 2 8 6 0 Chlorine 17 2 8 7 0 Argon 18 2 8 8 0 Potassium 19 2 8 8 1
For interactive answer, see - http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/eleorb.html
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UW and Brent K. Stewart PhD, DABMP 44c.f. http://www.ktf-split.hr/periodni/en/index.html
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UW and Brent K. Stewart PhD, DABMP 45
Raphex 2002 Question: Atomic Structure
G15. 22688Ra contains 88 __________ . A. Electrons B. Neutrons C. Nucleons D. Protons and neutrons