intro radiation atom-2013!01!31a

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


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?


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)


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


MRI

Transparency of Human Body to EM Radiation

c.f. Macovski, A. Medical Imaging Systems, p. 3.


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


NMR T1 for Tumor and Normal Tissue

c.f. Damadian, R, et al. PNAS 1974; 71: 1471-3.


A Systematic Approach to Medical Imaging

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

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

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

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

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


Spatial Resolution What are the limits?

c.f. Bushberg, et al. The Essential Physics of Medical Imaging, 2nd ed., p. 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)


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


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


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.


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



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


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


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



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]



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.


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.



G51. Which of the following has the highest photon energy? A. Radio waves B. Visible light C. Ultrasound D. X-rays E. Ultraviolet



G52. Which of the following has the longest wavelength? A. Radio waves B. Visible light C. Ultraviolet D. X-rays E. Gamma rays



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


Cartoon of the Day

c.f. www.physics.utah.edu/~mohit/Physics_Cartoons.html.


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).

UW and Brent K. Stewart PhD, DABMP 31c.f. http://www.ktf-split.hr/periodni/en/index.html


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 -)


For a more detailed discussion, see - http://hyperphysics.phy-astr.gsu.edu/hbase/chemical/eleorb.html


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,

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


Electronic Structure Electron Binding Energy


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

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.


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. Sorenson, et al. Physics in Nuclear Medicine, 1st ed., p.8.


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


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



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.



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



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



G15. 22688Ra contains 88 __________ . A. Electrons B. Neutrons C. Nucleons D. Protons and neutrons

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