Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Center for Radiological Research wikipedia , lookup
Nuclear medicine wikipedia , lookup
Backscatter X-ray wikipedia , lookup
Neutron capture therapy of cancer wikipedia , lookup
Radiosurgery wikipedia , lookup
Radiation burn wikipedia , lookup
Industrial radiography wikipedia , lookup
11/19/2014 2014-2015 Residents' Core Physics Lectures Mondays 7:00-8:00 am in VA Radiology and UCSDMC Lasser Conference Rooms 1 2 3 4 5 Topic Introduction and Basic Physics Interaction of Radiation and Matter RSNA Week No Lecture Computers X-Ray Production Christmas and New Year’s Holiday Generators Chapters 1, 2 3 4 5 5 Date M 11/17 M 11/24 M 12/01 M 12/08 M 12/15 M 12/22, 12/29 M 01/05/2015 Faculty Andre Andre Hall Andre Andre Nuclide Families Family Example Isotopes Atomic number (Z) I131, I125: Isobars Mass number (A) Mo99, Tc99: A=99 Isotones Neutron number (A-Z) 131: 53I Isomers A and Z same but different energy state Tc99m and Tc99: Z=43, A=99, ΔE=142 keV Textbook: The Essential Physics of Medical Imaging, Bushberg, et al., Philadelphia: Lippincott Williams & Wilkins, 2002, 2nd Edition Course Web Site??: http://3dviz.ucsd.edu/~radiology_residents/Home.html • Stable isotopes found along line N/Z = 1 at low Z • Stable isotopes found along line N/Z = 1.5 at high Z • Odd N and odd Z tend to be unstable • Odd Z elements offer potential for NMR (unpaired p+) Nuclides with Same: A ZX Z=53 131-53=78 X = element symbol Z = number of protons A = number of protons + neutrons 2 Chapter 3: Interaction of Radiation with Matter The Basis of X-Ray Imaging Next time we address these devices “Huge relevance to a Resident” A ZX X = element symbol Z = number of protons A = number of protons + neutrons or digital detector AAPM/ABR Syllabus Chapter 3: Interaction of Radiation with Matter in Radiology and Nuclear Medicine • • • • • Particle Interactions X- and Gamma-Ray Interactions Attenuation of X- and Gamma-Rays Absorption of Energy from X- and Gamma-Rays Imparted Energy, Equivalent Dose and Effective Dose Lots of new definitions here! Important to us for radiographic and CT image contrast, patient dose, x-ray production, Rad Tx, and more… Recall: Contrast, Sharpness, Noise, Distortion, Dose This topic affects Contrast, Noise and Dose Module 4: Interactions of Ionizing Radiation with Matter After completing this module, the resident should be able to apply the “Fundamental Knowledge” and “Clinical Applications” learned from the module to example tasks, such as those found in “Clinical Problem-Solving.” Fundamental Knowledge: 1. Describe how charged particles interact with matter and the resulting effects these interactions can have on the material. 2. Describe the processes by which x-ray and γ-ray photons interact with individual atoms in a material and the characteristics that determine which processes are likely to occur. 3. Indentify how photons are attenuated (i.e., absorbed and scattered) within a material and the terms used to characterize the attenuation. Clinical Application: 1. Identify which photon interactions are dominant for each of the following imaging modalities: mammography, projection radiography, fluoroscopy, CT, and nuclear medicine imaging procedures. 2. Understand how image quality and patient dose are affected by these interactions. 3. What are the appropriate x-ray beam energies to be used when iodine and barium contrast agents are used? 4. How does the type of photon interaction change with increasing energy, and what is the associated clinical significance? Clinical Problem-Solving: 1. Select an appropriate thyroid imaging agent based on its particulate emissions for pediatric imaging and for adult imaging. Would these agents use the same isotopes or different isotopes? How does dose differ between these imaging isotopes? 2. What is the purpose of adding Cu filters in vascular imaging? 3. What makes a contrast agent radiolucent instead of radio-opaque? 6 1 11/19/2014 Recall: Chapter 2 • Energy: Definition? – Ability to do Work • Radiation: Definition? – Propagation of energy through space • Types in Medicine – – – – – – – Heat (infrared) [EM] 1 eV Visible light [EM] X-Rays [EM] γ-Rays [EM] Microwaves (MRI) [EM] Particulate [Mass, charge, kinetic energy] Sound [Mechanical] e- 1V Which is/are true? The energy of a photon is: – A. Proportional to its wavelength – B. Proportional to its frequency – C. Inversely proportional to the exposure time – D. Inversely proportional to its wavelength – E. Can be expressed in terms of potential difference (volts) Chapter 3: Interaction of Radiation with Matter in Radiology and Nuclear Medicine Which is/are true? The energy of a photon is: – A. Proportional to its wavelength – B. Proportional to its frequency – C. Inversely proportional to the exposure time – D. Inversely proportional to its wavelength – E. Can be expressed in terms of potential difference (volts) E = hf = hc/λ E (keV) = 12.4 / λ (Å) Particles in Medicine Particle Symbol Relative Charge Mass (amu) Energy Equivalent (MeV) 3727 Alpha α, 4He2+ +2 4.0028 Proton p, 1H+ +1 1.007593 938 Electron e-, β- -1 0.000548 0.511 Positron e + , β+ +1 0.000548 0.511 Neutron n0 0 1.008982 940 Particles interact with matter through Scattering: •Elastic (no net Kinetic Energy loss) •Inelastic (KE imparted) • Excitation 1 eV e 1V • Ionization • Radiation loss • • • • • Particle Interactions X- and Gamma-Ray Interactions Attenuation of X- and Gamma-Rays Absorption of Energy from X- and Gamma-Rays Imparted Energy, Equivalent Dose and Effective Dose Lots of new definitions here! Important to us for radiographic and CT image contrast, patient dose, x-ray production, Rad Tx, and more… Recall: Contrast, Sharpness, Noise, Distortion, Dose This topic affects Contrast, Noise and Dose Excitation Excitation De-excitation with radiation • Imparted E < Binding Energy • Photon (low energy) • Results in e- at higher energy • Auger electron state • 70% of all particulate interactions are non-ionizing 2 11/19/2014 Light vs. Heavy Charged Particles Ionization • Imparted E > B.E. • Ion pair results • Secondary ionization Heavy Light • Linear Energy Transfer • LET = Energy/unit path length (eV/cm) • LET proportional to Q2/K.E. • LET (eV/cm) = Spec. Ion.(IP/cm) • Avg. E per IP (eV/IP) • LET largely determines “biological effectiveness” • High LET: α , p+ • Low LET: β+, β-, electromagnetic Bremsstrahlung [“Braking”] Radiation • Decelerate e- ( velocity) • Bremsstrahlung x-ray E = h = K.E. loss of e• Probability of interaction is proportional to Z2 of absorber • Results in spectrum of x-ray energies Why is this important to you? Excitation E Loss by Bremsstrahlung = K.E.(MeV) • Z E Loss by Excitation + Ionization 820 Summary of Particle Interactions • • • • • Scattering Excitation Ionization (Direct and Indirect) Radiation (Bremsstrahlung) Electron-Positron annihilation (Chapter 22, PET) Two 180º opposed 0.511 MeV photons • Neutron interactions (Chapter 19) – Interact with nuclei, mainly Hydrogen in tissue – Split nucleus (fission) – Or captured by nucleus Bremsstrahlung is the principal source of x-ray production in radiology (Chapter 5, next time) X- and Gamma-Ray Interactions • • Attenuation Absorption + Scattering * Methods of Interaction: 1. “Coherent or Rayleigh or Classical” Scattering 2. Compton Scattering 3. Photoelectric Absorption 4. Pair Production 5. Photo-disintegration * 3 11/19/2014 X- and Gamma-Ray Interactions Rayleigh Scattering • No net loss of energy by incident photon, no ionization • Excites entire atom • Results in change of direction of photon • Occurs in tissue only at low x-ray energies, E = h therefore low frequencies, long wavelengths • Less significant for diagnostic radiology • <5% of interactions above 70 keV • Maximum occurrence of 12% at 30 keV Compton Scattering (Incoherent) • 30 keV to 30 MeV: Photon interactions in soft tissue are predominantly Compton • Main source of undesirable scattered radiation which reduces image contrast Involves only Low B.E. e- Attenuation Absorption + Scattering * Methods of Interaction: 1. “Coherent,” “Rayleigh” or “Classical” Scattering 2. Compton Scattering (incoherent) 3. Photoelectric Absorption 4. Pair Production 5. Photodisintegration • #2 and #3 are * dominant in radiology • hinc = hscat + K.E. e• Scattered photon: 0° 180° • Scattered electron: 0° φ 90° φ Involves only Low B.E. e- Compton Scattering • Occurs for loosely bound electrons with negligible B.E. • Input: photon Output: photon + electron φ Compton Scattering Compton Scattering h scat • • h inc h inc 1 cos 511 keV • hscat = Energy of scattered photon • hinc = Energy of incident photon • = scatter angle of photon • As E of incident photon increases, (and φ) decrease, so they hit receptor • 2(scattered) = 1(incident) + [conserve E] • (E loss) is maximum when = 180° (backscatter) • Probability of Compton interaction P (C) 1/hinc = 1/Einc P (C) is not dependent on Z P (C) electron density ~ (g/cm3) 1 φ When low energy photon undergoes Compton interaction, majority of energy is retained by scattered photon and only slight amount is transferred to electron. 1. Example: 20 keV photon scattered at 180° h 2 = 18.6 keV Ek (electron) = 1.4 keV 2. Example: 2 MeV incident photon at 180° scatter h 2 = 226 keV Ek = 1774 keV (Motivation for Megavoltage Rx) φ 4 11/19/2014 Photoelectric Effect X- and Gamma-Ray Interactions • • Attenuation Absorption + Scattering * Methods of Interaction: 1. “Coherent,” “Rayleigh” or “Classical” Scattering 2. Compton Scattering (incoherent) 3. Photoelectric Absorption 4. Pair Production 5. Photodisintegration • #2 and #3 are dominant * in radiology • Products of interaction: – 1. Photoelectron (ejected electron) – 2. Positive ion (remaining atom) – 3. Characteristic radiation (discrete x-rays emitted when electron cascades to fill vacant shells) or Auger electrons – 4. Original photon disappears • X-ray energy is unique to the element (characteristic) 53I Photoelectric Effect Photoelectric Effect in Iodine • Probability of photoelectric interaction per unit mass – P (P.E.) Z3 – P (P.E.) 1/(h )3 = 1/E3 – P (P.E.) (g/cm3) – Higher probability when (h ) is close to EB.E. – Higher probability with higher EB.E. such as K shell 53I Ee- = h inc – EB.E. If h inc< EB.E. interaction does not occur Photoelectric Effect: K-Edge 53I K-shell electron binding energies • Prob. of Absorption (Photoelectric mass attenuation coefficients) for – Tissue (Z=7), – Iodine (Z=53), – Barium (Z=56) • Huge increase in Prob. Absorption above the K-shell B.E. Probability of Absorption Semi-log plot or “absorption edges” K-edge = 37.4 keV K-edge = 33.2 keV K-edge < 1 keV Atomic Number, Z Material K-Edge, keV 7.4 Avg Tissue 0.5 20 Calcium 4.04 53 Iodine 33.2 56 Barium 37.4 74 Tungsten 69.5 82 Lead 88.0 5 11/19/2014 Radiological Significance of Photoelectric Effect • No scatter radiation (characteristic x-rays in tissue have very low E, < 1 keV), “pure” x-ray contrast • P(P.E.) Z3 means that P.E. enhances subject contrast (differences in attenuation between tissues), inversely proportional to E3 • Higher doses to patient when it occurs in tissue: total absorption of photon, no energy escapes • Iodine and barium image contrast are highest when kVp is set match the k-edge Effect of Scatter on Radiographic Contrast Scatter masks image contrast (noise) Not collimated Scatter included Collimated Scatter reduced (grid) Pair Production • h > 1.02 MeV • Excess is K.E. of β’s • Probability of pair production – P (PP) Z – P (PP) h > 1.02 MeV – P (PP) (g/cm3) Which of the following is false? A photon can undergo a _____ interaction followed by a _____ interaction. a. b. c. d. Compton, pair production Compton, another Compton Compton, photoelectric Photoelectric, Compton Photodisintegration • High energy photon ejects a nuclear particle. • Except for beryllium, this occurs for h > 7 MeV. • Not significant for diagnostic radiology but important for Rx. Which of the following is false? A photon can undergo a _____ interaction followed by a _____ interaction. a. b. c. d. Compton, pair production Compton, another Compton Compton, photoelectric Photoelectric, Compton 6 11/19/2014 • = Rayleigh + Compton + Photoelectric + Pair Prod + Photodisint • is function of: E (h), Z, • / = mass attenuation coefficient (cm-2/g) • Removal of photons from beam, or sum of scatter and absorption (from all interactions) • For monochromatic (single energy) radiation of intensity I0 – I = Io e-x or N = No e-x – = linear attenuation coefficient (cm -1) – = ln 2/HVL – HVL (cm) = 0.693/ = thickness of absorber that attenuates beam by 1/2 – is function of: E (h), Z, Which is/are False? The linear attenuation coefficient: a. Is equal to the mass attenuation coefficient multiplied by the density of the absorbing material. b. Varies mainly due to changes in electron density. c. Is equal to the fractional reduction in the intensity per unit absorber thickness. d. Becomes less dependent on Compton interactions than on photo-electric interactions at higher energies. e. Is a constant for monoenergetic photon beam in a given absorbing material. Probability of Absorption Attenuation of X- and Gamma-Rays Which is/are False? The linear attenuation coefficient: a. Is equal to the mass attenuation coefficient multiplied by the density of the absorbing material. b. Varies mainly due to changes in electron density. c. Is equal to the fractional reduction in the intensity per unit absorber thickness. d. Becomes less dependent on Compton interactions than on photo-electric interactions as energy increases. e. Is a constant for monoenergetic photon beam in a given absorbing material. Measuring Attenuation of X- and Gamma-Rays Ice cubes Air bubbles • For monochromatic (single energy) radiation of intensity I0 – I = Io e-x or N = No e-x – = linear attenuation coefficient (cm-1) – = ln 2/HVL – HVL = 0.693/ = thickness of absorber that attenuates beam by 1/2 – is function of: h , Z, 7 11/19/2014 Avg Energy (quality) and HVL increases I e x I0 Beam Hardening Photon intensity (quantity) decreases Monochromatic X-Rays 1st HVL = 2nd HVL Polyenergetic X-Rays e.g., Diagnostic x-ray beam 2nd HVL > 1st HVL An attenuation curve for a 120 kVp x-ray beam yields the following data: 100 75 50 25 0 0 1 2 3 4 5 Added filtration (mm Al) 0 0.5 1 2 3 4 5 The second half value layer is approximately: a. 1.0 mm b. 1.7 mm c. 2.0 mm d. 2.2 mm e. 3.0 mm Relative Intensity 100% 50 40 27 20 15 12 Add 1 mm to the beam. What is the HVL now? a. 1.0 mm b. 1.5 mm c. 2.0 mm d. 2.5 mm e. 3.0 mm An attenuation curve for a 120 kVp x-ray beam yields the following data: 100 75 50 25 0 0 1 2 3 4 5 Added filtration (mm Al) 0 0.5 1 2 3 4 5 The second half value layer is approximately: a. 1.0 mm b. 1.7 mm c. 2.0 mm d. 2.2 mm e. 3.0 mm Relative Intensity 100% 50 40 27 20 15 12 Add 1 mm to the beam. What is the HVL now? a. 1.0 mm b. 1.5 mm c. 2.0 mm d. 2.5 mm e. 3.0 mm An attenuation curve for a 120 kVp x-ray beam yields the following data: 100 75 50 25 0 0 1 2 3 4 5 Added filtration (mm Al) 0 0.5 1 2 3 4 5 The second half value layer is approximately: a. 1.0 mm b. 1.7 mm c. 2.0 mm d. 2.2 mm e. 3.0 mm Relative Intensity 100% 50 40 27 20 15 12 Add 1 mm to the beam. What is the HVL now? a. 1.0 mm b. 1.5 mm c. 2.0 mm d. 2.5 mm e. 3.0 mm Next Session • Monday December 8, 7:00 a.m. @ VA – Chapter 4: Computers, Dr. Hall • Monday December 15, 7:00 a.m. @ VA – Chapter 5: X-Ray Production • No Lectures Monday December 22 or 29 8 11/19/2014 Attenuation of X- and Gamma-Rays Photon Fluence N A A narrow monoenergetic photon beam interacts with an absorber. Which is/are True? Photon Energy Fluence N Photon Flux A t N h A Fluence Rate a. b. c. d. The photon fluence decreases exponentially with increasing depth in the absorber. The photon fluence becomes zero beyond a maximum range determined by the photon energy. The LET depends on the depth in the absorber. The photon fluence is reduced by the same fraction, as the beam passes through equal thickness of the absorber at any depth. AAPM/ABR Syllabus A narrow monoenergetic photon beam interacts with an absorber. Which is/are True? a. b. c. d. The photon fluence decreases exponentially with increasing depth in the absorber. The photon fluence becomes zero beyond a maximum range determined by the photon energy. The LET depends on the depth in the absorber. The photon fluence is reduced by the same fraction, as the beam passes through equal thickness of the absorber at any depth. Module 5: Radiation Units After completing this module, the resident should be able to apply the “Fundamental Knowledge” and “Clinical Applications” learned from the module to example tasks, such as those found in “Clinical Problem-Solving.” Fundamental Knowledge: 1. Recognize that there are 2 different systems for units of measurement (i.e. SI and Classical) used to describe physical quantities. 2. Describe the SI and Classical units for measuring the ionization resulting from radiation interactions in air (e.g., exposure-related quantities). 3. Describe the concepts of dose‐related quantities and their SI and Classical units. Clinical Application: 1. Discuss the appropriate use or applicability of radiation quantities in the health care applications of imaging, therapy, and safety. Clinical Problem-Solving: 1. Explain radiation exposure and dose quantities in lay language to a patient. 52 Units of Radiation • Exposure (R) • Absorbed Dose (Gy) • Kerma (Gy) • Equivalent Dose (Sv) • Effective Dose (Sv) • Activity (Bq) 1 R = 2.58 x 10-4 C/kg 1 Gy = 100 rad = 1 J/kg = 1 erg/gm K.E. transferred to charged particles K = Ψ (tr/)E H = wR D = 100 rem E = ΣT wT HT 3.7x1010 Bq = 1 Ci (Also known as Quality Factor, largely based on LET) • Effective Dose (Sv) E = ΣT wT HT 9 11/19/2014 Which of the following is not equal to one Gray? a. 1.0 Joule/kg b. 100 rads c. 1.0 Sv/Quality Factor d. (100 R)•(f-factor) e. 100 ergs/gm Which of the following is not equal to one Gray? a. 1.0 Joule/kg b. 100 rads c. 1.0 Sv/Quality Factor d. (100 R)•(f-factor) e. 100 ergs/gm Next Session • Monday December 8, 7:00 a.m. @ VA – Chapter 4: Computers, Dr. Hall • Monday December 15, 7:00 a.m. @ VA – Chapter 5: X-Ray Production • No Lectures Monday December 23 or 30 Specific Ionization (Ion Pairs/mm) 7.69 MeV αlpha in air •Specific Ionization increases with charge of particle •Decreases with velocity of incident particle •E.g., alpha may be as high as 7,000 IP/mm in air compared to e- of 50-100 IP/cm •As α slows, Bragg peak occurs •Bragg peak may be useful for Rad Tx Two materials are irradiated by monoenergetic photons. Material A has an atomic number of 14 and B has an atomic number of 7. The photoelectric component of the mass attenuation coefficient of A is ______ times that of B. a. b. c. d. e. 16 8 4 2 0.5 10 11/19/2014 Two materials are irradiated by monoenergetic photons. Material A has an atomic number of 14 and B has an atomic number of 7. The photoelectric component of the mass attenuation coefficient of A is ______ times that of B. a. b. c. d. e. 16 8 4 2 0.5 P (P.E.) Z3 Mean Free Path MFP 1 1 0.693 HVL 1.44 HVL 11