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Interaction of x-ray and radiation effects
- 1. INTERACTION OF X-RAYWITH MATTER AND EFFECTS OF RADIATION Presented by ; Niroj Sandha B.Sc. MIT 1st year NAMS, BIR HOSPITAL
- 2. CONTENTS ATOM TYPES OF INTERACTION DIFFERENTIALABSORPTION EXPONENTITAL ATTENUATION EFFECTS OF RADIATION SUMMARY REFERENCES
- 3. ATOM Matter is anythingthat occupies space , is made up of atom which is composed of nucleon (i.e. neutron and proton) and electron. Neutrons are electrically neutral and protons have positive charge ,both are found in nucleus. Electrons are negatively charge and circulate around the nucleus . The Atomic numer (Z) is the no. of protons in the nucleus , it is equal to the no. of electrons . Total no. of protons and neutrons in the nucleus is known as Mass number(A).
- 4. ATOMIC STRUCTURE According toBohr’s atomic model : 1. Positively charged nucleus surround and revolve by the negatively charged electrons in a fixed orbits 2. Electron orbit shells are given the codes for identification K,L,M,N, and so forth from closest to nucleus to farthest from nucleus . 3. Maximum number of electrons that can exist in each shell increases with increase in distance from the nucleus i.e. 2n^2 where ‘n’ is the shell number .
- 6. Binding energy It isenergy acquired by the electrons due to strong electrostatic pull of attraction by the nucleus Energy required to remove an electron from an atom is called electron binding energy It is unique for each shell of each element It depend on the distance of an electron from 5ye nucleus i.e. inner shell electrons have high binding energy than outer shell electron
- 7. Binding energy oftungsten atom
- 8. Ionization Removal of oneor more electrons form the neutral atom leaving behind a positive ion . Electromagnetic radiation with sufficient energy to eject atomic electron is called ionizing radiation
- 9. EXICITATION Electrons of anatom move from inner shell to outer shell when energy is supplied to neutral atom is called excitation
- 10.
- 11. Photon beam interctaction Attenuation: removal of intensity of the radiation when it passes through the matter Absorption:transfer of energy from radiation to the medium Scattering :refers to change indirection of photons Transmission : x ray energy that penetrate through matter without any of above process
- 12. DUAL NATURE OFLIGHT X ray belongs to a group of radiation called Electromagnetic radiation . Electromagnetic radiation has dual characteristics i.e. it comprises both particle and wave Wave concept Propagate through space in the form of wave Waves of all type have wavelength and frequency C = / . V Where v= frequency , /= wavelength, c= speed of light
- 13. Electromagnetic wave kogif fig Wave theory of light explains phenomenon like interference , diffraction, polarization and coherent scattering
- 14. Particle concept When metalsurface is irradiated with light , an electron is ejwcted Depends on its energy( frequency) not its intensity The phenomenon of photoelectric effect and compton effect is explained on the basis of light consisting photons or quanta. Gif of duality
- 15. Interaction of xray with matter x ray interacts with matter through 5 different mechanism . They are : 1. Coherent scattering 2. Compton scattering 3. Photoelectric scattering 4. Pair production 5. photodisintegration
- 16. COHERENT SCATTERING Incident xray energy below 10kev interacts with the target atom causing it to become excited and release the excess energy as a scattered x ray Also called classical scattering or Thompson scattering There are two types of coherent scattering 1. Thomson scattering 2. Rayleigh scattering Scattered x ray is change in direction and wave length is equal to that of the incident x ray and therefore equal energy No ionization occurs as no transfer of energy of occurs /no ejection of the electrons . It is little importance to the diagnostic radiology
- 17. Figure of coherentscatteing
- 18.
- 19. COMPTON SCATTERING Incident xray interact with the outer shell electron target atom , thereby ionizing the atom . Ejected electron is called Compton electron Energy of Compton scattered x ray is equal to difference between the energy of incident x ray and ejected electron . This reaction produces an ion pair , a positive atom and a negative electron known as recoil electron It contributes around 20% in diagnostic radiography
- 20. Scatter photon hasless energy than the incident photon . Wavelength is longer than the incident photon Scatter photon undergo additional tissue interaction
- 22. Direction of scatterradiation Scatter radiation travel in a new direction depending upon deflection angle with the electron. It may be as great as 180 degree ( back scattering ) I. Back scatter can cause artefacts ,such as cassette strap image . II. These photons pose major radiation hazard to the staff ( especially during fluoroscopic examination )
- 23. Probabilty of occurrence Mostlikely to occur With outer shell electron and loosely bound electron As x ray energy increases Reduce probability of Compton effect As atomic number of matter increases No effect As mass density of matter increase More Compton scatter
- 24. PHOTOELECTRIC EFFECT • Incidentx ray interact with the innershell electron and is fully absorbed thereby ejecting an electron from its shell • the ejected electron escapes with the KE equal to difference between energy of incident x ray and the binding energy of the electron.
- 26. • Earned alberteinstein the 1921 nobel prize in physics . • For low atomic number atom , photoelectron eject with KE is equal to the energy of incident x ray . • For high atomic number atom , KE of photoelectron is proportionately lower in compared to binding energy of target atom .
- 27. The photoelectric effectyields 1. photo electron (-ve ion ) 2.Positive atom(+ve ion) 3.Characteristic x ray - •Energy of characteristics x ray are produces when the void in the k-shell is filled by the subsequent shell electrons , generally L- shell electrons . •Energy of characteristics x ray is equal to the difference of binding energy of both shells • It acts as secondary radiation and contributes nothing of diagnostic
- 28. Characteristic x rayafter photelectric
- 29. Probabilty of occurrence Incidentx ray must have energy equal or greater than the binding energy of k shell electron Inversely proportional to the third power of x ray energy Directly proportional to the third power of the atomic number of an atom.
- 31. Advantages of photoelectriceffect Contributes around 75% to the medical imaging . Does not produce scattered radiation Enhances natural tissue contrast I. Since the probability of interaction is proportional to the third power of atomic number , it magnifies the difference in tissue composed of different atomic numbers II. For example bone and soft tissue
- 32. Disadvantage of photoelectric Increasein patient radiation dose , since all the energy of incident photon is absorbed by the patient in the photoelectric interaction.
- 33. Pair production Production ofan electron and positron pair after complete absorption of the x ray photon. The energy equivalence of the mass of both particle is equal of 0.51MeV That’s why it only Occurs when incident photon has energy of atleast 1.02MeV Energy in excess of 1.02MeV is distributed equally as a kinetic energy It is unimportant in x ray imaging but is very much of important in PET imaging in nuclear imaging
- 34. Picture of pairproduction
- 35. Photodisintegration X ray ofenergy greater than 10Mev escapes interaction with the electron and nuclear electrostatic field and absorbed directly by the nucleus nucleus is raised to excited state and emits nucleon or nuclear fragments . It does not occur in diagnostic radiology
- 36.
- 37. DIFFERENTIAL ABSORPTION • Xrays that undergo photoelectric interaction provides diagnostic information as they do not reach the IR and produces light areas • whereas x ray transmitted through the patient without interaction produces the dark areas of a radiograph • this difference in absorption of x ray interacrion is called Differential absorption . • Both, x rays that are transmitted to the IR and that are absorbed photoelectrically are equally important • If all the x rays are transmitted then iimage would be uniformly black and also if all the x ray photons are absorbed then it will cause uniformly white . Neither of cases are appreiciated in diagnostic radiology .
- 38. • Differential absorptiondepends on following factors ; 1.Atomic number (Z) 2.Mass density 1. Atomic number • Probabilty of an x ray undergoing photoelectric is proportional the third power of At no. of the tissue and inversely proportional to the third power of x ray energy • So decrease in compton scattering is not as rapid as photoelectric with increase in energy . • Contd ...
- 40. 2.Mass density • Interactionof x ray with tissue is proportional to the mass demsity of the tissue regardless of type of interaction . • Mass denity is quantity of matter per volume. • We could image bone even if differential absorption is not (Z) related because bone has higher mass density than soft tissue .
- 42. EXPONENTIAL ATTENUATION When xray interact with any type of tissue , interaction occurs through any 5 mechanism but in diagnostic radiology only 2 types of interaction are important . these interaction depend on atomic no of tissue atoms , mass density and x ray energy. The reduction in beam intensity after penetration through a given thickness of tissue is called attenuation i.e. they are reduced in number by a certain percentage of each increment in thickness of the tissue they go through
- 43. Deterministic effect ofthe radiation The effect which have threshold value below which the effect doesn’t occur Once the threshold value has been reach the severity of an effect increase with radiation dose It includes 1. Acute radiation lethality 2. Local tissue damage 3. hematologic depression 4. Cytogenic depression
- 44. Acute radiation lethality sequenceof events followed by high radiation exposure leading to death within days or weeks is called acute radiation syndrome . Three lethal syndrome associated with acute radiation lethality are ; I. Prodromal period (immediate response ) II. Latent period ( no response ) III. Manifest illness ( haematologic, GI ,CNS syndrome )
- 45.
- 46. LD50/60 is thedose of radiation that will result in death of 50% of irradiated subjects within 60 days Table 33-3
- 47. Mean survival timedecreases as the radiation dose increase
- 48. Local tissue damage skin Dependson the intrinsic radiosensitivity , cell proliferation and maturation . Local tissues that are affected immediately are skin, gonads and bone marrow Damage to basal cells results in earliest manifestation of radiation injury to the skin . The resultant skin damage is seen as erythema and desquamation
- 49. Fig of erythemaand desquamtion
- 50. Gonads Human gonads arecritically important target and responds to doses as low as 100mGyt Even such low dose can reduce the number of spermatozoa in male testes and suppress menstruation in female Dose of approximately 2Gyt causes temporary infertility and 5Gyt cause permanent infertility Moderate such as 250mGy is sufficient to cause genetic mutation
- 52. Haemopoietic system highly radiosensitivesystem ,consists of bone marrow ,circulating blood and lymphoid tissue Derived from pluripotent stem cells which produce many stem cells like lymphocytes ,granulocytes ,thrombocytes ,erythrocytes.
- 53. Graph of haemopoeiticsystem
- 54. Cytogenetic effects Cytogenetic isthe study of cell ,particularly cell chromosome . Radiation induced chromosome aberrations follow non threshold dose response relationship Radiation may damage chromosome by following i. chromatid deletion –single hit ii. Dicentric / ring chromosome – multi hit iii. Reciprocal translocation –multi hit
- 57. Ring chromosome areproduced if two hits occur on the same chromosome. Dicentrics are produced when adjacent chromosome sustain one hit amd recombine .
- 58. It results inno loss of genetic material, simoly rearrangement of genes in incorrect sequence .
- 59. Stochastic effect Effects ofradiation that may occur by chance and are result of low dose delivered over a long period of time It follows linear ,non-threshold dose response relationship The principle stochastic effects are radiation induced malignancy and genetic effects .
- 60. Local tissue effects Chronicirradiation of skin can result in severe non-malignant changes such as development of very callaused , discolored ,weathered apperances in the skin Even a low dose can produce chromosome aberration that may not be visible even after many years of exposure
- 61. usually the radiationprotection guides are based on the stochastic effects of radiation and on linear non threshold dose relationship Consequently the precise dose response relationship are often not possible to formulate . hence, we resort Risk Estimates. They are : 1. Relative risk 2. Excess risk 3. Absolute risk
- 62. 1. Relative risk Ifone observe a large population for stocjastic radiation effects without having precise knowledge of radiatiom dose which they are exposed . It is computed by comparing the number of irradiated populations showing stochastic effect by the number of unexposed population showing the same stochastic effect Relative risk =observed case /expected cases
- 63. 2. Excess risk Itis difference between observed risk and expected risk Observed risk-Expected risk =Excess risk Leukemia is known to occur in non irradiated population but if leukemia incidence in irradiated population exceeds more than expected then difference betn observed cases and expected cases would be excess risk .
- 64. 3. Absolute risk Ifat least two dose levels are known , it may be possible to determine the possible risk factors It consist unit of case / population / dose According to the National committee on biological effects of Ionizing radiation , this value is 8*10^2 This is the risk coefficient used by the scientist to predict stochastic radiation response in exposed populations
- 65. Radiation Induced Malignancy Allthe radiation induced malignancy follow linear non threshold dose response relationship expect the radiation induced skin cancer Radiation induced malignancy like leukemia ,cancer increases with the increase in radiation dose
- 66. References Text book ofRadiology for Residents and Technicians Radiologic science for technologist
- 67.