Patient Interactions 1 Patient Interactions Review Tube Interaction
Patient Interactions 1
Patient Interactions Review Tube Interaction Heat Brems Characteristic Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration Why These are Important? Image Production Patient/Tech Safety 2
Patient Interactions Review of Tube Interactions: Heat Brems Characteristic 3
Heat 4
Brems 5
Characteristic 6
Patient Interactions Review Tube Interaction Heat Brems Characteristic Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration Why These are Important? Image Production Patient/Tech Safety 7
Patient Interactions Interaction in the body begin at the atomic level Atoms Molecules Cells Tissues Organs 8
Patient Interactions of X-rays with matter 1. No interaction: X-ray passes completely and get to image receptor 2. Complete absorption: no x-rays get to image receptor 3. Partial absorption with scatter-some x-rays get to image receptor but some get scattered 9
Patient Interactions What happens to our Primary Beam? 10
Patient Interactions EM Interactions with Matter General interactions with matter include: 1. Scatter – 2. With or without partial absorption Absorption – Full attenuation 11
Patient Interactions X-ray photons can change cells 12
Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous to living tissue. 1913 13
Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous to living tissue. 14 Hiroshima victim
Patient Interactions I don’t want that to happen to me!! 15
Patient Interactions Classical Compton Photoelectric Pair Production Photodisintegration 16
Patient Interactions 17
g n i r e t t a c S ) t n e r e h o C ( l a c i s s a l C Patient Interactions v v v Excitation of the total complement of atomic electrons occurs as a result of interaction with the incident photon No ionization takes place Electrons in shells “vibrate” Small heat is released The photon is scattered in different directions Energies below 10 k. V 18
Patient Interactions Classical scattering 19
Patient Interactions Classica l (Cohe rent) Net Result of Classical q No energy transfer q Photon changes direction with same energy q Occurs with LOW ENERGY photons q No ionization q Not diagnostic 20
Patient Interactions COMPTON SCATTERING 1. Outer shell electron in body 2. Interacts with x-ray photon from the tube 3. Moderate energy electron 21
Patient Interactions Recoil electron can produce another interaction if high enough energy. Compton scattering does not provide any useful diagnostic information. 22
Patient Interactions compton scattering (effect) 23
Patient Interactions v Moderate energy x-ray photon ejects an outer shell electron. v Energy is divided between scattered photon and the Compton electron (ejected e- or recoil electron) v Scattered photon has sufficient energy to exit body. v Since the scattered photon exits the body, it does not pose a radiation hazard to the patient. v Can increase film fog (reduces contrast) v Radiation hazard to personnel 24
Patient Interactions photoelectron Incoming photon interacts with inner shell electron. The “knocked-out” electron is called a photoelectron. The energy of the incoming photon is absorbed. 25
Patient Interactions photoelectric interaction 26
Patient Interactions 27 CASCADE
Patient Interactions v Moderate energy x-ray photon ejects inner shell electron (energy absorbed) v Leaves an orbital vacancy, releasing a photoelectron. (As vacancy is filled, another photon is produced-scatter radiation ) v More likely to occur in absorbers of high atomic number (bone, positive contrast media) v Contributes significantly to patient dose, v As all the photon energy is absorbed by the patient , this is responsible for the production of short-scale contrast. 28
Patient Interactions Electron (Negatron) positron 29
Patient Interactions 30
Very High Energy Photon…. . Mk. V Not used in Diagnostic X-ray 31
Patient Interactions Nuclear fragment 32
Patient Interactions 33
Very High Energy Photon…. . Mk. V Not used in Diagnostic X-ray 34
Patient Interactions Summary of Interactions q Classical Coherent q Low energy photons q No diagnostic effect q Contributes to scatter q Compton Effect (Scattering) q Moderate energy photons q No diagnostic effect q Contributes to scattering q Contributes to personnel dose q Photoelectric Effect q Moderate energy photons q Definite diagnostic effect q Contributes to image contrast q Atomic number dependent q Contributes to patient dose q Pair Production q High energy photons q Not useful in diagnostic range q Photodisintegration q High energy photons 35 q Not useful in diagnostic range
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What kind of interaction is this? 37
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What kind of interaction is this? 39
What kind of interaction is this? 40
What kind of interaction is this? 41
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What kind of interaction is this? 43
Things to Remember About X-ray Interactions with Matter Interactions with matter occur in biologic tissue Two interactions with matter important in diagnostic radiology: photoelectric & Compton Incoming photon or x-ray Interacts with: • inner shell electron = photoelectric effect • outer shell electron = Compton effect 44
Things to Remember About Diagnostic Radiation Production Results in: • ion and x-ray w/specific (discrete) energy = Characteristic • scattered e- and x-ray w/varying (continuous) energy = Bremsstrahlung 45
Patient Interactions Review Tube Interaction Heat Brems Characteristic Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration Why These are Important? Image Production Patient/Tech Safety 46
Summary of Interactions 47
Summary of Interactions summary of interactions 48
Why Interactions are Important? Image production Compton Effect Photoelectric Effect Biggest Contributor to Scatter Radiation, especially to tech Responds to atomic number, especially at lower k. V ranges No useful diagnostic information Biggest contributor to image contrast 49
Biggest Contributor to Personnel Hazard 50
During Fluoro – the patient is the largest scattering object 51
Image Production Both Compton and Classical cause scatter radiation. Why is one of these a concern to diagnostic radiography and one is not? Why is one a concern to patient safety and one is not? Why is one a concern to technologist safety and one is not? 52
Image Production and Patient Safety Ø Photoelectric absorption is what gives us our image contrast. Ø Photoelectric absorption is determined mostly by atomic number. The lower the k. V of the photons, the more it is affected by atomic number. The higher the k. V, the less atomic number factors into photon absorptions. Ø However, patient dose increases with photoelectric absorptions because the energy of the photon is deposited in the tissue. This affects patient dose. 53
Image Production Differential Absorption Results from the differences between x-rays being absorbed and those transmitted to the image receptor 1. 2. 3. Compton Scattering Photoelectric Effect X-rays transmitted with no interaction 54
Image Production Compton and Differential Absorption Provides no useful info to the image Produces image fog • dulling of the image • NOT representing diagnostic information At higher energies 55
Photoelectric and Differential Absorption Provides diagnostic information X-rays do not reach film because they are absorbed Lower energies (more differential absorption) Gives us the contrast on our image 56
Image Production Beam Attenuation is the reduction in intensity of an x-ray beam as it passes through an object due to the absorption and scattering of photons. The amount of attenuation that occurs depends on the intensity of the original x-ray beam and the physical properties of the object through which the x-ray beam passes. 57
Patient Interactions Review Tube Interaction Heat Brems Characteristic Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration Why These are Important? How our image is created Patient/Tech Safety 58
Patient/Tech Safety How do we measure Radiation and exposure to ensure patient safety? Units of measurement • R, rad, rem Types of measurements • conventional units, SI units Allowable dose limits • • general population patient dose fetal dose personnel doses Detection devices • • • -personal and field TLD Pocket Dosimeter OSL Dosimeter Geiger Muller counter Ionization Chamber Governing bodies for doses • NCRP • NRC • BEIR 59
UNITS OF RADIATION MEASUREMENT 1. To quantify the amount of radiation A: Received by Patient Employee Public 60
Units of Measure Roentgen Rad Rem 61
Unit of Exposure is a measure of the strength of a radiation field at some point in air. This is the measure made by a survey meter. The most commonly used unit of exposure is the roentgen (R). Roentgen: measures the amount of ionization in a certain amount of air after a certain measure of radiation exposure, abbreviated by “R” 62
ROENTGEN (R) I. Unit of measurement =measures ion pairs in a cubic centimeter at given conditions II. The quantity of radiation exposure in air III. Measures output of the x-ray tube IV. Does not indicate the actual patient dose or absorption 63
Absorbed Dose or Absorbed Dose: Dose Absorbed dose is the amount of energy that ionizing radiation imparts to a given mass of matter. In other words, the dose is the amount of radiation absorbed by and object. The abbreviation for absorbed dose is “rad”. 64
Absorbed Dose 65
Dose Equivalent: The dose equivalent relates the absorbed dose to the biological effect of that dose. The absorbed dose of specific types of radiation is multiplied by a "quality factor" to arrive at the dose equivalent. Rem is an acronym for "roentgen equivalent in man. " 66
Dose Equivalent 67
Roengten EQUIVALENT MAN (REM) 1. 2. Different types of radiation produce different responses The unit of dose equivalence, expressed as RAD x QF = REM 3. Used for occupational (employee) exposures 4. Can be used when for dose of patient 68
QUALITY FACTOR Qualifies what the damage is from different types of radiation Example: QF for X-ray is 1 QF for alpha is 20 Alpha is 20 x more damaging to tissue Type of Radiation X-Ray Gamma Ray Beta Particles Thermal Neutrons Fast Neutrons Alpha Particles 69 Rad 1 1 1 Q Factor 1 1 1 5 10 20 Rem 1 1 1 5 10 20
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Why did the bunny die? ? BUNNY A BUNNY B Received 200 rads 71
Why did the bunny die? ? BUNNY A 200 rads x 1 for X-RAY = 200 REMS BUNNY B 200 rads x 20 for alpha = 4000 REMS 72
Types of Measurement Conventional Units SI Units 73
Conventional vs. SI units v. British units used since 1920’s v. United States still uses this system v. New system developed in 1948 v. System of Units based on Metric measurements developed by International Committee for Weights and Measures v 1985 - officially adopted 74
Conv. Units SI Units 1. RADS 1. GRAYS 2. REMS 2. SIEVERT 3. R 3. C/KG 75
Comparsion of Units 76
Comparison of Units Exposure R C/kg 1 R=2. 58 x 10 -4 C/kg Absorbed Dose Rad Gray 1 rad=. 01 Gray=100 rad Dose Equivalent Rem Sievert 1 rem=. 01 Sv 1 Sv=100 rem 77
RADS REMS RADS REMS GRAYS SIEVERTS Patient absorbed dose Employee (technologists) = 78
REMS R - ROENTGENS OCCUPATIONAL EXPOSURE RADS – PATIENT DOSE 79
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The exposure from an x-ray tube operated at 70 k. Vp, 200 m. As is 400 m. R at 36 inches. What will the exposure be at 72 inches? 100 m. R The x-ray intensity at 40 inches is 450 m. R. What is the intensity at the edge of the control booth which is 10 feet away? . . . think carefully… 50 m. R A temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25 m. R at 72 inches. The area behind the chest stand in which the exposure intensity exceeds 1 m. R. How far away from the x-ray tube will this area extend? 30 feet 81
The exposure from an x-ray tube operated at 70 k. Vp, 200 m. As is 400 m. R at 36 inches. What will the exposure be at 72 inches? 100 m. R Use Inverse Square Law The first exposure value is 400 m. R. The first distance is 36 inches. The second intensity is what we are looking for. The second distance is 72” Square both 72 and 36. Cross multiply Cancel out “inches 2”, multiply, divide ? m. R= 100 m. R 82
The x-ray intensity at 40 inches is 450 m. R. What is the intensity at the edge of the control booth which is 10 feet away? . . . think carefully… Use the Inverse Square Law. The first intensity is 450 m. R, the Second intensity is unknown. The first distance is 40 inches. The Second distance is 10 feet…. . Convert feet to inches. So 10 feet is equivalent to 120 inches. Short cut method Cross multiply Cancel units 83
A temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25 m. R at 72 inches. The area behind the chest stand in which the exposure intensity exceeds 1 m. R. How far away from the x-ray tube will this area extend? 30 feet Use Inverse Square Law. The first intensity is 25 m. R, the second Intensity is 1 m. R. The first distance is 72 inches, the second distance Unknown. Cross Multiply 84
Patient/Tech Safety How do we measure Radiation and exposure to ensure patient safety? Units of measurement • R, rad, rem Types of measurements • conventional units, SI units Allowable dose limits • • general population patient dose fetal dose personnel doses Detection devices • • • -personal and field TLD Pocket Dosimeter OSL Dosimeter Geiger Muller counter Ionization Chamber Governing bodies for doses • NCRP • NRC • BEIR 85
Allowable Dose Limits An exposure of 500 roentgens in five hours is usually lethal for human beings. The typical exposure to normal background radiation for a human being is about 200 milliroentgens per year, or about 23 microroentgens per hour. In human tissue, one Roentgen of x-ray radiation exposure results in about one rad of absorbed dose (= 0. 01 Gy). When measuring dose absorbed in man due to exposure, units of absorbed dose are used (the related rad or SI gray), or, with consideration of biological effects from differing radiation types, units of equivalent dose, such as the related rem or the SI Sievert. 86
PUBLIC EXPOSURE NON MEDICAL EXPOSURE 10 % of Occupational exposure 0. 5 rad or 500 mrad or 50 mgray Under age 18 and Students 0. 1 rem 10 mrem 1 m. Sv 87
Education and Training Exposures Student’s must never hold patients during exposures Effective dose limit (Annual) 0. 1 rem or 1 m. Sv (1/50 of Technologist’s dose) 88
Permissible Occupational Dose Annual dose : 5 Rem/year 50 m. Sv/year 5000 mrem Cumulative Dose 1 rem x age or 10 m. Sv x age 89
Allowable DOSE - ANNUAL BRITISH UNIT SI UNIT 5 REMS 5 O m. Sv 90
OCCUPATIONAL EXPOSURES v 5 REMS / YEAR v. BUT NOT TO EXCEED 1. 25 REM/QUARTER 91
Allowable DOSE – TOTAL CUMMULATIVE BRITISH UNIT SI UNIT Age x 1 rem Age x 10 msv 92
Declared Pregnant Worker 93
Declared Pregnant Worker 2 badges provided 1 worn at collar (Mother’s exposure) 1 worn inside apron at waist level (baby exposure) Under 5 rem – negligible risk Risk increases above 15 rem Recommend abortion (spontaneous) 25 rem (“Baby exposure” approx 1/1000 of ESE) www. ntc. gov/NRC/RG/08/08 -013. html 94
Pregnancy & Embryo 1. Mother occupational worker 5 rem 2. Baby 500 m. Rem or. 5 rem/ year . 05 rem/month 5 m. Sv or . 5 m. Sv / month 95
Pregnancy & Embryo 96
Fetus Exposure Radiation exposure is most harmful during the first trimester of pregnancy Embryo-Fetus Exposure limit • 0. 05 rem or 0. 5 m. Sv PER MONTH • 0. 5 rem or 5 m. Sv total gestation 97
Fetus Exposure 98
Response of cells to radiation Cell • Type of cell sensitivity • Type of damage received is dependent • Type of radiation exposed to on: 99
Patient/Tech Safety How do we measure Radiation and exposure to ensure patient safety? Units of measurement • R, rad, rem Types of measurements • conventional units, SI units Allowable dose limits • • general population patient dose fetal dose personnel doses Detection devices • • • -personal and field TLD Pocket Dosimeter OSL Dosimeter Geiger Muller counter Ionization Chamber Governing bodies for doses • NCRP • NRC • BEIR 100
Detection Devices Personal Monitoring Device Field Monitoring Device 101
Personal Radiation Monitoring Monitors measure the quantity of radiation received by worker Any radiation worker must be monitored to determine the estimated exposure dose. 102
Personnel Monitoring Devices 1. Film Badges 2. Thermoluminescent Dosimeters (TLD) 3. Pocket Dosimeters 4. Optically Stimulated Luminescence (OSL Dosimeters) 103
Personnel Monitoring Devices Film badges • worn at collar by employee • film wedged between filters • susceptible to fog from variety of factors • should not be worn longer than 4 weeks 104
Personal Monitoring Devices. Film Badges – c changed monthly 105
Personnel Monitoring Devices Thermoluminescent Dosimetry (TLD) Based on property that xray can luminescence in certain materials Contains reusable crystal More expensive than film badge 106
Personnel Monitoring devices Pocket Dosimeter Pen-like device Contains an ionization chamber Visible scale which provides estimate of gamma dose 107
POSL 108
POSL Looks similar to film badges Contains a piece of aluminum oxide instead of film Easy to change out, keep track of records 109
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Field Survey Instruments • “Cutie Pie” Geiger Muller counter Ionization Chamber 111
Field Survey Instruments Ionization Chamber: • measures the ions in a gas chamber Several • Cutie Pie types of • Rad Cal Ionization Chambers • Geiger-Mueller counter Scintillation Detector 112 • Based on principle that certain crystals emit light when struck by x-rays
Patient/Tech Safety How do we measure Radiation and exposure to ensure patient safety? Units of measurement • R, rad, rem Types of measurements • conventional units, SI units Allowable dose limits • • general population patient dose fetal dose personnel doses Detection devices • • • -personal and field TLD Pocket Dosimeter OSL Dosimeter Geiger Muller counter Ionization Chamber Governing bodies for doses • NCRP • NRC • BEIR 113
Governing Bodies 114
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REGULATORY AGENCIES 1. NCRP - Reviews recommendation for radiation protection & safety. 2. Distributes information re: radiation awareness NRC Makes LAWS & enforces regulations 116
Review What is the annual allowable dose for a 32 year old Technologist? 117
What is the annual allowable dose for a 32 year old Technologist? 5 rem = 5000 mrem - 50 msv 118
What is the cummulative allowable dose for a 32 year old Technologist? 119
What is the cummulative allowable dose for a 32 year old Technologist? 32 REM or 320 m. Sv Or 3200 mrem 120
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