patient interactions

Patient Interactions

1

Review Tube Interaction Heat Brems Characteristic

Patient Interactions Classic Coherent Compton Photoelectric Pair Production Photodisintegration

Why These are Important? Image Production Patient/Tech Safety


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Review of Tube Interactions: Heat Brems Characteristic


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Heat

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Brems

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Characteristic

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Interaction in the body beginInteraction in the body beginat the atomic levelat the atomic level

AtomsAtomsMoleculesMoleculesCellsCellsTissuesTissuesOrgansOrgans

Patient InteractionsPatient Interactions

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Patient InteractionsInteractions 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

What happens to our What happens to our Primary Beam?Primary Beam?


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EM Interactions with MatterEM Interactions with Matter

General interactions with matter include:1. Scatter

– With or without partial absorption

2. Absorption– Full attenuation


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X-ray photons can change X-ray photons can change cellscells


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Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous

to living tissue.

1913

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Some radiations are energetic enough to rearrange atoms in materials through which they pass, and can therefore he hazardous

to living tissue.

Hiroshima victim


I don’t want that to happen to me!!

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Classical (Coherent) Scattering

Classical (Coherent) Scattering

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 10kV


Classical scattering


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Net Result of ClassicalNo energy transferPhoton changes direction with same energyOccurs with LOW ENERGY photonsNo ionizationNot diagnostic

Classical (Coherent)

Classical (Coherent)


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COMPTON SCATTERING

1. Outer shell electron in body

2. Interacts with x-ray photon from the tube

3. Moderate energy electron


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Recoil electron can Recoil electron can produce another produce another interaction if high interaction if high enough energy. enough energy. Compton scattering Compton scattering doesdoesnot provide any not provide any useful diagnostic useful diagnostic information. information.

compton scattering (effect)


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Moderate energy x-ray photon ejects an outer shell electron.

Energy is divided between scattered photon and the Compton electron (ejected e- or recoil electron)

Scattered photon has sufficient energy to exit body.

Since the scattered photon exits the body, it does not pose a radiation hazard to the patient.

Can increase film fog (reduces contrast)

Radiation hazard to personnel 24


photoelectron

Incoming photon interacts with inner shell electron. The “knocked-out” electron is called a photoelectron. The energy of the incoming photon is absorbed.

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photoelectric interaction


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27CASCADE



Moderate energy x-ray photon ejects inner shell electron (energy absorbed)

Leaves an orbital vacancy, releasing a photoelectron. (As vacancy is filled, another photon is produced-scatter radiation )

More likely to occur in absorbers of high atomic number (bone, positive contrast media)

Contributes significantly to patient dose,

As all the photon energy is absorbed by the patient , this is responsible for the production of short-scale contrast.

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positron

Electron (Negatron)

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30


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Very High Energy Photon…..MkV

Not used in Diagnostic X-ray


Nuclear fragment

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Very High Energy Photon…..MkV

Not used in Diagnostic X-ray


Classical Coherent Low energy photons No diagnostic effect Contributes to scatter

Compton Effect (Scattering) Moderate energy photons No diagnostic effect Contributes to scattering Contributes to personnel dose

Photoelectric Effect Moderate energy photons Definite diagnostic effect Contributes to image contrast Atomic number dependent Contributes to patient dose

Pair Production High energy photons Not useful in diagnostic range

Photodisintegration High energy photons Not useful in diagnostic range

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What kind of interaction is What kind of interaction is this?this?

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ssss


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ssssssssssssssssssss


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Things to Remember About X-ray Interactions with

Matter

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Things to Remember About Diagnostic Radiation

Production

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summary of interactions

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Image production

Why Interactions are Important?

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Biggest Contributor to Personnel HazardBiggest Contributor to Personnel Hazard

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During Fluoro – the patient is the largest scattering object

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Both Compton and Classical cause scatter Both Compton and Classical cause scatter radiation. radiation. Why is one of these a concern to diagnostic Why is one of these a concern to diagnostic radiography and one is not?radiography and one is not?Why is one a concern to patient safety and Why is one a concern to patient safety and one is not?one is not? Why is one a concern to technologist safety and one is not?

Image Production

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Image Production and Patient Safety

Photoelectric absorption is what gives us our image contrast.

Photoelectric absorption is determined mostly by atomic number. The lower the kV of the photons, the more it is affected by atomic number. The higher the kV, the less atomic number factors into photon absorptions.

However, patient dose increases with photoelectric absorptions because the energy of the photon is deposited in the tissue. This affects patient dose.

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Differential Absorption

Results from the differences between x-rays being absorbed and those transmitted to the image receptor

1. Compton Scattering2. Photoelectric Effect 3. X-rays transmitted with no interaction

Image Production

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Compton and Differential Absorption

Image Production

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Photoelectric and Differential Absorption

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Beam Attenuation

Image Production

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Why These are Important? How our image is created Patient/Tech Safety


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Patient/Tech Safety

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UNITS OF RADIATION MEASUREMENT

1.To quantify the amount of radiation

A: Received by Patient Employee Public

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Units of Measure

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Unit of Exposure

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).

RoentgenRoentgen: measures the amount of ionization in a certain amount of air after a certain measure of radiation exposure, abbreviated by “R”

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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

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Absorbed Dose

Dose or Absorbed DoseDose or Absorbed 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”.

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Absorbed Dose

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Dose Equivalent

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."

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Dose Equivalent

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Roengten EQUIVALENT MAN(REM)

1. Different types of radiation produce different responses

2. 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 patient68

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 Rad Q Factor RemX-Ray 1 1 1Gamma Ray 1 1 1Beta Particles 1 1 1Thermal Neutrons 1 5 5Fast Neutrons 1 10 10Alpha Particles 1 20 20

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Why did the bunny die??

BUNNY A

Received 200 rads

BUNNY B

Received 200 rads

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Why did the bunny die??

BUNNY A 200 rads x 1 for X-RAY = 200 REMS

BUNNY B200 rads x 20 for alpha

= 4000 REMS

Types of Measurement

Conventional UnitsSI Units

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Conventional vs. SI units

British units used since 1920’s

United States still uses this system

New system developed in 1948

System of Units based on Metric measurements developed by International Committee for Weights and Measures

1985- officially adopted

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Conv. Units SI Units

1. RADS

2. REMS

3. R

1. GRAYS

2. SIEVERT

3. C/KG

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Comparsion of Units

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Comparison of Units

Exposure R C/kg 1R=2.58x10-4 C/kg

Absorbed Dose

Rad Gray 1rad=.01Gray1Gray=100rad

Dose Equivalent

Rem Sievert 1rem=.01Sv1Sv=100rem

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RADS REMS

RADS

GRAYS

Patient absorbed dose

REMS

SIEVERTS

Employee(technologists) =

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R - ROENTGENS

RADS –

PATIENT DOSE

REMS

OCCUPATIONAL EXPOSURE

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A portable x-ray machine has an output intensity of 4mR/mAs at 40 inches. What will be the output intensity at 30 inches.

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22

2

1

d

d

I

I

2

2

40

30

?

4

inches

inches

mR

mR

inches

inches

mR

mR

1600

900

?

4

inchesmRinchesmR 900*?1600*4

900

6400? mR

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The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72 inches? 100mRThe x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which is 10 feet away?......think carefully… 50mRA temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25mR at 72 inches. The area behind the chest stand in which the exposure intensity exceeds 1 mR. How far away from the x-ray tube will this area extend?30 feet

The exposure from an x-ray tube operated at 70kVp, 200mAs is 400mR at 36 inches. What will the exposure be at 72

inches?

100mR

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21

22

2

1

d

d

I

I Use Inverse Square Law

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22

36

72

?

400

inches

inches

mR

mR The first exposure value is 400mR. The first distance is

36 inches. The second intensity is what we are looking for. The second distance is 72”

2

2

1296

5184

?

400

inches

inches

mR

mR Square both 72 and 36.

22 12964005184? inchesmRinchesmR Cross multiply

2

2

5184

1296400?

inches

inchesmRmR Cancel out “inches2”, multiply, divide

?mR= 100mR

The x-ray intensity at 40 inches is 450mR. What is the intensity at the edge of the control booth which

is 10 feet away?......think carefully…

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21

22

2

1

d

d

I

I Use the Inverse Square Law. The first intensity is 450mR, the

Second intensity is unknown. The first distance is 40 inches. TheSecond distance is 10 feet…..Convert feet to inches.

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22

40

120450

inches

inches

xmR

mR So 10 feet is equivalent to 120 inches.

2

2

1600

14400450

inches

inches

xmR

mR

2

2

1

9450

inches

inches

xmR

mR Short cut method

2

2

14400

1600450

inches

inchesmRxmR Cross multiply

Cancel units

2

2

9

1450

inches

inchmRxmR

mRxmR 50

A temporary Chest Unit is set up in an outdoor area. The technique used results in an exposure intensity of 25mR at 72 inches. The area

behind the chest stand in which the exposure intensity exceeds 1 mR. How far away from the x-ray tube will this area extend?

30 feet

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21

22

2

1

d

d

I

I

Use Inverse Square Law. The first intensity is 25mR, the secondIntensity is 1mR. The first distance is 72 inches, the second distanceUnknown.

2

2

721

25 x

mR

mR

2

22

51841

25

inches

inchesx

mR

mR

222 5184251 inchesmRinchesxmR Cross Multiply

mR

inchesmRinchesx

1

518425 222

222 129600inchesinchesx

22 129600inchesx inchesx 360

Patient/Tech Safety

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Allowable Dose LimitsAn exposure of 500 roentgens in five hours is An exposure of 500 roentgens in five hours is usually lethal for human beings.usually lethal for human beings.The typical exposure to normal background The typical exposure to normal background radiation for a human being is about 200 radiation for a human being is about 200 milliroentgens per year, or about 23 microroentgens milliroentgens per year, or about 23 microroentgens per hour.per hour.In human tissue, one Roentgen of x-ray radiation In human tissue, one Roentgen of x-ray radiation exposure results in about one rad of absorbed dose exposure results in about one rad of absorbed dose (= 0.01 Gy). (= 0.01 Gy). When measuring dose absorbed in man due to When measuring dose absorbed in man due to exposure, units of exposure, units of absorbed dose absorbed dose are used (the are used (the related related radrad or SI or SI graygray), or, with consideration of ), or, with consideration of biological effects from differing radiation types, biological effects from differing radiation types, units of units of equivalent doseequivalent dose, such as the related , such as the related remrem or or the SI the SI SievertSievert..

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PUBLIC EXPOSURE NON MEDICAL EXPOSURE

10 % of Occupational exposure0.5 rad or 500 mrad or 5mGray

Under age 18 and Students 0.1 rem

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Education and Training Exposures

Student’s must never hold patients during exposures

Effective dose limit (Annual) 0.1 rem or 1 mSv

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Permissible Occupational Dose

Annual dose : 5 Rem/year 50mSv/year 5000 mrem

Cumulative Dose 1 rem x age or 10mSv x

age

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Allowable DOSE - ANNUAL

CONVENTIONAL UNITS

5 REMS

SI UNIT

5O mSv

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OCCUPATIONAL EXPOSURES

5 REMS / YEAR

BUT NOT TO EXCEED 1.25 REM/QUARTER

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Allowable DOSE – TOTALCUMMULATIVE

CONVENTIONAL UNITS

Age x 1 rem

SI UNIT

Age x 10msv

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Declared Pregnant WorkerDeclared Pregnant Worker

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Declared Pregnant WorkerDeclared 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

www.ntc.gov/NRC/RG/08/08-013.html

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Pregnancy & Embryo

1. Mother occupational worker

5 rem

2. Baby 500 mRem or .5 rem/

year .05 rem/month

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Fetus Exposure

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Fetus Exposure

Patient/Tech Safety

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Detection Devices

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Personal Radiation Monitoring

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Personnel Monitoring Devices

1. Film Badges

2. Thermoluminescent Dosimeters (TLD)

3. Pocket Dosimeters

4. Optically Stimulated Luminescence (OSL Dosimeters)


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Personal Monitoring Devices-

Film Badges – c changed monthly

Thermoluminescent Dosimetry

(TLD)


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Based on property that x-ray can luminescence in certain materials

Contains reusable crystal

More expensive than film badge

Pocket Dosimeter

Personnel Monitoring devices

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Pen-like deviceContains an ionization chamberVisible scale which provides estimate of gamma dose-provides immediate dose estimate

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POSL

POSL

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Looks similar to film badgesContains a piece of aluminum oxide instead of filmLaser reads the luminescence to determine exposureEasy to change out, keep track of records

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Field Survey Instruments

Geiger Muller counter

• “Cutie Pie”

Ionization Chamber

Field Survey Instruments

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Patient/Tech Safety

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Governing Bodies

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REGULATORY AGENCIES

NCRP - Reviews recommendation for radiation protection & safety. Distributes information re: radiation

awareness

National Council on Radiation Protection and MeasurementsNational Council on Radiation Protection and Measurements

Nuclear Regulatory CommissionNuclear Regulatory Commission makes laws and enforces regulations

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What is the annual allowable dose for a 32 year old Technologist?

Review

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What is the annual allowable dose for a 32 year old Technologist?

5 rem = 5000 mrem - 50 msv

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What is the cummulative allowable dose for a 32 year old Technologist?

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What is the cumulative allowable dose for a 32 year old Technologist?

32 REM or 320 mSv Or 3200 mrem

patient interactions

Documents

em interactions

effectpatient interactions

mattergeneral interactions

cellspatient interactions

review of tube interactions

incident photon

patient interactionscompton

sufficient energy