Collected from Internet, text books, etc

1. Radiology
 X rays discovered on Nov. 8, 1898 by Wilhelm Conrad Roentgen-
German physicist
 1901 – he was awarded the noble prize
X rays are gamma rays of EMR
 X rays are gamma rays of EMR
Can be represented in sine wave model
V=n ƛ
 Energy= Plank’s constant x Speed of light
------------------------------------------------------------------
Wavelength
 Energy is inversely proportional to wave length
 The energy unit for EMR is the eV. One eV is energy of the
electron accelerated by potential difference of 1 V.
 EMR – energy greater than 15 eV, ------Produces ionization
within cells.

2.  Ionisation causes ion pairs to form
 A photon is a discrete bundle of EMR
 Ionisation in DNA may result in biologic amplification—ie
affecting the progeny of future generations
 Increased rate of mutation
 Rate of abortion or fetal abnormalities
 Susceptibility to diseases
 Shortened life span
 Cancer
 Cataracts

3.  Radiation protection:Roentgen, rad and rem---units to
quantify radiation exposure, absorption and equivalent
dose respectively. SI unit is coulomb per kg and joule per
kg.
 EMR have speed of light
 Properties:
 No charge, no mass, speed of light, invisible, cannot be felt,
travel in a st. Line , cannot be deflected by magnetic field,
penetrate all matter to some degree, cause certain
substance to fluoresce, can ionize atoms.
 The amount of radiation exposure is quantified by
measuring the no. Of ionization / electric charge produced
by x-rays in air.

4.  C/kg is based on no. Of ion pairs produced in air by the
incoming radiation.
 1 Roentgen=production of 2.58x10-4 C/kg in air. The high
absorber is bone and low absorber is air: absorption is
difference between the incident photon and output photon
after passing through the object.
 Absorption of the same dose in Gy from different types of
radiations may not produce the same biologic effect. For eg
damage from particulate radiation such as alpha particles
and neutrons is greater on a Gy for Gy basis than damage
from the same dose of x rays. This is related to differences
in ionization density for different types of radiation.

5.  A high mass , heavily charged particle such as an
alpha particle creates many ionizations that are very
close to one another in the tissue compared with low
mass lightly charged particle such as electron. So
deposition of 1 Gy from alpha particle absorption does
more ;biologic damage than deposition of 1 Gy from x
ray absorption.

6.  Absorbed dose: varies with object to object. SI unit for
the absorbed dose is gray. Amount of radiation such
that the absorbed energy is 1 joule j/kg of tissue.
 Before the unit of absorbed dose was the rad which is =
100 ergs/g. 1Gy=100 rad. The differential between the
exposure dose and absorbed dose is inversely
proportional to photon energy.

7.  Radiation Damage may be compared by weighting
factor which is a numeric factor describing the relative
effectiveness of a particular type of radiation to
photons. The weighting factor for photons is 1 and it is
greater than 1 for the charged or particulate types of
radiation such as e, n or alpha particles in the SI
system, the unit of dose equivalency is the Sievert (Sv).
 1 sv= absorbed dose in Gy x weighting factor
 REM= ABSORBED dose in rads x weighting factor
 1 Gy=100 rads, 1 Sv = 100 rem. 1 Gy=1 sv

8.  NRC nuclear regulatory commission is the official
source for establishing the guidelines for radiation
protection.
 Recommended that the annual occupational radiation
dose to individual adults should be limited to a
maximum of 0.05 Sv (5 rem)
 No upper ;limit for the cumulative exposure

9.  NCRP national council on radiation protection : to
prevent clinically significant radiation induced effects
by adhering to dose limits that are below the apparent
or practical threshold
 To limit the risk of cancer and heritable effects to a
reasonable level in relation to societal needs and
values and benefits gained.

10.  Max. Permissible dose is the max amt. Of absorbed
radiation that can be delivered to an individual as a whole
body dose or as a dose to a specific organ and still be
considered safe.
 Safe means no evidence of harmful immediate or long term
effects to the body as a whole or to any individual structure
or organ
 ALARA principle: as low as reasonably achievable. But as
no threshold can be established for smokers as to how
much frequency of smoking there will not be any damage
similarly no threshold for radiation has been established.
 NCRP recommendations :

11.  Lifetime effective dose should not exceed age in years x 10
m Sv (age in yrs x 1 REM) and no exposure is permitted
upto 18 yrs.
 So in REMS calculation the lifetime effective dose
equivalent in Rems should not exceed the value of his her
age in yrs
 The effective dose in any 1 yr should not exceed 50 mSv (5
rem)
 For general public should not exceed 1mSv (0.1 rem)
 Pregnancy once declared should not exceed 0.5mSv (0.05
rem)
 For occupationally exposed woman it is yet to be declared

12.  cosmic 8% terrestrial 8% Internal 11% Man made 18%
Medical x rays 11% Nuclear medicine 4% others 3%
 Ionizing radiation damage to DNA: Important target
of ionization
 Because body contains lot of water, lot of free radical
formation is there
 leads to DNA damage

13.  Muscle is not affected easily but growing fetus, BM,
gonadal cells are very sensitive to ionization damage.
 DNA strand breakage, DNA base damage (nucleotide),
DNA cross linkage
 This causes biologic amplification ie passes from
one generation to other
 Protective lead aprons and gloves have 0.5mm
thickness of lead
 Used against secondary radiations

14. •Radiation Badges may contain film (exposure is read by
observing the blackness and it may contain
thermoluminiscence dosimeter TLD) The incoming
radiations cause electron cloud to form and depending on the
no. Of electrons formed radiation dose is assessed.
•Radiation badges must be assessed at least quarterly

15. •When protective apron is worn the badge should be worn on
outside of the apron for monitoring the radiation environment
but inside when the estimate of body exposure is desired.
•Protective glasses provide 0.25 mm of Pb equivalent
•The thyroid shield , scrotal shield, gloves, aprons etc protect
from the radiations
•Primary beam should be properly collimated and should not
exceed the size of the cassette
•Smaller the focal spot better the detail on the RG

16. •Braking radiations or Bremstrauling radiation: two
mechanisms
•1. collision: high energy oncoming electron strikes the inner
shells and eject the electrons having high BE outside, the next
higher shell electrons / outer most orbit drops into the void of
inner shell: this produces radiating x ray which has the energy
proportional to difference in the BE of the two shells. So high
energy incident photon produce high energy x rays. (KV
increases the energy of the x rays). This produces a
characteristic x-ray

18. •2. Radiative/ braking : Just like applying of the brakes. When
oncoming electron brakes and bends around the nucleus
because of the charge difference it bends and changes its
direction this releases energy in the form of x rays. When the
deflected electron decelerates it releases EMR in the form of
an x ray. Because deflected electrons may pass within various
distances of the nucleus braking radiation has a spectrum of
energies.

20. Interaction of radiation with matter
1. Coherent scattering: Photon interacts with an object and changes its direction but
the subject does not absorb the photon and a change in photon energy does not
occur. This is very small in the patient. It may strike the x ray film and degrade the
quality of the image or increase the personnel exposure
2. Photoelectric effect: very effectively results in an image formation . Characteristic
radiation is given off. The energy of the characteristic radiation is a function of the
atomic number of the atom from which it arises. Thus with a large atomic no.
Atom such as tungsten the target of the x ray tube the characteristic x ray is
actually part of the useful x ray beam .

21. The probability of photoelectric interaction is directly proportional to the
cube of the atomic number and inversely proportional to the cube of the
photon energy .
• There is lack of scattered radiations with photoelectric effect because most of
it is absorbed. The decrease in probability of photoelectric absorption as the
energy of the photon beam increases result sin a loss of contrast between
tissue of various types when very high energy photon are use for radiography.
3. Comptons scattering : mainly contributes to the fogging. The outer shell
electron with low energy is ejected and radiation of low energy is is radiated
when this void is filled. It fogs and spoils the quality of film.
4. Photodisintegration
5. Pair production
Pair production and photodisintegration has no relevance with diagnostic
radiology