1. Introduction To Clinical
Radiology
Dr. Bijay Kumar Yadav
MD-Radiology Resident
I.K. Akhunbaev KSMA

2. Contents Of Study
• Types and properties of electromagnetic
waves.
• Physical and biological basis of radiation.
• Medical imaging.
• Prevention of radiation and Dosimetry.

3. Clinical Radiology
 It is a field of medicine which works by theory and
practical application of radiation for medical purposes.
 Include two main disciplines:
Diagnostic radiology and
Therapeutic radiology (radiation therapy).
 Without radiology today can not do any medical
discipline.

4. Radiology
Importance:
• Radiologists need communication with clinicians to
understand clinical problem.
• Clinician need communication with radiologists to
understand the strengths and limitations of the
investigations suggested.
• Suitable and sensible selection of imaging investigations and
interventions.
Approaches:
• Aimed in the direction of patient’s symptoms hoping that
something will turn up
• Trial and error: try one or two likely diagnoses and carry out
the appropriate test to support or refute these possibilities.
Keep in mind:
• Less expensive
• Less distress to the patient
• Critical clinical evaluation to choose appropriate tests.

5. Types Of Radiation
1. Electromagnetic waves
2. Elastic waves

6. Electromagnetic Waves Theory
• Electromagnetic waves are waves that are created as a result
of vibrations between an electric field and a magnetic field.
• In other words, EM waves are composed of oscillating
magnetic and electric fields.
• Electromagnetic waves are formed when an electric field
comes in contact with a magnetic field. They are hence known
as ‘electromagnetic’ waves.
• The electric field and magnetic field of an electromagnetic
wave are perpendicular to each other. They are also
perpendicular to the direction of the EM wave.

8. Radiation:
 It is the energy that comes from the source & travel
through the space & may be able to penetrate various
materials.
 Radiation can also be produced by high-voltage devices
(e.g. X-rays machine)
 Types of radiation:
i. Ionizing radiation
ii. Non-Ionizing radiation

9. Why We Concerned About Radiation??
Ionizing Radiation
Human cells
Atoms in cells form Ions
No changes in cells Change in cells Cell dies
Reproduces Replaced
Not replaced
Benign growth
Malignant growth

10. Radiation Causes Ionization Of:
Cells Which May Affect
Molecules
Tissues
Organ
The whole body
Which may affect
Which may affect
Which may affect

11. DNA Mutation

13. 1. Ionizing Radiation:
 Ionizing radiation is a form of energy that acts by
removing electrons from atoms & molecules that
include air, water & living tissues & it can travel unseen
& pass through these materials.
 Ionizing radiation is produced by unstable atoms.
 Unstable atoms differ from stable atoms because
unstable atoms have an excess of energy or mass or
both.
 Energy is “packaged” in small units known as photons
or quanta.

14.  EM radiation has no mass, is unaffected by either
electrical or magnetic fields, and has a constant speed in
a given medium.
 These include X- ray and gamma radiation.
Examples of ionizing radiation:
i. Natural:
low level radiation which come from natural sources.
- radiation from space (cosmic & solar radiation)
- radiation from earth (terrestrial radiation)
- radiation from building materials
ii. Man made:
- X-rays, CT, PET, Fluoroscopy, Nuclear medicine
procedure

15. Particulate Radiation
• The other type of radiation consist of small particles of
matter moving through space at a very high velocity
• Particle radiation differs from EMR in that the particles
consist of matter and have mass.
• Particle radiation is generally not used as an imaging
radiation because of its low tissue penetration.
• E.g. α and β- particles, protons, neutrons, electrons,
positrons, Heavy metal and other parts of the nucleus.

16. 2.Non-Ionizing radiation
 A type of low-energy radiation that does not have
enough energy to remove an electron (negative particle)
from an atom or molecule.
 Non-ionizing radiation includes:
i. Radio waves
ii. Microwaves
iii. Infrared
iv. Visible light
v. Ultraviolet
 Most types of non-ionizing radiation have not been
found to cause cancer.

17. Examples of Non-Ionizing radiation:
 Radiofrequency (RF) radiation used in many
broadcast & communications applications.
 Microwaves used in the home kitchen.
 Infrared radiation used in the heat lamp.
 Ultraviolet radiation from the sun.

18. Ionizing v/s Non-Ionizing Radiation
Ionizing Radiation Non-Ionizing Radiation
 Ionizes tissue  Don’t ionizes tissue
 Causes genetic damage  No known genetic damage
Modalities: Modalities:
• CT scans
• Fluoroscopy
• Conventional radiographs (plain films)
• Nuclear imaging modalities
(Photons and corpuscular radiation)
• MRI
• Ultrasound
• Thermography
X-
Ray

20. Ionization:
 Ionization is the principal means by which ionizing
radiations dissipate their energy in matter. In this process the orbital
electrons absorb energy from the incident photon, resulting in
ejection of that electron, leaving the atom positively charged
(positively ionized).
 This process in tissue can damage important molecules such as
DNA, that varies from minutes to weeks to years.

21. Understanding Ionization:

22. Electromagnetic Spectrum:
 Is the transport of energy through space as a
combination of electric and magnetic fields.
 Is produced by a charge (charged particle) being
accelerated. Electrons are consider as standing waves
around the nucleus and therefore do not represent
accelerating charges.
 Any accelerating charge not bound to atom will emit EM
radiation.

23. Electromagnetic Spectrum:
Ultraviolet Band: Non-Ionizing & Ionizing
The electromagnetic (EM) spectrum is the range of all types of EM radiation.

24. Electromagnetic Spectrum:
1. Ionizing Radiation:
Short wavelength, High frequency & Higher Energy
2. Non-Ionizing Radiation:
Longer wavelength, Lower frequency & Lower energy
 We can say wavelength & frequency is inversely proportion
where as frequency & energy is directly proportion.

25. Photoelectric Effect:
The photoelectric effect is the emission
of electrons when electromagnetic radiation, such as x-rays,
hits a material. Electrons emitted in this manner are called
photoelectrons.

26. FIGURE: Photoelectric Effect- The photoelectric effect is responsible for total
absorption of the incoming x-ray photon.

27. The Penetrating Power Of Radiation In
Matter

28. The Use Of Radiation In Medicine Is Based On
Four Properties Of Interaction With Matter

30. Radio Sensitivity
RS : Probability of a cell, tissues or organ of suffering
an effect per unit of dose.
Bergonie and Tribondeau (1906) : “RS LAWS” : RS
will be greater if the cell:
Is highly mitotic.
Is undifferentiated.
Has high cariocinetic future.

31. Radio Sensitivity (RS)
High RS Medium RS Low RS
Bone marrow Skin Muscle
Gonads
Mesoderm organ (Liver,
Lungs, Heart etc
Cartilage
Thymus Bones
Spleen Nervous system
Lymphatic nodes
Eye lens
Lymphocytes

32. Elastic Waves

34. Radiation Measurements:
• Radiation can measured in the same manner as other physical
concepts such as Time, Distance and Weight.
• International commission on radiation units and measurement
(ICRU) has established special units for the measurement of
radiation.
• Such units are used to define four quantities of radiation:
i. Exposure
ii. Dose
iii. Dose equivalent
iv. Radioactivity
• At present, two systems are used to define radiation measurements:
1. The older system is referred to as the traditional system, or
standard system
2. The newer system is the metric equivalent known as the SI
system.

35. Exposure
The term exposure refers to the measurement of ionization
in air produced by X-rays.
Standard unit – Roentgen (R)
SI unit – Coulombs per kilogram (C/kg)
Dose
Dose can be defined as the amount of energy absorbed by a
tissue.
Standard unit – Radiation absorbed dose (rad)
SI unit – Gray (Gy)

36. Dose Equivalent
Different types of radiation have different effects on
tissues, the dose equivalent measurement is used to
compare the biologic effects of different types of radiation.
Standard unit – Roentgen equivalent (in) man (rem)
Si unit – Sievert (Sv)
1 rem = 0.01 Sv
1 Sv = 100 rems

37. Radioactivity:
• It is the process by which a nucleus of an unstable atom
loses energy by emitting ionizing radiation.
– Standard unit- Curie (Ci)
– SI unit- Becquerel (Bq)
• One Curie is equal to 3.7×10^10 (37 billion Bq)
disintegration per second.
• One Becquerel is equal to one disintegration per second.

38.  Radioactivity: Spontaneous emission of radiation from
the nucleus of an unstable atom.
 Isotope: Atoms with the same number of protons, but
different number of neutrons.
 Radioisotope: Unstable isotope of an element that decays
or disintegrates spontaneously, emitting radiation.
Approximately 5,000 natural and artificial radioisotopes
have been identified.

39. Two Categories Of Radioactivity
1. Natural radioactivity: This is the spontaneous
disintegration of naturally occurring radio-nuclides to
form a more stable nuclide with the emission of
radiations of alpha, beta and gamma.
2. Artificial radioactivity: This is the spontaneous
disintegration of radio-nuclides when bombarded with
a fast moving thermal neutron to produce a new
nuclide with the emission of radiations of alpha, beta
and gamma and a large amount heat.

40. Radioactive sources

41. Radioactive Carbon (C-14)

42. Prevention Of Radiation Sickness:
• Avoid unnecessary exposure to radiation.
• Persons working in radiation hazard areas should wear
badges to measure their exposure levels.
• Protective shields should always be placed over the
parts of the body not being treated or studied during x-
ray imaging tests or radiation therapy.

43. What Are The Basic Measures In
Radiation Protection?
• Shortening the time of exposure,
increasing distance from a
radiation source and shielding
are the basic protective
measures to reduce doses from
external exposure.
• Time: The less time that people
are exposed to a radiation
source, the less the absorbed
dose.
• Distance: The farther away that
people are from a radiation
source, the less the absorbed
dose.

44. Shielding:
Barriers of lead, concrete or water can stop radiation or
reduce radiation intensity.

45. To Reduce Doses From Intake Of
Radioactive Substances, The Following Basic
Countermeasures Can Be Considered:
 Shortening time of exposure to contaminants.
 Preventing surface contamination.
 Preventing inhalation of radioactive materials in air.
 Preventing ingestion of contaminated foodstuffs and
drinking water.

46. Ways To Reduce Staff Radiation
Exposure
 Reduce exposure time
 Increase distance from radiation
 Use proper shielding
 Wear radiation film badge is exposed to multiple x-rays.

48. Ways To Reduce Patient Exposure To
Ionizing Rays
 Eliminate unnecessary radiographs and projections.
 Shield the most radiation sensitive areas (gonads, eye
lens, thyroid).
 Reduce area irradiated.
 Avoid x-rays in pregnancy.

49. Imaging Modalities
X-Rays
USG
CT-Scan
MRI
PET-Scan

50. Methods/Modalities Of Investigations:
1. Conventional radiography (x-rays)
a. Plain x-rays
b. Contrast radiography
c. Conventional angiography
d. Mammography
2. Digital radiography
3. Computed Tomography (CT scan)
a. Conventional CT
b. Spiral (helical) CT
c. Multi-slice (multi-detector) CT: faster, thin slide, 3D
reconstruction, angiography
d. CT angiography
e. 3D reconstruction CT
f. Contrast CT.

51. 4. Ultrasound
a. Conventional USG
b. 3D and 4D USG
c. Doppler imaging
5. MRI (magnetic resonance imaging)
a. T1-weighted scan
b. T2-weighted scan
c. MR angiography
d. Contrast MRI

52. 6. Radionuclide imaging: radioactive isotope
a. Conventional study (gamma camera)
b. SPECT (Single photon emission computed
tomography) using moving gamma camera
c. PET (positron emission tomography): to study
physiological procedure (perfusion, metabolism, etc.)
using short-lived positron-emitting isotopes
produced by cyclotron
7. PACS (picture archiving and communicating
systems): electronic transmission of images..

53. All X-ray Modalities Work On The Same
Basic Principle:
An X-ray beam is passed through the body where a
portion of the X-rays are either absorbed or scattered by
the internal structures, and the remaining X-ray pattern is
transmitted to a detector (e.g. film or a computer screen)
for recording or further processing by a computer.

54. THANK YOU