1. Unit 8 - Medical Physics
Nikki Kelso

2. Aims of this Session Production of and uses of thermographic images
Introduce the production of & dangers of using x- rays
Stochastic & Non Stochastic effects
Somatic & Hereditary effects
Uses of Radioisotopes & Nuclear Medicine
Production & uses of Medical Ultrasound
Magnetic Resonance Imaging (MRI)

4. Thermography • Infra-red detectors pick up IR radiation
• Amount of radiation increases with temperature therefore thermography allows you to visualise variations in temperature
• computer algorithms used to interpret data and produce a usable image

5. Why is this Useful?
Certain pathologies cause temperature differentials
Thermography detects these with high sensitivity & accuracy
Non – invasive
NO Ionising Radiation used

6. Types of Diagnosis Sports injuries Breast cancer screening
Monitoring of post operative infection

7. What we do in Radiology Departments
Plain film radiography
Contrast studies
Computerised Tomography
Radioisotope imaging
Ultrasound
Magnetic resonance imaging
Bone density measurement
Positron emission tomography

8. X Rays • Discovered in 1895 by Roentgen
• “X” Rays because he didn’t know what they were!
• An ionising radiation at a higher level on EM spectrum
• Higher frequency or shorter wavelength

9. X-ray Production

10. X rays, the risks and dangers.
Ionising Radiation – potentially damaging
Damage is influenced by:
amount of body tissue irradiated
type of body tissue irradiated
dose received
dose rate
Risk minimised using “ALARA” principle

11. Precautionary Measures
Legislation
Ionising Radiation Regulations 1999
IR(ME)R 2000
In Practice we use
radiation protection
ALARA principle

12. Staff Protection Not place themselves in the primary beam
Use of the inverse square law
Use of lead glass panels
Use of lead rubber coats/thyroid shields/lead glasses
Limit of time spent in fluoroscopy: especially during pregnancy
QA of the equipment
Dose monitoring

13. Patient Protection Correct exposure factors QA done daily on equipment
Collimation of the primary beam
Correct focus/film distance
Use of appropriate lead rubber protection where appropriate ie gonads/eyes/thyroid
Appropriate examination
Well trained staff

14. X Ray Effects Stochastic – no threshold for damage
Non stochastic – a quantifiable threshold
Effects can take place in somatic cells or be passed on (hereditary)

15. Stochastic Effects
Probability of the effect of radiation which can be either radiation induced cancers or genetic effects.
No safe dose limit
Statistically generated
Lower doses of radiation

16. Non Stochastic Effects
Also called deterministic effects
There is usually a threshold below which the effect will not occur
Examples are erythema (skin reddening) or epilation (hair loss)
Doses are large eg following radiotherapy or as a result of a radiation accident (Chernobyl)

17. Damage caused by radiation
SOMATIC caused to the individual
GENETIC passed onto future generations

18. How are effects measured?
• Sievert is unit of measurement – equivalent to a deposit of 1 joule of energy per kilogram mass of tissue
• Relates dose absorbed in tissue to biological damage caused – “effective” dose
• This will depend on the type of radiation
• Typical background radiation results in an effective dose of 2.4 mSv/year

19. Additional risk of cancer per exam
Examples of Doses
We’re all exposed to background radiation
Chest = few days
Skull = few weeks
Spine/Abdo = Few months or a year
CT Chest = few years
Additional risk of cancer per exam
1 in 1,000 to 1 in 1,000,000
Risk of cancer 1 in 3

20. Image production • Basic form uses photographic film
• Denser structures attenuate the x-rays
• When film is exposed to x rays it turns black
• Image is contrast between two
• Contrast can be manipulated using exposure factors and other aids such as contrast media

21. Variations in Contrast

22. Using contrast media

23. Factors affecting contrast
Transmission – x-ray photons that pass through the patient unchanged.
Absorbtion – x-ray photons that transfer their energy to the patient.
Absorbtion is proportional to the degree of attenuation – thickness, density & atomic number
Scatter – radiation that changes direction or is modified by decrease in energy as it passes through a body
Attenuation – process that x-rays lose power as it travels through matter

24. Plain film radiography

25. Mobile Radiography
Mobile unit can be moved to patients bedside, A&E dept or theatre
Can be mains or battery powered
Can produce images as good as purpose built units.

26. Digital imaging Images stored on computer No films Image manipulation
Multiple viewing
Storage
Volume
Physical principles remain the same
But because its Windows based

27. “C” arm for angiography

28. Ultrasound Ultrasound uses sound waves to produce images
Becoming highly skilled
Increasingly specialised
Images are very dependent on the ultrasonographers skill

29. Ultrasound images

30. Ultrasound images

31. Computerised Tomography

32. CT explained Tomography tomos – slice graphia – describing
Where digital geometry processing is used to generate a three-dimensional image of the internals of an object from a large series of two dimensional x-ray images taken around a single axis of rotation.

33. CT in practice Data is obtained digitally
Algorithms allow manipulation of data
Windowing is process of using a variety of Hounsfield Units
Setting a top and bottom of range allows various tissue types to be imaged
Can “get rid” of what you are not interested in

34. Magnetic Resonance Imaging
The latest imaging tool
Images are similar in appearance to CT but produced without radiation
Technology utilises radio waves and a huge magnet to produce images
The magnet must be kept cool to allow superconductivity. It has to be cooled with liquid helium to -270 degrees.

35. MR scanner

36. MR Precautions Not everybody can have an MRI scan
Metal implants eg cardiac pacemakers, aneurysm clips
Tattoos
Metallic foreign bodies
Pregnant women
claustrophobics

37. MRI Images

38. CT versus MR Principles of data collection are the same
MR is Non Ionising
Better at imaging softer tissue

39. Which Modality to use What are you attempting to image?
What level of information do you wish to obtain?
How do you wish to manipulate it?
What protection measures need to be considered?

40. Radioisotope Imaging What is an isotope?
Nuclei of atoms consist of protons and neutrons.
The number of protons is called the atomic number
The number of protons and neutrons is called the mass number
All the atoms of one element with the same atomic number but different mass number are called isotopes

41. Radioisotopes Isotopes behave chemically the same
some of the radioisotopes will be radioactive ie emit radiation
By attaching these radioactive isotopes to certain pharmaceuticals we can use the emitted radiation to produce images
Most commonly used isotope is Technetium99m because it decays by gamma emission

42. What is Radioactivity?
Certain elements have isotopes which are unstable
The unstable atoms emit particles or energy
The particles or energy are radiation
The process is unpredictable
It is measured in Becquerels – 1 Bq is one “decay” event per second

43. Radiation Types Alpha – helium nuclei stopped by paper
Beta – electron, can be stopped by light metal
Gamma – EM photon, requires dense material to absorb

44. Half Life
The time taken for half of the atoms of a given sample to decay
Stays the same for a given isotope regardless of the actual quantity
Expressed as a unit of time
Can be validated using experimentation and computer modeling

45. Uses for Isotopes Nuclear Medicine
Branch of imaging science which uses unsealed radioactive sources
Gamma sources are isotope of choice

46. How does it work?
Radioactive isotopes are labelled with pharmaceuticals
Now known as radiopharmaceuticals
Introduced into the body
Pharmaceuticals influence tissue type which absorbs isotope
Gamma emission is detected by a gamma camera
Image is digitally produced

47. Gamma Camera Detects individual Gamma photons
Builds up an image over a period of several minutes
Useful to show biological (metabolic) processes eg infections/secondary boney cancer deposits

48. Why do we use Nuclear Medicine?
Radiopharmaceuticals do not cause much harm in proportion to benefit derived
Body will excrete material
Radioactivity is short lived – matter of hours
Can be used to image anatomy and physiology
Can be integrated with other modalities (PET)

49. Production Most useful isotopes are not natural
Must be produced by reactors
Side product of used nuclear fuel
Used uranium fuel has a content of molybdenum99
Easily extracted
Technetium99 is a daughter product
A few micrograms of molybdenum99 will produce enough technetium 99 to image 10,000 patients

50. Radioisotope/NM Images

51. Positron Emission Tomography latest radiology tool to image patients

52. Positron Emission Tomography PET

53. QUESTIONS?