1. Medical Physics
Option 9.6.3
2006

2. Syllabus - Contextual Outline
The use of other advances in technology, developed from our understanding of the electromagnetic spectrum, and based on sound physical principles, has allowed medical technologists more sophisticated tools to analyse and interpret bodily process for diagnostic purposes. Diagnostic imaging expands the knowledge of practitioners and the practice of medicine. It usually uses non-invasive methods for identifying and monitoring diseases or injuries via the generation of images representing internal anatomical structures and organs of the body.
Technologies, such as ultrasound, compute axial tomography, positron emission tomography and magnetic resonance imaging, can often provide clear diagnostic pictures without surgery. A magnetic resonance image (MRI) scan of the spine, for example, provides a view of the discs in the back, as well as the nerves and other soft tissues. The practitioner can look at the MRI films and determine whether there is a pinched nerve, a degenerative disc or a tumour. The greatest advantage of these techniques are their ability to allow the practitioner to see inside the body without the need for surgery.
This module increases students’ understanding of the history of physics and the implications of physics for society and the environment.

3. Syllabus 9.6.1
The properties of ultrasound waves can be used as diagnostic tools

4. Syllabus 9.6.2
The physical properties of electromagnetic radiation can be used as diagnostic tools

5. Syllabus 9.6.3
Radioactivity can be used as a diagnostic tool

6. Syllabus 9.6.4 The magnetic field produced by nuclear particles
can be used as a
diagnostic tool

7. Ultrasound
X-rays
Medical
Physics
MRI
Nuclear - PET
Endoscopy

8. Brainstorm
Radioactivity
Individual
1 minute
Group
2 minutes

9. Syllabus 9.6.3
Radioactivity can be used as a diagnostic tool

10. Radioactive Isotopes and Half-lives
The atom
Electrons
Nucleus
Protons
neutrons
Quarks
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

11. Radioactive Isotopes Atomic nuclei contain protons and neutrons
The number of protons in the nucleus is called the atomic number
The atomic number determines which element an atom is e.g. all fluorine atoms have 9 protons in the nucleus
The number of neutrons in the nucleus of a particular element can vary
Only hydrogen has isotopes with special names
Atoms of the same element but with different numbers of neutrons are called isotopes
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

12. The atomic nucleus and isotopes
Collectively, protons and neutrons are called nucleons
The total number of nucleons in a nucleus is called the mass number
Nuclei are represented by the symbol for the element, and the mass and atomic numbers
Atoms of the same element but having different numbers of neutrons are called isotopes
mass number 18 F
fluorine 18 9
atomic number
technetium 99 Tc 99 43
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

13. Stable and unstable isotopes
stable nucleus F 19 9
Isotopes having too many or too few neutrons, relative to the number of protons are unstable C 14 6
unstable nucleus F 18 9
unstable nucleus
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

14. Radioactive Decay
Unstable isotopes may become more stable in several ways
Alpha decay (decay)
Beta decay (bdecay)
Gamma () emission
Positron emission (b+ decay)
Each unstable isotope undergoes a particular type of change, which is on average constant and unique to that isotope
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

15. Radioactive Decay
Unstable isotopes may become more stable in several ways
Alpha decay (decay)
Beta decay (bdecay)
Gamma () emission
Positron emission (b+ decay)
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

16. Radioisotopes Radioisotopes may be natural or they can be artificial
Artificial radioisotopes are produced in nuclear reactors or using particle accelerators called cyclotrons
Sydney has one medical cyclotron at Prince Alfred Hospital near Sydney University
Lucas Heights produces a range of artificial isotopes for medical use
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

17. Radioisotopes
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

18. Radioactive Decay
The time taken for 50% of a sample of the radioactive material to decay is called the half-life
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

19. P-210 has a half-life of 12 seconds
Radioactive Decay
Half-life
12 s
P-210 has a half-life of 12 seconds
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

20. Review Question - Half-life
What is the half-life of strontium-90?
28 years
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

21. Radioactive Decay
When beta decay occurs, a neutron in the nucleus changes into a proton (which remains in the nucleus) and an electron (which is ejected from the nucleus at high velocity).
In all nuclear reactions, mass and charge are conserved.
Propose what may happen in the nucleus to produce positron emission.
Answer
A proton changes into a positron and a neutron, which remains in the nucleus and the positron is ejected from the nucleus.
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

22. Decay producing a gamma ray
Technetium-99m nucleus
Gamma decay does not change either the atomic number or the mass number
The nucleus is left in a lower energy state as a result of losing energy in the form of gamma radiation
Gamma rays are very important in nuclear medicine
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

23. Radioactive Isotopes and Half-lives
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

24. Beta+ Decay of Artificial Isotopes
Positron (b+) decay occurs only in certain man-made isotopes
+ decay is medically very important (used in the process of PET scanning)
Positrons are anti-electrons
Positrons have the same mass as an electron, but the opposite charge (+1)
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

25. Penetration by Radiation
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

26. Review Define the term “isotope”.
Outline the characteristic of an isotope that causes it to be unstable and give an example of an element having stable and unstable isotopes.
Technetium-99 is an important medical isotope. Identify the type of radiation produced when Tc-99 decays.
Fluorine-18 decays to produce a positron. Describe the main characteristics of positrons and identify the other main decay product from F-18.
Isotopes are atoms of the same element, having different numbers of neutrons e.g. carbon-12 and carbon-14
Unstable isotopes are characterised by having too many or too few neutrons, relative to the number of protons. e.g. F-19 is stable however F-18 is unstable.
Tc-99 produces gamma radiation when it decays.
Positrons have the same mass as an electron but the same positive charge as a proton. When F-18 decays to produce a positron, an oxygen-18 nucleus is produced.

27. Properties of Radioactive Isotopes
Alpha: highly ionising (high mass and charge), low penetration
Not used medically
Beta: less ionising (low mass and single charge), low penetration
Not used medically
Gamma: least ionising (photon, no charge), high penetration
Used for imaging (gamma scan)
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

28. Properties of Radioactive Isotopes
Source: ANSTO brochure
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

29. Properties of Radioactive Isotopes
Source: ANSTO brochure
outline properties of radioactive isotopes and their half lives that are used to obtain scans of organs

30. Metabolism of Isotopes - Organ Accumulation
Source: ANSTO brochure
describe how radioactive isotopes may be metabolised by the body to bind or accumulate in the target organ

31. Metabolism of Isotopes - Organ Accumulation
Medical radioisotopes are metabolised to bind to specific organs either as elements or as a part of a molecule used by the body
e.g.
iodine-131 is used to monitor thyroid gland function because iodine is metabolised by this gland
Iodine-131 decays with a half-life of days with beta and gamma emissions
fluorine-18 is incorporated into a modified glucose (18 FDG) molecule to investigate a wide range of organ function, especially the brain
Source: ANSTO brochure
describe how radioactive isotopes may be metabolised by the body to bind or accumulate in the target organ

32. Metabolism of Isotopes - Organ Accumulation
Factors influencing the choice of isotopes for medical use
Half-life should be less than a few hours
Should be easily attached to a pharmaceutical agent
Can be delivered to hospital in a form to last several days
describe how radioactive isotopes may be metabolised by the body to bind or accumulate in the target organ

33. Metabolism of Isotopes - Organ Accumulation
Technetium-99m is a widely-used isotope in nuclear medicine
It decays from excited to the ground state by emitting a g ray
The parent isotope is molybdenum 99, having a half-life of 2.7 days
Half-life of technetium-99m is 6.01 hours + 42 99 43
Mo 
Tcm -
+ b
Half life 2.7 days
Half life 6.01 hours 43 99 Tc +
(140 keV) m g
describe how radioactive isotopes may be metabolised by the body to bind or accumulate in the target organ

34. Decays to the excited state of technetium 99
Milking the Cow
Molybdenum-99 is delivered to hospital inside the generator (cow)
Decays to the excited state of technetium 99
NaCl solution passed through cow
99Tcm removed in solution
Mixed with pharmaceutical for labelling
Injected into patient
Radionuclide
generator
describe how radioactive isotopes may be metabolised by the body to bind or accumulate in the target organ

36. Comparison of Bone Scan and X-ray Images
Inject patient with radiopharmaceutical labelled with radioactive isotope
Detect where gamma rays are coming from within the body
Use a gamma camera
Local concentration in patient permits diagnosis
‘Hotspot’ may indicate tumour*
* Tumours contain rapidly dividing cells… therefore metabolism occurs at a higher rate in the tumour… producing a higher than normal concentration of metabolites, in the cells. If tagged with radioisotopes this can be detected.
perform an investigation to compare an image of bone scan with an X-ray image

37. Comparison of Bone Scan and X-ray Images
Collimator restricts direction from which photons reach the camera
Made of lead with parallel holes running through it
Bigger, shorter holes means more photons, but more blurring and visa versa
Details need not be memorised

38. Gamma camera
Details need not be memorised

39. Comparison of Bone Scan and X-ray Images
Detector made from single crystal of sodium iodide
250 mm to 250 mm diameter
6 mm thick
Enveloped in thin aluminium can (light tight)
Light guide takes all light directly to photomultipliers
Glass plate with non-reflective coating
Improves efficiency of light coupling
Details need not be memorised

40. Delivery of Radioisotopes into the Body
Radioisotopes are usually injected* into the body
Short half-life isotopes are used to reduce risk
Isotopes that are excreted rapidly are used
Specific isotopes are chosen specific organs
* sometimes they are inhaled or swallowed

41. Delivery of Radioisotopes into the Body
Whole body bone scan made using a gamma ray camera. The image was produced using gamma emissions from phosphate tagged with technetium–99m.
The tracer was injected intravenously and the phosphate is metabolised mainly in the bones.
The test was done to determine whether cancer had spread to the patient’s bones.
The image is normal, showing that metastasis has not occurred.

42. Bone Scan vs X-Ray
perform an investigation to compare an image of bone scan with an X-ray image

43. Comparison of Diseased and Healthy Organs
Question
Compare a bone scan with an X-ray.
Similarities
Both x-ray and bone scans (gamma or PET) use high energy electromagnetic waves to produce the image
Both types of image show 3-dimensions projected onto a 2-dimensional image
Differences
A radiograph uses x-ray radiation whereas a bone scan uses gamma radiation
The source of x-rays for a radiograph is outside the body whereas the source of gamma rays for a bone scan is inside the body
A radiograph has a higher resolution than a bone scan image [due to the need to use a collimator for the bone scan]
A radiograph is a produces an image that shows structure whereas a bone scan produces an image resulting from functional differences (difference in metabolism - which may reflect structural differences)
perform an investigation to compare an image of bone scan with an X-ray image

44. Comparison of Diseased and Healthy Organs
What caused this hot spot?
Answer
The radioactive tracer was injected into the vein in the arm.
Traces of the radioactive material remain at the injection site.
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart
perform an investigation to compare an image of bone scan with an X-ray image

45. Comparison of Diseased and Healthy Organs
Bone scan
Recount how a bone scan is produced.
Answer
A radiopharmaceutical is put in the patient by injection, inhalation or ingestion. The patient waits while the radiopharmaceutical is metabolised. The radioisotope accumulates in the target organ.
The patient lies down and remains stationary on or under a gamma camera.
Gamma rays are emitted in all directions from the body, however the collimator allows only gamma rays following parallel paths to reach the gamma detector in the camera.
Signals from the detector are processed by a computer to produce an image showing functional information.
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

47. Positron Emission Tomography (PET)
PET is used for
bone imaging
monitoring tumours
monitoring the function of the heart
monitoring blood-flow in the heart
studying brain activity
Overview
A radiopharmaceutical that produces positrons is placed in the body, targeting a particular organ. The radioisotope accumulates in the desired organ. Positrons are emitted into the body as the isotope decays. Positrons annihilate electrons, producing a pair of gamma rays that travel in opposite directions. The pairs of gamma rays are detected by a ring of sensors. Signals from the sensors are processed by a computer to produce an image showing the location and concentration of the radioisotope in the body. The radioactive material is excreted or decays to form harmless products.

48. Radioactive Decay - Positron Production
Phosphorus-30 and fluorine-18 are two artificial radioisotopes that undergo decay that produces positrons
As a result of the radioactive decay of fluorine-18, a positron is emitted from the nucleus 18 F 18 O
b + 9 8 30 P 30 Si + b + 15 14
Explanation - because there are too many protons in the nucleus for it to be stable, one of the protons decays, producing a positron and a neutron which remains in the nucleus
identify that during decay of specific radioactive nuclei positrons are given off

49. Positron Annihilation - Gamma Ray Production
A positron interacts with an electron, annihilating both and producing two g-photons [energy = MeV]
positron + electron => gamma rays
The g-photons travel in opposite directions
Gamma photons produced use in PET
Gives high resolution compared with other gamma imaging technologies [but not as good as X-ray, CT, ultrasound, MRI]
Typical isotopes used: 18F, 68Ga, 15O
Isotopes produced using cyclotron
Main advantage - the image produced is a functional image i.e. it shows HOW the body is working
The most commonly used tracer is 18FDG
(18F fluorodeoxyglucose)
discuss the interaction of electrons and positrons resulting in the production of gamma rays

50. PET Scanner
This imaging technology is called tomography because the image is obtained and usually viewed as slices perpendicular to the long axis of the body. Because the data are analysed by a computer, it is also possible to create a computer-generated 3-D image from the scans.
describe how the positron emission tomography (PET) technique is used for diagnosis

51. Diagnosis Using PET
describe how the positron emission tomography (PET) technique is used for diagnosis

52. How PET Scanning is Performed
PET produces an image of a 2-D section through the body
Tomography: “slice” or “section”
Contrast this with a gamma scan, which produces a 2-D image of a 3-D volume
Similar to CT - HOW?
Many slices can be digitally combined to produce a virtual 3-D image
describe how the positron emission tomography (PET) technique is used for diagnosis

53. How PET Scanning is Performed
Positron + electron annihilate each other
Two g photons are emitted in opposite directions
PET uses annihilation coincidence detection (ACD)!!
Ring of gamma ray detectors around body
Time of arrival and intensity of gamma rays is recorded
2 simultaneous events give line of response (LOR)
Image is built up from LOR data
describe how the positron emission tomography (PET) technique is used for diagnosis

54. How PET Scanning is Performed
Positrons emitted from the tracer annihilate electrons producing gamma ray pairs
The gamma ray pair strikes detectors on opposite sides of the patient
A flash of light is produced by the detectors arranged in a circular ring
A computer compares the intensity of gamma ray pairs over time, and calculates the location of the positron-electron interactions to produce an image
describe how the positron emission tomography (PET) technique is used for diagnosis

55. How PET Scanning is Performed
The greater the depth of tissue through which the gamma rays travel, the greater the attenuation of the gamma rays - enabling the source point to be located by comparing intensities of gamma rays on opposite sides of the body.
describe how the positron emission tomography (PET) technique is used for diagnosis

56. How PET Scanning is Performed
describe how the positron emission tomography (PET) technique is used for diagnosis

57. How PET Scanning is Performed
describe how the positron emission tomography (PET) technique is used for diagnosis

58. Diagnosis Using PET PET Scan
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

59. Diagnosis Using PET
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

60. Diagnosis Using PET
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

61. Diagnosis Using PET
describe how the positron emission tomography (PET) technique is used for diagnosis

62. PET Images of the Brain Heart with myocardial infarction.
Arrows indicate diseased tissue
Normal heart (left)
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

63. PET Images of the Brain Normal brain (left)
Brain of 9 year old girl suffering from epilepsy.
Arrow indicates problem area, which was removed.
Normal brain (left)
gather and process secondary information to compare a scanned image of at least one healthy body part or organ with a scanned image of its diseased counterpart

64. Questions
Identify the particle produced by radioactive decay that is used for to produce PET images. (1M)
Identify the radiation detected to produce a bone scan. (1M)
Compare the processes of taking an X-ray image to producing a PET image. (4M)
Compare the type of images produced using ultrasound and PET. (2M)
Positron
Gamma rays
The radiation source is outside the body in the case of X-rays but it is inside the body in the case of a PET scan. Both processes use e/m radiation to produce the image; X-rays and gamma rays, however the gamma rays are produced inside the body by positron-electron annihilation whereas X-rays are produced using an X-ray tube.
Images produced using ultrasound are structural (showing anatomy) whereas PET produces functional images (showing physiology)

65. PET Images … or not?

66. A word from the creator This PowerPoint presentation was prepared by
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Hurlstone Agricultural High School
Please feel free to use this material as you see fit, but if you use substantial parts of this presentation, leave this slide in the presentation.
Share resources with your fellow teachers and students.

67. End

68. Answers to Questions Question Compare a bone scan with an X-ray.
Similarities
Both x-ray and bone scans (gamma or PET) use high energy electromagnetic waves to produce the image
Both types of image show 3-dimensions projected onto a 2-dimensional image
Differences
A radiograph uses x-ray radiation whereas a bone scan uses gamma radiation
The source of x-rays for a radiograph is outside the body whereas the source of gamma rays for a bone scan is inside the body
A radiograph has a higher resolution than a bone scan image [due to the need to use a collimator for the bone scan]
A radiograph is a produces an image that shows structure whereas a bone scan produces an image resulting from functional differences (difference in metabolism - which may reflect structural differences)

69. Answers to Questions