Dec 7th PET/SPECT

1,409 views

Published on

Published in: Business, Technology
0 Comments
1 Like
Statistics
Notes
  • Be the first to comment

No Downloads
Views
Total views
1,409
On SlideShare
0
From Embeds
0
Number of Embeds
2
Actions
Shares
0
Downloads
118
Comments
0
Likes
1
Embeds 0
No embeds

No notes for slide

Dec 7th PET/SPECT

  1. 1. Nuclear medicine Pet/Spect Chapters 18 to 22
  2. 2. Activity • Number of radioactive atoms undergoing nuclear transformation per unit time. Change in radioactive atoms N in time dt Number of radioactive atoms decreases with time (- minus sign) Α= − δΝ δτ
  3. 3. Activity • Expressed in Curie – 3.7x1010 disintegrations per second dps Becquerel discovers natural radioactive materials in 1896 the SI unit for radioactivity is the Becquerel. 1 becquerel = 1dps Α= − δΝ δτ
  4. 4. Nuclear medicine • Therapeutic and diagnostic use of radioactive substances • First artificial radioactive material produced by the Curies 1934 → “Radioactivity,” “Radioactive
  5. 5. Definitions: Nuclide • Nuclide: Specie of atoms characterized by its number of neutron and protons • Isotopes • Isotones • Isobars • (…)
  6. 6. Definitions: Nuclide • Isotopes are families of nucleide with same proton number but different neutron number. • Nuclides of same atomic number Z but different A → same element • A ZX • A mass number, total # of protons and neutrons • Z atomic number (z# protons) 6 12 Χ 6 13 Χ
  7. 7. Definitions: Nuclide • Radionuclide: Nuclide with measurable decay rate • A Radionuclide can be produced in a nuclear reactor by adding neutrons to nucleides 59 Co + neurtron -> 60 Co
  8. 8. Radioactive Decay • Disintegration of unstable atomic nucleus • Number of atoms decaying per unit time is related to the number of unstable atoms N through the decay constant (λ) − δΝ δτ = λΝ
  9. 9. Radioactive Decay • Radioactive decay is a random process. • When an atom undergoes radioactive decay -> radiation is emitted • Fundamental decay equation (Number of radioactive atoms at time t -> Nt Ντ = Ν0ε−λτ
  10. 10. Radioactive Decay • Father and daughter. • Is Y is not stable will undergo more splitting (more daughters) Ζ Α Ξ Ζ−2 Α−3 Ψ Father Daughter
  11. 11. Radioactive Decay Processes
  12. 12. Radioactive Decay Processes
  13. 13. Alpha decay • Spontaneous nuclear emission of α particles ∀ α particles identical to helium nucleus -2 protons 2 neutrons ∀ α particles -> 4 times as heavy as proton carries twice the charge of proton Ζ Α Ξ→Ζ−2 Α−4 Ψ+ 2 4 Ηε+2 + ενεργψ
  14. 14. Alpha decay • Occurs with heavy nuclides • Followed by γ and characteristic X ray emission • Emitted with energies 2-10MeV • NOT USED IN MEDICAL IMAGING Ζ Α Ξ→Ζ−2 Α−4 Ψ+ 2 4 Ηε+2 + ενεργψ
  15. 15. Positron emission β+ • Decay caused by nuclear instability caused by too few neutrons • Low N/Z ratio neutrons/protons • A proton is converted into a neutron – with ejection of a positron and a neutrino Z A X→ Z −1 A Y + β+ +ν +energy positron neutrino
  16. 16. Positron emission β+ • Decrease of protons by 1 atom is transformed into a new element with atomic # Z-1 • The N/Z ratio is increased so “daughter” is more stable than parent Z A X→ Z −1 A Y + β+ +ν +energy positron neutrino
  17. 17. Positron emission β+ 9 18 Φ→8 18 Ο + β+ + ν + ενεργψ ποσιτροννευτρινοFluorin oxygen
  18. 18. Positron emission β+ 9 18 Φ→8 18 Ο + β+ + ν + ενεργψ ποσιτροννευτρινοFluorin oxygen
  19. 19. Positron emission β+ • Positron travels through materials loosing some kinetic energy • When they come to rest react violently with their antiparticle -> Electron • The entire rest mass of both is converted into energy and emitted in opposite direction – Annihilation radiation used in PET
  20. 20. Annihilation radiation • Positron interacts with electron->annihilation • Entire mass of e and β+ is converted into two 511keV photons 511keV energy equivalent of rest mass of electron
  21. 21. β- decay • Happens to radionuclide that has excess number of neutron compared to proton • A negatron is identical to an electron • Antineutrino neutral atomic subparticle Ζ Α Ξ→Ζ+1 Α Ψ+ β− + ν ∼ + ενεργψ νεγατροναντινευτρινο
  22. 22. Electron captive ε • Alternative to positron decay for nuclide with few neutrons • Nucleus capture an electron from an orbital (K or L) Ζ Α Ξ + ε− →Ζ−1 Α Ψ+ ν + ενεργψ νευτρινο
  23. 23. Electron captive ε • Nucleus capture an electron from an orbital (K or L) • Converts protons into a neutron ->eject neutrino • Atomic number is decreased by one – new element Ζ Α Ξ + ε− →Ζ−1 Α Ψ+ ν + ενεργψ νευτρινο
  24. 24. Electron captive ε • As the electron is captured a vacancy is formed • Vacancy filled by higher level electron with Xray emission • Used in studies of myocardial perfusion 81 201 Τλ→89 201 Ηγ + ν + ενεργψ νευτρινο
  25. 25. Isomeric transition • During a radioactive decay a daughter is formed but she is unstable • As the daughter rearrange herself to seek stability a γ ray is emitted Ζ Αµ Ξ→Ζ Α Ξ + ενεργψ γραψ
  26. 26. Principle of radionuclide imaging Introduce radioactive substance into body Allow for distribution and uptake/metabolism of compound ⇒ Functional Imaging! Detect regional variations of radioactivity as indication of presence or absence of specific physiologic function Detection by “gamma camera” or detector array (Image reconstruction)
  27. 27. Radioactive nuclide • Produced into a cyclotron • Tagged to a neutral body (glucose/water/ammonia) • Administered through injection • Scan time 30-40 min
  28. 28. Positron Emission Tomography β Tomography?
  29. 29. Positron emission β+ 9 18 Φ→8 18 Ο + β+ + ν + ενεργψ ποσιτροννευτρινοFluorin oxygen
  30. 30. • Cancer detection • Examine changes due to cancer therapy – Biochemical changes • Heart scarring & heart muscle malfunction • Brain scan for memory loss – Brain tumors, seizures Lymphoma melanoma PET Positron emission tomography
  31. 31. Principles • Uses annihilation coincidence detection (ACD) • Simultaneous acquisition of 45 slices over a 16 cm distance • Based on Fluorine 18 fluorodexyglucose (FDG)
  32. 32. PET • Ring of detectors surrounds the patient • Obtains two projection at opposite directions • Patient is injected with a 18 fluorine fluorodeoxyglucose (FDG)
  33. 33. Pet principle • Ring of detectors
  34. 34. Annihilation radiation • Positron travel short distances in solids and liquids before annihilation • Annihilation COINCIDENCE -> photons reach detectors, we collect the photons that happen almost at the same time – coincidence? I don’t think so! Detector 1 Detector 2
  35. 35. True coincidence Detector 1 Detector 2
  36. 36. Random coincidence • Emission from different nuclear transformation interact with same detector Detector 1 Detector 2
  37. 37. Scatter coincidence • One or both photons are scattered and don’t have a simple line trajectory Detector 1 Detector 2 False coincidence
  38. 38. Total signal is the sum of the coincidences Ctotal = Ctrue +Cscattered+ Crandom
  39. 39. PET noise sources O T S A ij ij ij ijC C C C= + + • Noise sources: – Accidental (random) coincidences – Scattered coincidences • Signal-to-noise ratio given by ratio of true coincidences to noise events • Overall count rate for detector pair (i,j):
  40. 40. Pet detectors NAI (TI) Sodium iodide doped with thallium BGO bismuth germanate LSO lutetium oxyorthosilicate
  41. 41. PET resolution • Modern PET ~ 2-3 mm resolution (1.3 mm) MRI PET
  42. 42. PET evolution
  43. 43. SPECT • Single photon emission computed tomography ∀γ rays and x-ray emitting nuclides in patient
  44. 44. SPECT cnt • One or more camera heads rotating about the patient • In cardiac -180o rotations • In brain - 360o rotations • It is cheaper than MRI and PET
  45. 45. SPECT cnt • 60-130 projections • Technetium is the isothope • Decays with γ ray emission • Filtered back projection to reconstruct an image of a solid
  46. 46. Typical studies • Bone scan • Myocardial perfusion • Brain • Tumor
  47. 47. Scintillation (Anger) camera 1. Enclosure 2. Shielding 3. Collimator 4. NI(Tl) Crystal 5. PMT • Imaging of radionuclide distribution in 2D • Replaced “Rectilinear Scanner”, faster, increased efficiency, dynamic imaging (uptake/washout) • Application in SPECT and PET • One large crystal (38-50 cm-dia.) coupled to array of PMT
  48. 48. Anger logic • Position encoding example: PMTs 6,11,12 each register 1/3 of total Photocurrent, i.e.: I6 = I11 = I12 = 1/3 Ip • Total induced photo current (Ip) is obtained through summing all current outputs • Intrinsic resolution ~ 4 mm
  49. 49. L d Collimators • Purpose: Image formation (acts as “optic”) • Parallel collimator Simplest, most common 1:1 magnification • Resolution • Geometric efficiency • Tradeoff: Resolution  Efficiency ( )2a L z b R L + + = 2 4 open open unit A A G d Aπ = Aopen Aunit
  50. 50. Collimator types Tradeoff between resolution and field-of view (FOV) for different types: Converging:  resolution,  FOV Diverging:  resolution, FOV Pinhole (~ mm): High resolution of small organs at close distances Diverging L d d Converging L d
  51. 51. SPECT applications • Brain: – Perfusion (stroke, epilepsy, schizophrenia, dementia [Alzheimer]) – Tumors • Heart: – Coronary artery disease – Myocardial infarcts • Respiratory • Liver • Kidney

×