Raymond F. Muzic, Jr., Ph.D.

Raymond Muzic Protons

Neu

tron

s

0 40 80

80

40

0

120

Stable 12C Unstable 11C

Unstable 14C

3

Reactor- produced

Cyclotron- produced

Raymond Muzic

Insufficient number of n/too many p+

Competing decay processes Electron Capture: p+ + e– n + �̅�+ E Positron Decay: p+ n + β+ + 𝜈 + E

β+ decay Predominant over EC at lower Z 1.02 MeV threshold

Raymond Muzic

82Rb 76 sec 15O 122 sec 13N 10 min 11C 20 min 68Ga 68 min 18F 110 min 64Cu 12.7 hr 124I 5.2 d

Raymond Muzic

18O (p,n) 18F 14N (p, α) 11C 10B (d,n) 11C 16O (p,α) 13N 12C (d,n) 13N 14N (d,n) 15O 15N (p,n) 15O

Raymond Muzic

Raymond Muzic

H gas + e – in magn field plasma: p +,H –, H H – pulled from ion source chamber 2 or 4 dees are electrodes, radiofrequency Dees In high vacuum, 10 – 6 mTorr (10 – 9 atm) or better High magnetic field, 1 T or greater

Ions accelerated across gaps in dees, coast through dees on curved path

Saha Basics of PET Imaging, Chap 7

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Accelerate H+ vs H– or 2H+ vs 2H– H+ cyclotron housing becomes activated H –

beam can be split dual targets

Raymond Muzic

q charge M magnetic field, Gauss r radius of cyclotron m mass of particle

𝐾𝐾 = 𝑞𝑞𝑞 2

2𝑚

10 to 20 MeV typical for medical cyclotrons

Raymond Muzic

Raymond Muzic

Raymond Muzic

Power ~150 A at 208 V, 3-phase

Cooling ~5x104 Btu/h

Air exhaust > 500 cfm

Shielding Cyclotron ~25 cm Pb, ~75 cm concrete both with B Hot cell ~75 mm Pb

Floor loading Cyclotron ~4x104 kg; Hot cell 104 kg

Raymond Muzic

Shielding: HVLs, narrow-beam, ignore build-up Lead 4.1 mm Concrete 3.4 cm

Distance Can be more economical than shielding

Time Inject patient then stay away

Raymond Muzic

Raymond Muzic

Raymond Muzic

Nucleus ejects positron Positron slows, meets with

electron: annihilates Two photons rays created 180o (±0.25o FWHM) 0.511 MeV simultaneous β−

0.511 MeV

0.511 MeV

β+

~.25-3mm

Radionuclide

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Photons are emitted from radionuclide inside subject

0.511 MeV

0.511 MeV

Raymond Muzic

Photons detected in temporal coincidence same nucleus

Recorded coincidence data reflect sum of activity along line

Data are tomographically reconstructed to make image

Raymond Muzic

d1=35 cm

d2=45 cm

t1 = T+d1/c = T+1.2 ns

t2 = T+d2/c = T+1.5 ns

t2 - t1 = 0.3 ns

Confidence-weight backprojection Current scanners have timing resolution of 500 to 600 ps FWHM resolution 7.5 to 9 cm

∆𝑥 =𝑐 ∆𝑡

2

Raymond Muzic

Crystal materials for PET Old: NaI, CsF, BaF2, GSO, BGO Modern: LSO, LYSO, (LaBr3?)

Raymond Muzic

Decode analogous to Anger camera n PMTs read light from m crystals n < m

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Singles Trues Randoms Scatter

Raymond Muzic

The majority of photons that the scanner detects are not in coincidence with another photon

Raymond Muzic

The location of the annihilation is on the line between the detectors that sensed the photons in temporal coincidence

Raymond Muzic

By random chance two annihilations occur nearly simultaneously

Scanner detects one photon from each mispositioned coincidence

Keep activity “low” to minimize probability of random coincidence

Estimate and statistically correct using delayed coincidence window

Raymond Muzic

Photon undergoing Compton interaction is deflected or scattered

Scanner mispositions event

Energy discrimination can reduce

Software corrections for scatter

Raymond Muzic

Ahmad Hatami Zhenghong Lee Valdir Colussi

Raymond Muzic