maurizio conti, siemens molecular imaging, knoxville, tennessee, usa

1 Maurizio Conti: Introduction to PET1 Maurizio Conti: Introduction to PET - reproduction authorized for educational purposes only

Maurizio Conti, Siemens Molecular Imaging,

Knoxville, Tennessee, USA

Detectors for PET

2 Maurizio Conti: Detectors for PET - reproduction authorized for educational purposes only

Summary

introduction inorganic scintillators TOF detectors new light sensors and scintillators


Detection process:

positron emission and annihilation two emission

interaction in the patient body and absoption or scatter

interaction in the detectors (scintillator+photodetector or solid state devices)

Most common detector:

inorganic scintillator + Photo Multiplier Tube (PMT)


coincidence

e+

e-

detector

Light detector


detector: scintillator

PMT

detector: scintillator

Light detector(APD, SiPM)

detector = solid state detector(Si, CZT)

Detector components


E

X = A / (A + B)

X1 = 100 / (100 + 0) = 1 X2 = 55 / (55 + 45) = 0.55

A B

Detector architecture: the block


BA

AX

DC

CY

Anger Logic

Y

X


1986 - ECAT with Block Detector


PMTs

PMTs 52 cm

36 cm

light guide scintillator

scintillator

Detector architecture: the panel


Compton Effect

e-

E

E’

Eel

E -

E’

EC

)cos1(1'

2

mchvhv

hv


Photoelectric Effect

e-

E

E


Interaction cross sections

LSO LaBr3

Compton

photoelectric

511 keV 511 keV

x


A good detector must have:

high density and Z: ph ZandComp Z

high light output: energy and time resolution 1 / N1/2

short rise time and decay time: time resolution and dead time

if scintillator, > 400 nm emission wavelength (better for PMTs)

solid technology: not hygroscopic, uniform, easy to make, low cost, etc


Characteristics of Selected Scintillators


NEC, the noise equivalent count rate,

NEC = [(True+scatter)*(1-scf)]2/[True+scatter + randoms]

• NEC is related with image quality. ”The higher the NEC the better the images”.


Search for new scintillators

Ce3+ 5d-4f transition


P. Dorenbos, Presentedat SCINT09, JejuIsland, Korea, June 2009

Search for new scintillators


First Paper on LSO

Ce3+ 5d-4f transition


LSO Energy Spectrum

0

1000

2000

3000

4000

5000

6000

7000

8000

0 200 400 600 800 1000

176Lu backgroundLSO @511keV

energy


LSO manufacturing


Comparing fast scintillators with TOF PET potentiality

(experimental work, presented at SORMA conference, 2008)

Emission and excitation spectraDecay time Absolute light output Time resolutionFigure of merit for TOF PET


Materials

Scintillator composition sample size surface manufacturer

LSO(Ce) Lu2SiO5

5x5x5mm3,

10x10x10mm3as cut University of Tennessee

LuAG(Pr) Lu3Al5O12

5x5x5mm3,

10x10x10mm3

as cut or

polished

University of Tennessee,

Furukawa Co. Ltd.

LuYAP(Ce) Lu0.52Y0.48AlO3

5x5x5mm3,

10x10x10mm3polished SAES Srl.

LaBr3(Ce) LaBr3

cylinders, 13 mm dia,

13 mm height

polished,sealed,

with reflectantSaint-Gobain

LaCl3(Ce) LaCl3cylinders, 13 mm dia,

13 mm height

polished,sealed,

with reflectant

Saint-Gobain


Emission and excitation spectra

0

2000

4000

6000

8000

10000

12000

200 250 300 350 400 450 500

w avelength (nm)

LuAG emission LuAG excitation

0

500

1000

1500

2000

2500

200 250 300 350 400 450 500

w avelength (nm)

LuYAP emission LuYAP excitation

0

20

40

60

80

100

120

140

160

200 250 300 350 400 450 500

w avelength (nm)

LaBr emission LaBr excitation

0

1000

2000

3000

4000

5000

6000

7000

8000

9000

10000

200 250 300 350 400 450 500

w avelength (nm)

LaCl emission LaCl excitation

0

500

1000

1500

2000

2500

3000

3500

4000

4500

5000

200 250 300 350 400 450 500

w avelength (nm)

LSO emission LSO excitation


Decay time measurement

LSO

one component, 30-37nsPMT=XP2020Q Cs137 source

Trigger (anode)

Measure (anode)

Amp474(x10)

CFD935

delayCFD935

TAC567

start

stop

MCA



LuYAP

fast component, 16 ns (57%) 145 ns (22% 594 ns (21%)

LuAG

fast component, 18 ns (77%) 530 ns (23%)



LaBr3

one component, 17 ns

LaCl3

fast component, 18 ns (70%) 125 ns (21%) 220 ns (9%)


Absolute light output

Self-absorption observed: lower light output in larger crystals

Scintillator

Light

output

(ph/MeV)

fast

component (%)

Light output

fast (ph/MeV)

LSO(Ce) 32000 100 32000

LuAG(Pr) 18000 77 13900

LuYAP(Ce) 16000 57 9200

LaBr3(Ce) 58000 100 58000

LaCl3(Ce) 29000 70 20600 Lower than in data sheet

PMT=H3177

Spectroscopy Amplifier Ortec 672 (3s shaping)Pre Amplifier Canberra 2005

dynodeMCATukan-8k Cs137 source


Time resolution measurement

D#1 (anode)

CFD935

delayCFD935

TAC567

start

stop

MCA

Amp855(x40/5,1.5us)

SCA551

SCA551

FastCoinc414A

PreAmp113(100pF)

strobe

D#2 (anode)

D#1 (dynode)

D#2 (dynode)

FWHM of the gaussian fit

PMT=XP2020QNa22 source


0.0

100.0

200.0

300.0

400.0

500.0

600.0

0.000 0.010 0.020 0.030 0.0401/sqrt(N)

Tim

e R

es

olu

tio

n (

ps

)

Time resolution measurement

LuYAP

LuAG

LaClLSO

LaBr

N= ph-e (includes E and QE)


N= ph-e (includes E and QE)

Figure of merit to compare scintillators for TOF PET

Fast is not enough!

Needs to be bright and dense!


Figure of merit (conventional)

PPFe x )1(

2

Image quality (or SNR) depends on number of coincidence counts in the scan

Detection efficiency

Deposited energy (MeV)

Coincidence efficiency

PPF=PhotoPeakFraction


Hyman theory

pheNPMThHt

),,(

PMT noise/gain

Discriminator level

Decay time

1

),,( PMThH


Time resolution estimate

pheNt

0 < < 1

PET scanner system time resolution

pheNPMThHt

),,(

pheNt

pheNtt


Fast Photomultipliers for TOF PETT. Szczesniak, M. Moszynski, L. Swiderski, A. Nassalski, P. Lavoute, M.Kapusta2007 TNS conf record

Hyman theory

plastic

CsF2

LaBr3

LuAP

LaCl

YAP

LSO

LGSO

NaI


Figure of merit (with TOF)

Nt

t

DGTOF

TOF sensitivity gain or amplification

Conventional sensitivity 2Sens

N

GTOF 22Overall sensitivity of TOF PET scanner

N

GTOF


Figure of merit for TOF PET

Scintillatordecay time

(ns)

N(fast)

(ph/MeV)

(cm-1)

photopeak

fraction

(2 cm)sqrt(N

Lu2SiO5 37 32000 0.821 0.73 0.351 29.40 10.19

Lu3Al5O12 18 13900 0.710 0.77 0.345 27.79 9.58

Lu0.5Y0.5AlO3 16 9200 0.651 0.73 0.280 23.98 6.70

LaBr3 17 58000 0.432 0.43 0.061 58.41 3.56

LaCl3 18 20600 0.338 0.51 0.064 33.83 2.18

nonTOF TOF


Figure of merit for TOF PET scintillators

LaBr

LuYAP

LuAG

LaCl

LSO

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1A

rbit

rary

uni

ts

efficiency TOF gain eff*GTOF


DenseBrightFast

LSO/LYSO is dominating now….

N

tGTOF

222 1

dense bright

fast

New scintillators for TOF PET ?



Derenzo and Moses (LBNL, Berkeley):Systematic search of new scintillators, combining powders and testing with X-rays microcrystals

Hundreds of compounds tested.



New approaches:

Crystals with a highly populated donor band (ZnO)

Nanocrystals with quantum dots

Make use of Cerenkov light

Improve light collection with photonic crystals


LSO crystal

2.8mm

1.3

mm

0.6

mm

100x100m2

10 m2.5 m



When will SiPM get there ? ….

FastEfficientCount rate capabilitySmall dead areas, compact and scalable

New photodetectors for TOF PET ?


SiPM: new photodetectors for TOF PET ?

maurizio conti, siemens molecular imaging, knoxville, tennessee, usa

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