RPC2001 VI Workshop on Resistive Plate Chamber

RPC2001 VI Workshop on Resistive Plate Chamber

Perspectives in Positron Emission Tomography (PET) with RPCs

A.Blanco (1,5), P.Fonte (1,4), I.Lopes (1), R.Marques (1,2), V.Peskov (3), A.Policarpo (1,2), V.Tchepel (1)

(1) LIP, laboratorio de Instrumentacao e Fisica Experimental de Particulas(2) Departamento de Física da Universidade de Coimbra

(3) KTH, Stockholm(4) ISEC, Coimbra, Portugal.

(5) GENP, Dept. Fisica de Particulas, Univ. Santiago de Compostela, Spain.

What is and How PET works Positron Emission Tomography (PET) is a radiotracer imaging technique, in which tracer compounds labelled with positron emitting radionuclides are injected into the subject of the study. These tracers compounds can then be used to track biomedical and physiological process.


Coincidence events can be stored in arrays corresponding to projections through the object and reconstructed using standard tomographic techniques.

Perspectives in Positron Emission Tomography (PET) with RPC´s Alberto Blanco

Unstable parent nucleus

Proton decays to neutron in nucleus

Two anti-parallel 511 keV photons produced

Positron combines with electron and annihilates

Resulting image shows the tracer distribution throughout the object of the study.

positron and neutrino emitted

Electronic

Coincidence


TOF-PET


10ysensitivitoftImprovemen size[mm]object *2

][ pst

a) Reconstructed image without TOF. b) Reconstructed image using TOF information

[NIM A 471(2001) 200-204]

a) b)

2

][][

psmmX t

FWHM

X = 80 cm TOF = 2.6 ns


The basic idea

Incident photon

e-

Compton or photoelectric interaction

A previous work

“The Rutherford Appleton Laboratory´s Mark I Multiwire Proportional Counter Position Camera” J.E. Bateman et al. NIM 225 (1984) 209-231

....

High quantum efficiency material

Stacked plates

Gas gap

Quantum

Efficiency?

Geant simulations



Efficiency of a MWPC with 21 lead plates (250 um)

[from J.E. Bateman NIM 221 (1984 131-141]

5.5%

6.0%

6.5%

7.0%

7.5%

8.0%

8.5%

9.0%

0 100 200 300 400Thickness (um)

Qu

an

tum

Eff

icie

nc

y

.

Geant 4

J.E. Bateman

Experimental data Geant 4Can we trust Geant 4?


Geant seems accurate


10-2

10-1

100

10110

-4

10-2

100

Energy (MeV)

Ra

nge

(g

/cm

2)

Ranges of electrons in Aluminium

From NIST (National Institute of Standards and Technology).

2






Absorption curves of monoenergetic electrons of various energies in aluminium .

[From J. Marshall and A. G. Ward, Can. J. Research A15, 39 (1937)]

Measured projected positron range distribution

Isotope 18F 11C 68Ga 82Rb

Maximun +

energy (MeV)0.64 0.96 1.90 3.35

FWHM (mm) 0.13 0.13 0.31 0.42



82Sr

68Ga11C

18F

mm water equivalent

Proj

ecte

d P

SF d

ue to

ran

ge o

nly

From “Mathematical removal of positron range blurring in high resolution tomography” Derenzo et all. IEEE NS, vol 33

No1”



The basic idea

30 Stacked plates

0%

2%

4%

6%

8%

10%

12%

14%

0 200 400 600 800 1000 1200Thickness (um)

Qua

ntu

m E

ffic

iency

.

Lead

Lead GlassLead Acrylic

Data from the simulation on Geant 4 showing quantum efficiency vs. plate thickness for tree different materials and 30 stacked plates.

....

Stacked plates

Geant 4 simulation

Mechanically more convenient



The basic idea

100 stacked plates

0%

5%

10%

15%

20%

25%

30%

35%

0 200 400 600 800 1000 1200Thickness (um)

Qua

ntu

m e

ffic

iency

.

LeadLead GlassLead Acrylic

Data from the simulation on Geant 4 showing quantum efficiency vs. plate thickness for tree different materials and 100 stacked

plates.


....

Stacked plates

Geant 4 simulation

Mechanically more convenient

22 %


The detector blocks

X-Codification

Z-C

odif

icat

ion

Y-Cod

ifica

tion

Time


• n - stacked counters built with a high quantum efficiency material

• Tridimensional localisation of the photon interaction point.

• Time measurement independent of position measurement yielding a 50 ps resolution.


The detector blocks

X leftX right

Time signalHV

Y-strips(on PCB)

RC

passive netw

ork

RC passive network

X-strips(deposited on glass)

out left

out right

10 strips for eachcoordinate at 4 mm pitch


TESTED

Other position readout methods also possible


Expected spatial resolution

1 cm


Reconstructed point spread function [PSF] of the source.

1) RPC PET (100 m counter resolution) 180 m FWHM

2) RPC PET (500 m counter resolution) 490 m FWHM

No parallax effect

Geant 4 simulation of 3 point-like positron source (max energy 640 keV) surrounded by a water sphere and seen by a RPC-PET with spatial resolution of 100m.


Human PET Small animal PET

- TOF capability is of no value due to the small dimension of the object.

+ An higher radiation dose may be acceptable, with animals.

+ The lack of energy resolution play a minor role. The compton interactions in the object are almost negligible.

+ TOF capability compensates the low efficiency.

- The lack of energy resolution increase the compton background.

The two possible applications


+ Tridimensional localisation of the interaction point of photons, reducing the parallax effect, with high spatial resolution providing a good image quality.

+ The low cost.

+ The excellent timing allows to improve the background rejection.


The first prototypea small animal PET

• 2 head rotatory system

• 16 stacked glass-metal counters 2%

• 32 1mm wide X pickup strip

• Time measurement not yet included

4x3x1 cm3

Object

The detector in Geant.


Glass

Copper

Copper strips


Conclusions


Simulations suggest that RPC´s could be used for TOF-PET

Low cost large field of view increased sensitivity

High spatial resolution provides high definition images

RPC2001 VI Workshop on Resistive Plate Chamber

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