Development of New Detectors for PET Imaging at BNL

Development of New Detectors for PET Imaging at BNL

DOE/JLAB MeetingBethesda, MD

May 20, 2004

Craig WoodyPhysics Dept

Brookhaven National Lab

RatCAP Beta Microprobe

C.Woody, DOE/JLAB Meeting, 5/20/04 2

The RatCAP Project The RatCAP Project

Part of a larger project for Imaging The Awake Animalalso involving motion tracking in both PET and MRI

SUNY

BNL

C.Woody, DOE/JLAB Meeting, 5/20/04 3

RatCAP: Rat Concious Animal PETRatCAP: Rat Concious Animal PET

Mockup of the portable ring on the head of a rat

Readout chip

APD

LSO

Socket

Ring containing 12 block detectors of 2x2 mm2 x 5 mm deep LSO crystals with APDs

and integrated readout electronics

C.Woody, DOE/JLAB Meeting, 5/20/04 4

LSO Crystal ArraysLSO Crystal Arrays

Studying different types of crystal arrays to optimize light output and

energy resolution

CTI white powder reflector

Proteus unbonded 3M reflector

Proteus single crystals

C.Woody, DOE/JLAB Meeting, 5/20/04 5

Optimization of Light CollectionOptimization of Light Collection

crystal length (mm)

0 5 10 15 20 25

pe/M

eV

500

1000

1500

2000

2500

3000

unwrapped air

unwrapped cookie

wrapped cookie

wrapped air

Dashed = Measured Solid = Opticad

OPTICAD

Ray Tracing Program

2x2 mm2 single crystals wrapped in 3M reflector and coupled with a silicone

cookie to a calibrated PMT

Npe/MeV = N/MeV x x QE

2400 = 25,000 x 0.4 x 0.24

10 mm crystal (wrapped with cookie)

0.2

0.25

0.3

0.35

0.4

0.45

0.5

0.55

0.6

0 1 2 3 4 5 6 7 8 9 10

Distance along crystal

Ligh

t Col

lect

ion

Effic

ienc

y

C.Woody, DOE/JLAB Meeting, 5/20/04 6

Measurement of Light Output and Energy Resolution of Crystals Arrays

Measurement of Light Output and Energy Resolution of Crystals Arrays

Average light yield of final arrays ~ 5400 p.e./MeV (~ 22 % higher than prototype)

All final crystal arrays have been received and tested

Energy resolution ~ 16% for 137CsMeasured with 3rd prototype ASICAverage Npe/MeV

3500 4000 4500 5000 5500 6000 6500 7000

Nu

mb

er

0

2

4

6 ~ 13%

Total spread ~ ± 40%

C.Woody, DOE/JLAB Meeting, 5/20/04 7

Characterization of Avalanche PhotodiodesCharacterization of Avalanche Photodiodes

4x8 array 1.6 x 1.6 mm2

active pixel area

Hamamatsu S8550

Npe ~ 2700Typical G ~ 50

~ 135K signal e’s

Common voltage for each 16 channels

Dark current < 40 nA(~ 1.2 nA/ch)

Expected noise in final ASIC ~ 1100 e’s

(CT~ 10 pF)

APDs (101-115)Average gains (32 ch each)

0 100 200 300 400

Ga

in

1

10

100

Reverse bias (volts)

Measured APD dark currents (each curve represents the summed dark current for all 32 channels)

Reverse bias (volts)

320 330 340 350 360 370 380 390 400 410 420

Da

rk c

urr

en

t (n

A)

10

100

1000

apd 101 apd 102 apd 103 apd 104 apd 105 apd 106 apd 107 apd 109 apd 110 apd 111 apd 112 apd 113 apd 114 apd 115

G ~ 50

All final APD arrays have been received and tested

C.Woody, DOE/JLAB Meeting, 5/20/04 8

Test Setup with Crystal and APD ArraysTest Setup with Crystal and APD Arrays

Two arrays of 4x8 APDs and crystals using hybrid preamps

and shapers and CAMAC DAQ system

C.Woody, DOE/JLAB Meeting, 5/20/04 9

Source ImagesSource Images

Single 1 mm dia. 68Ge point source 1.6 mm off axis

2 mm

Multiple 68Ge point sources (~ 2mm) spaced ~ 4 mm

4 mm

4 mm

C.Woody, DOE/JLAB Meeting, 5/20/04 10

Wrist Monitor for Measuring the Arterial Input Function Wrist Monitor for Measuring the Arterial Input Function

For human studies, the input function is taken from the radial artery in the wrist.

Activity in the surrounding veins produce a significant background which can be rejected using the good spatial resolution of the wrist monitor.

Planar image of a 1 mm diameter 68Ge line sourceWrist Phantom

C.Woody, DOE/JLAB Meeting, 5/20/04 11

Beta Scintillation MicroprobeBeta Scintillation Microprobe

• Radioisotopes used in PET emit positrons with energies of a few hundred keV which have a range of several mm in blood or tissue. This range is comparable to the spatial resolution obtained in most PET cameras. • These positrons can be detected directly using plastic or crystal scintillators. With crystal scintillators which have high density, the positrons will range out, depositing all of their energy in the crystal and producing a large signal.

• Small scintillation probes can be used to directly measure the radiotracer concentration in the blood or tissue.

C.Woody, DOE/JLAB Meeting, 5/20/04 12

Probe ConstructionProbe Construction

LSO microprobe consisting of 0.5 mm diameter x 1.5 mm long LSO crystal wrapped with

several layers of white reflecting teflon and covered with polyester shrink tubing.

C.Woody, DOE/JLAB Meeting, 5/20/04 13

Rat Brain Studies with MicroprobeRat Brain Studies with Microprobe

Elapsed time (minutes)

-20 0 20 40 60 80 100 120 140

Co

un

ts/s

ec (

de

cay

corr

ecte

d)

0.1

1

10

100

0.5 mm x 1.5 mm LSO Microprobe

Uptake of 11C-methylphenidate in the nucleus accumbens region of

a rat brain with LSO probenucleus accumbens

~ 2 mm

C.Woody, DOE/JLAB Meeting, 5/20/04 14

Input Function Measured with MicroprobeInput Function Measured with Microprobe

Seconds

0 60 120 180

Co

un

ts/s

ec

(d

ec

ay c

orr

ecte

d)

0

10

20

30

40

50

60

ProbeWell counter

LSO microprobe (0.3 mm dia. x 0.5 mm) inserted inside an 18 gauge syringe needle for blood flow study.

Activity of 11C-tyrosine measured in baboon blood flow during a PET scan using a syringe mounted LSO microprobe.

Input function

C.Woody, DOE/JLAB Meeting, 5/20/04 15

Related Detector R&D in the Physics Department Related Detector R&D in the Physics Department

RHIC

The PHENIX group in the Physics Departmentworks closely with Chemistry, Instrumentation and Medical on

detector development for medical imaging

C.Woody, DOE/JLAB Meeting, 5/20/04 16

Areas of Detector DevelopmentAreas of Detector Development

• Scintillating crystals (LSO, PWO, BaF2, CsI, CeF3, PbF2,...)

• Photodetectors (PMTs, APDs, solid and gaseous deep UV photocathodes,...)

• Micropattern gas detectors (GEMs, Micromegas,...) • Time Projection Chambers (PHENIX, STAR detector upgrades)• Calorimetry (Pb/Sc, Si/W PHENIX upgrades)• High speed DAQ and trigger (PHENIX)• Offline data processing (PHENIX)

Areas of overlap with detector development for

medical imaging