clearpem, j. varela euromedim06, marseille, may 2006 1 clearpem: a pet imaging system dedicated to...

1 ClearPEM, J. Varela EuroMedIm06, Marseille, May 2006

CRYSTAL

CLEAR

ClearPEM: a PET imaging system dedicated to breast cancer diagnostics

J. VarelaLIP/IST Lisbon & CERN

EuroMedIm06, Marseille, May 2006


CRYSTAL

CLEARClearPEM Project

TAGUSPARK – Parque de Ciência e Tecnologia

LIP - Laboratório de Instrumentação e Partículas

Hospital Garcia Orta - Serviço Medicina Nuclear

IBEB - Instituto Biofisica e Engenharia Biomédica

IBILI - Instituto Biomédico de Investigação da Luz e Imagem

INESC - Instituto de Engenharia de Sistemas e Computadores

INEGI - Instituto de Engenharia Mecânica e Gestão Industrial

Sensitivity@350 keV (%)

central slice

4 cm off-axis

3 cm off-axis

2 cm off-axis

1 cm off-axis

Y-a

xis

(c

m)

X-axis (cm)

The ClearPEM scanner is developed in the framework of the Crystal Clear Collaboration at CERN

Consortium PET-Mammography, Portugal

CERN, Geneva VUB, Brussels


CRYSTAL

CLEAR

Good spatial resolution ( 2 mm, whole FoV) Fine crystal segmentation (2x2 mm)

DoI measurement with adequate resolution (FWHM ~2 mm)

High Sensitivity ( 0.05 cps/Bq, center FoV) Solid angle coverage as large as possible

High photon interaction probability (20 mm long crystals)

High efficiency to Compton events in the detector (> 75%)

Minimize dead time in data acquisition (<10 % at highest rate)

ClearPEM Requirements

Low Random Background ( <25%, close to the chest) Good time resolution (~ 1 ns)


CRYSTAL

CLEARClearPEM Imaging SystemClearPEM Imaging System

Breast and axilla examsBreast exams with the patient in prone position

The plates rotate around the breast

PEM plates can be rotated for axilla exams

PEM Robotic Device

PEM Detector Plates


CRYSTAL

CLEAR

ClearPEM detector model

ClearPEM Detector ClearPEM Detector

6300 LYSO:Ce crystals Avalanche photodiodes Low noise electronics

ClearPEM Detector: Two detection plates192 crystal matrices (8x4 crystals each)Front-back APD readout for DoI measurement

Optical simulation

Plate surface 14x16 cm2


CRYSTAL

CLEARCrystals Quality ControlCrystals Quality Control

Production of 6300 crystal pixels concluded

Measurements with miniACOS (CERN):

700 crystals measured Light yield dispersion (~12% rms)

Light Yield

2x2x20mm depolished

Energyresolution

miniACOS

LYSO:Ce Crystals 2 x 2 x 20 mm3


CRYSTAL

CLEARQuality Control of APD ArraysQuality Control of APD Arrays400 APD-arrays S8550-01 (Hamamatsu)

Quality Control: Bias voltage for M=50, 100, 200 Id/M per subarray dM/dV (%/V) Relative gain of individual pixels

S8550-01 APD arrays

Gain variation per Volt

Id (16 pixels) < 70 nA

Dark Current (Id)

APD Number

Relative gain of APD Pixels

= 4.6%

dM/dV<4%/V


CRYSTAL

CLEARPerformance of Detector ModulesPerformance of Detector Modules

LYSO/BaSO4 Matrix

Measurements of 24 Detector Modules

Quality Control: Gain uniformity Energy resolution DoI resolution Cross-talk

See also poster P3_212 “Long-term stability of Clear-PEM Detector Modules”, C. Ortigão et al.


CRYSTAL

CLEARGain Uniformity & Energy Resolution Flood irradiation Cs-137

Measurement of relative gain of Detector Module pixels Energy resolution at 662 keV

Results for 24 Detector Modules

Relative Pixel Gain

0

2

4

6

8

10

12

14

16

18

20

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 ave

Detector Module

En

erg

y R

es

olu

tio

n (

%)

Average = 13.4%

Energy Resolution

0

20

40

60

80

100

120

0,4 0,6 0,8 1 1,2 1,4 1,6

Relative gain (a.u.)

Nu

mb

er o

f P

ixel

s (#

)

RMS = 12.9%


CRYSTAL

CLEARDepth of Interaction

Each asymmetry peak corresponds to irradiation at one beam location DoI Resolution for 32 pixels of

one Detector Module

FWHM ~ 2 mm

A=(T-B)/(T+B)

Crystal

Collimated beam

+ 7 mm

TopBottom


CRYSTAL

CLEARTop-Bottom Asymmetry

Flood irradiation Cs-137

Measurement of the width of the asymmetry distribution

AsymmetryA=(T-B)/(T+B)

Quality Control of24 Modules

Asymmetry per Unit Length

0

0,5

1

1,5

2

2,5

3

3,5

4

4,5

5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 all

Matrix

Asy

mm

etry

(%

/mm

)


CRYSTAL

CLEARCross-TalkCross-Talk

Method: Select photopeak events in one crystal and study energy deposit in neighbor crystals

Average crosstalk: 2 - 3 %24 modules measured1056 walls

cross talk per matrix

0

1

2

3

4

5

6

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24

matrix number

mea

n x

talk

(%

)

Average cross-talk per Module

Na22 “flood”Red – select 511 keV Green – select 1274 keV


CRYSTAL

CLEAR

Single photon time resolution 2.1 ns (RMS)

Time ResolutionTime ResolutionNon-optimized electronics (peaking time ~150 ns)Sampling ADC 10 bits 100 MHz

Time differenceAPD(top) – APD (bottom)

Preliminary


CRYSTAL

CLEAR

Full System SimulationFull System Simulation

Monte – Carlo Simulations using GEANT4

NCAT phantom

Standardized uptake values one hour after the injection of 370 MBq.

Concentration of 2.1 kBq/cc for the soft tissue.

Detailed detector geometry

Includes trigger and data acquisition simulation

ClearPEM Simulation FrameworkClearPEM Simulation Framework


CRYSTAL

CLEAR

Counting RatesCounting Rates

Simulation setup

Breast size Detector

heads separation

True rateScatter fraction

Randoms / Trues

A small 15 cm 2.5 kHz 30%44% (no shield)28% (Pb shield)

B medium 13 cm 11.0 kHz 30%25% (no shield)20% (Pb shield)

Cmedium

compressed10 cm 16.5 kHz 30%

24% (no shield)19% (Pb shield)

B CA

Single rate per Detector Head ~ 2.2 MHz (E>50 keV)Fraction of Random Coincidences < 30%

Standard uptakes for FDG injection of 370 MBq; Breast uptake 2.1 KBq/mL


CRYSTAL

CLEARDAQ/Trigger PerformanceDAQ/Trigger Performance

DAQ and Trigger Efficiency:

- above 90% for E>200 keV

Time Resolution

- single photon rms ~1.5 ns - photostatistics contributes ~1 ns - electronic noise ~1000 e-


CRYSTAL

CLEAR

“Full simulation” sensitivity image (uniform activity in the FoV)

Sensitivity pattern: irregular variationPacking fraction: 52%FOV dimension: 16.2 x 14.5 cm2

Transverse view Coronal view Sagittal view

Coronal view

sequenceMonte Carlo Sensitivity ImageMonte Carlo Sensitivity Image


CRYSTAL

CLEARReconstruction PerformanceReconstruction Performance

Scanner rotation axis

NCAT Breast PhantomChain Phantom

Scanner rotation axis

Performance evaluation inoptimal imaging conditions

Performance evaluation inrealistic imaging conditions

Using Monte Carlo Simulated Data

Detector Plates in 2 orthogonal orientations


CRYSTAL

CLEAR

Axial Resolution

0

1

2

3

0 10 20 30 40

distance (mm)

FW

HM

(m

m)

FORE-J_OSEM

SSRB_OSEM

3D-OSEM

Transaxial Resolution

0

1

2

3

4

5

6

0 10 20 30 40

distance (mm)

FW

HM

(m

m)

FORE-J_OSEM

SSRB_OSEM

3D-OSEM

Point Source ReconstructionPoint Source Reconstruction

Chain phantom

• 10 mm between point sources;• No background activity.


CRYSTAL

CLEARLesion Reconstructed ImagesLesion Reconstructed Images

lesion : background activity concentration

1:13 1:10 1:5 1:4

10 m

m Ø

lesio

n5

mm

Ø le

sion

7 m

m Ø

lesio

n3

mm

Ø le

sion


1:13 1:10 1:5 1:4


1:13 1:10 1:5 1:4


1:13 1:10 1:5 1:4

Poor visibillityGood visibillity Not visible (5 min total acquisition)


CRYSTAL

CLEAR

Coincidence digital trigger: Digital algorithms (time and energy)

Time resolution ~ 1 ns

Good efficiency for multi-hit (Compton) events

Fast Data Acquisition: Data acquisition system able to cope with a single photon background rate of the order of 10 MHz

The data acquisition efficiency larger than 90%.

Pipeline structures for minimum dead time

Data Acquisition Requirements


CRYSTAL

CLEARArchitecture of Electronics SystemsArchitecture of Electronics Systems

Amplifier/ Multiplexer ASIC:Sampling ADC (100 MHz)Links LVDS

Crate 6U

4 DAQ boards

1 Trigger/DCC board

FPGAs 4 M gates

Digital triggerData reduction Data readout

DAE crate

PC

Off-Detector

600 MHzAmpliAnalogMux

192:2

ADC100 MHz

10 bit

On-Detector

Serializer

Frontend Boards

Service Boards

Data Acquisition ElectronicsFrontend Boards

Service BoardsAPD Bias Voltage regulationT, P monitoringPower distribution


CRYSTAL

CLEARFrontend ASICTechnology AMS 0.35 m CMOS

ASIC V1: sampled-data memory,

multiplexers, control logic OK input amplifier with unstable

bias levels

Input: 192 channelsNoise: ENC ~ 1000 e- Power per chip : < 2 mW/channelClock frequency : 100 MHzShaping: Peaking time 40 nsAnalog memories: 10 samplesOutput multiplexing: 2 highest channels

Frontend ASIC Specifications:

ASIC V1 Layout


CRYSTAL

CLEAR

Layout of Test ASIC V2

Control Logic4 channels

multiplexers + buffers

5900 m

1600

m

4 channels

Area – 9.44 mm2

8 channels + switches + control logic + self-test


CRYSTAL

CLEAR

Detector Supermodule

Frontend Electronics IntegrationFrontend Electronics Integration

Frontend Board

Compact system inside the PEM Detector Head: 6000 APD channels 400 HV lines 160 high speed (600 MHz) output lines High frequency clock (100 MHz)

DAQ CONN

ASIC

ASIC

ADC

OALVD

S

FE Serv LV

FE S

erv

HV OA

OA

OA

ADC

DAQ CONN

ASIC

ASI C

ADC

OA

LVDS

FE Serv LV

FE Serv HVOA

OA

OA

ADC


CRYSTAL

CLEARData Acquisition SystemData Acquisition System

DAQ module:- pipeline data storage- hit energy and time calculation

Filter Module:- rejects out-of-time data- rejects high multiplicity events

Trigger module:- performs coincidence trigger- random triggers- singles trigger

DCC module:- collects relevant data- data transfer to PC


CRYSTAL

CLEAR

Processing Deserializers

Control

DAQ Board

Trigger and Data Acquisition BoardsDAQ Board tested successfully

TRG/DCC Board

TRG/DCC Board is under test

Control

Processing

PCI Interface


CRYSTAL

CLEAR

Electromechanical safety switch

Cable carrier

Detector HeadsDetector Heads

Detector heads

Adapter for source mounting

Collision detection switches

Water distribution block

Patch Panel


CRYSTAL

CLEARRobotic Device Movements Movements

Prototype Under Assembly


CRYSTAL

CLEARConclusions

The ClearPEM mammography scanner promises to have an interesting performance.

Work is under way to conclude the prototype and to prove these expectations this year.

Clinical tests are foreseen in 2007


CRYSTAL

CLEAR


CRYSTAL

CLEAR

Backup


CRYSTAL

CLEAR

Along axis parallel to platesResults with full simulation: Sensitivity at FOV center = 0.06 cps/Bq

ClearPEM SensitivityClearPEM Sensitivity

Along axis perpendicular to platesPlate separation 10 cm


CRYSTAL

CLEAR

+ =

True coincidence background(Geant4 full simulation)

Random coincidence background(event generator)

Investigate impact of random coincidences from outside the FOV in the quality of PEM images

Events are mixed in the LMF file before image reconstruction

Torso region

18% less contrast

• 5 mm Ø at 6 cm from CFOV • Lesion uptake: 20.4 kBq/ml • Breast uptake: 2.1 kBq/ml• 2 orthogonal projections• 300 s acquisition• 3D-OSEM reconstruction

Simulation approach

Example:

+ =

Effect of Randoms to PEM Images


CRYSTAL

CLEAR

Breast configuration Axilla configuration

Mechanical SystemMechanical System

clearpem, j. varela euromedim06, marseille, may 2006 1 clearpem: a pet imaging system dedicated to...

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