Characterization of diffractive
optical elements for improving the
performance of an endoscopic TOFPET detector head
Student:
G. A. Fornaro
4/10/2015
Supervisor:
G. Battistoni
G.A. Fornaro
Outline
 PET principles
 EndoTOFPET-US: the project
 Time of light (TOF) principle
 Optical optimization by means of
micro optical element (MOE)
4/10/2015
G.A. Fornaro
PET Principles
γ
n
p n pne+
n nep+
p np
p
tracer
Injection
(18F-FDG)
Ring of
scintillators
γ
(511 KeV)
LOR
x
z
f
f
s
Parallel projections
4/10/2015
e-
e+
2π coincidences
Neutron-deficient
isotope
Projection
f
(511 KeV)
s
Reconstructionz
PET data (sinograms)
G.A. Fornaro
PET images
PET: origins of noise
Coincidence time window (Δt): time in which two detected photons
are considered to be originated in the same event
• True coincidences
Rt  S
• Scattered coincidences
2
• Random coincidences
Rr  t  S
Rt
Rs
In a PET detection system:

Single
count rate
1
t  S

t 
N
phe
Duration of scintillation
Number of phe in the
detector
In order to reduce the noise it is important to improve the time
resolution of the detecting system and thus to maximize the number
of photon extracted from the crystal
4/10/2015
G.A. Fornaro
EndoTOFPET-US
project
• First clinical target: pancreatic cancers;
• Develop new biomarkers;
• Develop a dual modality PET-US endoscopic probe with...
–
–
–
–
4/10/2015
Spatial resolution: 1mm
Timing resolution: 200ps FWHM coincidence
High sensitivity to detect 1mm tumors in a few minutes
Energy resolution: sufficient to discriminate against Compton events
G.A. Fornaro
EndoTOFPET-US
project
Aim:
4/10/2015
build a prototype of a PET-US endoscopic probe for
detection of early stage pancreatic tumors
G.A. Fornaro
EndoTOFPET-US
project
Aim:
build a prototype of a PET-US endoscopic probe for
detection of early stage pancreatic tumors
Ultrasound trasducer
Scintillating crystal matrix
Micro optical element
4/10/2015
d-SiPM
G.A. Fornaro
Biopsy
niddle
EndoTOFPET-US
project
US: detects regions in which the density of the
tissue changes (possible cancer)
4/10/2015
G.A. Fornaro
EndoTOFPET-US
project
External PET Plate
PET detector
4/10/2015
G.A. Fornaro
External PET Plate
EndoTOFPET project
4/10/2015
G.A. Fornaro
Time of Flight info reduce the
statistical noise variance
D
SNR TOF 
d
with
SNR CONV
d  c
t
2
tB
Detector B
d
Patient
D  3 cm
d1
e+
e-
tA
Detector A
t  tB  t A 
4/10/2015
 d  d 1   d  d 1 
c
G.A. Fornaro
 t  200 ps
Time of Flight info reduce the
statistical noise variance
d-SiPM with
t
D single SPAD readout for

d

c
with
SNR TOFsingle
 optical
SNRphoton
counting
CONV
2
d
tB
d
Detector B
Patient
Individual SPAD
d1
e+
D  3 cm
e-
tA
Detector A
t  tB  t A 
4/10/2015
 d  d 1   d  d 1 
c
G.A. Fornaro
 t  200 ps
MOE:
Aim and concept
Problem:
50% light of the crystal is lost in the dead zones of the d-SiPM
Crystal
4/10/2015
MOE
G.A. Fornaro
d-SiPM
MOE:
Aim and concept
Problem:
50% light of the crystal is lost in the dead zones of the d-SiPM
Crystal
MOE
d-SiPM
Solution: optical collimator btw crystal and photodetector
4/10/2015
G.A. Fornaro
Optical collimator/
Lenticular Lens
500µm
MOE:
Aim and concept
Problem:
50% light of the crystal is lost in the dead zones of the d-SiPM
Crystal
MOE
d-SiPM
Solution: optical collimator btw crystal and photodetector
1) Match pitches of d-SiPM (25µm active area);
25 µm 25 µm
800 µm
4/10/2015
G.A. Fornaro
MOE:
Aim and concept
Problem:
50% light of the crystal is lost in the dead zones of the d-SiPM
Crystal
MOE
d-SiPM
Solution: optical collimator btw crystal and photodetector
1) Match pitches of d-SiPM (50µm);
2) Concentrate the maximum of light into parallel rays
3) Create ‘differential’ light pattern on the SPAD
surface only;
4/10/2015
G.A. Fornaro
d-SiPM
MOE:
Aim and concept
Problem: 50% light of the crystal is lost in the dead zones of the d-SiPM
simulations forecast a transmission
d-SiPM
gain
of
1.3
Crystal
MOE
Solution: optical collimator between crystal and photodetector
1) Match pitches of d-SiPM (50µm);
2) Concentrate the maximum of light into parallel rays
3) Create ‘differential’ light pattern on the SPAD surface only;
4/10/2015
G.A. Fornaro
Benches for MOE
characterization
We have built and tested different benches for the optical characterization
of the MOE:
 Crystal + MOE in direct contact with the sensitive
area of a CCD used as photodetector
X- Rays
source
Matrix
MOE
CCD
 Characterization of light distribution at the output of
the crystal (input of MOE)
γ-Source
 Characterization of MOE in direct contact with CCD
(near field): by changing the angle of incidence of
light on the MOE we detected the transmitted light at
its output
UV Lamp
USB connection
PMT
crystal
pinhole
Rotating
disk
CCD+MOE
filter
 Complete characterization of MOE with the camera
(far field): by changing the angle of incidence of light
on the MOE we detected the light distribution at its
output
4/10/2015
G.A. Fornaro
Digital
θ Camera
filter
UV Lamp
γ
MOE
The works are in
progress…
Reach a convergence btw experimental parameter and the ones of
simulations in order to make the comparison of the results more and
more realistic
Final aim:
understand well the input parameters of the
MOE in order to be able to forecast its output’s
intensity profile
…
4/10/2015
G.A. Fornaro
Direct contact with CCD
X-Rays
direction
X- Rays
source
CCD
Average of
each vertical
array of pixels
Matrix
USB
connection
Horizontal array
of averages
intensities
Proteus/AGILE 4x4 crystal matrix :
• all crystals fully wrapped (Vikuiti)
• X-Rays (40 keV) could only penetrate
and excite the first vertical row of
crystal
Intensity (a.u.)
air interface crystal-CCD
Bare Matrix
Horizontal position (pixels)
4/10/2015
G.A. Fornaro
Direct contact with CCD
X- Rays
source
X-Rays
direction
Matrix
MOE
CCD
Average of
each vertical
array of pixels
USB
connecti
on
Proteus/AGILE 4x4 crystal matrix :
• all crystals fully wrapped (Vikuiti)
• X-Rays (40 keV) could only penetrate
and excite the first vertical row of
crystal
Intensity (a.u.)
air interface crystal-MOE and
MOE-CCD
Horizontal array
of averages
intensities
Bare Matrix
Matrix + MOE (air)
Horizontal position (pixels)
4/10/2015
G.A. Fornaro
Direct contact with CCD:
matrix in dry contact with MOE
Gain on single peaks
For evaluating the gain we would have in the active regions of a SPAD that will be put in front of the
MOE we calculated:
1.
2.
the integral of the intensity of light coming out from the crystal+MOE in a region of 25μm (≈5 pixels) around
each peak;
the integral of the intensity of light coming out from the bare crystal in the same regions of 25 μm
peak
1
2
3
4
5
6
7
8
9
10
11
12
13
14
A.R.
1.21
1.25
1.30
1.29
1.26
1.26
1.26
1.23
1.24
1.25
1.25
1.28
1.28
1.30
A.R. = gain in the active regions of a
SPAD
Average gain on the peaks = 1.26
Gain forecasted by simulations =1.7
Intensity (a.u.)
25μm
3 4 5 6 7 8 9 10 12 13 14
11
Bare Matrix
Matrix + MOE (air)
Horizontal position (pixels)
4/10/2015
G.A. Fornaro
WP1: UnivMed
Project Coordination
WP2: CERN
Crystals and optics
Scintillating fibers
and diffrative
coupling optics
4 years project
WP3: Delft TU
Photodetectors
Novel digital
photodetectors
WP5: DESY
Detector Integration
Miniaturized probe
Tracking&Image fusion
WP4: LIP
FE and DAQ
electronics
Highly integrated
TOF electronics
WP6: TUM
Clinical requirements & preclinical and pilot clinical studies
Feasibility tests on pigs, Pilot clinical tests, Impact on biomarker studies
4/10/2015
G.A. Fornaro