CENTER FOR ADVANCED IMAGING
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Charge division readout for SensL
SPMArray4 modules
(last update October 10, 2011)
Motivation:
Compactness
Higher MRI-compatibility
Cost
Approach: Develop multiplexing readout schemes minimizing the
number of readout channels, while maintaining high performance
(primarily spatial resolution).
First stage: definition of the performance limits using “resistive”
readout (4ch per module), including DOI operation
Second stage: develop row & column readout = 24 channels
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
The SPMArray4 module from
SensL equipped with resistive
4ch
readout
from
AiT
Instruments.
The
output
channels
integrated
and
digitized
in
the
AiT
Instruments FPGA DAQ module
(not shown).
SPMArray4 4ch readout
40ns/div
ADC Gate ~125ns
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AT WEST VIRGINIA UNIVERSITY
SPMArray4 4ch readout
1.5mm LYSO array
15.4% FWHM
@511 keV
15.0% FWHM
@511 keV
2.8mm window
15% FWHM
1274 kev/511 kev ratio = 2.51 vs 2.49 expected
Raw images, and a profile through one pixel raw, at 511 keV, and examples of energy
spectra for a 1.5mm step 10mm thick LYSO array.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
SPMArray4 4ch readout
1.0mm LYSO array
13.7% FWHM
@511 keV
14.7% FWHM
@511 keV
14.7% FWHM
2.8mm window
1.5mm window
Raw images, and a profile through one pixel raw, at 511 keV, and examples of energy
spectra for a 1mm step 10mm thick LYSO array.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
Array4p9 – a compact ~2” PM
Array4p9
Array4p9
H8500
1 channel
Sum of four
50ns
The SiPM based photomultipliers are in principle much more compact than standard PMTs, when
implemented with compact electronics. At right is the H8500 flat panel PMT from Hamamatsu
with four channel resistive readout. In the center is the Matrix9 module from SensL with alldigital pixel readout of all 144 3mm pixels. At left and at top right is the Array4p9 module from
SensL with AiT Instruments resistive 4ch readout. The four output channels (scope picture of one
is shown, as well as of the sum signal) are integrated and digitized in the AiT Instruments FPGA
DAQ module (not shown).
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
1.5mm LYSO array
81.1 F
15.6%
@511 keV
FWHM
16.5%
@511 keV
FWHM
16.2%
@511 keV
FWHM
16.5%
@511 keV
FWHM
Image at 511 keV and selected pixel energy spectra, at 81.1
deg F. 22Na source. Proteus LYSO array of 28x28 1.51 x 1.51
x10mm pixels (1.59 mm pitch) was coupled to the Array4p9
module through a 2mm thick acrylic spreader window. Optical
coupling grease (Visilox V-788) was applied to all optical
surfaces (wet coupling).
15.5%
@511 keV
FWHM
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
1.5mm LYSO array
43.2 F
Raw image and a profile at 511 keV through one pixel raw, at 42.3 deg F. 22Na source.
Proteus LYSO array of 28x28 1.51 x 1.51 x10mm pixels (1.59 mm pitch) was coupled
to the Array4p9 module through a 2mm thick acrylic spreader window. Wet coupling.
Pixel energy resolution @511 keV measured from 14.5 to 16.8% FWHM, depending on
the position of the LYSO pixel in the SiPM array. (Amplitude at this temperature was
about 1.6 higher than that at 81.1 deg F, when measured at the same bias voltage.)
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
1.5mm LYSO array ~74 F
Array4p9
1274 keV
H8500
511 keV
511 keV
Raw images obtained for 1274 keV and 511 keV photopeaks at room temperature (~
74 deg F) using the second SiPM module and slightly modified readout circuitry.
22Na source. Proteus LYSO array of 28x28 1.51 x 1.51 x 10mm pixels (1.59 mm
pitch) was coupled to the Array4p9 module through a 2.15mm thick acrylic spreader
window. A comparative measurement was done with the H8500 flat panel PMT using
the same LYSO array. Wet coupling. The image at 1274 keV can be used to provide
better definition of the crystal map, especially at the edges of the module.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
1.5mm LYSO array
511 keV
43.2 F
1274 keV
Raw images obtained for 1274 keV and 511 keV photopeaks at 43.2 deg F using the
first SiPM module. 22Na source. Proteus LYSO array of 1.51 x 1.51 x 10mm pixels
(1.59 mm pitch) coupled through a 2.15mm thick acrylic spreader window. Wet
coupling.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
1.5mm LYSO array
~75 F
511 keV
Raw image obtained after final re-optimization at 511 keV and at ~75 deg F. 22Na
source. Proteus LYSO array of 1.51 x 1.51 x 10mm pixels (1.59 mm pitch) coupled
through a 2.15mm thick acrylic spreader window. Wet coupling.
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AT WEST VIRGINIA UNIVERSITY
2mm LYSO array
43.2 F
17.6%
FWHM
16.0%
FWHM
511 keV
17.7% FWHM
@511 keV
Ratio: 2.53
1274 keV
15.8%
FWHM
16.4%
FWHM
Normalized energy for the
full detector.
Raw images at 511 keV and 1274 keV and energy spectra for selected LYSO pixels as well as
normalized energy for the full detector at 43.2 deg F. 22Na source. Proteus LYSO array of 2.0 x
2.0 x 15mm pixels (2.0 mm pitch) coupled through a 2.15mm thick acrylic spreader window. Wet
coupling.
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AT WEST VIRGINIA UNIVERSITY
2mm LYSO array
array array
80 F
18.5%
FWHM
17.5%
FWHM
19.2%
FWHM
16.1%
FWHM
511 keV
1274 keV
Raw images at 511 keV and 1274 keV and energy spectra for the four selected LYSO
pixels at 80 deg F using the first SiPM module. 22Na source. Proteus LYSO array of
2.0 x 2.0 x 15mm pixels (2.0 mm pitch) coupled through a 2.15mm thick acrylic
spreader window. Wet coupling.
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AT WEST VIRGINIA UNIVERSITY
Two identical Array4p9 modules with 4ch charge division readout from AiT
Instruments were coupled from both ends of a 10x10 1.5mm step 15 mm thick LYSO
array from Proteus optimized for DOI operation. Room temperature. Wet coupling
through 2mm thick spreader windows. Bias voltages: 29.2 and 29.6 Volt. ADC
integration gate: 100 nsec.
Out_2
Out_1
Out_2
Out_1
511 keV energy window
20%
80%
14.2%
FWHM
DOI=Out_1/Sum
Sum
All results
for one
selected
1.5mm LYSO
pixel and
broad 511
keV gamma
beam from
22Na.
Left: Raw image at 511 keV with row projection and energy spectra for the
selected LYSO pixel. Both outputs were combined to form ONE image, showing
good separation of individual 1.5mm pixels. Both individual energy spectra are
broad, as expected, due to the DOI feature of the scintillator array.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
Two identical Array4p9 modules with 4ch charge division readout from AiT
Instruments were coupled from both ends of a 10x10 1.5mm step 15 mm thick LYSO
array from Proteus optimized for DOI operation. Room temperature. Wet coupling
through 2mm thick spreader windows. Bias voltages: 29.2 and 29.6 Volt. ADC
integration gate: 100 nsec.
Out_2
Out_1
1.66mm
FWHM
20%
80%
DOI=Out_1/Sum
21.3%
FWHM
Out_1
20.7%
FWHM
Out_2
16.9%
FWHM
Out_2
Out_1
Sum
5mm
DOI=Out_1/Sum
All results
for one
selected
1.5mm LYSO
pixel and
narrow
collimated
511 keV
gamma beam
from a <1mm
22Na source.
Left: DOI results at 511 keV and energy spectra for the selected LYSO pixel and a narrow 511
keV gamma beam adjusted to be in the mid-plane of the LYSO array. To calibrate DOI spatial
resolution, the beam was moved to two additional and symmetrically placed 5mm spaced positions.
Measured spatial resolution includes beam size.
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
New 4ch charge division readout from AiT
21.2%
FWHM
1
2
Variant A
22.8%
FWHM
511 keV
1274 keV
1
Variant B
2
23.7%
FWHM
22.1%
FWHM
23.3%
FWHM
511 keV
3.11
2.98
3.0
3.05
2.99
1274 keV
Operation at 70 F. Bias voltage at 28.8 Volt. ADC signal integration gate of 200
nsec. 1mm pitch Proteus LYSO array of 24x24 LYSO 10mm long pixels. Only
about a quarter of the detector populated with the array. The corner region
indicated with an arrow. Variant B offers better performance.
1274/ 511 keV
Peak ratio
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20nsec/div
New 4ch charge division readout from AiT
511 keV
20.8%
FWHM
Sum pulse shapes with
the new 4ch readout
(Variant B)
Operation at 42 F. Bias
voltage at 29.5 Volt. ADC
signal integration gate of
175 nsec. Proteus 1.0 mm
pitch LYSO array of 24x24
10mm
long
pixels
was
coupled to the Array4p9
module through a 2.50 mm
thick
acrylic
spreader
window
using
coupling
grease. Only about a quarter
of the detector populated
with the array.
19.7%
FWHM
1274 keV
17.7%
FWHM
28.8%
FWHM
23.4%
FWHM
1274/ 511 keV peak ratio
2.79
2.88
2.76
3.47
2.88
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AT WEST VIRGINIA UNIVERSITY
New 4ch charge division readout from AiT
17.7%
FWHM
X
18.9%
FWHM
2.54
18.1%
FWHM
2.71
23.2%
FWHM
3.04
22.5%
FWHM
2.94
Operation at 42 F. Bias voltage at 29.5 Volt. ADC signal integration gate of 175
nsec. Proteus LYSO array of 28x28 1.51 x 1.51 x 10mm pixels (1.59 mm pitch) was
coupled to the Array4p9 module through a 2.50 mm thick acrylic spreader window
using coupling grease. Special thresholding scheme increases the ratio of 1274 keV
peak to 511 keV peak (from the 22Na source), as seen at right. Partially this effect
is compensated by electronics saturation effects, especially in the edge regions.
1274/
511 keV
Peak
ratio
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
New 4ch charge division readout from AiT
21.5%
FWHM
0.928
21.5%
FWHM
0.98
18.5%
FWHM
1.00
23.4%
FWHM
0.564
22.3%
FWHM
Operation at 72 F. Bias voltage at 29.5 Volt. ADC signal integration gate of 175 nsec.
Proteus LYSO array of 28x28 1.51 x 1.51 x 10mm pixels (1.59 mm pitch) coupled to the
Array4p9 module through a 2.50 mm thick acrylic spreader window using coupling grease.
0.705
511 keV
Peak
ratio
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Row & Column Readout Scheme for the SensL
Array4p9 array
19.4%
FWHM
R/C: (12 + 12) = 24
ch./144 pixels
20.8%
FWHM
20.5%
FWHM
19.1%
FWHM
Operation at 70 F. Bias voltage at 28.8 Volt. ADC signal integration gate of 150
nsec. Results @ 511 keV. Proteus LYSO array of 28x28 1.51 x 1.51 x 10mm pixels
(1.59 mm pitch) was coupled to the Array4p9 module through a 2.50 mm thick
acrylic spreader window. Wet (grease) coupling.
2.60
2.60
2.68
2.64
1274/ 511 keV
Peak ratio
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
Row & Column Readout Scheme for the SensL
Array4p9 array
20.2%
FWHM
24.8%
FWHM
R/C: (12 + 12) = 24
ch./144 pixels
29.7%
FWHM
25.2%
FWHM
Corner
23.1%
FWHM
Operation at 70 F. Bias voltage at 28.8 Volt. ADC signal integration
gate of 150 nsec. Results @ 511 keV. 24x24 pixel 1mm pitch LYSO
array from Proteus.
Only about 30% of the detector surface
populated with the array. The corner region indicated with an arrow.
2.81
2.93
2.94
2.94
2.81
1274/ 511 keV
Peak ratio
CENTER FOR ADVANCED IMAGING
AT WEST VIRGINIA UNIVERSITY
X-Y Readout Schemes for SensL
Array4p9 arrays
Example: 2x4 array - 72 ch./
~10cm x 20cm module
R/C: (12 + 12) - 24 ch./144 pixel
~ 5cm x 5cm module
Example: 2x2 array - 48 ch./
~10cm x 10cm module
Example: 4x4 array - 96 ch./
~20cm x 20cm module (2304 pixels)
CENTER FOR ADVANCED IMAGING
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X-Y Readout Schemes for SensL Array4p9 arrays
Example: 1x6 array - 84 ch./ ~5cm x 30cm module
Example: 2x6 array - 96 ch./ ~10cm x 30cm module
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Example: 2x12 (DOI) ring
X-Y Readout Schemes for SensL Array4p9
arrays
Readout:
- 24 sums for energy and DOI
- 12 trigger signals (for coincidence
matrix)
- position signals - summed both
sides – 12x12 outputs/module
- multiplexed six modules x 2 = 84
position channels
-Total number of position channels
= 168
- Total number of readout channels:
192 (for a total of 3456 individual
3mm pixels, reduction factor: 18)
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Summary
•The “resistive” 4ch readout for the SensL SPMArray4 module from AiT
Instruments works very well at room temperature (no cooling) down to 1mm
LYSO pixel sizes.
•The economical, simple and very compact 4ch-per-module readout of the 144
channel Array4p9 module can accommodate the requirements for adequate
performance for LYSO scintillation pixel arrays down to ~1.5-2mm pixel size.
•The operation is very stable with temperature, with the amplitude change (at
the same voltage bias) of less than a factor 2 over the wide tested range of
40-80 deg F.
•Initial evidence on DOI operation is that with that design of the readout
<2mm FWHM 3D resolution can be obtained using LYSO arrays specially
designed for DOI operation.
•To achieve 1mm resolution in the present configuration of 3x3 SPMArray4
modules in Array4p9, the row-and-column readout of 12X by 12Y provides this
performance at room temperature.
•The X and Y outputs from several modules can be multiplexed to produce
larger FOV array structures, retaining good spatial resolution, while still with
limited total number of ADC readout channels.
•Novel 4ch readout from AiT using signal circuitry with signal thresholding is
offering better performance than standard “resistive” readout. The
optimization of this concept still continues.
•Lowering temperature to 42F substantially improves performance.