Study of Silicon Photomultipliers for Positron Emission ...hep.uchicago.edu/~eric/work/docs/SiPM_forPET_335projectPaper.pdf · The result is the energy of the photoelectron (p.e)

Study of Silicon Photomultipliers for Positron

Emission Tomography (PET) Application

Eric Oberla

5 June 2009

Abstract

A relatively new photodetector, the silicon photomultiplier (SiPM), is well suited for PET

applications. It has similar sensitivity and gain to the industry standard photomultiplier

tube (PMT), but has advantages such as smaller size and insensitivity to magnetic field.

These properties make this detector an active area of research in the PET field. I will

study a simplified setup, comprised of two antiparallel SiPM/LSO coupled detectors using

a Na-22 positron source. The coincidence timing and energy resolution is determined

using two methods, a CAMAC system and a fast oscilloscope. The best coincidence

time resolution, 660 ps FWHM, was obtained using the digital oscilloscope. At best, the

energy resolution was found to be 16.4% FWHM. Results using two types of SiPM, 1600

and 400 pixel, are presented. Data from a GEANT4 simulation of the described setup

are also shown.

Introduction

Positron Emission Tomography (PET) is a medical imaging technique that is used to

observe functional processes in vivo. The functional process of interest is observed by in-

troducing a chemical tracer that is metabolized by certain tissues in the body. The tracer

is doped with a radioisotope that undergoes positive beta decay (positron emission). A

large majority of current PET scans use fluorodeoxyglucose (FDG), a glucose molecule

with a hydroxyl group replaced by radioactive 18F. FDG enters the same metabolic path-

ways as glucose and is utilized for oncology and brain imaging [1].

Upon injection in the body, the tracer is concentrated in specific tissues, such as a

tumor. Positrons emitted from beta decay annihilate with nearby electrons, generating

back-to-back 511 keV photons that can be detected by a scintillator crystal coupled to

1

a photodetector. The location of the annihilation event can by narrowed to a line of

response (LOR) from two coincident detections [1]. In PET systems with high timing

resolution, the annihilation location can be further constrained to a segment on the LOR.

This is known as time-of-flight (TOF) PET, in which high timing resolution results in the

reduction statistical noise. Advantages of TOF PET include faster computer processing

times and better image quality [1-2].

Photodetectors and PET

The standard photodetector in clinical PET machines is the photomultiplier tube (PMT).

The high gain, fast response and high sensitivity of PMTs have made them a viable

detector for PET, but there exist several drawbacks. One, the bulky size of PMTs puts

a limit on the spatial resolution of a detector [1]. PMTs are also highly sensitive to

magnetic fields. This makes it impossible to implement PET with magnetic resonance

imaging (MRI), considered the future of biomedical imaging because of the promise of

simultaneous metabolic and anatomical information [3-4].

An area of active research is the study and application of silicon photomultipliers

(SiPM). SiPMs are relatively compact and insensitive to magnetic fields while achieving

roughly the same gain and sensitivity as PMTs [4-5]. The SiPM is a semiconductor

device made up of avalanche photodioide (APD) pixels connected in parallel. Each APD

is an individual photon counter and the sum of all the APD pixels is the output of the

SiPM. The APDs are operated in Geiger Mode, where the bias voltage applied is greater

than the reverse breakdown voltage resulting in a large internal electric field. An incident

photon causes a carrier to be injected into this electric field creating a large pulse that

can be put into electronics. The specifications of the SiPM vary widely, but for PET

applications the greater number of pixels (lower fill factor) is desired because of the high

light input to the detector [3,5].

Studies of SiPMs have yielded promising results. Measurements of the inherent co-

incidence timing resolution using a splitted laser gave timing on the order of 100 ps,

suggesting the viability of SiPM for TOF PET [6]. The coincidence timing between two

LYSO/SiPM coupled detectors has been measured by Kim et al to be at best 240 ps

[7]. However, there are challenges to implementing SiPMs into a full scale PET machine.

There is a moderate dependence of gain with bias voltage, so each SiPM would require

its own voltage control. Temperature dependence is also an issue. Other challenges exist

and are discussed in reference [7], but the potential benefits of SiPM photodetectors for

PET make their implentation a promising next step in detector design.

2

Experiment

Characterization of SiPM

We first wanted to test for ourselves some basic properties of SiPMs. We focus on the 1600

pixel, 25 µm2 pixel size SiPM (Hamamatsu S10362-025C) because of the large number of

photons incident on the photocathode in PET. This sacrifices active area, but it ensures

that the photocathode will not be saturated. We will also analyze the properties of the

400 pixel, 50 µm2 pixel area SiPM (Hamamatsu S10362-050C).

Gain and dark count rate were measured using a single SiPM without an LSO crystal

or radioactive source. Detector was kept in black box for both experiments. For gain

measurement, SiPM output was amplified using 30 dB preamplifier and signal was read

out using a fast oscilloscope (TDC6154, 20 GS/s). Oscilloscope was triggered at 5 mV

increments from 5 mV to 50 mV and 1500 events were collected at each trigger level.

The result is the energy of the photoelectron (p.e) peaks after gain from both the SiPM

and preamp, shown Figure 1. By a linear fit of the amplified energy (charge) of the 1,2,3

and 4 p.e. peaks vs. the unamplified photon energy ,the gain of the 1600 pixel SiPM

was determined to be 2.0 ∗ 105. Similarly, the gain of the 400 pixel SiPM was found to

be 6.2 ∗ 105.

The dark count rate was also measured. The SiPM is a solid-state device with inherent

noise due to thermal excitations of the APD pixels, causing uncorrelated photon counts.

To make any reliable measurements, it is important to understand and quantify this

noise. In order measure the dark count, signal was ’counted’ at different levels of noise.

The SiPM output was sent to a 10x preamplifier, split and sent to two discriminator

inputs. Trigger levels of the discriminator were set to 0.5 p.e. and 1.5 p.e. respectively.

Figure 1: Photoelectron spectrum of SiPM (left

peak corresponds to 1 p.e., etc.)

Figure 2: Dark count rate vs. bias voltage, 1600

pixel

3

These levels varied with applied bias voltage and were set by observing the preamplified

pulse in oscilloscope. The discriminated signal was sent to a Lecroy 2551 100 MHz scaler

to give a counts per acquisition time for each threshold level. Bias voltage was varied

from 70.1 to 71.9 V and the result if shown in Figure 2.

For an operating voltage of 71.0 V, it is clear that the dominatant noise is from single

photoelectron counts. Although the noise rate is high (~110 kHz), the energy is much

smaller than a useful PET signal so it is easily filtered. However, if our goal was to count

individual photons, the SiPM would not be a good photodetector.

Methods

Two 1x1x10 mm3 LSO crystals were attached to a pair 1600 or 400 pixel SiPMs using

a small amount of fast-drying, transparent epoxy. The crystals were wrapped in teflon

tape to keep optical photons internally reflected. Both SiPMs were operated at a bias

voltage of 71.0 V. A 22Na source was used as a positron emitter and placed between the

two detectors, as shown in Figure 3.

CAMAC System

A CAMAC data acquisition system with NIM electronics was used to measure coincidence

timing and energy resolution.

The SiPM output was put directly in a LeCroy model 612 fast amplifier (10x) and

then split using a linear fan-in/fan-out module (LeCroy model 428F). One branch was put

in a LeCroy 623B discriminator with a minimum threshold of 30 mV. The discriminated

signal was sent to a coincidence unit set to ’AND’ logic so as to fire for a coincidence event.

Figure 3: Experimental setup

4

Figure 4: Electronic schematic for coincidence timing measurement using CAMAC system

This output was used for the ADC gate and the TDC start. The other branch of the

fan-out module was delayed and sent to the ADC channel inputs for energy information.

To extract timing information, the analog signal was amplified 100x and then put

into a discriminator. The discriminator level was set to the lowest possible level above

the noise threshold that was observed in oscilloscope. This was necessary to get the best

possible timing resolution from our system. Both discriminator outputs were delayed

with a 40 ns cable and sent to the stop channels in the TDC for timing information. See

Figure 4 for a schematic of the timing electronics.

TDC Calibration

TDC needed to be calibrated to interpret data. Discriminated pulse from a function

generator was sent to TDC with 0, 2, 4 ns delays. By measuring TDC values to the

delays, conversion factor of 41 ps/bit was obtained.

Fast Oscilloscope

In addition, the coincidence timing and energy resolution were analyzed using a Tektronix

DPO7000 series 40 GS/s digital oscilloscope. With the same set-up as in Figure 3, the

unamplified SiPM signals were sent to the scope and coincidence events were captured

using a logic ’AND’ trigger. Each channel was sampled at 20 GS/s and an event was 500

ns, providing 10000 points per saved waveform with a time interval of 0.05 ns between

samples.

5

Results/Analysis

From CAMAC Setup

Results from 1600 pixel SiPM shown in Figure 5. Fourty-thousand coincident events

in total were collected at a rate of about 12

Hz. The right peak in the charge (energy)

spectrum is due to the gamma photon depositing all 511 keV in the scintillator. The

left peak is of less enery, in which the gamma has Compton scattered, only depositing

a fraction of its energy in the crystal. These events degrade the time resolution and are

filtered out for timing measurements. The disparity in relative peak size was most likely

due to coupling differences between the SiPM surface and the LSO crystal of the two

detectors.

The coincidence timing is presented before (Delta T) and after (Delta T: cut) filtering

unwanted events. The timing resolution considering only those events in the 511 keV

peak is shown to be 820 ps FWHM. The best energy resolution (from SiPM 1) is 23.9 %

FWHM. The discriminator threshold level for timing was set at 50 mV for this timing

result. See Figure 6 for timing resolution as a function of varying this threshold.

Temperature sensitivity of the SiPM became apparent during this experiment as ADC

spectrum clearly shifted as time progressed. There has been shown to be a considerable

gain dependence on temperature in SiPMs [4] and this might be the cause of the spectrum

shift. This makes getting good energy resolution at low coincident rates a difficult task!

Charge (pc)0 50 100 150 200 250

0

20

40

60

80

100

120

140SiPM 0 Entries 40000

Mean 93.28RMS 58.88Integral 3.967e+04

/ ndf 2χ 528.7 / 438Constant 0.82± 68.84 Mean 0.2± 162.2 Sigma 0.19± 19.38

SiPM 0

Charge (pC)0 50 100 150 200 250

0

20

40

60

80

100

120

140

160

180

200SiPM 1 Entries 40000

Mean 102.3RMS 64.93Integral 3.968e+04


SiPM 1

Time (ns)−2 0 2 4 6 8 10 12 140

100

200

300

400

500

600

700

Delta T: T1−T2 Entries 40000

Mean 4.255

RMS 1.854

Integral 3.803e+04

Delta T: T1−T2

Time (ns)−2 0 2 4 6 8 10 12 140

20

40

60

80

100

120

140

160

180

200

Delta T: T1−T2 cut Entries 4026

Mean 4.189

RMS 0.4298

Integral 4014

/ ndf 2χ 38.93 / 44

Constant 3.8± 182.3

Mean 0.006± 4.184

Sigma 0.0050± 0.3503

Delta T: T1−T2 cut

Figure 5: Results: 1600 pixel SiPM, top: Energy Spectrum, bottom: Coincidence Timing

6

0.8

0.85

0.9

0.95

1

1.05

1.1

0 50 100 150 200 250 300

Tim

e [n

s]

Threshold Level [mV]

Timing Resolution - varying Threshold Level

Figure 6: Coincident timing as a function of threshold level

See figures 19 and 20 in the appendix for raw data.

Results from 400 pixel SiPM shown in figure 7. Coincidence timing was 850 ps FWHM

and the best energy resolution was 16.4% FWHM.

Charge (pc)0 50 100 150 200 250

0

20

40

60

80

100

120

140

160

SiPM 0 Entries 40000Mean 97.2RMS 52.33Integral 3.988e+04


SiPM 0

Charge (pC)0 50 100 150 200 250

0

20

40

60

80

100

SiPM 1 Entries 40000Mean 111.7RMS 60.22Integral 3.975e+04


SiPM 1

Time (ns)−2 0 2 4 6 8 10 12 140

100

200

300

400

500

Delta T: T1−T2 Entries 40000

Mean 5.997

RMS 2.411

Integral 3.753e+04

Delta T: T1−T2

Time (ns)−2 0 2 4 6 8 10 12 140

20

40

60

80

100

120

140

160

180

200

220

Delta T: T1−T2 cut Entries 4913

Mean 5.648

RMS 0.4961

Integral 4911

/ ndf 2χ 89.94 / 61


Mean 0.01± 5.64

Sigma 0.0042± 0.3634

Delta T: T1−T2 cut

Figure 7: Results: 400 pixel SiPM, top: Energy Spectrum, bottom: Coincidence Timing

7

Time(ns)0 50 100 150 200 250 300

Am

plitu

de(m

V)

−100

−80

−60

−40

−20

0

Event# 100 : Disc1Event# 100 : Disc1

Time(ns)0 50 100 150 200 250 300

Am

plitu

de(m

V)

−100

−80

−60

−40

−20

0

Event# 100 : Disc2Event# 100 : Disc2

Figure 8: Sample coincident event ac-

quired using digital oscillo-

scope.

Time(ns)40 45 50 55 60 65

Am

plitu

de(m

V)

0

20

40

60

80

Event Entries 0Mean x 0Mean y 0RMS x 0RMS y 0Integral 0

/ ndf 2χ 2479 / 18p0 3.736± −189.6 p1 0.07756± 4.09

/ ndf 2χ 2479 / 18p0 3.736± −189.6 p1 0.07756± 4.09

Event

Time(ns)40 45 50 55 60 65

Am

plitu

de(m

V)

0

20

40

60

80

Event Entries 0Mean x 0Mean y 0RMS x 0RMS y 0Integral 0

Entries 0Mean x 0Mean y 0RMS x 0RMS y 0Integral 0

/ ndf 2χ 1252 / 18p0 3.31± −231.9 p1 0.07756± 5.606

/ ndf 2χ 1252 / 18p0 3.31± −231.9 p1 0.07756± 5.606

Event

Figure 9: Zoom into rising edge of event in fig 8. Red line is

linear fit over n sample points at a specified voltage

threshold. Coincidence timing is extracted by exam-

ining difference in x-intercept of fits between chan-

nels.

From Oscilloscope

Using the 400 pixel SiPMs, 4000 coincidence events in total were collected. Example

waveforms from a coincidence event are shown in Figure 8. A linear fit was performed

on the rising edge of each waveform at a specified threshold as presented in Figure 9.

Coincidence time was found by examining the difference between x-intercept values of

the fit between the two channels. The best timing was extracted by fitting to 10 points,

corresponding to 500 ps, below threshold level.

Again, by selecting only those events in which all 511 keV of gamma photon energy

was deposited, the coincidence timing was found to be 660 ps FWHM. This is shown in

Figure 11. The threshold was set to 3 mV for this result, and coincidence timing as a

function of fitting threshold is provided in Figure 10. No improvement in time resolution

was found for a threshold lower than 3 mV since that was just above the noise level of

the signal.

The energy spectrum was determined by integrating discretely under each waveform.

The integrated charge was found by implementing the algorithm (from Ohm’s Law):

∆Q =1

R

Nsample∑i=1

V [i]∆ti =∆t

R

Nsample∑i=1

V [i] (1)

8

600

700

800

900

1000

1100

3 4 5 6 7

FW

HM

Coi

ncid

ence

Tim

ing

Res

olut

ion

[ps]

Threshold for linear fit [mV]

Timing Resolution vs. Threshold

Figure 10: Timing resolution as a function of the linear fit threshold to digitized waveform

Time (ns)−15 −10 −5 0 5 100

20

40

60

80

100

120

140

160

180Delta T: T1−T2 Entries 4000

Mean −4.766

RMS 2.451

Integral 3664

Delta T: T1−T2

Time (ns)−15 −10 −5 0 5 100

10

20

30

40

50

Delta T: T1−T2: Cut Entries 748

Mean −4.706

RMS 2.457

Integral 681

/ ndf 2χ 91.73 / 51


Mean 0.013± −5.155

Sigma 0.0112± 0.2893

Delta T: T1−T2: Cut

Charge(pC)0 20 40 60 80 100 120 140

0

20

40

60

80

100

120

140

160

180

200

220

SiPM 0 Entries 4000

Mean 42.69

RMS 17.62Integral 4000

/ ndf 2χ 10.68 / 14


Mean 0.17± 55.08 Sigma 0.150± 5.917

SiPM 0

Charge(pC)0 50 100 150 200 250

0

20

40

60

80

100

SiPM 1 Entries 4000

Mean 88.41

RMS 42.72Integral 3998

/ ndf 2χ 34.71 / 27


Mean 0.3± 130.4 Sigma 0.31± 10.69

SiPM 1

Figure 11: Results from scope: 400 pixel SiPM, top: Coincidence Timing, bottom: Energy Spectrum

where R is the scope imput impedence, ∆t, the time interval between sample points, is a

constant and V [i ] is the signal amplitude at each point. The number of sample points,

NSample, was 10000 for each event. The energy spectrum is shown in Figure 11. A

Gaussian fit to the 511 keV peak gives an energy resolution at best of 19.3% FWHM 1.

1Note: SiPM channels 0 and 1 switched between Fig 11 and Fig. 7 when comparing energy spectrum.

9

Figure 12: Simulation setup. Green lines indicate gamma path.

Simulation Study

A GEANT4 simulation was created to reproduce the experimental setup presented in

Figure 3. The ’world’ set-up is shown in Figure 12. Two 1x1x10 mm3 LSO crystals

were attached to a pair of SiPMs and back-to-back 511 keV gamma photons were created

directly between the two detectors, labeled ’up’ and ’down’. For each event, the gamma

trajectory in the crystal was simulated in a stepwise fashion, generating photons by

photoelectric or Compton processes. Once produced, each photon was tracked until

hitting the detector surface where it was recorded and terminated. The emission spectrum

and light yield (30,000 photons/MeV) of LSO was implemented as well.

Five-thousand simulation events were taken in 1000 event intervals. The data was

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

20

40

60

80

100

120

140

160

180

200

310×

Photon Spectrum Entries 2616530

Mean 431.7

RMS 30.42

Integral 2.617e+06

Photon Spectrum

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

0.05

0.1

0.15

0.2

0.25

0.3

0.35PDE of SiPM Entries 0

Mean x 0Mean y 0

RMS x 0RMS y 0Integral 0

PDE of SiPM

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

10000

20000

30000

40000

50000

Photon Spectrum After P.D.E. Entries 641356

Mean 430.1

RMS 29.33

Integral 6.414e+05

Photon Spectrum After P.D.E.

Figure 13: 1600 pixel, top-right: Incident pho-

ton spectrum, top-left: PDE, bot-

tom: Photon spectrum after applying

PDE

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

20

40

60

80

100

120

140

160

180

200

310×

Photon Spectrum Entries 2616530

Mean 431.7

RMS 30.42

Integral 2.617e+06

Photon Spectrum

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

0.1

0.2

0.3

0.4

0.5

0.6

PDE of SiPM Entries 0

Mean x 0Mean y 0

RMS x 0RMS y 0Integral 0

PDE of SiPM

Wavelength (nm)250 300 350 400 450 500 550 600 650 700 7500

20

40

60

80

100

310×

Photon Spectrum After P.D.E. Entries 1292740

Mean 428.8

RMS 28.97

Integral 1.293e+06

Photon Spectrum After P.D.E.

Figure 14: 400 pixel, top-right: Incident photon

spectrum, top-left: PDE, bottom:

Photon spectrum after applying PDE

10

analyzed for both 400 and 1600 pixel SiPMs. The number of incident photons at the

detector surface is shown in both Figures 15 and 16. It is identical for both SiPMs since

the same generated data was used for both. To find the number of fired pixels, we used

the expression given by [5]:

Nfired = Npixel

(1 − exp

(−Nphoton ∗ PDE

Npixel

))(2)

where Nphoton is the number of incident photons and the photon detection effeciency

1000 2000 3000 4000 5000 60000

5

10

15

20

25

# of incident photons : up Entries 306

Mean 2408

RMS 1507

Integral 300

# of incident photons : up

1000 2000 3000 4000 5000 60000

2

4

6

8

10

12

14

16

18

20

22

# of incident photons : down Entries 306

Mean 2267

RMS 1508

Integral 305

# of incident photons : down

# of pixels100 200 300 400 500 600 700 800 900 1000

0

0.5

1

1.5

2

2.5

3

3.5

4

# of fired pixels: up Entries 306

Mean 412.3

RMS 214.3

Integral 286

# of fired pixels: up

# of pixels100 200 300 400 500 600 700 800 900 1000

0

1

2

3

4

5

# of fired pixels: down Entries 306

Mean 393.2

RMS 215.7

Integral 288

# of fired pixels: down

Figure 15: 1600 pixel, top: Photons incident on SiPM, bottom: Fired pixels

1000 2000 3000 4000 5000 60000

5

10

15

20

25

# of incident photons : up Entries 306

Mean 2408

RMS 1507

Integral 300

# of incident photons : up

1000 2000 3000 4000 5000 60000

2

4

6

8

10

12

14

16

18

20

22

# of incident photons : down Entries 306

Mean 2267

RMS 1508

Integral 305

# of incident photons : down

# of pixels50 100 150 200 250 300 350 400 450 5000

10

20

30

40

50

60

70

# of fired pixels: up Entries 306

Mean 327.9

RMS 91.38

Integral 297

# of fired pixels: up

# of pixels50 100 150 200 250 300 350 400 450 500

0

10

20

30

40

50

60

# of fired pixels: down Entries 306

Mean 319.9

RMS 94.7

Integral 302

# of fired pixels: down

Figure 16: 400 pixel, top: Photons incident on SiPM, bottom: Fired pixels

11

(PDE) is provided in [5] and plotted in Figures 13 and 14. Since the photon spectrum

and PDE peak at the same energy, the PDE effectively reduces the photon spectrum by

a constant factor as shown in Figures 13 and 14. So, in equation (2), PDE was taken to

be a constant: 0.2 for 1600 pixel, 0.48 for 400 pixel SiPM.

The number of fired pixels is presented in Figures 15 and 16 for the 1600 pixel and

400 pixel SiPM, respectively. The 400 pixel SiPM shows clear saturation as most of the

events cause all 400 pixels to fire. The energy spectrum is directly related to the number

of fired pixels and is shown in Figures 17 and 18. A distinction between the Compton

and 511 keV peak is clear when using the 1600 pixel SiPM. This is not the case with the

400 pixel SiPM because of saturation.

Figure 17: 1600 pixel: Energy spectrum from sim-

ulationFigure 18: 400 pixel: Energy spectrum from simu-

lation, clearly shows signal saturation

Discussion

The best coincidence timing resolution was found to be 660 ps FWHM using waveworm

sampling. This is good enough for TOF-PET applications. The timing could likely be

improved by amplifying the SiPM signal before sending to oscilloscope, allowing for a

linear fit to a lower relative threshold level. The best energy resolution, 16.4 % FWHM,

was found using the 400 pixel SiPM. The SiPM dark noise was shown to be dominated

by low amplitude signals that are easily filtered from a typical PET signal.

Contrary to intuition, it appears the the 400 pixel SiPM would be better suited for

PET applications because of its better energy resolution. Because of the large number

of incident photons (on the order of thousands), a detector with 400 pixels is expected

to be saturated as shown in the simulation data (Figure 18). The experimental results

suggest otherwise, the detector does not become saturated. There is a distinct 511 keV

peak and events in this peak can be clearly analyzed for timing.

A possible explanation for this is the incorrect assumption that one pixel can detect

only one photon. For a 400 pixel SiPM, the duration of a single photoelectron pulse

is roughly 30 ns as shown in Figure 21 in the Appendix. An LSO signal, however, has

12

a width of about 200 ns (see Figure 8). This means that each pixel may fire multiple

times during an event, avoiding the saturation predicted by the simulation. In that case,

equation (2) can’t be applied blindly without considering this effect.

References

[1] T.K. Lewellen 2008 Recent Developments in PET Detector Technology Phys. Med.

Biol 53 R287-R317

[2] W.W. Moses 2007 Recent Advances and Future Advances in TOF PET Nucl. Instrum.

Methods Phys. Res. 580 919-924

[3] W.R. Leo 1994 Techniques for Nuclear and Particle Physics Experiment, 2nd Rev

Edition, Springer.

[4] S. Espana, et al 2008 Performance Evaluation of SiPM Detectors for PET Imaging in

the Presence of Magnetic Fields IEEE submitted November 14,2008

[5] Hamamatsu 2008 Multi-Pixel Photon Counter Specification Sheet

[6] Q. Xie et al 2007 Performance Evaluation of MPPC for PET Imaging 2007 IEEE

Nucl. Sci. Symp. Conf. Record 969-974

[7] C.L.Kim et al 2008 MPPC for TOF PET Detector and its Challenges 2008 IEEE

Nucl. Sci. Symp. Conf. Record 3586-3590

Acknowledgements

Many thanks to Heejong Kim whose help and guidance were greatly appreciated. He

provided the CAMAC acquisition programs, the GEANT4 simulation as well as Figures

1 and 21.

Thanks to the UChicago Electronics Shop for allowing the use of their expensive oscillo-

scope.

13

Appendix

Figure 19: Ch0 ADC spectrum, t=0 Figure 20: ADC spectrum, t = 12 hours later, 511

keV peak shifted off scale

Figure 21: Single photoelectron pulse, 400 pixel SiPM

14

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Study of Silicon Photomultipliers for Positron Emission ...hep.uchicago.edu/~eric/work/docs/SiPM_forPET_335projectPaper.pdf · The result is the energy of the photoelectron (p.e)