Qualification Test of a MPPC-based PET Module for Future MRI-PET Scanners

Yohta KUREIJ.Kataoka, T.Kato, T.Fujita, H.Funamoto, T.Tsujikawa (Waseda Univ.)S.Yamamoto (Nagoya Univ.)

5 September 2013 9th International “Hiroshima” Symposium @ International Conference Center Hiroshima, Japan

Contents2

1. PET and Detectors

2. Evaluation of images by PET

3. Evaluation of images by MRI

4. Future prospects and summary

Positron Emission Tomography3

Functional imaging with 511keV annihilation gamma-rayTime of Flight(ToF) information improve S/NDepth of Interaction(DoI) information improve image qualityToF

DoICancer

:glucose

normal cell cancer cell

Warburg effect Cancer cells like glucose⇒ FDG + F18

glucose isotope tracer

Isotope is accumulated in cancer

Characteristics of Modalities4

　 X-ray CT PET MRISpatial Resolution 0.5mm 4 ～ 8mm 1mmExposure (Dose) 10mSv~ ~2mSv nothing

Image structural functional structural

Featurehard tissuesex) bone, tooth

cancerAD

soft tissuesex) cartilage, ligament

MRI-PET

⇒insensitivity to B fields is required

CT-PET = already being made into a productbecoming common as a multimodality imaging device

internal and external exposure

⇒compactness, low power and high time resolution are required

ToF-PET, DoI-PET

No problem of extra exposure

Detectors5

However, PMT is …

PMT

Scintillatorintricate in constructionlarge sizesensitive to B fields

SD can overcome these points

PD, APD : compact semiconductor MPPC : 2D-array of Geiger-mode APDs

PMT is incorporated in conventional PET scanner

high gainlong history and proven

ex.)Super-Kamiokande

especially, MPPC has great characteristics

13.6mm

13.6mm

Characteristics of Detectors6

High gain(= doesn’t need CSA)⇒much better S/N⇒much better time resolution (suitable for ToF-PET)

　 PMT PD APD MPPCGain 　 　

Q.E.[%]Voltage[V]

Volume large smallStructure complex simple

Power Consumption high lowInterfered in B yes no

suitable for PET

Compact and simple structure⇒suitable for DoI-PET

⇒ K.Takeuchi’s talk yesterday (Compton Camera)widely varying use

Our PET Project w/ MPPC7

⇒ T.Ambe’s Poster

Kishimoto et al. 2013, IEEE

1mm cube

Patent application PCT/JP2012/008129(Waseda Univ., Furukawa K.K.)

Average jitter; 105ps(FWHM) Time resolution; 616ps(FWHM)

ToF technique

sandwich scinti b/w MPPCs

DoI technique

Characteristics of Detectors8

　 PMT PD APD MPPCGain 　 　

Q.E.[%]Voltage[V]

Volume large smallStructure complex simple

Power Consumption high lowInterfered in B yes no

No Interfered in static magnetic fields⇒ Can “future MRI-PET” apply?

Qualification Test9

　 Phantom image by MRI operating with the PET

influenced from MRI

influenced from MPPC

　 image by PET operating with the MRINa22

≪experiment environment≫BioView Inc.

MRI: Varian INOVA UNITY 4.7 T MRI(gradient coil: 10 gauss/cm ）

Test1: Imaging by PET10

MPPC+LYSO

static magnetic coil

RF coil

FSE ， GE ：procedures for taking MR image

x

y

z

• Outside MRI• Inside MRI （ under

FSE ）• Inside MRI （ under

GE ）

MPPC condition

　　 sourceNa22

Left: MPPC array Hamamatsu S11827-3344MG

Right: Ce:LYSO 12×12 array (1.0×1.0×10mm3 )

gradient coil

recieve responce

linear info.

Result of Test1: Imaging by PET11

outside

FSE

GE

Result of Test1: Imaging by PET12

outside

FSE

GE

Projection X (FWHM)

1.63±0.03 mm

1.65±0.07 mm

1.70±0.08 mm

Result of Test1: Imaging by PET13

outside

FSE

GE

Result of Test1: Imaging by PET14

outside

FSE

GE

1.48±0.03 mm

1.49±0.05 mm

1.55±0.13 mm

Projection Y (FWHM)

Test2: Imaging by MRI15

Images （ Cooperation ： BioView Inc. ）

(1)

(2)

(3)

No.1 No.2 No.3 No.4 No.5

Before(left) and after(right) removing the probe Slice No.1 ～5

Slice No.1 ～5

　 (1) inside MRI(MPPC powered on)　 (2) inside MRI(MPPC powered off)　 (3) remove MPPC

Result of Test2: Imaging by MRI16

power ON (red line)

power OFF (green line)

remove MPPC (blue line)

Result of Test2: Imaging by MRI17

Loss Ratio

Loss Ratio=(Power ON or OFF)/(Remove the Probe)×100 [%]

Only 5% Loss

How much noise ?

Result of Test2: Imaging by MRI18

Power on1

Power off1Only 6(noise) w.r.t. 255(signal)

Future prospectsPET/MRI have little impact on MRI/PET

19

A more advanced version of the MRI-PET gantry with 8 MPPC-based PET modules

Summary

We’re developing a more advanced version of the MRI-PET gantry with 8 MPPC-based PET modules

We developed a high resolution, compact PET module for future MRI-PET scanners

A slight degradation in the spatial resolutions of PET image operating with MRI

Signal Loss Ratio of MR image was only degraded by 5% operating with PET

Noise of MR image was only a few percent

20

Appendix

1mm cube2mm cube3mm cube

lengthMPPCMPPC

MPPCZ

21

1DoI position

Appendix: DoI TechniquePatent application PCT/JP2012/008129(Waseda Univ., Furukawa K.K.)

Kishimoto et al. 2013, IEEE

The setup of this experiment

ConnectorPlastic Case

CircuitFFC, CC→LEMO

Alumi. Case

:FFC 2m(signal)

ConnectorPlastic Case

MPPCPlastic Case

magnetic fieldsNo magnetic fields

： Coax Cable 5m(HV)

2. create LUT1. draw flood MAP

3. select 511keV in LUT

create imageby using the selecting events

MPPC

HV

5V power supply

Delay

CSADC

MPPC

Delay

Fan I/O

Fan I/O

Fan I/O

HV

Fan I/O

×4×16

×4

×4

×4

Discri.

Discri.

Coincidence G&D Generator 　Gate

G&D Generator 　D I/O×16

temperature compensation circuit

The principle of MRI.What is Fast Spin/Gradient Echo?

Axial directions and phases are in a divided state

N

S

Axial directions and phases are parallel and start to precess

apply static magnetic field into protons

N

S

proton receive the energy and lean by RF waves (excitation state)

RF

apply RF waves into protons

N

S

start to return parallel stateand radiate energy in the form of e.m. rays

RF

stop applying RF waves into protons

: electromagnetic ray (FID signal)

A) All are vertical in the vertical magnetic field and spinning on their long axis, but this illustration is in a rotating reference frame where the spins are stationary on average.

animationB) A 90 degree pulse has been applied that flips the arrow into the horizontal (x-y) plane.

C) Due to local magnetic field inhomogeneities, as the net moment precesses, some spins slow down due to lower local field strength while some speed up due to higher field strength and start getting ahead of the others. This makes the signal decay.

D) A 180 degree pulse is now applied so that the slower spins lead ahead of the main moment and the fast ones trail behind.

E) The fast moments catch up with the main moment and the slow moments drift back toward the main moment.

F) Complete refocusing has occurred and at this time the echo can be measured.

FSE ： 90 deg pulse + 180 deg pulse

RF waveincline proton

at a 90 deg angle

RF wave

the slower spins lead ahead of the main moment and the fast ones trail behind.

GE ： α deg pulse + inverse gradient

α ( 90deg)≦shorten the time

of incline

gradient magnetic field reversalNo Pulse = more shorter time

FSE ： a few minutesGE ： a few secondsWe want to receive FID signal, but we can’t because the signal decay very fast.

(This problem is caused by magnetic field inhomogeneity.)Then, we repeat applying 180deg pulse into proton after 90deg pulse.

and then the echo of resonance signal is occurred.

(Not array)spectrum under B field (S10362-33-050C)

spectrum under B field (S10362-33-050C)

3 kinds of circuit

outside MRI inside MRIinside MRI

+copper shield

　 check the waveform by OSC　 evaluate each E resolution

in static magnetic fieldsunder FSEunder GE

compared to outside MRI

MPPC is

MPPC

HV

Delay

CSADC

Fan I/O Discri. G&D Generator 　Gate

G&D Generator 　D I/O

filter circuit

5V power supply

temperature compensation circuit

FSE ， GE によるノイズoutside MRI

FSE

GE

511 keV

pulse

511 keV

pulse

no interference by set up discri ably

outside MRI inside MRIinside MRI

copper shield

static magnetic fields

MPPC is outside MRIGrand Level

circuit is

FSEGrand Level

outside MRI inside MRIinside MRI

copper shield

MPPC is outside MRI

circuit is

GEGrand Level

outside MRI inside MRIinside MRI

copper shield

MPPC is outside MRI

circuit is

511keVstatic magnetic fields

outside MRI inside MRIinside MRI

copper shield

MPPC is outside MRI

circuit is

511keVFSE

outside MRI inside MRIinside MRI

copper shield

MPPC is outside MRI

circuit is

511keVGE

outside MRI inside MRIinside MRI

copper shield

MPPC is outside MRI

circuit is

E resolution

MPPC is outside MRI

MPPC is inside MRI

MPPC isunder FSE

MPPC is under GE

circuit is outside MRI 16.0% 15.2% 15.9% 15.9%

circuit is inside MRI 15.5% 15.6% 15.8% 15.4%

inside MRI+

copper shield16.3% 15.6% 16.4% 15.9%

energy resolution （ 511keV, FWHM ）