Qualification Test of a MPPC-based PET Module for Future MRI-PET Scanners Yohta KUREI J.Kataoka, T.Kato, T.Fujita, H.Funamoto, T.Tsujikawa (Waseda Univ.) S.Yamamoto (Nagoya Univ.) 5 September th International “Hiroshima” International Conference Center Hiroshima, Japan

Contents 2 1.PET and Detectors 2.Evaluation of images by PET 3.Evaluation of images by MRI 4.Future prospects and summary

Positron Emission Tomography 3 Functional imaging with 511keV annihilation gamma-ray Time of Flight(ToF) information improve S/N Depth of Interaction(DoI) information improve image quality ToF DoI Cancer :glucose normal cell cancer cell Warburg effect  Cancer cells like glucose ⇒ FDG + glucoseisotope tracer Isotope is accumulated in cancer

Characteristics of Modalities 4 X-ray CTPETMRI Spatial Resolution0.5mm 4 ～ 8mm 1mm Exposure (Dose)10mSv~~2mSvnothing Imagestructuralfunctionalstructural Feature hard tissues ex) bone, tooth cancer AD soft tissues ex) cartilage, ligament MRI-PET ⇒ insensitivity to B fields is required CT-PET = already being made into a product becoming 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

Detectors 5 However, PMT is … PMT Scintillator intricate in construction large size sensitive 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 gain long history and proven ex.)Super-Kamiokande especially, MPPC has great characteristics 13.6mm

Characteristics of Detectors 6 High gain(= doesn’t need CSA) ⇒ much better S/N ⇒ much better time resolution (suitable for ToF-PET) PMTPDAPDMPPC Gain Q.E.[%] Voltage[V] Volumelargesmall Structurecomplexsimple Power Consumptionhighlow Interfered in Byesno 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/ MPPC 7 ⇒ T.Ambe’s Poster Kishimoto et al. 2013, IEEE 1mm cube Patent application PCT/JP2012/ (Waseda Univ., Furukawa K.K.) Average jitter; 105ps(FWHM)Time resolution; 616ps(FWHM) ToF technique sandwich scinti b/w MPPCs DoI technique

Characteristics of Detectors 8 PMTPDAPDMPPC Gain Q.E.[%] Voltage[V] Volumelargesmall Structurecomplexsimple Power Consumptionhighlow Interfered in Byesno No Interfered in static magnetic fields ⇒ Can “future MRI-PET” apply?

Qualification Test 9  Phantom image by MRI operating with the PET influenced from MRI influenced from MPPC  image by PET operating with the MRI ≪ experiment environment ≫ BioView Inc. MRI: Varian INOVA UNITY 4.7 T MRI (gradient coil: 10 gauss/cm ）

Test1: Imaging by PET 10 MPPC+LYSO static magnetic coil RF coil FSE ， GE ： procedures for taking MR image Outside MRI Inside MRI （ under FSE ） Inside MRI （ under GE ） MPPC condition source Left: MPPC array Hamamatsu S MG Right: Ce:LYSO 12×12 array (1.0×1.0×10mm 3 ) gradient coil recieve responce linear info.

Result of Test1: Imaging by PET 11 outside FSE GEGE

Result of Test1: Imaging by PET 12 outside FSE GEGE Projection X (FWHM) 1.63±0.03 mm 1.65±0.07 mm 1.70±0.08 mm

Result of Test1: Imaging by PET 13 outside FSE GEGE

Result of Test1: Imaging by PET 14 outside FSE GEGE 1.48±0.03 mm 1.49±0.05 mm 1.55±0.13 mm Projection Y (FWHM)

Test2: Imaging by MRI 15 Images （ Cooperation ： BioView Inc. ） (1) (2) (3) No.1No.2No.3No.4No.5 Before(left) and after(right) removing the probe Slice No.1 ～ 5 (1) inside MRI(MPPC powered on) (2) inside MRI(MPPC powered off) (3) remove MPPC

Result of Test2: Imaging by MRI 16 power ON (red line) power OFF (green line) remove MPPC (blue line)

Result of Test2: Imaging by MRI 17 Loss Ratio Only 5% Loss

How much noise ? Result of Test2: Imaging by MRI 18 Power on1 Power off1 Only 6(noise) w.r.t. 255(signal)

Future prospects PET/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 cube 2mm cube 3mm cube DoI position Appendix: DoI Technique Patent application PCT/JP2012/ (Waseda Univ., Furukawa K.K.) Kishimoto et al. 2013, IEEE

The setup of this experiment

Connector Plastic Case Circuit FFC, CC→LEMO Alumi. Case :FFC 2m(signal) Connector Plastic Case MPPC Plastic Case magnetic fieldsNo magnetic fields ： Coax Cable 5m(HV)

2. create LUT1. draw flood MAP3. select 511keV in LUT create image by using the selecting events

MPPC HV 5V power supply Delay CSADC MPPC Delay Fan I/O HV Fan I/O ×4 ×16 ×4 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 N S S Axial directions and phases are parallel and start to precess apply static magnetic field into protons

N N S S proton receive the energy and lean by RF waves (excitation state) RF apply RF waves into protons

N N S S start to return parallel state and 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. animation B) 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 deg pulse RF wave incline 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 reversal No Pulse = more shorter time FSE ： a few minutes GE ： a few seconds We 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 (S C)

3 kinds of circuit outside MRIinside MRI + copper shield  check the waveform by OSC  evaluate each E resolution in static magnetic fields under FSE under GE compared to outside MRI MPPC is

MPPC HV Delay CSADC Fan I/ODiscri. 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 GEGE 511 keV pulse 511 keV pulse no interference by set up discri ably

outside MRIinside MRI copper shield static magnetic fields MPPC is outside MRI Grand Level circuit is

FSE Grand Level outside MRIinside MRI copper shield MPPC is outside MRI circuit is

GEGE Grand Level outside MRIinside MRI copper shield MPPC is outside MRI circuit is

511keV static magnetic fields outside MRIinside MRI copper shield MPPC is outside MRI circuit is

511keV FSE outside MRIinside MRI copper shield MPPC is outside MRI circuit is

511keV GEGE outside MRIinside MRI copper shield MPPC is outside MRI circuit is

E resolution MPPC is outside MRI MPPC is inside MRI MPPC is under FSE MPPC is under GE circuit is outside MRI 16.0%15.2%15.9% circuit is inside MRI 15.5%15.6%15.8%15.4% inside MRI + copper shield 16.3%15.6%16.4%15.9% energy resolution （ 511keV, FWHM ）