BRAINPET - A NEW INSERT FOR PET-MR

PROTOTYPE

21.08.2018 I DAVID ARUTINOV

CONTENT

• INTRODUCTION

• PET REQUIREMENTS FOR MR

• CONCEPT OF THE PET INSERT

• SUMMARY & STATUS

21 August 2018 Page 2

INTRODUCTION

• The idea of the project is to mix two modalities, PET and MR inside a single device.

• Synergy of the two modalities brings simultaneous, non-invasive diagnostics to the next level as

it combines morphological and functional imaging

• A completely new, high-resolution, and highly sensitive PET insert must be designed to operate

in combination with UHF MR with the field up to 9.4T

MAIN IDEA

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PET-MRIimage

MRI image

PET image

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INTRODUCTIONWORKING PRINCIPLES OF TWO MODALITIES

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• A body acts as a radio transmitter in a very high

magnetic field if it is exposed to an EM wave.

• An image is obtained from the “echo radio

transmission” of your body.

• Detection: mostly regions including fat and water

• Problems for electronics:

• Very high static magnetic fields (up to 9.4T)

• Additional dynamic magnetic field

• Very low EM signal

,

• A trace amounts of short-lived radioactive

labeled molecules are injected into

bloodstream

• Radioactive decay can reveals dynamics of

metabolic processes

• Problems for electronics:

• Complex / fast readout electronics

• Large amount of data to be processed

MR PET

21 August 2018

PET REQUIREMENTS FOR MR

Restrictions on the PET electronics:

- Works inside static B0 magnetic fields up to a 9.4T.

- … fast changing gradient field of several tens of militesla.

- … accompanying RF environment

Requirements for PET Insert from the MR system:

- should not emit certain frequencies and harmonics thereof.

- Parts close to the MR bore should contain as low amount of

magnetic material as possible (at best, after 5 Gauss line).

- PET insert should be disinfectable, human safe

(no current leakage), total weight is limited, etc.

REQUIREMENTS OF THE PET INSERT

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Applies certain restriction on a choice of data transmission

Avoid using ferrites, mechanical cooling FANs, vacuum tubes, etc.

No real countermeasures are available. avoid large areas of conductive materials

Proper shielding, but should be transparent to gradient field

from [1]from [1]

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CONCEPT OF THE PET INSERT

• PET module comprised of detector stacks

• Communication via optical link

• Air cooled

• Carbon shielded [2]

The detector stack based on dSiPM [2].

1. Scintillator

2. Philips dSiPM sensor module

3. FPGA based readout module

4. Powering

DETECTORS

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CONCEPT OF THE PET INSERTDETECTOR RING AND THE GANTRY

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PET

Module 2

PET

Module 4

PET

Module 6

PET

Module 8

• Total amount of PET modules - 8

• Total amount of detector stacks - 120

• Total amount of isolated voltages - 96

(avoid loops in the magnetic field)

• Total amount of optical links - 16

• Total current (with safety margin) [A] ~ 400

• The field-of-view of the insert (cm) - 23/26

• PET resolution (mm) ~ 1.5

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CONCEPT OF THE PET INSERTDATA READOUT AND CLOCK DISTRIBUTION

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PCIe Expansion Rack

Server

PCIe 5DAQ

FPGA Card

PET Module 3

SFPClk

SFP+Data

PET Module 4

SFP+Data

SFP+Clk

Board to Board Connection

PLC Splitter

PET Module 5

SFPClk

SFP+Data

PET Module 6

SFP+Data

SFP+Clk

PET Module 7

SFPClk

SFP+Data

PET Module 8

SFP+Data

SFP+Clk

PET Module 1

SFPClk

SFP+Data

PET Module 2

SFP+Data

SFP+Clk

SFP+Data

SFP+Data

PCIe 4DAQ

FPGA Card

SFP+Data

SFP+Data

PCIe 2DAQ

FPGA Card

SFP+Data

SFP+Data

PCIe 1DAQ

FPGA Card

SFP+Data

SFP+Data

PCIe 3Timer

FPGA Card

SFPClk

PCIe Gen.3 Host Inter-face Card

PCIe Gen.3 Switch

PCIe Gen.3X16 Data

PCIe Cable

PCIe Gen.3X16 Data

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CONCEPT OF THE PET INSERT

21 August 2018

All the data is transmitted over the backend Interface and stored into an external

memory (a. k. a. debugging mode)

Total memory bandwidth: ~ 6GB/s

DATA PROCESSING: MODE I

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CONCEPT OF THE PET INSERT

21 August 2018

Different filters and algorithms reduce the data, and only part required for further

analysis and image reconstruction gets transmitted over the backend Interface and

stored in the external memory (server).

DATA PROCESSING: MODE II

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GAIN Correction

TimestampSorting

ClusteringMaximum Likelihood Positioning

Filtered

Data Out

Time Skew Correction

CONCEPT OF THE PET INSERT

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V1,V2,V3,V4,V5,V6

V1,V2,V3,V4,V5,V6

V1,V2,V3,V4,V5,V6

V1,V2,V3,V4,V5,V6

V1,V2,V3,V4,V5,V6

V1,V2,V3,V4,V5,V6

6

6

6

6

6

6

V1,V2,V3,V4,V5,V66

V1,V2,V3,V4,V5,V6

6

fiber optic

Ethernet, RS-232, RS-485, I2C,CAN...TBD

48

DPPU (WP4 hardware)

brainPET DATASERVER

RF shielding box

Optional: wheelsAlternative: fixations

Shielding of electrical communication lines

If PS is located inside MR-cage – running non-optical communication cable through the filter plate is advisable

One of the two communication lines is an alternative

Optional filter plate level connectors – belongs to MRI facility

Connector panel. Optional filter functionality

Shielded power cables. Optional mechanical cable management

Supporting ring for power connectors

GantryPET modules

Power connector

Single power supply module with:1. galvanically isolated outputs2. voltage adjustment functionality due to cable resistance

Optional: RackAlternative: RF-shield as mechanical structure

Cables directly wired (e. g. using terminals) to the PET module or via internal module connectorsAt this point, cable shielding is connected to the module shielding

Cable length: 6...20m

Static H*

Variable H*

<= 0.5...5mT<=5...50G

>=2.5T <=9.4T>=25kG <=94kG

<300uT<3G

>=300uT<=92mT

>=3G<=920G

Shielded power cables

66

6

66

6

6

6

6

6

6

6

6

66

6

* rough estimation of the intervals depends on exact position of a particular entity of the diagram

POWER SUPPLY

SUMMARY AND STATUS

21 August 2018

• Development of the electronics for high magnetic fields requires a lot of care, since

conventional designs might not be applicable. The literature is scarse, not much

experienced people either.

• Our current concept went through several redesigns and we will have a final version

soon.

• In order to eliminate other risks and better focus on project complexity we will try to

base most of the hardware on already existing products on the market.

Thanks You!

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REFERENCES

21 August 2018

[1] D. W. Harberts and M. van Helvoort, "MRI image distortion due to magnetic materials in medical i

mplants," 2015 IEEE International Symposium on Electromagnetic Compatibility (EMC), Dresden,

2015, pp. 1463-1466.

[2] Weissler, Björn, et al. "Design concept of world's first preclinical PET/MR insert with fully digital

silicon photomultiplier technology." Nuclear Science Symposium and Medical Imaging Conference

(NSS/MIC), 2012 IEEE. IEEE, 2012.

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