seoul national university functional & molecular imaging system lab progress in nuclear imaging...

Seoul National University Functional & Molecular Imaging System Lab

Progress in Nuclear Imaging

Mikiko Ito, PhDDept. of Nuclear Medicine, Seoul National Univ., Seoul

심광숙 교수님 퇴임기념 워크샵June. 11-12, 2011


1. PET/MRI

2. New DOI detector

Seoul National University FMIS Lab

Positron Emission Tomography

What is PET• based on the coincidence detection of a

pair of positron annihilation gamma-rays


Positron Emission Tomography

What is PET• based on the coincidence detection of a

pair of positron annihilation gamma-rays

• Provide biochemical information by

using positron-emitter labeled

pharmaceuticals

• have higher performance for resolution,

sensitivity, and quantitative accuracy

compared with SPECT


Imaging Technique

Range of EM Wave

Spatial Reso-lution

Sensitivity Anatomical Imaging

Molecular Imaging

PET 511 keV 1 ~ 10 mm10-11 ~ 10-12 mole/L + +++

MRI Microwave 25 ~ 100 μm10-3 ~ 10-5 mole/L +++ +

CT X-ray 50 ~ 200 μm +++

PET MRI CT

Motivation for PET/MRI


MR-Compatible SiPM PET Insert

PET insert with12 detector modules

(D=13.6 cm)

Dedicated FPGA-basedacquisition system

LGSO (1.5x1.5x7.0 mm3)

20x18 arraySiPM (4x4 MPPC) 2x2 array

Shielding box

Position encoding (64 4 ch)

LGSO & SiPM

Temperature sensor& Amplifiers


Simultaneous PET/MR Imaging

Siemens MAGNETOM Trio 3T MRI

4-cm loop receiver coilX2


With RF shielding

MR Compatibility of SiPM PET

Without RFInside 3T MRI

T2 Turbo Spin Echo


Simultaneous PET/MRI Studies

T2 MRI Fusion SNU SiPM PET

FDG PET & T2 MRI in BALB/c Mouse

Kidneys


1. PET/MRI

2. New DOI detector


Why DOI Measurement?

Long crystal

Small cross section

Small diameter

Small-ring PET system: Small animal, breast, brain…• Small cross section of crystal• long crystal



Small-ring PET system: Small animal, breast, brain…• Small cross section of crystal• long crystal

If the DOI position is unknown

Parallaxerror



If the DOI position is unknown

Parallaxerror

If the DOI position is known

Depth of interac-tion (DOI)


Multi-layer detectorMulti-layer detector

DOI Detector Designs

Multi-anode PMT

Typically5~10 mm

• Discrete DOI information• High manufacturing cost

Dual-ended readout detector

• Continuous DOI information • High manufacturing cost• Damage of front sensor by gamma rays


Multi-layer detectorMulti-layer detector


Multi-anode PMT

Typically5~10 mm




Cons


Dual-ended readout detectorDual-ended readout detector


Multi-anode PMT

Typically5~10 mm

Multi-layer detector



Cons



Multi-anode PMT

Typically5~10 mm

Multi-layer detector




ProsCons

Cons


Direct DOI measurement

DOI Detector DesignsDirect DOI measurement

Flex circuit

PS-APD

Crystal

• Discrete DOI with high resolution• Low packing fraction• Large output channels• High manufacturing cost

WLS strip

Crystal

SiPM




Flex circuit

PS-APD

Crystal


WLS strip

Crystal

SiPM

ProsCons




Flex circuit

PS-APD

Crystal


WLS strip

Crystal

SiPM

ProsCons

Aim of our study

: To develop new DOI detector that does not require

additional crystals or photo-sensors


Concept of DOI Measurement

Single-layer crystal array + Single-ended readout

Cost-effectiveness

Multi-anode PMT

Triangular teethreflector



Tailoring light spread

Continuous DOI

Multi-anode PMT

Reflector grid

Single-layer crystal array + Single-ended readout

Cost-effectiveness




Multi-anode PMT

Reflector grid


Reflector grid: constructed by crossing

the triangular-teeth strips



Multi-anode PMT

Reflector grid


yx

z






yx

z



Upper-half

Lower-half

Direction of light dispersion

• Within the upper-half block : in the y direction• Within the lower-half block : in the x direction

Amount of dispersion

: depends on the DOI position




yx

z






: depends on the DOI positionUpper-half

Lower-half








: depends on the DOI position


yx

z

Upper-half

Lower-half

DOI information : by comparing X and Y signal distributions


Detector Design

Triangular-teeth shape

Conventional strip shape

Detector design• Unpolished LYSO (22 x 22 array)• Crystal : 2.0 x 2.0 x 28 mm3

• H8500 PMT (8 x 8 anode array)


yx

z


( bx , by , (ax – ay + A )/E )

DOI Response

2 mm

26 mm

6 mm10 mm14 mm18 mm22 mm

H8500 PMT

3D DOI response function

2yb

2xb

(ax –

a y +

A )

/E

26 mm

22 mm

18 mm

14 mm

10 mm

6 mm

2 mm

3D DOI response map

“Side on” irradiation


DOI Response

Estimation of DOI resolution

3D DOI response map

2yb

2xb

(ax –

a y +

A )

/E

Bbb xy 22

7

3

(ax –

a y +

A )

/E

B

DOI

Cou

nts DOI resolution

: 3.52 mm

2D projection map histogramDOI

Average DOI resolution : 3.5 mm for 28 mm crystal array


Crystal Identification

Flood image

40 cm

“Front on” irradiation

22 x 22 array

All crystal positions were well separated in flood image

H8500 PMT


Summary

1. New DOI detector

: monolayer crystal array + single-ended readout

2. DOI dependency

: 2D light dispersion tailored by geometry of reflector

frame (triangular teeth shape)

3. Initial performances

- Average DOI resolution of 3.5 mm for 2.0 x 2.0 x 28 mm crystals

- Energy resolution of 15.8 ~ 18.8 %

- Time resolution of 1.2 ~ 1.8 ns

- All crystals are separated in flood image


Thank you for your attention


Dept. of Nuclear Medicine

seoul national university functional & molecular imaging system lab progress in nuclear imaging...

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