OAK RIDGE NATIONAL LABORATORY

U.S. DEPARTMENT OF ENERGY

U.S. DEPARTMENT OF ENERGY

Image Reconstruction of Restraint-Free Image Reconstruction of Restraint-Free Small Animals with Parallel and Multipinhole Small Animals with Parallel and Multipinhole

Collimation: Progress and PlansCollimation: Progress and Plans

Royal Prince Alfred Hospital

Key Personnel for Image ReconstructionKey Personnel for Image Reconstruction

• • Jefferson LabJefferson Lab

- Mark Smith, Tim Tran - Mark Smith, Tim Tran

• • Oak Ridge National LaboratoryOak Ridge National Laboratory

- Shaun Gleason, Jim Goddard- Shaun Gleason, Jim Goddard

• • Royal Prince Alfred HospitalRoyal Prince Alfred Hospital

- Steve Meikle- Steve Meikle

Image Reconstruction Flowchart

LIST-MODE SINGLE PHOTON DATA time-stamp detector head index x, y coordinates of projection pixel gantry rotation angle

LIST-MODE SINGLE PHOTON DATA, SMALL ANIMAL REFERENCE FRAME (SARF) time-stamp x, y, z coordinates of projection pixel in SARF pinhole locations in SARF

HEAD MOTION FILE time-stamp head linear velocity function head angular velocity function

IMAGE RECONSTRUCTION edit data as desired (e.g. if excessive head velocity) list-mode iterative MLEM reconstruction in SARF

TRACKING DATA FILE time-stamp raw data from small animal tracking system

TRANSFORMATION DATA FILE time-stamp coordinate transformation (translation and rotation) from gamma camera reference frame to small animal reference frame

List-Mode Iterative MLEM Image Reconstruction with Animal Motion

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sjn+1=

sjn

ckjmk=1

K∑

m=1

M∑

⋅cki jmi

cki lmisln

l=1

L∑i=1

N∑

predicted countspredicted countsprojection pixel projection pixel kki i , mouse pose , mouse pose mmii

probability for detection in projection pixel probability for detection in projection pixel kkat mouse pose at mouse pose mm of emission from source voxel of emission from source voxel jj

sum over sum over NN detected events detected events

Small Animal Reference FrameSmall Animal Reference Frame(SARF)(SARF)

scintillation arrayscintillation array

multipinhole maskmultipinhole mask• • • • • • • • • •

• • • • • • • • • •

SPECT Acquisition with Animal MotionSPECT Acquisition with Animal MotionTransform Pinhole andTransform Pinhole and

Projection Pixel CoordinatesProjection Pixel CoordinatesTo SARF for ReconstructionTo SARF for Reconstruction

sum over sum over MM mouse poses mouse poses

list-mode iterativelist-mode iterative MLEM update equationMLEM update equation

source voxel source voxel j j

Major ChallengesMajor Challenges

• • Implementation of animal motion into list-mode image reconstructionImplementation of animal motion into list-mode image reconstruction

Two detector strategyTwo detector strategy

• • single or multipinhole collimator: better resolution and sensitivity but with single or multipinhole collimator: better resolution and sensitivity but with image truncation or projection data multiplexingimage truncation or projection data multiplexing

• • parallel hole collimator: sacrifice resolution and sensitivity for full field of viewparallel hole collimator: sacrifice resolution and sensitivity for full field of view

• • Quality control and calibration parametersQuality control and calibration parameters

• • registration between reconstruction, detector, tracking reference framesregistration between reconstruction, detector, tracking reference frames

• • orientation of detector and collimator in SPECT reference frameorientation of detector and collimator in SPECT reference frame

• • calibration phantom development with ORNL (Bequé calibration phantom development with ORNL (Bequé et al.et al. analysis) analysis) - focal length, distance to AOR, mech. offset, electrical shifts, tilt, twist- focal length, distance to AOR, mech. offset, electrical shifts, tilt, twist

• • Computation time Computation time

• • (15 poses/sec ) x (1200 sec)=18,000 poses for 20 min scan(15 poses/sec ) x (1200 sec)=18,000 poses for 20 min scan

• • One- or few-pass list-mode MLEM algorithm (Reader One- or few-pass list-mode MLEM algorithm (Reader et alet al.).)

Side view of the small animal imaging system

tube

detector

multipinhole

mask

3 cm

2 cm

20 cm

7 cm

mouse brain

Single and multipinhole masks

ph1

Multipinhole Collimatorsfor Small Animal SPECT

ph5 ph13a ph13b

Mouse Model

brain and bodyactivity

Simulated Projections

ph1 ph5 ph13a ph13bbrain

3 mCi dose, 30 min acquisition, 120 angles

Multipinhole Image Reconstructions Mouse Model, No Motion, OSEM (10 subsets)

Coronal

Transaxial

ph12 iterations

ph54 iterations

ph13a6 iterations

ph13b6 iterations

SNR vs Contrast, 3.0 mCi

0

4

8

12

16

0.2 0.3 0.4 0.5 0.6 0.7

Contrast

SNR

ph_1

ph_5

ph_13a

ph_13b

Iterations 1-8

SNR and Contrast for the High (H) and Low (L) Activity 2.5 mm diam. Cylinders in Mouse Brain

C=(H-L)/(H+L)SNR=(H-L)/(H+L)

RPAH: micro Deluxe Resolution Phantom

1 pinhole on detector A

1 pinhole on detector A, 2 pinholes on detector B

1 pinhole on detector A, 4 pinholes on detector B

aperture projection image

Simulation of a Moving MouseSimulation of a Moving Mouse

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Parallel(ideal)

Parallel (detector blur)

Moving Line Source AcquisitionsMoving Line Source Acquisitions

Parallel Pinhole

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Next StepsNext Steps

• • Image reconstruction code implementation and testing for simulated Image reconstruction code implementation and testing for simulated moving mouse studiesmoving mouse studies• • use simulated list-mode data with different activity levelsuse simulated list-mode data with different activity levels

• • Acquisition and analysis of QC calibration data for parallel hole and Acquisition and analysis of QC calibration data for parallel hole and pinhole collimationpinhole collimation

• • Incorporation of complete set of QC parameters into reconstruction Incorporation of complete set of QC parameters into reconstruction codecode

• • Image reconstruction of simple geometric phantoms with motionImage reconstruction of simple geometric phantoms with motion• • line source, mouse-sized Schramm phantomline source, mouse-sized Schramm phantom

• • Image reconstruction of miceImage reconstruction of mice• • possibly ex-vivo mice with 3-D motion possibly ex-vivo mice with 3-D motion • • unanesthetized, unrestrained live miceunanesthetized, unrestrained live mice