“From man to mouse” …Human PET

microPET

mouse

mouse

rat

rat

infantmonkey

human

.. and back again

                                                                                 

UltrasoundUltrasound

PET/SPECTPET/SPECT

MRIMRI

CTCT

Molecular(?) Imaging Modalities

OpticalOptical(Bioluminescence,(Bioluminescence,fluorescence)fluorescence)

StructureStructure

Tissue Density, ZTissue Density, ZAA

AA

AA

AA

TopographyTopography

H ConcentrationH Concentration

RadiotracerRadiotracer

MM

MM

MM~1-2 mm~1-2 mm

<10<10-12-12 mole mole= = quantitativequantitative

-galactocidase-galactocidase0.1 µmole H / µmole 0.1 µmole H / µmole 3131PP

~10~1033 cells cells quantitativequantitative

FF

FF

FF

DopplerDoppler

BOLD, DCEBOLD, DCE

20-50 µm20-50 µm

0.1 mm0.1 mm

0.1 mm0.1 mm

µm to mmµm to mm

Mechanic Collimation

b a

Pinhole

b a

Coded

Aperture

2

4bdEfficienza ⎟⎠⎞⎜

⎝⎛∝

⎟⎠⎞⎜⎝

⎛ += M11dResolution

abM =

Better Resolution Little Field of View Low Efficiency

( )bLLdResolution +=

22

tdd

bldEfficiency ⎟

⎠⎞⎜

⎝⎛

+⎟⎠⎞⎜

⎝⎛

+∝

L

d

t

Resolution & Efficiency inversely related

⎟⎠⎞⎜⎝

⎛ += M11dResolution

2

4bdNEfficienza ⎟⎠⎞⎜

⎝⎛∝

abM =

Better Resolution

High Efficiency Complicated Reconstruction

b a

Parallel

Holes

Normal Myocardial Perfusionat stress and rest

Single Vessel Coronary Artery Diseaseat stress and rest

SPECT image exhibits full perfusion(bright, donut shape) both at rest

and under stress

SPECT image shows limited perfusion(horseshoe shape rather than donut)

especially under stress.

Cardiac SPECT Images

Geant 4 simulation

- pixellated CsI(Tl) (0.8 - 0.4 mm pitch)- LaBr3 continuous (3 mm thick, different surface(s) treatment(diffusive vs absorptive)- 6 x 6 mm2, 3 x 3 mm2, 1.5 x 1.5 mm2

(PMT anode pixel size)

1000 counts/view/resol.elem.1 plaque = 10 mCi,10 resol.elem.

aorta: ~ 2 mm diameter

plaque size: 0.5 x 1 x 4 mm3

system sensitivity: ~ 10 cps/Ci

detector area: 100 x 100 mm2

spatial resolution: ~ 500 m

Trying to Image apoptosis by proper tracer (e.g.99mTcINIC-Annexin-V)

Performances not good enough for imaging biological process in vivo in small animals (mice)

Man Rat Mouse

Body weight ~70 kg ~200 g ~20 g

Brain ~105 mm ~10 mm ~6 mm

Heart ~300 g ~1 g ~0.1 g

Aorthic cannula ~ 30 mm 1.5 – 2.2 mm 0.9-1.3 mm

(0.5 mm)man rat

Preliminary pinhole SPECT reconstruction results from the CsI detectorImages are displayed as MIP (maximum-intensity-re-projections) animations

2 point sources APOE mouse (kidneys shown)

Flood imageSample projectio

nimage

Fig. 28 APOE mice

Caratteristiche insufficienti per l’imaging di processi biologici in piccoli animali (topi). E’ necessario migliorare la risoluzione spaziale e

l’efficienza Man Rat Mouse

Body weight ~70 kg ~200 g ~20 g

Brain(cortex apex-temporal lobe)

~105 mm ~10 mm ~6 mm

Heart ~300 g ~1 g ~0.1 g

Aorthic cannula () ~ 30 mm 1.5 – 2.2 mm 0.9-1.3 mm

(0.5 mm)Human Rat

2 mm FWHM (8 mm3)

1 mm FWHM ( 1 mm3)

Required spatial resolution:

6 mm FWHM (200 mm3)

Small size detectors (high pixellization) Individual detectors or

“perfect” coding