Prostate probe with SPECT techniqueNSS – MIC 2010 - November 5 - Knoxville F. Garibaldi- INFN – Roma1 – gr. Coll. ISS

the medical problem

the proposal Layout Multimodality SiPM/electronics

summary and outlook

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Radionuclides imaging techniques

Patient injected with radioactive drug. Drug localizes according to its metabolic properties.Gamma rays, emitted by radioactive decay, that exit the patient are imaged.

1.CollimatorOnly gammas that are perpendicular to imaging plane reach the detector

2.ScintillatorConverts gammas to visible light3.Photodetector

Convert light to electrical signal

4.Readout ElectronicsAmplify electrical signal and interface to computer5.Computer decoding procedureElaborate signal and gives image output

PETCompton Cameramechanical collimation

Multi pinhole

Source

Image Plane

1st Detector

2nd DetectorScattered - Rays

Single photon techniques

- simple(r)

- cheape(r)

- extending the radiotracers available

- dual tracer looking at two different biological processes

pros

cons- efficiency- spatial resolution

Compton Prostate Imaging Probe

Internal Compton Probe External Compton Probe

Predicted Internal Probe Performance

4mm Point-to-Point, 1cm from probe (Monte Carlo simulation + ML reconstruction)

141keV 171keV 245keV 364keV 511keV

Imaging Distance 10 cm

Compton ProbeHigh-Sensitivity CollimatorHigh-Resolution Collimator

Efficiency Resolution 1.8e-3 2.47mm 1.11e-4 15.9mm 4.00e-5 10.5mm

Comparison with SPECT for In-111

Relative Uptake of In-111 Prostascint

Organ Relative Uptakes

Prostate 1.0

Liver 2.0

Blood 1.5

Bone 0.7

Kidney 1.0

Spleen 1.0

Bladder 0.6

Rectum 0.4

Testes 0.6

Averaged from three In-111 Prostascint SPECT scans

Conventional SPECT Reconstructions

5:1 10:1 15:1 20:1

w / tumor

bkgd

171 and 245 keV, 8.8M events / 40 slices

Spatial resolution ~15mm FWHM

Prostate

Compton Prostate Probe Reconstructions

5:1 10:1 15:1 20:1

w / tumor

bkgd

245 keV only, 1.2 million events, 8mm lesion

Prostate

Spatial resolution ~2mm FWHM

Internal Detector Details

10–12 layers of 1mm thick Si detectors + position and orientation sensor

Exploded View

Assembled Unit

Compton Probe Promising but Challenging

• First detector– Energy resolution – largely addressed– Timing resolution – still an issue– Packaging – solvable

• Second detector– Countrate capability – solvable – Cost – always an issue

• System– Image reconstruction – solvable

Detector Packaging

Unfolded energy spectrum

“Raw” energy spectrum

Use Tape Automated Bonding (TAB)

(Very thin kapton tape with aluminum traces)

Kapton microcables

Detector

VATA ASIC

Kapton “hybrid” board

Timing

0 50 100 150 200 250 3000

0.5

1

1.5

2

2.5

x 10-9

Time (ns)

Sig

na;

200 V = Vdep

Threshold

0 50 100 150 200 250 3000

0.5

1

1.5

2

2.5

x 10-9

Threshold

500V = Vdep + 300V

Time (ns)

Sig

nal

• Desired time resolution <10ns FWHM

• Poor timing from Si is evident

• Slower signal generation from events near backplane

• Large range of pulse-height coupled with leading-edge trigger is a big issue time-walk

• Signal generation depends on 3D interaction position and recoil electron direction time-jitter

Signal generation at two biases for three depths

BGO-Silicon timing spectrum for 511 keV source

How Challenges Affect Performance• Consider anticipated countrate with In-111 Prostascint (from Monte

Carlo simulations):– ~4 Mcps on second detector– ~40 kcps on scattering detector– 50 ns time window for present Si detectors (may need to be even

larger)• Crandom= 2 x 4x106 x 4x104 x 50x10-9 = 16,000 cps !

• Ctrue was only ~10 kcps (or less)

• Performance dominated by randoms!

• Energy sum window can be used to reject randoms but only if the second detector also has good energy resolution

Source

Image Plane

1st Detector

2nd DetectorScattered - Rays

Single photon Compton camera ( N. Clinthorne. Michigan )

External Multipinhole Alternative

External probes will have small FOV and limited-angle tomography but…

• SPECT/CT can identify prostate region

• Probe can be computer-steered to image desired FOV

• Conventional SPECT can be used to “complete” probe data

Endorectal Multipinhole?

Pinhole aperture array -- side view

Pinhole aperture array -- bottom view

Detector

Probe Shell

Pinhole Collimation (multiplexed or not)

30mm

~15mm

• Some tomographic capability

• Requires high detector resolution (0.5–1 mm + depth-of-interaction)

• High enough efficiency and resolution?

W. Moses – Rome workshop 2005

111In-ProstaScint is not a good radiotracer but a new one proposed by M. Pomper looks promising.

Radionuclides Single photon

The single photon endorectal probe provides 2D imaging. We have to try to have 3 D images

( using multipinhole collimation and/or adding

up a SPECT tomograph (spatial resolution would

be dominated by the small probe (see later, the PET

case))

our proposal-insert scintillator pixels into square holes of the collimator

better performances (spatial resolution (?) and sensitivity (thicker scintillator))

-using diverging collimator better performances (reducing scan time)

-using multipinhole collimation better performances (increasing sensitivity, tomographic

recinstruction)

New radiotracers coming soon (M. Pomper , Johns Hopkins)Radiotracers available for SPECT and PET

(from “New agents and Techniques for Imaging prostate cancer” A. Zahreer, S. Y. Cho, M. Pomper”, to be published on JNM)SPECT: Prostascint, Bombesyn, 99mTechnetium nanocolloid (limphonodes), other coming soon…PET C—11 Choline, F-18-Choline, Ga-68 Dotabomb (Hofmann (Rome workshop)) many others coming… (collaboration with Johns Hopkins for testing in ISS (mice models for prostate available) and/or at JHU)

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