in-vivo multi-probe tracker
based on astrophysicalgamma-ray detector technologies
Shin’ichiro Takeda(Institute of Space and Astronautical Science / JAXA )Hirokazu Odaka, Shin-nosuke ishikawa,Shin Watanabe, Tadayuki Takahashi (ISAS/JAXA)
Yousuke Kanayama, Makoto Hiromura, Shuichi Enomoto (RIKEN)
Acknowledgements for Takashi Nakano (Gumma U.) Yoshitaka Yamaguchi,
Naoki Kawachi (JAEA), Yosikatsu Kuroda (MHI)ASTRO-H (2014)

Detector technologies for ASTRO-H
Gamma-ray imaging systems
・Fine pitch CdTe strip imager

250 V

122 keV57Co14 keV

136 keV

250 um pitch double-sided
CdTe strip detector
3.2 cm wide, 0.75 mm thick
ADC implemented VATAs(-> talks by Takahashi & Watanabe)

・Si/CdTe Compton camera(-> this talk )Si/CdTe Compton camera
Accumulation structure of high resolution(ΔE, ΔX) semiconductor detectors
The direction of incident gamma-ray ;Siθ

2cosθ = 1 − me c

(X1,E1)!

11−E2
E1 + E2"Advantage ;CdTe・Good angular resolution (~1 @ 500 keV )(X2,E2)

・Good energy resolution (~1% @ 500 keV )・Operation at around room temperature・Imaging without a mechanical collimator
Wide energy band including SPECT/PET probes

Upgrade of a Si/CdTe Compton camera
Compton camera Mrk3

Soft Gamma-ray Detector(First prototype for medical imaging)(ASTRO-H)
Compton camera Mrk5

250 um pitch Si-DSD
400 um pitch Si-DSD

250 um pitch CdTe-DSD

CdTe pixel detectors

0.23 x 10-6 @ 356 keV
10 cm

3.4 x 10-6 @ 356 keV
10 cm~ 400 x 10-6 @ 356 keV
10 cm(cf. clinical gamma camera 100 x 10-6 )Upgrade of a Si/CdTe Compton camera
Compton camera Mrk3

Soft Gamma-ray Detector(First prototype for medical imaging)(ASTRO-H)
Compton camera Mrk5

250 um pitch Si-DSD
400 um pitch Si-DSD

250 um pitch CdTe-DSD

CdTe pixel detectors

0.23 x 10-6 @ 356 keV
10 cm

3.4 x 10-6 @ 356 keV
10 cm~ 400 x 10-6 @ 356 keV
10 cm(cf. clinical gamma camera 100 x 10-6 )Compton camera Mark 3
Key elements
Double-sided Silicon strip detector

4-layer stacked CdTe pixel detector

27.6mm25.6 mm wide, 300 um thick,400 um strip pitch∆E : 1.5 keV (FWHM) @ 60 keV

mm2513.5 mm wide, 500 um thick,pixel size 1.35 mm

4 module∆E / E : 1.0 % (FWHM) @ 511 keV

Low noise & low power analog ASIC, VATA (with Gamma Medica-Ideas)Image reconstruction
Back-projection
Sθ

XΔθ

Lxσ

Δθ~1 degree

w = 2 Additional correction for the decrease of the sensitivity due tosolid angle of the camera as viewed from a voxel is needed.
( ex. LM-ML-EM method, Takeda et al. 2009 for 2-D phantom)

w = 0 No L-dependance, meaning that the correction forsolid angle is done during back-projection process.
(Takeda et al. IEEE TNS submitted )Position resolution
by simple back-projection
Source size : D=1mmZ

w=0detectorsize

Y20mm

pitc
h133 Ba

X30 mm[mm]

4.7 mm (FWHM)
4.7 mm

DSSD

CdTe

2.6 x 10-6 @ 356 keV, 30 mm

12 mm

[mm]

(Takeda et al. IEEE TNS submitted )Demonstration of multi-probe tracker
First imaging test with a living mouse by Si/CdTe Compton camera.
(Motomura et al. 2007 by Ge strip Compton camera)

Injected radiopharmaceuticals;
Mrk3
CdTe

Iodinated (131I) methylnorcholestenol(18.7 MBq: 5,4 and 3-days before imaging)used for adrenal scintigraphy
45 mm

DSSD

marked accumulation to a thyroid~15 mm85SrCl2 solution
heatingStage pad

(2 MBq: 1-day before imaging)taken up in new bone growthscanning for bone lesions

Spectrum after 6 hours observation

131I (364 keV)[counts/bin=0.4 keV]

85Sr (514 keV)

[keV]

Imaging results

thyroid

skull

spine
adrenallumbarfemur

genitals

Feasibility of a multi-probe tracker is demonstrated !!

Conclusion and future prospects
1. We have developed compact Compton imaging systems
based on Si and CdTe detector.
2. Feasibility of a multi-probe tracker is demonstrated
by Compton imaging.
3. Position resolution and efficiency in this stage aren’t sufficientfor practical applications. Experiments using Mrk5, consisting of250 um pitch Si-DSD and CdTe-DSD, are on going.
4. Application to clinical imaging has been started withTakashi Nakano, Yoshiyuki Suzuki,Kota Torikai (Gumma U.)