Andrej Studen, Karol Brzezinski, Enrico Chesi, Vladimir Cindro, Neal H. Clinthorne, Milan Grkovski, Borut Grošičar, Klaus Honscheid, S. S. Huh, Harris Kagan, Carlos Lacasta, Gabriela Llosá , Marko Mikuž , Vera Stankova, Peter Weilhammer

and Dejan Žontar

Jožef Stefan Institute, Ljubljana, University of Michigan, Ohio State University, IFIC/CSIC-UVEG Valencia, University of Ljubljana

Email: andrej.studen@ijs.si

Silicon detectors for combined MR-PET and MR-SPECT imaging

D. Burdette et al. A device to measure the effects of strong magnetic fields on the image resolution of PET scanners, Nucl Inst Meth A 609 (2–3): 263-271, 2009.

Compression in positron range measured at 7 T with high resolution silicon PET

Silicon detectors for nuclear medicineAdjusted pad (pixel) detectors with characteristics:• Resistivity > 100 kOhmcm• Thickness of 1 mm• P+nn+ structure formed with planar

processing• P+ side segmented to square pads, 1.4 mm

sized (1 mm under test)• Size of 4.4 by 2.2 cm2, 512 pads• Readout with parallel amplifiers, 128 per

ASIC• ASIC: VATAGP series by GM-IDEAS (ver. 3

and 7)• 150 ns fast shaper for trigger, 500 ns -3 us

slow shaper for energy• Insensitive to magnetic fields• Compact, flexible, sturdy.

Cochran, E et al. Performance of electronically collimated SPECT imaging system in the energy range from 140 keV to 511 keV. 2008 NSS Conf Rec: 4618-4621, 2008.

Potentially MRI compatible SPECT:Compton camera

Suggested MRI compatible design

(Non MRI) Compton camera demonstrator at UoM

Silicon detector combined with a standard (ADAC) gamma camera without a collimator. Collimator only used to compress imaging field to a single slice.

Reconstruction based on Compton kinematics tracked by impact position measurement in both sensors and energy measured in the silicon scatterer. Different sources used.

99mTc 140 keV

131I 364 keV

22Na 511 keV

The scatterer could be used as a probe within the MRI bore with external gamma camera placed in the low field environment.

N.H. Clinthorne et al. Silicon as an unconventional detector in positron emission tomography, accepted to Nucl Inst Meth A: 10.1016/j.nima.2012.05.026.

MRI compatible high resolution PET

Based on the dual ring efforts. The inner ring is silicon based & MRI compatible.Tested in single slice mode with F-18 filled high-resolution Derenzo phantom (rods 1.2 mm to 4.8 mm). Number of collected counts indicated, MLEM reconstruction used for 60 angular views. Tested with Na-22 point sources in volumetric mode. No septa, 60 angular views.

Photograph of the inner ring make-up in single slice mode. The object is placed on a rotary table. Lead collimators used to filter the image slice.

A dedicated positron range setup To test beneficial positron range compression in high magnetic field. Silicon detectors combined with MRI compatible mechanics were placed in 7 T large bore MRI magnet at OSU.No degradation in performance due to magnetic field was observed.Detectors were separated by 17 cm , the sources were placed on a pneumatically driven rotary table with 2 degree reference marks.

68Ga - e+ 1.9 MeV

• Lorentz force acting on the passing positron curves its path so it annihilates closer to the creation point.

• Tested with higher energy positron emitters (94mTc, 68Ga) where effect is more pronounced.

Artifacts from out of plane sources alleviated by accounting for positron range in MLEM reconstruction.

1 mm 2 mm

3 mm

Off plane offset0 T 7 T

Effect is highly directional, in orientation along the field, no compression is attained. Multiple orientations restore symmetry of the point spread function.

Out of plane artifacts & multiple field orientation

Beneficial resolution improvement in the axial

plane.

B

1.4 x 1.4 mm2

Volume PET

Single slice PET

2D3D