CdTe Strip Detector Performance for a High Resolution Small Animal PET System

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CdTe Strip Detector Performance for a High
Resolution Small Animal PET System

• Gregory S Mitchell1, Shrabani Sinha1, Jennifer R
  Stickel1,
• Spencer L Bowen1, Leonard J Cirignano2,
  Purushottam Dokhale2,
• Hadong Kim2, Kanai S Shah2, Simon R Cherry1
• 1Department of Biomedical Engineering,
• University of California, Davis, Davis, CA
• 2Radiation Monitoring Devices, Inc., Watertown,
  MA

department of biomedical engineering center for
molecular and genomic imaging
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High Resolution PET

• Small animal PET imaging -- resolution
  significantly better than 1 mm?
• At 1 mm small animal PET is still limited by
  pixel size, not limited by positron physics or
  interdetector scatter
• JR Stickel and SR Cherry, Phys. Med. Biol. 50
  (2005) 179195
• Excellent resolution requires good sensitivity,
  for a compact design this requires DOI capability
• Scintillator fabrication into small pixels is
  difficult
• Semiconductor Detectors CdTe?

mtotal (cm-1) _at_ 511 keV
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Prototype CdTe Strip Detectors

• CdTe obtained from Acrorad, dimensions 0.5 mm x
  2 cm x 2 cm

previous talk in MR1  MIC RTSD Joint Session
(Wed.)
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Prototype Detector Mounting
CdTe detector negative bias applied to coarse
strip side (typ. 300 V applied through 100 MW,
2mA leakage current--gttrue bias 100 V) readout
into Cremat CR-110 preamplifiers
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Energy Resolution
One anode (0.5 mm) strip, each of two prototype
detectors 1 ms shaping, 68Ge source
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Timing Resolution Measurements CdTe vs. LSO/PMT
Timing versus bias setting 22Na source, 10 ns
int/diff on CdTe signal
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Timing Resolution CdTe vs. CdTe

• 68Ge source, two CdTe strips in coincidence, each
  into
• Ortec 579 FFA-gtTennelec 453 CFD-gtTennelec 863
  TAC-gtAmptek MCA
• (low threshold 100 keV)

FWHM 23.9 ns How much due to lower threshold?
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Timing from Waveforms

• 68Ge source, 10k waveform pairs
• 10 GS/s (1 GHz) LeCroy Wavepro 7100
• software algorithm to extract event times

Photoelectric interactions 8 ns coincidence
timing
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Intrinsic Position Resolution
3.5 mCi 18F in a 30 gauge needle (ID 150
mm) column of 0.85 x 0.85 mm x 15 mm LSO mounted
on PMT
Intrinsic position resolution 0.51 mm (same size
as strip)
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Scanner Design
g-rays incident on detector edges - wide strips
for DOI stacks of 40, readout by flexible circuit
(100 mm thick)

• inner diameter 5.8 cm
• each block is 40 strip detectors
• total channels for 2 rings
• 2x8x40x(408) 30720

• Sensitivity for point source at CFOV
• commercial animal PET scanners 1-5
• proposed CdTe scanner (GATE simulation) 1 ring
  1.2, 2 rings 2.5

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Summary and Outlook

• CdTe strip detectors are a promising technology
  for a high resolution small animal PET scanner.
• Such a scanner would have excellent energy
  resolution (3), excellent intrinsic spatial
  resolution (0.5 mm), good sensitivity.
• Current results for timing resolution (13 ns
  FWHM for E1,E2gt200 keV) indicate a need for some
  improvement.
• Other challenges lie in packing fraction, readout
  of multiple strips data acquisition.