A silicon microstrip sensor for use in dental digital radiography

1
A silicon microstrip sensor for use in dental
digital radiography

• P.F. van der Stelt
• Academic Centre for Dentistry Amsterdam,
• Amsterdam, the Netherlands
• F.A. Triantis - University of Ioannina, Ioannina,
  Greece
• R.D. Speller - University College London, London,
  United Kingdom
• G. Hall, G.M. Iles - Imperial College, London,
  United Kingdom

2
Introduction

• Many medical imaging procedures are now digital
• Main requirements are
• size large enough to cover the ROI
• resolution diagnostically adequate
• patient dose clinically acceptable

3
Solid state sensor systems

• pixel sensors
• high event rate capability
• high overhead requirement
• strip sensors
• simpler readout structures
• event rate limiting ambiguities

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Aim

• To develop and evaluate a new sensor using
• silicon microstrip technology
• for 2-D medical and dental radiographic imaging

5
Technology

• metal strips embedded in silicon
• perpendicular on both sides of the chip
• photons produce secondary electrons
• electrical charge is depleted by the strips

dacq electronics
front-end electronics
data acquisition electronics
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Technology

• photon

• silicon

• microstrips

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SMS technology

• photon counting characteristics (different from
  conventional, integrating sensors)
• enabling dual energy techniques
• possibility of increased resolution by weighed
  read-out of adjacent strips
• using existing chips

8
Results of Monte Carlo simulation

• detection efficiency is sufficient for dental
  applications when a 300 µm sensor is used
• pixel counts of lt1000 can provide good image
  quality
• even at 200 counts per pixel, high contrast
  details of 300 µm are detectable.
• Speller et al. Nucl Instr and Meth A 457 (2001)
  359

9
Prototype silicon microstrip detector

• 300 µm double-sided silicon sensor (SINTEF, Oslo,
  Norway)
• p-side 427 strips on a 50 µm pitch
• n-side 128 strips on an 80µm pitch
• effective area 2.185 x 1.024 cm2

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Prototype (contd)

• four APV chips (each 128 channels) with pitch
  adaptor to read out the p-side (427 strips)
• one APV chip with pitch adapter to read out the
  n-side (128 strips)

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P-side
427 strips, 4 APVs (2 bonded at this time)
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N-side
128 strips, 1 APV
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Hybrid architecture
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Data procssing and image correction

• gain variation of individual strips corrected for
  by subtraction of factor obtained from flat field
  image
• pixels in dead strips were assigned average of
  pixels on either side
• different aspect ratio of pixels corrected by
  using each pixel 2 times along the 80 µm and 3
  times along the 50 µm direction.

15
Imaging results

• Test images of real dental objects to determine
  the physical and diagnostic image quality
• molar
• incisor
• jaw section

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Image preprocessing
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Image preprocessing
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First images

• Molar
• enamel
• dentine
• root canal

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First images

• Incisor
• enamel
• dentine
• root canal
• restoration
• crack in enamel

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First images

• Jaw segment
• tooth structures
• tooth ligament
• bone architecture

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Conclusion

• 2-D silicon microstrip technology is a promising
  technology for building imaging sensors for use
  in dental radiography.

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Future work

• Improvement of read-out electronics
• Dose measurements
• (in addition to the theoretical calculations)
• Reduction in sensor size

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Acknowledgement

• This project has been funded by the European
  Commission under the Biomed-2 scheme, contract
  no. BMH4-CT96-1119,
• Biomedical Radiography and Radioscopy
  using Silicon Microstrip Sensors
• (BRSMS)