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A silicon microstrip sensor for use in dental digital
radiographyP.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
KingdomG. Hall, G.M. Iles - Imperial College, London, United Kingdom
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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
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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
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Technology
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data acquisition electronicsdata acquisition electronicsdata acquisition electronicsdata acquisition electronics front-end front-end electronicselectronics
front-end front-end electronicselectronics
• metal “strips” embedded in silicon• perpendicular on both sides of the chip• photons produce secondary electrons• electrical charge is depleted by the strips
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Technology
microstrips
photon
photon
electrons
silicon
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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
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Results of Monte Carlo simulation
• detection efficiency is sufficient for dental applications when a 300 µm sensor is used;
• pixel counts of <1000 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
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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 (cont’d)
• 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 APV’s (2 bonded at this time)
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N-side
128 strips, 1 APV
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Hybrid architecture
Signal
Conditioning5x APV output
Sensor APV 0
APV 4APV 3APV 2APV 1
Hybrid
Clock and TriggerSlow Control
VME Crate
SEQSI
I2C
RIO2
FED
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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.
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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
Raw data
Removing non-uniformities by flat field subtraction
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Image preprocessing
Dead-strip correction
Aspect ratio correction
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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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AcknowledgementThis 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)
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