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. Oral and Maxillofacial Radiology 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. Oral and Maxillofacial Radiology 3 Solid state sensor systems pixel sensors –high event rate capability –high overhead requirement strip sensors –simpler readout structures –event rate limiting ambiguities

4. Oral and Maxillofacial Radiology 4 Aim To develop and evaluate a new sensor using silicon microstrip technology for 2-D medical and dental radiographic imaging

5. Oral and Maxillofacial Radiology 5 Technology dacq electronics data acquisition electronics front-endelectronicsfront-endelectronics metal “strips” embedded in silicon perpendicular on both sides of the chip photons produce secondary electrons electrical charge is depleted by the strips

6. Oral and Maxillofacial Radiology 6 Technology microstrips photon electrons silicon

7. Oral and Maxillofacial Radiology 7 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. Oral and Maxillofacial Radiology 8 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

9. Oral and Maxillofacial Radiology 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 cm 2

10. Oral and Maxillofacial Radiology 10 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)

11. Oral and Maxillofacial Radiology 11 P-side 427 strips, 4 APV’s (2 bonded at this time)

12. Oral and Maxillofacial Radiology 12 N-side 128 strips, 1 APV

13. Oral and Maxillofacial Radiology 13 Hybrid architecture Signal Conditioning 5x APV output Sensor APV 0 APV 4APV 3APV 2APV 1 Hybrid Clock and Trigger Slow Control VME Crate SEQSISEQSI I2CI2C RIO2RIO2 FEDFED

14. Oral and Maxillofacial Radiology 14 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. Oral and Maxillofacial Radiology 15 Imaging results Test images of “real” dental objects to determine the physical and diagnostic image quality –molar –incisor –jaw section

16. Oral and Maxillofacial Radiology 16 Image preprocessing Raw data Removing non-uniformities by flat field subtraction

17. Oral and Maxillofacial Radiology 17 Image preprocessing Dead-strip correction Aspect ratio correction

18. Oral and Maxillofacial Radiology 18 First images Molar enamel dentine root canal

19. Oral and Maxillofacial Radiology 19 First images Incisor enamel dentine root canal restoration crack in enamel

20. Oral and Maxillofacial Radiology 20 First images Jaw segment tooth structures tooth ligament bone architecture

21. Oral and Maxillofacial Radiology 21 Conclusion 2-D silicon microstrip technology is a promising technology for building imaging sensors for use in dental radiography.

22. Oral and Maxillofacial Radiology 22 Future work Improvement of read-out electronics Dose measurements (in addition to the theoretical calculations) Reduction in sensor size

23. Oral and Maxillofacial Radiology 23 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)