Applications in Nuclear Medicine and Radiology

1. Applications in Nuclear Medicine and Radiology Professor Bob Ott Institute of Cancer Research and Royal Marsden Hospital

2. Topics • Digital x-ray imaging • Fast CT scanning • SPECT scanners for small animals • SPECT/CT scanning • PET scanners for small animals • New crystals for PET and SPECT • Active pixel sensors in medical imaging

3. Imaging requirements • X-ray imaging of anatomy energies between ~20keV and 140keV performed in integrate mode contrast between tissues often small • Single photon emission computed tomography (SPECT) imaging tissue function gamma ray energies between 80-364 keV • Positron emission tomography (PET) imaging of tissue function gamma ray energy 511 keV • PET and SPECT in pulse counting mode

4. Digital planar X-ray imaging • Systems have been based on the use of: storage phosphor plates flat panel detectors such as amorphous silicon or selenium scanning slot devices with CCDs phosphors imaged with a CCD or CMOS devices • Typically 70 microns spatial resolution is possible for breast imaging with ~100% photon detection at ~20keV • 10 lp/mm possible compared to 15 lp/mm with film

5. Indirect flat panel sensor for x-ray imaging

6. Diagnostic X-ray CT scanning • Historically detectors based on the use of CsI coupled to silicon diodes or Xe gas detectors • More recent developments involve the use of CdWO4 or ceramic scintillators such as Yttrium Gadolinium Oxide which have ~2x the light output of CdWO4 • New fast ceramic detectors use gadolinium oxide (GDOS) have a short decay time and reduced afterglow (by 400 times). • Can make fast images with 30% less radiation dose

7. Comparison of afterglow from scintillators used in CT

8. Diagnostic X-ray CT scanning • Main developments are in multi-slice imaging to speed up scanningallowing heart scanning in 5 beats

9. Curved View (1) and X-Section (2) views showing the calcified plaque on the LAD

10. X-ray CT future developments • Toshiba have developed a new 256 x 0.5mm row detector array which is soon to be commercial • GE and Siemens are developing flat panel detector CT systems which can be used for RT planning but are presently too slow for diagnostics

11. High resolution animal SPECT • The HiSPECT system is an add-on to existing NaI(Tl)-based gamma cameras to give multi-pinhole aperture sensitivity and enhanced resolution. • The Nano-SPECT system is a purpose built (Mediso) small animal imaging gamma camera system with a resolution of <0.8mm and with multi-pinhole sensitivity.

12. HiSPECT with multipinhole collimator

13. HiSPECT images of mouse using Tc-99m tracers

14. Nano-SPECT system

15. Nano-SPECT images of mouse taken in helical mode

16. SPECT/CT scanning • Following the development of PET/CT scanners several SPECT/CT scanners have now been developed • Provide improved attenuation/scatter correction plus anatomy as well as function • Siemens and Philips have just connected double headed gamma cameras to conventional CT scanners • GE have produced a gamma camera gantry incorporating a low cost CT scanner

17. SPECT/CT images

18. The new LabPET system Made with APDs coupled to individual scintillating crystals (LSO)

19. Properties of the LabPET system

20. Images from the LabPET system F-18-FDG F-18 fluoride

21. HIDAC MWPC PET system

22. HIDAC MWPC PET system F-18 fluoride F-18 FDG

23. The new PETMOT system • The system will combine phoswitch- PET and micro-lens array optical tomograph • Optical lens system is 1cm2 block containing 100 x 1mm lenses • Optical collimator used to reject non-orthogonal rays • Coupled to photodiodes

24. Multi lens array assembly for a single block Without (l) and with (r) optical collimator

25. PET-MOT system Transaxial With and without optical collimator

26. PET-MOT system • Allows both optical and positron emission tomography simultaneously • The optical system inside the PET array has little effect on the 511keV photons and is insensitive to them • J Peter and W Semmler, German Cancer Centre, Heidelberg

27. An MR compatible PET system for small animals • LSO multi ring PET system mounted inside the MR magnet with a purpose-built RF coil within PET ring • 104 2mm x 3mm x 5mm crystals coupled to 2mm diameter optical fibres • Fibres connected to MC-PMTs mounted in an RF screened box • Ring diameter 75.5 mm • P Marsden et al at St Thomas’ Hospital

28. PET- MR system layout Off-set concentric PET rings PET scanner within MR bore

29. PET – MR resolutions 15cm 3.4m 3.4m 3.4m spatial pulse height timing 1.4-1.9mm ~45% in 1m 10.9ns

30. New crystals for PET/SPECT

31. LaBr3:Ce scintillation camera • Pani et al have developed a small scintillation camera using this new scintillator coupled to a flat panel PSPMT • Achieve an energy resolution of 6.5% and a spatial resolution of 1.1mm FWHM • Efficiency at 140 keV is twice that of NaI(Tl) with a 6mm crystal

32. LaBr3:Ce TOF PET scanner • Karp et al have developed a ring PET scanner using LaBr3:Ce crystals 4mm x 4mm by 30mm coupled via continuous light guide to PMTs • Energy resolution (8.5%) is better than the equivalent LSO scanner (>20%) leading to a reduced scatter fraction (22% vs 42%) • Peak NEC rates are better than the LSO scanners • Timing resolution is ~315ps!!

33. Active Pixels Sensors in Medical Imaging • Active pixel sensors are being developed under the MI-3 basic technology grant • Will allow on-chip intelligence and ‘individual pixel/ROI’ read-out • Applications include: High resolution (sub-mm) gamma camera imaging Digital X-ray imaging High resolution (<5) digital autoradiography

34. Summary • Still plenty of mileage in new detectors for both NM and Radiology to: improve image contrast improve spatial resolution combine modalities reduce radiation dose pixel intelligence