FYS 4250

1. FYS 4250 Biomedical instrumentation Chapt 12b: Nuclear imaging methods

2. Overview • Gamma camera • Positron emission technology (PET) • Computer tomography (CT) • Proton therapy • Electrical impedance tomography (EIT)

3. Scintillation-detector

4. Gamma Camera • A camera for nuclear imaging. The most used so far was invented by H. Anger in the 1960’s (The Anger camera)

5. Anger camera Photons with a proper direction are let through the collimator, into the detector and photomultipliers

6. Anger Camera (cont.)

7. Gamma-camera

8. Collimator focusing

9. Actual isotopes(1)

10. Actualisotopes(2) half life half life ”parents”

11. Line spread and MTF

12. PET camera

15. Annihilation coincidence detection • Emitted positrons lose their kinetic energy by causing excitation and ionization • A positron that has lost most of the energy will interact with an electron by an annihilation • This annihilation will convert the mass of the electron-positron pair into two 511-keV photons, emitted in contrary directions

17. Annihilation coincidence detection • If a simultaneous photon is registered in two different detectors, the annihilation came into being along a straight line between the two detectors . The electronics within a scanner detects the simultaneous hits in a process called annihilation coincidence detection • When two simultaneous hits have been detected, a line between the two detectors is calculated

18. True, random, and scatter coincidences • A true coincidence = detection is the result of a single nuclear annihilation • A random coincidence = photons from different nuclear transformations are detected simultaneously at the detectors. May give erroneous results. • A scatter coincidence = one or both photons from a single annihilation are scattered in different directions but still detected in the detector

20. Design of a PET scanner • PET = scintillation crystals coupled to photomulitiplier tubes (PMT) • The signals are then processed in pulse mode in order to find the position, energy and the timestamp for each interaction • The energy levels can be used to discriminate between scatter coincidences and true coincidences • Early PET scanners coupled each scintillation crystal to a single PMT • Size of individual crystal largely determined spatial resolution of the system • Modern designs couple larger crystals to more than one PMT • Relative magnitudes of the signals from the PMTs coupled to a single crystal used to determine the position of the interaction in the crystal

23. PET-CT • Usually combined with CT in order to localize activity in the body

24. Non-invasive surgery Kilde: NIRS, Chiba, Japan

25. Non-invasive surgery Heavy ion therapy (Proton-terapi) http://www.nature.com/nature/journal/v449/n7159/box/449133a_BX1.html Kilde: NIRS, Chiba, Japan http://www.triumf.info/public/about/virtual_tour.php?section=3&single=18

26. Non-invasive surgery A treatment for patients with a local tumor not possible to treat with regular therapeutic methods Kilde: Magne Guttormsen, Fysisk Institutt, UIO

27. Non-invasive surgery Better dose distribution to the tumor Source: Magne Guttormsen, Fysisk Institutt, UIO

28. Non-invasive surgery Kilde: NIRS, Chiba, Japan

29. Non-invasive surgery Minimalized heavy ion therapy centre Tung-kjerne terapi sentre • Less size than today’s centres • Reduced investmentcost, approximately 800 mill NOK Kilde: NIRS, Chiba, Japan

30. Computertomography (CT)

31. Computertomograph (CT)

32. What is the CT? • Mathematical transform to the measured data. • Reconstruct n dimension function (image) => projection data of n – 1 dimension • Radon Transform (1917)“Two dimension and three dimension object can be reconstructed from the infinite set of projection data”. • The First CT: 1973 in the U.S.4 minutes scan, thickness of 10mm

33. Concept of CT ・Getting the shape by back projection of the projection data. ・For example, outward view is the quadrangle => it is the cylinder CT Algorithm

34. X Blur Basic principle of CT-Reconstruction of 2 dimensional image- Projection Data curvilinear integral of absorption coefficient regarding Y y y X-ray detector array Y X x x object X X-ray tube Reconstruction field Data Acquisition field Simple Backprojection

35. 1., 2. and 3. generation scannerLinear translation + rotationCirkular scanningVolume scanning

36. CT picture old technology

37. CT picture new technology Source:http://tidsskriftet.no/article/877021

38. Geometry of a CT-scanner

39. Image reconstruction

40. Back- projection (1)

41. Back- • projection (2)

42. y X x x ω or x Basic principle of CT -Reconstruction of 2 dimensional image- Projection Data x ＊ Filtered Projection data Reconstruction Filter Multidirectional Backprojection Filtered Backprojection

43. CT image

44. CT 3-D image

45. 2D og 3D images

46. Rapidscanner

47. Multislice CT • Several rings of detectors for multiple scanning of several layers. • Time efficiant, a 4 slice multislice CT is up to 8 times faster than a single slice CT • Possible monitoring of a beating heart ++

48. Reconstruction process

49. Reconstruction process Data acquisition at angle : 0 – 180 degree Obtain F(u,v) and then 2D IFFT -> reconstruction Radon Transform is equivalent to Filtered backprojection !

50. Example of Simulation Model Image SimpleBackprojection Filtered Backprojection