Technology in Nuclear Medicine

Transkript

1 Prof. Dr. S. I. Ziegler Technology in Nuclear Medicine Winter Term 2010/2011

2 Outline of the Lecture 1. Date Principles of Nuclear Medicine, Radionuclides 2. Date Interaction of Radiation with Matter, Detectors 3. Date Gamma Camera, SPECT Technology 4. Date Development of Gamma Camera/SPECT 5. Date PET Equipment Technology 6. Date Tools for High Resolution PET 7. Date Image Reconstruction 8. Date Quantification 9. Date Dual Modality Tomography 10. Date Nuclear Medical Applications 11. Date Tour of Nuklearmedizin MRI

3 Dual Modality Tomography PET/CT and MR/PET Sibylle Ziegler María José Martínez

4 Computed Tomography (CT) Basic Principles

5 Computer Tomography Coronal Sagittal Transverse What is represented What How do in we the measure? images?

6 CT Principles Gantry X-ray source Patient Bed Detectors

7 CT principles: X-ray generation X-ray source detectors Tightly collimated X-ray beam sweeps full circle around the patient

8 CT priniciples: What is measured? X-ray source absorber detectors

9 CT principles: What is measured d Intensity I of X-rays I( d) = I 0 e µ d Intensity (I) I 0 µ I X-rays are attenuated by Compton scattering and photoelectric effect Thickness (d) the attenuation A of X-rays A I0 = ln = µ d I the linear attenuation coefficient µ µ = 1 ln d Homogeneous material and monochromatic beam! I I 0

10 CT principles: What is measured Heterogeneous material A = µ 1 d1 + µ 2 d2 + µ 3 d3 + K = µ d = µ ds n i= 1 i i d 0 d 1 d 2 d n I 0 µ 1 µ 2 µ n I Intensity d 1 d 2 d 3 Polychromatic beam I E max = 0 I 0 ( E) e r µ ( E, ) ds de Thickness

11 CT Scanner Geometries 1 st Generation 2 nd Generation 3 rd Generation 4 rth Generation

12 CT Detectors Most common detectors are: 1.xenon gas detectors (convert directly radiation into electrical signal) 2.scintillators-photodiode solid state detectors Cesium-iodide (CsI) Cadmium Tungstate (CdWO 4 ) Modern ceramic scintillators (most efficient based on Yttriumgadolinium oxides)

13 Scintillator detectors for CT tomographs Very high quantum efficiency (minimize patient dose) Minimal radiation drift (Xe-gas detectors are the gold standard) Minimal afterglow (good material preparation) Good scintillation light yield Resistance to external influences

14 Xe-gas detector geometry Gas pressure very high (250 kpa) Pressure vessel Chamber septs Input window Dead layer Chamber very deep (8cm) Signal Amplifier Supply voltage Same principle as ionization chamber

15 Ultra Fast Ceramic (UFC) detector geometry Transmitted X-ray Generation of visible light in the scintillator crystal - Highly efficient - Highly expensive Photodiode

16 Data Measurement System Measurement of detector s analog signal Data acquisition Transformation into a digital signal ADC ADC ADC Image Reconstruction

17 CT Adaptive Array Detector (AAD) geometry X-ray source Volume acquisition! y X-ray cone-beam geometry z x Variable physical slice thickness: mm

18 CT Output Data Pictures taken from

19 3D Image Tranverse Planes 3D final image is obtained from 2D transverse images (transverse planes). Each plane contains usually 512 x 512 voxels. voxel Volume Data

20 What is represented in the images? The measured µ i of the voxels are converted into CT numbers (Hounsfield units (HU)) µ w =att. Coef. Water µ i =att. Coef. in voxel

21 What is represented in a CT-Image HU 3000 bones spleen pancreas kidney blood heart liver 0 water glands -100 mamma air fat lung

22 Computer Tomography Coronal Sagittal Transverse What is represented in the images?

23 Computer Tomography No contrast media Contrast media Iodine compound (high density) Contrast media used to enhance structures

24 Fields of application CARDIOLOGY Coronary calcium deposits (artery calcification) NEUROLOGY Cerebral blood flood RADIOTHERAPY Treatment planning Bone mineral content

25 Summary of CT CT is a 3D imaging modality - the 3D image is obtained from 2D transverse slices CT images show anatomical information in terms of tissue densities (HU) - Pixel values are equivalent to linear attenuation coefficients of tissues at X-ray energies The images are obtained by measuring the attenuation of a polychromatic X-ray beam after traversing patient body - Modern ceramic scintillators coupled to photodiodes offer the best performance

26 Summary of CT Multislice detector geometries allow whole-body reduced scanning times (of a few seconds) - Reducing patient discomfort and movement artifacts in images To enhance some structures with similar tissue density values, contrast media (high density substances) are used - For instance iodine compounds are given to enhance abdominal structures

27 PET/CT Dual modality Tomography

28 PET/CT Principle Combines PET and CT in a single device - Provides simultaneous structural and biochemical information (fused images) under almost identical conditions. - Minimizes the temporal and spatial differences between the two imaging modalities. CT PET PET/CT are whole-body tomographs

29 Some Commercial Clinical PET/CT Tomographs Philips Allegro/Gemini TM PET/CT GE Discovery TM LS PET/CT CPS Innovations Biograph TM S

30 PET/CT Standard Protocol PET/CT tomograph Fused image PET image Topogram Upper limit CT PET 3D reconstruction FORE + OSEM Lower limit CT acquistion CT-based attenuation and scattering corrections

31 PET Acquisition Protocol Typical PET acquisition protocol 370 MBq [ 18 F]-FDG Injection 60-minute uptake 3 min measuring time /bed position Image Reconstruction: FORE AW-OSEM (8 iterations, 4 subsets) Gaussian filter (5 mm)

32 Acquisition and Fusion Software PET CT Fused Image

33 16-slice spiral geometry 24 parallel banks of detectors 672 columns in radial direction, 16,128 UFC detectors Variable slice thickness: mm Max rotation speed: 0.5 sec Siemens Somaton Sensation 16 CT scanner Axial length (z): 24 mm X-ray tube 16 * 0.75 mm slices 16 * 1.5 mm slices

34 LSO Accel scanner specifications 3D scanner, 24 detector rings (82.4 cm φ) 9,216 standard LSO detectors (6.45 x 6.45 x 25 mm 3 ) Transverse FOV: 58.5 cm Axial FOV: 16.2 cm Coincidence timing window: 4.5 ns Energy window width: kev

35 Existing improvements of the Biograph TM S16 Standard LSO crystal block High Resolution LSO crystal block Images courtesy of CPS, Knoxville Standard LSO Detector 64 x (6.4 x 6.4 mm 2 ) elements 0.3 mm joints HI-REZ LSO Detector 169 x (4.0 x 4.0 mm 2 ) elements 0.03 mm joints 35

36 CT based attenuation coefficients Attenuation correction factors (ACFs) derived from the CT scan Mean of X-ray energy kev must be scaled to the PET energy of 511 kev. µ (511 kev) = µ (CT) x scaling factor

37 Scale CT Image Smooth to match PET Res. CT based attenuation coefficients Forward project for ACFs µ 511 (cm -1 ) scale factor = scale factor = non-bone tissue bone-like tissue H.U air water cortical bone 300 H.U

38 Respiratory Movement PET/CT Trigger(s) End inspiration Image taken from End expiration Respiratory gating system: Pressure sensor Gate(s) Computer Patient Belt + List Mode Acquisition

39 MR/PET

40 Hybride MR-PET Bildgebung Onkologie Indikationen, bei denen MRI und PET synergistisch sind Logistische Vorteile (one-stop-shop) Mehrwert durch bessere Koregistrierung, PET-Bewegungskorrektur basierend auf MR-Signal CUP SCC in cervical lymph node Contrast enhanced CT MRI T1w + Gd-DTPA MR-PET image fusion A. Beer 2010

41 System Design Tandem Design Sequentieller Ganzkörper PET-MR Achieva 3T MRT und PET Gemini TF (Philips) Installed in Mount Sinai NY, Dec 2009 Vor- und Nachteile : + Existierende Technologie verwendbar + Minimale Interferenz zwischen PET und MR - Gr - Nic

42 MR/PET PET

43 System Design Integriertes Design Integrierter Ganzkörper PET-MR für simultane Bildgebung + zeitliche Korrelation von PET und MR + multiparametrische Aufnahmen + MR-Bewegungskorrektur Delso et al., 2009 Vor- und Nachteile : - technisch an - neue T

44 Technologie MR-PET Ziel: möglichst simultane Datenerfassung Forderungen: Kein Einfluß von MR auf PET Detektoren? Signalübertragung? Kein Einfluß von PET auf MR Magnetische Materialien? Detektor-Größe?

45 Lange Lichtleiter und externe Photomultiplier Y. Shao, S.R. Cherry et al. IEEE TNS 1997 P.K. Marsden et al. Brit. J Radiology 2002

46 Experimentelle MR-PET Systeme LSO-APD Blockdetektor 10 x 10 LSO Kristalle (2 x 2 x 12 mm 3 ) 3 x 3 APD Matrix (5 x 5 mm 2 ) B.J. Pichler et al. J Nucl Med 2006

47 PET/MRI Preclinical System Nuklearmedizinische Klinik und Poliklinik Pichler et al. PET scanner parameters Crystal size 1.6 x 1.6 x 4.5 mm³ Crystal material Number of detector blocks FOV axial / transaxial Coincidence timing resolution Quadrature TRX coil installed inside the PET insert Resolution LSO mm / 38 mm 8 ns < 2 mm Laboratory for Preclinical Imaging & Imaging Technology University of Tübingen, Germany

48 Insert Design Siemens BrainPET Prototyp innerhalb MAGNETOM TIM installiert LSO Szintillatoren APDs - axial FOV = 19 cm - PET Auflösung = 2.5 mm Catana et al., MGH Bos

49 System Design Integrierte Ansätze Siemens: PET Detektorring zwischen HF- und Gradienten-Spulen Philips: Gesplitteter Gradient, dazwischen PET Ring HYPERImage

50 Schwächungskorrektur in PET Schwächungskorrektur Standalone PET PET/CT? 18 F-FDG PET nicht schwächungskorrigiert PET/MR 18 F-FDG PET schwächungskorrigiert

51 MR basierte Schwächungskorrektur I Gewebeklassifizierung Segmentierung von Weich-, Fett- und Lungengewebe + Einfach und schnell + Keine Annahme über Patientenanatomie - Ungenauigkeit bei Knochenläsionen (Fehler bis zu ~13% SUV) MR MR Seg CT CT-based AC Martinez-Möller et al. J Nucl Med 2009 MR-based AC Keereman et al. J Nucl Med 2010

52 MR basierte Schwächungskorrektur II Einsatz von Atlas & Mustererkennung Koregistrierung vom MR zu einem Atlas + Knochen werden erkannt - Erschwerte Koregistrierung & Atlas-Erstellung - Gefahr bei Abweichung von der Standardanatomie Schreibmann et al. Med Phys 2010 Hofmann et al. Eur J Nucl Med 2009

53 Weitere Herausforderungen Begrenztes MR-Sichtfeld Schwächung durch Spulen Ergänzung mittels PET- Emissionsdaten Verwendung vorberechneter Schwächungsmodelle der Spulen