Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 231Lucas Parra, CCNYCity College of New YorkBME I5000: Biomedical ImagingLecture 6Nuclear ImagingLucas C. Parra, [email protected] some slides inspired by lecture notes of Andreas H. Hilscher at Columbia University.Blackboard: http://cityonline.ccny.cuny.edu/2Lucas Parra, CCNYCity College of New YorkSchedule1. Introduction, Spatial Resolution, Intensity Resolution, Noise2. X-Ray Imaging, Mammography, Angiography, Fluoroscopy3. Intensity manipulations: Contrast Enhancement, Histogram Equalisation4. Computed Tomography5. Image Reconstruction, Radon & Fourier Transform, Filtered Back Projection6. Nuclear Imaging, PET and SPECT7. Maximum Likelihood Reconstruction8. Magnetic Resonance Imaging9. Fourier reconstruction, k-space, frequency and phase encoding 10. Optical imaging, Fluorescence, Microscopy, Confocal Imaging11. Enhancement: Point Spread Function, Filtering, Sharpening, Wiener filter12. Segmentation: Thresholding, Matched filter, Morphological operations13. Pattern Recognition: Feature extraction, PCA, Wavelets14. Pattern Recognition: Bayesian Inference, Linear classification3Lucas Parra, CCNYCity College of New YorkNuclear Imaging●Molecules tagged with radioactive isotopes are injected.●Disperse through the body according to biologic function.●Meta-stable isotopes emit gamma rays in radioactive decay. ●Gamma rays are detected and converted into images as in x-ray CT.●Images represent concentration of radiating isotopes in the body.●Called emission tomography (as opposed to transmission tomography)●Images represent anatomy and function!Example: PET of the brain4Lucas Parra, CCNYCity College of New York Biomedical ImagingImaging Modality Year Inventor Wavelength EnergyPhysical principleX-Ray 1895 Röntgen (Nobel 191)3-100 keV Measures variable tissue absorption of X-RaysSingle Photon Emission Comp. Tomography (SPECT)1963 Kuhl, Edwards150 keV Radioactive decay. Measures variable concentration of radioactive agent.Positron Emission Tomography (PET)1953 Brownell, Sweet150 keV SPECT with improved SNR due to increased number of useful events.Computed Axial Tomography (CAT)1972 Hounsfield, Cormack (Nobel 1979)keV Multiple axial X-Ray views to obtain 3D volume of absorption.Magnetic Resonance Imaging (MRI)1973 Lauterbur, Mansfield (Nobel 2003)GHz Space and tissue dependent resonance frequency of kern spin in variable magnetic field. Ultrasound 1940-1955many MHz Measures echo of sound at tissue boundaries.5Lucas Parra, CCNYCity College of New YorkNuclear Imaging – IsotopesNucleus consists of proton and neutrons++++++++++protonneutronNomenclature:XAZXAorA := mass number (number of protons + neutrons)Z := atomic number (number of protons)Species with same Z but different A are called “isotopes.”E.g.: 64Zn, 66Zn, 67Zn, 68Zn, 70Zn (49%, 28%, 4%, 19%, 0.6%)6Lucas Parra, CCNYCity College of New YorkNuclear Imaging – Isotopes●Electrostatic repulsion is counter balanced by 'strong' nuclear force. As the number of protons Z increases the number of neutrons has to increase to counterbalance increased electrostatic repulsion.●At large nucleus sizes more neutrons are needed to keep nucleus stable because strong force decays rapidly with distance.●As Z increases there tends to be a larger range of metastable isotopes.7Lucas Parra, CCNYCity College of New YorkNuclear Imaging – Radioactive decay●Alpha radiation: Mass rich nuclei emit alpha particle (He+2)●Beta radiation: ●Neutron rich nuclei emits electron (e-) by converting a neutron into a proton. ●Proton rich nuclei converts a proton into a neutron and emits positron (e+).●Gamma radiation: After beta decay nucleus is in exited state and relaxed with gamma (electromagnetic) radiation.8Lucas Parra, CCNYCity College of New YorkNuclear Imaging – Gamma Radiation●Gamma radiation: After beta decay nucleus is in exited state and relaxed with gamma (electromagnetic) radiation.●Important in SPECT9Lucas Parra, CCNYCity College of New YorkNuclear Imaging – Positron Emission●After emission the positron (antimatter) annihilates as soon as if encounters an electron crating a pair of gamma quants (510keV) at a 180o angle. ●Important in positron emission tomography (PET)10Lucas Parra, CCNYCity College of New YorkNuclear Imaging – Radioactive decayLikelihood of decay is proportional to the number of radioactive isotopes.Half time: dNdt=−λ N (t) ⇒ N (t)=N0e−λt12=NN0=e−λ T1 /2⇒ T1 / 2=ln 2λ11Lucas Parra, CCNYCity College of New YorkNuclear Imaging – useful IsotopesNuclear imaging useful for diagnosis. Altered metabolism in decease state leads to selective uptake of radio-labelled tracer molecules. A few examples:12Lucas Parra, CCNYCity College of New YorkNuclear Imaging - SPECTSingle photon emission computed tomography (SPECT)●Parallel-hole collimator needed to establish origine of radiation (filters large fraction of the radiation) ●Photo multiplier covers large area. To obtain location of detected event anger network combines output of multiple photo-multipliers.●Individual events are detected (unlike x-ray imaging) with typical event counts of 200K-1M.●Energy of gamma quant is measures and used to filter scattered radiation which lacks information on the source.99mTc13Lucas Parra, CCNYCity College of New YorkNuclear Imaging - SPECT14Lucas Parra, CCNYCity College of New YorkNuclear Imaging - SPECTExample: Lung Perfusion Scan•Inject micro-bubbles (15 µm diameter) labelled with 99mTc into vein.•Micro-bubbles lodge in lungs before dissolving into blood steam.•SPECT images blood flow in lung.•Used to detect pulmonary embolus.15Lucas Parra, CCNYCity College of New YorkNuclear Imaging Advantage of SPECT: •Simple mechanism•Inexpensive•Many possible isotopes.Disadvantage of SPECT•Collimation reduces photon count resulting in poor SNR and/or high does.Solution: •Use positron emission which gives directional information.16Lucas Parra, CCNYCity College of New YorkNuclear Imaging - PET •Coincidence detection (<12ns) ensures directional information.•Energy filter at 511keV filter Compton scattered events.•Reduced patient dose as no collimation is required!•SNR usually 5 times improved over SPECT (+13dB).•Detectors must cover 180o increased cost over SPECT•Due to poor SNR resolution only