Lucas Parra CCNY City College of New York BME I5000 Biomedical Imaging Lecture 6 Nuclear Imaging Lucas C Parra parra ccny cuny edu some slides inspired by lecture notes of Andreas H Hilscher at Columbia University Blackboard http cityonline ccny cuny edu 1 Lucas Parra CCNY City College of New York Schedul e 1 Introduction Spatial Resolution Intensity Resolution Noise 2 X Ray Imaging Mammography Angiography Fluoroscopy 3 Intensity manipulations Contrast Enhancement Histogram Equalisation 4 Computed Tomography 5 Image Reconstruction Radon Fourier Transform Filtered Back Projection 6 Nuclear Imaging PET and SPECT 7 Maximum Likelihood Reconstruction 8 Magnetic Resonance Imaging 9 Fourier reconstruction k space frequency and phase encoding 10 Optical imaging Fluorescence Microscopy Confocal Imaging 11 Enhancement Point Spread Function Filtering Sharpening Wiener filter 12 Segmentation Thresholding Matched filter Morphological operations 13 Pattern Recognition Feature extraction PCA Wavelets 14 Pattern Recognition Bayesian Inference Linear classification 2 Lucas Parra CCNY City College of New York Nuclear 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 brain 3 Lucas Parra CCNY City College of New York Biomedical Imaging Imaging Modality Year Inventor Wavelength Physical principle Energy X Ray 1895 R ntgen Nobel 191 3 100 keV Measures variable tissue absorption of X Rays Single Photon Emission Comp Tomography SPECT 1963 Kuhl Edwards 150 keV Radioactive decay Measures variable concentration of radioactive agent Positron Emission Tomography PET 1953 Brownell Sweet 150 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 19401955 many MHz Measures echo of sound at tissue boundaries 4 Lucas Parra CCNY City College of New York Nuclear Imaging Isotopes Nucleus consists of proton and neutrons proton Nomenclature neutron A Z X or A X A 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 5 Lucas Parra CCNY City College of New York Nuclear 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 6 Lucas Parra CCNY City College of New York Nuclear 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 7 Lucas Parra CCNY City College of New York Nuclear Imaging Gamma Radiation Gamma radiation After beta decay nucleus is in exited state and relaxed with gamma electromagnetic radiation Important in SPECT 8 Lucas Parra CCNY City College of New York Nuclear 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 9 Lucas Parra CCNY City College of New York Nuclear Imaging Radioactive decay Likelihood of decay is proportional to the number of radioactive isotopes dN N t dt Half time 1 N T e 2 N0 1 2 t N t N 0 e ln 2 T 1 2 10 Lucas Parra CCNY City College of New York Nuclear Imaging useful Isotopes Nuclear imaging useful for diagnosis Altered metabolism in decease state leads to selective uptake of radio labelled tracer molecules A few examples 11 Lucas Parra CCNY City College of New York Nuclear Imaging SPECT Single 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 200K1M Energy of gamma quant is measures and used to filter scattered radiation which lacks information on the source Tc 99m 12 Lucas Parra CCNY City College of New York Nuclear Imaging SPECT 13 Lucas Parra CCNY City College of New York Nuclear Imaging SPECT Example Lung Perfusion Scan Inject micro bubbles 15 m 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 14 Lucas Parra CCNY City College of New York Nuclear 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 15 Lucas Parra CCNY City College of New York Nuclear 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 about 1cm Time of flight detection gives some location information 1ns 30cm 16 Lucas Parra CCNY City College of New York Nuclear Imaging Clinical PET Typical isotopes in PET Radionuclide 11 C 15 O 13 N 18 F Half live min 20 4 2 07 9 96 1009 7 Common tracer 18F labelled glucose Fluorodeoxyglucose FDG But many other tracers available to follow the path of a number of important metabolic interactions Applications Neurology Oncology