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의학영상응용 Chapter 1 Introduction To Medical Imaging Text • The Essential Physics of Medical Imaging – Radiology, University of California, Davis • • • • Jerrold T. Bushberg, Ph.D. J. Anthony Seibert, Ph.D. Edwin M. Leidholdt, JR., Ph.D. Jon M. Boone, Ph.D. • 3rd edition, – December 20, 2011 – LIPPINCOTT WILLIAMS & WILKINS Image Data in 2 dimension X Psys=120mmHg Pdia=95mmHg BW=80.5Kg Height=179cm D<1 Y Time D=1 D=2 Y Z D=3 D=4 X Time Medical Imaging Microscope Endoscope Visual Image Ophthalmoscope MRI Radiography CT Ultrasound SPECT Gamma Camera PET Thermograph Human Body Imaging • Requires energy – reflecting or penetrating tissues • Needs interaction – With atoms • Absorption, attenuation, scattering – With molecules: radioactive isotope • Metabolic, physiological – Information by interaction • Sensors to detect modulated energy Information Flow Source Energy Subject Modulated Energy Detector (Transducer) Electrical Signal Display (Result) Digital Data Processing Energy for Medical Imaging • Visible light: Visible observation – Skin photography, endoscopy, microscopy • X-ray: Radiography – Fluoroscopy, mammography, CT • • • • -ray: Gamma Camera, SPECT, PET Radiofrequency: MRI Sound: Ultrasound Imaging Infrared: Thermography Modality: different modes of making images Electromagnetic Spectrum 10-12eV 106m 장파 중파 wave 10-9eV -----------------------------------105m 10-6eV 10-3eV 102m AM방송 FM방송 TV방송 Frequency MRI -------------------------------------10-3m eV KeV MeV GeV Energy Microwave 적외선 가시광선 Hyper Thermia Thermography Medical Laser Wavelength -----------------------------------10 m -6 10-9m 10-12m 10-15m 자외선 X-선 감마선 Wavelength Diagnostic Radiology Therapeutic X-Ray Nuclear Medicine Energy particle Electromagnetic Energy • Electric Field + Magnetic Field 횡파 Wavelength ( : Å, nm, mm ) f=c E = hc/ 1109(/sec)0.3(m)=3108(m/sec) 0.00248(KeV)=1.24/500(nm),[blue] Frequency ( f: KHz, MHz, GHz) Energy E = hf ( E: eV, KeV, MeV) 0.00248(KeV)=4.1310-6600(THz),[blue] EM Spectrum Boundaries Unit Radio waves Microwaves Extreme infrared Far infrared Middle infrared Near infrared Visible Ultra violet X rays, Wavelength, (m) 1 -3 10 15 x 10-6 6 x 10-6 6 3 x 100.75 x 10-6 0.4 x 10-6 12 x 10-9 Frequency, (Hz) Energy (eV) 3 x 108 3 x 1011 13 2 x 10 13 5 x 10 14 1 x 10 4 x 1014 7.5 x 10 14 2.4 x 1016 1.24 x 10-6 1.24 x 10-3 0.083 0.207 0.414 1.65 3.1 100 3 6 9 10 ~10 ~10 KeV~MeV~GeV Visible EM Spectrum Unit Red Orange Yellow Green Blue Indiogo Violet Wavelength, (m) -9 750 x 10 -9 610 x 10 590 x 10-9 570 x 10-9 -9 500 x 10 450 x 10-9 400 x 10-9 Frequency, (Hz) Energy (eV) 4.0 x 1014 14 4.9 x 10 14 5.1 x 10 14 5.3 x 10 14 6.0 x 10 6.7 x 1014 7.5 x 1014 1.65 2.03 2.10 2.17 2.48 2.76 3.10 Diagnostic Utility • Depends on image quality – Technical quality and acquisition condition • Balance between quality and safety Radiation dose Image quality Acquisition time Clinical usefulness Power Level Examination costs Modality by Energy Visual Image Microscope SPECT CT Ultrasound PET Endoscope MRI RF Thermograph IR Ophthalmoscope Visible Radiography X-ray Gamma Camera γ-ray Medical Imaging Timeline X-ray discovery(Roentgen) BOLD MRI(Ogawa) Radioactivity(Bequerel) FDG 18 for PET Gamma ray(Villard) Atom structure(Rutherford) Isotope(Soddy) 1st MR Image(Lauterbur) Image Reconstruction(Cormack) Proton(Rutherford) Positron(Dirac) 1895 1896 1911 1900 1913 1914 1930 1917 SONAR(Langevin) Bucky grid(Bucky) X-ray equipment(GE,Siemens) 2nd WW 1963 1953 1970 1967 1973 1979 1991 71 75 1977 Fast MRI(Mansfield) RT US Imaging Mammography(Gros) SPECT(Anger) PET(Hoffman) 1st CT(Hounsfield) Medical Imaging Market (Nuclear Medicine) X-rays, Ultrasound & MRI SNU Hospital Modality 2009 2011 비고 Radio-, fluoro-, C-arm, mobile, Mammo-, X-ray 22 45 Angiography CT 9 7 10 9 MRI SPECT PET Ultrasound Endoscope System 6 8 12 4 90 3 60 17 SPECT-CT 포함 PET-CT 포함 Scope[197대] 제외 Radiography X-ray Imaging • 1st Medical Imaging Technology • Most widely using MI modality • By Wilhelm Roentgen: – In 1895, Nov. 8 – 1st X-ray image – Most properties of X-ray – Roentgenography Hand of Mrs. Roentgen Wilhelm C. Roentgen • Born in Lennep, Germany(1845-1923) • Educated at the University of Zurich. • X-ray discovery – November 8th 1895 – Report of his discovery of short-wave radiations [ X-rays, Roentgen rays ] The Nobel Prize in Physics 1901 “In recognition of the extraordinary services he has rendered by the discovery of the remarkable rays subsequently named after him" Work in 50 days • During the effect test of vacuum tubes – Fluorescence effect on barium platinocyanide screen – Made by Philipp Leonard • Nobel prize in 1905, on Cathode ray • Test on X-ray on 8th November 1895, FRI – And following weeks secretly • Ate and slept in laboratory – Investigated most of X-ray properties • Original paper: "On A New Kind Of Rays" – Über eine neue Art von Strahlen – On 28 December 1895; 50 days later • Refused to take out patents – Wanted mankind to benefit from practical applications X-ray Machine by Edison X-ray machine in 1896 GE from Edison General Electric Company CT in 1976 X-ray tube in 1913 Images by Roentgen • These days • • • 22nd Dec 1895 • 23rd Jan 1896 Wife of Roentgen • Hand of Albert von Kölliker “I have seen my death” - Swiss anatomist & physiologist Radiography Skia(Shadow)graph Shadow by visible light Shadow by X-ray Distribution of X-ray 1. Input: Short duration of X-ray • Uniform distribution from X-ray tube 2. Modified by body tissues • • • X-ray attenuation: Information While transmitting body tissue By Absorption, scattering 3. Detection • • Photographic film: Screen-film radiography Electronic detector Radiography • Transmission Imaging – Source Body Detector • Projection Imaging – Straight line trajectory single point in image • Rapid acquisition, low cost, low risk, high diagnostic value – Broken bones, lung cancer, CV disorders Pleural effusion: greater than normal attenuation in lower lobes Interaction: Macro • Attenuation : - Reduction in intensity - Depend on quantity & quality • Attenuation coefficient : -Linear Attenuation Coefficient : -Depend on absorber, energy of X-ray • N = N0e-x Interaction: Micro • Interaction with atoms: - With orbital electrons • Photoelectric effect • Coherent & Compton Scattering Photoelectric effect Compton scattering Imaging Sensors PSP Imaging plate: Screen-Film Cassette (Photo Stimulable Phosphor) Mammography • Radiography of Breast – Screen asymptomatic women for breast cancer • Masses and calcification • Transmission & Projection Imaging Mode • Lower X-ray Energy – 20,40 KeV < 100KeV • High sensitivity, low cost, excellent benefit to the risk. Fluoroscopy • Continuous acquisition of X-ray image – Real-time X-ray movie – Scotopic vision – Real-time feedback: • Positioning catheter – Anatomical motion: • Heart, esophagus – Lower Radiation dose • Fluorescent plate/Image Intensifier • Transmission & Projection Imaging Mode Image Intensify Tube • Light amplification - Photopic vision, higher spatial resolution • Input layer – X-ray light photons electrons • Electron lenses – Focusing electrons • Output phosphor – Electrons visible light (Vacuum bottle) Angiography • Fluoroscopic system for vessels - Diagnosis of vascular disease - Assisting interventional procedure • Stent placement, balloon angioplasty, thrombosis • Digital subtraction angiography[DSA] Subtraction Angiography A-B Shoe Fitting Fluoroscopy • You SEE your child’s foot IN THE SHOE. – 1930-40 – 40kVp, 3~8mA – 5-45sec • Safety problem – Banned in 1957 in USA Foot-O-Scope Pedoscope Ultrasound Imaging Sound • Mechanical energy • Longitudinal – Compression/rarefaction • Require medium – Different from X-ray • Audible range – 15Hz ~ 20kHz • Infrasound – Less than 15Hz • Ultrasound: Higher than 20kHz Ultrasound • Ultrasound(cf: supersonic) - Higher than 20KHz - Medical use: 2MHz~10MHz • 1912 : Titanic 호의 추적 • Sonar(Sound Navigating and Ranging ) : World War II • 1940 ~ 1950: Medical Application : Transducer, Ultrasound beam : Display의 개발 : Start to use in obstetrics Interaction with Matter • Reflection: at tissue boundary – Due to the difference in acoustic impedance • Refraction – Change in direction of transmission • Scattering: cause beam diffuse – By reflection and refraction • Absorption – Energy loss by converting into heat • Attenuation – Absorption + scattering Propagation Speed • c(m/sec)= f =c/f – f: cycles/sec, :wave length • c(m/sec)= (B/)1/2 kg/msec2 – B: bulk modulus, measure of stiffness – : density: kg/m3 • 2MHz in soft tissue – =c/f=1540/2106 =0.77mm Material Density Speed (kg/m3 ) (m/sec) air 1.2 330 lung 300 600 fat 924 1450 water 1000 1480 soft tissue 1050 1540 kidney 1041 1565 blood 1058 1560 liver 1061 1555 muscle 1068 1600 bone 1912 4080 PZT 7500 4000 Acoustic Impedance • Z(kg/m2sec)= c – 1 rayls = 1 kg/m2sec • Determines reflection – Small Z difference small reflection – Large Z difference large reflection Material Density (kg/m3 ) Speed (m/sec) Z (106 rayls) air 1.2 330 0.0004 lung 300 600 0.18 fat 924 1450 1.34 water 1000 1480 1.48 soft tissue 1050 1540 1.62 kidney 1041 1565 1.63 blood 1058 1560 1.65 liver 1061 1555 1.65 muscle 1068 1600 1.71 bone 1912 4080 7.8 PZT 7500 4000 30.0 Reflection • At boundary interface • Due to the difference in acoustic impedance • Reflection coefficient – Fraction of reflected pressure I • Rp= Pr/Pi =(Z2 – Z1)/(Z2 + Z1) – Fraction of reflected intensity • RI= Ir/Ii =(Z2 – Z1)2/(Z2 + Z1)2 • Transmission coefficient – TI =1- RI T R Z1 Z2 Reflections between tissues • RI,(Fat Muscle)=[(1.71-1.34)/(1.71+1.34)] =0.015 • RI,(Muscle Air)= [(1.71-0.0004)/(1.71+0.0004)] =0.999 2 2 – Impossible to image beyond lung – Need coupling gel to avoid air gap between transducer and skin Tissue interface Intensity Reflected Intensity Transmitted Liver-Kidney 0.003 % 99.7 % Liver-Fat 1.1 % 98.9 % Fat-Muscle 1.5 % 98.5 % Muscle-Bone 41.0 % 59.0 % Muscle-Lung 65.0 % 35.0 % Muscle-Air 99.9 % 0.001 % Generation & Detection Pulse Generation Electrical energy change in dipole arrangement pressure(ultrasound) Pulse Detection Ultrasound (pressure) change in dipole arrangement electrical signal Ultrasound Imaging • Sound: Mechanical Energy • Transducer: Short duration of ultrasound pulse travels and reflects echo detector image reconstruction • Reflection by interface of internal structures • Less harmful than ionizing radiation – Preferred for obstetric patient – Not suitable for lung & bone 1st Ultrasound Scanner • Somagram: In water-bath, pulse echo, 2MHz – In 1952 by Douglass Howry – B/W image on scope Ultrasound Imaging System Computerized Tomography CT or CAT • Computerized Axial Tomography – 1st modality for slice by slice inner body imaging – Computers in medicine • 1st CT: EMI Mark I – 8080 pixel 512 512 – Acquisition time: 4.5min/slice Fraction of second – Reconstruction time: 1.5min/slice Almost real-time 512512 pixels=262,144 unknowns 800 rays 1000 angles = 800,000 data values Basic Principle • Projected 2D data 3D information • Radon in 1917 – Unknown object could be produced with infinite number of their projections • Projected data over 360° The First Scanner Early CT Image Hounsfield & Cormack • • • • Sir Godfrey N. Hounsfield, UK Central Research Laboratories, EMI, London, UK 1919 – 2004 • • • • Allan M. Cormack, USA Tufts University Medford, MA, USA 1924 - 1998 The Nobel Prize in Physiology or Medicine 1979 “For the development of computer assisted tomography" Godfrey Hounsfield • 8 August 1919~12 August 2004 – Nottinghamshire UK – Never married, BS only(not Ph.D) • English Electrical Engineer Electric & Musical Industries Ltd. – Faraday House Electrical Engineering College – EMI since 1951 • Guided weapon, radar, 1st all transistor computer in Europe • Hounsfield Unit(HU) – Quantitative measure of radiodensity in CT scans – HU(x,y)=1000[u(x,y)-uwater]/uwater • Air(-1000), Water(0), Bone(400) Allan Cormack • February 23, 1924 – May 7, 1998 – Johannesburg, South Africa • South Africa UK South Africa USA – Naturalized citizen of the United States in 1966 • American physicist – Particle physics – Theoretical underpinnings of CT scanning • Side interest in x-ray technology • 2 papers in J. of Applied Physics in 1963, 64 – Little interest until Hounsfield’s 1st CT scanner in 1971 The Beatles made CT possible • EMI: Godfrey Hounsfield’s sole employer – Electrical & Musical Industries • Beatles: 200 million records – Enough money for longerrange projects – Application of postwar electronics and primitive computers • 1st CT image in 1968 – With gamma ray – 9days for a phantom 1962-1970 1st CT Images • Atkinson Morley's Hospital in Wimbledon • EMI Scanner($300,000) – Sold to Picker Marconi Phillips PneumoEncephaloGraphy(PEG) • For more clear brain structure in X-ray – Hole in the skull drain of CSF from brain replace by air, oxygen, or helium • Invasive – Side effect: headache & vomitting – 2-3 months for natural CSF recovery • Extensively used in early 20th - Before CT Image Reconstruction ? from projected Data only How to reconstruct? Need COMPUTER! Reconstruction 256 1 65281 c1,c2,c,3,….c256 Requires inversion of 6553665536 matrix C1 C2 C3 . . . . . C65536 w1,1 w1,2 … w1,65536 = w2,1 w2,2 … w2,65536 . . . . . . w65536,,1 …w65536,,65536 1 2 3 . . . . 65536 By Back Projection Iterative Reconstruction Object 8 9 7 16 .5 1 5 6 .5 12 14 10 8 8 3 3 11 -.5 Next Iteration 11 +.5 7.5 8.5 11 2.5 3.5 -1.5 st 1 Iteration 7 1 11 +1.5 9 7 1 5 9 5 Filtered Back Projection f(x,y)[f(r, )] projection f(r) transform S() back projection f’(r) f’(r) S()|| inverse transform filtering Axial Tomography • Optically by analog back-projection – Patent in 1940 by Gabriel Frank CT Generations 1st Pencil Beam 3rd Wide Fan Beam 2nd Narrow Fan Beam 4th Stationary Ring Detector CT Generations 5th Electron beam CT 6th Helical, Spiral CT 7th Multi Slice CT Helical Multi-Slice CT Solid State Detectors CT Images Images from EMI scanner Abdomen CT Sagittal Brain CT Axial Brain CT 3D Brain 3D Abdomen Magnetic Resonance Imaging Nuclear Magnet • Nucleus: spinning ball of charge – Create nuclear magnetic dipole field nuclear magnetic momentum, – Align with external magnetic field in lowest potential energy • Flipping of magnetic moment – Absorb energy and twist magnet into opposite direction – Eflip = (h/2) Bo – Release energy afterward Nuclear Magnetic Resonance • Spectroscopic study – of magnetic property – of the nucleus of atom – Protons, neutrons • Resonance – Selected absorption of energy and later release – Properties of material • Selection of location by field gradient – Imaging properties of tissue material: MRI Nobel Prize on NMR • 1943, physics – Otto Stern : discovery of the magnetic moment of proton • 1944, physics – Isidor I.Rabi: NMR in molecular rays • 1952, physics – Felix Bloch: detection of NMR in bulk matter – Edward M.Purcell: detection of NMR in bulk matter • 1981, physics – Nicolaas Bloembergen: theory of NMR relaxation • 1991, chemistry – Richard Ernst: high resolution NMR spectroscopy • 2002, chemistry – Kurt Wütrich: NMR methods of protein structure analysis • 2003, medicine – Paul C.Lauterbur: magnetic resonance imaging – Sir Peter Mansfield: magnetic resonance imaging Lauterbur & Mansfield • Paul C. Lauterbur – 1929~2007, born in Sidney, Ohio, USA – University of Illinois, Urbana, IL, USA – "Image formation by induced local interaction; examples employing magnetic resonance" – 16th March 1973, Nature • Sir Peter Mansfield – Born in 1933, London, UK – University of Nottingham School of Physics and Astronomy Nottingham, UK – First Clinical MRI in 1983, fast imaging The Nobel Prize in Physiology or Medicine 2003 “For their discoveries concerning magnetic resonance imaging" Controversy • The New York Times twice, The Washington Post, The Los Angeles Times and one of the largest newspapers in Sweden, Dagens Nyheter Raymond Damadian • Born in NY 1936 – BS in Mathematics, U. of Wisconsin Madison – MD in Einstein C. of Medicine. NY • “Tumors can be distinguished by NMR” – In Science 1971 • 1st patent in MRI field • Established MRI company FONAR – Royalty of 129 M$ against GE • Many Prizes and honors – Lemelson-MIT Prize • "the man who invented the MRI scanner – National Medal of Technology – National Inventors Hall of Fame 1st Whole Body MRI Scanner Exclusion of Damadian • Damadian’s invention – To locate cancer without producing an image. – Not proved clinical reliablity in detecting cancer – Not developed nor suggested the current way of creating images. • Long debate on Damadian’s role – So, Nobel prize delayed so long • Damadian’ whining – "If I had not been born, would MRI have existed? I don't think so. If Lauterbur had not been born? I would have gotten there. Eventually.“ – “Lauterbur and Mansfield should have rejected the Nobel Prize unless Damadian was given joint recognition” Magnetic Gradient Magnetic Resonance Imaging • Body in Magnetic Field – 0.5~3.0 Tesla (Earth Magnet field:30 Tesla) • Nuclear Magnetic Resonance of Proton – Very abundant in biologic tissue – Magnetic moment in magnetic field(1.5T) preferentially absorb RF energy at resonance frequency(63MHz) Reemit absorbed energy detect by antenna • Change magnetic field of location by gradient coil select slice MRI System 1st MRI • 1973 in Nature by Paul C. Lauterbur • Zeugmatography – 1mm H2O column – In 4.2nmm D2O cylinder – 4 different gradient direction • 700Hzcm-1 gradient MRI System MRI System • Tomographic Imaging • Competition with CT – – – – – Proton density and micromagnetic properties Higher sensitivity on anatomical variation No radiation hazard Relatively long scan time Limitation due to strong magnetic field • Use of equipment • Patient selection – Pacemaker, Clips, implants… MRI Images 1st MRI Image Brain Diffusion MRI MR Angiography Pelvis Functional MRI Gamma Ray Imaging System Imaging in Nuclear Medicine • Radio-isotope chemical or compound – Orally, Injection, Inhalation – Distribution according to physiologic status – Radiation emission(-ray) during decay • Emission/Projection Imaging Mode • Functional rather than anatomical – Thallium on normal tissue, not on ischemic tissue cold spot – Iodine for Thyroid Imaging Nobel Prizes in Nuclear Medicine • 1903(Physics): Henri Bequerel, the Curies, – Spontaneous Radioactivity • 1911(Chemistry): Marie Curie – Discovery of radium & polonium, radium isolation • 1935(Chemistry): Frédéric Joliot & Irène Curie – Synthesis of new radioactive elements" • 1943(Chemistry): George de Hevesy – Use of isotopes as tracers Curie Family Planar Imaging • 2-D maps of radio-isotope distribution. • Scintillation/Gamma Camera SPECT • Radiography: CT=Planar Imaging: SPECT • Single Photon Emission Computed Tomography • Single Slice Image PET • Positron Emission Tomography – Positron emitting isotope into metabolically active compound – Positron + electron = 2 -ray photons • Annihilation radiation: opposite direction – Annihilation detector • Expensive than SPECT – More sensitive & detect very subtle pathology – Many physiological isotopes: • 18FDG: Glucose metabolism: primary tumors and metastases How PET Works ? Combined Modalities • Functional + anatomical • (SPECT, PET) +(CT, MRI) PET/CT SPECT/CT Imaging Modality Summary Imaging Modality Radiography Fluoroscopy CT SPECT/PET Ultrasound MRI Energy X-ray X-ray X-ray Gammaray Ultrasound Radio frequency Detector Film/ Imaging Plate Image Intensifier Solid state Scintillation Camera Piezo crystal Coil antenna Resolution High Moderate High Low Low High Soft tissue contrast Weak Weak High Moderate /High Moderate High Characteristics Anatomy Anatomy Anatomy Physiology Anatomy Physiology Anatomy Physiology Cost Lowest Low High Moderate Low Highest Image Contrast Modality X-ray -ray CT, PET, SPECT MRI Ultrasound Contrast Affecting Factors Density, Atomic number, Energy of X-ray Radioisotope concentration, Pharmacological interaction Absence of out-of-slice structure Proton density, relaxation phenomena, blood flow Acoustic impedance, blood flow Spatial Resolution • Limited by wavelength of the energy Modality Resolution Resolution Limiting Factors Screen-Film Rad. 0.08mm Focal spot, detector resolution Digital Radiography 0.17mm detector resolution Fluoroscopy 0.125mm Focal spot, detector resolution Screen-Film Mammo. 0.05mm Focal spot, detector resolution CT 0.4mm Detector size Camera, SPECT 7mm Scintillator & Detector size PET 5mm Positron Travel Distance MRI 1mm Magnetic field strength Ultrasound 0.3mm Sound Wavelength Airport Body Scanner Millimeter wave: 24-30GHz Back Scattered X-ray: 50-450keV Back Scattered X-ray Imaging • Back Scattered X-ray – Compton scattering • Source & detector on same side – 2D scanning by pencil beam • Rotating collimator & conveyer – Large area detector with low dose – 7~10sec/image Back Scattered X-ray Imaging • Compton backscatter: – High for lower atomic number – Detect stowaways, explosives, drugs, organic contraband. Millimeter Wave Scanner Passive Millimeter Wave unit Active Millimeter Wave Scanner Passive Millimeter-Wave Scanner • Dielectric Lens collecting millimeter-Wave – 77GHz(24~30GHz) thermal noise – Transparent to fog, clothes, paper, fire and smoke • Bundling & amplifying by Image Sensor Array. PMMW Images Visible & PMMW image of runaway w & w/o fog Active Millimeter-Wave Scanner • Antenna array: 24-30GHz(12.5-10mm) – Circle subject & transmit and receive waves • Image wave reflectivity pass through clothing – Bounce by dense material(skin, metal) – Hologram 3D figure in 7 sec Automatic treat detection Lower energy and no tissue damage www.invisionguide.com
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