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Medical Imaging Systems: 

Medical Imaging Systems 1.mm X-ray, Computerized Tomography (CT) & Image reconstruction 2.mm Magnetic Resonance Imaging (MRI) 3.mm PET, Gamma camera & Ultra Sound Imaging 4.mm  3D volume representation 5.mm Visit to Hospital

Agenda X-ray: 

Agenda X-ray Fundamentals about radiation Interaction with medium X-ray generation Detection and Imaging CT scanning

Willem Röntgen: 

Willem Röntgen His first image 1895

History of medical imaging: 

History of medical imaging 1895: First Image in Wurzburg by Röntgen Nobel prize 1901 1896: H. A. Becquerel finds radiation from uran, Nobel prize 1903 Ing. O. Leppin: Radiation damage of his own hand 1898: Marie und Pierre Curie: finds radiation from Polonium und Radium. Nobel prize 1903. 1902: Guido Holzknecht: first meassuring eqipment 1910: P. Krause, C. Bachem und H. Günther: use of Bariumsulfat af contrast agent 1929: W. Forssmann: Katheter in his ovn heart. Nobel prize 1956 1946: E. Purcell und F. Bloch: Spin resonance: Nobel prize 1952 1953: H. Anger: first Gamma camera 1958: I. Donald: Ultrasound of unborn child 1971: G. N Hounsfield: first CT-scanner Nobel prize 1979 1973: P. C. Lauterbur: first Magnetic Resonance Imaging 1975: M. M. Ter Pogossian: PET Scanner 1980: first Digital X-ray Image (Japan)

X-rays: 

X-rays 2. Particle or photon with Energy proportional to frequency E = h * f h = Planck's constant = (4.13 e-18) [KeV sec] 1 eV = 1.6 e-19 [Joule]

X-rays: 

X-rays Particles or Photons with energy > a few eV can ionizise atoms (i.e. knocking an electron out of its orbit) Photons with energy > a few keV can change molecule bindings and is dangeous

Electro Magnetic Waves: 

Electro Magnetic Waves

X-ray energy: 

X-ray energy Diagnostic X-ray l 100nm - 0.01nm Light l 700nm - 450nm Planks konstant h = 4.13 10-18 [keVsec] = 6.6 10-34 [joule] = 1nm ~ E = hf = hc/l E = 4.13 10-18 * 103 * 3 108/10-9 = 1200 [eV] = 1.2[keV] l= 100nm ~ E = 0.012 [keV] l= 0.01nm = 10Ångstrøm ~ E = 120[keV] Planck's constant = 6.626068 × 10-34 m2 kg / s

Statistics: 

Statistics Raindrop experiment ~ Nuclear process Number of events pr. Sec. within an area is a Poisson distribution If N>>10 then Poisson->Normal distribution (m,s) (N,sqrt(N)) m = N; s = sqrt(N) Signal/Noise ratio, m/s; S/N = N/sqrt(N) = sqrt(N)

Dose vers. Image quality: 

Dose vers. Image quality Image size 100x100 pixel Question: which image has S/N = 20db ??? S/N = 20 db 20 db ~10 times S/N = 10 = sqrt(N) N = 100 events/pixel 100*100 =10.000pixel Total 1mill. events

Slide11: 

Dose vers. Image quality Image size 128x128

Interaction between X-rays and matter: 

Interaction between X-rays and matter Coherent Scattering Photoelectric effect Compton Scattering Pair Production Photodisintegration

Diagnostic X-ray spectrum: 

Diagnostic X-ray spectrum

Slide14: 

Scattered X-ray photon Incident X-ray photon Coherent Scattering Low energy photons only scattering, no Ionization and only little energy loss

Photoelectric effect: 

Photoelectric effect Photon with energy 40keV enters Photoelectron from K-shell with energy (40-33.2)=6.8keV exits Electron from M- to K-shell Characteristic radiation at (33.2-0.6)= 31.6KeV in a random direction. The Atom now has positive charge K L M Iodine Energy levels K -33.2keV L -4.3keV M -0.6keV Example

Compton Scattering: 

Compton Scattering E Energy of incident photon E’ -”- scattered photon mc2 mass equivalent energy of 1electron

Pair production: 

Pair production A photon with Energy > 1.02Mev might completely disappear under the production of an electron and a positron (electron with positive charge) The energy equivalent of an electron mass is 0.51Mev Ephoton = h*f = e- + e+ + 2Ekin

X-ray: 

X-ray Photodisintegration: not used in X-ray diagnostics E<1Mev ~ Coherent scattering Photo electric effect and Compton scattering

Linear Attenuation: 

Linear Attenuation

Mass Attenuation Coefficient (a) / X-ray Energy: 

Mass Attenuation Coefficient (a) / X-ray Energy

X-ray generation: 

X-ray generation Two important data. Max energy controlled by anode voltage Vt [keV] Radiation Dose controlled by current and time [mas]

X-ray generation: 

X-ray generation Electrons hitting the anode material produces white radiation up to an energy [keV] = anode voltage

X-ray spectrum: 

X-ray spectrum

Beam shaping: 

Beam shaping

Use of collimator: 

Use of collimator h/g reduces scattered radiation

Optical gain ~ Resolution: 

Optical gain ~ Resolution

Photo multiplying tube: 

Photo multiplying tube

Slide29: 

X-ray film cross section

Contrast Enhancement Histeq.: 

Contrast Enhancement Histeq.

Mechanical slicing or focusing: 

Mechanical slicing or focusing

CT scanners: 

CT scanners 1.Generation. 1 detector 2. Generation Linear detector array 3. Generation Both source and det. Rotates 4. Generation Rotating source 5. Generation Spiral moving source

Slide33: 

Fan Beam Cone Beam

Reconstruction from projections: 

Reconstruction from projections