Imaging modalities - PowerPoint - PowerPoint by fDQ7Zq

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									    PHY100 Medical Radiation Physics


Sketches of Medical Imaging
         Modalities
             Dr Xiaoming Zheng
   School of Dentistry and Health Sciences
  Building 30, Room 270; Ph: (02) 69332068
          Email: xzheng@csu.edu.au
               Why Physics?
•   What is medical imaging?
•   How medical imaging works?
•   What are the major modalities?
•   How do these modalities work?
•   Why study Physics?
•   How do these physics topics related to
    medical imaging?
     What is medical imaging?
• Medical imaging is the technique and process
  used to create images of the human body (or parts
  and function thereof) for clinical purposes
  (medical procedures seeking to reveal, diagnose or
  examine disease) or medical science (including the
  study of normal anatomy and physiology).
            Medical Imaging
•   Remote sensing of the human body using:
•   Electromagnetic radiation
•   Sound waves
•   Radioactivity
•   etc….
•   Physics is the foundation!
How medical imaging works?
         What is Radiation?
• Energy Sources
  – Electromagnetic
  – Mechanical etc.
• Ionising Radiation
• Non-ionising radiation
• How radiations interact with matters?
    Major Clinical Imaging Modalities
•   X-ray Imaging
•   CT Scanning
•   Magnetic Resonance Imaging
•   Nuclear Imaging
•   Single Photon/Positron Emission Tomography
•   Ultrasound
             Some History
• X-ray Discovered in 1895. Mainstay of
  medical imaging till 1970’s
• 1950s-60s- Nuclear imaging.
• 1971 - CAT (CT) scanning.
• 1977 - PET scanning; 1978 – Digital
  Radiography
• 1980 Magnetic Resonance Imaging
X-Ray Imaging
X-Ray System
              X-Ray Tube
                    Filament
Cathode

                                 Rotor




      Anode               Vacuum envelope
X-Ray Images
CT Scanner
Computed Tomography
                                   CT Principle
            Single X-ray source




Translate – rotate
movement




                       Single detector
CT Principle
Image Reconstruction
Image reconstruction from projections

      Simple backprojection:
             m
 f ( x, y)   p( y cos j  x sin j , j ) 
             j 1
 Where:
 j - the jth projection angle.
 m - number of projection views.
  - The angular spacing between adjacent projections.
CT Images
MRI Scanner
Electromagnetic Radiation Energy


                              X-Ray, CT




                               MRI
            Magnetic Moment
            B                      B
                I
                           L
                                       m  tmax / B
L                                  W
                    F                      IA


                                       tmB
                                         m B sin
    F = IBL             t = IBLW =
                        IBA
    Force                     Torque
Proton Spins
     Net magnetization is the
macroscopic measure of many spins

   Bo
                           M




                             Bo
                        M c
                             T
MRI Images
     Nuclear Imaging

Use of G rays, Radionuclides and
Radiopharmaceuticals in medical
            imaging.
Gamma Camera
Atomic Physics
Nuclear Decays
Radionuclide for imaging
Gamma Camera System
Nuclear Projection Images
SPECT System Configurations
Dual Heads Gamma Camera
Image reconstruction
      
                    Pixel I
                    Activity ai
                    Intersected area fi
                r

                P(r,)
SPECT Images
          Positron (+) Decay



                                Nucleus


18F-FDG                         Neutrons
                        +   +
                    +
                                Protons

                                Electrons
              Positron annihilation

• Annihilation gives
   – 2x 511 keV gamma rays
   – 180 degrees apart
   – Line of response         511 keV
                                             e+
• Positron range & gamma
                                        e-
  noncollinearity
• Scanner is just a photon                        511 keV
  counter!
   – Counts gamma-ray pairs
     vs. single gammas
   – Time window ~ 1 ns
Raw Data & Image Reconstruction
                                          “sinogram”
                                    0


                                    90




                  90 projection
                                   180

                                              image
                                          reconstruction




  0 projection
        Prototypical PET Detector

                  Optical reflector
                                      light is converted to an electrical signal
                                      & amplified
Gamma Ray
               Scintillation                           Pre-Amplifier
                                       PMT
                 Crystal                               + Electronics

        Gamma photon
                               photons are             Front-end electronics
        converts to optical
                               collected at the end    condition the signal for
        photons
                               of the crystal          further processing
        (proportional to
        gamma energy, typ.
        1000’s)
PET Scanner
PET Images
             Sound?
•Sound is a mechanical, longitudinal
 wave that travels in a straight line

•Sound requires a medium through which
 to travel
       What is Ultrasound?

•Ultrasound is a mechanical, longitudinal
 wave with a frequency exceeding the
 upper limit of human hearing, which is
 20,000 Hz or 20 kHz.
•Medical Ultrasound between 2MHz to 16
 MHz
ULTRASOUND – How is it produced?


Produced by passing an
electrical current through
 a piezoelectrical crystal
Transducer Construction
      Ultrasound Production
• Transducer contains piezoelectric
  elements/crystals which produce the
  ultrasound pulses (transmit 1% of the time)
• These elements convert electrical energy
  into a mechanical ultrasound wave
     Piezoelectric Crystals
• The thickness of the crystal determines the
  frequency of the scanhead




      Low Frequency   High Frequency
          3 MHz           10 MHz
       The Returning Echo
• Reflected echoes return to the
  scanhead where the piezoelectric
  elements convert the ultrasound wave
  back into an electrical signal
• The electrical signal is then processed
  by the ultrasound system
Ultrasound Scanner
Ultrasound Images

								
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