Medical Image Analysis Interaction of Electromagnetic Radiation with Matter in Medical Imaging Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

X-rays ◦ Roentgen received the first Nobel Prize for his discovery of X-rays in X-ray Computed Tomography ◦ Godfrey Hounsfield and Allen Cormack in 1972 ◦ Share the Nobel Prize for Medicine in 1979 PET ◦ The clinical use of Positron Emission Tomography was demonstrated by G. Brownell in 1953 Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Electromagnetic (EM) Radiation Wave Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Figure comes from the Wikipedia,

Electromagnetic (EM) Radiation Quantum or photon Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Figure comes from the Wikipedia,

Electromagnetic (EM) Radiation Penetration Scattering ◦ A partial loss of energy and a change of the direction Photoelectric absorption Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

EM Radiation for Image Formation X-rays ◦ The X-ray photons usually travel in a straight line and are attenuated, depending on the density and atomic properties of the matter in the medium ◦ Bone, soft tissue, fluid Gamma-ray emission ◦ Radioactive tracer in the object ◦ Metabolic or functional Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Radiation Interaction with Matter Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Photon Energy (keV)  (cm 2 /g) Rayleigh Scattering Photoelectric Absorption Scattering Compton Scattering Total Mass Attenuation Coefficient Figure 3.1. The mass attenuation coefficients of water under the 511 keV energy range.

Radiation Interaction with Matter Coherent or Rayleigh scattering ◦ Elastic collision of the photon with the matter that causes a slight change in the direction of the photon travel with no loss of energy ◦ Low-energy photons in the range of a few kiloelectron volts Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Figure comes from the Wikipedia,

Radiation Interaction with Matter Photoelectric absorption ◦ A photon loses its energy by interacting with a tightly bound electron in the body matter, which is subsequently ejected from the atom due to the increased kinetic energy ◦ Emission of a fluorescent radiation ◦ Low-energy photons are absorbed by M and L shells of the atomic structure, while the high- energy photons are absorbed in the inner K- shell Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Radiation Interaction with Matter Compton scattering ◦ Photon energies are comparable to the electron rest energy of 511 keV Pair production ◦ Above MeV Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Radiation Interaction with Matter Compton scattering ◦ An inelastic collision of a photon with an outer-shell electron with a negligible binding energy ◦ After the collision, the photon with reduced energy is deflected while the electron with an increased energy is ejected from the atom ◦ The deflections in scattering events cause uncertainties in photon localization as it becomes difficult to keep the desired radiation transmission path Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Radiation Interaction with Matter Pair production ◦ A high-energy photon of the order of 1 Mev interacts near the nucleus of an atom in a manner similar to the positron emission in a radioactive decay ◦ Not used in diagnostic radiology Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Radiation Interaction with Matter Diagnostic radiological imaging with X- rays at 20keV or higher energy levels ◦ The sum of Photoelectric Absorption and Compton Scattering Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Linear Attenuation Coefficient Assume the medium is homogeneous and the radiation beam is obtained from a monochromatic energy source Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Photon Energy (keV)  (cm 2 /g) Fat Compact Bone 50 Figure 3.2. The mass attenuation coefficients of compact bone and fat.

Radiation Detection Spectrometric detectors ◦ Ionization and scintillation Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Radiation Detection Ionized chambers and proportional counters Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

+ Anode - Cathode Quantum Collimator + - ions Figure 3.3: A schematic diagram of an ionization chamber based detector.

Radiation Detection Semiconductor detectors ◦ The particle energy is transformed into electric pulses at the junction region of the semiconductor material ◦ Apply positive voltage to the n region and negative voltage to the p region ◦ The depletion layer serves as an ionization chamber ◦ A quantum interacting with the surface of the detector will create electron-hole pairs in the depletion layer Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Figure comes from the Wikipedia,

Radiation Detection Advantages of semiconductor detectors ◦ Fabricated with smaller e~3.6eV for silicon E value becomes independent of the mass and charge of the particle Provide small charge collection time (<10ns) Cause very small recombination losses due to fast charge collection Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.

Radiation Detection Scintillation detectors ◦ A scintillation phosphor and a photomultiplier tube ◦ The charged particles interact with the scintillation material to excite molecules ◦ The excited molecules emit optical photons during the relaxation process to return to the ground state ◦ Photomultiplier tubes are used to amplify the optical photon intensity and produce voltages proportional to the energy of the particle creating scintillation

Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Anode - Photocathode Quantum Collimator dynodes Figure 3.4: A schematic diagram of photomultiplier tube.

Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, Figure comes from the Wikipedia,

Radiation Detection The number of electrons emitted by the photocathode can be given as Figures come from the textbook: Medical Image Analysis, by Atam P. Dhawan, IEEE Press, 2003.