OVERVIEW OF MEDICAL IMAGING

1. OVERVIEW OF MEDICAL IMAGING Dr. Amr A. Abd-Elghany CHAPTER 1 For Fourth Level Applied Medical Sciences

2. Course plan and objectives • RSMI 241: Introduction to medical imaging, 2 Credits (2+0) • Prerequisites: PHY (106). • Course outlines • Chapter 1 overview of medical imaging field. • Chapter 2 Physical concepts of medical imaging. • Chapter 3 Different imaging modalities. • Chapter 4 Health care organization.

3. References • MRI The Basics, Ray H. Hashemi, William G. Bradley, Jr., California, USA. • The Essential Physics of Medical Imaging 2nd edition, Jerrold T. Bushberg, J. Anthony, Edwin M. Leidholdt, John M. Boone, California, USA. • Medical Imaging Physics 4th edition, William Hendee, Russell Ritenour. • Amr A. Abd-Elghany Student lectures notes.

4. Learning activities A) Lectures: the handouts for each lecture will be available to you on the day of the lecture. B) Study requirements: 1) Read the assigned material before class, 2) Attend all lectures and be on time, 3) Take notes and highlights as advised during the lecture, 4) Review your notes within 4 hours to transfer information into long term memory, 5) Reread the text within 8-12 hours and add additional information to notebook, 6) Become a part of the group learning discussion, 7) Come to my office hours for clarification of learning difficulties. C) Evaluation: Attendance and activities 10% First mid term 20% Second mid term 20% Final exam 50%

5. Medical Imaging • Non-invasive visualization of internal organs, tissue, etc. • Is endoscopy an imaging modality? • Image – a 2D signal f(x,y) or 3D f(x,y,z) • Is a 1D non-imaging sensing techniques an imaging modality? • Primary purpose is to identify pathologic conditions. • Requires recognition of normal anatomy.

6. Medical images are pictures of tissue characteristics that influence the way energy is emitted, transmitted, reflected and so on, by the human body. PRINCIPLE OF MEDICAL IMAGING Energy source incident (x-rays) Or Injected (radioactive material) Tissue properties Employed in Medical imaging Detection system e.g. computer, Radiographic film, etc Interacts, Penetrates, Or reflected Medical image

7. EXAMPLES OF MEDICAL IMAGING TECHNIQUES Tissues of the chest have different mass densities Incident x-rays Radiographic film Interacts Transmitted

8. Tissues of the cervices Magnetic fields + Radiofrequency Computer system

9. Major Modalities • Plain x-rays • CT scan • MRI • Nuclear imaging/PET • Ultrasound • Mammography • Angiography • Fluoroscopy Which of these modalities use ionizing radiation?

10. Overall Concept object Imaging algorithm Imaging device data Reconstructed Cross-sectional image

11. Anatomical vs Functional Imaging

13. ADVANCES IN MEDICAL IMAGING To From Physiobiochemical Anatomic Static Dynamic Qualitative Quantitative Analog Digital Nonspecific agents Tissue targeted agents Diagnosis Diagnosis/Therapy

14. Some Important Physical Concepts Electron Binding Energy and Energy Levels • Electrons are bound to the nucleus (the binding energy). • -The binding energy of an electron (Eb) is defined as the energy required to completely separate the electron from the atom. • -When energy is measured in the macroscopic world of everyday experience, units such as joules and kilowatt-hours are used. • -In the microscopic world, the electron volt is a more convenient unit of energy. • -The kinetic energy (the “energy of motion”) of the electron depends on the potential difference between the electrodes. • -One electron volt is the kinetic energy imparted to an electron accelerated across a potential difference (i.e., voltage) of 1 V.

15. -The electron volt can be converted to other units of energy: 1 eV = 1.6 × 10−19 J = 1.6 × 10−12 erg Note: 103 eV = 1 keV 106 eV = 1 MeV Kinetic energy of electrons specified in electron volts. A: The electron has a kinetic energy of 1 eV. B: Each electron has a kinetic energy of 10 eV.

16. Electron Transitions, Characteristic and Auger Emission -When an electron is removed from a shell, a vacancy or “hole” is left in the shell. -An electron may move from one shell to another to fill the vacancy. This movement, termed an electron transition. -To move an inner-shell electron to an outer shell, some external source of energy is required. -On the other hand, an outer-shell electron may drop spontaneously to fill a vacancy in an inner shell. This spontaneous transition results in the release of energy. equals the difference in binding energy between the two shells involved in the transition. -The transition energy is released as a photon. -The energy released during an electron transition is transferred to another electron. This energy is sufficient to eject the electron from its shell. The ejected electron is referred to as an Auger electron. A: Electron transition from an outer shell to an inner shell. B: Electron transition accompanied by the release of a characteristic photon. C: Electron transition accompanied by the emission of an Auger electron.

17. Fluorescence Yield -Characteristic photon emission and Auger electron emission are alternative processes that release excess energy from an atom during an electron transition. -Either process may occur. While it is impossible to predict which process will occur for a specific atom, the probability of characteristic emission can be stated. -This probability is termed the fluorescence yield, ω, where Number of characteristic photons emitted Number of electron shell vacancies ω = The fluorescence yield is one factor to be considered in the selection of radioactive sources for nuclear imaging, because Auger electrons increase the radiation dose to the patient without contributing to the diagnostic quality of the study.

18. MOLECULAR MEDICINE AND MEDICAL IMAGING -Another important imaging application of molecular medicine is the use of imaging methods to study molecular and genetic processes. • -For example, cells may be genetically altered to attract ions that • alter the magnetic susceptibility, thereby permitting their identification by magnetic resonance imaging techniques; • or • (2) are radioactive and therefore can be visualized by nuclear imaging methods. -Imaging technologies useful or potentially useful at the cellular and molecular levels: -Fluorescent labels. -Physiologic indicators. -Magnetic resonance imaging microscopy. -Single-copy studies of proteins and oligonucleotides. -Video microscopy. -Laser-scanning confocal microscopy.

19. Electromagnetic Radiation An x-ray is one type of electromagnetic radiation. Electromagnetic radiation represents the movement of energy through space as a combination of electric and magnetic fields. All types of electromagnetic radiation, which also includes Radio-waves, TV waves, visible light, microwaves and gamma rays, travel at the speed of light (186,000 miles per second). They travel through space in wave form.

20. W F = 3 W F = 2 D The waves of electromagnetic radiation have two basic properties: wavelength and frequency. The wavelength (W) is the distance from the crest of one wave to the crest of the next wave. The frequency (F) is the number of waves in a given distance (D). If the distance between waves decreases (W becomes shorter), the frequency will increase. The top wave above has a shorter wavelength and a higher frequency than the wave below it.

21. radio waves tv waves visible light gamma rays cosmic rays x-rays Which of the above examples of electromagnetic radiation has the shortest wavelength? Which of the above has the lowest frequency? Cosmic rays Radio waves