1. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Medical X-ray Imaging System Imaging Science Fundamentals

2. Chester F. Carlson Center for Imaging Science Medical X-ray Systems u Chest x- rays (Abnormalities in lungs, heart, other abdominal organs, broken ribs) u Mammography (Calcifications/abnormalities in breast tissues) u Dental x-ray (Cavities, wisdom teeth) u Others include detecting broken bones.

3. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Typical Imaging Chain for Medical X-ray Systems X-ray source Collimator Object Film processing Image

4. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Electromagnetic Radiation u EM radiation can be thought of as oscillating electric field which generates oscillating magnetic field which generates oscillating electric field…and so on. u Can also be thought of as photons (particles), as in CCD detection of visible light. u This is called the “wave-particle duality” of EMR. Gamma Rays Ultraviolet Rays X Rays Light Infrared (IR) Microwave Radio wave

5. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Wavelength  (lambda) is called wavelength, the distance between two identical points on a wave.

6. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Frequency   (nu) is called frequency, the number of cycles per unit of time.  It is inversely proportional to the wavelength. time unit of time

7. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Wavelength and Frequency Relation: review  Wavelength is proportional to the velocity, v.  Wavelength is inversely proportional to the frequency.  eg. AM radio wave has a large wavelength (~200 m), therefore it has a low frequency (~KHz range).  In the case of EM radiation, the equation becomes  v   c  Where c is the speed of light: 3 x 10 8 m/s

8. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Photons: review  Photons are little “packets” of energy.  Each photon’s energy is proportional to its frequency.  A photon’s energy is represented by “h ” E = h Energy = (Planck’s constant) x (frequency of photon)

9. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science X-Rays Gamma Rays Ultraviolet Rays X Rays Light Infrared (IR) Microwave Radio wave  Usually detected as particles of energy (photons).  Discovered in 1895 by Wilhelm Conrad Roentgen. 10 -9 m (1 nm) 10 -11 m (0.01 nm) “soft” “hard”

10. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science X-Ray Production  Electrons are accelerated from cathode to anode.  When high energy electrons hit atoms of heavy metals, the atoms produce X-ray photons. e-e- e-e- h Anode (+) Cathode(-) h

11. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Object  What can happen to an X-ray when it encounters the object to be imaged?  Passes right through the object.  Absorbed completely by the object.  Scattered by the object

12. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Attenuation Coefficient Attenuation coefficients tell you the “x-ray blocking power” of a material. 5 1050100150 1 0.1 Attenuation Coefficient Photon Energy (keV) 500 Bone Muscle Fat

13. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Attenuation Coefficient u Coefficient depends on the property of the material. u Density (Bone has a high density compared to soft tissues) u Chemical Make-up (Lead blocks x-rays; lead screening used to protect patient & technicians)

14. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Detector u A special photographic film is used to capture the x-ray photons which passed through the object. u The film is then processed. u Film turns dark where it was exposed to x-ray photons. Exposure (Capture) ProcessingImage

15. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Typical X-Ray Images X-ray image of hand Mammogram Dental X-ray

16. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Image Quality Factors u Source u Energy of the photons u Collimation u Object u Attenuation coefficient u Source-object geometry u Detector u Object-detector geometry u Efficiency

17. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Advantages of Standard Diagnostic Medical X-ray Imaging Systems u Readily available u Reasonably cheap u Simple systems to maintain u Many experienced and trained personnel due to the fact that technology has existed for a while

18. Imaging Science FundamentalsChester F. Carlson Center for Imaging Science Disadvantages of Diagnostic Medical X-ray Imaging Systems u Exposure to harmful radiation. u Not much contrast between different soft tissues. u Image is a shadowgram (projection image) with no depth information.