1. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 1 Medical Imaging and Pattern Recognition Lecture 6 X-ray Imaging Oleh Tretiak

2. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 2 Wilhelm Conrad Roentgen Roentgen discovered penetrating radiation on 8 November 1895. The famous radiograph made by Roentgen on 22 December 1895, and sent to physicist Franz Exner in Vienna. This is traditionally known as "the first X-ray picture" and "the radiograph of Mrs. Roentgen's hand. " Roentgen received the first Nobel prize in physics in 1901

3. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 3 X-rays at Present Superior definition Clear images of bones Some indication of tissue No tissue detail (tendon, muscle, skin) Negative image: bone is white, air is black

4. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 4 Talk Outline Examples of X-ray imaging procedures Physics: X-ray attenuation, transmission, and contrast X-ray recording systems Summary and new developments

5. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 5 Chest X-ray Clear images of bone –ribs, vertebra, clavicles Soft tissue: shoulder muscles, hart, abdomen Pattern of passages in lungs

6. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 6 Abdominal X-ray Visible: Bony structures –Vertebra, pelvic bones, legs, ribs Soft tissues –liver, stomach, leg muscles Confusing image of intestines –Intestinal gas, walls Cannot see: –Details of liver, back muscles, kidneys

7. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 7 Abdomen - more Abdomen after Barium contrast enema Large intestine easily visible

8. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 8 Another Abdomen Contrast medium in aorta (angiography) Visible: –descending aorta, –renal arteries, –iliac arteries

9. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 9 Pelvic X-Ray Can see –Fracture in pelvis –Femur Cannot see –Soft tissues

10. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 10 Skull Can see bones, scalp Cannot see ventricles, blood vessels

11. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 11 Skull: Subtraction Angiography

12. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 12 Summary X-ray imaging is a successful modality Limitations: Cannot distinguish among soft tissues Limitations can be overcome under some conditions with contrast media

13. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 13 X-Ray Schematic of x-ray imaging

14. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 14 What are X-rays? X-rays (Roentgen rays) are electromagnetic, like radio waves and light There are three ways to measure the “quality” of electromagnetic waves –Wavelength –Frequency –Photon energy f - frequency, Hertz (Hz) - wavelength, meters (m) E - photon energy, electron volts (Ev) c - speed of light, 3x10 10 m/sec h - Planck’s constant, 4.1x10 -15 Ev/Hz

15. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 15 Examples FrequencyWavelength Photon Energy Radio 1e6 Hz 1 Mega Hz 300 m 4e-9 Ev 4 nanoV Green light5.45e14 Hz 0.55e-6 m 0.55  m 2.2 Ev X-ray7.3e18 Hz4.1e-11 m 3e4 Ev 30 kEv

16. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 16 Generation of X-rays X-rays are generated when electron hit a target

17. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 17 X-ray Spectrum An X-ray tube produces a broad spectrum of energies

18. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 18 X-ray Attenuation For medical imaging, we can assume that X-rays travel along straight lines (rays). In the presence of matter, X-rays are removed from from a beam. This process is called attenuation. For homogeneous material and X-rays, attenuation follows an exponential law.  - linear attenuation coefficient, in cm -1

19. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 19 Attenuation Coefficient Values Tables of X-ray attenuation and absorption coefficients can be found on the web - for example, http://physics.nist.gov/PhysRefData/XrayMassCoef/ta b4.html http://physics.nist.gov/PhysRefData/XrayMassCoef/ta b4.html

20. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 20

21. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 21 Examples Conclusion: High voltage photons are needed to penetrate thick objects. Values of transmission, T = exp(-  t)

22. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 22 Contrast If |(  0 –  1 )t 1 | is small,

23. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 23 Contrast and Photon Energy Contrast is increased if the difference in attenuation coefficients between tissues is larger At 20 kev,  muscle -  fat = 0.320 At 50 kev,  muscle –  fat = 0.040 To increase contrast, use lower voltage!

24. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 24 Recording X-rays Direct film recording (like Roentgen) –Very low efficiency: film is thin, most X-rays pass through the film emulsion Screen-film combination –Fluorescent screen captures X-rays and produces light –Film exposed by light –Much more sensitivity than with film alone

25. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 25 Recording X-rays Fluoroscope: Television camera observes fluorescent screen –Useful for real-time viewing –Lower image quality than screen-film recording Computed radiography: use imaging plate instead of film to record image. –The plate is scanned with a laser and a digital image is obtained

26. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 26 Recording X-rays Digital radiography –Digital recording system (like digital camera, but as large as an X-ray film) produces electrical signals that are digitized –Can be used for fluoroscopy

27. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 27 Comparison SF ~ screen-film recording, CR ~ computed radiography, DR ~ digital radiography –Image quality: SF is best –Initial cost: SF is lowest –Operating cost: DR is lowest, film is highest –Sensitivity (patient exposure): DR and and CR are better –Operating convenience: DR is best Conclusion: Each system has a use –Digital recording is displacing film

28. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 28 Big Picture Types of imaging procedures –Screening: detect disease when there are no symptoms –Diagnosis: a disease is probably present, identify the type of disease –Staging: we know the disease, what type of treatment? –Treatment monitoring. Would like to screen, but there are few diseases that warrant it

29. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 29 Breast Cancer Screening Breast cancer screening requires high resolution and contrast Mostly done with screen- film at low voltage

30. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 30 Computer Interpretation Reason for computer interpretation: –Better accuracy than human? –Less expensive than human? –Human expert not available? Much research, many claims –In the US, a system must be tested and approved by the Federal Drug Administration (FDA) –There is an FDA approved system for mammography interpretation –At present, used as adjunct for human doctors.

31. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 31 Other X-ray Applications Image from X-ray telescope Nebula left by exploding star X-ray telescopes are on satellites because X -rays do not penetrate the atmosphere

32. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 32 Summary X-rays are 100 years old Created a revolution in medicine Useful for many diagnostic tasks –Limitation: cannot distinguish between soft tissues –Contrast radiography helps

33. MIPR Lecture 6 Copyright Oleh Tretiak, 2004 33 Developments in X-rays Digital recording systems are replacing film –Decrease in image quality –Improvement in sensitivity –More convenient Computer interpretation of X-rays is here –Now assisting mammography. May become better. –I expect that procedures for cardiography are next.