1. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey The Physics of Seeing Inside People An introduction to the science of Medical Imaging or “MRI for beginners” Dr. S. J. Doran

2. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Summary of today’s lecture What is Medical Imaging? How does MRI work? What can we do with the images? How does all this relate to what a typical Physics undergraduate might be doing for the three years at University?

3. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey What is Medical Imaging? Medical imaging as seen on TV ! Hi-tech scanner Patient goes in Images (preferably wacky colours) come out

4. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey What is Medical Imaging? The application of basic Physics to see inside the human body Not one subject but many — lots of different techniques Each one measures a different physical property of the sample. UltrasoundComposite MRI + PETX-ray CT

5. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Data source :Toshiba America Medical Systems Visualisation :Vitrea 2, Vital Images Data source : Mayo Clinic Why use different methods of imaging ? Different methods reveal different features Plane-film X-ray maps the total attenuation of X-rays along a path through the body, giving a projection image. Good for bone structure in accidents. X-ray CT measures the X-ray attenuation coefficient of the body at each point. True 3-D images. Ultrasound maps the reflection and attenuation of sound.

6. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Data source : SMIS Ltd Why use different methods of imaging ? Different methods reveal different features (cont.) MRI maps the distribution and “environment” of water molecules in the body. PET maps the distribution of radioactively labelled compounds. MEG maps directly the magnetic fields generated by currents flowing in the brain. Data source : CSUA, Berkeley Data source:FORENAP, Rouffach, France

7. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey The Physics of MRI Electromagnetism Statistical Mechanics Classical and Quantum Mechanics Nuclear Physics Mathematics, Signal and Image Processing

8. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Magnet for Whole-Body Imager Image source : GE Medical Systems, VA Imaging Centre, University of Florida What is the tunnel into which the patient slides? I n turns / unit length B =  0 n I

9. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey What happens in a scan? Fundamentals of MRI  A spinning charged particle has a magnetic moment. Mechanics  Newton’s Law says that a torque will cause the dipole to precess in a direction perpendicular to the torque and the spin vector. Spin Nuclear Physics  Many nuclei have an intrinsic spin

10. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Magnetism  We exert a couple on the nuclear spin by placing a magnetic field across the sample. B What happens in a scan? Magnetic fields and resonance m Precession Spin  If the particle were not spinning, it would align like a compass, but, because of the spin, it precesses instead. Resonance  An electromagnetic field that oscillates at exactly the same frequency as the nucleus will be absorbed.  Under certain conditions, the nucleus will also emit a quantum of RF energy

11. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Resonant frequency is related to the magnetic field. f   B What was happens in a scan? Magnetic field gradients x B Head Feet If we vary the magnetic field across the sample, then the frequency of emitted radio waves varies.

12. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey A computer to process the data What happens in a scan? Equipment being used A large (normally superconducting) magnet Image source : GE Medical Systems An aerial to transmit and receive radiofrequency signals A “gradient set” to create a varying magnetic field

13. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Basic Level 2 Physics tells us how to create our magnetic field gradient. Maxwell Pair Saddle Coil / Golay Pair What happens in a scan? The MRI gradient set It also explains why the gradients make a knocking noise.

14. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey aOur NMR signal is made up of the sum of lots of different frequencies, corresponding to different spatial positions. What happens in a scan? Processing the data cFourier transforms, from Level 2 Maths, can unscramble the data and make an image. bAcquiring multiple signals gives us a 2-D dataset.

15. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey The Human Brain as seen by MRI Data sources : Left - The Whole-brain Atlas, K. A. Johnson and J. A. Becker, Harvard; Right - SMIS UK Ltd.

16. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Image contrast in the brain (1) We can inject a chemical called a contrast agent into the bloodstream. This allows us to calculate the concentration of the agent. We can use this to find out various parameters of the blood supply to the brain tissue. As it reaches the brain, the signal intensity rises. Data source:James D’Arcy and David Collins, Institute of Cancer Research, Sutton

17. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey MR images can be sensitised to the rate of diffusion of water molecules. Data source: Geoff Parker, Institute of Neurology, London Image contrast in the brain (2): neural fibre tracking Water diffuses faster along nerve fibres than perpendicular to them. This allows us to map the local direction of a fibre and create a map of the fibres. Finally, we can overlay them on a computer model of the head.

18. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Data source:Functional Imaging Laboratory, London Combined PET / MRI study Image contrast in the brain (3): Functional imaging We acquire one image of the brain in a “resting” state. We follow this by a corresponding image where the brain is active. Any differences between these two images correspond to places where the brain is working. We can see you think!!

19. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey MRI can image much more than just the brain... Data source : SMIS Lumbar spine Knee  sports injuries Data source : SMIS LiverLung Liver motion during normal breathing Data source : ICR, Sutton

20. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey A virtual tour round the human colon... Computer-generated “flythrough” model Original MR images Data source : Dr David Lomas, Dept. of Radiology, Addenbrokes Hospital, Cambridge

21. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey More about image contrast … MR angiography The contrast in MR images can be made sensitive either to “flowing” material, or to an externally administered contrast agent. In both cases, one can obtain images of the body’s blood vessels with exquisite detail. Prof. Arlart, Katharinen Hosp., Stuttgart, Germany Data source, via GE publicity material

22. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey MRI in cardiology High resolution anatomical imaging Imaging of coronary arteries “Movies” — data acquired in < 20 s

23. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey And finally … the state of the art in cardiac imaging Data source: GE Medical Systems

24. The Physics of Seeing Inside People — Presentation by Simon J Doran, Dept of Physics, University of Surrey Conclusion It is money — the human brain is a very valuable thing — which has led to the incredible developments that we see today. It is study of basic Physics (electromagnetism, nuclear physics, mechanics) which has discovered the principles. The different methods tell us different things. There are many different ways of imaging the human body.