BMED-4800/ECSE-4800 Introduction to Subsurface Sensing and Imaging Systems

1. BMED-4800/ECSE-4800 Introduction to Subsurface Sensing and Imaging Systems Lecture 18: MRI Kai Thomenius1 & Badri Roysam2 1Chief Technologist, Imaging Technologies, General Electric Global Research Center 2Professor, Rensselaer Polytechnic Institute Center for Sub-Surface Imaging & Sensing

2. Summary • OCT has grown from a curiosity to a commonly used tool in ophthalmic clinics worldwide • Many other/newer variations of OCT exist, but we didn’t cover them • Frequency-domain OCT • 3D OCT…etc. • Rapidly evolving field • Trends point towards smaller (handheld), cheaper, faster, and more versatile OCT devices • Sub-micrometer resolution now possible

3. Fundamentals of MRIModule 1: Quick Overview From the notes of Charles Dumoulin, PhD Thomas Foo, PhD and other sources May 27, 2014

4. Magnetic Resonance ImagingOverview • What is Magnetic Resonance Imaging? • What are the intrinsic parameters? • Are there biohazard and safety issues? • What are some of the clinical applications?

5. MRI & Other Imaging Modalities Source • X-ray • Source/detector geometry • Projective and computed tomography • Ultrasound • Source/detector at same location • Real time 2D imaging • Real time 3D/4D imaging • Magnetic Resonance • Source of signal from within body • 2D and 3D imaging Detector

6. Measured Parameters of Other Imaging Modalities • X-ray • Electron density • Attenuation • Ultrasound • Variations in tissue compressibility & density • Velocity of target tissue, e.g. red blood cells • Positron Emission Tomography (PET) • concentration of radio-labeled metabolites

7. Measured Parameters of MRI • Nuclear spin density • Motion on molecular scale • T1 • T2 • Motion on the microscopic scale • diffusion • perfusion • Macroscopic motion (velocity, acceleration etc.) • Chemical composition • Chemical exchange • Temperature • Mechanical and magnetic properties of tissue MRI has a very rich set of parameters for imaging.

8. Costs of ImagingInstrumentation • X-ray • Portable units inexpensive (< $100K) • CT scanners ($500K - $1.2 million) • Angiography suites ($700K - $1.7 million) • Ultrasound • $5K-$150K • Magnetic Resonance • $500K - $2 million Cost Ultrasound X-ray CT MR

9. Safety and Biohazards of Imaging Modalities • X-ray • Ionizing radiation • Morbidity associated with contrast agents • Ultrasound • No safety or biohazard problems • Magnetic Resonance • No biohazards • However, safety is an issue

10. A Note on Magnetic Fields • Most often used unit: Tesla • Unit of magnetic flux density • Equivalent to 1 Weber per sq. meter or 10,000 Gauss http://www.coolmagnetman.com/magflux.htm

11. Magnet Safety The whopping strength of the magnet makes safety essential. The magnetic field is never turned off. Things fly into the bore – Even big things! Source: www.howstuffworks.com Source: http://www.simplyphysics.com/ flying_objects.html Perhaps more dangerous are small items, screw drivers, scissors, etc.

12. Magnet Safety http://www.simplyphysics.com/flying_objects.html One can imagine the reaction of the buffer operator …

13. Removal of a Chair from an MRI

14. Patient Safety • Anyone going near the magnet – subjects, staff and visitors – must be thoroughly screened: • Subjects must have no metal in their bodies: • pacemaker • aneurysm clips • metal implants (e.g., cochlear implants) • intrauterine devices (IUDs) • some dental work (fillings okay) • Subjects must remove metal from their bodies • jewelry, watch, piercings • coins, etc. • wallet • any metal that may distort the field (e.g., underwire bra) • Subjects must be given ear plugs (acoustic noise can reach 120 dB) This subject was wearing a hair band with a ~2 mm copper clamp. Left: with hair band. Right: without. Source: Jorge Jovicich

15. Clinical Applications of Magnetic Resonance Imaging • Brain • Stroke • Cancer • MS • Parkinson’s, Alzheimer's etc. • Spine • Spinal cord • Disks • Abdomen • Vascular • Neuro • Peripheral • Joints • Knees • Shoulder

16. Emerging Applications of Magnetic Resonance Imaging • Cardiac • Myocardial function • Cardiac dynamics • Coronary artery disease • Interventional • Image guided Biopsy • Minimally invasive surgery • Vascular interventions • Functional MRI

17. Why MRI in medical imaging? • Water and fat are two major constituents of our bodies. • Both have many hydrogen atoms. • Hydrogen nuclei have an NMR signal. • Hence: • MRI primarily images the NMR signal from hydrogen nuclei. • This assumes that the hydrogen density varies with tissue types & clinical conditions.

18. N N S S The Origin of the MR Signal • The Nucleus of a Hydrogen Atom is a Charged Particle. • The Nucleus of a Hydrogen Atom has a Nuclear Spin. • A Spinning Charged Particle, e.g., the Hydrogen Atom, will Produce a Magnetic Dipole • Dipole magnetic moment • Where • g is the gyromagnetic ratio • h-bar is Planck’s constant • I-bar is a unit vector

19. MRI or NMR? • MRI is a tomographic imaging technique used in medical imaging. • Magnetic resonance imaging • NMR is a spectroscopic technique used to obtain microscopic chemical and physical info about molecules. • Nuclear magnetic resonance • MRI produces images from thin slices of NMR signals. • MRI was initially called NMR but this term was dropped due to the negative connotation associated with the term “nuclear”. • In 2003, there were appr. 10,000 MRI units in use & 75M MRI scans were made. http://www.cis.rit.edu/htbooks/mri/inside.htm

20. New Technologies for Magnetic Resonance Imaging • New magnet designs • Higher fields • Open geometry • Faster and more powerful gradient subsystems • MR-compatible devices

21. What happens in an MRI Scan? • 1) Put subject in big magnetic field, like 3 Tesla (leave him/her there) • 2) Transmit radio waves into subject [about 3 ms] • 3) Turn off radio wave transmitter • 4) Receive radio waves re-transmitted by subject • Manipulate re-transmission with magnetic fields during this readout interval [10-100 ms: MRI is not a snapshot] • 5) Store measured radio wave data vs. time • Now go back to 2) to get some more data • 6) Process raw data to reconstruct images • 7) Allow subject to leave scanner (this is optional) Source: Robert Cox’s web slides

22. Conventional Cylindrical Magnet

23. 0.7 Tesla Open Magnet

24. MR imaging

25. MR imaging

26. MR thermal imaging

27. Contrast Agents in MRI Contrast Enhanced MR Angiogram

28. fMRI image of the brain during finger tapping Left Hand Right Hand Image courtesy of University of Melbourne

29. MR imaging

30. Future of Magnetic Resonance Imaging • MR will continue to grow at a rapid rate, particularly outside the field of radiology. • This may be limited somewhat by our healthcare financial crisis. • MR will displace many diagnostic methods in use today. • The cost of MR will continue to drop.

31. Summary • We have discussed: • Relation of MRI with respect to other imaging modalities. • Safety of MRI related magnetic fields • MRI images • Next time • MR Imaging physics • How do we make images with the spins?

32. Acknowledgments • Thanks to Drs. Charles Dumoulin and Thomas Foo of GE Global Research for most of these slides. • We have borrowed stuff from several sites on the web with excellent intros to MRI • http://www.bme.umich.edu/~dnoll/primer2.pdf • http://www.erads.com/mrimod.htm • http://www.cis.rit.edu/htbooks/mri/mri-main.htm • http://airto.loni.ucla.edu/BMCweb/BMC_BIOS/MarkCohen/abstracts/Basic/BasicMRPhysics.html

33. Instructor Contact Information Badri Roysam Professor of Electrical, Computer, & Systems Engineering Office: JEC 7010 Rensselaer Polytechnic Institute 110, 8th Street, Troy, New York 12180 Phone: (518) 276-8067 Fax: (518) 276-6261/2433 Email: roysam@ecse.rpi.edu Website: http://www.rpi.edu/~roysab NetMeeting ID (for off-campus students): 128.113.61.80 Secretary: TBD, JEC 7012,

34. Instructor Contact Information Kai E Thomenius Chief Technologist, Ultrasound & Biomedical Office: KW-C300A GE Global Research Imaging Technologies Niskayuna, New York 12309 Phone: (518) 387-7233 Fax: (518) 387-6170 Email: thomeniu@crd.ge.com, thomenius@ecse.rpi.edu Secretary: TBD