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MRI: Magnetic Resonance Imaging

MRI: Magnetic Resonance Imaging. Tyler Bradshaw University of Utah 2010. Overview. Introduction Medical imaging MRI uses History How does magnetic resonance work? Magnetic fields Atomic spin Resonance Relaxation Magnetic resonance imaging Hydrogen in the body Scanners

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MRI: Magnetic Resonance Imaging

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  1. MRI: Magnetic Resonance Imaging Tyler Bradshaw University of Utah 2010

  2. Overview Introduction Medical imaging MRI uses History How does magnetic resonance work? Magnetic fields Atomic spin Resonance Relaxation Magnetic resonance imaging Hydrogen in the body Scanners Imaging Getting an MRI scan Why get one? The scanner room The scan The future of MRI

  3. Medical Imaging Medical Imaging: Creating images of the human body for clinical or scientific purposes •Ultrasound • Fluoroscopy • Computed Tomography (CT)/X-ray • Positron Emission Tomography (PET) • Single Photon Emission Computed Tomography (SPECT) • Magnetic Resonance Imaging (MRI)

  4. MRI Uses One of the best diagnostics exams for soft- tissue injuries, such as: • Musculoskeletal system; joints • Brain; Spinal cord • Heart; aorta; arteries • Internal organs (liver, kidney, lungs, etc.) • Breasts

  5. History • 1946 - Felix Bloch and Edward Purcell discovered magnetic resonance; won Nobel prize in 1952 • At first could only analyze chemical and physical properties • 1971 – discovered that magnetic resonance could show differences between tissue • 1977 – first human MRI exam (5 hours) • 1980 – first commercial MRI scanner • Over 20,000 MRI scanners in use today

  6. How Does it Work? Magnetic Resonance Imaging Its based on how atoms react to magnetic fields

  7. To understand magnetic resonance, we first need to understand 2 things… 1) Magnetic Fields 2) Spin

  8. Magnetic Fields Definition: A field surrounding a magnet that will exert a force on other magnetic material Magnetic field

  9. Spin •Every particle (proton, neutron, electron) have a spin value • It’s a fundamental property of the particle (like charge, or mass) • Similar to a sphere rotating on its axis Spin axis

  10. Magnetic Fields & Spin • Spins have a random orientation in the absence of a magnetic field • The atom’s spin will cause it to react to a magnetic field • Most spins will align with the direction of the magnetic field

  11. Resonance • Atoms can absorb specific radio waves • This can cause them to change spin-directions in the magnetic field • This is known as resonance Radiowave Resonance

  12. Relaxation After the atom experiences resonance it will want to rotate back and realign with the magnetic field This is called relaxation During relaxation an atom will release a radio wave Radio signals can be easily detected Radio wave (detectable)

  13. MRI Excitation and Relaxation

  14. So how does MRI use resonance and relaxation to image the body?

  15. Hydrogen • The human body is about 60% water • (by weight) • About 20% fat • The human body is therefore about • 63% hydrogen • -Hydrogen has spin and can experience • resonance H

  16. MRI Scanners An MRI scanner uses a very powerful magnet to align the hydrogen in your body Magnetic Field MRI MRI

  17. How powerful is the magnet?

  18. MRI - Resonance • After the hydrogen spins are aligned they are hit with radio waves • Resonance occurs and the spins change Magnetic Field MRI

  19. MRI - Relaxation • When the hydrogen “relaxes” they release radio waves • These signals are detected by the MRI scanner • Each radio wave is transmitted to a computer as data • The computer interprets all the data points, constructs a 3 dimensional image

  20. Areas where there are more hydrogen will absorb and release more signal

  21. MRI - Images The images represent different densities of hydrogen in the body

  22. What’s it like to get an MRI?

  23. A doctor will order the MRI for you in order to…. -Visualize torn ligaments -Visualize shoulder injuries -Diagnose multiple sclerosis (MS) -Diagnose tumors -Diagnose infections in the brain, spine or joints -Diagnose tendonitis -Evaluate masses in the soft tissues of the body -Evaluate bone tumors, cysts and bulging or herniated discs in the spine -Diagnose strokes in their earliest stages

  24. The MRI Room • • Constructed to isolate the scanner from outside signals • • No metal allowed! • Dress in hospital gown • Not even bras or hair clips • -Orthopedic implants usually • ok (except in the eye or brain) • Most pacemakers and • internal defibrillators not • allowed • Beware of unknown • shrapnel!

  25. The Scan • Closed – better image quality, but can cause claustrophobia • Open – More comfortable, lower image quality, fit larger patients • Can image a specific body part • Scans usually last 30-60 minutes • The magnets make a loud noise • Costs $400-$3,000

  26. Future of MRI It’s not leaving anytime soon… MRI and CT were ranked as most important medical innovations by physicians MRI doesn’t harm the patient (unlike PET, CT) The future… Small scanners to scan specific body parts Hyperpolarized gas (imaging lungs) Color

  27. References Discovery Communications. “How MRI Works”. <http://www.howstuffworks.com/mri.htm> (March 2010) Aziz, Salwa and Christina Derbidge, “Magnetic Resonance Imaging” University of Utah. Simply Physics. “Introduction to MRI Physics”. < http://www.simplyphysics.com/page2_1.html> (March 2010) Hornak, Joseph, PhD. “The Basics of MRI”. 1996-2003. <http://www.cis.rit.edu/htbooks/mri/index.html> (March 2010)

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