How MRI Works Connor Schentag

Topics Background & History Construction Physics Transducers Images Specializations Recent Advances

Background MRI: Magnetic Resonance Imaging Noninvasive medical imaging device Uses magnetic fields and radio waves to generate images

History 1937 - Dr. Isidor I. Rabi discovers NMR 1950’s - First MR image is produced 1971 - Raymond Damadian discovers different signals from different tissues 1977 - Raymond Damadian builds the first MRI scanner

Construction

Physics Hydrogen atoms are abundant in the human body All have a strong magnetic moment When the magnetic field is applied, all align and cancel except a few.

Physics An MRI applies a Radio Frequency specific to hydrogen, 42.58 MHz/T (The Larmor Frequency) The unmatched atoms produce ‘resonance’ and spin in the other direction When the RF pulse is turned off, the atoms revert to the original alignment and give off RF energy This is picked up by the RF coils

Transducer Computer receives all frequencies measured by the RF coils A Fourier Transform is used to convert these points to a 2D or 3D image where Inverse for image:

Transducer

Transducer

Images Each tissue returns to equilibrium based on T1 (spin- lattice) and T2 (spin-spin) relaxation Can create T1-weighted or T2-weighted based on when signal is measured T1: Often used for cerebral cortex, fatty tissue, general morphological information T2: Useful for detecting edema and inflammation, such as revealing white matter lesions

Images: T1 T1 Bright: Fat, hemorrhage, slow flowing blood, protein rich fluid T1 Dark: Bone, air, high water content such as tumour, inflammation

Images: T2 T2 Bright: High water content such as tumour, inflammation T2 Dark: Bone, air, fat, protein-rich fluid

Organ Specializations Neuroimaging: Very popular due to contrast between grey and white matter Musculoskeletal: Used for joint disease and soft tissue tumours

Organ Specializations Liver and Gastrointestinal: Often used with a contrasting agent, can detect lesions in pancreas and liver Angiography (Arteries): Contrasting agents often used to evaluate for aneurysms

Specialized Configurations Diffusion MRI: Measures diffusion of water molecules in tissue Functional MRI: Measures signal changes in the brain due to changing neural activity Real-Time MRI: “Filming” MRI, or the continuous monitoring of moving objects, such as joints or organs Many more

Recent Advances Siemens new system can acquire many MRI images simultaneously rather than sequentially Lung MRI is now possible, using Toshiba’s new Ultrashort Echo Time (UTE) Cardiac MRI has been greatly simplified, and can now take a full 3D chest volume scan GE’s new Silent Scan technology to actively cancel the loud noise of MRI scans

Conclusion Began in the 70’s with Dr. Damadian Has its basis in NMR Create images with a Fourier Transform Can create various images based on what needs to be examined Many different configurations for specialized needs An actively researched field leading to many new advances

References https://www.healthcare.siemens.com/magnetic-resonance-imaging http://www.two-views.com/mri-imaging/history.html#sthash.5jhkDZpw.dpbs http://web2.uwindsor.ca/courses/physics/high_schools/2006/Medical_Imaging/ mrihistory.html https://en.wikipedia.org/wiki/Magnetic_resonance_imaging https://en.wikipedia.org/wiki/Physics_of_magnetic_resonance_imaging http://science.howstuffworks.com/mri.htm https://mrimaster.com/characterise%20physics.html https://www.itnonline.com/article/recent-advances-mri-technology