Basics of MRI
Vinai Roopchansingh
Functional MRI Facility, National Institute of Mental Health, National Institutes of Health,DHHS
June 15, 2015
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 1 / 34
Outline
1 Medical Imaging OverviewGeneral Imaging PrinciplesPETX-Ray/CTUltra-soundMRI
2 MRI - Breaking down the acronymMagneticResonance
3 ImagingLocation EncodingImage Contrast
4 MR SafetyWhy
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 2 / 34
Outline
1 Medical Imaging OverviewGeneral Imaging PrinciplesPETX-Ray/CTUltra-soundMRI
2 MRI - Breaking down the acronymMagneticResonance
3 ImagingLocation EncodingImage Contrast
4 MR SafetyWhy
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 3 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General PrinciplesMost common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General PrinciplesMost common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Most medical imaging systems work by transmitting energy with knowcharacteristics, then measuring the difference in what comes backfrom sample.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Most medical imaging systems work by transmitting energy with knowcharacteristics, then measuring the difference in what comes backfrom sample.
Main exception to this rule: PET (Positron Emission Tomography).
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Most medical imaging systems work by transmitting energy with knowcharacteristics, then measuring the difference in what comes backfrom sample.
Main exception to this rule: PET (Positron Emission Tomography).X-Ray and CT: Emit X-Rays, and reconstruct images based on signalattenuation.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Most medical imaging systems work by transmitting energy with knowcharacteristics, then measuring the difference in what comes backfrom sample.
Main exception to this rule: PET (Positron Emission Tomography).X-Ray and CT: Emit X-Rays, and reconstruct images based on signalattenuation.Ultra-sound: emit high-frequency sound waves, and measure echocharacteristics (≈ sonar) to generate images.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
General Principles
Most common imaging systems (eye, cameras, film, telescopes) workby capturing/measuring light/energy.
Most medical imaging systems work by transmitting energy with knowcharacteristics, then measuring the difference in what comes backfrom sample.
Main exception to this rule: PET (Positron Emission Tomography).X-Ray and CT: Emit X-Rays, and reconstruct images based on signalattenuation.Ultra-sound: emit high-frequency sound waves, and measure echocharacteristics (≈ sonar) to generate images.MRI: Emit radio waves (≈ radar), then look at properties of“reflected” signals to produce images.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 4 / 34
MRI
Similar principle to X-Ray and Ultra-sound: transmit somethingknown.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 8 / 34
MRI
Similar principle to X-Ray and Ultra-sound: transmit somethingknown.
Measure characteristics of modified signal that comes back to deriveimages.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 8 / 34
MRI
Similar principle to X-Ray and Ultra-sound: transmit somethingknown.
Measure characteristics of modified signal that comes back to deriveimages.
Much richer and subtle encoding scheme: can enhance contrastbetween tissues (and even between oxygenated and deoxygenatedhemoglobin - basis of BOLD MRI / FMRI).
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 8 / 34
Outline
1 Medical Imaging OverviewGeneral Imaging PrinciplesPETX-Ray/CTUltra-soundMRI
2 MRI - Breaking down the acronymMagneticResonance
3 ImagingLocation EncodingImage Contrast
4 MR SafetyWhy
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 11 / 34
Magnetic
Certain nuclei (odd number of protons and/or neutrons) havemagnetic properties (i.e. magnetic moment - 1952 Nobel Prize inPhysics, to Bloch and Purcell).
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 12 / 34
Magnetic
Certain nuclei (odd number of protons and/or neutrons) havemagnetic properties (i.e. magnetic moment - 1952 Nobel Prize inPhysics, to Bloch and Purcell).
Includes 13C, 23Na, 31P, 129Xe, and ...
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 12 / 34
Magnetic
Certain nuclei (odd number of protons and/or neutrons) havemagnetic properties (i.e. magnetic moment - 1952 Nobel Prize inPhysics, to Bloch and Purcell).
Includes 13C, 23Na, 31P, 129Xe, and ...
1H !
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 12 / 34
Planck and Larmor Equations
E = hν = hf0
2πf0 = ω0 = γB0
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 14 / 34
Resonance - resulting from precession
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 15 / 34
Resonance - resulting from precession
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Precession
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 15 / 34
Resonance - resulting from precession
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Precession
Resonance and excitation
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 15 / 34
Outline
1 Medical Imaging OverviewGeneral Imaging PrinciplesPETX-Ray/CTUltra-soundMRI
2 MRI - Breaking down the acronymMagneticResonance
3 ImagingLocation EncodingImage Contrast
4 MR SafetyWhy
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 16 / 34
Creating image from signal
Data acquisition in “Fourier domain” encoded with spatial gradients.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 22 / 34
Creating image from signal
Data acquisition in “Fourier domain” encoded with spatial gradients.
Fourier transform acquired data to give image.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 22 / 34
Creating image from signal
Data acquisition in “Fourier domain” encoded with spatial gradients.
Fourier transform acquired data to give image.
Nobel Prize in Physiology or Medicine in 2003 to Lauterbur andMansfield.
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 22 / 34
Creating image from signal
Paper on Fourier Transform in MR: DOI:10.2214/AJR.07.2874
American Journal of Roentgenology, 2008, Vol 5, 1396-1405
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 23 / 34
Relaxation times
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 24 / 34
Relaxation times
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Longitudinal (a.k.a T1) relaxation
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 24 / 34
Relaxation times
https://www.youtube.com/playlist?list=PLAE12114468910462
(Tyler Moore - Videos for MR Tutorial)
Longitudinal (a.k.a T1) relaxation
Transverse (a.k.a T2) relaxation
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 24 / 34
Basic tissue contrast
MP2-RAGE: NeuroImage:49 (2010), 1271 - 1281
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 26 / 34
BOLD contrast
PNAS, 1990 Vol 87(24):9868-9872 - Ogawa et.al .
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 28 / 34
BOLD contrast
PNAS, 1990 Vol 87(24):9868-9872 - Ogawa et.al .
PNAS, 1992 Vol 89(12):5675-5679 - Kwong et.al .
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 28 / 34
BOLD contrast
PNAS, 1990 Vol 87(24):9868-9872 - Ogawa et.al .
PNAS, 1992 Vol 89(12):5675-5679 - Kwong et.al .
MRM, 1992 Vol 25:390-397 - Bandettini et.al .
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 28 / 34
BOLD contrast
PNAS, 1990 Vol 87(24):9868-9872 - Ogawa et.al .
PNAS, 1992 Vol 89(12):5675-5679 - Kwong et.al .
MRM, 1992 Vol 25:390-397 - Bandettini et.al .
PNAS, 1992 Vol 89(13):5951-5955 - Ogawa et.al .
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 28 / 34
Diffusion contrast
Nature Reviews Neuroscience 4, 469-480 (June 2003) —DOI:10.1038/nrn1119
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 30 / 34
Other types of contrast
PNAS, 2007 Vol 104(28):11796-11801 - Duyn et.al . - Phase imaging
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 32 / 34
Other types of contrast
PNAS, 2007 Vol 104(28):11796-11801 - Duyn et.al . - Phase imaging
MRM, 1992 Vol 23:37-45 - Detre et.al . - Perfusion imaging
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 32 / 34
Other types of contrast
PNAS, 2007 Vol 104(28):11796-11801 - Duyn et.al . - Phase imaging
MRM, 1992 Vol 23:37-45 - Detre et.al . - Perfusion imaging
MRM, 1989 Vol 10:135-144 - Wolff and Balaban - MagnetizationTransfer
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 32 / 34
Other types of contrast
PNAS, 2007 Vol 104(28):11796-11801 - Duyn et.al . - Phase imaging
MRM, 1992 Vol 23:37-45 - Detre et.al . - Perfusion imaging
MRM, 1989 Vol 10:135-144 - Wolff and Balaban - MagnetizationTransfer
...
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 32 / 34
Outline
1 Medical Imaging OverviewGeneral Imaging PrinciplesPETX-Ray/CTUltra-soundMRI
2 MRI - Breaking down the acronymMagneticResonance
3 ImagingLocation EncodingImage Contrast
4 MR SafetyWhy
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 33 / 34
Hazards around MR
Static strong magnetic field → motion
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 34 / 34
Hazards around MR
Static strong magnetic field → motion
Radio-frequency fields → high power
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 34 / 34
Hazards around MR
Static strong magnetic field → motion
Radio-frequency fields → high power
Gradient fields → can induce currents
Vinai R. (FMRIF/NIMH/NIH/DHHS) MRI Basics 2015.06.15 34 / 34