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Transcript 
Basic MRI
Chapter 1 Lecture
Introduction


MRI uses radio waves and a magnetic field to
make images
Other methods make images in other ways
Radiography – x-ray attenuation
 CT – x-ray with computer
 NM – gamma rays from radionuclides
 US – sound waves

MR Images




The image is a display of the radiofrequency (RF) signal
intensity
The source of the RF signal from the patient is the
“condition of magnetization produced when the
patient is placed in the magnetic field.”
Magnetization occurs when magnetic nuclei (like H
nuclei or protons) are present
Magnetization is changed during imaging, and the rate
of change depends on tissue characteristics
Tissue Characteristics






PD
T1
T2
Flow
Diffusion
Spectroscopy/chemical shift
Major Tissue Characteristics



PD– proton density
T1– longitudinal relaxation time; spin-lattice
relaxation time
T2– transverse relaxation time; spin-spin
relaxation time
Minor Tissue Characteristics



Flow
Diffusion
Spectroscopy/chemical shift
What do you see on an MR image?

RF signal intensity, influenced by
Tissue magnetization, including saturation pulses
 Proton (hydrogen nuclei) density
 Relaxation effects from T1 and T2

Spatial Characteristics



Slices
Voxels
Pixels
Image Quality



Detail/Resolution
Noise/Signal-to-Noise ratio
Artifacts
In-Plane Resolution
This is a photo that has
been taken at 165x256
resolution
In-Plane Resolution
This is a photo that has
been taken with 329x512
resolution
In-Plane Resolution

Original Resolution
720x1150
Signal-to-Noise
Signal-to-Noise
Signal-to-Noise
Signal-to-Noise
Aliasing: Example
Wraparound Artfacts in 3D
Chemical Shift Effect
Chemical Shift
Chemical Shift - Example
Chemical Shift Artifacts
Signal Truncation
Truncation Artifacts
Partial Volume Effect
Motion Artifacts - Periodic
Motion Artifacts - Periodic
Motion Artifacts - Random
Flow Motion Artifacts - CSF
Magic Angle Artifacts
FT of Realistic RF Signal
RF Zipper Artefact
RF Feed through Zipper Artifact
RF Noise
Magnetic Inhomogeneity Artifacts
Diamagnetic Susceptibility Artifact
Paramagnetic Effect of
Deoxyhemoglobin
Ferromagnetic Susceptibility
Artifacts
Susceptibility Artifacts
Gradient Non-linearity
Geometric Distortion:
Gradient Non-Linearity
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