Basic MRI Chapter 1 Lecture Introduction MRI uses
Basic MRI Chapter 1 Lecture
Introduction MRI uses radio waves and a magnetic field to make images n Other methods make images in other ways n Radiography – x-ray attenuation n CT – x-ray with computer n NM – gamma rays from radionuclides n US – sound waves n
MR Images n n 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 n T 1 n T 2 n Flow n Diffusion n Spectroscopy/chemical shift n
Major Tissue Characteristics PD– proton density n T 1– longitudinal relaxation time; spin-lattice relaxation time n T 2– transverse relaxation time; spin-spin relaxation time n
Minor Tissue Characteristics Flow n Diffusion n Spectroscopy/chemical shift n
What do you see on an MR image? n RF signal intensity, influenced by Tissue magnetization, including saturation pulses n Proton (hydrogen nuclei) density n Relaxation effects from T 1 and T 2 n
Spatial Characteristics Slices n Voxels n Pixels n
Image Quality Detail/Resolution n Noise/Signal-to-Noise ratio n Artifacts n
In-Plane Resolution This is a photo that has been taken at 165 x 256 resolution
In-Plane Resolution This is a photo that has been taken with 329 x 512 resolution
In-Plane Resolution n Original Resolution 720 x 1150
Signal-to-Noise
Signal-to-Noise
Signal-to-Noise
Signal-to-Noise
Aliasing: Example
Wraparound Artfacts in 3 D
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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