Basic MRIBasic MRI
Chapter 1 LectureChapter 1 Lecture
IntroductionIntroduction
MRI uses radio waves and a MRI uses radio waves and a magnetic field to make imagesmagnetic field to make images
Other methods make images in other Other methods make images in other waysways Radiography – x-ray attenuationRadiography – x-ray attenuation CT – x-ray with computerCT – x-ray with computer NM – gamma rays from radionuclidesNM – gamma rays from radionuclides US – sound wavesUS – sound waves
MR ImagesMR Images
The image is a display of the radiofrequency The image is a display of the radiofrequency (RF) signal intensity(RF) signal intensity
The source of the RF signal from the patient is The source of the RF signal from the patient is the “condition of magnetization produced the “condition of magnetization produced when the patient is placed in the magnetic when the patient is placed in the magnetic field.”field.”
Magnetization occurs when magnetic nuclei Magnetization occurs when magnetic nuclei (like H nuclei or protons) are present(like H nuclei or protons) are present
Magnetization is changed during imaging, Magnetization is changed during imaging, and the rate of change depends on tissue and the rate of change depends on tissue characteristicscharacteristics
Tissue CharacteristicsTissue Characteristics
PDPD T1T1 T2T2 FlowFlow DiffusionDiffusion Spectroscopy/chemical shiftSpectroscopy/chemical shift
Major Tissue Major Tissue CharacteristicsCharacteristics
PD– proton densityPD– proton density T1– longitudinal relaxation time; T1– longitudinal relaxation time;
spin-lattice relaxation timespin-lattice relaxation time T2– transverse relaxation time; spin-T2– transverse relaxation time; spin-
spin relaxation timespin relaxation time
Minor Tissue Minor Tissue CharacteristicsCharacteristics
FlowFlow DiffusionDiffusion Spectroscopy/chemical shiftSpectroscopy/chemical shift
What do you see on an MR What do you see on an MR image?image?
RF signal intensity, influenced byRF signal intensity, influenced by Tissue magnetization, including Tissue magnetization, including
saturation pulsessaturation pulses Proton (hydrogen nuclei) densityProton (hydrogen nuclei) density Relaxation effects from T1 and T2Relaxation effects from T1 and T2
Spatial CharacteristicsSpatial Characteristics
SlicesSlices VoxelsVoxels PixelsPixels
Image QualityImage Quality
Detail/ResolutionDetail/Resolution Noise/Signal-to-Noise ratioNoise/Signal-to-Noise ratio ArtifactsArtifacts
In-Plane ResolutionIn-Plane Resolution
This is a photo that This is a photo that has been taken at has been taken at 165x256 resolution165x256 resolution
In-Plane ResolutionIn-Plane Resolution
This is a photo that This is a photo that has been taken has been taken with 329x512 with 329x512 resolutionresolution
In-Plane ResolutionIn-Plane Resolution
Original Resolution Original Resolution 720x1150720x1150
Signal-to-NoiseSignal-to-Noise
Signal-to-NoiseSignal-to-Noise
Signal-to-NoiseSignal-to-Noise
Signal-to-NoiseSignal-to-Noise
Aliasing: ExampleAliasing: Example
Wraparound Artfacts in 3DWraparound Artfacts in 3D
Chemical Shift EffectChemical Shift Effect
Chemical Shift Chemical Shift
Chemical Shift - ExampleChemical Shift - Example
Chemical Shift ArtifactsChemical Shift Artifacts
Signal TruncationSignal Truncation
Truncation ArtifactsTruncation Artifacts
Partial Volume EffectPartial Volume Effect
Motion Artifacts - PeriodicMotion Artifacts - Periodic
Motion Artifacts - PeriodicMotion Artifacts - Periodic
Motion Artifacts - RandomMotion Artifacts - Random
Flow Motion Artifacts - CSFFlow Motion Artifacts - CSF
Magic Angle ArtifactsMagic Angle Artifacts
FT of Realistic RF SignalFT of Realistic RF Signal
RF Zipper ArtefactRF Zipper Artefact
RF Feed through Zipper RF Feed through Zipper ArtifactArtifact
RF NoiseRF Noise
Magnetic Inhomogeneity Magnetic Inhomogeneity ArtifactsArtifacts
Diamagnetic Susceptibility Diamagnetic Susceptibility ArtifactArtifact
Paramagnetic Effect of Paramagnetic Effect of DeoxyhemoglobinDeoxyhemoglobin
Ferromagnetic Ferromagnetic Susceptibility ArtifactsSusceptibility Artifacts
Susceptibility ArtifactsSusceptibility Artifacts
Gradient Non-linearityGradient Non-linearity
Geometric Distortion: Geometric Distortion: Gradient Non-LinearityGradient Non-Linearity