logging in or signing up chap3 2 Jolene Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINTLite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1230 Category: Entertainment License: All Rights Reserved Like it (1) Dislike it (0) Added: October 16, 2007 This Presentation is Public Favorites: 3 Presentation Description No description available. Comments Posting comment... By: framil (26 month(s) ago) simpy and perfect Saving..... Post Reply Close Saving..... Edit Comment Close By: vempire (29 month(s) ago) its nice and good Saving..... Post Reply Close Saving..... Edit Comment Close By: 453210 (42 month(s) ago) thank you Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Magnetic Resonance Imaging – Basic Principles –: Magnetic Resonance Imaging – Basic Principles – EVELYNE BALTEAU e.balteau@ulg.ac.be Cyclotron Research Centre Overview: Overview Brief history of MRI Magnetic properties of the nuclei Interaction with B0 Interaction with B1 Relaxation Signal Localization ContrastBrief history of MRI: Brief history of MRI index 1946 – Bloch & Purcell independently describe the NMR phenomenon 1952 – Bloch & Purcell Nobel Prize in Physics NMR developed as analytical tool (no medical application) 1973 – Lauterbur : Back-projection MRImaging 1971 – Damadian : NMR used to distinguish healthy and malignant tissues medical application but imaging technique… 1975 – Ernst : Fourier Transform based MRI (demonstrated by Edelstein in 1980) 1977 – Mansfield : Echo-Planar Imaging 1991 – Ernst Nobel Prize in Chemistry 1990 – Ogawa : functional MRI (BOLD) 2003 – Lauterbur & Mansfield Nobel Prize in Medicine MRI : magnetic stuff !!: MRI : magnetic stuff !! index 60000 the earth’s magnetic field !!!! FM radio-waves : 88.8 – 108.8 MHz !!Magnetic properties of the nuclei : Magnetic properties of the nuclei index The Hydrogen nucleus the most abundant (~⅔ of the atoms in living tissues)Behaviour of the nuclei interacting with :: Behaviour of the nuclei interacting with : 1. The external magnetic field B0 Equilibrium state 2. The electromagnetic field B1 (RF) Disturbance indexInteraction with B0: Interaction with B0 index 1. Orientation :Interaction with B0: Interaction with B0 2. Energy states : index DE = għBo = ħwoInteraction with B0: Interaction with B0 3. Precession : index Rotation or precession about the axis of the magnetic field Bo with frequency : wo = gBo wo = Larmor frequency g = gyromagnetic ratioInteraction with B0: Interaction with B0 3. Precession : index At the equilibrium state : - rotation in phase - no transverse magnetization Mxy Interaction with B0: Interaction with B0 index 4. Summary : at the equilibrium state : 1. spin orientation « up » > « down » longitudinal magnetization Mz 2. precession no transverse magnetization Mxy Interaction with B1 Resonance phenomenon: Interaction with B1 Resonance phenomenon index !!! RF frequency = Larmor frequency = w0 !!!Interaction with B1: Interaction with B1 index Two different processes : 1. Transitions E1 E2 Mz decreases 2. Rephasing Mxy increases The macroscopic magnetization flips from the z-axis to the xy-plane and precesses From the macroscopic point of view…Relaxation back to the equilibrium state…: Relaxation back to the equilibrium state… indexRelaxation back to the equilibrium state…: Relaxation back to the equilibrium state… index Two different processes : 1. Transitions E2 E1 Mz increases T1 relaxation 2. Dephasing Mxy decreases T2 (exponential) relaxation Free Induction Decay : received signal !! informations from the tissues of interestSignal localization: Signal localization index Up to now : the signal received contains information from the entire body !! Not interesting ! Use field gradients to spatially encode the signal Three steps : 1. Slice selection slice = matrix 2. Frequency-encoding columns 3. Phase-encoding linesSignal localization: Signal localization index 1. Slice selection gradient Resonance Phenomenon : wRF = wo !!! Before Gz is applied : all the spins precess with the same Larmor frequency wo all could resonate !! During application of Gz : the spins precess with w only spins with frequency = wRF resonateSignal localization: Signal localization index 2. Frequency-encoding gradient Slice selection : but still no spatial discrimination within the slice ! Before Gx is applied : all the spins precess with the same Larmor frequency wo During application of Gx : the spins precess with frequencies Fourier Transform of the signal allows discrimination between columns !Signal localization: Signal localization index 3. Phase-encoding gradient Before Gy is applied : all the spins precess with the same Larmor frequency wo During application of Gy : the spins precess with frequencies induces phase difference between the lines After application of Gx : all the spins precess again at the same Larmor frequency, but with different phase shifts from line to line…Contrast in MRI: Contrast in MRI index Grey-level images : the intensity of a voxel depends on the intensity of the corresponding signal.Contrast in MRI: Contrast in MRI indexContrast in MRI: Contrast in MRI index Contrast depends on : 1. tissue properties : T1, T2, r user-independent 2. sequence parameters : TR, TE, … TR = repetition time = time interval between two RF pulses TE = echo time = when the acquisition is performed user-dependentContrast in MRI: Contrast in MRI index Sequence parameters : TR and TEContrast in MRI: Contrast in MRI index T2-weighted image : long TR – long TEContrast in MRI: Contrast in MRI index T2-weighted image : long TR – long TEContrast in MRI: Contrast in MRI index T1-weighted image : short TR – short TEContrast in MRI: Contrast in MRI index T1-weighted image : short TR – short TEContrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T1 – TE court et TR variable Cas d’une impulsion RF initiale de 90°Contrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T1 – TE court et TR variable Cas d’une impulsion RF initiale de 180°Contrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T2 – TR long et TE variable (Impulsion RF initiale de 90°)The 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreThe 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreThe 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreSlide34: index You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.
chap3 2 Jolene Download Post to : URL : Related Presentations : Share Add to Flag Embed Email Send to Blogs and Networks Add to Channel Uploaded from authorPOINTLite Insert YouTube videos in PowerPont slides with aS Desktop Copy embed code: (To copy code, click on the text box) Embed: URL: Thumbnail: WordPress Embed Customize Embed The presentation is successfully added In Your Favorites. Views: 1230 Category: Entertainment License: All Rights Reserved Like it (1) Dislike it (0) Added: October 16, 2007 This Presentation is Public Favorites: 3 Presentation Description No description available. Comments Posting comment... By: framil (26 month(s) ago) simpy and perfect Saving..... Post Reply Close Saving..... Edit Comment Close By: vempire (29 month(s) ago) its nice and good Saving..... Post Reply Close Saving..... Edit Comment Close By: 453210 (42 month(s) ago) thank you Saving..... Post Reply Close Saving..... Edit Comment Close Premium member Presentation Transcript Magnetic Resonance Imaging – Basic Principles –: Magnetic Resonance Imaging – Basic Principles – EVELYNE BALTEAU e.balteau@ulg.ac.be Cyclotron Research Centre Overview: Overview Brief history of MRI Magnetic properties of the nuclei Interaction with B0 Interaction with B1 Relaxation Signal Localization ContrastBrief history of MRI: Brief history of MRI index 1946 – Bloch & Purcell independently describe the NMR phenomenon 1952 – Bloch & Purcell Nobel Prize in Physics NMR developed as analytical tool (no medical application) 1973 – Lauterbur : Back-projection MRImaging 1971 – Damadian : NMR used to distinguish healthy and malignant tissues medical application but imaging technique… 1975 – Ernst : Fourier Transform based MRI (demonstrated by Edelstein in 1980) 1977 – Mansfield : Echo-Planar Imaging 1991 – Ernst Nobel Prize in Chemistry 1990 – Ogawa : functional MRI (BOLD) 2003 – Lauterbur & Mansfield Nobel Prize in Medicine MRI : magnetic stuff !!: MRI : magnetic stuff !! index 60000 the earth’s magnetic field !!!! FM radio-waves : 88.8 – 108.8 MHz !!Magnetic properties of the nuclei : Magnetic properties of the nuclei index The Hydrogen nucleus the most abundant (~⅔ of the atoms in living tissues)Behaviour of the nuclei interacting with :: Behaviour of the nuclei interacting with : 1. The external magnetic field B0 Equilibrium state 2. The electromagnetic field B1 (RF) Disturbance indexInteraction with B0: Interaction with B0 index 1. Orientation :Interaction with B0: Interaction with B0 2. Energy states : index DE = għBo = ħwoInteraction with B0: Interaction with B0 3. Precession : index Rotation or precession about the axis of the magnetic field Bo with frequency : wo = gBo wo = Larmor frequency g = gyromagnetic ratioInteraction with B0: Interaction with B0 3. Precession : index At the equilibrium state : - rotation in phase - no transverse magnetization Mxy Interaction with B0: Interaction with B0 index 4. Summary : at the equilibrium state : 1. spin orientation « up » > « down » longitudinal magnetization Mz 2. precession no transverse magnetization Mxy Interaction with B1 Resonance phenomenon: Interaction with B1 Resonance phenomenon index !!! RF frequency = Larmor frequency = w0 !!!Interaction with B1: Interaction with B1 index Two different processes : 1. Transitions E1 E2 Mz decreases 2. Rephasing Mxy increases The macroscopic magnetization flips from the z-axis to the xy-plane and precesses From the macroscopic point of view…Relaxation back to the equilibrium state…: Relaxation back to the equilibrium state… indexRelaxation back to the equilibrium state…: Relaxation back to the equilibrium state… index Two different processes : 1. Transitions E2 E1 Mz increases T1 relaxation 2. Dephasing Mxy decreases T2 (exponential) relaxation Free Induction Decay : received signal !! informations from the tissues of interestSignal localization: Signal localization index Up to now : the signal received contains information from the entire body !! Not interesting ! Use field gradients to spatially encode the signal Three steps : 1. Slice selection slice = matrix 2. Frequency-encoding columns 3. Phase-encoding linesSignal localization: Signal localization index 1. Slice selection gradient Resonance Phenomenon : wRF = wo !!! Before Gz is applied : all the spins precess with the same Larmor frequency wo all could resonate !! During application of Gz : the spins precess with w only spins with frequency = wRF resonateSignal localization: Signal localization index 2. Frequency-encoding gradient Slice selection : but still no spatial discrimination within the slice ! Before Gx is applied : all the spins precess with the same Larmor frequency wo During application of Gx : the spins precess with frequencies Fourier Transform of the signal allows discrimination between columns !Signal localization: Signal localization index 3. Phase-encoding gradient Before Gy is applied : all the spins precess with the same Larmor frequency wo During application of Gy : the spins precess with frequencies induces phase difference between the lines After application of Gx : all the spins precess again at the same Larmor frequency, but with different phase shifts from line to line…Contrast in MRI: Contrast in MRI index Grey-level images : the intensity of a voxel depends on the intensity of the corresponding signal.Contrast in MRI: Contrast in MRI indexContrast in MRI: Contrast in MRI index Contrast depends on : 1. tissue properties : T1, T2, r user-independent 2. sequence parameters : TR, TE, … TR = repetition time = time interval between two RF pulses TE = echo time = when the acquisition is performed user-dependentContrast in MRI: Contrast in MRI index Sequence parameters : TR and TEContrast in MRI: Contrast in MRI index T2-weighted image : long TR – long TEContrast in MRI: Contrast in MRI index T2-weighted image : long TR – long TEContrast in MRI: Contrast in MRI index T1-weighted image : short TR – short TEContrast in MRI: Contrast in MRI index T1-weighted image : short TR – short TEContrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T1 – TE court et TR variable Cas d’une impulsion RF initiale de 90°Contrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T1 – TE court et TR variable Cas d’une impulsion RF initiale de 180°Contrast in MRI: Contrast in MRI index Illustration : une pomme dans un verre d’eau… Contraste en T2 – TR long et TE variable (Impulsion RF initiale de 90°)The 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreThe 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreThe 3.0 Tesla Allegra MR scanner at the Cyclotron Research Centre: The 3.0 Tesla Allegra MR scanner at the Cyclotron Research CentreSlide34: index