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Marketing MR review

Marketing MR review. 02/08/06. Scan Factors. TR-Repetition time The length of time between pulses Controls T1 Is repeated in a pulse sequence the # of phase encoding steps X NEX(NSA) TE- Echo time The length of time the sequence waits to collect data Controls T2. TR/TE.

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Marketing MR review

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  1. Marketing MR review 02/08/06

  2. Scan Factors • TR-Repetition time • The length of time between pulses • Controls T1 • Is repeated in a pulse sequence the # of phase encoding steps X NEX(NSA) • TE- Echo time • The length of time the sequence waits to collect data • Controls T2

  3. TR/TE

  4. Longitudinal (T1) (spin lattice) Regrowth of magnetization along the longitudinal direction (with the field) Energy is given off Each different tissue has a unique molecular component (bound/free in macromolocules) Therefore tissue like Liver have a shorter T1 than fluids. Transverse (T2)(spin spin) Decay of FID back to its initial state (zero) A measure of time in which the transverse has decayed to 37% of its initial value T2 must be less than or equal to T1 Caused by dephasing of protons T1 relaxation Dipolar interaction of the spins Inhomogeniety of the field Local inhomogeneities caused by susceptibility Relaxation

  5. T1 relaxation

  6. T1 • Is weighted towards materials with short T1 times • Short TR/TE • Good for anatomy • Fat is bright

  7. T2 decay

  8. T2 • Weighted towards long T2 times. • Long TR/TE • Pathology weighted • Fluid is bright

  9. PD • Weighted towards elements with high proton density • Mod. TE/TR • Really Gray

  10. Fat Supression • Nulls out fat • 2 ways • FSAT on scanner • STIR sequence • Gets rid of bright fat so the rest is easier to see. • Useful with Gado images

  11. 180° 90° RF t RF r SE pulse sequence

  12. Magnets • Super conducting Coils of wire Produce horizontal field Liquid helium to keep wire cold(4’Kelvin) Current flow freely with no resistance • Permanent 2 Large bar magnet Vertical field • Resistive Use a continuous current Very expensive to operate

  13. Resonance • The transition of nuclei from low energy to high energy following the application of an RF pulse at the same frequency as the precessing nuclei. • Over time the proton will “relax” back to its normal state. The energy it emits is measured by an antenna (coil) and this creates our image.

  14. Magnets • Super conducting Coils of wire Produce horizontal field Liquid helium to keep wire cold(4’Kelvin) Current flow freely with no resistance • Permanent 2 Large bar magnet Vertical field • Resistive Use a continuous current Very expensive to operate

  15. RF coils • Radio antennas that transmit energy • Must be perpendicular to the main magnetic fields (Bo) in order to image a pt. • Transmit/Receive coils. Must not touch (couple) or there will be a decrease in performance

  16. Weighting • T1 • T2 • Proton Density • T2*

  17. Longitudinal (T1) (spin lattice) Regrowth of magnetization along the longitudinal direction (with the field) Energy is given off Each different tissue has a unique molecular component (bound/free in macromolocules) Therefore tissue like Liver have a shorter T1 than fluids. Transverse (T2)(spin spin) Decay of FID back to its initial state (zero) A measure of time in which the transverse has decayed to 37% of its initial value T2 must be less than or equal to T1 Caused by dephasing of protons T1 relaxation Dipolar interaction of the spins Inhomogeniety of the field Local inhomogeneities caused by susceptibility Relaxation

  18. Saturation Pulses • RF pulses placed in or around the slice to decrease artifact or eliminate flow. • Increases RF deposition, and reduces # of slices per TR

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