Mri system block diagram
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This document provides an overview of MRI system components and basic MRI physics concepts. It includes: 1) A diagram of the main components of an MRI system, including RF coils, gradient coils, and amplifiers. 2) Tables listing common NMR-active nuclei and their properties important for MRI. 3) Explanations of spin alignment in magnetic fields, Larmor frequency, spin excitation, free induction decay, Bloch equations, T1 and T2 relaxation, and slice selection techniques.
![Bloch Equations
dMz(t) = − [Mz(t) − M0]
dt T1
dMxy(t) = − Mxy(t)
dt T2
Mz
Mxy
Mz Mz
Mxy
Mxy](https://image.slidesharecdn.com/o7sprchash6hppniv2kx-signature-32d797e46816d2f1ad04b19f9671fd9c01ddaa51c8250008594a8e918e443472-poli-160917224221/85/Mri-system-block-diagram-14-320.jpg)
![T1 Relaxation
Mz(t) = M0 + {Mz(0) − M0}exp(-t/T1)
Mz Mz
t t
saturation–
recovery
inversion–recovery
dMz(t) = − [Mz(t) − M0]
dt T1
M0 M0
Mz(0) = 0 Mz(0) = −M0](https://image.slidesharecdn.com/o7sprchash6hppniv2kx-signature-32d797e46816d2f1ad04b19f9671fd9c01ddaa51c8250008594a8e918e443472-poli-160917224221/85/Mri-system-block-diagram-15-320.jpg)
Mri system block diagram
- 1. MRI System Block Diagram RF amp spectrometer r.f.coil gradient coil X amp Y amp Z amp
- 2. Principle of Gradient Coil ∂Bz ∂x ∂Bz ∂z
- 3. Isotope Spin %age γ I abundance MHz/T 1 H 1/2 99.985 42.575 2 H 1 0.015 6.53 13 C 1/2 1.108 10.71 14 N 1 99.63 3.078 15 N 1/2 0.37 4.32 17 O 5/2 0.037 5.77 19 F 1/2 100 40.08 23 Na 3/2 100 11.27 31 P 1/2 100 17.25 Common NMR Active Nuclei
- 4. Alignment of Spins in a Magnetic Field spin magnetic moment B0 field M M=0
- 5. Energy in a Magnetic Field (Zeeman Splitting, Spin ½) E+1/2= −γB0/2 E-1/2= +γB0/2 P+1/2= 0. 5000049 P-1/2= 0.4999951 1.5T, T=310K, P(E)∝exp(−E/kT) mI = +½ mI = −½
- 6. Larmor Frequency E+1/2= −γB0/2 E-1/2= +γB0/2 Allowed transitions ∆E = γB0 = ω0 mI = −½ mI = +½ ω0 = γB0
- 7. Quantum Mechanical Description (Spin ½ Case) ψ> = a−½−½> + a+½+½> I=½, 2I+1 Zeeman splittings mI = −½ mI = +½ Mz = <ψIzψ> = a+½2 − a−½2 Mxy = <ψIx+ iIyψ>
- 8. Coupling with a B1 Field B0 B1 Birdcage coil A time
- 9. Spin Excitation M M M rotating frame laboratory frame
- 11. Free Induction Decay M M M 90° 90° 90° small positive shim mis-set medium positive shim mis-set large positive shim mis-set
- 12. Free Induction Decay M M M 90° 90° 90° small negative shim mis-set medium negative shim mis-set large negative shim mis-set
- 13. Product Operators Mx → Mx My → Mycosθ + Mzsinθ Mz → Mzcosθ − Mysinθ θx θx θx Mx → Mycosθ − Mzsinθ My → My Mz → Mzcosθ + Mxsinθ θy θy θy Mx → Mxcosωt + Mysin ωt ω t My → Mycosωt − Mxsin ωt ω t Mz → Mz ω t r.f. free precession x y z
- 14. Bloch Equations dMz(t) = − [Mz(t) − M0] dt T1 dMxy(t) = − Mxy(t) dt T2 Mz Mxy Mz Mz Mxy Mxy
- 15. T1 Relaxation Mz(t) = M0 + {Mz(0) − M0}exp(-t/T1) Mz Mz t t saturation– recovery inversion–recovery dMz(t) = − [Mz(t) − M0] dt T1 M0 M0 Mz(0) = 0 Mz(0) = −M0
- 16. Spin Echo M M M 180° 180° 180°90° 90° 90° small positive shim mis-set medium positive shim mis-set large positive shim mis-set
- 17. Spin Echo M M M 180° 180° 180°90° 90° 90° small negative shim mis-set medium negative shim mis-set large negative shim mis-set
- 18. T2 Relaxation Mxy(t) = Mxy(0) exp(−t/T2) Mxy t dMxy(t) = − Mxy(t) dt T2