1. MRI

2. Magnetic Resonance 1.Principle first observed in 1946 2.Used for spectroscopy and imaging 3.Imaging techniques are a form of tomography, where slices are ’cut’ and depict 4.MRI utilizes signals from the body 5.MRI is non-ionizing, operating in radiofrequency range, unlike CT, PET, SPECT 6.Resolution is not limited to radio wave lengths 7.MRI is pricy 2

3. Nuclear spin A nucleui possesses a spin angular momentum, (p) Can be view as a rotation of the nuclei I is the quantum number of the spin. The spin gives raise to a magnetic moment: Where  is the gyromagnetic ratio 3

4. Nuclear spin I can be an intenger, half an intenger, or 0 If I is 0 there is no spin and no magnetic moment The natural isotope 12 C has quantum spin of 0 whereas 13 C has ½. 4

5. Nuclei in a magnetic field – The classics Torque on the nuclei Torque makes the muclei precess chancing p ω 0 is the Larmor frequency, the frequency that the nuclei precesses with 5

6. Nuclei in a magnetic field – Quantum mechanics p is quantified allowed 2I +1 states Eg a proton 1H is allowed two states or directions parallel to the field (spin up) antiparallel to the field (spin down) 6

7. Many nuclei in a magnetic field An equlibrium between spin up and spin down will emearge A small excess of nuclei in the low energy state,  N 7

8. Back to the Larmor Frequency , the gyromagnetic konstant ‘material’ constant , Can be affected by chemical bounds The magnetic field may be inhomogeneous 8

9. The Chemical shift effect Shielding electrons reduces the magnetic field ’seen’ by the nucleus The resonance frequency is also reduced  is the shielding constant  ~5e-6  depends on local chemical envionment Used for gaining knowledge about chemical structure; Spectroscopy 9

10. Bulk / Macroscopic / Sum magnetization N s is the number of atoms in a sample  i is the magnetic moment of the i-th atom M is always aligned to B in equilibrium M can be pertubed and will precess 10

11. Excitation Adding a field B 1 perpendicular to B 0 at Lamor frequency will excite the system An ocillating magentic field at 1 – 500 MHz is a Radio frequency wave B 1 ~ 50 mT & B 0 ~ 1-5T  is the flip angle A pertubation pulse is often named after the flip angle 90° pulse 180 ° pulse 11

12. Excitation B 1 is the envelope function The duration of the pulse  affects the flip angle  =  B 1  or if different amplitudes are allowed 12

13. Induced current In Eqlibrium M z = M 0 M x = M y = 0 ~ M xy After perturbation 13

14. Free Indusction Decay (FID) The M xy component decays to 0 The frequency is the peak The decay rate T2 is proportional to the width at half max Area under the envolope is the hight of the spectral amplitude 14

15. Relaxation M xy  0 : Spin-spin relaxation T2 time to 36.7% of M 0 M z  M 0 : Spin-lattice relaxation T1 time 63.2% of M 0 Important for contrast in images 15

16. Inversion recovery 180-TI-90-FID 16

17. Invertion recovery 17

18. Spin Echo 18

19. Magnetic Field Gradients G is the gradient of a magnetic field 19

20. Slice selection By applying a gradient G the resonance frequency becomes dependent on direction The bandwidth of the pulse determines the thickness of the slice 20