1 Introduction to Magnetic Resonance Imaging درس مقدمه ای بر فیزیک پزشکی Sahand University of Technology Faculty of Electrical Engineering M. Shamsi

2 Magnetic Resonance Imaging Non-invasive medical imaging method, like ultrasound and X-ray. Clinically used in a wide variety of specialties. AbdomenSpineHeart / Coronary

3 Magnetic Resonance Imaging Advantages: Excellent / flexible contrast Non-invasive No ionizing radiation Arbitrary scan plane Challenges: New contrast mechanisms Faster imaging

5 Topics MRI Physics Hardware

6 Topics MRI Physics Hardware

6 Magnetic Resonance Certain atomic nuclei including 1 H exhibit nuclear magnetic resonance. Nuclear “spins” are like magnetic dipoles. 1H1H MRI Physics

7 Polarization Spins are normally oriented randomly. In an applied magnetic field, the spins align with the applied field in their equilibrium state. Excess along B 0 results in net magnetization. No Applied FieldApplied Field B0B0 MRI Physics

8

9 Static Magnetic Field Longitudinal Transverse B0B0 z x, y MRI Physics

10 Precession Spins precess about applied magnetic field, B 0, that is along z axis. The frequency of this precession is proportional to the applied field: MRI Physics

11 Relaxation Magnetization returns exponentially to equilibrium: Longitudinal recovery time constant is T 1 Transverse decay time constant is T 2 Relaxation and precession are independent. PrecessionDecayRecovery MRI Physics

12 Signal Reception Precessing spins cause a change in flux (  ) in a transverse receive coil. Flux change induces a voltage across the coil. Signal y x B0B0 z  MRI Physics

Origin of the MR Signal Before Excitation After Excitation Excitation tips the net magnetization (M) down into the transverse plane, where it can generate current in detector coils. During Excitation (t o ) During Excitation (t 1 ) The amount of current oscillates at the (Larmor) frequency of the net magnetization. MRI Physics

14 Topics MRI Physics Hardware

MRI hardware 15

x 60,000 = The Big Magnet Main field = B 0 Continuously on Very strong : Earth’s magnetic field = 0.5 Gauss / 1 Tesla (T) = 10,000 Gauss 3 Tesla = 3 x 10,000  0.5 = 60,000 x Earth’s magnetic field B0B0 Robarts Research Institute 3T MRI hardware 16

MRI hardware 17

MRI hardware 18

MRI hardware 19

MRI hardware 20

MRI hardware 21 At $2 million, the most expensive equipment in the hospital…

MRI hardware 22

Superconducting Magnet MRI hardware 23

Resistive Electromagnet MRI hardware 24

Permanent MRI System MRI hardware 25

MRI hardware 26

MRI hardware 27

MRI hardware 28

29 MRI hardware

30 MRI hardware Head Coil

31 Head Coil MRI hardware 31

RF Receiver Coils MRI hardware

Three Sets of Gradient Coils MRI hardware 33

GRADIENTS MRI hardware 34

MRI hardware 35

MRI hardware 36

MRI hardware 37

MRI hardware 38

MRI hardware 39

MRI hardware 40

MRI hardware 41

MRI hardware 42

43 Surface Coils MRI hardware 43

MRI hardware 44

MRI hardware 45

Exclusion of Various Objects MRI hardware 46

Exclusion of Ferromagnetic Objects MRI hardware 47

Shielding of MRI Room MRI hardware 48

49 Delivery of 1.5T Superconducting MagnetDelivery of 1.5T Superconducting Magnet MRI hardware 49

T Open MRI with permanent magnet (11 tons) 0.2 T Open MRI with permanent magnet (11 tons) MRI hardware 50

T Open MRI with superconducting magnet 0.7 T Open MRI with superconducting magnet MRI hardware 51

52 Body Array and Head Array Coils MRI hardware 52

MRI hardware 53