1. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 1 Nuclear Magnetic Resonance (NMR) is a phenomenon discovered about 60 years ago. Since then it has been used for many biomedical engineering applications from medical imaging to the molecular and tissue structure and function. Using NMR one can measure NMR spectra, diffusion coefficients, electric current, flow velocity, temperature, blood oxygenation, brain function, muscle metabolism, reaction rates and much much more. The IBBME is the proud owner of a TeachSpin PS1-A NMR spectrometer. This is a device that can (in its present state) demonstrate many basic features of NMR but little else. Introduction

2. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 2 Identify a biomedical application of NMR of interest to your group and find out: 1.What is problem that NMR helps to solve? 2.How is NMR is used to solve this problem in theory? 3.How is NMR is used to solve this problem in practice? 4.What are the specifications and price of the NMR equipment required? 5.Why are the above specifications important? 6.Could the TeachSpin PS1-A NMR spectrometer be modified (if necessary) to meet these specifications? If so how and if not why not. Problem

3. BME1450 Intro to NMR November 2002 The Basics The Details www.ecf.utoronto.ca/~joy

4. September, 2003BME 1450 Introduction to NMR 4 Example of MRI Images of the Head Bone and air are invisible. Fat and marrow are bright. CSF and muscle are dark. Blood vessels are bright. Grey matter is darker than white matter.

5. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 5 MRI Imagers GE 1.5 T Signa Imager GE 0.2T Profile/i imager

6. BME1450 Intro to NMR November 2002 The Basics The Details www.ecf.utoronto.ca/~joy

7. September, 2003BME 1450 Introduction to NMR 7 Magnetic Resonance (MR) An object in a magnetic field B 0 will become magnetized and develop a net Magnetization, M. Most of M arises from the orbital electrons but a small part is the Nuclear Magnetization . The nucleus has a magnetic dipole moment, , and angular momentum, J. |  |/|J| = , the gyromagnetic ratio. For Hydrogen  = 43 MHz/T. J and  The Details  Magnetization is “magnetic dipole moment per unit volume”.

8. MR: Precession The 1.5T magnetic, B 0 field of the MR Imager makes the Hydrogen Nuclei precess around it. The precession rate,, is the Larmor frequency. f L =  B 0 = 43*1.5 = 64MHz for Hydrogen in water +- 300Hz in other molecules. Y Z J or  X B0B0 |B 0| t The Details

9. Summary The magnetization,M, is the density of nuclear magnetic dipole moments. If you tip M away from B 0 it will precess, at frequency  B 0, producing a measurable RF magnetic field. The precessing M will induce an RF voltage in the receive coil if it is not perpendicular to B 0 This signal is called the FID (free induction decay) Y Z J or  or M X B0B0 |B 0| t The Details Receive Coil

10. MR Excitation pulse You can tip M by applying a circularly polarized RF magnetic field pulse, B 1, to the sample. If B 1 is at the Larmor frequency,  B 0 you get this. M is now precessing about two magnetic fields. B 1 is effective because it tracks M. Y Z J or  or M X B0B0 |B 0 | t B1B1 |B 1 | t The Details B0B0 B1B1 Excitation coils

11. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 11 The Rotating Frame It is much easier to visualize all this if you observe it from a frame of reference which is rotating at the Larmor frequency, f L =  B 0. B 1 appears motionless in this rotating frame and B 0 effectively disappears and… During the excitation pulse, M precesses only about B 1 at frequency  B 1 !! Y’ Z M X’ B1B1 |B 1 | t M y’ MZMZ The Details Rotating Frame

12. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 12 The Rotating Frame When the excitation pulse is over, M is stationary in the rotating frame. In the Lab frame, however, it is still precessing. Y’ Z M X’ M y’ MZMZ The Details Rotating Frame

13. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 13 Magnitisation Relaxation (Decay) The transverse (M  ) and longitudinal (M || ) components of the magnitization change with time. Two relaxation times T 1 (longitudinal) and T 2 (transverse). T 1  T 2 M(t) || M 0 t T 2 The Details

14. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 14 Basic NMR Pulse Sequence The Details What flip angle gives biggest FID???? RF Excitation Time FID 100 ms Rotation by  degrees Flip angle 10  s 5ms << T 2 !!!

15. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 15 The Main Magnet NMR Instrumentation Ideally B 0 is uniform to 1or 2 ppm In the teach spin magnet it is not as good B 0 non-uniformity over a sample means that it produces a range of RF frequencies around  B o mean FID decay in T 2 * < T2 Spectral lines become blurred The sample Move the sample holder to the most uniform spot

16. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 16 The CP Spin echo sequence NMR Instrumentation This sequence overcomes the T 2 *non-uniformity effects allowing T 2 to be measured. RF Excitation FID 30 ms  degrees Flip  degrees Flip

17. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 17 Why CP Spin echo makes an echo NMR Instrumentation http://www.physics.monash.edu.au/~chrisn/espin.html This animation shows the rotating frame coordinates. The two RF pulses (  /2 &  ) are along the rotating x axis. The arrows are magnetisation at various points in the sample. Most arrows precess faster or slower than the rotating frame.

18. The mixer NMR Instrumentation The FID is amplified and then shifted down in frequency in the “mixer”. X FID ~15 MHz mixer RF oscillator 15 MHz Mixer output DC time

19. www.ecf.utoronto.ca/~joy September, 2003BME 1450 Introduction to NMR 19 An FID and four Echos NMR Instrumentation FID Four Echos Scope sweep 10ms / div