22. Medical MRI and Chemical NMR
Freshman Organic Chemistry II (CHEM 125B) Magnetic resonance imaging (MRI) requires gradients in the applied magnetic field, while chemical nuclear magnetic resonance (NMR) requires a highly uniform field. When protons in different parts of the body can be driven to broadcast different frequencies, tomography allows reconstructing a three-dimensional image showing water location. Dependence of the signal intensity on relaxation allows BOLD functional MRI that shows brain activity. When the applied magnetic field is sufficiently uniform, chemical NMR spectra differentiate proton signals according to local field variations within molecules. Modern research in a chemical laboratory like Yale's depends on the availability of many magnetic resonance spectrometers. Peak integrals show the relative number of protons in different molecular environments, while peak frequencies or "chemical shifts" show the bonding environment of groups of protons. Often downfield (deshielded) or upfield (shielded) shifts are correlated with local electron density. 00:00 - Chapter 1. Tomography, Field Gradients, and Magnetic Resonance Imaging 16:16 - Chapter 2. The Development of NMR Spectroscopy 29:16 - Chapter 3. Counting Protons by Integration 37:33 - Chapter 4. Local Magnetic Fields and the Chemical Shift Complete course materials are available at the Open Yale Courses website: http://oyc.yale.edu This course was recorded in Spring 2011.