How Science Affects People’s Lives  Health  Medical Imaging  X-Rays  C(A)T [Computerized (Axial) Tomography] Scanning  PET [Positron Emission Tomography] Scanning  MRI [Magnetic Resonance Imaging] – More appropriately called Nuclear Magnetic Resonance [NMR] Imaging  Ultrasound 9/16/09

X-Rays and Computerized Axial Tomagraphy CAT Scanning 9/16/09

CAT Scanned Liver Slice 9/16/09

Positron Emission Tomagraphy PET Scanning 9/16/09

Nuclear Magnetic Resonance and MRI Precession of a Spinning Top A top that is spinning slightly off the vertical axis “precesses” about about the vertical axis. 9/16/09

Nuclear Magnetic Resonance and MRI Polarization Hydrogen atoms have one proton in their nucleus. Protons have an “intrinsic spin,” by which we mean that they behave as though they are little bar magnets and spinning tops. All of the proton spins will align with the magnetic field in one direction or the other, a principal of quantum mechanics. The vast majority of the aligned spins cancel each other out, but, as shown here, in any sample there are a few "extra" protons spins pointing in one direction. We call this phenomenon “polarization.” Hydrogen Atoms in a Magnetic Field 9/16/09

Nuclear Magnetic Resonance and MRI Precession of a Hydrogen Atom We now apply a radio frequency (RF) pulse of energy to the ensemble of protons at a frequency that causes their spins to tilt with respect to the magnetic field. The “resonant” frequency depends on the strength of the magnetic field and the magnetic property of the proton. As in the case of the top, the spins begin to precess around the field. When the RF pulse ends, the spins relax to their natural alignment along the field, and as they do so, they release their precessional energy in a form that is detected by a “pick-up coil.” The slight excess of spins in one direction creates a characteristic signature. By altering the magnetic field over a volume, we can observe the difference in the proton (hydrogen) content at different locations. In this way we can create images of any tissue containing hydroge.. 9/16/09

How Science Affects People’s Lives  Health  Medical Imaging  X-Rays  C(A)T [Computerized (Axial) Tomography] Scanning  PET [Positron Emission Tomography] Scanning  MRI [Magnetic Resonance Imaging] – More appropriately called Nuclear Magnetic Resonance [NMR] Imaging  Ultrasound  Pharmaceuticals  Information Technology (IT)  Stem Cells 9/16/09

Assignment for 09/29/09 You are a curator at a science museum, and you have to provide a word description for an exhibit. Select one exhibit from among the following: Ethanol: The Fuel of the Future is Here Now The Human Genome: Cures of the Future The Laporoscope: Minimally Invasive Surgery CAT Scan: Physics in Medicine MRI: Imaging Soft Tissue Lasik: Correcting Vision Without Glasses Nuclear Fission: Powering the World Without Carbon Nuclear Fusion: Clean Power Without Waste Power from the Sun: Photovoltaics Power from the Sun: Wind Energy Hydrogen Fuel Cells: The Car of the Future The Global Positioning System (GPS): Never Get Lost Again The Light Emitting Diode (LED): Saving Energy in Lighting Smart Weapons: Minimizing Civilian Casualties in Times of War Epoxy/Carbon Fiber: Revolutionizing Sports and Fighter Planes 9/16/09