CPEM 2004
Conference on Precision Electromagnetic Measurements

Monday

Plenary Session

"Snap-shot MRI"
P. Mansfield

Magnetic resonance imaging (MRI) emerged from nuclear magnetic resonance (NMR) in the early 1970s. It was clear from the first images that a conceptual breakthrough was required to speed up the imaging process from around one hour for those early images to something more acceptable in medical diagnosis. This step forward came in 1975-6 with the realisation that single-shot images could be obtained in principle by exploiting the properties of spin-echoes commonly used in NMR. The thinking was that an echo train contained, in effect, picture information in one-dimension if obtained in the presence of an external magnetic field gradient. The problem was how to encode the data along the orthogonal axes. The simple initial solution was to add a low-level read gradient while the spin-echoes were forming. This procedure did indeed lead to an image but it contained more image artefacts, which needed to be corrected. Subsequent development removed most of the problems so that today we can produce echo-planar images (EPI), which are subsequently free of artefacts and therefore are of diagnostic value.

"Femtosecond Laser Frequency Combs for Ultraprecise Spectroscopy"
T. Hänsch

During the past five years, femtosecond laser frequency comb synthesizers have firmly established their role as ultraprecise tools for optical frequency metrology. The development of these comb synthesizers will be reviewed, and their present and future role in physics and metrology will be discussed.