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White Light Velocimetry
Measure velocity of objects using light from ordinary lamps.
Expensive high coherence lasers no longer required.
Contact: David Erskine, erskine1@llnl.gov, 925-422-9545, Lawrence Livermore Nat. Lab.
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Ultrasound application: finding tumors with improved Doppler imaging
The white light velocimetry technique demonstrated here in optics can be applied to ultrasound. Furthermore, velocimetry can easily be combined simultaneously with rangefinding. The use of the same wide bandwidth illumination for rangefinding and velocimetry has not been done before and promises improved spatial resolution while simultaneously sensitively discriminating targets by velocity. This could improve the clarity of medical Doppler ultrsound images, particular when trying to indentify fine blood vessels associated with tumors.
In conventional ultrasound, wide bandwidth illumination is not used to perform Doppler measurement-- long coherence length monochromatic illumination is used instead. This means that although the presence of moving blood can be detected, the position of the blood vessels having that particular velocity cannot be determined with fine spatial resolution.
In our new WLV technique, the illumination is passed through a preparatory interferometer which imprints an echo. This creates partial coherence at a particular delay value. After reflecting from a target, the signal is passed through a detecting interferometer having the same delay as the preparatory interferometer. Changes in target velocity cause fringe shifts in the time integrated signal outputted from the detecting interferometer. Hence, the velocity can be measured even when the illumination has a bandwidth many times exceeding the Doppler shift. Cross-correlation provides range information. Hence both range and velocity can be measured to high quasi-high precision. (Because essentially a pair of pulses are used, the uncertainty principle is not violated because a new large range ambiguity is created.)
The fundamental basis for this technique has recently been demonstrated in ultrasound at LLNL by Dave Chambers, in a 1999 LDRD funded feasibility study. They used a wideband ultrasound test facility existing in B343.
Documentation
-----Description of basic principle, and the retro-reflecting configuration in particular:
"White-light Velocimetry", D. J. Erskine & N. C. Holmes, Nature 377, 317-320 (1995). Downloadable version WLV_Nature.pdf
----Demonstration of the double-interferometer configuration, which simplifies measuring velocity over an image:
"Imaging White Light VISAR", D. J. Erskine & N. C. Holmes, High-speed Photography and Photonics conf. proceed., SPIE 2869, 1080-1083 (1997). Downloadable version, SantaFeUCRL.pdf
Related Patents
Below are just the front pages. For full text I recommend going to IBM patent server at
| "White Light Velocity Interferometer" | 5,642,194 | Basic WLV principle |
| "White Light Velocity Interferometer" | 5,910,839 | Differs from the above in the claims section |
| "Noise Pair Velocity and Range Echo Location System" | 5,872,628 | Adds velocity discriminated rangefinding to the WLV idea; other radar/ultrasound issues |
| "Multichannel Heterodyning for Wideband Interferometry, Correlation and Signal Processing" | 5,943,132 | How to make a long yet coherent delay, in order to implement radar WLV |
UCRL-MI-136029
