Laser Doppler imaging
Laser Doppler imaging | |
---|---|
Purpose | measure blood flow in eye |
Based on | Digital holography |
Laser Doppler imaging (LDI) is an imaging method that uses a laser beam to scan live tissue. When the laser light reaches the tissue, the moving blood cells generate doppler components in the reflected (backscattered) light. The light that comes back is detected using a photodiode that converts it into an electrical signal. Then the signal is processed to calculate a signal that is proportional to the tissue perfusion in the scanned area. When the process is completed, the signal is processed to generate an image that shows the perfusion on a screen.[1]
The laser doppler effect was first used to measure microcirculation by Stern M.D. in 1975.[2][3] And it is used widely in medicine, some representative research work about it are these: [4][5][6]
Use in ophthalmology
The
Measurement of surface waves on the skin
The local velocity of blood flow measured by laser Doppler holography in the digit (photoplethysmogram) and the eye fundus has a pulse-shaped profile with time. These remote pulse wave measurements can be done clinically to reveal hemodynamics in arteries and veins and can be readily measured non-invasively. Principal component analysis of digital holograms[10] is an efficient way of performing temporal demodulation of digital holograms reconstructed from on-axis interferograms and can be used to reveal surface waves on the hand.
Use in obstetrics and gynaecology
LDI provides a direct measure of female sexual response that does not require genital contact; signals are gathered at a depth of two to three millimetres below the skin's surface.[11] Two studies have suggested that LDI is a valid measure of female sexual arousal.[11][12] Waxman and Pukall[11] showed that LDI has discriminant validity; that is, it can differentiate sexual response from neutral, positive, and negative mood induced states. Compared to vaginal photoplethysmography (VPG), LDI is advantageous because it does not require genital contact. Also, LDI provides a direct measure of vasocongestion and has an absolute unit of measurement, consisting of flux or units of blood flow. The disadvantages of LDI are that it cannot provide a continuous measure of sexual response and the laser Doppler perfusion imager is much more costly that other methods of genital sexual arousal assessment, such as VPG.[11]
See also
- Hot-wire anemometry
- Laser Doppler velocimetry
- Laser Doppler vibrometer
- Laser surface velocimeter
- Molecular tagging velocimetry
- Particle image velocimetry
- Particle tracking velocimetry
- Photon Doppler velocimetry
- Photoplethysmogram
References
External links
- LDA/LDV principle Archived 2011-07-12 at the Wayback Machine
- LDV overview