Microangiography of the
optic disc region of the human retina, by laser Doppler imaging. The image was rendered computationally by optical wave propagation and measurement of optical fluctuations.
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
eye offers a unique opportunity for the non-invasive exploration of
cardiovascular diseases. LDI by
digital holography can measure blood flow in the
retina and
choroid.[7] In particular, the
choroid is a highly vascularized tissue supplying the retinal pigment epithelium and photoreceptors. Yet investigating the anatomy and flow of the choroid remains challenging. LDI provides high-contrast visualization of local blood flow in choroidal vessels in humans, with a spatial resolution comparable to state-of-the-art indocyanine green angiography.[8] Differences in
blood pressure drive the flow of blood throughout the circulation. The rate of mean blood flow depends on both blood pressure and the hemodynamic resistance to flow presented by the blood vessels. LDI can enable mapping of the local
arterial resistivity index, and the possibility to perform unambiguous identification of retinal arteries and veins on the basis of their
systole-
diastole variations, and reveal ocular
hemodynamics in human eyes.[9]
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]
^Puyo, Leo; Bellonnet-Mottet, Loic; Martin, Antoine; Te, Francois; Paques, Michel; Atlan, Michael (2020). "Real-time digital holography of the retina by principal component analysis".
arXiv:2004.00923 [
physics.med-ph].
^
abcdWaxman, Samantha E.; Pukall, Caroline F. (2009). "Laser Doppler Imaging of Genital Blood Flow: A Direct Measure of Female Sexual Arousal". The Journal of Sexual Medicine. 6 (8): 2278–2285.
doi:
10.1111/j.1743-6109.2009.01326.x.
PMID19493290.
^Styles, SJ; MacLean, AB; Reid, WMN; Sultana, SR (2006). "Short communication: Laser Doppler perfusion imaging: A method for measuring female sexual response". BJOG: An International Journal of Obstetrics & Gynaecology. 113 (5): 599–601.
doi:
10.1111/j.1471-0528.2006.00894.x.
PMID16637901.
S2CID31409255.