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 Perfusion is the passage of fluid through the circulatory system or lymphatic system to an organ or a tissue, usually referring to the delivery of blood to a capillary bed in tissue. Perfusion is measured as the rate at which blood is deliver ...

in the scanned area. When the process is completed, the signal is processed to generate an image that shows the

on a screen. The laser doppler effect was first used to measure

microcirculation The microcirculation is the circulation of the blood in the smallest blood vessels, the microvessels of the microvasculature present within organ tissues. The microvessels include terminal arterioles, metarterioles, capillaries, and venules. ...

by Stern M.D. in 1975. And it is used widely in

medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...

, some representative research work about it are these:

Use in
Ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a me ...

The eye offers a unique opportunity for the non-invasive exploration of

cardiovascular diseases Cardiovascular disease (CVD) is a class of diseases that involve the heart or blood vessels. CVD includes coronary artery diseases (CAD) such as angina and myocardial infarction (commonly known as a heart attack). Other CVDs include stroke, ...

. LDI by digital holography can measure blood flow in the

retina The retina (from la, rete "net") is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which the ...

and

choroid The choroid, also known as the choroidea or choroid coat, is a part of the uvea, the vascular layer of the eye, and contains connective tissues, and lies between the retina and the sclera. The human choroid is thickest at the far extreme rea ...

. In particular, the

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. Differences in

blood pressure Blood pressure (BP) is the pressure of circulating blood against the walls of blood vessels. Most of this pressure results from the heart pumping blood through the circulatory system. When used without qualification, the term "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 Systole ( ) is the part of the cardiac cycle during which some chambers of the heart contract after refilling with blood. The term originates, via New Latin, from Ancient Greek (''sustolē''), from (''sustéllein'' 'to contract'; from ...

diastole Diastole ( ) is the relaxed phase of the cardiac cycle when the chambers of the heart are re-filling with blood. The contrasting phase is systole when the heart chambers are contracting. Atrial diastole is the relaxing of the atria, and ventricu ...

variations, and reveal ocular

hemodynamics Hemodynamics or haemodynamics are the dynamics of blood flow. The circulatory system is controlled by homeostatic mechanisms of autoregulation, just as hydraulic circuits are controlled by control systems. The hemodynamic response continuously m ...

in human eyes.

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 In medicine, a pulse represents the tactile arterial palpation of the cardiac cycle (heartbeat) by trained fingertips. The pulse may be palpated in any place that allows an artery to be compressed near the surface of the body, such as at the n ...

-shaped profile with time. These remote pulse wave measurements can be done clinically to reveal

in arteries and veins and can be readily measured non-invasively.

Principal component analysis Principal component analysis (PCA) is a popular technique for analyzing large datasets containing a high number of dimensions/features per observation, increasing the interpretability of data while preserving the maximum amount of information, and ...

of digital holograms 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 Obstetrics is the field of study concentrated on pregnancy, childbirth and the postpartum period. As a medical specialty, obstetrics is combined with gynecology under the discipline known as obstetrics and gynecology (OB/GYN), which is a sur ...
and
Gynaecology Gynaecology or gynecology (see spelling differences) is the area of medicine that involves the treatment of women's diseases, especially those of the reproductive organs. It is often paired with the field of obstetrics, forming the combined ar ...

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. Two studies have suggested that LDI is a valid measure of female sexual arousal. Waxman and Pukall 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.

References

External links

LDA/LDV principle
{{Webarchive, url=https://web.archive.org/web/20110712214301/http://www.holomap.com/lda.htm , date=2011-07-12
LDV overview
Laser applications Doppler effects Measurement Optical imaging Female genital procedures

Use in Ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a me ...

Measurement of surface waves on the skin

See also

References

External links

Use in
Ophthalmology Ophthalmology ( ) is a surgical subspecialty within medicine that deals with the diagnosis and treatment of eye disorders. An ophthalmologist is a physician who undergoes subspecialty training in medical and surgical eye care. Following a me ...