Assessment of microvascular circulation
View Patent ↗Methods and compositions are disclosed to quantitatively measure in vivo blood vessel diameter, blood velocity, and other flow dynamics. Such methods and compositions can optimize therapeutic interventions designed to prevent or reduce the risk of cardiovascular and blood disorders. In one aspect, the methods and apparatus involve calculating blood vessel characteristics from a two dimensional image of a blood vessel in the conjunctiva of a subject's eye. In another aspect, a series of temporal images of a blood vessel are obtained to determine blood flow properties. The apparatus can include, for example, a biomicroscope, an illuminating light source and a high speed camera to acquire the series of temporal images with the data then analyzed by a programmed processor.
1. A method for determining blood velocity in a conjunctiva of an eye, comprising:
acquiring a series of temporal frames with registered images of at least one vessel in the conjunctiva of the eye, wherein the registered images are registered to compensate for eye motion;
identifying at least one blood cell present in each of a plurality of frames;
calculating blood velocity within the vessel based on a distance travelled by the blood cell in the vessel between frames; and
compensating for involuntary target movement by tracking eye movements.
2. The method of claim 1 , wherein the step of acquiring the images further comprises illuminating the conjunctiva of the eye with light having a wavelength in a range of about 500 nm to 560 nm.
3. The method of claim 1 further comprising determining blood flow in the blood vessel by:
obtaining a two-dimensional image of the vessel in the conjunctiva of the eye;
determining dimensions of the vessel from the two-dimensional image; and
calculating blood flow within the vessel based on blood cell velocity and blood vessel dimensions.
4. A hemodynamics measurement apparatus comprising:
a light source configured to project radiation onto a target tissue;
optics configured to image at least one vessel in the tissue;
a detector to capture a series of temporal images of the vessel;
a processor to calculate blood flow dynamics in the vessel from the series of images; and
an eye tracking mechanism that compensates for involuntary movement of the eye from one temporal image to another,
wherein the apparatus is configured to image at least one blood vessel in the conjunctiva of a subject's eye.
5. The apparatus of claim 4 , wherein the apparatus further comprises a biomicroscope.
6. The apparatus of claim 4 , wherein the light source generates light of at least one wavelength in the range of about 450 to 600 nm.
7. The apparatus of claim 6 , wherein the light source generates light at a wavelength in a range from about 500 nm to about 600 nm.
8. The apparatus of claim 7 , wherein the light source generates light at a wavelength in a range from about 500 nm to about 560 nm.
9. The apparatus of claim 4 , wherein the eye tracking mechanism is configured to detect changes in pupil position.
10. The apparatus of claim 4 , wherein the detector comprises a camera.
11. The apparatus of claim 10 , wherein the camera is a charge-coupled device (CCD).
12. The apparatus of claim 10 , wherein the apparatus further comprises a camera controller configured to acquire a plurality of images over a time interval.
13. The apparatus of claim 12 , wherein the camera controller is configured to acquire images at least 40 Hz.
14. The apparatus of claim 4 , wherein the detector is configured to acquire two-dimensional images.
15. The apparatus of claim 4 , wherein the apparatus is a handheld apparatus.