Laser doppler microscopy methods and instruments

• US 5,778,878 A
• Filed: 05/26/1995
• Issued: 07/14/1998
• Est. Priority Date: 06/04/1994
• Status: Expired due to Fees

• Current Assignee: Keith Kellam
• Original Assignee: Keith Kellam
• Inventors: Kellam, Keith
• Primary Examiner(s): Casler, Brian L.
• Application Number:
  US08/451,771
• Time in Patent Office: 1,145 Days
• Field of Search: 128/691, 128/633, 128/666, 128/665, 128/661.08, 128/664, 128/653.1
• US Class Current: 600/473
• CPC Class Codes: A61B 5/0261 using optical means, e.g. infrared light
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: G01P 5/26 by measuring the direct influence of the streaming fluid on the properties of a detecting optical wave
• CPC Class Codes: G01S 17/58 Velocity or trajectory determination systems; Sense-of-movement determination systems

Abstract

The velocity of blood cells in skin or other tissue capillaries is determined by a laser Doppler technique. A laser beam is focussed on to a capillary by means of a lens, mirror and beam splitter system and measurement of the velocity of the blood cells in a direction substantially perpendicular to the surface of the tissue is effected by detecting directly back-scattered radiation.

Claims

1. An instrument for use in the determination of blood cell velocity in a capillary in a tissue by a laser Doppler technique, said instrument comprising:

means for generating a laser beam;

means for directing the laser beam on to a surface of the tissue so as to impinge on a capillary within which blood cells are traveling with a component of velocity substantially perpendicular to the surface of the tissue;

a camera having an image plane for observing impingement of the laser beam on the surface;

means for measuring the velocity by detecting directly back-scattered laser radiation; and

a lens system which collects the back-scattered laser beam and focuses the Doppler-shifted back-scattered radiation on to a photodetector via at least one beam splitter, said lens system also serving to effect focussing of radiation back-scattered by surrounding tissue and not subjected to Doppler-shifting.

2. An instrument as claimed in claim 1, which includes two beam splitters and two mirrors for directing the Doppler-shifted back-scattered radiation on to the photodetector.

3. An instrument as claimed in claim 1, comprising:

means for producing an electrical signal in the photodetector having a frequency component proportional to the blood cell velocity in response to autodyne beating of Doppler-shifted and non-Doppler shifted radiation signals.

4. An instrument as claimed in claim 3, which includes an ADC (Analogue to Digital Converter) to which the output from the photodetector is fed and a FIFO (First In First Out Buffer) connected to the ADC and in which the output of the ADC is buffered, said ADC including means for amplifying and bandwidth limiting the photodetector output before conversion by the ADC.

5. An instrument as claimed in claim 1, in which means are provided for illuminating the capillary by means of green light or blue/green light, and in which the green or blue/green light reflected from the capillary is collected by the objective lens and focussed on the image plane of the camera.