On-line measurement of microvascular diameter and red blood cell velocity by a line-scan CCD image sensor

A line-scan charge-coupled device (CCD) image sensor (256 photo sites) was equipped for on-line measurement and calculation of red blood cell velocity and microvascular diameter. The principle of measurement is based on a sequential readout of the CCD-sensor photo signal at predefined time intervals. The velocity is calculated by a computer by cross correlation of a given set of readouts. Rotation of the sensor into a position perpendicular to the microvessel axis allows measurement of the diameter, which is related to the red blood cell column moving under the sensor. At low magnification (up to 38-fold) diameters up to 80 microns can be measured. Calibration, which was performed by comparing diameters measured in vivo by the CCD-based system with microphotographically obtained measurements, revealed a mean CCD/photo ratio of 0.98 +/- 0.08. Calibration of velocity measurements in glass tubes of different diameters by a calibrated pump with known bulk flow resulted in a mean conversion factor of 1.59 +/- 0.2 (mean +/- SD). The CCD sensor is mounted such that it can freely rotate on the microscope. In conjunction with a programmable scanning table, several vessels can be measured sequentially in one preparation. The interval between two combined measurements and calculations of velocity and diameter is 1.1 sec.