Photoelectric device for the recording of diameter changes of opaque and transparent blood vessels in vitro

A new photoelectric device for measuring blood vessel diameters is described. The principle of this device consists in locating the vessel within a beam of parallel light at right angles to the beam direction, and eliminating all light striking the vessel. Thus only the light passing by the side of the vessel determines the signal strength of a photocell. The elimination of the light by the vessel due to reflection, refraction, diffraction, or scattering, is achieved with the aid of a lens and pinhole representing a spatial filter. This arrangement is effective irrespective of whether the vessel is opaque or transparent. The resolving power of the device in measuring changes of outside diameter is better than 0.5 μm for vessels up to 3 mm in diameter. The upper frequency limit is 300 Hz (−3 dB). The application of the method is demonstrated by two examples of measurements obtained on a small muscular artery.