Britton Chance

Fluorescent heterogeneities in turbid media: limits for detection, characterization, and comparison with absorption

The fundamental limits for detection and characterization of fluorescent (phosphorescent) inhomogeneities embedded in tissuelike highly scattering turbid media are investigated. The absorption and fluorescence contrast introduced by exogenous fluorophores are also compared. Both analyses are based on practical signal-to-noise ratio considerations. For an object with fivefold fluorophore concentration and lifetime contrast with respect to the background tissue, we find the smallest detectable fluorescent object at 3-cm depth in tissuelike turbid media to be ~0.25 cm in radius, whereas the smallest characterizable object size is ~0.75 cm in radius, given a model with 1% amplitude and 0.5 degrees phase noise. We also find that, for fluorescence extinction coefficients epsilon </= 0.5 x 10(5) cm(-1) M(-1), the fluorescence measurement mode is superior to the absorption mode for detecting an inhomogeneity. The optimal choice of modulation frequency for the frequency-domain fluorescence measurements is also discussed.

Stable Spectrophotometry of Small Density Changes

Measurement and control circuits for recording small density changes by use of several photo‐tube circuits are given. The minimum drift rates obtained are 1×10−6 part per minute with a differential photo‐tube circuit, 3×10−5 part per minute with a single photo‐tube circuit, and 4×10−4 part per minute with a photo‐multiplier circuit. The differential and single photo‐tube circuits have been used to measure density increments of roughly 2×10−4 and 1×10−3 with an accuracy of about 5 percent. These spectrophotometers are employed in studies of the kinetics of unstable intermediates in enzyme action. Although slow drift has been rendered negligible by suitable control circuits and stable amplifiers, the theoretical limit of performance is not achieved by this apparatus.

Some Precision Circuit Techniques Used in Wave‐Form Generation and Time Measurement

This paper contains a survey of the characteristics and uses of non‐linear circuit elements in the generation of wave forms particularly useful in precision timing circuits. The use of these non‐linear circuit elements in detection and time measurement is also included.

Optimal selection of frequencies for diffuse optical tomography

The use of diffuse photon density waves (DPDW) at multiple modulation frequencies is a significant tool for Diffuse Optical Tomography (DOT). Use of higher frequencies offers higher contrast between scattering and absorbing objects and allows higher resolution to be achieved. Here we focus on the optimal use of frequencies in simultaneously resolving absorbing and scattering objects using simulated data.

Some Designs and Applications for Packaged Amplifiers Using Subminiature Tubes

Design and construction details of d.c. and a.c. amplifier packages using subminiature tubes are given. In addition, applications to control and measurement circuits are shown. The purpose of these amplifiers is to decrease the time lost in the construction and repair of complicated electronic equipment for biophysical and other experiments.

The interconnection of dead-reckoning and radar data for precision navigation and prediction

Abstract A simplified method for the interconnection of radar and dead-reckoning data has been presented and used to illustrate the application of this principle to ship and aircraft navigation problems. This interconnection facilitates the interpretation of radar data and increases the accuracy of the dead-reckoning data. Furthermore, the prediction of time of arrival of a craft at a stationary or a moving object is readily computed.