Wavelength-Resolved 3-Dimensional Fluorescence Lifetime Imaging

We have developed a compact system for wide-field fluorescence imaging, resolved in three spatial dimensions, lifetime and wavelength, that is based on a gated optical intensifier and an all-solid-state diode pumped Cr:LiSAF oscillator-amplifier system. Exploiting spectral separation, the system has been applied to human teeth, obtaining good lifetime contrast between enamel, dentin and caries. Exploiting spectral separation combined with depth resolution, the study of fluorescent microspheres led to an enhancement in both lifetime contrast and lateral resolution.     

Book reviews

MODERN CRYSTALLOGRAPHY I, by B. K. Vainshtein, Springer Series in Solid State Sciences 15. Springer-Verlag, New York, 1981. 399 pp., USf47.50.

SPECTROSCOPY IN CHEMISTRY AND PHYSICS: Modern Trends, Edited by F. J. Comes, A. Muller and W. J. Orville-Thomas (Elsevier Scientific Publishing Company). Price US $87.75, Dfl 180.00.

ELECTRONIC STATES OF MOLECULES AND ATOM CLUSTERS-Foundations and Prospects of Semiempirical Methods, by G. Del Re, G. Berthier and J. Serre. Springer Lecture Notes in Chemistry, Vol. 13. Price: US817.50 (Springer-Verlag, Berlin, 1980).

MATERIALS FOR THE FUTURE, Edited by P. M. Kelly, Australian Academy of Science, 1981.     

Superconductivity and the b.c.c. to A-15 transformation in Nb-Au alloys2

Nb-Au alloys near the composition Nb₃Au can be quenched from the high temperature α solid solution phase field, retaining the b.c.c. structure. We report results on their superconducting, mechanical and physical properties as a function of composition. Short low temperature anneals transform these materials to the equilibrium A-15 structure with T_c up to 11K. We report results on the superconducting and physical properties of the transformed A-15 structure materials and describe how the properties of the transformed materials are affected by annealing temperature and time.     

Detection of a systemic effect of malignancy in vivo by magnetic resonance imaging

In animals bearing tumors prolongation of spin lattice relaxation time (T1) has been detected in vitro in organs not directly affected by the malignancy. This has been termed the "Systemic Effect." In this study the possible existence of such an effect in the liver, muscle and fat of humans with lymphoma has been investigated. In vivo T1 measurements were made using a low field strength (0.08 Tesla) magnetic resonance imager. The mean liver T1 for 19 lymphoma patients with normal liver histology was 206 ms, compared with a mean of 191 ms for 61 volunteers (p less than 0.0001). Among these patients prolongation of liver T1 was related to the extent of disease elsewhere in the body. For 23 patients with Hodgkin's disease (HD) examined at the time of diagnosis, liver T1 was significantly correlated with other known markers of disease extent or activity (alkaline phosphatase level, erythrocyte sedimentation rate and the presence of systemic symptoms). No such correlations were observed among 25 patients with non-Hodgkin's lymphoma (NHL). Muscle and fat T1 was measured in 26 patients with lymphoma, 14 patients with acute leukemia and 88 volunteers. Seven of the patients with lymphoma and 2 of those with leukemia had muscle T1 values above the range observed for volunteers. Similarly, 3 patients with lymphoma and 1 with leukemia had prolonged fat T1. These findings indicate that a systemic effect of malignancy on T1 is detectable in a proportion of humans with lymphoma or leukemia.     

Excitation mechanisms in CW He-Hg lasers

The collision processes responsible for populating and de-populating upper and lower levels of the cw He-Hg ion laser are investigated using flowing afterglow techniques. It is shown that the superior performance of the laser at 6150 Å compared to that at 7945 Å is not due to a difference in excitation mechanism — both are excited by charge transfer from He⁺ — but instead reflects a greater effectiveness of second kind collisions of electrons in depopulating the 7p²P_{$\text{1}\text{2}$} upper level of the 7945 Å transition. The charge transfer, excitation rate constants for several Hg II levels are compared, and values for the rate constant for the electron collision de-excitation process are deduced.     

Parallel interconnection and neural network systems employing semiconductor array technology and computer-generated holography

An experimental 16-channel parallel interconnection system able to support 100 Mbits^–1 per channel and an opto-electronic neural network operating at up to 50 Mbits^–1 have been constructed to demonstrate the potential of optics in processing systems. Both experiments operate at a wavelength of 1.5m. Components developed for these systems include arrays of InGaAs/InP MQW surface modulators for low-power electrical-to-optical conversion; InGaAs/InP for detector arrays, which are hybrid integrated with GaAs amplifier arrays; and computer-generated holograms for efficient beam splitting and to encode weights in the optical beam intensities. Each of these demonstrations has considerable scope for increasing the degree of parallelism and the operating speed. Recent modifications to the neural network enable the weights to be varied and training has been demonstrated with a novel algorithm that uses the high operating speed to advantage.