A miniature gamma camera.

We have described a mobile miniature-gamma-camera system for use in electrical trauma units and have presented images and imaging characteristics of a prototype system. The system has as its principal component a miniature gamma camera based on a PSPMT. The camera is 92 mm x 92 mm x 190 mm in size, weighs 5 kg, has a 48 mm x 48 mm field of view, and has an intrinsic resolution of approximately 3 mm FWHM and 6 mm FWTM. It is expected that devices of this type will be useful as imaging tools in electrical trauma units and laboratories where imaging studies regarding uptake mechanisms of radiopharmaceuticals for assessing tissue viability are carried out.

Oscillating intensity display of soft tissue lesions in MRI.

A new postprocessing method for improving visualization of soft tissue lesions in MR images is described. Abnormal tissues are detected by a computerized tissue characterization algorithm which is based on measurements of intensity in a spatially matched pair of T1- and T2-weighted images. Simultaneous display of information from this pair of static images is achieved by using a temporal parameter (amplitude or frequency of intensity oscillation) to encode abnormal pixels. Specifically, a movie is created in which pixel intensities of abnormal tissues are made to oscillate so that the amplitude (or frequency) of oscillation is proportional to an abnormality index which depends on the difference between intensities of normal and abnormal tissues in the original image pair. The visual effect is that of a churning motion within the lesion, while surrounding normal tissues are displayed as stable structures. This technique increases the conspicuity of the lesion by exploiting the eye's great sensitivity to motion.

Optimum detector spatial resolution for discriminating between tumour uptake distributions in scintigraphy.

The optimum detector spatial resolution has been determined for a scintigraphic decision task in which the observer must discriminate between two different distributions of radioactivity in tumours. The two kinds of tumour used are: (i) a solid sphere of increased uptake relative to background, and (ii) a thin spherical shell with high uptake in the shell and no radioactivity within the shell. Both tumours are embedded at the same depth within a cylinder of tissue-equivalent material containing a uniform distribution of radioactivity. On the basis of statistical decision theory, the optimum detector spatial resolution for discriminating between the two tumour activity distributions is predicted. The result of an observer performance experiment substantially agreed with the theoretical prediction, though some discrepancy was found, apparently due to a decrease in observer efficiency at poorer spatial resolution. The experimental result suggests that the optimum FWHM of detector spatial response for the discrimination task considered is about 65% of the tumour radius.

The geometric transfer function component for scintillation camera collimators with straight parallel holes.

A theoretical approach has been developed that allows the geometric transfer function component for conventional scintillation camera collimators to be predicted in closed form. If transfer function analysis is to be useful in describing imaging system performance, the image of a point source must not depend on source position in a plane parallel to the detection plane. This shift invariance can be achieved by analysis of system response in terms of an effective point spread function, defined as the normalised image of a point source that would be obtained if the camera collimator were uniformly translated (but not rotated) during image formation. The geometric component of the corresponding effective transfer function is shown to be expressed simply by the absolute square of the two-dimensional Fourier transform of a collimator hole aperture, with the spatial frequency plane scaled by a factor which depends on collimator length, source-to-collimator distance, and collimator-to-detection plane distance. Closed form algebraic expressions of the geometric transfer function have been obtained for all four common hold shapes (circular, hexagonal, square and triangular). Monte Carlo simulations and experimental measurements have shown these theoretical expressions to be highly accurate.

Analysis of recorded image noise in nuclear medicine.

The concepts of autocovariance function and Wiener spectrum have been applied to describe the recorded image noise in nuclear medicine. They were derived as functions of the expected detected count density and the detector and exposure point spread functions. It was shown that the detector system affects only the noise magnitude, whereas the recorder system affects both noise magnitude and texture. In experimental studies, the autocovariance function and Wiener spectrum of recorded image noise were measured by one-dimensional time-series analysis. Due to the non-linearity of the recording film, the best agreement between the theoretical predictions and the experimental results is found when the detected count density is sufficiently high and the size of the exposure spot is sufficiently large for the density fluctuations in the recorded noise image to be relatively low.

A comparison of optimum detector spatial resolution in nuclear imaging based on statistical theory and on observer performance.

An expression for the expected image of a spherical tumour in a uniform background was derived in terms of background thickness and concentration of radioactivity, the tumour size, depth and uptake ratio, the gamma-ray energy and the detector response function. Three models of human observer performance for tumour detection were developed from different signal-to-noise ratio measures based on the statistical theory of detection. The optimum detector spatial resolution predicted by each model was then compared to that obtained from an observer performance study in which the subjects viewed computer-simulated scintigrams. The predictions from two of these models seem to be consistent with the results of the observer performance study. Model II involves a comparison of the counts integrated over the tumour region with the counts integrated over a background region of the same area. Model III compares the count density estimates of signal-plus-background and background obtained from application of non-uniform weighting functions to the image data.

Gallium-67 scintigraphy in well-differentiated lymphocytic lymphoma of the skin.

Skin lymphomas are now divided into "T" or thymic cell lymphomas (mycosis fungoides being the principal type) and "B" cell lymphomas after the bursa of Fabricius. The "T" cell lymphomas all are identified by the thymic or cerebriform cell. Those lymphomas of the skin which do not contain these characteristic cells are derived from the bursa cells and are termed "B" cell lymphomas. A large percentage of these non "T" cell lymphomas have been histologically diagnosed as lymphocytic lymphoma of the skin (1). The authors had an opportunity to scan a patient with histologically proven lymphocytic lymphoma of the skin with Ga-67 and obtained on excellent correlation between gallium accumulation in the skin lesions and histologic confirmation of lymphocytic lymphoma.

Issues of imaging science for future consideration.

Acceleration of the emergence of imaging science as a new discipline will require the development of new organizational structures to foster research and educational programs that integrate components of the traditional disciplines, all of which stand to benefit. However, the greatest impact of imaging science will likely be from computer-based general educational programs that present both visual and verbal materials utilizing software that is not only interactive but also analytic, diagnostic, and adaptive in response to individual students. Ultimately, this powerful learning paradigm will have profound effects on all aspects of our culture. Imaging science will not have emerged fully until the conceptual, organizational, educational, cultural, and ethical issues it raises have been addressed.

Overview of imaging science.

The traditional disciplines of science are grounded in the observation and measurement of object properties. Recent advances in digital computer technology have spawned numerous computer-based imaging systems that extend the range of observation and measurement into realms that would otherwise be inaccessible. More importantly, the same set of principles, concepts, strategies, and methods may be used to address the generic issues involved in the production and use of all digitized images. Recognition of this fact is giving rise to the new discipline of imaging science, with its own intellectual agenda.