Construcion of a functional image from spatially localized rate constants obtained from serial camera and rectilinear scanner data.

Abstract

SCANNING IS widely accepted as a means of detecting abnormalities in the regional function of certain organs. For example, labeled particles such as macroaggregates of albumin can be used to portray the regional perfusion of the lung. In a related manner, the distribution of colloidal particles reveals the reticuloendo-thelial function within the body, and the thyroid scan indicates the distribution of the function of iodide uptake. In these cases, the amount of radioisotope accumulated by a given region is an index of that region's function. In a sense, the scanning image may be thought of as a map of regional function. If we express this relationship between function and the amount of radioactivity in mathematical terms, it may be written as : F= (q).......(1) where F is regional function and q is the amount of radioisotope accumulated in the region. At times, regional function can be better measured by the rate of change. For example, regional blood flow measured by 133Xe washout from a region may be expressed as a rate constant k, assuming that the washout follows the equation Ae-kt. Measurement of ventilation by means of 133Xe, of hepatic blood flow by the rate of uptake of rose bengal, and of renal function by accumulation of chlormerodrin are other examples of this type of study. The general mathematical expression is : F = (q,t)..........(2) where F and q are the same as in Equation (1) and t is time. This is a more general relationship than that shown in Equation (1). When the relationship between function and the amount of radioisotope is expressed by Equation (2), the regional function is usually measured by placing a detector over the region of interest, producing a curve which shows the time course of the amount of activity. Spatial resolution is limited by the type and number of detectors used. Recently, both the Anger camera and the rectilinear scanner have been combined with quantification systems such as multi-scalers and paper punch or magnetic tape. These systems make it possible to record the amount of activity in small regions as a function of time and to store the data. Thus, when the rate of change with time may be expressed by Equation (2), it is possible to calculate the function of all regions separately and portray the results in the form of an image. Since the amount of data to be handled is large, it is helpful to use computer-processing methods. In this study we have applied these principles to the construction of an image from the values that represent regional function and we have obtained a new type of functional image. Material and Methods Quantification of the Data: The quantification of the scanning image was performed by the system developed in our laboratory, the details of which have been reported elsewhere (1).