Abstract: In conventional backprojection, each pixel value is calculated separately. With N pixels N.sup.3 additions are necessary. According to the invention, the summation is instead divided into partial sums which are then used to form new partial sums in a hierarchial way. A substantial computational reduction is obtained because a partial sum has approximately the same value for many neighboring points, and that interpolations are feasible. Instead of N.sup.3 additions, the number of additions can be reduced to the order of magnitude of N.sup.2 log N.

Abstract: An in vitro method of evaluating the antagonistic versus agonistic effects of a receptor-binding test substance on a selected type of cells containing endogenous intra-cellular hormone receptors, is disclosed. Said test substance, and separately a reference substance, known to be either an antagonist or an agonist, are incubated with said selected type of cells, and the magnitude of the selected cellular response resulting from hormone/receptor interaction, is analyzed. In case the method is performed on at least two selected types of cells which derive from different kinds of tissues, it is possible to evaluate the pattern of antagonistic versus agonistic effects of the selected test substance on said kinds of tissues.

Abstract: A test dummy head for measuring impact surface forces and pressures applied thereto comprises a pressure-sensing face incorporated to a dummy skull structure. A plurality of thin pressure-sensitive electric films are attached to the face. The films provide electrical signals representative of a time history of pressure or force applied up to 100 individual areas of the face. A pressurized calibration chamber is employed to simplify the calibration process.