Orthogonal tangent correction (OTC) is in troduced as an improvement of the processing technique for transverse section imaging. The initial step in this processing technique is to take an orthogonal pair of tangent data lines and form a matrix distribution that reflects the proportionality that exists between them. The matrix data are then redistributed to conform to the proportionality of each succeeding or thogonal pair of tangent lines without destroy ing the compatibility achieved in previous steps. The final section matrix is a high contrast image of the cross-section, the matrix distribution is compatible with all tangent values, and there is a linear relationship between matrix counts and radioactivity in the scanned object. We have already applied Orthogonal Tangent Correction to clinical brain scanning with advantage but we regard its more important role to be as an other significant step toward quantitative imag ing for estimate of radioactivity localised in three dimensions.