New method for volumetric estimation of functioning thyroid tissue

摘要

99m-Tc-pertechnetate SPECT studies of thyroid phantoms, with volumes in 13-198 cc range, and of a number of patients were performed. A modified reconstruction and analytic methods were applied to the data analysis. It involved: (1) transformation of the initial ECT data by a suitable mathematical function to compress the dynamical range of the data; (2) tomographic reconstruction resulting in transaxial (TV) images; (3) decompression of TV images via a reverse function; (4) Gaussian smoothing of the decompressed TV (dTV) images; (5) subtraction of a Compton dTV images from photopeak dTV images, (6) parallel operation on dTV images: Sobel edge detection and impulse filtering; (7) combining the filtered images via the AND operator; (8) edge tracing in the combined image by a human operator; (9) volume estimation by a computer. Based on the phantom studies it was established that the proposed technique yielded volumes with the relative error not exceeding 10%. For patient studies, the obtained volumes were also compared with palpation estimation. It has been found that inter-observer variability of the thyroid volume estimate is a function of physician's experience in utilization of manual palpation and it may result in the relative errors exceeding 50%.