Focal Artefacts in Skeletal Scitigraphy
Objective: to clarify and systematize the causes that can induce focal artefacts in skeletal scintigraphy with <sup>99m</sup>Tc-pyrophosphate (PyP), their semiotics, principles and methods of differentiation from bone pathology. Material and methods. Results of skeletal scintigraphy from 1568 patients were analyzed. Scanning in “whole body” mode started in 3 hours after 740 MBq of radiotracer activity intravenous administration, and performed in anterior and posterior projections in continuous table motion mode at rate of 12 cm per minute. Single photon emission computed tomography/computed tomography was additionally performed when necessary. Results. Focal artifacts were detected in 40 patients (2.55%) and were divided into “cold” and “hot” according to the nature of the bone system changes they simulated. “Cold” spots (n = 29) were the result of the shielding effect of metal accessories (n = 10), implants, endoprostheses (n = 18), and barium suspension residues in the large intestine (n = 1). “Hot” spots (n = 11) mimicking metastatic lesion of bone structures were the results of the projection effect of extraosseous uptake of <sup>99m</sup>Tc-PyP (n = 9) or urinary contamination (n = 2). “Hot” spots in the projection of the upper pole of the kidney (n = 5) could be the result of both calicostasis (n = 3) and injury of the adjacent rib (n = 2). The high uptake of <sup>99m</sup>Tc-PyP in thyroid nodule (n = 3) simulated a “hot” spot in the lateral part of the cervical vertebra. Abnormal accumulation of <sup>99m</sup>Tc-PyP in the nipple-areola areas of the breast was projected onto the posterior segments of the ribs. Urinary contamination imitated focal pathology of the pelvic bones. To differentiate the focal pathology of the ribs and calicostases, the patients were examined in the standing position. The “mask in” program was used to clarify the localization and projection correspondence of “hot” foci. Conclusion. Analysis of focal artefacts formation causes in skeletal scintigraphy contributes to an adequate assessment of the data obtained, allows to choose the necessary method for their diagnosis and to avoid false results of osteoscintigraphy.