QUANTIFICATION OF THE EFFECTS OF RESPIRATION AND PARALLAX ON INFERIORVENA-CAVAL FILTER POSITION

PURPOSE: The change in inferior vena caval (IVC) filter position at fo llow-up relative to the filter position at implantation has been used as a criterion for evaluation and comparison of these devices. Perceiv ed changes in filter position may be due to respiratory movement and/o r changes in parallax between the initial and follow-up imaging studie s. In this study the authors evaluated and attempted to quantify the e ffects of respiratory movement and parallax. PATIENTS AND METHODS: Aft er placement of an IVC filter, radiographs of the abdomen were taken a t maximum inspiration and maximum expiration in 30 patients. The effec t of parallax on apparent filter movement was studied by using a phant om. RESULTS: The average filter movement on inspiration/expiration rad iographs (corrected for magnification) was 3.6 mm +/- 2.2. An 8.5-mm m aximal change secondary to parallax was seen in the phantom study. CON CLUSION: When follow-up images are obtained, efforts should be made to closely reproduce patient positioning and patient respiration to redu ce errors in the interpretation of filter migration.