Quantification of the effects of respiration and parallax on inferior vena caval filter position.

Purpose: The change in inferior vena caval (IVC) filter position at follow-up relative to the filter position at implantation has been used as a criterion for evaluation and comparison of these devices. Perceived changes in filter position may be due to respiratory movement and/or changes in parallax between the initial and follow-up imaging studies. In this study the authors evaluated and attempted to quantify the effects of respiratory movement and parallax.

Patients And Methods: After placement of an IVC filter, radiographs of the abdomen were taken at maximum inspiration and maximum expiration in 30 patients. The effect of parallax on apparent filter movement was studied by using a phantom.

Results: The average filter movement on inspiration/expiration radiographs (corrected for magnification) was 3.6 mm +/- 2.2. An 8.5-mm maximal change secondary to parallax was seen in the phantom study.

Conclusion: When follow-up images are obtained, efforts should be made to closely reproduce patient positioning and patient respiration to reduce errors in the interpretation of filter migration.