Magnetic resonance imaging analysis of extremely slow flow in a model shunt system.

Abstract

Shunt malfunction is common and its diagnosis may require invasive testing that may be inaccurate or result in complications. Magnetic resonance imaging (MRI) may prove to be a useful noninvasive test of shunt function as it has been shown that MRI is capable of measuring cerebrospinal fluid (CSF) flows from 2 ml/h to 40 ml/h in model systems. Since flows in functioning shunt systems can be less than 2 ml/h, MRI must be sensitive enough to detect flow in this range in order to be a valid test for shunt function. Continuing previous studies, we have studied MRI flow-related enhancement at flow rates from 0 to 2 ml/h. Multiple spin echo scans (TR2000, TE20) were made through a specialized section of tubing in a model shunt system. The intensity of the MRI signal at points known to demonstrate maximal flow-related enhancement was measured. A linear relationship was demonstrated between signal intensity and flow as low as 0.8 ml/h. These results add support to the concept that MRI is sensitive enough to detect the lowest flows present in functioning shunt systems and therefore may be useful as a noninvasive test of shunt function.