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

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.