 Pressure recordings of the injected fluid will be obtained using disposable off-the-shelf sterile pressure transducers which are typically used for intracranial and arterial pressures monitoring readily available in the operating room. First, the surgeon will attempt to flush the catheter using the Alcyone in-line Flusher device. If this fails, the surgeon may elect to attempt to flush using a standard syringe attached to the catheter. The flow rates will be measured by video, recording the syringe during the flushing maneuver, and then extracting plunger motion information by applying image processing on the acquired videos. In the event the recording equipment is not available in that these operations are usually unscheduled and sometimes urgent, the same irrigation techniques may be used without the pressure recordings. 