Rapid computed tomography technique to measure ventricular volumes in the child with suspected ventriculoperitoneal shunt failure I. Validation of technique with a dynamic phantom.

OBJECTIVES

Assessment of ventricular volume change is critical and can be difficult in the child with suspected shunt failure. Objective techniques described to measure ventricular volumes have used limited anatomic sampling or have been computationally intensive. Phantoms used to evaluate these techniques have used static volumes. The purpose of this study was to construct a computed tomography (CT) phantom to simulate changing ventricular volumes and to evaluate a new program to measure volumes.

METHODS

The phantom is 5 Foley catheters embedded in gelatin. The balloons were filled and then scanned at 15-mL increments from 0-300 mL. The program measures the voxels of specified density within a larger volume created by applying a region of interest to a stacked volume. Calculated volumes and percent changes were compared with actual volumes and percent changes.

RESULTS

Calculated volumes were consistently 7%-9% (mean: -7.8%) less than actual injected volumes across the entire 0- to 300-mL range. For true changes between -50% and +50%, all calculated changes were within +/-2.5% points of true percent change; for true changes between +50% and +100%, all calculated changes were within +/-5% points of true percent change.

CONCLUSIONS

A dynamic CT phantom simulating changing ventricular volumes can be constructed from readily available materials. A new volumetric program accurately measures ventricular volumes and percent change from baseline across a wide range of volumes.