In diseases such as hydrocephalus, the cerebral ventricles enlarge. The treatment options for these patients are presently based on pressure, which has limited capabilities. We present the design of a volume sensor as an alternative monitoring option. Through the use of computer aided design and simulation, we optimized a sensor in silico with fewer resources. Specifically, we designed a sensor for animal experimentation with a scalable procedure for human sensors. In this paper, we present a rational design approach for a sensor that integrates advances in medical imaging. Magnetic resonance data sets of both normal and diseased subjects were used as a virtual laboratory. Finite element simulations were performed under pathological disease states of the brain as a contribution toward an accelerated device design. An optimized sensor was then fabricated for these subjects based on the outcome of the simulations. In this paper, we explain how a computer aided subject-specific design was used to help fabricate and test our sensor.