The most widely used architecture in large area amorphous silicon (a-Si) flat panel imagers is the passive pixel sensor (PPS), which consists of a detector and a readout switch. While the PPS has the advantage of being compact and amenable towards high-resolution imaging, reading the low PPS output signal requires external circuitry such as column charge amplifiers that produce additional noise and reduce the minimum readable sensor input signal. This work presents a voltage mediated active pixel sensor (APS) on-pixel readout circuit for diagnostic medical imaging to minimize external component count and hence external readout noise sources. Preliminary results indicate excellent APS linearity along with a pixel readout time suitable for mammography or radiography.