A device for improved on-line histogramming of data acquired in a Positron Emission Tomography (PET) scan. The device is a Smart DRAM (SD) PCI card, of which more than one can be used in combination within a PC-based architecture for on-line histogramming. The SD PCI card is applied as either of a Gating Buffer, a histogramming card, and a normalization buffer. The Gating Buffer card alternately stores an arriving PET data packet stream into two dedicated DRAM banks. The two DRAM banks store and retransmit the packet stream in the order of arrival for an entire physiological cycle. The histogramming SD RMW PCI cards provide a very high rate of histogramming. The extendible daisy-chain of SD RMW PCI cards supports large memory banks across potentially hundreds of SD RMW PCI cards. Under a single PC, a multiple PCI Expansion chassis is employed such that a large number of PCI cards are supported.