The flat panel detector is an array comprising a plurality of pixels in the form of a matrix. Each pixel comprises scintillating layer in contact with an array of photo diodes which converts impinging X-ray signals to charge signals. A semiconductor switch is used to select the rows read from the detected charge signal at the flat panel detector. A two dimensional image is produced by the flat panel detector of an object radiated by the x-ray source. This two-dimensional X-ray image is converted to an electric signal for imaging analysis and displaying. During read-out of the X-ray detector, rows of transistors are turned on sequentially, and an entire row of detector elements is read out at the same time.
Because of imperfections in the transistors, a time-dependent background current is generated when the transistors are turned on and off or as is commonly know as switching states. The result is an offset signal that is unrelated to X-ray exposure. The offset signal is typically referred to as switching charge retention. Since the rows are read sequentially, a portion of the switching charge retention is row correlated or roughly the same for all elements in a given row, but varies from row to row. However, the switching charge retention for a given row changes with the frame rate of the imaging system.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for reducing signal conversion time by adjusting for offset signals. There is also a need for improving x-ray images through offset correction.