The physical components of the device will consists of: movable X ray generator and cassette holder, the x-ray tube, movable patient table unit, the collimator, wireless flat-panel detector, the Bucky film tray and grid system. Technical characteristics will include digital display of mAs and kV, and an electronic timer, kV range at least 50 kV to 150 kV, digitally displayed, mA range at least 0 to 600 mA, Exposure time range at least 1 ms to 5 s, Automatic exposure control facility, Tube power rating at least 60 kW, Resolution to be better than 5 line pairs / mm, a rotating anode with focal spot size less than 1mm, Heat storage capacity of the anode at least 350,000 HU, and Adjustable multileaf collimator, rotatable ±90 deg with patient centering.
Plain X-ray imaging uses a single kilovoltage beam generated by a normal x-ray generator. The beam passes through the target and is attenuated by the tissues. It then strikes radiographic film where it causes a chemical reaction to occur, leading to image production.
Due to the kilovoltage energies used, plain x-rays are attenuated predominately by the photoelectric effect. Attenuation is therefore related to the cube of the atomic number (Z3). In human tissues, this leads to a marked difference in attenuation between soft tissues (Z ~ 8) and bone (Z ~ 13). This is seen on the image, where bone causes significant attenuation, soft tissues cause fewer attenuation, and air/lung cause minimal attenuation.
The radiographic film is covered by a filter which reduces the amount of scattered x-rays which can cause a chemical reaction. Coherent scattering is more common at very low kilovoltage energies and can reduce image contrast. The film itself is a polyester sheet covered with a silver bromide (Ag+ Br- ) emulsion. When ionising radiation interacts with the emulsion, free electrons may be captured by the silver ion, forming a stable silver atom. This atom comes out of the solution and attaches to the polyester film. When treated, areas exposed to ionising radiation will appear darker on the film due to the silver atoms.
X- rays have a wavelengths in the range of 10^-8 m to 10^-11 m (10nm – 0.01nm). Their frequency range is 3x10^16Hz to 3x10^19Hz.