Final answer:
To compensate for the addition of an 8:1 grid to the original non-grid exposure settings, the milliampere-seconds (mAs) must be multiplied by the grid conversion factor of 4. The new mAs value will be 16 mAs.
Step-by-step explanation:
The question asks for the new mAs value to be calculated if an 8:1 grid is added to the original non-grid exposure settings of 90 kVp and 4 mAs. In radiographic imaging, when a grid is added, the mAs must be increased to maintain image density, because grids absorb scattered radiation but also some of the useful radiation, thereby requiring more exposure to achieve the same effect.
To calculate the new mAs when using a grid, we use the grid conversion factors which are specific multipliers that correspond to the type of grid used. For an 8:1 grid, the common conversion factor is 4. This means the original mAs value needs to be multiplied by 4. Hence, the new mAs would be:
Original mAs × Grid conversion factor = New mAs
4 mAs × 4 = 16 mAs
This is the required mAs when using an 8:1 grid based on the initial non-grid technique.