Information For Radiographers

Room or table dependent

We would advice that each ruler is marked for which room or table it was designed. Using a ruler with a different cut-off point in another room will introduce a magnification error. Wolverson provides an engraving service.

Film Focus distance control essential

It important for the radiographers performing the calibration procedure to understand that the X-CalibR ruler was designed for 120cm film-focus distance. Not sticking to the protocol will introduce an unknown accuracy error which will adversely affect the orthopaedic templating procedure afterwards.

Dish edged table protocol

Pressing the ruler into a soft mattrass will introduce a variable error. We recommend the ruler base is always placed on a hard surface. If a ruler was specified to be used from the dished top (see Ordering), then this should be highlighted in the protocol.

Error introduced by rounding to the nearest matching ruler

Ideally each ruler should be cut to compensate for the exact table to detector distance. The error introduced by selecting from 3 different pre-cut rulers is in a worst case scenario 1 cm at any point on the ruler scale. A 1 cm distance anywhere on the ruler (the scale is non-linear) introduces less than 1% error. Ruler can be cut to a customer specified length.

On the use of grids

For accurate measurements X-CalibR has to be used at 120cm FFD. Obviously this is not a problem when using without a grid but some users may be concerned if they have grids in their tables that are focused to 100 or 110 cms. This should not cause a problem as a 100cm focus grid will tolerate FFDs of 90 – 120cms and a 110cm focus grids will tolerate 100 – 130cms. If the X-CalibR is to be used with a vertical Bucky users must check the focus length of the grid as some are fitted with 150cm focus grids or even 180cm focus grid for chest work. A 150cm grid should just be OK with 120cms FFD. It would not be possible to use 120cm FFD with a 180cm focus grid as it is out of its range but this is not a common grid in vertical Buckys.