So what exactly is the problem with just guessing?
So you’re taking an X-ray but you’re six feet away with a field of view no larger than your pen and you can’t touch the patient who is covered with a towel and so is your X-ray machine: welcome to theatre radiography!
Radiographers in theatre have traditionally used their intuition and experience to guess how far and even in which direction to move the C-arm with varying results. In addition they consider the anatomy of the image and relate this to the patient to see which way they need to move. This technique results in a lack of control with repeated images being taken and missing being seen as quite normal.
Unfortunately screening in theatre is not like driving a car. It would be if the view through your windscreen was sometimes the wrong way around and the wrong way up, whilst distances appeared doubled or tripled and you were peering through a small porthole that showed where you were some moments ago. So driver style 'look and go' is not the best way to manoeuvre your C-arm.
Whilst considering anatomy can be extremely helpful it is also sometimes not. There are many near symmetrical structures in the body which give little or no indication of direction from left to right. Spine and pelvis, long bones in the mid-section etc. Even the radius and ulna cannot be relied upon when the surgeon flips and rotates them causing confusion about which way to move.
In the foreseeable future laser centring will make it much easier to stay on target for extremity positioning. For now however most lasers are simply not bright enough to be visible under direct theatre lighting. Lasers also have more limited success in pinpointing the area of interest for examining the trunk and hips, a lot of our work in Orthopaedic Theatre Radiography.