Our ‘P1-Alignment’ Method
It can be difficult to take a good DP radiograph (for measurement purposes) when horses are ‘toed-out’ or ‘toed-in’. How can we best align the x-ray generator and the x-ray detector panel with the leg? After looking a lots of terrible DP radiographs for a couple decades, we developed the P1-Alignment scheme. The nearly-vertical blue line on our report image is easily found and well defined by the shape of the P1 bone. We claim that if the blue line is perpendicular to the nearly-horizontal green line at the distal end of P2, then the image was ‘well-taken’.
Because the P1 bone slopes away from the x-ray generator, the blue line has a significant component from front-to-back of the leg. As one rotates the x-ray generator around the hoof - that line will go out of perpendicularity with the green line. If the generator is around too far to the medial side of the hoof, it tilts one way, if it’s too far to the lateral side of the hoof, it tilts the other way. When the blue and green lines are perpendicular, the generator is perfectly aligned with the boney column.
To prove this assertion, we studied about 5,000 DP radiographs taken by many different practitioners located in many countries around the world. These images were taken without the guidance of our P1-Alignment scheme, as it hadn’t been published yet. We computed the distribution of our P1-Alignment metric as seen in these 5,000 images. We found that the median value of P1-Alignment was 0.017 degrees! Very close to zero! What does this mean? It means that practitioners are trying to align in the way we describe - some miss to one side, some miss to the other side, but on average they seem to be trying to hit the value of ‘P1-Alignment’ being zero. So, we do not believe we are suggesting anything strange or new when using the P1-Alignment to tell you if you’ve taken a good shot - its what practitioners have always been aiming for. Since its computed for you automatically in Metron-IQ it is a win-win!