Chiropractic Radiology

Setting Up a Technique Chart

By Deborah Pate, DC, DACBR

What do you do when you get a new or refurbished x-ray unit or new cassettes? Many times we will not receive advice or we'll be given a technique chart that never comes close to giving us optimum results with our individual machine. Don't panic, all is not lost; you won't need to retake the next 10 series. First, go dig out your old Super-Tek or Reed x-ray technique computer you had in chiropractic school. Then make certain your processor is working perfectly. Many times poor films are the result of processing problems, not the technique of the x-ray unit. Once you are certain you have no processing problems, you're ready to start setting up a technique chart.

The following is an outline of the standard procedure for developing a technique chart for an individual machine. First, remember that kVp is the only factor that controls contrast, therefore the easiest way to decide on what factors to use is to set your kVp and vary the mAs according to the thickness of the part. The optimum kVp values have been published in numerous books on x-ray technique and vary little from author to author. A shorter version of a grid-ratio chart is provided at the end of this article and should serve only as a guide for choosing the optimum technique for your individual x-ray unit.

Now you have a grid-ratio chart and Reed computer or Super-Tek in hand; all we are missing is a phantom to use as a standard. If you can't afford a $2,000 x-ray phantom, your CA will do, as long as she will volunteer and she is 22 to 24 cm at the central ray and between the ages of 15 to 55 years. Next take three films, one each at 30 mAs, 60 mAs, and 120 mAs at the kVp suggested by the grid-ratio chart. Develop these films at maximum time temperature factors, according to the manufacturer's recommendations. Choose the film that best fits your estimate of diagnostic quality. If none of these are quite to your liking, adjust the mAs accordingly.

If you are using the Super-Tek, you should now be able to set the correction factor inherent to your x-ray machine. Once this is determined, you can match the kVp to centimeter thickness and according to the type of screens you are using, the appropriate MAS factors can be found on the back of the slide. If you have a Reed slide rule, follow similar instructions for developing a technique chart. Two points need to be remembered: (1) The kVp constants on the grid-ratio chart were developed to be used on persons between the ages of 15-55. For older persons or postmenopausal females, an eight percent reduction in the kVp level will provide a better film contrast. (2) If it is necessary to adjust the mAs or kVp, a 25 percent change in mAs and a four percent change in kVp are necessary to produce a visible change on the radiography.

If you still have problems with developing your own technique chart or with film quality, consult an expert; there are numerous reasons for not obtaining quality films.

Grid-Ratio Chart
Grid	6:01	8:01	12:01	16:01
AP Lumbar or Pelvis:	75	80	90	105
Lat. Lumbar	85	95-100	100-115	105-125
AP Thoracic	75	80	90	105
Lat. Thoracic	75	80	90	105
AP Cervical	70	75	80	105
Lat. Cervical	70	75	85	105

Deborah Pate, DC, DACBR
San Diego, California

---

Click here for more information about Deborah Pate, DC, DACBR.