Correct Use of the Calipers

Calipers are used to measure the thickness of an anatomic part. This measuring tool is nothing more than a ruler with a fixed bar and a moveable bar parallel on it. The upright portion along with the moveable bar moves is marked in both centimeters and inches. Be certain to read the centimeter scale when using the caliper as the technique chart is based on centimeter readings. To use the caliper the thickest portion of the anatomic part to be rediographed is placed between the two bars. The moveable bar is moved to allow the bars to lightly fit around the part being measured. Always read the scale at the point just below the moveable bar. Do not read the scale above the moveable bar, as this produces an erroneous reading.
There is an example of how the caliper is used. Suppose the carpal, or wrist joint, of a dog is to be radiographed. The two views requested are AP and ML. First the right carpus is placed between the two bars with the leg in the AP position. The stationary bar is behind the joint, and the moveable bar rest lightly on top of the joint. Suppose the lower edge of the moveable bar rests on the centimeter scale at 3 cm. Record the measurement in centimeters under the “cm�?area of the logbook and the direction AP in the “view�?section of the same row. After taking this first radiograph, measure the joint again but this time the stationary bar is on the medial side of the joint, and the moveable bar rests on the centimeter scale. This time the reading might be 5 cm because the carpus is usually wider than it is thick. Record the masurement of 5 cm and the direction of measurement which is ML in the logbook. Use this information to set the exposure tactors in the x-ray machine using the technique chart. Record that information in the same row with the patient’s name, other data, and the “view�?and “cm�?information.
Remember to keep the caliper near the logbook so it is readily located when needed. There is a temptation, as expertise develops, to “eyeball�?a patient rather than actually use the calipers. This only lead to poor quality films and more frequent retakes. Time is actually saved by taking a few moments to measure each anatomic part and for rach direction. Always remember to measure the thickest portion of the area being studied. Correct use of the calipers serves as one of the fundamentals leading to quality films.
Preparation
1. Have patient at hand.
2. Confirm patient identity.
3. Confirm studies requested.
4. Review patient positioning.
5. Locate calipers.
6. Locate logbook and pen.
Procedure
1. Place the fixed portion of the caliper at the site the beam is to exit.
2. Slide the moveable bar over the site the beam is to enter.
3. Move the caliper along the study site to the thickest portion of the area.
4. Read the centimeter scale at the portion of the moveable bar closest to the patient’s body.
5. Record the measurement in “cm�?and the ”view�?in the logbook on the same row as other data from the patient.
6. X-ray the patient.
7. Repeat the process above for the second radiograph taken, except the second view is perpendicular to the first radiograph.
Follow-up
1. Always return the caliper to the same place after use.
2. Always record both the measurement and the view for each film.