What is the ideal position that a subject should adopt during a thermography data collection? In today's article we will see the errors that are most commonly made when making thermal images. Continuing with the series of common mistakes in thermography data collection, we will see how to carry out a perfect legs protocol and, above all, what points must be respected.

Ideal position

The ideal position of the subject in a thermography data collection is relatively simple, since it only needs to meet 3 requirements, as shown in figure 1:

1. Parallel feet: to achieve this position, the subject must start from an intermediate rotation of the hips. It is very common for the subject to adopt a position in external rotation, which causes the feet to lose the parallel line. In addition, in a position of external rotation of the hips, the thighs are more likely to be in contact, which would prevent compliance with point 2.
2. Thighs without contact: this is another of the conflicting points in this protocol, since it is very common for the thighs to come into contact and, therefore, for the inguinal region not to be shown. It is common to find it associated with requirement number 1.
3. Hands behind the neck: when performing the leg protocol, the hands hang naturally at the level of the thighs, however, they should not cover any region of interest on the thigh. For this reason, it is advisable to raise the hands, so that they do not appear at this height and place them on the head or the nape of the neck, so as not to alter the temperature of the skin of the trunk.

Figure 1. Ideal position of the subject during thermography data collection in the lower anterior protocol. Thermogram (a), segmented thermogram (b), and avatar (c).

Hip rotation problems

These types of errors are usually found when the subject adopts an anatomical, natural or comfortable position, when asked to stand up to take data. Most people place their feet about 15° apart. However, the thermographic protocol insists on placing the feet completely parallel. In this way, we ensure that the protocol is standardized and allows comparison between different people and in the same person at different times. If each time a data collection is made, the subject is positioned differently, data cannot be compared, which is why it is so important to record this position. Figure 2 shows three of the most common incorrect positions:

Figure 2. Examples of different errors in the position of the subject in the thermography data collection. Excessive external rotation (a), asymmetric foot position (b), excessive internal rotation (c).

Touching thighs

By definition, the groin region must always be visible, which means that the thighs in the adductor region cannot be in contact. In most cases this is not a problem, however, in people with obesity or with a lot of hypertrophy of the quadriceps and adductors, to avoid this contact it will be necessary to ask the subject for greater abduction. In addition, as we saw before, excessive rotation, both internal and external, of the hips can cause premature contact in this region.

In figure 3 we can see examples in which the position of the subject does not respect the rule of no contact between thighs. In image 3a, we see a subject with the thighs in contact, which causes a relatively incorrect segmentation (see height of the knees). In image 3b, a complete contact of the entire lower limb can be seen, giving rise to an unprocessable image.

Figure 3. Examples of contact in the lower limb: contact of the thighs (a) and contact of the entire lower limb (b).

Hands that appear in the image

When taking data from the lower protocol, all the elements of the upper protocol must be left out of the image, including the hands. It is relatively common that in this protocol the hands hang naturally along the body, which can cause them to cover some region of the thighs. It is important to avoid it if we want to obtain the thermal information of the lower limb. In figure 4, we see how the segmentation is incorrect by including the hands within the regions of interest of the thigh. Obviously this leads to an incorrect thermal analysis, as the avatar demonstrates.

Figure 4. Error in which the hands appear in the lower image, producing incorrect segmentation (a) and, therefore, incorrect thermal data (b).

Conclusion of the position of the subject

As we have already seen in other articles in this series, the thermographic protocol ensures quality data collection. Respecting it allows us that the thermal information obtained after the analysis and its subsequent interpretation are based on reliable data. Or what is the same, committing any of these errors in the position of the subject necessarily produces a decrease in the quality of the thermal images, which considerably reduces the power of the thermography assessment.

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