7 errores frecuentes en la toma de datos de Termografía (Actualizado)

7 errores frecuentes en la toma de datos de Termografía (Actualizado)

08/17/2022 By : Alejandro del Estal Destacada

One the worst nightmares that a thermography user can have while analyzing a thermal image is receiving this notification, after making one or more of the 7 common mistakes during a data collection:

Figure 1: ThermoHuman’s notification when the image is unreadable.

As we saw in this post about this article, we all know that in order to perform a good quality thermography data collection, the thermographer must pay special attention to the acclimation time, the influence factors and… how to properly handle the camera while taking the pictures if we want to avoid problems like in figure 1.

This is why today we are talking about how not to make any mistake:

1. Horizontal or vertical?

Without any doubt, this is the most common mistake people usually make. Do I need to take the picture horizontally or vertically? Sometimes, it is necessary to choose one and some others, the other one. It all depends on the protocol you want to get analyzed. Whole-body protocols are vertical, while specific protocols are horizontal. Take a look at figure 2:

Figure 2: left side and center, shows the four whole-body protocols (blue) that must be taken with the camera in vertical position. Right side shows the four specific protocols (green) that must be taken with the camera in horizontal position.

So, you already know what is horizontal and vertical as an image. And figure 3 resumes how you need to place the camera depending on each situation.

Figure 3: the correct way of handling the camera in vertical (left, blue) and horizontal (right, green) protocols.

And what happens when I take the pictures the other way? For example, if a feet protocol (specific, so horizontal) is taken in a vertical position? You can see the result in figure 4:

Figure 4: ThermoHuman software tries to recognise feet as if they were in a horizontal position, but they are in a vertical position. Conclusion: disaster!

If you want to go deeper in the subject, click here.

2. Framing

Even if it looks quite simple, it is actually common to see this kind of mistake. Taking a thermal image is paying attention to so many things at the same time, that the most obvious ones are sometimes forgotten.

So, please, be sure that all the regions you want to be analyzed actually appear on your screen. Otherwise, your image will have no value. Take a look at figure 5 to see an example.

Figure 5: left: example of an incorrect framing that is unreadable. Right: example of a correct framing with its avatar analyzed.

If you want to go deeper in the subject, click here.

3. Focus

When you are taking a picture with your smartphone, realizing if it is blurry is flagrant, you can detect it in a glimpse of an eye. But thermograms are not like photos: detecting it is less evident because we are not used to seeing the world through this lens. But with two practical tips it will be more affordable.

The first image shows an example of a close focus (around 30cm, but the person is at 2,5m). The result is an obviously blurry image. As you can see in figure 6, this image cannot even be analyzed.

Figure 6: left: example of an incorrect focus that is unreadable. Center: example of an incorrect focus that is analyzed incorrectly. Right: example of a correct focus with its avatar analyzed.

The second image shows an example of focus on the background (around 3m, but the person is at 2,5m). The result is an image where you can see a slight green aura around the outline because the focus is on the wall behind the person.

The third image shows an example of a correct focus on the surface of the skin (around 2,5m, the same distance as the person is at 2,5m). The result is a clear image, where we can perfectly distinguish the profile.

In order to have the best focus, first of all, press the focus button pointing directly to the surface of the skin, always in perpendicular. In the example, we pointed to the knee.

Secondly, look at the outline of the person, if there is a green aura, it means the focus is in another distance (in the examples, closer and further). If this is the case, try to press again the focus button pointing to the knee to have a better focus.

If you want to go deeper in the subject, click here.

4. Vertical angle (the 90º rule)

We always talk about the fact that we have to be at the height of the middle of the image we want to photograph. What does this mean? If we want to take a proper thermal image, we should place the camera approximately at the level of the person’s chest. What if we want to take a picture of the legs? Attention! We will have to place ourselves at knee height, that is, we will have to kneel for it.

A very common mistake is standing up when taking pictures of the legs, like in figure 6: left. The problem is that from this height we will not be able to be at the same distance from the feet as from the hips, so the image will be incorrect. Notice the huge differences in the analysis when comparing the different angles.

Figure 6: left: example of an incorrect angle that is analyzed incorrectly. Right: example of a correct angle with its avatar analyzed.

If you want to go deeper in the subject, click here.

5. Lateral angle (the 90º rule)

As with the height angle, loss of perpendicularity can lead to unrealistic results. If we think about it, it is very logical, since if the person is slightly tilted with respect to the camera (as in figure 7: left), what is seen is not the front profile of the legs, but a more internal portion of the right leg and another external portion of the left leg.

Figure 7: left: example of an incorrect perpendicularity that is analyzed incorrectly. Right: example of a correct perpendicularity with its avatar analyzed.

During a thermography data collection, this common mistake is very frequent when we use a one-hand camera, such as the FLIR E8 or the FLIR E54-EST, since the lens and the screen are not perfectly parallel and that gives a false sense of perpendicularity that must be corrected manually, as seen in figure 8.

Figure 8: left: vertical-screen handling of the camera results in a non-perpendicular screen-subject angle. Right: handling the camera with the lens in vertical makes a 90º screen-subject angle.

If you want to go deeper in the subject, click here.

6. Subject position

The position in which the subject is placed is extremely important, since it is from a standardized posture that the automatic segmentation is performed. This means that if any of the protocol instructions are not respected, the analysis may not be correct. In the example in figure 9: left, we can see that the subject has the legs more closed than the below subject. This makes the thighs touch and modifies the segmentation causing the rest of the regions of interest to be positioned incorrectly.

Figure 9: left: incorrect position with the legs too close and the thighs in contact; all the ROIs are not segmented properly. Right: correct position with the legs well separated and the ROIs properly segmented.

This applies to all other postures. For example, in the upper protocol, this error is seen in the armpit: if the arm touches the trunk, the segmentation is done incorrectly.

To avoid this type of error, it is important to adhere to all the ThermoHuman data collection protocol specifications.

7. Underwear

And the last frequent problem is related to underwear and shorts. When the pants are placed too low, the software will analyze the temperature of the pants, not the skin. Actually, that data does not interest us, since what we need to know is the temperature of the skin that is immediately below.

In addition, there is one more problem associated with the latter: when the underwear is placed asymmetrically. This causes comparisons to be made between the temperature of the clothing and that of the skin. The result is a disaster.

Figure 10: left: the shorts are covering the skin, that means the analysis is not correct. Right: analysis is perfectly correct, as all the regions segmented are exposed skin.

This is what we can see in the example in figure 10: left, where the left leg of the shorts is below the adductor line and is also asymmetrical with respect to the right. This produces an important asymmetry, but not at all significant: it is not real, because it does not compare skin to skin, therefore useless as a measurement.

The easiest way to solve this problem is to be sure to roll up the sleeves above the horizontal line of the adductors (the point where the thighs touch themselves). Thus, we ensure a quality measurement.

If you want to go deeper in the subject, click here.

Conclusion

As you may have imagined, it is not very difficult to fulfill each of the points separately. The complicated thing is to do it with all the requirements at the same time. If so, you have gathered good quality information, then the analysis will depend on the metrics.

But do not give up the first time, it is nothing more than a matter of practice. No one was born knowing.


If you have any questions or would like to make a comment, do not hesitate to write to us. We will be happy to read you.

Europa Thermohuman ThermoHuman ha contado con el apoyo de los Fondos de la Unión Europea y de la Comunidad de Madrid a través del Programa Operativo de Empleo Juvenil. De igual manera ha participado en el Programa de Iniciación a la Exportación ICEX Next, contando con el apoyo de ICEX y con la cofinanciación del fondo europeo FEDER.

CDTI ThermoHuman ha recibido financiación del Centro para el Desarrollo Tecnológico Industrial (CDTI), con la participación del Fondo Europeo de Desarrollo Regional (ERDF), para la creación de una nueva herramienta basada en termografía para la prevención y predicción de artritis reumatoide. Ver detalle del proyecto.