What is ‘calibration’ exactly and why is it so important?
Imagine you’re driving along the road and your speedometer is not working properly. You look at it and it claims you’re moving along at 30 mph. But you notice that everyone else is driving past you and you seem to be going too slowly…
This probably indicates that your speedometer is no longer properly calibrated. The original calibration will have happened in the manufacturing process. A device will have matched the speedometer settings (numbers) with the appropriate speed (to within an acceptable margin).
The same occurs with lasers. These must also be calibrated so we know how much energy is being delivered to the skin during treatments.
So, if you want to deliver, say, 25 J/cm2 to the skin, then you would choose this fluence on your device’s screen. But, if your device has not been properly calibrated, how will you know what is really being delivered?
What does the calibration process involve?
To properly calibrate a laser you need to measure the output energy for each input level. To do this we set the device to its lowest setting – this might be 10 or 50 or 100 on your screen. It really doesn’t matter – those are just ‘random’ numbers.
Then we fire the laser into a meter and record the energy (I usually fire five shots). Next we increase the screens setting to the next level and repeat the energy measurements. We continue this process until we reach the maximum output level for the device.
Below is an example table of measurements:
| Device Setting | Measured output energy (mJ) |
| 50 | 0.1, 0.1, 0.095 |
| 100 | 0.13, 0.131, 0.134 |
| 150 | 0.18, 0.174, 0.181 |
| 200 | 0.22, 0.21, 0.23 |
Now we need to measure the spot sizes for each energy level. I use photo paper and fire a few shots at it. The burn patterns can be used to find the diameters of each spot for each energy level.
So now we have a table of energies and spot diameters for each setting on the screen.
Using the formula for energy density (or fluence), we can then calculate the fluences which correspond to each setting in the device – see table below:
| Device Setting | Actual Energy Density (Fluence – J/cm2) |
| 50 | 1.1 |
| 100 | 1.6 |
| 150 | 2.3 |
| 200 | 2.9 |
| 250 | 3.5 |
Now, we have a table (which can be presented as a graph, if required) which indicates the actual fluence delivered to the skin for each setting on the screen.
The device is now calibrated…
This calibration will change over time as the flash lamp loses efficiency – as it will with use. It is for this reason that calibration should be done regularly – either with every service visit, or more often if the device is used often.
Here’s a calibration chart I made earlier…
Clinical endpoints
How can you tell if your device is running ‘low’?
Well, usually your patients/clients will begin to report a lack of progress or pain or any sensation. But, you should be able to spot it before this happens. When treating many skin conditions, you will usually see some erythema (a reddening appearance) soon after applying the light energy (usually within 60 seconds, or so). If you don’t see this, then it’s likely there is not enough energy reaching the targets.
Also, in many cases you will also see some swelling of the area soon after treatments – although this can take a few minutes to be obvious.
These two clinical endpoints are very common after many laser/IPL treatments. They indicate that the skin is reacting to the light energy.
If you don’t see them, then either your device is incorrectly set by you, or, it is not generating sufficient energy output. Either way, you need to remedy the situation, otherwise you will not get good results.
Conclusion
What this tells us is that calibration is very important. Without it, we cannot know what is actually being delivered to the skin. Nor can we be sure that we will achieve good clinical results.
Hope this helps,
Mike.
PS Ournext MasterClass is in Luton in September. There are only a handful of places left. If you wish to attend, please email Lisa.dermalase@gmail.com.
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