IPL, Laser and LED: Dosimetry

Dr Caerwyn Ash, PhD

Advanced Research Scientist

1. CyDen Institute of Light Therapy

2. School of Medicine, Swansea University, UK

Intense Pulsed Light Systems

How They Work! • Flashlamp based system

• Visible light heat highly absorbing melanin in hair without

heating surrounding tissue matrix.

• Pulses within a time duration typically 10’s milliseconds

• Optical filters are used to attenuate harmful wavelengths

• Acne Vulgaris

• Hair management – now also on dark skin

• Photodamage Types I, II, (and III with PDT)

• Vascular lesions

• Pigmented lesions

• Psorasis

• Creams and potions

• Breast Firming

• Alopecia

Treatments IPL based systems are becoming increasingly more versatile treatment devices

Absorption of Chromophores

Absorption of Chromophores

These published papers expose

some of what we don’t know:

Measuring key parameters of intense pulsed

light (IPL) devices

Town G, Ash C, Eadie E, Moseley H. J Cosmetic

Laser Therapy 2007; 9:3:148-160.

Relevance of the structure of time-resolved

spectral output to light-tissue interaction using

intense pulsed light (IPL)

Ash C, Town G and Bjerring P. Lasers in

Surgery and Medicine 2008; Vol 40:2: 83-92.

Key Parameters

Fluence – Energy density (J/cm2)

Spectral Distribution – intensities of the range of

wavelengths

Pulse duration – the total period of light emission

Beam profile – is the distribution of discharged energy

across the treatment area

Lamp discharge profile - is an important factor as it

bears importance to the change in fluence with the pulse

duration

Time resolved spectral data – shows the change in

spectral distribution and fluence with time

Interaction of Key Parameters

Measurements made for

Comparison Study

• 18 different devices from 15 different manufacturers and 36 applicators (different cut-off filters) from USA, UK, Israel, Sweden, Switzerland, China and Italy were tested by the authors.

• Data on fluence, pulse duration, pulse structure, cut-off filters and UV content was gathered on-site between patient appointments over a 6-month period in clinics where devices were in daily use.

• Manufacturers’ information was collected from user manuals, company web sites and literature for verification.

Flashlamp Physics

• IPL light source is a handmade flashlamp

• A flashlamp deteriorates with every discharge

• Manufacturers limit shot life to prevent energy

decreasing to become clinically ineffective

Comparing Fluence Values

30 IPL applicators were measured at maximum fluence of which

11 were more than 20% below and 8 were more than 10% above

fluence levels given on the device display or claimed in user

manuals, even where brand-new lamps were tested.

Comparing Fluence Values

9 IPL devices out of 18 had applicators that were outside of the standard for medical Class 4 lasers (> +/-20%)

Filter Performance

•Good, sharp 530 nm cut-off filter

• No significant UV.

• Spectrum analysis of light contains

• Discrete line structure

• Continuum radiation.

• Filter position measured different to that

stated

Filter Performance

• Patient dissatisfaction can be caused

epidermal damage caused by significant UV or

blue content.

• Dichroic filters become damaged through long

term use by high energy IPL systems

overloading a thin dichroic coating.

Filter Performance

• Epidermal damage produced by significant UV / blue spectral

content, caused by degraded filter

• Injury causes pain and discomfort - dissatisfaction to patient

• Possible legal proceeding against salon/clinic

Comparing Electrical Discharge

• Only three systems measured possess a square pulse discharge

• Three systems proved not to have a square pulse

• Most systems utilise simple free discharge

• Others delivery methods stack pulses together to extend pulse duration

Comparing Pulse Duration & Structure

• Only 14 out of 29 pulse duration measurements were

within ±20% of the manufacturers stated or system

displayed values.

• Photodiode measurements of total pulse duration did

not disclose where the effective spectral output

occurred during the pulse.

• Several manufacturers claimed ‘square pulse’ output

without explaining its significance.

• Several manufacturers ‘stacked’ sub-pulses

to achieve a ‘biological’ square pulse.

Digital Revolution

Time-resolved spectrum sampled every 1 ms using an Ocean

Optics HR2000+ spectrometer and SpectraSuite software to

demonstrate the stability and efficiency of spectral output for

free-discharge vs. square pulse systems

Free Discharge Square Pulse

Comparing Time-Resolved Spectral

Output

Comparing Time-Resolved

Spectral Output

time resolved video of 1ms frame capture of the difference in

the temporal characteristics of a free discharge and partial

discharge pulse system. Slowed in time to observe changes

25ms Free Discharge Pulse 25ms Square Pulse

Free Discharge

Manufacturer claims a 25ms pulse duration but when

measured using time resolved spectrometer only circa 3ms

of useful energy is present

The anatomical target for hair

removal

• Effective pulse duration for follicular damage = 20-40ms

• Melanin heated to circa 70ºC causes destroys follicular cells

• Surrounding tissue matrix spared from heating effect

• Free discharge systems are not optimum in delivering

energy within such time regime

• Fluence is delivered evenly during the pulse duration

• A controlled square pulse can produce pulse durations that are biologically effective and efficient

• All wavelengths in the spectrum are equally represented during the exposure

• Less adverse reactions

Optimum IPL light pulse

Pulse Stacking

• Fluence decays during the pulse duration

• Pulse stacking is used by certain manufacture to extend total pulse duration

• Close stacked pulses are effectively a single pulse of decaying energy as the off time between pulses are short

• Spectral shift is highly present during exposure

Pulse Stacking

• Fluence varies of each short pulse during the pulse train due to separate capacitors

• Pulse stacking is used by certain manufacturers to extend total pulse duration but with long off times, thermal energy that is absorbed by melanosomes is dissipated to surrounding tissue within off times.

• Greatest number of adverse reactions reported

Spatial Distribution

• Recent study shows energy distribution across treatment area

• Area of increased energy – hyper, hypopigmentation, blistering

• Area of reduced energy – Possible paradoxical hair growth

• Need to overlap treatment area thus extra time by operator

What about LED Systems?

• Advances in LED technology had provided new products

• LEDs have shown to provide results

• LEDs alone produce subtle changes in tissue matrix

Summary

• Many manufacturers of IPLs make claims for fluence, pulse duration and spectral emission that are not substantiated as measured by this study - This may lead to increased risk of under- or over-treatment or burn injury to the IPL patient

• Manufacturers operating an ISO 9000 quality system (Medical CE-mark) showed greater consistency of stated and actual values for fluence, pulse duration and spectral cut-off filter accuracy over the stated lifetime of the applicator / lamps

• Square Pulse Systems:

Produce the lowest possible intensity for a given fluence thus minimising discomfort and other side effects such as skin burns

• Free Discharge Systems:

Produce high intensity energy in short pulse durations with spectral shift and less efficient spectral distribution

Conclusion: Characteristics of an

Optimum IPL System

• Energy output level at least within +/- 20% of stated value, medically CE marked systems have a tendency to provide such tolerance

• Cut off filter should be that stated match the absorbance spectrum of the desired skin chromophore

• Pulse duration should be within close range of the Thermal Relaxation Time, square pulse technology is greatly suited to provide this

• Constant energy level during the entire pulse duration is optimum for maximum heating for follicular structure. Lower energies are required than a variable pulse thus greater patient comfort.

• Patients and operators want professional service choose a business that provides a good experience when using their IPL system

Thank you !