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 !