Richard Smith discusses the history of Evidence-based Medicine with Iain Chalmers, Kay Dickersin, Paul Glasziou, Muir Gray, Gordon Guyatt, Brian Haynes, Drummond Rennie and David Sackett. Watch the videos at http://ebm.jamanetwork.com.
“Most alternative laser medicine is not supported by basic physics, and cannot be reproduced by mainstream researchers. If it were reproducible it would not be called alternative medicine, and it would not require a belief system for it to work.”
The increased interest in Alternative Laser Medicine (ALM), predominately Low Level Laser Therapy (LLLT), and its applications is mostly a product of pathological science, and partly due to a financial incentive to sell easy solutions for difficult problems.
ALM is well established in the veterinary field where patients cannot describe their experience, and the level… Continue reading
Photon recycling is basically an attempt to improve the efficiency of poorly designed devices. The small amount of energy provided by recycled photons can be achieved by simply turning the fluence of the device up just a few per cent. Additionally, photon recycling results in unwanted heat at the surface and almost no increase in the effectiveness at the intended target. This results in added discomfort and no increase in clinical efficacy. A best design practice for lasers and flashlamps is to reduce or eliminate this unwanted recycled light. A better choice is to increase the fluence a small amount,… Continue reading
Absorption spectrum of melanin, hemoglobin, oxihemoglobin, and water. Continue reading
The short video illustrates the differences between gaussian beam profiles and top-hat beam profiles showing the typical energy distribution. The useful energy and the diameter or a top-hat profile are shown to be well defined, whereas a gaussian profile leaves lots of room for marketing interpretations of the beam specifications. When discussing gaussian beam parameters it is important to be precise with regard to terminology.
laser tubes used in medical CO2 lasers use DC or RF excitation to energize the laser gas. The main difference in performance is related to the fact that systems with DC-excited tubes typically enable the user to adjust both power level and pulse width, whereas RF-excited tubes, such as that used in the Ultrapulse, only allow the user to vary pulse width. The power level for RF-excited tubes is usually set by adjusting the duty cycle at a fixed power level resulting in an adjustment to the average power during the pulse. Continue reading
There is a some of discussion on the interneet forums about IPL pulsing formats and websites with some manufacturers claiming that their IPL device delivers a square pulse that provides constant energy to tissue during the exposure, and is clinically better. This claim is not quite accurate, somewhat misleading. and an example of marketing leading the physics.
The square pulse as advertised for these devices provides a constant power level, and constant irradiance at the tissue, not constant energy. The energy or fluence delivered is accumulated over time period of the pulse, and is the integral of this… Continue reading
These are marketing terms. All modern medical CO2 lasers are pulsed by electronic gating, and all can run continuously (referred to as CW) for short time periods. Chopped is a historical term that refers to mechanically gating the laser beam with a mechanical shutter of that actually chopped the beam.
All modern lasers are electronically gated or chopped. In general RF-excited lasers are designed to operate at a CW fixed power level, (240w for the Ultrapulse), and are pulsed by gating their CW power level. DC-excited lasers are also pulsed by electronic gating, but have the ability for superpulse… Continue reading
There are as many opinions as spot sizes. In general, with the correct parameters, slightly difference spot sizes will result in indistinguishable clinical results. It is more or less a utilitarian choice in that larger spot sizes are easier to use for full field resurfacing, and fractional spot sizes are less visible to the eye if they are smaller. Most modern CO2 lasers have diffraction limited beams, and can all provide about the same spot sizes with the proper selection of lenses, so it is usually a deign choice. My preference is to use the largest spot that is aesthetically pleasing. Aesthetic medicine is a subjective field after all. Anything less than 300 µm in diameter seems to blend very well without noticeable spots in a day or two. A side issue is that there is no standard definition used by manufacturers for the spot size specification so comparing lasers with different advertised spot sizes can be misleading. So when comparing spot sizes you need to know if they are defining it as the half power points, the area containing 90% of the energy, the pattern burned on laser paper, or the 1/e2 power points. Are they including the thermal coagulation zone or just the drilled channel, or are they measuring the laser beam itself? The lack of a precise and standard definition leaves a lto of room for marketing. Continue reading
This video gives a simplified view of the components common to almost all IPL handpieces, and demonstrates their primary functions.
Flashlamps are typically standard components that can be supplied from several vendors, though their performance and lifetime are highly influenced by how the lamps are energized. All IPLs have a reflector to concentrate optical energy, a light guide to direct light to the surface of skin, and a filter to select the spectral energy delivered. Continue reading