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Laser ToeNail Physics 101

Discussion in 'General Issues and Discussion Forum' started by Dr. Eric Bornstein, Mar 27, 2014.

  1. Dr. Eric Bornstein

    Dr. Eric Bornstein Active Member

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    I would like to place some scientific facts on this new thread concerning basic Laser/Tissue interactions as it relates to nails and onychomycosis. This is to assist Podiatric physicians in making informed decisions about the different OM laser systems available to them.

    Podiatric physicians are taught to think in terms of classical Newtonian mechanics when treating mycotic nails. These principles (based mostly on mechanical debridement) convey an understanding about:

    (a) how mechanical work from the force of a drill on a mycotic nail (debridement) produces heat via friction and

    (b) how (because of this work) large mycotic particulate matter is aerosolized as it is removed from the nail by the drill, and spread into the immediate environment.

    Every Podiatric physician that has ever debrided a nail with an electric hand-piece intuitively understands these simple mechanical and thermodynamic consequences.

    However, this simple Newtonian interaction (drilling on the nail) is completely superseded by the instantaneous ablative laser interactions that occur at relativistic speeds (ie. the speed of light – 186,000 miles/sec) with pulsed Nd:YAG lasers.

    The first relativistic interaction with an Nd:YAG laser on a toenail is the almost instantaneous “ejection plume” of micron sized mycotic material, smoke and bio-burden, that occurs when super pulsed or q-switched laser energy interacts with the mycotic nail in 10-6 or 10-9 second bursts (that is a millionth or a billionth of a second) from an Nd:YAG laser, depending on the laser’s configuration.

    A second example of a relativistic interaction is the possibility of unintended pulse stacking of the laser energy, that could result in the burning of a patient’s nail bed and matrix. This can occur, because the laser is pulsing far faster (10-6 or 10-9 second bursts) than the human reaction time, (only .215 seconds "average" or 2/10ths of a second). This is coupled to the fact that there is almost complete lack of peer-reviewed treatment protocols available for the treatment of onychomycosis with many of the differently configured Nd:YAG lasers.

    Podiatric physicians need to be aware of the different logic and thermodynamics associated with ablative lasers that produce instantaneous ejection plumes and non-ablative lasers, so that they can make educated and proper judgments in patient treatment and safety with these laser technologies.

    Exploiting these laser-tissue interactions, a clinician using an Nd:YAG has the ability to apply an intense burst of laser energy, for a very short time interval, to attempt to effect a desired outcome, in this case, thermal mechanical ablation of mycotic organisms in the human toenail. However, this ablation phenomenon comes with a “Thermal Price” that must also be understood.

    First, Kozarev (2009) measured the temperature on the nails during and after 1064 nm Nd:YAG lasing and determined that the nail is fully covered (scanned) in approximately 15 sec, reaching 50°C

    Second, Boni Elewski MD at the (2012) annual meeting of the American Academy of Dermatology reported on in vitro studies and in vivo studies that she found the following temperatures and times necessary to kill the following fungus:

    T rubrum 50° C for 15 minutes
    E. floccosum 50° C for 10 minutes
    Scytalidium 55° C for 5 minutes.

    She reported:
    " Nail temperatures that reach 40-41° C cause enough pain for patients to pull away, and the maximum nail temperature patients could tolerate was 45° C," said Dr. Elewski, professor of dermatology at the University of Alabama at Birmingham.”

    These Nd:YAG temperature realities are particularly challenging for the physician performing the procedure, as he/she must be careful not to employ the manual thermally damaging event called pulse stacking. Pulse stacking is an overlapping localization of laser pulses (going over the same small spot more than once) that occurs from the inconsistent manual aiming of small to medium laser spot sizes over large areas of tissue. This can lead to excessive heating of areas of treatment, and potentially ablate healthy tissues. This takes a lot of skill to avoid, as the laser energy from these systems is pulsing a far greater speeds, than (1) the operator or (2) the patient can react to.

    These thermal and photo-thermal-mechanical issues are the reality of the physics of these lasers, and have been written about and reviewed many times in the last 25 years.

    For comparison, a continuous wave diode laser (such as the Noveon Nail Laser) does not have the high peak power or ablative abilities of the Nd:YAG.

    A CW Diode laser has far longer pulse durations in milliseconds (10-3 sec or thousandths of a sec), with far less peak power, that will not reach the ablation threshold in soft tissues. .

    The Noveon Nail Laser (Diode laser) works on a completely different mechanism of action. This device expands the laser/spot size to 1.5 cm diameter to cover the entire nail area simultaneously, in a hands free manner, vs a pulse by pulse manual procedure with an Nd:YAG laser.

    With the Noveon, the sub-thermal temperatures and novel photo-biology can make use of the non-ablative ability, to stay well below the damage threshold in the treatment of skin and nail.

    According to Henriques (1947), Eichler (1991) and Dewhirst (2003) (producing voluminous data), it can be deduced that as long as the tissue temperature being irradiated (with any system) is at or below about 45 C (113 F), there is little chance of Irreversible Tissue Damage.

    The Noveon diode and non-ablative therapy, published in peer-reviewed publications and under IRB guidance does not go over 101 F when treating human nails.

    With the Noveon device, there is:

    1) No ablation,
    2) No manual moving of a fiber handpiece or holding an individual toe,
    3) No worry of pulse stacking,
    4) No training or skill involved, as the device is computer driven, for the same dose every time.

    Dr. Eric Bornstein
    Chief Science Officer
    Nomir Medical Technologies

    Kozarev, D. O. D., & Mitrovica, S. (2009). Laser treatment of nail fungal infection. In Proceedings of the Berlin Conference of the European Academy of Dermatology and Venereology.

    Marjaron B, Plestenjak P, Luka CM: Thermo-mechanical laser ablation of soft biological tissue: modeling the micro-explosions. Applied Physics B 69:71-80, 1999.

    Venugopalan V, Nishioka NS, Mikic BB: The thermodynamic response of soft biological tissues to pulsed infrared-laser irradiation. Biophysical Journal 70:2981-2993, 1996.

    Dawson E, Willey A, LEE K: Adverse events associated with nonablative cutaneous laser, radiofrequency, and light-based devices. Semin Cutan Med Surg 26:15-21, 2007.

    Bornstein ES: A Review of Current Research in Light-Based Technologies for Treatment of Podiatric Infectious Disease States Journal of the American Podiatric Medical Association Volume 99 Number 4 348-352 2009

    Henriques and Moritz, Am. J. Path., 23,. 531-549 (1947)

    Eichler and Sieler, Lasertichnik in der Medizin, Springer, Berlin (1991)

    Dewhirst MW, et al. Basic principles of thermal dosimetry and thermal thresholds for tissue damage from hyperthermia. Int J Hyperthermia. 2003 May-Jun;19(3):267-94. Review.

    Bornstein E., Hermans W., Gridley S., and Manni J. Near infrared Photo-inactivation of bacteria and fungi at physiologic temperatures. Photochemistry and Photobiology

    Bornstein ES: A Review of Current Research in Light-Based Technologies for Treatment of Podiatric Infectious Disease States Journal of the American Podiatric Medical Association Volume 99 Number 4 348-352 2009
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  3. Dr. Eric Bornstein

    Dr. Eric Bornstein Active Member

    Here are some references to look at regarding the physics of ablation and plumes with pulsed lasers like Nd:YAGs. Important for a DPM's safety and understanding, if using a 10-6 or 10-9 pulsed laser on OM, warts or tattoos.

    Vogel, Alfred, and Vasan Venugopalan. "Mechanisms of pulsed laser ablation of biological tissues." Chemical Reviews 103.2 (2003): 577-644.

    Zhigilei, Leonid V., and Barbara J. Garrison. "Microscopic mechanisms of laser ablation of organic solids in the thermal and stress confinement irradiation regimes." Journal of Applied Physics 88.3 (2000): 1281-1298.

    Zhigilei, L. V. "Dynamics of the plume formation and parameters of the ejected clusters in short-pulse laser ablation." Applied Physics A 76.3 (2003): 339-350.

    Nahen, Kester, and Alfred Vogel. "Plume dynamics and shielding by the ablation plume during Er: YAG laser ablation." Journal of biomedical optics 7.2 (2002): 165-178.

    Dr Eric Bornstein
    Chief Science Officer
    Nomir Medical Technologies

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