Electromagnetic interference from lasers and intense light sources in the treatment of patients with artificial pacemakers and other implantable cardiac devices.

Measurements of the electric and magnetic field strengths surrounding six laser systems and one intense pulsed light system were carried out. The results were compared to exposure limits published by cardiac device manufacturers to assess the risk of electromagnetic interference to implantable cardiac devices such as pacemakers or implantable cardioverter defibrillators. The majority of lasers assessed in this study were found to produce electric and magnetic field strengths below the published exposure limits for cardiac devices. However, the low-frequency electric field and static magnetic field of both the CO2 laser and the ruby laser were found to exceed these limits. Ensuring that a small separation is maintained at all times between the laser unit and any patient with a pacemaker or implantable cardioverter defibrillator appears to be a sensible expedient in avoiding overexposure of an implantable cardiac device to electromagnetic interference. Due to the single-shot fast discharge nature of the intense pulsed light system, changes in electromagnetic field strength were too fast for some of the measuring equipment used in this study to register accurate readings during operation.

Cutaneous lasers and skin camouflage make-up: a useful alternative intervention for periorbital hairy congenital melanocytic naevus.

Periorbital congenital melanocytic naevi can be very disfiguring and difficult to treat effectively. Although surgical excision and reconstruction is the most widely accepted treatment strategy, we describe a case in which cutaneous lasers treatment followed by the application of cosmetic skin camouflage make-up provided an alternative solution delivering a good cosmetic improvement.

Finite element analysis of thermal and acoustic processes during laser tattoo removal.

BACKGROUND AND OBJECTIVE: Q-switched laser therapy is commonly used for the removal of tattoos. However, despite ever increasing demand for this intervention, a better understanding of the mechanisms that result in pigment reduction is required in order to optimise outcomes and reduce the number of treatment episodes. STUDY DESIGN: A finite element analysis computer simulation was developed to model the fragmentation response of ink granules during irradiation of a professional black tattoo using a Q-switched Nd:YAG laser. Thermal and acoustic mechanisms were considered, allowing the optimal laser settings to be predicted throughout the course of treatment. Changes in the thermal properties of the ink during heating were taken into account to improve the reliability of the results obtained. RESULTS: The simulated results are in close agreement with clinical observations. Thermal fragmentation was shown to be the dominant mechanism in pigment reduction when using a 6 nanoseconds pulse at 1,064 nm. In order to provide maximum clearance whilst maintaining acceptable levels of tissue thermal damage, later treatments were shown to benefit from higher fluence levels than initial treatments. Larger spot diameters were also preferable throughout the course of treatment. CONCLUSIONS: The results from the simulation build upon previous work carried out in the field, applying ink thermal coefficients which vary with temperature for the first time. These results compliment clinical knowledge, suggesting that a proactive increase in fluence during a course of treatments is likely to improve the response to laser therapy.

Determination of the thermal and physical properties of black tattoo ink using compound analysis.

Despite the widespread use of laser therapy in the removal of tattoos, comparatively little is known about its mechanism of action. There is a need for an improved understanding of the composition and thermal properties of the tattoo ink in order that simulations of laser therapy may be better informed and treatment parameters optimised. Scanning electron microscopy and time-of-flight secondary ion mass spectrometry identified that the relative proportions of the constituent compounds of the ink likely to exist in vivo are the following: carbon black pigment (89 %), carvacrol (5 %), eugenol (2 %), hexenol (3 %) and propylene glycol (1 %). Chemical compound property tables identify that changes in phase of these compounds lead to a considerable reduction in the density and thermal conductivity of the ink and an increase in its specific heat as temperature increases. These temperature-dependent values of density, thermal conductivity and specific heat are substantially different to the constant values, derived from water or graphite at a fixed temperature, which have been applied in the simulations of laser therapy as previously described in the literature. Accordingly, the thermal properties of black tattoo ink described in this study provide valuable information that may be used to improve simulations of tattoo laser therapy.

Simulating light transport through skin for color prediction of port wine stain lesions: a review.

A survey of the literature is presented regarding the simulation of port wine stain (PWS) skin color. Knowledge of PWS features, such as the depths and diameters of affected vessels, is essential for informing laser treatment. These may be determined through the inverse application of a skin model. The techniques which have been applied to achieve this are analyzed in detail. Radiative transfer (RT) is found to be the preferred method of simulation. By far the most common approximations to RT are the diffusion approximations, which have been applied successfully in the past and Monte Carlo techniques, which are now the methods of choice. As the requirements for improvement of laser treatment on an individual basis continues, the needs for further work towards accurate estimations of individual optical coefficients and robust, flexible simulation techniques are identified.

Optical properties of human skin.

A survey of the literature is presented that provides an analysis of the optical properties of human skin, with particular regard to their applications in medicine. Included is a description of the primary interactions of light with skin and how these are commonly estimated using radiative transfer theory (RTT). This is followed by analysis of measured RTT coefficients available in the literature. Orders of magnitude differences are found within published absorption and reduced-scattering coefficients. Causes for these discrepancies are discussed in detail, including contrasts between data acquired in vitro and in vivo. An analysis of the phase functions applied in skin optics, along with the remaining optical coefficients (anisotropy factors and refractive indices) is also included. The survey concludes that further work in the field is necessary to establish a definitive range of realistic coefficients for clinically normal skin.

Neuromuscular electrical stimulation for children with cerebral palsy: a review.

The aim of this review paper is to consider the application of neuromuscular electrical stimulation (NMES) to improve gait or upper limb function in children with cerebral palsy (CP). Although most NMES research has been directed at adults with neurological conditions, there is a growing body of evidence supporting its use in children with CP. In line with a recent meta-analysis, the use of electrical stimulation to minimise impairment and activity limitations during gait is cautiously advocated. A detailed commentary on one of the most common lower limb NMES applications, tibialis anterior stimulation (either with or without gastrocnemius stimulation) is given. Although there is a lack of randomised controlled trials and a predominance of mainly small studies, this review further concludes that the balance of available evidence is in favour of upper limb exercise NMES offering benefits such as increased muscle strength, range of motion and function in children with CP. The use of dynamic splinting with NMES has been shown to be more effective than either treatment on its own in improving function and posture. There is at present little published work to support the application of botulinum toxin type A to temporarily reduce muscle tone as an adjunct intervention to NMES in this population, although the presence of parallel applications to manage similar symptoms in other muscular disorders is noted.

Adverse effects following Q-switched ruby laser treatment of pigmented lesions.

A retrospective study was conducted to investigate the incidence of adverse effects following Q-switched ruby laser treatment of pigmented lesions at the Wessex Specialist Laser Centre. Sixty-one patients received a total of 151 treatments between January 2006 and January 2008. This is the largest series to date of patients on whom adverse effects have been reported following Q-switched ruby laser treatment of an assortment of pigmented lesions. Patients with traumatic or decorative tattoos were excluded from this study. Two of the treatments (1.3%) resulted in adverse effects. One patient developed hyperpigmentation and the other experienced scabbing and subsequent textural change following abrasion of the scab. No predisposing medical or other factors were observed in either patient. This low incidence of adverse effects is consistent with the highly selective absorption of ruby laser light by melanin. The presence of these adverse effects highlights the importance of test patch treatments, the necessity for patients to follow good post-treatment advice and the case for vigilance in monitoring the quality of the laser output.

Adverse effects reported in pulsed dye laser treatment for port wine stains.

A retrospective study was conducted over a 762-day period to investigate the incidence of adverse effects following pulsed dye laser treatment for port wine stains using the Chromos 585 nm pulsed dye laser (PDL). Treatment energy densities typically ranged from 4.0 J/cm(2) to 7.5 J/cm(2). Treatment was predominantly delivered as a 7 mm-diameter pulse of laser light, although a 5 mm pulse was occasionally used. Nine patients experienced one adverse event each, with scabbing, blistering (prolonged in one case that persisted for more than 2 months), hypopigmentation or hyperpigmentation; one of the nine patients developed both blistering and hypopigmentation. The incidence of adverse effects per treatment was 1.4% (1.7% for adults and 0.6% for children). The lower leg was the most common site for an adverse effect; four out of 22 patients (18%) receiving PDL treatment for lower leg port wine stains (PWSs) suffered an adverse effect (three cases of hyperpigmentation and one of hypopigmentation and blistering). Four patients suffered an adverse effect following an increase in the energy density of the laser treatment. There was no statistically significant correlation between laser performance and the occurrence of adverse effects.

Reliability and sensitivity of a wrist rig to measure motor control and spasticity in poststroke hemiplegia.

BACKGROUND: Objective assessment of impairments after stroke is vital for evidence-based therapy and progress monitoring. OBJECTIVE: This study determines the utility of outcome measures obtained from an instrumented wrist rig for future rehabilitation trials. The tests undertaken were evaluated in terms of sensitivity to detect differences between normal and impaired participants, test-retest repeatability (repeatability coefficient and intraclass correlation coefficient [ICC]), and interrater agreement (Bland and Altman limits of agreement). METHODS: Twelve participants with chronic poststroke hemiparesis (mean 5.6 years); and 12 unimpaired volunteers performed a series of tasks in the rig. The hemiparetic arm (impaired group) and dominant arm (unimpaired group) were tested in 3 sessions on the same day by 2 assessors. Signals were analyzed to derive a tracking index (motor control), stretch index (spasticity), flexor modulation index (FMI) (muscle activation), force angle index (FAI) (stiffness), range of movement, and isometric force. RESULTS AND CONCLUSIONS: The means of all tests differed between impaired and unimpaired participants except for range of movement into flexion, the FAI, and the FMI. Repeatability coefficients for each test are presented as benchmark values for use in future trials in which the wrist rig tests may be used to detect change. Test-retest reliability was excellent in the impaired group (ICC = 0.88-0.98) and poor to excellent in the unimpaired group (ICC = 0.06-0.89). The Bland-Altman ranges showed no bias between assessors, and that the interassessor variability was similar to that between repeats by the same assessor for most tests.

Adverse effects reported in epilatory ruby laser treatment.

A retrospective study was conducted to investigate the incidence of reported adverse responses after epilatory laser treatment to control the growth of facial hair in patients with polycystic ovary syndrome. Forty-eight patients received a median of 6 (range 2-11) treatments with an Aesculap ruby laser during a 704 day monitoring period at Salisbury District Hospital. Nine adverse skin responses such as blistering, scabbing, sustained localised erythematous reactions or hyperpigmentation were reported. The energy output of the laser was also recorded at the start of every clinical session during this period using an external energy meter. The measured energy output of the laser was plotted alongside incidents of adverse responses, although no statistically significant correlation was found. The question of whether or not some adverse effects in ruby laser treatment can be attributed to laser performance remains open.

Depth of penetration of an 850nm wavelength low level laser in human skin.

Low Level Laser Therapy is used for a wide variety of conditions including superficial skin sores, musculoskeletal and joint problems, and dentistry. Knowledge of the penetration depth of laser radiation in human skin is an essential prerequisite to identifying its method of action. Mathematical simulations and estimates from the literature suggest that the depth of penetration of laser radiation using wavelengths from 630nm up to 1100nm may be up to 50mm. The aim of this study is to directly measure the penetration depth of a Low Level Laser in human tissue. Human abdominal skin samples up to 0.784mm thickness were harvested by dermatome following abdominoplasty procedures. These samples were irradiated by a Gallium Aluminium Arsenide Laser (Wavelength 850nm near infra-red invisible light, 100mW, 24kHz, 0.28mm diameter probe) and the transmitted radiation measured with an Ophir Optronics 'Nova' external energy meter. The intensity of laser radiation reduced by 66% after being transmitted through a 0.784mm sample of human abdominal tissue. In this study most laser radiation was absorbed within the first 1mm of skin.

Monitoring the ups and downs of pulsed dye laser energy output.

The internal energy meter reading of a Chromos pulsed dye laser (PDL) set at 50% of maximum pumping energy was recorded at the start of every clinical session over an 898 day period and compared with the measurement from an Ophir Optronics 'Nova' external energy meter. This quick and inexpensive process improved quality control procedures for the use of the PDL and enabled the performance of laser components such as the dye, pumping mechanism and optics to be monitored. The stability of the laser output energy was also monitored during three simulated clinics on days 665, 870 and 898. External energy meter readings were recorded every 100 pulses during each simulated clinic comprising six series of 500 pulses. As the energy output was shown to be stable during each clinic (SD<4.7%) recalibration during treatments of up to 500 pulses with this laser was deemed to be unnecessary. However, it was noted that this output energy stability was maintained by varying the pumping energy from 42 to 88% of maximum. Subsequent measurements of pulse width conducted with an ET-2000 Silicon Photodetector demonstrated that although the nominal pulse width was 450 mus, this varied from 240 to 390 mus as the pumping energy increased from 20 to 50%.

How well does your ruby laser work?

The safe and effective use of cutaneous lasers is dependent upon the selection of a clinically appropriate laser energy level. Therefore, the accuracy of the stated laser output is critical. The energy output of an Aesculap ruby laser was recorded at the start of every clinical session over a 704-day period using an external energy meter. Regular review of these records enabled trends of energy output to be recognised and appropriate action to be taken prior to adverse clinical sequelae. This monitoring procedure is a quick and inexpensive method of improving quality control in the use of medical lasers.