The corneal damage effects induced by 1319-nm transitional near-infrared laser have been investigated for years. However, the damage threshold dependence on exposure duration has not been revealed. The in vivo corneal damage thresholds (ED50s) were determined in New Zealand rabbits for 1319-nm laser radiation for exposure durations from 75 ms to 10 s. An additional corneal ED50 was determined at 1338 nm for a 5-ms exposure. The incident corneal irradiance diameter was fixed at 2 mm for all exposure conditions to avoid the influence of spot size on threshold. The ED50s given in terms of the corneal radiant exposure for exposure durations of 5 ms, 75 ms, 0.35 s, 2 s, and 10 s were 39.4, 51.5, 87.2, 156.3, and 311.1 J/cm2, respectively. The 39.4 J/cm2 was derived from the ED50 for 1338 nm (27.0 J/cm2). The ED50s for exposure durations of 75 ms to 10 s were correlated by a power law equation, ED50=128.9t0.36 in J/cm2, where t was the input in the unit of second, with correlation coefficient (R) of 0.997. Enough safe margins existed between the ED50s and the maximum permitted exposures from current laser safety standard.
The flash electroretinography is a standard electrophysiological method and widely employed in basic research and
ophthalmology clinics, of which the stimulus is usually white flash from dome stimulator. However, little is known about
the electroretinograms (ERGs) evoked by monochromatic laser flash stimuli. The goal of this research effort is to
quantify the ERGs of dark-adapted New Zealand rabbits elicited by He-Ne laser flash with wavelength 632.8 nm. The
flash field was a Maxwellian viewing disc with angular subtense of 8.5°, 13.3° or 20.2°. The stimulus duration was 12
ms, 22 ms, 70 ms or 220 ms. The laser flash power incident on the cornea varied from 2.2 nW through 22 mW. Under the
condition of 20 ms stimulus duration and 20.2° flash field, the ERG of New Zealand rabbit was compared with that of
Chinchilla gray rabbit. Results showed that for the ERG b-wave, with the increase of laser energy, the amplitude first
increased, then met a trough and finally increased again, the implicit time decreased first and then met a platform. While
for the ERG a-wave, the amplitude increased and the implicit time decreased monotonically. Longer stimulus duration
led to lower b-wave amplitude under equal flash power level. The flash field size showed limited effect on the ERG,
especially on the low energy end. As compared with the pigmented rabbit, the albino rabbit was more sensitive and the
threshold energy for b-wave excitation was about 10 times lower.
The near infrared laser technique can activate cutaneous nociceptors with high specificity and reproducibility and be
used in anti-riot equipment. This study aimed to explore cutaneous pain effect and determine the threshold induced by
Nd:YAG and CO2 laser stimuli. The corresponding wavelength was 1.32μm and 10.6μm. The pain effect was assessed in
three healthy subjects (1 woman and 2 men) on the skin of dorsum of both hands. The energy of each pulse and whether
the subjects felt a painful sensation after each stimulus were recorded. A simplified Bliss Method was used to calculate
the pain threshold which were determined under three pulse durations for Nd:YAG laser and one pulse duration for CO2
laser. As a result the pain thresholds were determined to be 5.6J/cm2, 5.4J/cm2 and 5.0J/cm2 respectively when using
Nd:YAG laser, 4.0mm beam diameter, 8ms, 0.1s and 1s pulse duration. The pain threshold was 1.0J/cm2 when using CO2
laser, 4.0mm beam diameter and 0.1s pulse duration. We concluded that the threshold of cutaneous pain elicited by
1.32μm laser was independent upon the pulse duration when the exposure time ranged from 8ms to 1s. Under the same
exposure condition, the threshold of cutaneous pain elicited by 1.32μm laser was higher than that elicited by 10.6μm
laser.
To study the risk of retinal thermal injury from 532 nm laser during photodynamic therapy (PDT) for choroidal
neovascularization (CNV) by measuring the retinal temperature increase of rabbit eyes. A microthermocouple technique
was developed to measure retinal temperature increase during PDT in pigmented and non-pigmented rabbit eyes. The
532 nm laser exposures were performed with 100-s duration, 2-mm spot size, and retinal irradiance ranging from 400 to
1600 mW/cm2. A K-type microthermocouple was inserted through the sclerotomy and advanced until the tip reached the
retina at the posterior pole. The thermocouple was connected a computer that recorded and analyzed retinal temperature
data. The results showed that the retinal temperature increase during laser exposure was proportional to retinal irradiance
with a particular spot diameter, exposure duration, wavelength, and fundus pigmentation. And the measured retinal
temperature increases in pigmented rabbits were a little higher than those in albino rabbits under the same radiant
condition. Retinal threshold irradiance required for visible lesions at laser wavelength of 532 nm with 2.0-mm spot size
and 100-s duration was 1657 mW/cm2 in albino and 1003 mW/cm2 in pigmented rabbits, respectively, corresponding to
retinal temperature increase of about 8 °C and 6 °C. The measured temperatures in albino and pigmented rabbit eyes
were both lower than the model predictions, especially in pigmented rabbits. Therefore, further parameter modifying
should be performed to obtain accuracy prediction of retinal temperature.
The laser-tissue interaction has not been well defined at the 1319 nm wavelength for brain exposure. The goal of this
research effort was to identify the behavioral and histological changes of brain lesion induced by 1319 nm laser. The
experiment was performed on China Kunming mice. Unilateral brain lesions were created with a continuous-wave
Nd:YAG laser (1319nm). The brain lesions were identified through behavioral observation and histological haematoxylin
and eosin (H&E) staining method. The behavior change was observed for a radiant exposure range of 97~773 J/cm2. The
histology of the recovery process was identified for radiant exposure of 580 J/cm2. Subjects were sacrificed 1 hour, 1
week, 2 weeks, 3 months, 7 months and 13 months after laser irradiation. Results showed that after laser exposure,
behavioral deficits, including kyphosis, tail entasia, or whole body paralysis could be noted right after the animals
recovered from anesthesia while gradually disappeared within several days and never recurred again. Histologically, the
laser lesion showed a typical architecture dependent on the interval following laser treatment. The central zone of
coagulation necrosis is not apparent right after exposure but becomes obvious within several days. The nerotic tissue
though may persist for a long time, will finally be completely resorbed. No carbonization granules formed under our
exposure condition.
To study the risk of thermal injury in photodynamic therapy for choroidal neovascularization by calculating the retinal temperature of rabbits, a mathematical model for laser induced thermal effect on retina was developed. Homogeneous layer retinal models of different pigmented rabbits were presented to analyze the light distribution. The finite element method realized by Matlab software was used to solve classical bio-heat transfer model - Pennis equation, in which heat loss due to choroidal blood flow was considered. The retinal temperature was calculated with different laser parameters, including different wavelengths (532nm, 578nm and 690nm), power density (200~1600 mW/cm2), spot diameter (1mm, 2mm and 3mm) and different pigmented eye fundi. The prediction results showed the retinal temperature increased first, then reached maximum in a few seconds and kept constant during laser irradiation. Once laser exposure ended, the temperature decreased quickly to normal. With the increase of laser power density and spot size, the retinal temperature raised too. The temperature reduced exponentially with the distance from laser spot increased. The maximum temperature of non-pigmented rabbits was lower than that of pigmented rabbits. The temperature induced by 578nm laser irradiation was highest, the next was by 532nm laser and the lowest was by 690nm laser. For current parameters used to treat choroidal neovascularization (690nm, 600mW, 2mm, 83sec), the maximum retinal temperature calculated was less than 45 °C, which indicating no thermal damage induced.
Railway blocking system is the system with the high demanding of real-time performance. Firstly, the tasks and the time limits, which had to be handled for the blocking system, were introduced. The FCFS and the Markov chain were used to set the model for it. By analyzing the performance of the system with the FCFS model found out that it was not satisfied to the real-time performance. Secondly, NPPR model to evaluate the software real-time performance of the blocking processor was proposed. By evaluation, analysis and comparison, the results indicate that the NPPR model is prevail over the model of (M/M/1): (N/N/FCFS) in real-time performance. And the priorities of the tasks in the system should be given according to their time limit. With the principle of (M/M/1): (N/N/NPPR), if the priority was given to the tasks properly, the satisfied real-time performance will be gotten. The models were tested in forms software and the satisfied result has been gotten in practice.
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