The role of pulse length in limiting distant damage to vascular tissue caused by the Nd-YAG laser

The total damage caused by equivalent doses of energy given to human cadaver vascular tissue over the same time scale from three Nd-YAG lasers of different pulse lengths is quantified. The continuous wave (c.w.) laser produces vacuolation and coagulation around a vaporized crater; the 100 μs pulsed laser produces less surrounding damage and the 10 ns pulsed laser none at all. The areas of damage in five craters made with 10 J energy were measured from histology slides using a digitising platten, and it was found that in each case the total amount of damage was the same, even though the depth of the craters made varied. The dose response for vaporization of the 10 ns pulsed laser was the greatest at 35 μm/J and that of the c.w. laser was least at 8 μm/J. A pulse length of 100 μs may not be the optimum for limiting surrounding tissue damage during laser angioplasty but it produces much less damage than a c.w. laser and unlike the 10 ns pulses is easily transmissible down an optical fibre.     

Transluminal laser treatment with metal-capped optical fibres of normal coronary arteries in live dogs: an angiographic and histological study of the acute effects

Transluminal laser treatment of coronary arteries with bare optical fibres frequently results in perforation, mainly owing to misalignment of the laser beam. To overcome this problem, a 300 μm-diameter optical fibre, fitted with a 1.5 mm metal cap, was used to convert argon-laser energy to heat. In 12 anaesthetized dogs, a 8.3 French Sones guiding catheter was placed, via the right carotid artery, in the left coronary ostium, and the optical fibre was advanced into the circumflex artery. After argon laser treatment at 6 W for 1s, the fibre was withdrawn by increments of 0.5–1.0 cm; laser treatment was repeated after each repositioning, by using 6W and increasing exposure times of 2, 3, 4 and 5 s. In six dogs the laser was applied in the beating heart, and in six in the asystolic heart, to assess the effects in the absence of a coronary blood flow. Angiography, before and after the laser treatment, did not reveal coronary perforation or other major acute complications. Post-mortem examination showed that the number of sites with evidence of intimal vaporization was higher in dogs treated in the asystolic heart than in the others (14 versus 6 sites, respectively,P<0.02). The post mortems confirmed that perforation did not occur in either case. Laser treatment for 5 s resulted in intimal vaporization in 11 of the 12 arteries (91%); for 4s in seven of the arteries (60%); and for 3 s in two arteries (16%). Thus, intimal vaporization of normal coronary arteries in both the beating and the asystolic dog heart can be achieved without perforation or other major acute complications by transluminal laser treatment with metal-capped optical fibres.     

The treatment of vascular malformation of the brain with laser source

The first three cases of vascular malformations in humans (two artero-venous aneurysms and one saccular aneyrysm) treated with the association of CO₂ laser and Neodymium: Yag lasers, are presented here. The post-operative course has been very good. However, it is still necessary to examine a larger number of cases to see if, how, and when this treatment can be utalized in place of traditional methods.     

Study of mechanical and thermal damage in brain tissue after ablation by Erbium-YAG laser

This work studied the ablation of bovine brain tissue by free-running Erbium-YAG laser pulses. Single-shot interactions were investigated by means of an ultra-fast imaging technique. Thin sections of the treated tissue were processed for histochemical analysis of enzyme activity to assess the extent of thermal/mechanical damage. Thereafter, a scanning beam technique was employed to deliver multiple pulses over a definite region of tissue. An analytical balance was used to measure the removed mass in order to calculate the ablation efficiency. The present quantity has been compared to the amount of the tissue damaged, as assessed by the histochemical analysis. The present work shows that the interaction of the Erbium-YAG laser pulses with a soft tissue may cause a large amount of mechanical damage, while thermal damage is restricted within a thin layer around the ablation crater. A precise control of fluence and operating conditions prevents overwhelming side-effects, and possibly allows the use of the Erbium-YAG laser for the ablation of brain and other soft tissues.     

The use of the Nd-YAG and the CO2 laser in neurosurgery

Summary Over the last 3 years 120 patients have been operated on using laser techniques. This technique was chosen where technical difficulties were anticipated due to the size, the vascular supply or the localization of the process. Although the use of laser technique requires experimental work, before it can be applied clinically some distinct advantages could be demonstrated when compared with the use of the bipolar cautery.Due to its shrinking effect the laser beam is target oriented and makes the surgical procedure safe without the use of additional instruments. The Nd-YAG laser was preferred in tumors with a rich vascular supply. Thus there was a definitely decreased need for blood transfusions in patients operated on with the laser. Even those parts of the tumors that can not easily be reached, using conventional techniques can now be eliminated by laser irradiation.The variable distance between the handpiece of the laser instrument and the target organ allows a pin point as well as a more diffuse irradiation. Since it is not necessary to touch the tissue, laser techniques are particularly useful in critical areas, e. g. close to the brainstem or the spinal cord, because they make it unnecessary to touch the tissue.The question as to whether the use of laser technique will reduce the rate of recurrent tumor growth needs further studies based on longer follow-up periods. Further technical improvements are needed to make the laser device a true microinstrument. Finally a combination of both laser types — that is the Nd-YAG laser for coagulation and the CO₂ laser for cutting -might be a definite advantage.Dedicated to Prof. Dr. Dr. h. c. K. J. Zülch on occasion of his 70th birthday.     

Evaluation of the Ar+ laser thermal effect in rabbit brain tissue by means of optical absorption coefficients. Photoacoustic measurements

Summary In predicting Ar⁺ laser-neural tissue interaction a determination of the optical absorption properties of brain parenchyma appears indispensable. In this study a determination of absorption spectra of different areas of rabbit brain at the wavelength of an Ar⁺ laser beam is made. The areas considered in the study are frontal and occipital gray and white substance, thalamus, basal ganglia, cerebellar cortex and choroid plexus. Specimens of these areas measuring 2×3×3 mm were obtained from coronal sections 1 cm thick of 20 rabbit brains. The analysis of optical properties was made by means of a photoacoustic spectrometer which appears the only suitable technique for testing the optical absorption properties of biological materials. The absorption coefficient results were similar in magnitude and constant in all the areas examined, measuring approximately 50 cm^–1. The prediction of lack of any selective effect for the different areas is confirmed by the sizes of lesions made in cerebral specimens of the same areas of the contralateral hemisphere by means of Ar⁺ laser: the lesions increase in size in proportion to the increase in output power and exposure time, independently of the areas considered. Also the histological examination of the areas shows the same morphology to be independent of the variations of both output power and exposure time. The only differences were the presence for short exposure time and low output power of a carbonized layer inner to the layer of coagulative necrosis.