Percutaneous discetomy has become a viable alternative in the treatment of herniated intervertebral disc. This study determined the effectiveness of holmium: YAG laser for ablation of human disc tissue. Human cadaveric intervertebral disc was harvested and stored in cold saline-soaked gauze for evaluation within 24 hr of removal. Using a specially designed apparatus, a 600 microns diameter fiber was advanced perpendicular through the annulus fibrosis at a controlled force of 0.098 Newtons (10 g). Samples were lased in air (n = 17) and in room temperature saline (n = 32). The laser energy was delivered at 5 Hz, 250 microseconds pulsewidth, and from 50 mJ/mm2 to 1,100 mJ/mm2 fluence. Three to six holes were lased using identical parameters in each tissue specimen and were evaluated histologically and by morphometric analysis. The maximum zone of thermal necrosis and thermal denaturation occurred at 700-1,100 mJ/mm2; 140 microns and 590 microns in air and 80 microns and 730 microns in saline, respectively. At fluences between 200 and 700 mJ/mm2, the thermal necrosis ranged from 20 to 60 microns in air and from 10 to 50 microns in saline, the zone of denaturation also being less. The holes created with the 600 microns fiber were circular in shape, with a mean diameter of 500 microns (n = 3). The etch rates (penetration/pulse) appeared to increase with increasing fluences. In saline, the etch rate ranged from 7 to 53 microns/pulse (r = 0.57, P less than or equal to 0.10), and, in air, the values ranged from 7 to 65 microns/pulse (r = 0.79, P less than or equal to 0.03).(ABSTRACT TRUNCATED AT 250 WORDS)

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The ablation of atherosclerotic lesions without collateral thermal or shock wave damage is thought to be a key element for successful laser angioplasty. This study evaluated the effectiveness of pulsed holmium:YAG laser (2.1 microns wavelength) for this application. Fresh normal tissue (n = 139) and arteriosclerotic canine arteries (n = 21) as well as formalin-preserved normal canine (n = 31) and atherosclerotic human arteries (n = 177) were irradiated under saline via a 600 microns diameter fiber placed perpendicular to the intimal surface with 0-10 gm of force. The laser was operated in the free running mode (FRM; 250 microseconds pulsewidth, 5 Hz, 30-7,100 mJ/mm2) and in the Q-switched mode (QSM; 200 nsec pulsewidth, 6 Hz, 30-1,100 mJ/mm2). Following the experiments, the samples were prepared for histologic and morphometric analysis. Ablation thresholds in the FRM were 60 and 180 mJ/mm2 in fresh and preserved canine tissue, respectively. Ablation thresholds in the QSM for fresh and preserved canine tissues were 75 and 180 mJ/mm2, respectively. Thresholds for human atherosclerotic tissue were dependent on the amount of calcification. In the QSM and FRM, there were no samples that could not be penetrated at 1,100 mJ/mm2 and above. Histologic examination of the FRM samples revealed confined columns of tissue ablation, with approximately 55-250 microns and 70-140 microns zones of thermal effect being apparent in the fresh and formalin-preserved samples, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

This study evaluates the in vivo correlation' ofintravascular ultrasonography and uniplanar angiography in determining the luminal dimensions of normal and moderately atherosclerotic human arteries. Five French and 8F rotating A scan intravascular ultrasound catheters were used to obtain 48 images in four superficial femoral arteries, five iliac arteries, and one aorta in eight patients undergoing vascular surgery. Cross-sectional areas measured by intravascular ultrasonography were compared to cross-sectional areas calculated by uniplanar angiography of the same location in the vessel. Maximum and minimum luminal diameters were also measured from intravascular ultrasound images. An ellipticity index was defined as the maximum/minimum diameter ratio (max/min) and ranged from 1.0 to 1.8 (mean, 1.2). Comparison of the cross-sectional areas measured from intravascular ultrasound images and those calculated from uniplanar angiography showed no significant difference at any level of ellipticity studied. However, when the values of cross-sectional areas were analyzed in groups corresponding to the diameter of the vessel, that is, aortic, iliac, and femoral, the values for the iliac arteries calculated from uniplanar angiography were significantly greater by 9.8% -+ 0.7% (n = 29, p = 0.03)