Search PubMed⌕ Search

Biomedical subjects

M Motamedi

Publications and source records attributed to M Motamedi.

67 records · Page 4Linked to original sources
PubMed1994

Modeling of intraluminal heating of biological tissue: implications for treatment of benign prostatic hyperplasia.

A computer model for predicting the thermal response of a biological tissue to different intraluminal heating modalities is presented. A practical application of the model is to calculate the temperature distributions during thermal coagulation of prostate by contact heating and radiative heating. The model uses a two-dimensional axisymmetric diffusion approximation method to calculate the light distribution during radiative heating. The traditional Pennes' bio-heat equation is used to calculate the temperatures in the presence of blood flow. An implicit finite difference scheme with nonuniform grid spacings is used to solve the diffusion equation for light distribution and the bio-heat equation. Model results indicate that the radiative heating of prostate by Nd:YAG (1064 mm) and diode (810 mm) lasers can be a more effective and efficient means of coagulating a large volume of prostate, as compared to contact heating of the tissue. Blood perfusion is shown to provide a considerable heat sink as the laser exposure time is increased. Surface cooling by irrigation during the laser irradiation of tissue is shown to be an effective method for delaying tissue explosion and obtaining a large volume of coagulated tissue. The model also shows that the volume of the coagulated tissue is appreciably altered by a change in the rate of energy deposition.

Animals↗
PubMed1994

Dye-enhanced ablation of enamel by pulsed lasers.

Laser removal of dental hard tissue has been proposed as a replacement for or augmented approach to the dental handpiece. The main limitation for widespread usage of lasers in dentistry has been inefficient ablation of dental hard tissue, accompanied by potential laser-induced damage to the surrounding tissue. The research focuses on a novel approach for enhancement of tissue ablation and confinement of laser interaction to a small tissue volume by controlled placement of an exogenous dye on the enamel surface. Studies were done with both pulsed alexandrite and pulsed Nd:YAG lasers, with indocyanine green and India ink, respectively, used as photo-absorbers. These dye-enhanced laser processes demonstrated the feasibility of this technique for cavity preparation. While control studies produced little or no appreciable crater, average preparation depth for the dye-enhanced ablation was from 1 to 1.5 mm, with a diameter of approximately 0.6 mm. Knoop hardness measurements show that, surrounding the crater, there is small annular region slightly softened by the laser action. SEM studies of the interior structure of the tooth did not show significant damage to the surrounding tissue. Temperature measurement studies indicated that the pulsed nature of the laser, combined with the photo-absorbing dye, effectively prevented significant temperature rise at the pulp. The remarkable effectiveness of this technique in creating cavity preparations and the absence of any notable collateral damage to the surrounding tissue suggest that dye-enhanced pulsed-laser ablation could be used as an alternative to the dental handpiece in selected procedures.

Carbon↗
PubMed1993

Continuous wave laser ablation of tissue: analysis of thermal and mechanical events.

Thermal and mechanical events during continuous wave (CW) laser ablation of biological and phantom media were investigated. Porcine aortae, collagen fibers, and polyacrylamide control samples were subjected to argon laser irradiation while infrared and high-speed (240 images/s) video cameras were used to monitor their surfaces. Subsequent analysis of simultaneous changes in surface temperature and physical features correlated thermal and mechanical events. Video images recorded prior to ablation onset of tissue slabs clearly revealed two distinct phases: 1) progressive growth of a surface dehydration zone, and 2) surface deformation, implying subsurface bubble formation. Surface temperature recordings and video imaging revealed that the onset of CW ablation of soft biological media often initiated with a violent explosion, surface tearing, and tissue ejection. Histological inspection revealed intense coagulation in superficial layers near the irradiation site, whereas chiefly mechanical disruption was noted at the base of the crater. Ablation characteristics were consistent with theoretical calculations which indicate subsurface temperature peaks that increase in magnitude and surface proximity as energy deposition rates are increased. Results also suggested that mechanical properties of target media strongly influenced the extent of pressure built up, the nature of ablation onset, and the characteristics of the overall ablation pathway.

Acrylic Resins↗
PubMed1992

Origin of arterial wall dissections induced by pulsed excimer and mid-infrared laser ablation in the pig.

To study adjacent tissue damage after delivery of holmium, thulium and excimer laser pulses, porcine thoracic aortas were irradiated in vivo. After 3 days, microscopic analysis of 67 craters produced by all three lasers demonstrated large dissections extending from the craters. The mean diameter of the dissections was smaller for excimer-induced craters (1.38 +/- 0.42 mm; n = 22) than for holmium-induced (2.7 +/- 0.87 mm; n = 22) and thulium-induced (2.37 +/- 0.42 mm; n = 14) craters (p less than 0.01 vs. mid-infrared dissections). In addition, microscopic analysis demonstrated necrosis adjacent to the crater. The lateral necrotic zones of the thulium-induced craters were smaller than the holmium- and excimer-induced necrotic zones (p less than 0.01). To identify the origin of the excessive tissue tearing, laser-saline and laser-tissue interaction were compared in vitro by time-resolved flash photography. In saline solution, the mid-infrared lasers showed bubble formation on a microsecond time scale. The excimer laser produced similar bubbles in the vicinity of tissue. For all three lasers, elevation of the tissue surface was shown during in vitro ablation. Dimension (diameter up to 4 mm) and time course (rise time of 100 to 300 microseconds) of bubble formation and tissue elevation were strikingly similar. Thus, tissue dissections are caused by the expansion of a vapor bubble within the target tissue. Coronary dissections after excimer and mid-infrared laser angioplasty might be related to the forceful bubble expansion.

Angioplasty, Laser↗
PubMed1991

Laser thermal ablation.

Continuous wave and pulsed laser ablation of tissue is described as an explosive event. A subsurface temperature maximum and superheated tissue produce high pressures that eject fragments from the tissue. Decreased water content due to dehydration and vaporization decreases thermal conductivity which reduces heat conduction. Also, a decrease in water content dramatically alters the local rate of heat generation of laser radiation above 1.3 microns since water is the primary absorber. In contrast, at UV wavelengths protein and DNA are the primary absorbers so destruction of tissue bonds is due to direct absorption of the laser light rather than heat transfer from water.

Animals↗
PubMed1990

Disparate absorption of argon laser radiation by fibrous versus fatty plaque: implications for laser angioplasty.

The thermal response of white fibrous atheromatous plaque to argon laser irradiation was compared with the thermal response of yellow fatty plaque and normal aortic wall to the same type of radiation. Samples of normal aorta, fibrous, and fatty plaque were irradiated in air with 3.5 Watts of laser power on a 2 mm spot for 5 and 10 seconds. Heterogeneous foci, each covering normal aorta and either fibrous or fatty plaque, were additionally irradiated with 7 Watts on a 1 cm spot for 30 seconds to 2.5 minutes. Tissue surface temperature was monitored during laser irradiation via a 3-5 micron infrared camera. For the 2 mm spot and 5 second exposure time, argon laser irradiation of normal aorta produced popping and surface tearing at a peak temperature of 145 +/- 10 degrees C. Irradiation of fatty plaque produced popping and crater formation at a peak temperature of 200 +/- 10 degrees C. However, fibrous plaque was nonablatively discolored by the same dose of laser radiation with a peak temperature of only 85 +/- 10 degrees C. Irradiation for 10 seconds caused crater formation and carbonization in the fatty plaque but failed to produce ablation in the fibrous plaque. Irradiation of the heterogeneous foci confirmed the disparity in the temperature attained by these two types of plaque and their degree of damage. Therefore, this study suggests that the ablation threshold for soft atheroma is strongly dependent on the optical properties of the particular type of tissue. Yellow fatty plaque preferentially absorbs argon laser radiation, but white fibrous plaque absorbs this radiation less readily than normal aortic wall.

Angioplasty, Balloon↗
PubMed1990

[Atypical aspects of the electroencephalogram in subacute sclerosing panencephalitis].

Diffuse paroxysmal and periodic discharges in subacute sclerosing panencephalitis (SSPE), have a specific temporo-spatial character in about 90% of cases. A random selection of 100 among 358 cases was performed in this study and the following results were obtained. Twelve cases showed no initial diffuse paroxysmal and periodic discharges but an atypical pattern consisting in: 1) unilateral periodic activity (three cases); 2) bifrontal rhythmic delta activity (two cases); 3) epileptic discharges, one of which was absence (four cases); focal delta activity (one case); 5) normal EEG (two cases). One apparently benign case is also reported.

Adult↗
PubMed1989

A theoretical study of the effect of optical properties in laser ablation of tissue.

The role of optical properties in the distribution of laser light and the resulting thermodynamic processes in biological tissue is studied from a theoretical perspective. Light distribution is modeled by a discrete ordinate method and heat transfer and ablation is modeled by an immobilized finite element method. The effect of parametric variation of absorption, scattering anisotropicity on the dynamics of the ablation process is examined. The manifestation of higher than the ablation threshold temperature in the subsurface tissue is observed and discussed. Results indicate significant differences in the ablation behavior which may have important clinical implications.

Hot Temperature↗
PubMed1988

Plaque-media rewelding with reversible tissue optical property changes during receptive cw Nd:YAG laser exposure.

Laser dosimetry for thermal fusion of plaque-wall separations during laser balloon angioplasty (LBA) is dependent upon the optical properties of the atheromatous arterial wall during one or more exposures to cw Nd:YAG laser radiation. An integrating sphere technique was used to measure relative transmission and reflection continuously during irradiation of human postmortem atheromatous aortic sections. Tissue luminal surface temperature was recorded continuously with a thermographic video imager during repetitive 20-30-sec, 8-15-watt exposure of a 3-mm nominal spot. In all specimens, transmission fell progressively during each exposure by 10-70% of baseline values. This effect was reversible with normalization of transmission during the initial phase of each subsequent exposure. Changes in transmission were inversely related to temperature over a 50-170 degrees C range, whereas relative reflection remained constant. Accompanying reversible transmission changes was the observation that the weld strength of plaque-aortic wall separations was unchanged by repetitive laser welding and tissue separation of individual sections. In conclusion, temperature-dependent reversible optical and physical properties of plaque occur during exposure to 1.06 microns cw laser radiation.

Angioplasty, Balloon↗
PubMed1987

Laser probe ablation of normal and atherosclerotic human aorta in vitro: a first thermographic and histologic analysis.

The metal-tipped optical fiber or "laser probe" has been extensively studied in animal preparations in vivo and in human clinical trials of revascularization. The aim of this study was to evaluate the thermal characteristics of laser probe tissue ablation and to contrast the vascular tissue response to exposure to the laser probe and bare optical fiber. A 2 mm laser probe was heated with up to 4 W of argon-ion laser irradiation and applied to six postmortem strips of human nonatherosclerotic aorta as well as to five atherosclerotic aortic specimens. Surface temperature maps of the laser probe and of the vascular tissue in air were obtained via 8 to 12 micron thermographic imaging. Laser probe temperature was additionally monitored via thermocouples. Two strips each of normal and diseased aorta were irradiated directly with the bare optical fiber. Thus a total of 43 laser probe application sites and 19 bare fiberoptic laser irradiation sites on a total of 15 aortic strips were analyzed both thermographically and histologically. Based on measured temperature rises and histologic findings, the following observations were made: (1) The laser probe heats initially at its tip and attains a uniform surface temperature distribution within 5 sec. The steady-state temperature attained by the probe is inversely related to the thermal conductivity of the surrounding media. In all media studied, probe temperature increases linearly with applied laser energy. (2) Tissue ablation starts at temperatures greater than 100 degrees C, and ablation temperatures typically exceed 180 degrees C. Adventitial temperatures during laser probe application may reach 70 degrees C. Tissue ablation is enhanced both by greater laser energy deposition in the probe and by higher force at which the probe is applied to tissue. (3) Ablation of fibrofatty atheromata is more extensive than of nonatherosclerotic aortic tissue. This may be due to the lower thermal conductivity of atheromatous tissue. (4) In contrast to direct argon-ion laser ablation of aortic tissue, laser probe-mediated ablation occurs in a controlled fashion, is not associated with extensive subintimal dissections, and allows uniform conduction of heat to tissue as reflected by essentially "isothermal" injury lines.

Aorta↗
PubMed1985

Effect of laser radiation on tissue during laser angioplasty.

The thermal properties of adipose and ceramic atherosclerotic plaque deposits and normal arterial vessel wall were measured in the temperature range of 25-95 degrees C. In general, the data indicate that fatty plaques exhibit the lowest thermal conductivity and thermal diffusivity of the three types, whereas calcified plaques seem to have the highest values. By using a video scanning thermograph, temperature rise was recorded in normal vessel wall and plaque during ablation of tissue. Theoretical analysis suggested that realistic modeling of laser angioplasty should account for scattering of light, water content, and ablation. This paper is a preliminary report of these results.

Arteriosclerosis↗
PubMed1977

The pathogenesis of Pott's paraplegia and the effect of surgical intervention in its course and prognosis.

14 cases of Pott's disease of the spinal column treated by surgery is described. The operation was performed by an anterior approach and evacuation of abscess, removal of granulation tissue, seguesterated bone and disc material achieved. Any mechanical compression by bony ridges, dense fibrotic tissue or fibrotic posterior longitudinal ligament was removed making it possible for anti TB treatment to have full effect. Stability of the spine was achieved by means of anterior bone grafts which accelerated bony fusion and eradication of the disease. It is stressed that this type of radical surgery in Pott's allows for histological diagnosis, corrects the deformity thus preventing future cardio-respiratory complications, prevents paraplegia of late onset, and shortens the duration of hospital stay allowing the patient to return to his previous occupation.

Adolescent↗