Picosecond time-resolved fluorescence measurements were performed on fibrous and calcified atherosclerotic plaque and normal coronary artery with 351nm picosecond excitation of a mode-locked Nd-glass laser. Double exponential decay profiles were measured. The fast component of lifetimes of fibrous plaque is different than that of normal artery or calcified plaque and can be used to discriminate fibrous plaque from normal artery.

The purpose of this investigation was to determine which illumination wavelength produces the largest differences between the fluorescence emission spectra of normal and atheromatous vascular tissue. The fluorescence spectra for 12 excitation wavelengths ranging between 270 nm and 470 nm were examined and compared. The Hotelling trace, a figure of merit describing class separability, was used to compare the excitation wavelengths. Preliminary results indicate that illumination in the range from 314 nm to 334 nm consistently performed well. Wavelengths in the 364 nm to 436 nm range also showed promising performance for a limited data set. These results were found to be relatively independent of the catheter angel and distance to the tissue.

Multispectral imaging was investigated as a technique to exploit the spatial and spectral information available in the diagnosis of atherosclerosis. A diagnostic system is proposed that could provide direct viewing of a standard endoscopic or a total-fluorescence image. In addition, multiple spectral-feature images, each associated with a separate, narrow spectral band, could be obtained and processed to produce an optimized contrast image. In this study, a 'white-light' image and a total-fluorescence image were obtained. In addition, a three- dimensional, multispectral data set was generated, and two methods of utilizing this data were explored: (1) a per-pixel ratio of fluorescence intensities, and (2) an optimized superposition of the spectral-feature images. Fluorescence imaging is found to provide a rich data set possessing great potential for improving the detection and characterization of atheromatous disease.

Resonantly enhanced fluorescence emission induced by a tunable dye laser can be used for the identification of ablated atherosclerotic tissue. This method has been tested with anorganic samples exposed to air and to saline solution. A XeCl excimer laser pulse ((lambda) = 308 nm), delivered by a fused silica optical fiber, causes an efficient ablation of the irradiated samples. The wavelength of the narrow-band dye laser radiation is set to a strong transition of a specific species to be detected in the ablation plume. Taking into account the formation of the plume, the dye laser pulse is applied with a certain delay in order to excite resonantly the selected species in the plume. The resulting resonance fluorescence then is guided by optical fibers to an optical multi-channel analyzer system. Compared to the broad-band fluorescence during excimer laser ablation the resonance fluorescence signal shows a distinct and easily detectable sharp peak. The signal-to-background ratio is improved by one order of magnitude.

Ablation and tissue removal of normal and atherosclerotic arterial wall by pulses of λ = 308 nm laser radiation have been probed by visible pulsed dye laser radiation. Photographs have been taken where the samples are irradiated in saline solution. The pulsewidth of the ablating XeCl excimer laser is about Δτ = 30 ns FWHM. The pulses have been transmitted through a fused silica fiber with a core diameter of 600 micrometers . The pulse energy was set to 20 mJ at the distal end of the fiber corresponding to a fluence of 7.5 J/cm2, which is well above the ablation threshold. Visible radiation of a dye laser operated at a wavelength of λ = 580 nm (Δτ ~ 10 ns FWHM) is used to illuminate the tissue surface and the ablation plume. The delay time of the probing pulses with respect to the 308 nm pulses is varied in the nanosecond range up to several hundred microseconds. The ablation process and the resulting plume above the tissue surface are recorded with a CCD camera attached to a PC-based image-processing system. All samples under investigation were fresh human cadaver aortic and femoral artery specimens (less than or equal to 48 h), which had been shock-frozen. The arterial segments showed different types of lipid rich and calcified plaques.

The influence of (Beta) -carotene content upon the laser induced total fluorescence was evaluated in human arteries in vitro using 30 mw argon laser beam at 488 nm. Experiments showed that the (Beta) -carotene content in normal arteries increases with longer period of incubation in (Beta) -carotene solution. This is consistently associated with a drop in total fluorescence. The arterial absorption at 488 nm resulting from (Beta) -carotene deposition is twice as great as that before incubation causing a decrease of total fluorescence by 48%. These experimental data were highly correlated with theoretical analysis derived using a multi- layer model by introducing a parameter describing the quantity of (Beta) -carotene bound to the arterial tissue (R=0.94). Total fluorescence from 138 samples of various types of atherosclerotic plaques was compared with that from normal arteries which were used as controls. The total fluorescence gradually decreases with longer incubation period in (Beta) - carotene solution. Seventy-nine plaques with surface fissures exhibited obvious reduction in total fluorescence. This study shows that the pretreatment with (Beta) -carotene may enhance the ability of the diagnosis of atherosclerotic plaque from normal artery using total fluorescence intensity.

Three potential guidance mechanisms for pulsed laser angioplasty were tested for their ability to discriminate between different tissue types. Holmium:YAG laser energy (wavelength=2.1 um, 100 mJ/pulse, 12.7 J/mm² fluence) was delivered through a 100 um fiber into normal artery, fibrous plaque, and calcified plaque, as well as saline and blood. Plasma emission, mechanical fiber recoil, and acoustic shock wave were all measured during laser irradiation of these different substances. Plasma emission was detected by a photodiode at the proximal end of the fiber. Mechanical fiber recoil was detected using a phono cartridge mechanically coupled to the fiber 60 cm from the distal end. Acoustic sound waves were detected with a hydrophone in close proximity to the target site. The probability of generating plasma emission and the relative magnitudes (1-4) of the mechanical recoil and acoustic signal are as follows: Signal Blood Normal Aorta White Plaque Calcified Plaque plasma 0% 0% 0% 99% acoustic 4 1 1 4 recoil 1 2 2.5 4 A Fourier transform of the acoustic signal showed differences between blood, normal artery or non-calcified plaque, and calcified plaque. Mechanical recoil does not provide additional information. These techniques do not differentiate normal tissue from fibrous plaque but will discriminate calcified plaque from blood, normal artery, and non-calcified plaque. These techniques are relatively easy to implement and provide potentially useful feedback to guide laser ablation. Conclusion: The presence of plasma is a good indicator of calcified plaque; when used in conjunction with the acoustic signal it could indicate whether the fiber catheter is on calcified plaque, non-calcified tissue, or in blood.

A laser angioplasty technique is presented, which utilizes a set of suitably developed catheters to enlarge in subsequent steps the recanalized neolumen.

Excimer Laser Angioplasty was attempted in 47 patients (36 males, 11 females, mean age 62+/- 7 years, range 39-77 years), affected by peripheral vascular disease. Thirty-seven patients had a total occlusion of the superficial femoral artery, 3 of the iliac artery and 1 of the popliteal artery; 6 patients showed a subocclusive stenosis of the superficial femoral artery. Occlusions and subocclusive stenoses were classified by length: < 10 cm (28 cases), > 10 cm (19 cases). A commercial excimer laser (Technolas Max-10) was used at the Xenon- Chloride wavelength of 308 nm. The laser operated at 60 ns pulse length and at 20-40 Hz repetition rate. Applied energy fluence was 20 mJ/pulse. The energy was delivered through a multifiber catheter, which combines 12 (7F) or 18 (9F) fibers (260 micron diameter each), concentrically arranged. Balloon dilatation was associated to complete the procedure in 38 cases. The treated arteries were successfully recanalized in 41 out of 47 patients (87%). Hemodynamic improvement was confirmed by a significant increase of ankle/brachial systolic pressure index (from 0.60+/- 0.17 to 0.79+/- 0.20, p < 0.005). Failure to recanalize arterial occlusion occurred in 6 cases, and was due to dissection in 3 patients and inability to cross the final segment of a long occlusion in 3 patients. The success rate was higher for lesions < 10 cm in length. Early reocclusion was observed in 7 patients and was associated with poor run-off. The cumulative patency rate at 1 month was 90.7%. Preliminary results are encouraging. More suitable catheters and better selection of patients should improve the efficacy of laser angioplasty and should allow to perform laser procedures without combining balloon angioplasty.

We report on a medical excimer laser system developed for laser angioplasty. One of the unique features of this excimer laser is the required low frequency of gas replenishment. Data presented, showing the time between gas changes, is approaching six months. As of December 1, 1990, more than 500 percutaneous coronary cases have been performed using this system. The catheters used for the majority of the cases are composed of 100 micron fiber bundles. The cutting depth per pulse is shown to be proportional to the catheter active area.

The temperature increase of porcine aortic tissue irradiated with 220 ns XeCl 308 nm excimer laser pulses above ablation threshold have been measured by means of an IR camera. The decay of the temperature increase after a laser pulse is characterized by a fast decay during the first few milliseconds followed by a slow decay over a prolonged period, suggesting temperature accumulation at repetition rates used in laser angioplasty. The decay is adequately described by the theoretical prediction of the diffusion of heat after adiabatic heating of the tissue by a short laser pulse. From the temporal behavior of the decrease of temperature after a laser pulse, attenuation coefficients at 308 nm could be estimated. Attenuation coefficients after a single pulse are smaller than attenuation coefficient after multiple pulses. The temperature increases found in the experiments might explain thermal damage in myocardial tissue in earlier experiments. In an experimental set up simulating the situation during clinical excimer laser angioplasty, temperature increases of 43 degree(s)C average were found.

Ray-tracing was used to calculate the beam profiles and spatial intensity distributions of modified fiber tips used in laser angioplasty. The position of the highest irradiance and the increase in power density relative to the power density at the tip of a bare fiber were calculated for probes made of silica or sapphire, in air and water. The computations were compared to paraxial theory and measurements on ball-shaped fibers and hemispherical probes. The calculated beam profiles and the irradiance distributions of the probes were in agreement with the measurements. The position of the highest irradiance and the power density increase depended on the ratio between the radius of the sphere R_s and the fiber R_f and on the refractive index. Intermal reflections limited the power density increase for smaller ratios R_s/R_f. In water, the description of beam propagation from silica probes using paraxial optics theory was not in agreement with the ray-tracing results. Ray-tracing is useful to analyze the optical characteristics and to optimize the design of optically modified fiber tips when paraxial optics theory cannot be applied.

Recanalization of occluded limb arteries can be accomplished using a pulsed dye laser. Either ball-tipped 600 micrometers fused quartz optical fibers or over-the-wire multifiber catheters are used to deliver laser energy. The alignment of the device is adjusted to achieve maximal transmitted power. To monitor power output during surgery the authors have developed an in- line powermeter (ILP). On leaving the laser the ball-tipped optical fiber is magnetically clamped in a V-groove. Radial light emission is converted to an electrical signal which is integrated to give an analogue output proportional to power. The reading is adjusted to be concordant with that from the bolometer. Over the range 20 to 200 mJ per pulse the linearity was better than 2.5% of full scale. The coefficient of variation of the ILP output following repeated placement of the same aligned fiber in the V-groove was less than 7%. Flexing the fiber through 90 degree(s) 10 cm from the V-groove caused the registered power to fall by up to 7%. In the case of the multifiber catheter a modified clamping arrangement was used. Linearity for a 7 Fr catheter comprising 15 fibers 200 micrometers in diameter was better than 5% of full scale; the coefficient of variation for repeated alignment of a catheter was 14%. The catheters do not have a circular section, which accounts for this large variation. Flexing the catheters had no consistent effect on registered power, but changes of up to +/- 10% could be obtained by extreme bending of the catheter. The output of the ILP does not appear to be affected by the nature of the target. Changes in output power and/or delivery device alignment can be detected and corrected during laser angioplasty. Accurate control of power delivered without exposing the tip of the fiber reduces the risk of injury from inadvertent laser discharge and aids optimal ablation of atheroma. The ILP ensures that effective power is maintained throughout the procedure.

Laser balloon angioplasty has been used in recent years to treat peripheral artery disease. Despite a primary success the technique is plagued by a high restenosis rate. Directional atherectomy was performed in a small group of patients affected by primitive stenosis or restenosis after an invasive procedure. Light microscopy, immunohistochemistry, and transmission electron microscopy have identified the cellular component of intimal hyperplasia as smooth muscle cells in an active synthetic phenotype. The arterial healing process after invasive procedures seems to develop similarly independently of the device employed.

Holmium-YAG (2.1 (mu) ) laser recanalization was attempted in 10 totally occluded miniature swine iliac arteries using a lensed fiber delivery system. The iliac artery occlusions were created in a Yucatan miniature swine model of atherosclerosis by means of a high cholesterol diet and balloon endothelial denudation. In order to increase the spot size, a spherical silica lens was attached to the distal end of a 300 micrometers core diameter silica optical fiber. The holmium-YAG laser was operated in the free-running mode with 250 microsecond(s) ec pulses at 4 Hz. The energy delivered was 225 mJ per pulse for the 1.0 mm lensed fiber and 200 mJ per pulse for the 1.3 mm lensed fiber. Laser energy was delivered in 2 to 5 second bursts. Successful recanalization was achieved in all 10 arteries attempted without perforation of the arterial wall. The average length of the occlusions was 5.0 +/- 1.8 cm. Following successful laser recanalization significant stenoses (>50%) remained in all of the arteries as judged by angiography. In conclusion, the lensed fibers coupled to the pulsed holmium-YAG laser were safe and effective in recanalizing these difficult lesions in relatively straight iliac arteries. There is potential clinical utility for this system as an adjunct to balloon angioplasty in patients with lesions which are unable to be crossed with guidewires.

Laser angioplasty has been proposed as a less invasive alternative to bypass surgery for the treatment of occlusive vascular disease in the coronary and peripheral circulation. A major limitation of most laser angioplasty systems has been the inability to create a new lumen, which is larger than the diameter of the laser catheter. The principal reason for this shortcoming has been the fact that most laser angioplasty catheters, yet developed, have projected the laser energy from the distal tip of the catheter, parallel to the central axis of the catheter. This approach works well for the removal of plaque directly in front of the distal tip of the catheter, but it not very effective for debulking eccentric stenoses or lesions larger than the catheter diameter. To address this limitation, we decided to develop a laser angioplasty catheter from which the laser energy exits from the side of the catheter, instead of the tip. The critical element in a lateral-aiming laser catheter is an optical fiber which will project laser energy perpendicularly to its central axis. The fiber design would have to be mechanically stable, heat resistant, and capable of operating with high power cw and pulsed lasers. Thus, a small-diameter catheter including such an optical fiber may be able to effectively debulk large or eccentric stenoses.

Laser-balloon angioplasty (LBA) may potentially be used for local application of pharmacologically active agents which will reduce thrombogenic and proliferative responses after the angioplasty. In this study, the feasibility of applying covalently conjugated heparin- albumin microparticles onto arterial luminal surface was demonstrated. The covalent linkages were formed by reaction with 1-ethyl-3-dimethyl-aminopropyl-carbodiimide (EDC), and the resultant conjugates were used for preparation of microparticles by employing standard emulsification and heat-crosslinking techniques. The heparin release rate from the microparticles was found to be dependent upon the degree of crosslinking. When a thin coagulum of a suspension of microparticles was formed with heat on a glass surface, the treated surface demonstrated resistance to clot formation in contact with non-anticoagulated blood. A suspension of the microparticles applied during laser-balloon angioplasty onto the luminal surface of dog carotid and femoral arteries showed persistence for up to one week without thrombus formation or occlusion of the vessel. Since the rate of biodegradation is primarily dictated by the extent of crosslinking, an optimal degree of thermal denaturation will permit longer persistence of the carrier while allowing adequate release of the entrapped pharmacologic agent. A variety of antithrombotic and antiinflammatory agents are being considered as candidate bioprotective materials for local application after angioplasty.

The goal of this study was to investigate the relationship between ultrasonic tissue ablation and passive mechanical elasticity. Experience with ultrasonic angioplasty in experimental settings (in-vivo and in-vitro) together with clinical experience in peripheral vascular disease is reported. A model composed exclusively of a hydroxyproline ballistic gelatin matrix showed a negative correlation between material elasticity and the rate of ultrasonic ablation. This model provided a means of studying the effects of collagen content on ablation, exclusive of other biologic components. Ballistic gelatin ablation (mg/sec) was found to increase logarithmically with decreasing protein concentration over the range studied (20.00 to 1.25%). Ablation as a function of gelatin elasticity behaved in a similar manner. Temperature of the material ablated was also demonstrated to affect the rate of ablation. We conclude that the previously reported differences in ablation between thrombi and blood vessel are predictable based on the large difference in their mechanical elasticity, and that this difference provides a wide margin of safety.

The Q-switched Alexandrite laser (750 nm/375 nm; 150 ns-2microsecond(s) ) may be a solid-state alternative to excimer and pulsed dye lasers in laser angioplasty. The aim of this study was to determine whether laser induced fluorescence spectroscopy performed at 375 nm excitation could guide an Alexandrite laser angioplasty system. Thirty three segments of femoral arteries - classified as normal aorta, yellow fatty atheroma, and calcified plaque - were irradiated at a fluence of 0.2 J/cm² and investigated spectroscopically in vitro. Calcified plaque and normal aortic LIF spectra showed a fluorescence peak at 450 nm, yellow fatty plaque spectra revealed an additional peak of equal or lower intensity at 520 nm. The ratio of the laser-induced fluorescence intensity at 465 nm and 530 nm was used to discriminate yellow fatty atheroma from normal artery wall. This fluorescence intensity ratio was 2.55+/- 0.25 for normal aorta, 2.35+/- 0.33 for calcified plaque, and 1.42+/- 0.27 for yellow fatty plaque, respectively. Using a discrimination threshold of 2.0, 95% of the yellow fatty plaque could be classified correctly. Thrombs showed no fluorescence signal. An Alexandrite laser system might allow the simultaneous ablation and identification of vascular tissue in laser angioplasty.

To overcome the abrupt closure and late restenosis after percutaneous transluminal coronary angioplasty (PTCA), new technology termed 'hot balloon angioplasty' has been considered. A novel laser-heated hot balloon catheter has been developed to address these problems. Its feasibility and acute thermal effects in the porcine coronary arteries in vitro was studied. As the balloon material was teflon (heat-resistant up to 240 degree(s)C). The temperature of the balloon could rise abruptly. So, intima~media were welded while marked thermal injury was not detected in adventitial tissue.

Nonsurgical ablation techniques have been proposed to cease conduction through accessory pathways which electrically connect the atrium and ventricle. The intent of this research was to investigate further the potential use of laser energy, delivered via a balloon catheter in the canine coronary sinus to photocoagulate the myocardial fibers responsible for accessory pathway conduction. Based on histological evaluation of the lesions created in acute and chronic studies, the extent of coagulation necrosis is sufficient to ablate most pathways which lie adjacent to the coronary sinus. Results from surface temperature measurements using repetitive laser exposures suggest that optical and/or thermal changes occurring in the myocardium are of greater importance than those occurring in the adipose tissue. Since the laser balloon catheter is surrounded by various tissue types, a Monte Carlo model was developed to determine the distribution of light in the atrioventricular groove.

The changes in total reflection and transmission of porcine myocardium due to thermal coagulation were measured during tissue heating in a temperature-controlled water bath, at different temperature ranging between 54 degree(s)-63 degree(s)C. At 633 nm, the measurements yield a picture of continuous decrease in transmission and a peak with a subsequent fall (approximately 10% from the peak) in reflection measurements of the tissue during coagulation process. Utilizing these measurements and an inverse solution to the radiative transfer equation, the optical properties of tissue, absorption, (mu)_a, and effective scattering, (mu)_s=(mu)_s(1-g) were calculated. A one-dimensional diffusion approximation was used to demonstrate the effects of thermally induced changes in the optical properties of tissue on light distribution in tissue. The pattern of changes in (mu)_a and (mu)_s seem to indicate that several simultaneous rate processes may be responsible for tissue coagulation. A postulate is put forward to use one such rate process to characterize threshold thermal damage to porcine myocardium and the accompanying protein denaturation.

The early experience using intra-operative endovascular ultrasonography (EU) is reported in eight patients undergoing lower extremity revasularization. In four patients, intra-operative EU successfully characterized inflow stenoses that were inadequately imaged with pre- operative arteriography. Two patients were found to have hemodynamically significant inflow stenoses, and were treated with intra-operative balloon angioplasty followed by repeat EU. The other two patients were found to have non-hemodynamically significant inflow stenoses requiring no treatment. Additional outflow procedures were required in all four patients. In the remaining four patients, EU was used to evaluate the completeness of TEC rotary atherectomy, of Hall oscillatory endarterectomy, of thrombectomy of the superficial femoral and popliteal arteries, and of valve lysis during in situ saphenous vein grafting, respectively. In the latter case, the valve leaflets were not clearly seen. In the other cases, EU assisted the surgeon. Angioscopy and angiography were available for comparison. In one case, angioscopy failed because of inability to clear the field while inspecting retrograde the limb of an aorto-bi-femoral graft. EU however was possible. No complications of EU occurred. EU is a safe procedure indicated when characterization of a lesion is needed prior to an intervention or when evaluation of the intervention's success is desired. We did not find it useful in valve lysis for in-site grafting.

This study compared carbon dioxide (CO₂) gas and saline as an irrigation medium for angioscopy in the femoral and coronary artery of 6 dogs. All angioscopy procedures were performed percutaneously and antegrade and, in the femoral artery, with and without proximal balloon occlusion. With saline and carbon dioxide gas, successful peripheral angioscopy with proximal occlusion could be performed in five and six dogs, respectively. Without proximal occlusion no angioscopy procedure was successful with saline, whereas with carbon dioxide gas in four dogs successful angioscopic images could be obtained. No complications occurred after peripheral CO₂ gas angioscopy. However, CO₂ gas angioscopy in the coronary arteries was lethal in all animals.

The combined guidance technique using angioscope and fluoroscope (i.e. angiography) images for CO laser angioplasty was demonstrated in vivo animal experiment. The newly developed total occlusion model which has been produced by a long term transplantation of Chitin^R tube in canine femoral artery was ablated by the contact irradiation of CO laser. A thin laser angioscope catheter, 5F in outer diameter, was inserted from total carotid artery to femoral artery by selective catheterization technique under fluoroscopy. A thin CO laser cable of which diameter was less than 0.6mm was advanced from the tip of the angioscope catheter. A As-S chalcogenide glass fiber of which diameter was 200micrometers was installed in the laser cable. The laser cable connected to the CO laser device which was developed for medical use. The angioscope catheter and laser cable could be seen by the fluoroscopy. The authors used the angioscope image of the occlusion end and the angiography image to check the direction of ablation hole. The simultaneous use of these images which include quite different kinds of information was extremely useful for the safety guidance of laser angioplasty for total occlusion. The histological specimen from the ablated occlusion showed that the repetitive ablation procedure made a larger lumen than the laser cable diameter.

Recent advances in catheter-based ultrasound imaging technology have led to the clinical reality of imaging coronary arteries and other vasculature in a manner that was not possible in the past. For the first time dynamic cross-sectional views of blood vessels can be obtained in patients in real time. Currently available instruments include catheters that contain a mechanically rotating ultrasound probe, catheters in which the ultrasound crystal is fixed but a rotating mirror transmits and receives ultrasound in a circumferential format and catheters with synthetic aperture array processing. Considerable amount of in vitro work has given a fundamental basis for interpreting intravascular ultrasound images and for using the technique in a quantitative manner to assess vascular anatomy. The feasibility studies, the current cited clinical applications and the areas where further work is required are reviewed.

This paper describes the in vitro (40 MHz) and in vivo (30 MHz) results of studies performed on human vessels using a mechanically rotated single element ultrasonic imaging system. The in vitro images were matched with the corresponding histologic cross-sections. Morphology of vessels and possibility to determine the extent of atherosclerosis were assessed by two blinded observers. Echographic images with an echolucent zone were seen to correspond with muscular type of arteries. The echographic images showing no echographic distinction between the various layers were seen to correspond with either elastic type of arteries, veins, veins used for bypass, or bypass Goretex grafts. The extent of atherosclerosis could only be assessed in the muscular type of artery. The data showed close correlation with histology (r = 0.89). In vivo studies (30 patients) revealed a characteristic three-layered appearance of the distal iliac and femoral artery. Normal cross-sections were readily differentiated from non- obstructive and obstructive lesions. In all these patients the hypoechoic muscular media served as an important landmark.

The purpose of this study was to investigate a Doppler guided catheterization system as an adjunctive or alternative methodology to overcome the disadvantages of left heart catheterization and angiography. These disadvantages include the biological effects of radiation and the toxic and volume effects of iodine contrast. Doppler retrograde guidance uses a 20 MHz circular pulsed Doppler crystal incorporated into the tip of a triple lumen multipurpose catheter and is advanced retrogradely using the directional flow information provided by the Doppler waveform. The velocity detection limits are either 1 m/second or 4 m/second depending upon the instrumentation. In a physiologic flow model of the human aortic arch, multiple data points revealed a positive wave form when flow was traveling toward the catheter tip indicating proper alignment for retrograde advancement. There was a negative wave form when flow was traveling away from the catheter tip if the catheter was in a branch or bent upon itself indicating improper catheter tip position for retrograde advancement. In a series of six dogs, the catheter was able to be accurately advanced from the femoral artery to the left ventricular chamber under Doppler signal guidance without the use of x-ray. The potential applications of a Doppler guided retrograde catheterization system include decreasing time requirements and allowing safer catheter guidance in patients with atherosclerotic vascular disease and suspected aortic dissection. The Doppler system may allow left ventricular pressure monitoring in the intensive care unit without the need for x-ray and it may allow left sided contrast echocardiography. With pulse velocity detection limits of 4 m/second, this system may allow catheter direction and passage into the aortic root and left ventricle in patients with aortic stenosis. A modification of the Doppler catheter may include transponder technology which would allow precise catheter tip localization once the catheter tip is placed in the aortic root. Such technology may conceivably assist in allowing selective coronary catheterization. These studies have demonstrated that Doppler guided retrograde catheterization provides an accurate method to catheterization the aortic root and left ventricular chamber without x-ray. In humans, it may prove useful in a variety of settings including the development of invasive ultrasonic diagnostic and therapeutic technology.

This study evaluates the ability of intravascular ultrasound (IUS) to image normal and mildly diseased human ileo-femoral vessels during angioplasty or vascular bypass procedures. Five Fr. and 8Fr. rotating A scan IUS catheters were used to obtain 43 images in 4 superficial femoral arteries, and 5 iliac arteries in 8 vascular surgery patients. Luminal cross sectional (LCS) areas measured by IUS were compared to LCS areas calculated by uniplanar angiography (ANGIO) at the same location in the vessel. The correlation between the areas (IUS vs ANGIO) for all images was significant (n = 43, r = 0.90, P<0.05). Mean LCS area calculated from ANGIO (33.7 +/- 21 mm²) was greater than LCS area measured by IUS (30.6 +/- 19.5 mm²) with n = 43; P = 0.02. In addition to providing accurate luminal determinations, IUS images displayed transmural morphology, the location of the atherosclerotic lesions and the thickness of the vessel wall. We conclude that IUS imaging provides accurate, novel information regarding human vessel wall anatomy and luminal dimensions. This technology may play a significant role in future diagnostic and interventional therapies.

The Magellan^TM coronary laser atherectomy system is described. It uses high- resolution ultrasound imaging and electromagnetic sensing to provide real-time guidance and control of laser therapy in the coronary arteries. The system consists of a flexible catheter, an electromagnetic navigation antenna, a sensor signal processor and a computer for image processing and display. The small, flexible catheter combines an ultrasound transducer and laser delivery optics, aimed at the artery wall, and an electromagnetic receiving sensor. An extra-corporeal electromagnetic transmit antenna, in combination with catheter sensors, locates the position of the ultrasound and laser beams in the artery. Navigation and ultrasound data are processed electronically to produce real-time, transverse, and axial cross-section images of the artery wall at selected locations. By exploiting the ability of ultrasound to image beneath the surface of artery walls, it is possible to identify candidate treatment sites and perform safe radial laser debulking of atherosclerotic plaque with reduced danger of perforation. The utility of the system in plaque identification and ablation is demonstrated with imaging and experimental results.

It has been a long sought goal to visualize the morphology and structures of internal organs nonmvasively. Two dimensional imaging of body regions has proven to very successful in clinical and diagnostic medicine. Since the early work on three-dimensional (3D) display' of biomedical images by Greenleaf et. aL2 there is a growing realization that visualizing the actual shape and function of an organ in three-dimensional space and in time will enhance the diagnosis and possibly aid the management of patient therapy. The increasing speed of computations at decreasing costs, and the fact that many of the modem imaging methods generate images in digital form has made volumetric imaging feasible. Although the production of 3D images in the least time, with a greater accuracy, and at a reduced cost continues to be a desirable goal, significant progress has been made in this area in the past several years. The majority of studies in the discipline of 3D images has concentrated on the use of data from computed tomography or from magnetic resonance. The construction of three dimensional imaging from ultrasound data is not as common. This is partly due fact that the resthcted acoustic access of organs does not pmvide sufficient views to generate complete volume of imaged organs. As a consequence, the surfaces of the organs have been displayed as wire-frame models3' 'ISuch displays of medical images have although proven to be helpful in estimating volumes of the organ, they do not provide realistic organ visualization to which physicians can easily relate to for diagnosis. With the improvement in image technology, some of the problems have now been overcome by either rotating transducer through 180 degrees through apical acoustic window for heart5, or by scanning small peripheral limbs in transmission mode through water path6. Such scanning procedures provide data with sufficient integrity to synthesize realistic 3D images of organs. Also, the advent of catheter based ultrasonic technology provides a potential for three-dimensional imaging of blood vessels and is the topic of discussion in this paper. With the introduction of mechanical atherectomy and laser angioplasty there is an increasing risk of vessel perforation. This, along with other factors, has stimulated interest in developing methods for imaging surfaces underlying endothelial cell of arteries. High frequency ultrasonic imaging systems capable of providing 360 degree views of vessel cross-sections are now available commercially and are in clinical use amongst many researchers. Although, there are some initial encouraging results7 on 3D imaging, it is not yet fully established if it is feasible to (a) use a clinical scanner to obtain contiguous cross-sectional images of arteries; and (b) to use such serial cross-sections for volumetric imaging. This paper aims at providing perspectives on these issues of this rapidly evolving technology.