Cardiovascular Laser Application

With the invention of the laser, many clinical disciplines have taken advantage of this new energy source. Its precision, intensity and energy density is superior to all other known surgical devices. Based on the principle of light amplification from a photon-emitting resonator, the monochromaticity, collimation and coherence provide the high-energy density of the laser beam for medical applications. The state-of-the-art and future potential of laser use in cardiovascular diseases will be reviewed. Most of the work in this field has been accomplished during the past decade with numerous research projects. Although many technical advances have been made, so far the results in cardiovascular medicine are in the areas of vessel anastomosis, ablation of conduction passes for arrhythmia therapy, and angioplasty. In this paper, special attention will be given to the recent success in XeCl excimer laser application for photodecomposition of tissue with a goal of improved recanalization. The high-power density of the XeCl excimer laser provides significant advantages for the disruption of both embolic and calcified plaque. Regardless of the type of tissue ablated, gross, histologic, and ultra-structural analysis confirmed the absence of thermal injury in luminar recanalization as well as in animal studies. Progress in the manufacture of catheters, with multiple very small diameter fibers, led to the decisive breakthrough in clinical laser angioplasty. Peripheral as well as coronary arteries have been successfully recanalized followed by balloon dilatation. The ease of application and the success achieved thus far have resulted in an optimistic assessment for laser medicine.     

The Doppler guide wire: clinical applications in neuroendovascular treatment

The application of Doppler-tipped guide wires to measure blood flow velocity in coronary and peripheral arteries has been described previously as a valuable means of functional assessment in interventional cardiological procedures. In animal studies intravascular Doppler has been used in the cerebrovascular system, and this appears to be an important field of application for this new technique. We used intravascular haemodynamic monitoring by the Doppler guide wire during neuroendovascular procedures in patients with different cerebrovascular diseases and evaluated the clinical feasibility of the method. We found it a safe technique which complements morphological angiographic information with valuable functional data. Further studies may be expected to demonstrate the relation of flow parameters to clinical outcome. Received: 16 January 1996 Accepted: 30 January 1996     

Blood flow acceleration in the carotid and brachial arteries of healthy volunteers: respective contributions of cardiac performance and local resistance

Summary— The influence of local resistance and cardiac performance on peripheral blood acceleration was investigated in 14 healthy male volunteers. Steady and pulsatile flow was studied in the brachial and in the common carotid arteries, ie, two territories that exhibit marked differences in resistive characteristics. Instantaneous blood velocity (V), mean blood velocity (V_m) and artery diameter (D) were evaluated at rest by an ultrasonic range-gated pulsed Doppler flowmeter using a double transducer probe, thus allowing the calculation of mean blood flow (Q). Mean local resistance (R) was obtained by dividing the mean arterial pressure by Q. The peak value of the local acceleration of the blood was obtained by computer-assisted calculation of the first derivative of instantaneous blood velocity (G_max = +dV/dt_max). Peak aortic blood acceleration (GAo) was simultaneously measured from the suprasternal notch using a pulsed Doppler velocity meter. In the brachial and the common carotid arteries, G_max was of a similar magnitude (551 ±30 and 555 ± 44 cm/s², respectively) despite major differences in the respective D, V_m, Q and R values. In neither artery was there a relationship between G_max and either resting Q or R. At the brachial artery level, G_max was positively related to GAo ( r = 0.79, P = 0.0008). At the common carotid artery level, there was a weak, although non significant relationship between G_max and GAo ( P = 0.08). Our results indicate that the local acceleration of peripheral blood flow in the brachial artery is related rather to upstream central impulse than to downstream hemodynamics, and suggest some regional differences in the hemodynamic determinants of the local acceleration of peripheral blood flow.     

Role of Papillary Muscle Dysfunction in the Pathogenesis of Mitral Regurgitation in Myocardial Infarction:

To elucidate the pathogenesis of mitral regurgitation (MR) after myocardial infarction (MI), the incidence of papillary muscle dysfunction (PMD), mitral annular size, and the extent of wall-motion abnormalities were examined in 81 patients with previous MI by two-dimensional echocardiography and real-time two-dimensional Doppler flow imaging. The prevalence of pathological MR was lower in patients with anterior MI (36%) than in those with inferior (65%) or anterior and inferior MI (88%) (P < 0.01 vs anterior MI group). The incidence of PMD in patients with MR in the anterior MI group (15%) was lower than that in the inferior (50%, P < 0.01) or anterior and inferior MI group (43%, P < 0.05). The mitral annular dimension in patients with MR was significantly greater than in those without MR, but it was similar among the three groups. The extent of wall-motion abnormality correlated significantly with the area of MR jet in the anterior MI group (y = 3.1x + 15.5, r = 0.52, P < 0.01) and in the inferior MI group (y = 8.3x + 32.7, r = 0.57, P < 0.01). However, the slope of this relationship was significantly steeper in the inferior MI group than in the anterior MI group (P < 0.05). These results indicated that the degree of MR with inferior MI was greater than with anterior MI for a given MI area. PMD may play an important role in the higher prevalence and greater degree of MR in inferior MI.     

Minimizing macrovessel signal in cerebral perfusion imaging using independent component analysis.

The pronounced susceptibility effect of macrovessels in MR bolus-tracking studies induces spots of artificially high blood flow and volume in perfusion parameter images. These high-intensity regions impede the detection of perfusion changes and lead to elevated perfusion parameters in adjacent tissues. The purpose of this work was to explore postprocessing methods to reduce the influence of macrovessel signal in dynamic MRI. After data reduction was performed with the use of a principal component analysis (PCA), an independent component analysis (ICA) was applied to separate signal components of different compartments. Based on this decomposition, the dynamic time series were reconstructed with minimized contributions of macrovessel signal and noise. The influence of the temporal resolution and signal-to-noise ratio (SNR) of the source data were investigated by means of a simulation study. A region-of-interest (ROI)-based analysis of corrected and uncorrected in vivo data demonstrated that the influence of arteries and veins was reduced at least by 50%, while gray matter (GM) and white matter (WM) tissues were nearly unaffected by the correction process. Hemodynamic parameter images of the cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) were calculated from corrected and uncorrected scans. The corrected parameter images showed a clearly reduced macrovessel signal and an improved perceptibility of microvascular perfusion changes compared to the uncorrected ones.     

有效控制与控制不佳的MRI阴性的GTCS病人发作间期SPECT对照研究

目的:利用单光子发射计算机断层摄影(SPECT)半定量分析有效控制与控制不良的MRI阴性的全面性强直阵挛发作癫(GTCS)病人的局部脑血流差异,探讨脑血流灌注与其预后的关系.材料和方法:对29例有效控制的和12例控制不佳的MRI阴性的GTCS病人进行发作间期99mTc-ECD-SPECT脑血灌流显像,10例年龄匹配的健康人作对照,用感兴趣区(ROI)的不对称指数(%AI)进行半定量分析.将SPECT分析结果与病人的临床表现与EEG相比较.结果:①控制不佳组与有效控制组在丘脑和基底节区的%AI存在显著性差异(P<0.05);②控制不佳组SPECT脑显像的异常率(83.3%,10/12)明显高于有效控制组的异常率(17.2%,5/29),两组具有显著性差异(P<0.01);而两组病人的EEG异常率分别为58.3%、44.8%(7/12、13/29),无显著性差异(P>0.05).结论:控制不佳的MRI阴性的GTCS病人往往存在发作间期的低血流灌注脑区,提示癫的难治性;而控制良好的病人多无明显异常发现,可能预后较好.     

Normal cerebral perfusion measurements using arterial spin labeling: reproducibility, stability, and age and gender effects.

Before meaningful conclusions can be drawn from clinical measures of cerebral blood perfusion, the precision of the measurement must be determined and set in the context of inter- and intrasubject sources of variability. This work establishes the reproducibility of perfusion measurements using the noninvasive MRI technique of continuous arterial spin labeling (CASL). Perfusion was measured in 34 healthy normal subjects. Intersubject variability was assessed, and age and gender contributions were estimated. Intersubject variation was found to be large, with up to 100% perfusion difference for subjects of the same age and gender. Repeated measurements in one subject showed that perfusion remains remarkably stable in the short term when compared with intersubject variation and the large capacity for perfusion change in the brain. A significant decrease in the ratio of gray-matter to white-matter perfusion was found with increasing age (0.79% per year (P < 0.0005)). This appears to be due mainly to a reduction in gray-matter perfusion, which was found to decrease by 0.45% per year (P = 0.04). Regional analysis suggested that the gray-matter age-related changes were predominantly localized in the frontal cortex. Whole-brain perfusion was 13% higher (P = 0.02) in females compared to males.     

Quantification of perfusion fMRI using a numerical model of arterial spin labeling that accounts for dynamic transit time effects.

A new approach to modeling the signal observed in arterial spin labeling (ASL) experiments during changing perfusion conditions is presented in this article. The new model uses numerical methods to extend first-order kinetic principles to include the changes in arrival time of the arterial tag that occur during neuronal activation. Estimation of the perfusion function from the ASL signal using this model is also demonstrated. The estimation algorithm uses a roughness penalty as well as prior information. The approach is demonstrated in numerical simulations and human experiments. The approach presented here is particularly suitable for fast ASL acquisition schemes, such as turbo continuous ASL (Turbo-CASL), which allows subtraction pairs to be acquired in less than 3 s but is sensitive to arrival time changes. This modeling approach can also be extended to other acquisition schemes.     

Laser irradiation and balloon dilatation in experimental transluminal angioplasty

Percutaneous transluminal balloon angioplasty (PTA) is being currently used in patients with coronary artery disease. Laser irradiation (LI) has been effective in vaporizing atherosclerotic plaques. The purpose of this work was twofold: to compare PTA and LI techniques in the recanalization of experimental obstructive arterial lesions, and to evaluate the possibility of reducing the failures and local complications and increasing the success rate of PTA by the combined use of LI. Atherosclerotic iliac stenoses were induced in 27 rabbits; lesions were evaluated angiographically before and after intervention and were studied histologically and by electron microscopy. Argon-ion LI delivered through microlens-tip optic fibers reduced the stenotic area from 64.2 +/- 21.8% to 40.3 +/- 10.7% (n = 10, P less than .01) and PTA from 60.7 +/- 15.9% to 30.4 +/- 7.7% (n = 9, P less than .01). However, percentage reduction was higher in PTA-treated stenoses (48.4 +/- 10.1% vs 34.5 +/- 13.5%, P less than .0125). In eight more rabbits, low power LI (4.55 +/- 1.25 J) was delivered after PTA in dilated segments. Post-PTA LI further decreased stenoses (from 31.2 +/- 7.8% to 29.1 +/- 8.1%, P less than .0125); laser-irradiated segments showed diffuse carbonization of the disrupted intimal layer. The normalized transtenotic pressure gradient decreased significantly in all groups: LI reduced the gradient from .40 +/- .25 to .17 +/- .07 (P = .005); PTA from .37 +/- .14 to .11 +/- .04 (P = .001); LI after PTA from .40 +/- .16 to .12 +/- .06 (P = .001). Thus, LI is effective (less than PTA) in relieving experimental atherosclerotic stenoses and seems useful when combined with PTA.