Deckelbaum L I, Desai S P, Kim C, Scott J J
Department of Medicine (Cardiology), Yale University School of Medicine, New Haven, Connecticut 06510, USA.
Lasers Surg Med. 1995;16(3):226-34. doi: 10.1002/lsm.1900160304.
Laser-induced fluorescence spectroscopy (LIFS) may be capable of guiding laser angioplasty by discriminating normal and atherosclerotic artery and by determining catheter-tissue environment. Previous optical multichannel analyzer based LIFS systems have been expensive and cumbersome. To simplify LIFS, a system based on photomultiplier tubes was developed and evaluated.
STUDY DESIGN/MATERIALS AND METHODS: Tissue fluorescence was induced by a helium cadmium laser (wavelength = 325 nm, power = 0.2-0.5 mW), collected by clinical multifiber laser angioplasty catheters and directed through one of two filters (10 nm bandpass, 380 nm or 440 nm peak transmission) to a photomultiplier tube. An LIFS ratio was defined as the relative intensity at 380:440 nm after calibration with an elastin fluorescence spectrum; 157 coronary artery cadaveric specimens were evaluated spectroscopically and histologically. To evaluate the utility of LIFS to optimize catheter position by determining catheter-tissue contact, by determining saline dilution of blood, and by orienting eccentric multifiber catheters a new variable, the total fluorescence intensity (TFI) was defined as the sum of arterial fluorescence intensities at 380 nm and 440 nm. TFI was recorded in vitro through multifiber catheters from 20 arterial specimens in vitro in blood and evaluated as a function of the catheter-to-tissue distance (d) over a range from 0 to 400 mu.
Defining normal specimens as those with an intimal thickness < or = 200 mu, and atherosclerotic as those with an intimal thickness > 200 mu, 47/50 (94%) normal and 85/107 (79%) atherosclerotic specimens were correctly classified using a threshold LIFS ratio of 2.0. Mean (+/- SE) normal ratio was 1.76 +/- 0.02 and mean atherosclerotic ratio was 2.78 +/- 0.08 (P < or = 0.01). The classification accuracy of atherosclerotic specimens increased with intimal thickness so that 95% of atherosclerotic specimens (69/73) with intimal thickness > or = 400 mu were correctly classified. TFI was capable of determining catheter-tissue contact as maximal TFI was recorded with the catheter in contact with the tissue (d = 0 mu) and decreased markedly with distance (to 52 +/- 6% at d = 100 mu, 19 +/- 4% at d = 200 mu, and 3 +/- 1% at d = 300 mu). TFI was recorded from ten arterial specimens in blood/saline mixtures ranging in hematocrit from 0% (saline) to 50% (whole blood). TFI was capable of detecting saline hemodilution of blood as TFI decreased markedly at higher hematocrits such that TFI could only by recorded at hematocrits < 10% for catheter-to-tissue distances > or = 300 mu. TFI was recorded through ecentric multifiber catheters from 25 arterial specimens and eval-uated as a function of the degree of catheter-tissue overlap. TFI was capable of detecting maximal catheter-tissue overlap as TFI correlated linearly with the area (A) of overlap (TFI = 1.12 A + .07, r = 0.92).
By discriminating atherosclerotic from normal tissue and by confirming catheter-tissue contact and saline hemodilution, fluorescence feedback should minimize irradiation of normal tissue and/or blood and enhance the safety and efficacy of laser angioplasty.
激光诱导荧光光谱法（LIFS）或许能够通过区分正常动脉和动脉粥样硬化动脉以及确定导管与组织的环境来指导激光血管成形术。以往基于光学多通道分析仪的LIFS系统价格昂贵且操作繁琐。为简化LIFS，开发并评估了一种基于光电倍增管的系统。
研究设计/材料与方法：组织荧光由氦镉激光（波长 = 325 nm，功率 = 0.2 - 0.5 mW）诱导产生，通过临床多光纤激光血管成形术导管收集，并经两个滤光片之一（10 nm带通，峰值透射波长为380 nm或440 nm）导向光电倍增管。LIFS比率定义为用弹性蛋白荧光光谱校准后380 nm与440 nm处的相对强度；对157个冠状动脉尸体标本进行了光谱和组织学评估。为评估LIFS通过确定导管与组织的接触、确定血液的盐水稀释以及定位偏心多光纤导管来优化导管位置的效用，定义了一个新变量，即总荧光强度（TFI），它是380 nm和440 nm处动脉荧光强度之和。通过多光纤导管在体外对20个动脉标本在血液中进行TFI记录，并在0至400μm的范围内评估其作为导管与组织距离（d）的函数。
将内膜厚度≤200μm的标本定义为正常标本，内膜厚度＞200μm的标本定义为动脉粥样硬化标本，使用阈值LIFS比率2.0时，47/50（94%）的正常标本和85/107（79%）的动脉粥样硬化标本被正确分类。正常标本的平均（±标准误）比率为1.76±0.02，动脉粥样硬化标本的平均比率为2.78±0.08（P≤0.01）。动脉粥样硬化标本的分类准确率随内膜厚度增加，以至于内膜厚度≥400μm的动脉粥样硬化标本中有95%（69/73）被正确分类。TFI能够确定导管与组织的接触，因为当导管与组织接触（d = 0μm）时记录到最大TFI，且随距离显著降低（在d = 100μm时降至52±6%，在d = 200μm时降至19±4%，在d = 300μm时降至3±1%）。在血细胞比容从0%（盐水）到50%（全血）的血液/盐水混合物中，对10个动脉标本记录TFI。TFI能够检测血液的盐水稀释，因为在较高血细胞比容时TFI显著降低，以至于对于导管与组织距离≥300μm的情况，仅在血细胞比容＜10%时才能记录到TFI。通过偏心多光纤导管对25个动脉标本记录TFI，并评估其作为导管与组织重叠程度的函数。TFI能够检测最大导管与组织重叠，因为TFI与重叠面积（A）呈线性相关（TFI = 1.12A + 0.07，r = 0.92）。
通过区分动脉粥样硬化组织与正常组织以及确认导管与组织的接触和盐水稀释，荧光反馈应能使正常组织和/或血液的照射最小化，并提高激光血管成形术的安全性和有效性。
