用于成像性能测试的荧光发光模拟系统 下载: 677次
Fluorescence molecular imaging is widely used in clinical practice. Different hardware and software designs in different fluorescence imaging systems lead to differences in imaging performance between instruments. However, unlike radiographic imaging, fluorescence imaging currently has no mature specifications or standards to test the performance of imaging instruments. Phantoms are tools used in standardized imaging performance testing and are commonly used in radiography. Unlike human tissues, phantoms have preset shapes and contrasts that simulate specific tissue parameters over time. These properties allow phantoms to be used to measure, evaluate, and confirm the performance of imaging instruments. In research on near-infrared fluorescent phantoms, fluorescent agents and quantum dots are used as samples for fluorescence imaging performance testing. However, owing to the different materials and preparation methods used in the samples, as well as the stability of the materials themselves, there is still no stable sample for accurately simulating the fluorescence spectrum as a standardized test tool. In this study, a fluorescence emission simulation system for simulating fluorescent samples is proposed. Imaging instruments can exhibit the same response as real fluorophores when imaging a fluorescence simulation system. Compared with traditional fluorescent agents, the fluorescence emission simulation (FES) system can more accurately simulate fluorescence emission characteristics in a stable manner.
In this study, we propose a fluorescent light-emitting system that uses an optical system to simulate fluorophores. First, according to the characteristics of the fluorescent agent, a simulation method for fluorescence excitation efficiency, spatial distribution, and fluorescence emission spectrum characteristics is designed such that the fluorescence imaging instrument has the same response as the real fluorescent agent when imaging the FES system. The system controls the intensity of the outgoing fluorescence according to the intensity of the detected excitation light, thereby simulating the fluorescence excitation efficiency of the fluorescent agent sample. The design of the optical entrance and exit based on the integrating sphere can simulate the spatial distribution of outgoing fluorescence. In this study, a spectral simulation method based on a linear filter LVF and liquid crystal display (LCD) is used, and based on this method, an improved least squares spectral fitting algorithm is designed to automatically simulate arbitrary fluorescence spectra.
The performance verification shows that the subspectra of the FEM system have linear additivity (Fig. 5), and the subspectrum satisfies a certain gray-transmittance relationship [Fig. 6(a)]. A grayscale transmittance curve of the sub-spectrum was obtained [Fig. 6(b)]. Functional verification of the system is realized by fluorescence emission simulation of ICG. The simulation of the fluorescence emission spectrum characteristics [Fig. 7(a)] and fluorescence excitation efficiency [Figs. 7(b)-(d)] of the ICG aqueous solution samples with different concentrations is performed using the FES system. The simulation system obtains the same test results as the fluorescent samples (Fig. 8), and compared with traditional fluorescent agents, the FES system more accurately simulates the fluorescence emission characteristics in a stable manner, which verifies the feasibility of the system as a standardized test tool.
In this study, a method for simulating fluorescent samples with an optical system is proposed. A programmable FES system is built and an optical system is used to simulate fluorescent agents for the standardization test of near-infrared fluorescence imaging performance. The FES system can simulate the fluorescence excitation efficiency, spatial distribution, and fluorescence emission spectrum characteristics of the fluorescent sample such that the fluorescence imaging instrument has the same response as the real fluorescent agent when imaging the FES system. A spectral simulation method based on a linear filter and liquid crystal display is also proposed and an improved least squares spectral fitting algorithm is designed, which can automatically simulate any fluorescence spectrum. Finally, based on the FES system, the fluorescence imaging sensitivities of different near-infrared fluorescence imaging instruments are tested and the test results of different instruments are compared. The test results show that compared with traditional fluorescent agents, the FES system can more accurately simulate the fluorescence emission characteristics in a stable manner, which verifies the feasibility of the system as a standardized test tool.
1 引言
荧光分子成像作为一种靶向成像技术在生物医学领域得到了越来越广泛的应用[1-2]。不同荧光成像系统硬件和软件上的不同设计导致了仪器间成像性能的差异[3]。不同于放射成像,荧光成像目前还没有成熟的对成像仪器性能进行检测的规范和标准[4-5]。在放射成像领域,国际电工委员会(IEC)和美国电气制造商协会(NEAM)已经发布了一系列质量控制手册,并将其作为核磁共振成像/电子计算机断层扫描/正电子发射计算机断层扫描(MRI/CT/PET)成像仪器性能检测与评估的标准。2006年,中华人民共和国卫生部也发布了《医用核磁共振成像(MRI)设备影像质量检测与评价规范》,并将其作为MRI成像仪器性能检测与评估的标准[6]。仿体是标准化成像性能测试中的常用工具,最初被用于医学物理学和健康物理学[7]。不同于人体组织,仿体有预设的形状和对比度,可以长期模拟特定的组织参数。这些特性使得仿体可以用于测量、评估和确认成像仪器的性能[8-11]。
吲哚菁绿(ICG)是目前唯一被美国食品药品监督管理局(FDA)认证的可用于临床的近红外荧光造影剂,因此,对近红外荧光仿体的研究通常是围绕ICG成像展开的。最常用的近红外成像性能测试方法是将ICG分散在液态[12]或固态[13-14]介质中的荧光剂样品中进行测量。直接用ICG作为仿体造影剂的优势是可以精准地测试成像仪器的光谱响应,但是由于ICG在水中会随着时间延长而聚合[15]和降解[16-17],荧光的强度和光谱特性会随之改变[18-19];而且,ICG的荧光在非避光环境下或者长时间使用后会因为光漂白而淬灭。这些特性使得ICG仿体非常不稳定,无法长期使用。Sevick-Muraca团队[20]用量子点Qdots800代替ICG制备了仿体。相较于传统的荧光剂,量子点的荧光发射光谱可调、荧光寿命长、荧光强度高[21-23],最重要的是量子点的荧光稳定性高[24],量子点荧光仿体可以长期使用[25]。为了促进荧光影像标准的建立,Sevick-Muraca团队[26]还在量子点研究的基础上提出了一种可溯源到国际标准(SI)单位的近红外成像设备的性能测试方法。Ntziachristos团队[27]设计了一种用于荧光成像性能测试的综合仿体,并在综合仿体的基础上提出了一种近红外荧光成像性能测试的标准化方法[4]。量子点的斯托克斯位移较大,任何波长小于荧光波长10 nm的激发光源都可以激发量子点,而ICG的斯托克斯位移很小,吸收谱和发射谱有重叠,量子点仿体无法精确地模拟荧光团的光谱特性,导致成像系统对量子点仿体的成像响应与对真实荧光团的成像响应之间存在偏差,故而使用量子点仿体测量的结果无法反映真实的荧光成像效果。针对这一问题,Pogue团队[28]将IR-125作为荧光剂,制作了模拟ICG荧光特性的仿体。IR-125具有与ICG高度相似的吸收谱与发射谱,同时具有比ICG稳定性更好的荧光光谱[29];但是,IR-125本质上是一种荧光团,荧光团和量子点的光漂白性会使荧光淬灭[30],而且随着使用时间和使用次数增加,荧光团的荧光强度会逐渐降低,仿体的测试结果也将发生改变。
电子发光器件相对于材料而言具有发光稳定的优势,因此,使用电子器件进行模拟可以获得长期稳定的光学参数。为了实现快速和定量的成像性能测试,Salter团队[31]使用激光扫描生成二维和三维荧光图案,激光生成的荧光图案可以测量横向分辨率、照明均匀性、透镜畸变等。Xu等[32]使用高保真度的高光谱图像投影仪(HIP)搭建了一套数字组织仿体(DTP)平台,该平台可以重建组织高光谱成像时的光谱特性;同时,Xu等验证了使用DTP进行光谱成像设备定量校准、评估和优化的可行性。在荧光成像性能标准化测试方面,目前还缺少一种可以充当测试工具且能够精确模拟荧光光谱的长期稳定的系统。
本团队设计了一套荧光发光模拟系统,该系统可以模拟荧光样品的激发效率、荧光发射谱特性以及荧光的空间分布特性,可以替代真实的荧光剂仿体对荧光成像仪器进行量化表征。该系统根据检测到的激发光强度控制出射荧光的强度,以模拟荧光剂样品的荧光激发效率;同时,该系统基于积分球的光学出入口设计模拟出射荧光的空间分布。本团队还提出了一种基于线性滤光片(LVF)和液晶显示器(LCD)的光谱模拟方法,并设计了一种改进的最小二乘光谱拟合算法,该算法可以自动模拟任意荧光光谱。与传统荧光剂相比,荧光发光模拟系统可以稳定精准地模拟荧光的发光特性。荧光成像灵敏度的测试结果验证了所设计的荧光发光模拟系统作为标准化测试工具的可行性。
2 系统设计
荧光发光模拟系统的设计目标是使用荧光成像系统对其成像时能达到与对荧光团成像相同的成像响应。影响成像系统响应的主要因素有荧光的激发效率、空间分布及光谱特性。其中的荧光激发效率是荧光样品的本征参数,表征了荧光样品在特定情况下发射荧光的能力。荧光剂一般能溶于水或其他介质。成像时,激发光照射介质后发生散射,之后被荧光团吸收发射出荧光,荧光光子发射的方向是不确定的,经过介质时也会发生散射,因此,荧光最终朝空间的各个方向出射。因为荧光团在发射荧光时无论电子被激发到哪一个能级,荧光的产生都是从第一单重激发态的最低振动能级开始的,所以荧光有一个发射带[33]。在一定的测试条件下,当荧光成像系统对荧光剂成像时,荧光激发效率决定了荧光发射的光子数,荧光的空间分布决定了荧光在各个方向上的光子密度,荧光光谱决定了荧光团发射的光子的波长分布。由于相机有一定的视场角,采集的是一定空间角内出射的光子,不同的成像传感器对不同波长的光子有不同的响应,所以在荧光成像时荧光剂的荧光激发效率、空间分布和光谱特性是影响荧光成像响应的关键因素。
2.2 荧光模拟方法
2.2.1 荧光空间分布模拟方法设计
荧光模拟系统受激发光照射后出射荧光。对于真实的荧光剂样品而言,激发光的照射和荧光出射同时发生在荧光样品表面,荧光剂样品的激发光入射和荧光出射也应该在同一个区域。同时,荧光模拟系统需要实时探测激发光的强度,以模拟荧光激发效率,故而需要一个具有激发光入口、激发光探测接口、模拟荧光入口及出口,并且出射荧光在空间中均匀分布的光学结构。本文选用基于积分球的设计来实现该光学结构。
2.2.2 荧光激发效率模拟方法设计
量子产率η是荧光团分子的本征参数。针对某一种荧光样品,其荧光强度和入射激发光强度的比值为kη,其中k是由荧光剂的摩尔吸收系数[33]、样品厚度、样品中荧光剂的浓度决定的系数。对于某一特定荧光剂样品,k与η一样是本征参数,kη为样品的荧光激发效率。荧光发光模拟系统的荧光激发效率的模拟方法是:根据照射到荧光剂的激发光的光强发射荧光,并控制荧光强度和激发光强度的比值为kη。
2.2.3 荧光光谱模拟方法设计
荧光剂发光模拟系统因要模拟有特定光谱特性的荧光出射,其光源应为光谱可调光源,以实现光谱模拟。本文的光谱模拟选用光谱振幅调制的方法,即:先对光谱的光源进行分光,使不同波长的光获得某种空间分布,然后根据目标光谱对不同波长的光进行幅度调制。
1) 分光方法设计
本文提出的荧光发光模拟系统主要用于模拟近红外荧光,因此需要在空间上实现近红外波段的分光。线性渐变滤光片[34]是继光栅、棱镜之后发展起来的一种新型的分光元件。线性渐变滤光片之所以被称为“线性”是因为其不同位置的滤光特性不同,而且其滤光特性随着空间位置呈线性变化。线性滤光片是采用离子束溅射法或离子辅助法等工艺在基底表面镀制多层厚度变化的膜系得到的,因此其光谱特性线性变化。相比于棱镜和光栅等分光元件,线性滤光片具有体积小、质量轻、通带多、通带位置可以任意设计等优点。同时,基于线性渐变滤光片的分光方式具有高稳定性、高集成度和高分辨率等特点,适用于模拟近红外荧光的分光。
2) 光谱幅度调制方法设计
分光之后需要对光谱的幅度(即光谱上不同波长对应的光强)进行调制,以获取目标光谱分布。在对光源分光后,不同波长的光分布在空间中的不同位置。在不同波长光的传播路线上控制光的透过率,就可以对光谱进行光强调制。
调节光透过率的方法有很多,比如,添加衰减片等光学元件的方法。若要对分光之后的波长随空间位置不同而变化的光进行衰减,就要对衰减片进行设计,使其在不同波长对应的位置有不同的衰减特性。可以采用光刻等方法制备衰减片,但这种方法得到的衰减片只能模拟具有特定形状的光谱。LCD[35]是一种借助薄膜晶体管驱动的有源矩阵显示器。LCD的每个像素由悬浮于两个透明电极之间的一列液晶分子层以及外侧两个偏振方向互相垂直的偏振片组成。通过控制电压可以控制液晶分子排列的扭曲程度,实现LCD不同灰度的控制,从而达到不同的光透过率。LCD可以实现透光率的可编程控制。
本文提出了一种基于线性渐变滤光片和LCD的光谱模拟方法。光谱光源通过线性渐变滤光片后随波长有不同的空间分布,之后用LCD调制光强,通过LCD不同位置的像素灰度控制不同波长光的透过率,就可获得目标光谱分布。
2.3 系统方案设计
根据以上荧光模拟方法设计,本团队提出了一种基于积分球的荧光发光模拟系统,该系统可以检测激发光并主动发射可编程控制的出射光,模拟任意荧光物质的发射光谱特性。
图 1. 荧光发光模拟系统结构及功能示意图
Fig. 1. Schematic of structure and function of fluorescence emission simulation system
图 2. 荧光发光模拟系统。(a)荧光发光模拟系统示意图;(b)光谱模拟方法示意图,准直后的宽谱光源先经过线性滤光片分光,然后经过线性偏振片和LCD进行幅度调制以模拟目标光谱,之后通过端口3入射至积分球
Fig. 2. Fluorescence emission simulation system. (a) Schematic of fluorescence emission simulation system; (b) schematic of spectral simulation method. The collimated broad-spectrum light source is first spatially filtered by a LVF, and then amplitude-modulated with linear polarizers and LCD to simulate target spectrum. The light source is incident into integrating sphere through port 3
2.4 光谱模拟算法
图 3. 基于最小二乘曲线拟合的光谱模拟算法示意图
Fig. 3. Schematic of spectral simulation algorithm based on least squares curve fitting
光谱模拟算法整个过程为:输入要模拟的目标光谱Sfluo(λ),对系统宽谱光源进行采样和调制,获得模拟目标光谱的模拟荧光。光源通过线性滤光片后入射至LCD面板,LCD的每一列像素对应控制宽谱光源的一个子光谱的透过,LCD像素列的灰度范围为[0,255]。灰度为0时,LCD像素为黑色,此时光不通过,透过率t=0;当灰度值为255时,LCD像素全开(为透明),透过率为t=1(100%)。第n列像素全打开时的透过子光谱为
为获得与目标光谱相同的光谱分布,应有
式(2)可用线性最小二乘曲线拟合来求解。t(gn)是求解得到的第n个子光谱的权重,即透过率tn,则第n列像素的灰度值应为
g(tn)为灰度-透过率关系,由LCD的特性决定,可测量获得。之后,将灰度值gn映射到[0,255]并控制面板显示,完成光谱拟合。
图 4. 基于最小二乘曲线拟合的光谱模拟算法流程图
Fig. 4. Flowchart of spectral simulation algorithm based on least squares curve fitting
3 系统性能验证
若要用所提出的发光模拟系统实现基于线性最小二乘光谱拟合算法的光谱模拟,需要保证系统子光谱具有线性相加性,并且需要先测得子光谱的灰度-透过率曲线。
3.2 光谱线性相加性验证
首先对所有的子光谱进行采样。通过程序控制LCD每列像素依次打开,打开时灰度值为255,即全开状态,记录每列像素全开时的透过光谱。由于光谱采样数据过多,
图 5. 系统子光谱线性相加性。(a)系统像素列透过光谱采样结果示例;(b)系统光谱线性相加性验证结果,其中additive spectrum为像素列逐列打开后测得的子光谱的相加结果,fully-open spectrum为像素列全开时测得的透过光谱,error为两种方法得到的光谱的偏差
Fig. 5. Linear additivity of system sub-spectra. (a) Example of system pixel column transmittance spectrum sampling result; (b) verification of spectral linear additivity of the system, where“additive spectrum”is the result of adding sub-spectra of each column,“fully-open spectrum”is transmission spectrum measured when pixel columns are all turned on, and“error”is the deviation between spectra obtained by the above two methods
3.3 灰度-透过率特性验证
最小二乘拟合得到的子光谱的权重值是光谱的透过率,而光谱的透过率由像素的灰度值控制,要从拟合出的透过率得到像素应该显示的灰度值,需要验证像素列透过子光谱的灰度-透过率特性,并获得灰度-透过率曲线。验证方法为:控制每列像素的灰度值,从0到255逐渐增加像素列的灰度,记录像素列的不同灰度值对应的透过光谱,然后对采集到的数据进行分析。这里定义透过率为某灰度值下透过光谱上某波长的透过光强与灰度为255时(即全开时)透过光强的百分比。对不同像素列的透过光谱上的不同波长位置进行取样,观察灰度-透过率规律。5个像素列的取样结果如
图 6. 系统灰度-透过率特性。(a)第1150、第1200、第1250、第1300、第1350列像素透过光谱上不同波长的取样结果;(b)像素列的子光谱灰度-透过率曲线拟合结果
Fig. 6. System gray-transmittance characteristics. (a) Results of sampling at different wavelengths on transmittance spectrum of pixels in columns 1150, 1200, 1250, 1300, and 1350; (b) fitting result of sub-spectral grayscale-transmittance curve of pixel columns
4 系统功能验证
ICG是唯一被FDA认证的可用于临床的近红外荧光造影剂,因此关于近红外荧光成像仪器性能测试的研究多数是围绕以ICG为造影剂的近红外成像进行的。最常用的近红外成像性能测试方法是将ICG分散在处于液态或固态介质中的荧光剂样品内进行临床试验前仪器性能的评估,所以本文荧光发光模拟系统的功能验证也采用此方法。
4.2 ICG荧光样品的模拟
ICG的吸收谱和发射谱分布在近红外波段,其中吸收谱的分布与ICG浓度有关,吸收峰值在约800 nm处;ICG溶液的荧光发射峰在815 nm左右;ICG水溶液的荧光发射强度与浓度有关,其质量浓度在0.008 mg/mL以上继续增加或在0.008 mg/mL以下继续降低时,荧光发射强度都将会逐渐降低。针对目前无法获取具有长期稳定ICG荧光发光特性的荧光剂样品的问题,使用本文提出的荧光发光模拟系统对ICG样品进行模拟,可以得到能精确模拟ICG荧光光谱的长期稳定的样品,并用于荧光成像系统的标准化测试。
首先使用荧光发光模拟系统对ICG的荧光发光特性进行模拟。ICG在水中的溶解度为128 μmol/L,使用超纯水配制浓度分别为0、0.3、1、3、10、20、100、200、1000 nmol/L的ICG溶液,并使用F7100分光光度计采集ICG水溶液的光谱。向系统输入
图 7. ICG荧光模拟。(a)ICG荧光光谱特性的模拟结果,其中ICG spectrum是使用F7100分光光度计测得的ICG水溶液光谱,fitting spectrum是荧光发光模拟系统输出的模拟荧光光谱,fitting error展示了两光谱之间的偏差;(b)20 nmol/L荧光溶液样品的荧光激发效率模拟,上排为不同激发光强度下荧光的ROI图像,下排为荧光发光模拟系统的模拟荧光图;(c)荧光发光模拟系统输出光强与荧光图像灰度值之间的关系;(d)不同浓度荧光剂样品的荧光激发效率模拟,左轴为荧光图像灰度与激发光强度的关系,右轴为荧光发光模拟系统输出荧光强度与激发光强度的关系
Fig. 7. ICG fluorescence simulation. (a) Simulation of ICG fluorescence spectrum, where“ICG spectrum”is measured spectrum of ICG aqueous solution by F7100 spectrophotometer,“fitting spectrum”is simulated fluorescence spectrum output by fluorescence emission simulation system, and“fitting error”shows deviation between the two spectra; (b) fluorescence excitation efficiency simulation of 20 nmol/L ICG fluorescence solution sample, the upper row is ROI image of fluorescence under different excitation light intensities, and the lower row is simulated fluorescence image of fluorescence emission simulation system; (c) relationship between output light intensity of fluorescence emission simulation system and gray value of fluorescence image; (d) fluorescence excitation efficiency simulation of different concentrations of fluorescent agents, left axis is the relationship between gray value of fluorescence image and excitation light intensity, and right axis is the relationship between output fluorescence intensity of fluorescence emission simulation system and excitation light intensity
对于不同的荧光样品,其荧光激发效率可用荧光强度和样品表面激发光强度的比值来模拟。0.008 mg/mL(即1030 nmol/L)的ICG水溶液对应最高的激发效率。在相同条件下,当ICG水溶液的质量浓度高于或低于0.008 mg/mL时,激发效率都会下降。ICG荧光灵敏度的研究通常关注较低浓度的ICG[3],所以本文模拟ICG荧光时选择浓度为0.3~1000 nmol/L。如
4.3 荧光发光模拟系统的成像性能检测
对不同浓度的ICG溶液样品的模拟参数进行测试后,用荧光发光模拟系统进行荧光样品的模拟,并基于荧光发光模拟系统进行荧光成像性能测试。分别使用10 bit MV-GE130M-T MindVision相机、12 bit MV-CA013-20GN Hikvision相机、10 bit EO-0413M CMOS Edmund相机与装有两个FF01-832/37-25滤光片的0814MMl镜头、780 nm激发光光源搭建了荧光成像系统。由于荧光成像系统的荧光灵敏度测试实验的目的是探测荧光成像仪器所能探测到的最弱的荧光,所以测试时应将成像系统调至最佳成像参数。三个系统测试时的工作距离均为20 cm,激发光强度均为40.4 W/m2,MV-GE130M-T MindVision相机的曝光时间设定为500 ms,MV-CA013-20GN Hikvision相机的曝光时间设定为400 ms,EO-0413M CMOS Edmund相机的曝光时间设定为300 ms。
对于每套成像系统,首先分别用0、0.3、1、3、10、20、100、200、1000 nmol/L的ICG溶液进行测试,选取荧光图像ROI记录测试结果。荧光成像结果如
图 8. 不同成像系统的荧光成像灵敏度的测试结果及对比。(a)成像系统对不同浓度ICG溶液样品的荧光成像结果;(b)成像系统对荧光发光模拟系统模拟的不同浓度的ICG溶液样品的荧光成像结果;(c)不同成像系统的荧光图像灰度与样品浓度之间的对数关系;(d)对数输出结果分析
Fig. 8. Fluorescence imaging sensitivity test results and comparison of different imaging systems. (a) Fluorescence imaging results of ICG solution samples with different concentrations by imaging systems; (b) fluorescence imaging results of fluorescence emission simulation system simulated ICG solution samples with different concentrations by imaging systems; (c) logarithmic relationship between fluorescence image grayscale and sample concentration for different imaging systems; (d) analysis of logarithmic output results
5 讨论与结论
本文提出了一种用光学系统模拟荧光样品的方法,设计了一套荧光发光模拟系统,使用光学系统模拟荧光剂,用于近红外荧光成像性能标准化测试。荧光发光模拟系统可以模拟荧光样品的荧光激发效率、荧光空间分布及荧光发射光谱特性,可以替代真实的荧光剂仿体对荧光成像类仪器进行量化表征。系统根据检测到的激发光强度控制出射荧光的强度,基于积分球的光学出入口设计模拟出射荧光的空间分布。本文还提出了一种基于线性滤光片和LCD的光谱模拟方法,并设计了一种改进的最小二乘光谱拟合算法,该算法可以自动模拟任意荧光光谱。基于荧光发光模拟系统对不同的近红外荧光成像仪器的荧光成像灵敏度进行了测试,并对不同仪器的测试结果进行对比,结果表明:用荧光发光模拟系统可以得到与荧光样品相同的测试结果;与传统的荧光剂相比,荧光发光模拟系统可以稳定精准地模拟荧光发光特性,有望取代传统荧光剂对荧光成像仪器进行标定和测试。
通过模拟ICG对荧光发光模拟系统的功能进行了验证。实际上,该荧光发光模拟系统可以模拟可见光到近红外波段内的任意荧光。未来可通过软件优化,将系统升级成为一个自适应的发光模拟器:系统数据库内存有大量常用荧光特性数据,在使用时选择荧光类型,并选择相应的浓度、样品环境等,系统就可以自动调节输出相应的荧光。由于目前的测试研究未涉及不发光的场景,所以没有对荧光的吸收特性进行模拟。未来拟在积分球内加入衰减片或吸收片,实现荧光剂吸收特性的模拟。目前,该荧光发光模拟系统可以稳定地精准模拟荧光剂的荧光特性,对成像系统的成像灵敏度进行测试。未来,该系统还可以进行分辨率、动态范围、成像深度等方面的测试。本工作作为荧光光谱模拟新技术的初步探索,还有待从多方面进行优化:对于系统光谱线性相加性和灰度-透过率拟合误差进行进一步测试与分析,将有助于硬件和软件的设计,提高系统的模拟精度;对负反馈调节算法进行研究也将进一步提高系统输出的精度和稳定度。荧光成像性能测试标准化的建立需要有可溯源的测量结果,在以后的研发中可以使用标准光源,并对发射荧光进行测量,同时将测量的量关联到国际标准单位,这样在改进的基础上可以发展一套基于荧光剂模拟平台的近红外荧光成像性能标准化测试方法;在该方法中定义近红外仪器测试的性能参数、单位、测试方法、测试条件等,不同的仪器厂商就可以根据这套标准对仪器进行参数测试、校准和标定。
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Article Outline
李晨梦, 邵鹏飞, 吴柄萱, 孙明斋, 姚鹏, 申书伟, 刘鹏, 徐晓嵘. 用于成像性能测试的荧光发光模拟系统[J]. 中国激光, 2022, 49(24): 2407204. Chenmeng Li, Pengfei Shao, Bingxuan Wu, Mingzhai Sun, Peng Yao, Shuwei Shen, Peng Liu, Xiaorong Xu. Fluorescence Emission Simulation System for Imaging Performance Testing[J]. Chinese Journal of Lasers, 2022, 49(24): 2407204.