Fluorescence Lifetime Imaging System using a double-modulated Excitation Source

基于二维光探测器和双调制激发源的外差探测的荧光寿命成像系统已经研制成功。像增强器(I.I.，V3063U型，滨松光电子公司)利用光电阴极的增益控制特性，实现了低电压控制信号的外差探测。为了同时检测直流荧光图像和荧光寿命信息，利用串联式A/O调制器对作为激发源的Ar离子激光强度进行了不同频率的调制。其中一个A/O调制器在另一个A/O调制器的20,000 MHz的调制频率和I.I.管的19,990 MHz的增益调制频率之间以不同的频率进行调制。耦合到I.I.的CCD摄像机测量外差荧光图像并将其存储在个人计算机的存储器中。根据存储的数据计算相分辨图像，即寿命图像。系统的时间分辨率约为1 ns。

Fluorescence lifetime imaging systems based on heterodyne detection using two dimensional photo-detector and a double-modulated excitation source have been developed. An image intensifier (I.I., Model V3063U, Hamamatsu Photonics Co.) was used as the two dimensional photo-detector.The gain control characteristics of the photo-cathode in the I.I. Tube are utilized to allow heterodyne detection with low-voltage control signal. Heterodyning the modulated fluorescence and reference signals at the photo-cathode of the I.I. Tube provides high-frequency response up to a few hundred MHz.In order to detect DC fluorescence image and fluorescence lifetime information simultaneously, Ar ion laser beam intensity as an excitation source was modulated at different frequencies, simultaneously, by tandem A/O modulators. One of the A/O modulators was modulated at a difference frequency between the modulation frequency of 20,000MHz for the other A/O modulator and the gain modulation frequency of 19,990MHz for the I.I. tube.A CCD camera coupled to the I.I. Measures the heterodyned fluorescence image and stores them in the memory of a personal computer. The phase resolved image, I.e. the life time image is calculated the stored data. The time resolution of the systems is about 1 ns.