Fluorescence lifetime imaging microscopy (FLIM) for image guided surgery

Yinghua Sun et al., from the University of California used the 4 Picos intensified CCD camera at the first time application of an endoscopic fluorescence lifetime imaging microscopy (FLIM) system.

Ultra-fast shutter speeds of the high-speed ICCD camera 4 Picos enable 2D fluorescence lifetime measurements of human tissue.

With the ultra high shutter speed of the 4 Picos ICCD camera two dimensional FLIM measurements are possible. The 2D fluorescence lifetime endoscope permits the intraoperative differentiation of normal tissue and brain tumor.

Treatment of brain tumors

The median survival time of the most common and aggressive brain tumor in humans, glioblastoma multiforme (GBM), is 12 to 15 months. Optimal therapy consists of maximal safe surgical resection, followed by a chemoradio-therapy. Studies proven that the extent of surgical resection is a determinant of progression-free and overall survival. However, the total resection is challenging for the surgeon. Since, the direct pathologic discrimination of normal and tumor-bearing tissue can not be provided by any intraoperative techniques. The endoscopic fluorescence lifetime imaging microscopy (FLIM) prototype may provide a solution for intraoperative diagnosis of brain tumors.

Apparatus of the FLIM endoscope

The endoscopic FLIM apparatus consists of a pulsed laser, a flexible fiber-image guide-based endoscope, a filter wheel and a gated intensified CCD (ICCD) camera. The pulsed nitrogen laser induces tissue autofluorescence and a customized endoscope probe remotely delivered the fluorescence emission to the fast gating 4 Picos ICCD camera. In front of the camera a bandpass filter with the centre wavelength of 460nm was placed. For a fluorescence lifetime measurement a series of up to 29 time-gated images with increasing delay times to the Laser pulse were taken. With this time scan a position dependent fluorescence lifetime is determinant.

ICCD cameras enable 2D fluorescence lifetime

The 4 Picos ICCD camera from Stanford Computer Optics provides highest shutter speeds and enables gating times down to 200ps. This distinctive feature allows a time resolution necessary for 2D fluorescence lifetime measurements of human tissue. The external trigger option, the in 10ps steps freely programmable delay time and up 32 bit dynamic range are unique features make the endoscopic fluorescence lifetime imaging microscopy diagnosis possible.

Information gain by lifetime measurements

The figure shows at top the normal tissue, in the middle brain tumor and on the bottom can be seen the differentiation of normal tissue and tumor depending on the fluorescence lifetime. Where the left column shows the overall fluorescence intensity and the middle column the 2D fluorescence lifetime image. The 2D fluorescence lifetime image is calculated from series of images each with a increasing delay to the stimulating Laser Pulse. A histogram of the individual pixels can be found in the right column. In comparison of the left and middle column it can be clearly said that the lifetime measurement add significant information to the measurement. Hence, fast gating ICCD cameras enables 2D FLIM with sub-nanosecond time resolution for differentiation of normal tissue from brain tumor.

Title: Fluorescence lifetime imaging microscopy for brain tumor image-guided surgery
Author: Yinghua Sun, et al.
Institute: University of California, Davis, California, USA