Didier Goujon

In vivo autofluorescence spectroscopy of human bronchial tissue to optimize the detection and imaging of early cancers

We are developing an imaging system to detect pre-/early cancers in the tracheo-bronchial tree. Autofluorescence might be useful but many features remain suboptimal. We have studied the autofluorescence of human healthy, metaplastic and dysplastic/CIS bronchial tissue, covering excitation wavelengths from 350 to 480 nm. These measurements are performed with a spectrofluorometer whose distal end is designed to simulate the spectroscopic response of an imaging system using routine bronchoscopes. Our data provide information about the excitation and emission spectral ranges to be used in a dual range detection imaging system to maximize the tumor vs healthy and the tumor vs. inflammatory/metaplastic contrast in detecting pre-/early malignant lesions. We find that the excitation wavelengths yielding the highest contrasts are between 400 and 480 nm with a peak at 405 nm. We also find that the shape of the spectra of healthy tissue is similar to that of its inflammatory/metaplastic counterpart. Finally we find that, when the spectra are normalized, the region of divergence between the tumor and the nontumor spectra is consistently between 600 and 800 nm and that the transition wavelength between the two spectral regions is around 590 nm for all the spectra regardless of the excitation wavelength, thus suggesting that there might be one absorber or one fluorophore. The use of backscattered red light enhances the autofluorescence contrast.

In vivo autofluorescence imaging of early cancers in the human tracheobronchial tree with a spectrally optimized system

The changes in the autofluorescence characteristics of the bronchial tissue is of crucial interest as a cancer diagnostic tool. Evidence exists that this native fluorescence or autofluorescence of bronchial tissues changes when they turn dysplastic and to carcinoma in situ. There is good agreement that the lesions display a decrease of autofluorescence in the green region of the spectrum under illumination with violet-light, and a relative increase in the red region of the spectrum is often reported. Imaging devices rely on this principle to detect early cancerous lesions in the bronchi. Based on a spectroscopic study, an industrial imaging prototype is developed to detect early cancerous lesions in collaboration with the firm Richard Wolf Endoskope GmbH, Germany. A preliminary clinical trial involving 20 patients with this spectrally optimized system shows that the autofluorescence can help to detect most lesions that would otherwise have remained invisible to an experienced endoscopist under white light illumination. A systematic off line analysis of the autofluorescence images pointed out that real-time decisional functions can be defined to reduce the number of false positive results. Using this method, a positive predictive value (PPV) of 75% is reached using autofluorescence only. Moreover, a PPV of 100% is obtained, when combining the white light (WL) mode and the autofluorescence (AF) mode, at the applied conditions. Furthermore, the sensitivity is estimated to be twice higher in the AF mode than in WL mode.

Absolute autofluorescence spectra of human healthy, metaplastic, and early cancerous bronchial tissue in vivo

Autofluorescence is emerging as a useful tool for the detection of early cancers in the bronchi. It has already produced interesting results, which have been implemented in commercial imaging devices. Their design relies on the spectroscopy of the tissues of interest. However, a large majority of these autofluorescence spectroscopy studies have been presented in arbitrary units. This is a drawback for, in particular, the designing of imaging devices based on autofluorescence. Using correction factors and a spectral sensitivity correction curve, we determined the absolute spectral distribution of the tissue autofluorescence in vivo. These measurements were performed on healthy, metaplastic, and dysplastic bronchial tissues at several excitation wavelengths ranging from 350 to 495 nm. Moreover, we measured at a fixed distance between the tissue and the probe to avoid geometric distortions of the spectra that are due to the optical characteristics of tissue. We found that the order of magnitude of the autofluorescence brightness was stable as the excitation wavelengths varied (on the order of 5 pW/muW x nm at the maximum of the fluorescence emission spectra).

Detection of early bronchial cancer by autofluorescence: results in patients with H&N cancer

Head and neck (H&N) cancer patients have a high incidence of second primary tumours in the tracheobronchial tree. Diagnostic autofluorescence bronchoscopy (DAFE) has shown promising results in the detection of early neoplastic and pre-neoplastic changes in the bronchi. We have investigated the medical impact of DAFE in a population of H&N cancer patients. The bronchoscopies were performed using a modified commercially available DAFE system. Endoscopic imaging of the tissue autofluorescence (AF) was combined with an online image analysis procedure allowing to discriminate between true and false positive results. White light (WL) bronchoscopy was performed as a control. Twenty-one patients with high lung cancer risk factors underwent WL and AF bronchoscopy with this improved system. Forty-one biopsies were taken on macroscopicall suspicious (WL or AF positive) sites. Seven patients were found to have second primary tumours in the bronchi. The sensitivity for the detection of these early lesions with the DAFE was 1.6 times larger than the sensitivity of WL bronchoscopy only. The positive predictive value (PPV) for AF is 79% (33% for WL alone). The PPV of both methods together is 100%. DAFE proved to be efficient for the detection of second primary lesions in H&N cancer patients and can be used as a simple addition to pre-operative work-up or follow-up in this patient population.

In-vivo fluorescence spectroscopy to optimize the detection of early bronchial carcinoma by autoflourescene imaging

Autofluorescence bronchoscopy is a promising approach to detect and characterize precancerous and early cancerous lesions. Nevertheless, many spectral features of photodetection systems remain unclear and sub-optimal at the present time. We report here a comprehensive study of the autofluorescence of the human healthy, metaplastic, dysplastic and cancerous bronchial tissues, covering a range of excitation wavelengths going from 350 nm to 480 nm. Moreover, the absolute values of these tissue autofluorescence yields were determined. These measurements were performed with a spectrally and intensity calibrated optical fiber-based spectrofluorometer which has been designed to optimize the spectroscopy conditions encountered by an endoscopic fluorescence imaging system. Our data yield information about the excitation and emission windows to be used in a bispectral detection imaging system. We found that the order of magnitude of the autofluorescence brightness is stable as the excitation varies from 350 to 495 nm (on the order of 5 nW/mW x nm). We also found that the use of backscattered red light instead of red autofluorescence enhances the lesion/normal tissues contrast. The excitation wavelengths yielding the highest contrasts are between 400 and 480 nm with a peak at 405 nm. It was finally observed that the transition wavelength for bispectral fluorescence imaging systems is around 590 nm, regardless of the excitation wavelength.