Friedrich-Alexander-Universität Erlangen-Nürnberg

Exploration of new concepts for sensor based tissue specific laser surgery

Exploration of new concepts for sensor based tissue specific laser surgery

The advantages of laser surgery can be diminished by the lack of tactile feedback during the ablation of tissue. A surgeon receives no information about the exact laser beam penetration depth or type of the ablated tissue at the bottom of the cut. Hence, there is a risk of iatrogenic damage or destruction of anatomical structures like peripheral nerves. Therefore laser surgery is only used on tissue surface structures so far and still is not a generally useable surgical tool. That’s way additional means are required to control laser ablation according to tissue-specificity. In this research project an interdisciplinary work group investigates the sensor based tissue specific laser surgery of normal/healthy tissue. The research project is especially focused on nerve preservation by remote optical tissue type discrimination during hard and soft tissue laser surgery. Two surgical procedures are chosen for the experiments which typically inherit a high risk of iatrogenic nerve damage: the osteotomy of the mandible in the vicinity of the inferior alveolar nerve and the surgery of the parotid gland in the vicinity of the facial nerve. The tissue types which will be investigated are: nerve, fat, salivary gland, muscle, cortical bone and cancellous bone. Especially the discrimination of nerve, salivary gland and fat tissue is a great challenge. Because of biological and/or structural similarity of these tissues a simple visual differentiation offhand is not possible. The ex vivo experimental examinations are performed on tissue specimens from domestic pigs. The tissue discrimination is attempted by diffuse reflectance and auto-fluorescence spectroscopy combined with optical process emissions caused by Er:YAG laser tissue ablation.

The tissue differentiation is performed by principal components analysis (PCA) followed by linear discriminant analysis (LDA). The central idea of PCA is to reduce the dimensionality of a data set by reducing the number of dimensions, without much loss of information. The LDA is a statistical technique of data classification by using significant group features. Specificity and sensitivity were calculated by receiver operating characteristic (ROC) analysis. The area under ROC curve (AUC) is a measure of accuracy of the differentiation method. The evaluation of the results shows that both the diffuse reflectance and the auto-fluorescence in combination with a statistical analysis are suitable methods for tissue differentiation.

Non-standardized diffuse reflectance spectra for different hard and soft tissues
PC loading. PC 1 has a consistent contribution of loading along the investigated wavelength range; PC 2 and PC 4 show a higher variation of loading with prominent peaks at 410, 540 and 580 nm; PC 5 and 9 are more disturbed by the influence of noise (not shown in the figure)
Figure 3: ROC curve for comparison between nerve and salivary gland tissue (as example for the ROC-curves derived from the data analysis) [4]



  1. STELZLE, F.; TANGERMANN-GERK, K.; ADLER, W.; ZAM, A.; SCHMIDT, M.; DOUPLIK, A.; NKENKE, E.: Diffuse Reflectance Spectroscopy for Optical Soft Tissue Differentiation as Remote Feedback Control for Tissue-Specific Laser Surgery. In: Lasers in Surgery and Medicine, 2010, Volume 42, Issue 4, pp. 319-325
  2. STELZLE, F.; ZAM, A.; ADLER, W.; TANGERMANN-GERK, K.; DOUPLIK, A.; NKENKE, E.; SCHMIDT, M.: Optical Nerve Detection by Diffuse Reflectance Spectroscopy for Feedback Controlled Oral and Maxillofacial Laser Surgery. Lasers in Surgery and Medicine, 2010, 42:319–325
  3. ZAM, A.; STELZLE, F.; TANGERMANN-GERK, K.; ADLER, W.; NKENKE, E.; SCHMIDT, M.; DOUPLIK, A.: Tissue differentiation by diffuse reflectance spectroscopy for automated oral and maxillofacial laser surgery: ex vivo pilot study. In: Photonics West 2010 - Proceedings of SPIE Vol. 7555-755515 “Advanced Biomedical and Clinical Diagnostic Systems VIII”, 6 pages, DOI: 10.1117/12.841674.
  4. STELZLE F, ZAM A, ADLER W, TANGERMANN-GERK K, DOUPLIK  A, , NKENKE E, SCHMIDT M. Optical Nerve Detection by Diffuse Reflectance Spectroscopy for Feedback Controlled Oral and Maxillofacial Laser Surgery. Journal of Translational Medicine 2011, 9:20
  5. STELZLE F, ZAM A, ADLER W, TANGERMANN-GERK K, KNIPFER C, DOUPLIK  A, , SCHMIDT M, NKENKE E. In Vivo Optical Tissue Differentiation by Diffuse Reflectance Spectroscopy: Preliminary Results for Tissue-Specific Laser Surgery. Journal of Surgical Innovation, accepted for publication, October 2011


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