Laser Doppler imaging for intraoperative human brain mapping.

The identification and accurate location of centers of brain activity are vital both in neuro-surgery and brain research. This study aimed to provide a non-invasive, non-contact, accurate, rapid and user-friendly means of producing functional images intraoperatively. To this end a full field Laser Doppler imager was developed and integrated within the surgical microscope and perfusion images of the cortical surface were acquired during awake surgery whilst the patient performed a predetermined task. The regions of brain activity showed a clear signal (10-20% with respect to the baseline) related to the stimulation protocol which lead to intraoperative functional brain maps of strong statistical significance and which correlate well with the preoperative fMRI and intraoperative cortical electro-stimulation. These initial results achieved with a prototype device and wavelet based regressor analysis (the hemodynamic response function being derived from MRI applications) demonstrate the feasibility of LDI as an appropriate technique for intraoperative functional brain imaging.

In vitro measurement conditions for optical coherence tomography (OCT).

CONCLUSION: Tissue marking with soot-covered fine needles enables the optical coherence tomography (OCT) scanning plane to be localized within the histological specimen to an accuracy of approximately 50 microm. Tissue water content is an especially important parameter for in vitro measurements. Dehydration tends to produce an increase in surface reflections and a reduction in imaging depth. OBJECTIVES: The aim of this in vitro study was to evaluate parameters relevant to the visualization and conservation process to allow optimal images to be generated for later differentiation between healthy and degenerated tissue in vivo. MATERIALS AND METHODS: Various methods of marking samples were applied in vitro to achieve accurate overlaps of the OCT scanning plane and the corresponding section of the histological specimen. The influence of temperature and tissue water content was investigated using both porcine and human tissue. Samples were marked using fine needles, ablation craters generated by laser application, and colour markers introduced into the tissue. RESULTS: It was demonstrated that the water content of tissue exerts a direct influence on OCT imaging, whereas above 15 degrees C temperature had no effect on image quality. With regard to the marking of samples, the best results were obtained using sooted fine needles.

[Application of Optical Coherence Tomography (OCT) in middle ear surgery]. / Erste Anwendungen der optischen Kohärenztomographie (OCT) in der Mittelohrchirurgie.

BACKGROUND: Middle ear surgery has reached an advanced stage of development over the last few decades. The use of biocompatible materials offers new possibilities in ossiculoplasty. The exact calculation concerning the length of the implant to be used, however, still poses considerable difficulties and is an additional cause for a remaining air conduction difference or a further surgical intervention. METHODS: Optical coherence tomography (OCT) is a non-invasive imaging procedure for the imaging of tissue structures with a resolution accurate to micrometres. OCT can be operated touch-free and for this reason does not require any means of contact between applicator and sample. In the present study an optical coherence inferometre was coupled to an operating microscope and used in 5 stapedoplasties and 5 tympanoplasties type III in order to determine the length of the prosthesis to be used. RESULTS: The use of OCT implies an intraoperative measuring time of only a few seconds. The coupling in the optical path of an operating microscope allows trouble-free handling. The measurement of middle ear structures has an accuracy of 30 micrometer. The postoperative audiological results show a good auditory performance. CONCLUSIONS: Initial experience with OCT indicates that the technology will be extremely interesting for otosurgery. Improvements in functional pattern will enable routine intervention in connection with an operating microscope. Further OCT applications for tissue differentiation will have to follow.