To investigate vessel coagulation depth and tissue damage in therapy with the flashlamp-pumped pulsed dye laser (585 nm, 5 mm spot size, 450 microsecond pulse duration, 6-8 J/cm2), we used the nitroblue-tetrazolium chloride stain in 22 post-treatment biopsy specimens from patients with port wine stain. With this method, thermally damaged tissue can be easily differentiated from unchanged tissue to the level of single cells. The results showed that in superficial port wine stain vessels up to 150 microns in diameter, vessel coagulation was complete and selective without further dermal damage. With the increase of vessel diameter, strong superficial hemoglobin absorption led to only partial vessel-wall coagulation and, in some cases, to superficial dermal damage. Likewise, deeper vessels were not coagulated because of shadow effects by superficial vessel layers. Thus, the overall vessel-wall coagulation depth of the flashlamp-pumped dye laser was limited to a maximum of 0.65 mm (mean 0.37 mm). In addition, some degree of epidermal damage was present in most specimens, which significantly increased with epidermal melanin content and resulted in epidermal coagulation and blistering in pigmented skin. Our results explain the occurrence of crusting, hyperpigmentation, and hypopigmentation in therapy with the flashlamp-pumped dye laser and its limited effect on dark or hypertrophic port wine stains in adults featuring large vessel diameters or multiple vessel layers.

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Intraoperative precision in computer-assisted surgery depends on the characteristics of a navigation system, the precision of correlation between object and data set, the position, number and fixation of landmarks, and the parameters of the data set. The characteristics of a navigation system, in particular the immanent precision, can be detected by the use of the geometric model and navigation analyzer developed at the University of Regensburg with the support of Carl Zeiss, Germany. The precision of five navigation systems of different types and technology was measured: Viewing Wand (ISG, mechanical system), the SMN microscope (Carl Zeiss, infrared system with laser autofocus), the MKM system (Carl Zeiss, robot platform with laser autofocus) and the STP pointer (Leibinger, infrared system). The immanent precision of these systems ranges from 0.1 to 2.0 mm. An electromagnetic system (3-Space Digitizer, Polhemus) was compared; this produces serious spherical deviations of 10.0 to 20.0 mm in the presence of metal, surgical and rotating instruments, and circuits. The application of these different systems for craniomaxillofacial surgery is discussed.

The precision of a new laser-guided navigation system (the "MKM") was compared with the "Viewing Wand" mechanical navigation system. We describe the inherent deviations in each positioning system as well as errors caused by data acquisition and referencing between the CT data set used for navigation and the original object. Two thousand individual measurements were performed on geometric test models scanned by CT. The technical accuracy of the mechanical navigation system varied between 0.48 mm in the most favorable area of the working field and 1.8 mm in the more inaccurate areas. For the laser-guided system a precision of 0.27 mm was found for all areas of the working field. After referencing between the CT data set and the original object, the error of measurement increased in both navigation systems: i.e., 0.83 mm for the Viewing Wand and 0.49 mm for the MKM system.

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