Biomedical subjects

Gerd Häusler

Publications and source records attributed to Gerd Häusler.

6 recordsLinked to original sources

PubMed2006

Automatic coarse registration of three-dimensional surfaces by information theoretic selection of salient points.

We describe a new method to register surface data measured by optical three-dimensional (3-D) sensors from various views of an object. With our method, complete 3-D models of objects can be generated without user interaction. Circumferential acquisition of 3-D objects is done by taking several views from different directions. To generate a complete 3-D-model, the views must be aligned with each other. This process is called registration and is commonly done interactively by searching for so-called corresponding points in the different views and by use of these points to calculate the appropriate rotation and translation. Our approach is based on automatically finding points that are eye catching or salient compared with other surface points. We derive a quantitative measure of point salience and a feature definition for free-form surfaces by introducing a concept to measure pragmatic information. Experiments confirm that our salient points can be robustly located on general free-form surfaces, even if there are no corners or edges. Furthermore, the neighborhoods of the salient points are highly distinguishable from each other. This results in a large reduction of the complexity of the subsequent geometric matching. The computing time is only a few seconds. We present results from various fields of application.

Journal Article↗

PubMed2006

Intraoperative noncontact, nonionizing, optical 3D exophthalmometry during repositioning of dislocated globes: first results.

PURPOSE: This study reports on the intraoperative use of noncontact, nonionizing, optical 3-dimensional (3D) exophthalmometry during the repositioning of dislocated globes as a result of trauma. PATIENTS AND METHODS: Ten patients (4 female, 6 male, 41.4+/-15.2 years) with a relative enophthalmos of the globe as a result of zygomatic fractures were included in the study. Preoperatively, en- and exophthalmometry data were assessed from axial CT slices and optical 3D imaging. 3D data were analyzed twice for the assessment of measurement errors. Intraoperatively, optical en- and exophthalmometry was carried out to control the globe position. Surgery was considered successful when the relative en- or exophthalmos no longer exceeded 2 mm. Optical 3D en- and exophthalmometry data were reassessed 5 days and 3 months after surgery. RESULTS: Method error was 0.184 mm for optical 3D en- and exophthalmometry. The preoperatively assessed en- and exophthalmometry data determined from axial CT scans and from optical 3D images did not differ significantly statistically (P=.538). When the preoperative en- and exophthalmometry data were compared to the values assessed at the end of surgery, a significant improvement in globe position was found (P=.005). Although a relative en- or exophthalmos of 2 mm was not exceeded in any of the patients 3 months after surgery, en- and exophthalmometry data differed significantly statistically from the data assessed at the end of the operation (P=.005). CONCLUSIONS: Intraoperative optical en- and exophthalmometry is an effective means to support the surgeon in objectively optimizing the globe position with small measurement errors.

Adult↗

PubMed2005

White-light interferometer with dispersion: an accurate fiber-optic sensor for the measurement of distance.

We present a fiber-optical sensor for distance measurement of smooth and rough surfaces that is based on white-light interferometry; the sensor measures the distance from the sample surface to the sensor head. Because white light is used, the measurement is absolute. The measurement uncertainty depends not on the aperture of the optical system but only on the properties of the rough surface and is commonly approximately 1 microm. The measurement range is approximately 1 mm. The sensor includes no mechanical moving parts; mechanical movement is replaced by the spectral decomposition of light at the interferometer output. The absence of mechanical moving parts enables a high measuring rate to be reached.

Journal Article↗

PubMed2003

Information theoretical optimization for optical range sensors.

Most of the known optical range sensors require a large amount of two-dimensional raw data from which the three-dimensional (3D) data are decoded and so are associated with considerable cost. The cost arises from expensive hardware as well as from the time necessary to acquire the images. We will address the question of how one can acquire maximum shape information with a minimum amount of image raw data, in terms of information theory. It is shown that one can greatly reduce the amount of raw data needed by proper optical redundancy reduction. Through these considerations, a 3D sensor is introduced, which needs only a single color (red-green-blue) raw image and still delivers data with only approximately 2-microm longitudinal measurement uncertainty.

Journal Article↗

PubMed2003

Relative en- and exophthalmometry in zygomatic fractures comparing optical non-contact, non-ionizing 3D imaging to the Hertel instrument and computed tomography.

AIM: It is the aim of the present study to introduce non-contact, non-invasive optical 3D imaging to relative exophthalmometry and to compare the resulting data to exophthalmometry values assessed by the Hertel instrument and computed tomography. PATIENTS AND METHODS: 20 patients (3 female, 17 male, 44.4+/-16.6 years) without orbital pathology, who were examined by computed tomography of head and neck for the exclusion of different diseases, and seven patients (1 female, 6 male, 40.1+/-14.4 years), who received routine orbital computed tomography because of zygomatic fractures, were included in the study. Optical 3D images of the facial surface were assessed and Hertel exophthalmometry was carried out to determine the relative globe position. In patients with zygomatic fractures the assessment of optical 3D images and Hertel values was repeated 5 days after surgery. RESULTS: For patients without orbital pathology relative exophthalmometry data were 1.4+/-1.1 mm for the Hertel instrument, 0.9+/-1.0 mm for computed tomography and 0.5+/-0.5 mm for optical 3D imaging. The values for Hertel exophthalmometry and computed tomography did not differ statistically significantly (p(Herteldifferencepreop/CTdifferencepreop)=0.284), while there was a significant difference between Hertel exophthalmometry and optical 3D imaging (p(Herteldifferencepreop/opticaldifferencepreop)=0.008). In the cases of zygomatic fractures, Hertel exophthalmometry revealed less pronounced relative differences in globe position than CT and optical 3D imaging data (Hertel 0.7+/-1.1 mm, CT 1.9+/-1.0 mm, optical 3D imaging 1.9+/-1.0 mm). Postoperatively, relative Hertel exophthalmometry showed an increased value revealing a more pronounced enophthalmos (1.7+/-1.0 mm), while the corresponding value of the optical 3D images decreased as a sign for normalization of the globe position (1.1+/-0.7 mm). CONCLUSION: Because of its reliance on the lateral orbital rims Hertel exophthalmometry can lead to an under- or overestimation of enophthalmos, when soft tissue oedema or a dislocation of the orbital rim are present. The combination of computed tomography as baseline measurement and optical 3D imaging for the follow-up examinations reveal more realistic data in cases of zygomatic fractures. Therefore, they should be preferred to the determination of Hertel values especially in more complex cases.

Adult↗

PubMed2003

Validation of in vivo assessment of facial soft-tissue volume changes and clinical application in midfacial distraction: a technical report.

The purpose of this study was to validate the assessment of visible volume changes of the facial soft tissue with an optical three-dimensional sensor and to introduce new parameters for the evaluation of the soft-tissue shape achieved from three-dimensional data of selected cases of midfacial distraction. Images of a truncated cone of known volume were assessed repeatedly with an optical three-dimensional sensor based on phase-measuring triangulation to calculate the volume. Two cubic centimeters of anesthetic solution was injected into the right malar region of 10 volunteers who gave their informed consent. Three-dimensional images were assessed before and immediately after the injections for the assessment of the visible volume change. In five patients who underwent midfacial distraction after a high quadrangular Le Fort I osteotomy, three-dimensional scans were acquired before and 6 and 24 months after the operation. The visible soft-tissue volume change in the malar-midfacial area and the mean distance of the accommodation vector that transformed the preoperative into the postoperative surface were calculated. The volume of the truncated cone was 235.26 +/- 1.01 cc, revealing a measurement uncertainty of 0.4 percent. The injections of anesthetic solution into the malar area resulted in an average visible volume change of 2.06 +/- 0.06 cc. The measurement uncertainty was 3 percent. In the five patients, the average distance of maxillary advancement was 6.7 +/- 2.3 mm after 6 months and 5.4 +/- 3.0 mm after 2 years. It was accompanied by a mean visible volume increase of 8.92 +/- 5.95 cc on the right side and 9.54 +/- 4.39 cc on the left side after 6 months and 3.54 +/- 3.70 cc and 4.80 +/- 3.47 cc, respectively, after 2 years. The mean distance of the accommodation vector was 4.41 +/- 1.94 mm on the right side and 4.74 +/- 1.32 mm on the left side after 6 months and 1.62 +/- 1.96 mm and 2.16 +/- 1.52 mm, respectively, after 2 years. The assessment of visible volume changes by optical three-dimensional images can be carried out with considerable accuracy. The determination of volume changes and accompanying accommodation vectors completes the cephalometric analysis during the follow-up of patients undergoing midfacial distraction. The new parameters will help to assess normative soft-tissue data on the basis of three-dimensional imaging with a view to an improved three-dimensional prediction of the operative outcome of orthognathic surgery.

Adolescent↗