Endoscopic orientation correction.

An open problem in endoscopic surgery (especially with flexible endoscopes) is the absence of a stable horizon in endoscopic images. With our "Endorientation" approach image rotation correction, even in non-rigid endoscopic surgery (particularly NOTES), can be realized with a tiny MEMS tri-axial inertial sensor placed on the tip of an endoscope. It measures the impact of gravity on each of the three orthogonal accelerometer axes. After an initial calibration and filtering of these three values the rotation angle is estimated directly. Achievable repetition rate is above the usual endoscopic video frame rate of 30 Hz; accuracy is about one degree. The image rotation is performed in real-time by digitally rotating the analog endoscopic video signal. Improvements and benefits have been evaluated in animal studies: Coordination of different instruments and estimation of tissue behavior regarding gravity related deformation and movement was rated to be much more intuitive with a stable horizon on endoscopic images.

Time-of-Flight 3-D endoscopy.

This paper describes the first accomplishment of the Time-of-Flight (ToF) measurement principle via endoscope optics. The applicability of the approach is verified by in-vitro experiments. Off-the-shelf ToF camera sensors enable the per-pixel, on-chip, real-time, marker-less acquisition of distance information. The transfer of the emerging ToF measurement technique to endoscope optics is the basis for a new generation of ToF rigid or flexible 3-D endoscopes. No modification of the endoscope optic itself is necessary as only an enhancement of illumination unit and image sensors is necessary. The major contribution of this paper is threefold: First, the accomplishment of the ToF measurement principle via endoscope optics; second, the development and validation of a complete calibration and post-processing routine; third, accomplishment of extensive in-vitro experiments. Currently, a depth measurement precision of 0.89 mm at 20 fps with 3072 3-D points is achieved.

Inverse C-arm positioning for interventional procedures using real-time body part detection.

The automation and speedup of interventional therapy and diagnostic workflows is a crucial issue. One way to improve these work-flows is to accelerate the image acquisition procedures by fully automating the patient setup. This paper describes a system that performs this task without the use of markers or other prior assumptions. It returns metric coordinates of the 3-D body shape in real-time for inverse positioning. This is achieved by the application of an emerging technology, called Time-of-Flight (ToF) sensor. A ToF sensor is a cost-efficient, off-the-shelf camera which provides more than 40,000 3-D points in real-time. The first contribution of this paper is the incorporation of this novel imaging technology (ToF) in interventional imaging. The second contribution is the ability of a C-arm system to position itself with respect to the patient prior to the acquisition. We are using the 3-D surface information of the patient to partition the body into anatomical sections. This is achieved by a fast two-stage classification process. The system computes the ISO-center for each detected region. To verify our system we performed several tests on the ISO-center of the head. Firstly, the reproducibility of the head ISO-center computation was evaluated. We achieved an accuracy of (x: 1.73 +/- 1.11 mm/y: 1.87 +/- 1.31 mm/z: 2.91 +/- 2.62 mm). Secondly, a C-arm head scan of a body phantom was setup. Our system automatically aligned the ISO-center of the head with the C-arm ISO-center. Here we achieved an accuracy of +/- 1 cm, which is within the accuracy of the patient table control.

Time-of-flight sensor for respiratory motion gating.

In this technical note we present a system that uses time-of-flight (ToF) technology to acquire a real-time multidimensional respiratory signal from a 3D surface reconstruction of the patient's chest and abdomen without the use of markers. Using ToF sensors it is feasible to acquire a 3D model in real time with a single sensor. An advantage of ToF sensors is that their high lateral resolution makes it possible to define multiple regions of interest to compute an anatomy-adaptive multidimensional respiratory signal. We evaluated the new approach by comparing a ToF based respiratory signal with the signal acquired by a commercially available external respiratory gating system and achieved an average correlation coefficient of 0.88.

Calibration of laryngeal endoscopic high-speed image sequences by an automated detection of parallel laser line projections.

High-speed laryngeal endoscopic systems record vocal fold vibrations during phonation in real-time. For a quantitative analysis of vocal fold dynamics a metrical scale is required to get absolute laryngeal dimensions of the recorded image sequence. For the clinical use there is no automated and stable calibration procedure up to now. A calibration method is presented that consists of a laser projection device and the corresponding image processing for the automated detection of the laser calibration marks. The laser projection device is clipped to the endoscope and projects two parallel laser lines with a known distance to each other as calibration information onto the vocal folds. Image processing methods automatically identify the pixels belonging to the projected laser lines in the image data. The line detection bases on a Radon transform approach and is a two-stage process, which successively uses temporal and spatial characteristics of the projected laser lines in the high-speed image sequence. The robustness and the applicability are demonstrated with clinical endoscopic image sequences. The combination of the laser projection device and the image processing enables the calibration of laryngeal endoscopic images within the vocal fold plane and thus provides quantitative metrical data of vocal fold dynamics.