Christian Schaller

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 patients 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 multi-dimensional 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.

Time-of-flight sensor for patient positioning

In this paper we present a system that uses Time-of-Flight (ToF) technology to correct the position of a patient in respect to a previously acquired reference surface. A ToF sensor enables the acquisition of a 3-D surface model containing more than 25,000 points using a single sensor in real time. One advantage of this technology is that the high lateral resolution makes it possible to accurately compute translation and rotation of the patient in respect to a reference surface. We are using an Iterative Closest Point (ICP) algorithm to determine the 6 degrees of freedom (DOF) vector. Current results show that for rigid phantoms it is possible to obtain an accuracy of 2.88 mm and 0.28° respectively. Tests with human persons validate the robustness and stability of the proposed system. We achieve a mean registration error of 3.38 mm for human test persons. Potential applications for this system can be found within radiotherapy or multimodal image acquisition with different devices.

ROCHADE: Robust Checkerboard Advanced Detection for Camera Calibration

We present a new checkerboard detection algorithm which is able to detect checkerboards at extreme poses, or checkerboards which are highly distorted due to lens distortion even on low-resolution images. On the detected pattern we apply a surface fitting based subpixel refinement specifically tailored for checkerboard X-junctions. Finally, we investigate how the accuracy of a checkerboard detector affects the overall calibration result in multi-camera setups. The proposed method is evaluated on real images captured with different camera models to show its wide applicability. Quantitative comparisons to OpenCV’s checkerboard detector show that the proposed method detects up to 80% more checkerboards and detects corner points more accurately, even under strong perspective distortion as often present in wide baseline stereo setups.

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.

Touchscreen ohne Touch Berührungslose 3D Gesten-Interaktion für den OperationssaalTouchscreen without Touch Touchless 3D Gesture Interaction for the Operation Room

Zusammenfassung Time-of-Flight-Kameras bieten die Möglichkeit, berührungslos in Echtzeit Distanzen zu messen. Diese technischen Möglichkeiten werden genutzt, um die dreidimensionale Zeigerichtung einer Hand relativ zu einem Monitor zu berechnen. Dadurch kann berechnet werden, wohin der Nutzer auf dem Monitor zeigt und der Mauszeiger an die entsprechende Position gesetzt werden. Durch das Heben und Senken des Daumens wird ein Klick ausgelöst. Somit werden die Basis-Funktionalitäten eines Touchscreens, ohne ihn dabei berühren zu müssen, zur Verfügung gestellt. Das berührunglose Messverfahren der Time-of-Flight-Kameras eignet sich hervorragend für den Einsatz im Operationssaal, da dort unter Sterilitätsbedingungen gearbeitet werden muss. Das vorgeschlagene Interaktionsparadigma ist wegen seiner intuitiven Nutzbarkeit auch gerade für die Nutzung durch Ärzte geeignet, was durch durchgeführte Studien bestätigt wird.

Surface-Based Respiratory Motion Classification and Verification

To ensure precise tumor irradiation in radiotherapy a stable breathing pattern is mandatory as tumors are moving due to respiratory motion. Consequentially, irregularities of respiratory patterns have to be detected immediately. The causal motion of tissue also differs due to different physiological types of respiration, e.g., chest-or abdominal breathing. Currently used devices to measure respiratory motion do not incorporate complete surface deformations. Instead only small regions of interest are considered. Thereby, valuable information to detect different breathing patterns and types are lost. In this paper we present a system that uses a novel camera sensor called Time-of-Flight (ToF) for automatic classification and verification of breathing patterns. The proposed algorithm calculates multiple volume signals of different anatomical regions of the upper part of the patient’s body. Therefore disjoint regions of interest are defined for both, the patient’s abdomen and thorax. Using the calculated volume signals the type of respiration is determined in real-time by computing an energy coefficient. Changing breathing patterns can be visualized using a 2-D histogram, which is also used to classify and detect abnormal breathing phases. We evaluated the proposed method on five persons and obtained a reliable differentation of chest- and abdominal breathing in all test cases. Furthermore, we could show that the introduced 2-D histogram enables an accurate determination of changing breathing patterns.

3D annotation and manipulation of medical anatomical structures

Although the medical scanners are rapidly moving towards a three-dimensional paradigm, the manipulation and annotation/labeling of the acquired data is still performed in a standard 2D environment. Editing and annotation of three-dimensional medical structures is currently a complex task and rather time-consuming, as it is carried out in 2D projections of the original object. A major problem in 2D annotation is the depth ambiguity, which requires 3D landmarks to be identified and localized in at least two of the cutting planes. Operating directly in a three-dimensional space enables the implicit consideration of the full 3D local context, which significantly increases accuracy and speed. A three-dimensional environment is as well more natural optimizing the users comfort and acceptance. The 3D annotation environment requires the three-dimensional manipulation device and display. By means of two novel and advanced technologies, Wii Nintendo Controller and Philips 3D WoWvx display, we define an appropriate 3D annotation tool and a suitable 3D visualization monitor. We define non-coplanar setting of four Infrared LEDs with a known and exact position, which are tracked by the Wii and from which we compute the pose of the device by applying a standard pose estimation algorithm. The novel 3D renderer developed by Philips uses either the Z-value of a 3D volume, or it computes the depth information out of a 2D image, to provide a real 3D experience without having some special glasses. Within this paper we present a new framework for manipulation and annotation of medical landmarks directly in three-dimensional volume.