F. van der Heijden

Measurement Errors and Uncertainty

No matter what precautions are taken, there will always be a difference between the result of a measurement and the true value of a quantity. This difference is called the measurement error. A measurement is useless without a quantitative indication of the magnitude of that error. Such an indication is called the uncertainty. Without knowing the uncertainty, the comparison of a measurement result with a reference value or with results of other measurements cannot be made. This chapter addresses the problem of how to define measurement errors, uncertainty, and related terms. The chapter also addresses the question of how to determine the uncertainty in practice. Under this, it summarizes the related statistical issues. Further, various sources of errors and the various types of errors is discussed. Methods to specify these errors are also highlighted. The chapter concludes with some techniques used to reduce the effects of errors.

A feasibility study of optical flow-based navigation during colonoscopy

Introduction In endoscopic surgical procedure, surgeons need to manipulate endoscopes and surgical instruments inside of the body cavity in order to observe a large field-of-view and estimate the distance between the surgical instruments and anatomical area of interest. This is a difficult task while watching 2-D endoscopic images on a monitor. So, there is a risk of the surgical instruments or the endoscope physically damaging the internal organs. Wasol Co., Ltd has developed a 3-D endoscope that has a single optical channel and CCD camera. This 3-D endoscope can acquire left and right endoscopic images at different viewpoints by using a rapidly-rotated transparent plate in front of the CCD camera. However, the diameter of the single optical channel must be large so that the endoscope can acquire endoscopic images of a sufficient quality for stereovision. Shinko Optical Co., Ltd. has developed a 3-D endoscope that has two 1/10-inch CCD cameras at the distal end of its sleeve. This 3-D endoscope enables surgeons to easily estimate the distance between the instruments and anatomical area of interest. Although this method is a simple solution for stereovision, its diameter is difficult to reduce because two CCD cameras are placed in parallel at its distal end. We have previously developed a u5-mm 3-D endoscope with a single CCD camera and vibration mechanism using a cam mechanism. This endoscope can acquire left and right endoscopic images for stereoscopic vision in a way which is synchronized with the periodical motion generated by the vibration mechanism. The image quality is high enough for stereoscopic vision and more than 65 % of volunteers can perceive depth correctly, however the cam-vibration mechanism is large and unsterilizable; and for this reason, this endoscope cannot be used for real surgery. To overcome these problems, we have developed a high-imagequality and thin 3-D endoscope with a single CCD camera and sterilizable pneumatic vibration mechanism. Methods The developed 3-D endoscope system consists of a 1/10-inch CCD camera (SONY), an outer sleeve (7 mm in outer diameter, 100 mm in length, stainless), an inner sleeve (5 mm in outer diameter, 200 mm in length, stainless), a pneumatic vibration mechanism consisting of a case with two ports (Fluororesin) and a slider with o-rings (light curing resin), an air compressor (TFP04B-10C, ANEST IWATA Corporation), an air dryer (RDG-22C, ANEST IWATA Corporation), an auxiliary air tank (SAT-33H-100, ANEST IWATA Corporation), two air solenoid valves (MHA2-MS1H-3/2G-2-K, Festo Corporation), a digital output board (PCI-2426C, Interface Corporation), two image capture boards (IP7000BD, Hitachi Information & Control Solutions Co., Ltd.) and a monitor for stereovision (LCD-SK3, Shinko Optical Co., Ltd.) (Fig. 1a). The 1/10-inch CCD camera is attached to the distal end of the sleeve and has an 80 horizontal field-of-view and a 66 vertical field-of-view. The pneumatic vibration mechanism is attached to the proximal end of the sleeve. A fulcrum point is set at middle of the inner sleeve as shown in Fig. 1a. The distance between the fulcrum point and the 1/10-inch CCD camera is 100 mm. The pneumatic vibration mechanism, which is made of sterilizable plastic, generates a triangular wave as follows: When compressed air is pumped into Port A, the slider moves to the right. In the inverse condition, when compressed air is pumped into Port B, the slider moves to the left (Fig. 1b). The sequence is repeated for the proximal end of the sleeve, which is attached to the slider, to vibrate and thus the vibration is transmitted to its distal end with the 1/10-inch CCD camera. The peak-to-peak amplitude and frequency of the vibration are 0.5 mm and 10 Hz respectively (Fig. 2a). The 1/10-inch CCD camera alternately acquires left and right images when its displacement is at maximum or minimum of the amplitude (at this point, the velocity of the 1/10-inch CCD camera is Fig. 1 a System configuration. b Pneumatic vibration mechanism Left Compressed air is pumped into Port A, Right Compressed air is pumped into PortB

Towards virtual surgery in oral cancer to predict postoperative oral functions preoperatively.

Our aim was to develop a dynamic virtual model of the oral cavity and oropharynx so that we could incorporate patient-specific factors into the prediction of functional loss after advanced resections for oral cancer. After a virtual resection, functional consequences can be assessed, and a more substantiated decision about treatment can be made. In this study we used a finite element model of the tongue, which can be implemented in the total virtual environment in the future. We analysed the movements and changes in volume, and the effects of changes in the material variables, to mimic scar tissue. The observed movements were in accordance with descriptions of in vivo movements. Affected movements caused by the mimicked scar tissue were also similar to expectations. Some changes in volume were measured, particularly in individual elements. We have taken the first steps in the development of a finite element model of the tongue. Now, refinement is necessary to make the model suitable for future use in virtual surgery.

A new method for three-dimensional evaluation of the cranial shape and the automatic identification of craniosynostosis using 3D stereophotogrammetry

Craniosynostosis is a congenital defect which can result in abnormal cranial morphology. Three dimensional (3D) stereophotogrammetry is potentially an ideal technique for the evaluation of cranial morphology and diagnosis of craniosynostosis because it is fast and harmless. This study presents a new method for objective characterization of the morphological abnormalities of scaphocephaly and trigonocephaly patients using 3D photographs of patients and healthy controls. Sixty 3D photographs of healthy controls in the age range of 3-6 months were superimposed and scaled. Principal component analysis (PCA) was applied to find the mean cranial shape and the cranial shape variation in this normal population. 3D photographs of 20 scaphocephaly and 20 trigonocephaly patients were analysed by this PCA model to test whether cranial deformities of scaphocephaly and trigonocephaly patients could be objectively identified. PCA was used to find the mean cranial shape and the cranial shape variation in the normal population. The PCA model was able to significantly distinguish scaphocephaly and trigonocephaly patients from the normal population. 3D stereophotogrammetry in combination with the presented method can be used to objectively identify and classify the cranial shape of healthy newborns, scaphocephaly and trigonocephaly patients.

Numerical optimisation in spot detector design

Spots are image details resulting from objects, the projections of which are so small that the inner structure of these objects cannot be resolved from their image. Spot detectors are image operators aiming at the detection and localisation of spots in the image. Most spot detectors can be tuned with parameters. This paper addresses the problem of how to select the parameters. We propose to use carefully designed test images, a performance measure, and numerical optimisation techniques to solve this problem. Several optimisation methods are compared, and their adequacy for spot detector design is tested.

Cranial shape comparison for automated objective 3D craniosynostosis surgery planning

Virtual planning of open cranial vault reconstruction is used to simulate and define an pre-operative plan for craniosynostosis surgery. However, virtual planning techniques are subjective and dependent on the experience and preferences of the surgical team. To develop an objective automated 3D pre-operative planning technique for open cranial vault reconstructions, we used curvature maps for the shape comparison of the patient’s skull with an age-specific reference skull. We created an average skull for the age-group of 11–14 months. Also, we created an artificial test object and selected a cranial CT-scan of an 11 months old trigonocephaly patient as test case. Mesh data of skulls were created using marching cubes and raycasting. Curvature maps were computed using quadric surface fitting. The shape comparison was tested for the test object and the average skull. Finally, shape comparison was performed for the trigonocephalic skull with the average skull. Similar shapes and the area on the patient’s skull that maximally corresponded in shape with the reference shape were correctly identified. This study showed that curvature maps allow the comparison of craniosynostosis skulls with age-appropriate average skulls and a first step towards an objective user-independent pre-operative planning technique for open cranial vault reconstructions is made.

Predictive model for functional consequences of oral cavity tumour resections

Purpose Against traditional medical teaching, web-based medical learning tools offer a number of advantages, like timeand distance-independent learning [1]. There exist a few online medical learning platforms, e. g., SurgyTech, BioDigital Systems or Zygote Body. But the majority of these online platforms only provide movies of surgical interventions or they are often limited to a small number of cases. The anatomical situs is often reconstructed using 3D-modeling tools [2]. Real patient-specific anatomical and pathological conditions and selfassessment tools that provide immediate feedback to the learner are largely missing. In this article, we describe the development of a webbased medical learning tool: the LiverAnatomyExplorer. The system provides clinical 2D image data as well as interactive polygonal 3D models. In close collaboration with medical experts at the Asklepios Clinic Barmbek, Hamburg, Germany, we selected appropriate patient cases with liver tumors, metastases and vessel anomalies. We provide an integrated training package that includes diagnosis and surgical reports, clinical image data with colored overlays, easy-to-use interactive 3D models, surgical video clips and self-assessment exercises. Methods We started with a detailed requirements analysis with potential end users: 176 medical students and 19 clinicians filled an online questionnaire. It turned out that many students would benefit from clinical case collections with medical imagery and 3D representations of anatomical basics. Most of the clinical subjects (76 %, 10/13) are interested in providing interactive 3D graphics, clinical imagery and movies as complementary learning materials for trainees. The analysis also showed that 97 % (171/176) of the students and 54 % (7/13) of the medical experts never or rarely used 3D visualizations so far. We used MeVisLab to process and convert 13 real clinical cases. After identifying and segmenting the important structures, they need to be exported in a web-compatible format. In our case, the segmentations of liver, tumors and vascular structures have been performed by medical experts with deep anatomical knowledge at MeVis Distant Services, Bremen, Germany. In order to achieve a fast online access of anonymized patient data, we chose JPG as export image format. The resulting segmented areas are automatically exported as SVG files. For web-based rendering of 3D models, the size of the meshes is more crucial than for local use. The simplified surface mesh has an overall size of about 5–10 MB (ca. 100,000 polygons), which enables fast web-based rendering. The surface mesh is exported as a single X3D file. We use X3D, an ISO Web3D standard, since X3D files can be easily integrated and rendered in real-time, without any plugin, using WebGL and X3DOM [3]. The exported clinical 2D data and segmented areas are presented in our combined 2D/3D viewer based on HTML, SVG, JavaScript and WebGL (Fig. 1left/right). The WebGLrendered 3D scene can be rotated, panned and zoomed freely in the 3D viewer. Immediate customized feedback mechanisms are essential for students to gain knowledge and to monitor individual learning curves [4]. Therefore, we have integrated a multifunctional selfassessment tool. Beside typical textual multiple choice questions, we enhance the quiz to interactive 2D and 3D click answer options. Highquality surgical images or movies composed and annotated by an expert surgeon, can be used by the learner as additional learning material. Results We conducted an evaluation with 54 medical students (average age: 24, gender: 40 f/14 m, 7th to 9th semester) to investigate the user experience and learning aspects of the LiverAnatomyExplorer. After testing the web application, the subjects were asked to fill an online questionnaire (statements are scaled using a five-point likert scale (1 = ‘‘Strongly disagree’’ to 5 = ‘‘Strongly agree’’). The analysis of the user study showed that the website has a modern and attractive design (average of 3.94) and the navigation is self-explanatory (average of 4.22). The orientation guides in the 3D viewer and the tutorial were highlighted by many subjects to be very helpful. The learning aspects of the LiverAnatomyExplorer were also rated ‘‘good’’, with some exceptions. On the one hand, the subjects highly rated the reality of the learning contents (average of 3.98) and the knowledge gain due to the multi-modal, individual liver anatomy data (average of 3.96). On the other hand, it turned out that the questions concerning liver segments and vessel anomalies are too specialized for medical students at this education level. Conclusion Our architecture could be easily adapted to other organs, since we use X3D as free ISO exchange file format and WebGL as heterogeneous free rendering engine. Further interviews with medical experts are

Particle smoothing for solving ambiquity problems in one-shot structured light systems

One-shot structured light systems for 3D depth reconstruction often use a periodic illumination pattern. Finding corresponding points in the image and projector plane, needed for a triangulation, boils down to phase estimation. The 2πN ambiguities in the phase cause ambiguities in the reconstructed depth. This paper solves these ambiguities by constraining the solution space to scenes that only contain objects with flat surfaces, i.e. polyhedrons. We develop a new particle filter that estimates the depth and solves the ambiguity problem. A state model is proposed for piecewise continuous signals. This state model is worked out to find the optimal proposal density of the particle filter. The approach is validated with a demonstration.

Design of Measurement Systems

This chapter reviews the essential steps in the design and decision process. The design process is decomposed into a number of basic steps, with feedback loops and iteration sequences. Most of these studies distinguish three major levels—task definition, concept generation, and evaluation. Any design should start with a description of the requirements the system should finally be able to meet. Important specifications of a measurement system concern information handling performance; technical performance; environmental conditions; and economically related aspects. The design of a measurement system is not a trivial task. Even for the measurement of a single parameter, a variety of measurement principles is available, and for each principle many sensor types, measurement configurations and different ways of signal processing and data handling are available. This leads to an almost infinite number of possible measurement systems for each measurand.

Measurement of Chemical Quantities

This chapter discusses the basics of electrochemical sensing and sensors. As is the case with physical sensors in the electrical domain, the retrieved information can be represented by a voltage, a current, or an impedance. For chemical sensors based on electrochemical measuring principles, this subdivision turns out to be a fundamental one because different means of mass transport are involved. Information represented by a voltage, a current or an impedance is retrieved by potentiometric sensors, by amperometric sensors or by electrolyte conductivity sensors, respectively. This chapter describes some fundamentals of potentiometry, amperometry, and electrolyte conductivity.