Heinrich Martin Overhoff

Total knee arthroplasty: coordinate system definition and planning based on 3-D ultrasound image volumes

Abstract The main problem for the long-term quality of total knee arthroplasties (TKA) is the correct placement, especially for the femoral prosthesis. Most pre-operative planning procedures and intra-operative realizations actually rely on lower limb X-rays and extra- or intramedullary devices. Due to imprecise alignment of images and devices and fuzzy referencing procedures, this may lead to implant displacements. We defined precise coordinate systems referencing on superficially located direct visible bone landmarks. By use of 3-D ultrasound (US) and automatic image segmentation, we generated virtual models of the distal femur for 10 knee joints. The defined landmark systems could be detected on these models, which then were used for interactive planning. The investigation demonstrates that 3-D US can provide data of position and size of bony structures. Bone models created by analysis of 3-D US image volumes are useable for the simulation of TKA implantations.

Automatic determination of the newborn's femoral head from three-dimensional ultrasound image data

The infants femoral head form and position relative to the acetabulum are the major parameters for the diagnosis of a hip joint dysplasia. The analysis can be performed using conventional ultrasound 2D-images, which virtually cut the hip joint in a specific plane. The joints shape is scored by geometric measures taken from the image. The imaging in a defined plane is tedious and demands some experience. Furthermore the reporting of a spatial geometry through 2D-images tends to be subjective and incomplete. To consider the entire joint geometry, a 3D-data set of conventional ultrasound images is recorded along with the transducer movement. The femoral head is measured automatically in the spatially arranged images by fitting a virtual sphere, which approximates the femoral heads contours. A pilot study based on 20 3D-ultrasound data sets of hip joints of infants aging 2 days–12 weeks shows highly accurate coincidence of the automatically calculated diameter and centre parameters with those of control measurements, i.e. virtual spheres interactively placed and parametrized.

Visualization of a newborn's hip joint using 3D ultrasound and automatic image processing

Grafs method is a successful procedure for the diagnostic screening of developmental dysplasia of the hip. In a defined 2-D ultrasound (US) scan, which virtually cuts the hip joint, landmarks are interactively identified to derive congruence indicators. As the indicators do not reflect the spatial joint structure, and the femoral head is not clearly visible in the US scan, here 3-D US is used to gain insight to the hip joint in its spatial form. Hip joints of newborns were free-hand scanned using a conventional ultrasound transducer and a localizer system fixed on the scanhead. To overcome examiner- dependent findings the landmarks were detected by automatic segmentation of the image volume. The landmark image volumes and an automatically determined virtual sphere approximating the femoral head were visualized color-coded on a computer screen. The visualization was found to be intuitive and to simplify the diagnostic substantially. By the visualization of the 3-D relations between acetabulum and femoral head the reliability of diagnostics is improved by finding the entire joint geometry.

Reliable identification of sphere-shaped femoral heads in 3D image data

A new method is presented, which enables the reliable measurement of the femoral head sphere parameters (center coordinates and diameter) from tomographic image data, even when the raw data are erroneous. The hip joints of 13 newborns were scanned by a self developed 3-D ultrasound system. After automatic image segmentation, the femoral head is represented by spatially arranged voxel clouds. The 3-D image data are substantially corrupted by different types of errors. Moreover, the data only describe a segment of a sphere, whose area is about 10% of the sphere. This circumstance increases the identification problem. The problem of fitting the sphere parameters is solved by a robust technique based on rejection strategies for irrelevant points and data sets. The method was applicable in 21 of 26 cases. Substantial differences between automatically and expert determined sphere parameters were only observed for highly corrupted data sets, where the identification problem is inherently unstable. The identification method yielded correct and reliable identification of geometric measures from 3-D ultrasound image volumes and promises to be applicable also for other parameterized geometries and other tomographic image modalities as X-ray CT or MRI.

Computer-Based Determination of the Newborn's Femoral Head Coverage Using Three-Dimensional Ultrasound Scans

An automatic image analysis method is presented, which finds the diagnostic landmarks for the determination of the femoral head coverage according to Graf’s method in a 3-D ultrasound image volume. Some of the process steps depend on tuneable parameters. It is a typical experience that the quality of images differs between investigators and patients respectively. An image analysis algorithm therefore should produce results which are robust against such varying image quality. The sensitivity of intermediary and final image analysis process steps versus expert defined parameters is investigated. This analysis are performed in a pilot study on 3-D image data of 10 newborns.

Concept and realization of an object-oriented class library designed for 3D-image processing and visualization in medical diagnostics

For interactive diagnostics or therapy planning on tomographic images hard- and software as well as concept specific dependencies should be avoided to reduce development costs and to increase portability to other platforms. A set of object-oriented class libraries was designed to work on several operating system and respects actual programming standards. The conceptual link between pixels, slice orientation, and geometry was incorporated to a topology class. It manages the spatial image orientation and handles regularly and irregularly arranged image volumes. An image analysis library includes numerous operators applicable to single-channel and multi-channel images. A 3D model and visualization library allows to reconstruct anatomical structures, which can be interactively measured and virtually cut. Due to the topology management a Cartesian re-arrangement of irregularly oriented images with increasing storage demands can be avoided. Because the libraries are implemented using C++ and Open Inventor, applications can be easily prototyped and identical visualization and planning features can be used independent of the operating system. By the use of platform independent concepts, programing languages and standards, the program libraries could be used in multiple environments. Application development time was drastically reduced.

Using smart glasses for ultrasound diagnostics

Abstract Ultrasound has been established as a diagnostic tool in a wide range of applications. Especially for beginners, the alignment of sectional images to patient’s spatial anatomy can be cumbersome. A direct view onto the patient’s anatomy while regarding ultrasound images may help to overcome unergonomic examination. To solve these issues an affordable augmented reality system using smart glasses was created, that displays a (virtual) ultrasound image beneath a (real) ultrasound transducer.

Visualisierung anatomischer Strukturen von Oberbauchorganen mittels automatisch segmentierter 3D-Ultraschallbildvolumina Ergebnisse einer Pilotstudie

Das Auffinden und das Staging von Tumoren und ihrer Metastasen in parenchymatosen Organen des Epigastriums wird durch moderne bildgebende Gerate wesentlich erleichtert. Fur Befunde, die in “kurativer” Absicht operativ entfernt werden sollen bzw. konnen wurde die Machbarkeit einer ultraschallbild-basierten Diagnostik und Therapieplanung untersucht. In 3-D Ultraschall-Bildvolumina von 20 Patienten wurden charakteristische anatomische Strukturen (z.B. Gefase, Abszesse, Tumoren) mittels spezifisch adaptierter automatischer computerbasierter Segmentierung gefunden und visualisiert. Das Auffinden pathologischer Befunde, ihre Quantifizierung und ihre raumlichen Beziehungen zu anatomischen Leitstrukturen wurden durch die 3D-Bildakquisition und die 2D- und 3D-Visualisierung wesentlich vereinfacht.

Interactive PC-based volume rendering of CT datasets.

In radiology, the reading of large CT volumes is a time consuming task. Interactive volume rendering (iVRT) is a promising new technique. Using dedicated hardware (VP1000, Terarecon Inc.) it can now be realized on a standard PC in a cost effective manner. For this purpose, a program built using the Visualization Toolkit with integrated functionality for the VP 1000 is used for almost real-time iVRT (8-9 frames/second). It is possible to embed opaque and translucent polygon surfaces (e.g., segmented structures). By interactively varying the opacity, color and gradient transfer functions as well as using freely placable cutting planes, the visualization can easily be adapted to different diagnostic needs.

OpenGLSL-based Raycasting - Comparison of Execution Durations of Multi-pass vs. Single-pass Technique

Real time volume rendering of medical datasets using raycasting on graphics processing units (GPUs) is a common technique. Since more than 10 years there are two established approaches for realizing GPU ray casting: multi-pass (Kruger and Westermann, 2003) and single-pass (Röttger, et al., 2003). But the required parameters to choose the optimal raycasting technique for a given application are still unknown. To solve this issue both raycasting techniques were implemented for different raycasting types using OpenGLSL vertex and fragment shaders. The different techniques and types were compared regarding execution times. The results of this comparison show that there is no technique faster in general. The higher the computational load the more indicates the use of the multi-pass technique.