Daniel Stromer

3-D reconstruction of historical documents using an X-Ray C-Arm CT system

There exist historical documents that can not be inspected without damaging them. We present a non-invasive method for the reconstruction of historical documents which have been written with iron gall ink. Iron gall ink has been used since the 5th century and is still in use as an indelible ink for writings and drawings. The fact, that this kind of ink is based on metallic particles leads to the assumption that modern X-Ray scanners could image the writings such that it can be differentiated from the paper mainly consisting of cellulose. Our work shows a method that is capable of imaging writings written with iron gall ink by using a modern X-Ray imaging system that is commonly used for medical applications. Even though the imaging system is not optimized for the given task, the writing can be identified. Furthermore, we present a method that is able to reconstruct the volume even if the phantom is not centered properly or misaligned. Applying this method makes it possible to image books, writings or drawings based on all metal-containing inks without page-turning or unrolling the paper.

Non-destructive Digitization of Soiled Historical Chinese Bamboo Scrolls

For about 2000 years, no paper was used as a media in China but writings and drawings were captured on bamboo and wooden slips. Several slips were bound together with strips and rolled up to a scroll. The writings and drawings were either brushed or even carved into the wood. Those documents are very precious for culture inheritance and research, but due to aging processes, the discovered pieces are sometimes in a poor condition and also soiled. Because cleaning the slips is not only challenging but also writings could be erased, we developed a method to digitize such historical documents without the need of cleaning. We perform a 3-D X-ray micro-CT scan resulting in a 3-D volume of the complete document. With our approach, we were able to investigate the scroll without any manual labor (e.g. unwrapping or cleaning). We showed that the method also works for heavily soiled scrolls where nothing is readable with the naked eye. This can help conservators to store all writings before they may be erased by the cleaning process. Finally, we present a manual technique to virtually unwrap and post-process the documents resulting in a 2-D image of all bamboo slips.

Browsing through sealed historical manuscripts by using 3-D computed tomography with low-brilliance X-ray sources

Severely damaged historical documents are extremely fragile. In many cases, their secrets remain concealed beneath their cover. Recently, non-invasive digitization approaches based on 3-D scanning have demonstrated the ability to recover single pages or letters without the need to open the manuscripts. This can even be achieved using conventional micro-CTs without the need for synchrotron hardware. However, not all manuscripts may be suited for such techniques due to their material and X-ray properties. In order to recommend which manuscripts and which inks are best suited for such a process, we investigate six inks that were commonly used in ancient times: malachite, three types of iron gall, Tyrian purple, and buckthorn. Image contrast is explored over the complete pipeline, from the X-ray CT scan and page extraction to the virtual flattening of the page image. We demonstrate, that all inks containing metallic particles are visible in the output, a decrease of the X-ray energy enhances the readability, and that the visibility highly depends on the X-ray attenuation of the ink’s metallic ingredients and their concentration. Based on these observations, we give recommendations on how to select the appropriate imaging parameters.

Segmentation of Fat and Fascias in Canine Ultrasound Images

The connective tissue between fat and muscle termed fascia has been of interest to the recent clinical and biological research. However, in the canine and human medicine, the anatomic knowledge is still limited. To analyze the superficial fascia in canine medicine, a database with around 200 ultrasound images of one dog has been created. The superficial fascia contains fat compartments and is closely connected to the surrounding structures such as the skin’s dermis and the epimysium of the muscles. This work proposes a semi-automatic and fully-automatic segmentation algorithm separating the different layers of ultrasound images of canine. Both algorithms were evaluated on a set of 24 expert-labeled images achieving high accuracy scores up to 95.9%.

Comparison of SART and ETV reconstruction for increased C-arm CT volume coverage by proper detector rotation in liver imaging

In this work, we present a method to increase the lateral field-of-view of a C-arm CT system by rotating the detector such that the diagonal of the detector lies on the u-axis of the detectors coordinate system. We investigated three different 3-D scan trajectories for liver imaging of an obese patient (waist circumference 130 cm) — a Short Scan, a Large Volume Scan and a Helical Large Volume Scan. We reconstructed a data set of the Visible Human Project with the SART and the eTV algorithm. Tests revealed that the coverage was increased with the presented method by 25.3 % for the Short Scan and 28.5 % for the Large Volume Scan. Performing helical scans compensated the axial data loss. The two implemented iterative approaches both provide acceptable results, with the eTV algorithm reducing the RMSE compared to SART by about 29 %. Given a liver imaging task, the rotated detector is able to image the entire liver section of the abdomen with a single Large Volume Scan.

Image Quality Analysis of Limited Angle Tomography Using the Shift-Variant Data Loss Model

This paper investigates the application of the shift-variant data loss (SVDL) model in image quality assessment for a state-ofthe-art reconstruction technique, the weighted total variation (wTV), in limited angle tomography. The SVDL model is used to analyze the acquired frequency information in 2-D fan-beam limited angle tomography. The wTV algorithm is applied to reconstruct some specific mathematical phantoms. The experiments show that the reconstructed image quality depends on the relation of the source trajectory and geometric structure of the imaged object, position, shape, size and orientation in particular.

Data Completeness Estimation for 3D C-Arm Scans with Rotated Detector to Enlarge the Lateral Field-of-View

In this paper, we describe a method to enlarge the field-ofview of those scan modes by rotating the detector such that instead of the detector width the diagonal of the detector limits the lateral field-of-view for a Short and two Large Volume Scan trajectories. After implementation of the modifications we obtain a gain of 25.8% in field-of-view diameter accompanied by a simultaneous loss of height of about 50 %. The coverage is increased by 20% for the Short Scan and by 16.7% for the Large Volume Scans. After introducing a detector shift trade-off we still increase the coverage field-of-view width while compensating the axial loss. Also a reduced source-to-detector distance has been investigated, which further increases the coverage. Finally, a Helical Large Volume Scan trajectory was simulated leading to the same width gain and coverage but increasing the height by 20.8% for the maximal shift and 33.3% for the trade-off version in comparison to a standard Large Volume Scan.

Approximation der Projektionsmatrizen einer C-Bogen 3D-Fahrt anhand der Odometriedaten

Bei aktuellen boden-montierten C-Bogen Rontgengeraten wird durch eine neue Motorsteuerungstechnologie die Aufnahme der Odometriedaten ermoglicht. In dieser Arbeit wird ein Algorithmus beschrieben, der anhand einer bestehenden Datenbank, die mit Geometrie- Kalibrierungen und deren synchron aufgenommenen Odometriedaten, die Projektionsmatrizen fur eine spatere Rekonstruktion approximiert. Nachdem Gutekriterien fur eine 3D-Fahrt ausgewahlt wurden, wird ein Algorithmus vorgestellt, der die am besten passenden Projektionsmatrizen fur die jeweilig durchgefuhrte Fahrt annahert. Die Genauigkeit der berechneten Matrizen wird dann anhand der Originalmatrizen uberpruft. Die Auswertung ergab eine durchschnittliche Fehlerreduzierung um bis zu 30.7%. Dies wird auch in den resultierenden Rekonstruktionen ersichtlich.