André Aichert

• Dr.-Ing.
• Research Scientist at Siemens Healthineers

This paper presents the derivation of the Epipolar Consistency Conditions (ECC) between two X-ray images from the Beer-Lambert law of X-ray attenuation and the Epipolar Geometry of two pinhole cameras, using Grangeat's theorem. We motivate the use of Oriented Projective Geometry to express redundant line integrals in projection images and define a...

We present image-based methods for tracking teeth in a video image with respect to a CT scan of the jaw, in order to enable a novel light-weight augmented reality (AR) system in orthodontistry. Its purpose is guided bracket placement in orthodontic correction. In this context, our goal is to determine the position of the patient maxilla and mandibl...

Recent advances in the field of computer graphics have enabled ex-tremely fast and high quality rendering of volumetric data. However, these al-gorithms have been developed and optimized for visualization on single view displays, and not for stereoscopic augmented reality systems. In this paper, we present our implementation and results for the int...

In this paper, we present an interactive X-Ray perceptual visualization technique (IXPV) to improve 3D perception in standard single-view X-Ray images. Based on a priori knowledge from CT data, we re-introduce lost depth information into the original single-view X-Ray image without jeopardizing information of the original X-Ray. We propose a novel...

Beyond unicellular and multicellular organisms, there is a third type of structural complexity in living animals: that of the mechanical self-assembly of groups of distinct multicellular organisms into dynamical, functional structures. One of the most striking examples of such structures is the army ant bivouac, a nest which self-assembles solely f...

The use of computed tomography (CT) imaging has become of increasing interest to academic areas outside of the field of medical imaging and industrial inspection, e.g., to biology and cultural heritage research. The pecularities of these fields, however, sometimes require that objects need to be imaged on-site, e.g., in field-work conditions or in...

Two X-ray projection images of a rigid object may have different points of view, yet redundant information can be identified in such images. Not unlike a checksum, these occur naturally in the data and are known as consistency conditions. Real acquisitions, however, result from a measurement process which is affected by inaccurate geometric calibra...

Background The beam hardening effect is a typical source of artifacts in x‐ray cone beam computed tomography (CBCT). It causes streaks in reconstructions and corrupted Hounsfield units toward the center of objects, widely known as cupping artifacts. Purpose We present a novel efficient projection data‐based method for reduction of beam‐hardening a...

Rotational coronary angiography using C-arm angiography systems enables intra-procedural 3-D imaging that is considered beneficial for diagnostic assessment and interventional guidance. Despite previous efforts, rotational angiography was not yet successfully established in clinical practice for coronary artery procedures due to challenges associat...

In cone-beam CT, involuntary patient motion and inaccurate or irreproducible scanner motion substantially degrades image quality. To avoid artifacts this motion needs to be estimated and compensated during image reconstruction. In previous work we showed that Fourier Consistency Conditions (FCC) can be used in fan-beam CT to estimate motion in the...

We improve data extrapolation for truncated computed tomography (CT) projections by using Helgason-Ludwig (HL) consistency conditions that mathematically describe the overlap of information between projections. First, we theoretically derive a 2D Fourier representation of the HL consistency conditions from their original formulation (projection mom...

C-arm cone-beam CT systems have an increasing popularity in the clinical environment due to their highly flexible scan trajectories.Recent work used these systems to acquire images of the knee joint under weight-bearing conditions. During the scan, the patient is in a standing or in a squatting position and is likely to show involuntary motion, whi...

Recent C-arm CT systems allow for the examination of a patient’s knees under weight-bearing conditions. The standing patient tends to show involuntary motion, which introduces motion artifacts in the reconstruction. The state-of-the-art motion correction approach uses fiducial markers placed on the patients’ skin to estimate rigid leg motion. Marke...

Rotational coronary angiography allows for volumetric imaging but requires cardiac and respiratory motion management to achieve meaningful reconstructions. Novel respiratory motion compensation algorithms based on data consistency conditions are applied directly in projection domain and, therefore, overcome the need for uncompensated reconstruction...

Purpose Rotational coronary angiography enables 3D reconstruction but suffers from intra-scan cardiac and respiratory motion. While gating handles cardiac motion,respiratory motion requires compensation. State-of-the-art algorithms rely on 3D-2D registration that depends on initial reconstructions of sufficient quality. We propose a compensation me...

We outline a generic framework for single-frame, detector-domain material decomposition. The method involves a segmentation and a background estimation step yielding a virtual mask image that can be used for subtraction. In many cases, material decomposition yields non-truncated difference images enabling the use of novel motion estimation methods...

Multi-frame super-resolution algorithms reconstruct high-resolution images by exploiting complementary information in multiple low-resolution frames. However, despite their success under ideal conditions, most existing methods rely on simplistic approximations to the physics of image acquisition and show limited robustness in real-world application...

Purpose: To allow for a purely image-basedmotion estimation and compensation in weight-bearing cone-beam computed tomography of the knee joint.

Over the last decade, increased effort has been made to acquire three dimensional images of knee joints under weight-bearing condition. Cone-beam CT systems are popular because of their high flexibility with respect to patient position and scan trajectory. However, scans in a standing or squatting patient position are affected by involuntary patien...

Flat detector CT perfusion (FD-CTP) is a novel technique using C-arm angiography systems for interventional dynamic tissue perfusion measurement with high potential benefits for catheter-guided treatment of stroke. However, FD-CTP is challenging since C-arms rotate slower than conventional CT systems. Furthermore, noise and artefacts affect the mea...

We observe and induce conformational switching of individual molecules via scanning tunneling microscopy (STM) at and close to room temperature. 2H-5,10,15,20-Tetrakis-(3,5-di-tert-butyl)-phenylporphyrin (2HTTBPP) adsorbed on Cu(111) forms a peculiar supramolecu-lar ordered phase in which the molecules arrange in alternating rows, with two distinct...

Fundus imaging is one of the most frequently used modalities for screening, diagnosis of eye diseases and some vascular abnormalities. Due to its wide availability, automatic evaluation of fundus images offers great potential benefits to current clinical practice. The basis of many automatic evaluations or diagnosis is the segmentation of the eye b...

CTP is an important imaging modality for diagnosis of ischemic stroke, which is computed from of a series of consecutive CT-scans during the injection of contrast agent. Contrast flow at any point in space can be tracked as minor changes in intensity over a period of about 40 seconds to one minute, represented as a time-attenuation curve (TAC) for...

Tissue perfusion measurement using C-arm angiography systems capable of CT-like imaging (flat detector CT (FD-CT)) is a novel technique with high potential benefit for catheter-guided treatment of stroke in the interventional suite. New high speed protocols (HSP) with increased C-arm rotation speed enable fast acquisitions of FD-CT volumes and allo...

Medical imaging has come a long way since the first X-Ray pictures were taken in 1895 and X-Ray is still a primary image source for diagnosis and intra-operative guidance in today’s clinical setting. However, grayscale X-Ray images have some limitations, especially lacking proper depth cues visible to the clinician. In the area of psychology, color...

Visual discomfort is a major problem for head-mounted displays and other stereo displays. One effect that is known to reduce visual comfort is double vision, which can occur due to high disparities. Previous studies suggest that adding artificial out-of-focus blur increases the fusional limits, where the left and right image can be fused without do...

Recent advances in GPU programmability and performance have enabled development of real-time high quality volume visualization algorithms. Medical augmented reality systems can benefit from these developments. Task-specific visualization aids physicians in better un-derstanding the patient's anatomy and supports navigation of medical instruments in...

Multi-modality alignment of CT and ultrasound adds value to diagnostic examinations, as well as treatment planning and execution of various clinical procedures. Particularly automatic image-based alignment of such data is challenging, mostly because both modalities have very different imaging physics and characteristics. We present a method for den...