Biomedical subjects

Michael Bajka

Publications and source records attributed to Michael Bajka.

5 recordsLinked to original sources

PubMed2006

Three-dimensional fiber architecture of the nonpregnant human uterus determined ex vivo using magnetic resonance diffusion tensor imaging.

The global muscle and collagen fiber orientation in the human uterus has been analyzed hitherto by various standard microscopic techniques. However, no widely accepted model of the fiber architecture of the myometrium could be acquired. The purpose of the present study was to investigate the uterus by magnetic resonance (MR) diffusion tensor imaging (DTI) in a 3D macroscopic approach. Ex vivo MR DTI measurements were performed on five uteri from nonpregnant patients. The main diffusion directions reflecting the orientation of directional structures in the examined tissues were determined from diffusion-weighted spin-echo measurements. A fiber tracking algorithm was used to extrapolate the fiber architecture. The method was validated against histological slides and indirectly through the analysis of leiomyomas, which exhibit less anisotropy than normal myometrium. Significant anisotropy was found in most regions of all examined nonpregnant human uteri. But only two systems of fibers were found running circularly along the intramural part of the uterine tubes. They merged caudally and built a close fitting envelope of circular layers around the uterine cavity. On the cervix, circular fibers were observed in the outer part as well as mostly longitudinal fibers in the inner part. These results confirm the existence of directional structures in the complex fiber architecture of the human uterus. They also indicate that MR DTI is a beneficial and complementary tool to standard microscopic techniques to determine the intrinsic fiber architecture in human organs.

Adult↗

PubMed2006

Highly-realistic, immersive training environment for hysteroscopy.

The primary driving application of our current research is the development of a generic surgical training simulator for hysteroscopy. A key target is to go beyond rehearsal of basic manipulative skills, and enable training of procedural skills like decision making and problem solving. In this respect, the sense of presence plays an important role in the achievable training effect. To enable user immersion into the training environment, the surrounding and interaction metaphors should be the same as during the real intervention. To this end, we replicated an OR in our lab, provided standard hysteroscopic tools for interaction, and generate a new virtual scene for every session. In this setting, the training starts, as soon as the trainees enter the OR, and ends when they leave the room.

Competency-Based Education↗

PubMed2005

Mechanical properties of the human uterine cervix: an in vivo study.

Experimental results of in vivo measurements to characterize the mechanical behaviour of human uterine cervices are documented. Aspiration experiments were performed on eight uteri in vivo, before vaginal/abdominal hysterectomy, and four uteri were also tested ex vivo, approximately 1.5h after extraction. The reproducibility of the mechanical data from the in vivo aspiration experiments has been analysed. For an introduced "stiffness parameter" the organ specific SD is 22%, so that the proposed experimental procedure allows detections of 30% changes with respect to a reference value of the stiffness parameter. A comparison of in vivo and ex vivo data from the same organ has shown that: (i) the ex vivo mechanical response of the uterine cervix tissue does not differ considerably from that observed in vivo; (ii) some differences can be identified in tissue pre-conditioning with ex vivo showing a stronger history dependence with respect to in vivo; (iii) the differences in the time dependence of the mechanical response are not significant and might be masked by the variability of the measured data. This study represents a first step of a clinical application aiming at analysing the mechanical response of normal cervical tissue at different gestational ages, and identifying the mechanical properties that characterize pathologic conditions such as cervical insufficiency leading to preterm delivery.

Biomechanical Phenomena↗

PubMed2005

Real-time synthesis of bleeding for virtual hysteroscopy.

In this paper we present a method for simulating bleeding in a virtual reality hysteroscopic simulator for surgical training. The simulated bleeding is required to be visually appealing while at the same time instantaneously responsive to any feedback that the surgeon may be conducing to the virtual environment. In order to meet these real-time requirements, we have based the simulation on graphical fluid solvers. These solvers primarily work best over a 2D domain. For correct visualization in the hysteroscopic simulator, it is, however, necessary to perform the simulation fully in 3D. Therefore in this paper we also present the design modifications for 3D graphical fluid solving and show how to use parallelization to maintain real-time behavior. We also discuss how the incorporation of massless particles into the simulation can improve the visual quality of the results by limiting numerical dissipation effects.

Blood Flow Velocity↗

PubMed2004

Evaluation of the mechanical properties of human liver and kidney through aspiration experiments.

A proper mechanical characterization of soft biological tissues of the human body has a strong impact on several medical applications such as surgical planning, virtual reality simulators, trauma research, and for diagnostic purposes. Adequate experimental data are needed to describe quantitatively the mechanical behaviour of those organs. We present a technique for the acquisition of such data from soft tissues and its post processing, based on a continuum mechanics approach, to determine some parameters of the tissue's mechanical properties. A small tube is applied to the target organ and a weak vacuum is generated inside the tube according to a predefined pressure history. A video camera grabs images of the deformation profile of the aspirated tissue, and a pressure sensor measures the correspondent vacuum level. The images are processed and used to inform the fitting of uniaxial and continuum mechanics models. Whilst the aspiration test device is suitable for in vivo applications, under sterile conditions during open surgery, we hereby present first results obtained by testing cadaveric tissues.

Biomechanical Phenomena↗