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Michael Baumann

Publications and source records attributed to Michael Baumann.

13 recordsLinked to original sources
arXiv2025

Confinement-induced Ultrafast Conductivity in 2D Perovskites resolved by correlative Terahertz-NIR Spectroscopy

Quantum wells made of two-dimensional organic-inorganic hybrid perovskites (2D-PKs) offer a high degree of flexibility in tailoring optoelectronic properties through carrier confinement and functional interlayers. Compared to their 3D counterparts, 2D-PKs exhibit tunable photoluminescence, excitonic binding at room temperature and enhanced structural stability. However, the dynamics of photo-induced charge carriers and their transport properties are highly intertwined due to the interplay of diverse excitation species, charge carrier cooling, transport, and radiative and non-radiative recombination. In this study, we employ optical-pump terahertz-probe spectroscopy (OPTP) to analyze the local conductivity dynamics of 2D and 3D methylammonium lead iodide (MAPI) perovskites at timescales down to picoseconds. Remarkably, we observe an intensity-dependent, 2D-specific buildup of an ultrafast, few-picosecond decay in local conductivity. By combining OPTP with transient absorption (TA) and picosecond time-resolved photoluminescence (TRPL), we demonstrate the disentanglement of photoconductivity and carrier population. This allows us to attribute the 2D-specific ultrafast THz response to delayed hot-carrier cooling and subsequent exciton formation, which effectively reduces the free-carrier conductivity. This intensity-dependent, ultrafast THz response is a signature of the recently identified hot-carrier bottleneck in 3D MAPI, and this effect manifests itself in a unique form in the 2D material. These results encourage further investigations on the impact of functional organic interlayers and provide insights into designing tunable carrier responses for ultrafast devices via adapted heterostructures and confinement.

cond-mat.mtrl-sci↗
arXiv2022

Waveguide coupled III-V photodiodes monolithically integrated on Si

The seamless integration of III-V nanostructures on silicon is a long-standing goal and an important step towards integrated optical links. In the present work, we demonstrate scaled and waveguide coupled III-V photodiodes monolithically integrated on Si, implemented as InP/In0.5Ga0.5As/InP p-i-n structure. The waveguide coupled devices show a dark current down to 0.048 A/cm2 at -1 V and a responsivity up to 0.2 A/W at -2 V. Using grating couplers centered around 1320 nm, we observed a cutoff frequency f3dB exceeding 70 GHz and data reception at 50 GBd with OOK and 4PAM. When operated in forward bias as light emitting diode, the devices emit light centered at 1550 nm. Furthermore, we also investigate the self-heating of the devices using scanning thermal microscopy and find a temperature increase of only ~15 K during the device operation as emitter, in accordance with thermal simulation results.

physics.app-ph↗
arXiv2012

Development of a Novel Robot for Transperineal Needle Based Interventions: Focal Therapy, Brachytherapy and Prostate Biopsies

Purpose: We report what is to our knowledge the initial experience with a new 3-dimensional ultrasound robotic system for prostate brachytherapy assistance, focal therapy and prostate biopsies. Its ability to track prostate motion intraoperatively allows it to manage motions and guide needles to predefined targets. Materials and Methods: A robotic system was created for transrectal ultrasound guided needle implantation combined with intraoperative prostate tracking. Experiments were done on 90 targets embedded in a total of 9 mobile, deformable, synthetic prostate phantoms. Experiments involved trying to insert glass beads as close as possible to targets in multimodal anthropomorphic imaging phantoms. Results were measured by segmenting the inserted beads in computerized tomography volumes of the phantoms. Results: The robot reached the chosen targets in phantoms with a median accuracy of 2.73 mm and a median prostate motion of 5.46 mm. Accuracy was better at the apex than at the base (2.28 vs 3.83 mm, p <0.001), and similar for horizontal and angled needle inclinations (2.7 vs 2.82 mm, p = 0.18). Conclusions: To our knowledge this robot for prostate focal therapy, brachytherapy and targeted prostate biopsies is the first system to use intraoperative prostate motion tracking to guide needles into the prostate. Preliminary experiments show its ability to reach targets despite prostate motion.

cs.RO↗
arXiv2011

Prostate biopsy tracking with deformation estimation

Transrectal biopsies under 2D ultrasound (US) control are the current clinical standard for prostate cancer diagnosis. The isoechogenic nature of prostate carcinoma makes it necessary to sample the gland systematically, resulting in a low sensitivity. Also, it is difficult for the clinician to follow the sampling protocol accurately under 2D US control and the exact anatomical location of the biopsy cores is unknown after the intervention. Tracking systems for prostate biopsies make it possible to generate biopsy distribution maps for intra- and post-interventional quality control and 3D visualisation of histological results for diagnosis and treatment planning. They can also guide the clinician toward non-ultrasound targets. In this paper, a volume-swept 3D US based tracking system for fast and accurate estimation of prostate tissue motion is proposed. The entirely image-based system solves the patient motion problem with an a priori model of rectal probe kinematics. Prostate deformations are estimated with elastic registration to maximize accuracy. The system is robust with only 17 registration failures out of 786 (2%) biopsy volumes acquired from 47 patients during biopsy sessions. Accuracy was evaluated to 0.76$\pm$0.52mm using manually segmented fiducials on 687 registered volumes stemming from 40 patients. A clinical protocol for assisted biopsy acquisition was designed and implemented as a biopsy assistance system, which allows to overcome the draw-backs of the standard biopsy procedure.

cs.CV↗
arXiv2011

Prosper: image and robot-guided prostate brachytherapy

Brachytherapy for localized prostate cancer consists in destroying cancer by introducing iodine radioactive seeds into the gland through hollow needles. The planning of the position of the seeds and their introduction into the prostate is based on intra-operative ultrasound (US) imaging. We propose to optimize the global quality of the procedure by: i) using 3D US; ii) enhancing US data with MRI registration; iii) using a specially designed needle-insertion robot, connected to the imaging data. The imaging methods have been successfully tested on patient data while the robot accuracy has been evaluated on a realistic deformable phantom.

cs.RO↗
arXiv2009

Prostate Biopsy Assistance System with Gland Deformation Estimation for Enhanced Precision

Computer-assisted prostate biopsies became a very active research area during the last years. Prostate tracking makes it possi- ble to overcome several drawbacks of the current standard transrectal ultrasound (TRUS) biopsy procedure, namely the insufficient targeting accuracy which may lead to a biopsy distribution of poor quality, the very approximate knowledge about the actual location of the sampled tissues which makes it difficult to implement focal therapy strategies based on biopsy results, and finally the difficulty to precisely reach non-ultrasound (US) targets stemming from different modalities, statistical atlases or previous biopsy series. The prostate tracking systems presented so far are limited to rigid transformation tracking. However, the gland can get considerably deformed during the intervention because of US probe pres- sure and patient movements. We propose to use 3D US combined with image-based elastic registration to estimate these deformations. A fast elastic registration algorithm that copes with the frequently occurring US shadows is presented. A patient cohort study was performed, which yielded a statistically significant in-vivo accuracy of 0.83+-0.54mm.

cs.OH↗
arXiv2009

Mapping of transrectal ultrasonographic prostate biopsies: quality control and learning curve assessment by image processing

Objective: Mapping of transrectal ultrasonographic (TRUS) prostate biopsies is of fundamental importance for either diagnostic purposes or the management and treatment of prostate cancer, but the localization of the cores seems inaccurate. Our objective was to evaluate the capacities of an operator to plan transrectal prostate biopsies under 2-dimensional TRUS guidance using a registration algorithm to represent the localization of biopsies in a reference 3-dimensional ultrasonographic volume. Methods: Thirty-two patients underwent a series of 12 prostate biopsies under local anesthesia performed by 1 operator using a TRUS probe combined with specific third-party software to verify that the biopsies were indeed conducted within the planned targets. RESULTS: The operator reached 71% of the planned targets with substantial variability that depended on their localization (100% success rate for targets in the middle and right parasagittal parts versus 53% for targets in the left lateral base). Feedback from this system after each series of biopsies enabled the operator to significantly improve his dexterity over the course of time (first 16 patients: median score, 7 of 10 and cumulated median biopsy length in targets of 90 mm; last 16 patients, median score, 9 of 10 and a cumulated median length of 121 mm; P = .046). Conclusions: In addition to being a useful tool to improve the distribution of prostate biopsies, the potential of this system is above all the preparation of a detailed "map" of each patient showing biopsy zones without substantial changes in routine clinical practices.

physics.med-ph↗
arXiv2008

Framework for 3D TransRectal Ultrasound

Prostate biopsies are mainly performed under 2D TransRectal UltraSound (TRUS) control by sampling the prostate according to a predefined pattern. In case of first biopsies, this pattern follows a random systematic plan. Sometimes, repeat biopsies can be needed to target regions unsampled by previous biopsies or resample critical regions (for example in case of cancer expectant management or previous prostatic intraepithelial neoplasia findings). From a clinical point of view, it could be useful to control the 3D spatial distribution of theses biopsies inside the prostate. Modern 3D-TRUS probes allow acquiring high-quality volumes of the prostate in few seconds. We developed a framework to track the prostate in 3D TRUS images. It means that if one acquires a reference volume at the beginning of the session and another during each biopsy, it is possible to determine the relationship between the prostate in the reference and the others volumes by aligning images. We used this tool to evaluate the ability of a single operator (a young urologist assistant professor) to perform a pattern of 12 biopsies under 2D TRUS guidance.

cs.OH↗
arXiv2008

3D-Ultrasound probe calibration for computer-guided diagnosis and therapy

With the emergence of swept-volume ultrasound (US) probes, precise and almost real-time US volume imaging has become available. This offers many new opportunities for computer guided diagnosis and therapy, 3-D images containing significantly more information than 2-D slices. However, computer guidance often requires knowledge about the exact position of US voxels relative to a tracking reference, which can only be achieved through probe calibration. In this paper we present a 3-D US probe calibration system based on a membrane phantom. The calibration matrix is retrieved by detection of a membrane plane in a dozen of US acquisitions of the phantom. Plane detection is robustly performed with the 2-D Hough transformation. The feature extraction process is fully automated, calibration requires about 20 minutes and the calibration system can be used in a clinical context. The precision of the system was evaluated to a root mean square (RMS) distance error of 1.15mm and to an RMS angular error of 0.61 degrees. The point reconstruction accuracy was evaluated to 0.9mm and the angular reconstruction accuracy to 1.79 degrees.

cs.OH↗
arXiv2007

Medical image computing and computer-aided medical interventions applied to soft tissues. Work in progress in urology

Until recently, Computer-Aided Medical Interventions (CAMI) and Medical Robotics have focused on rigid and non deformable anatomical structures. Nowadays, special attention is paid to soft tissues, raising complex issues due to their mobility and deformation. Mini-invasive digestive surgery was probably one of the first fields where soft tissues were handled through the development of simulators, tracking of anatomical structures and specific assistance robots. However, other clinical domains, for instance urology, are concerned. Indeed, laparoscopic surgery, new tumour destruction techniques (e.g. HIFU, radiofrequency, or cryoablation), increasingly early detection of cancer, and use of interventional and diagnostic imaging modalities, recently opened new challenges to the urologist and scientists involved in CAMI. This resulted in the last five years in a very significant increase of research and developments of computer-aided urology systems. In this paper, we propose a description of the main problems related to computer-aided diagnostic and therapy of soft tissues and give a survey of the different types of assistance offered to the urologist: robotization, image fusion, surgical navigation. Both research projects and operational industrial systems are discussed.

cs.OH↗
arXiv2007

Towards 3D ultrasound image based soft tissue tracking: a transrectal ultrasound prostate image alignment system

The emergence of real-time 3D ultrasound (US) makes it possible to consider image-based tracking of subcutaneous soft tissue targets for computer guided diagnosis and therapy. We propose a 3D transrectal US based tracking system for precise prostate biopsy sample localisation. The aim is to improve sample distribution, to enable targeting of unsampled regions for repeated biopsies, and to make post-interventional quality controls possible. Since the patient is not immobilized, since the prostate is mobile and due to the fact that probe movements are only constrained by the rectum during biopsy acquisition, the tracking system must be able to estimate rigid transformations that are beyond the capture range of common image similarity measures. We propose a fast and robust multi-resolution attribute-vector registration approach that combines global and local optimization methods to solve this problem. Global optimization is performed on a probe movement model that reduces the dimensionality of the search space and thus renders optimization efficient. The method was tested on 237 prostate volumes acquired from 14 different patients for 3D to 3D and 3D to orthogonal 2D slices registration. The 3D-3D version of the algorithm converged correctly in 96.7% of all cases in 6.5s with an accuracy of 1.41mm (r.m.s.) and 3.84mm (max). The 3D to slices method yielded a success rate of 88.9% in 2.3s with an accuracy of 1.37mm (r.m.s.) and 4.3mm (max).

cs.OH↗
arXiv2007

Aid to Percutaneous Renal Access by Virtual Projection of the Ultrasound Puncture Tract onto Fluoroscopic Images

Background and Purpose: Percutaneous renal access in the context of percutaneous nephrolithotomy (PCNL) is a difficult technique, requiring rapid and precise access to a particular calix. We present a computerized system designed to improve percutaneous renal access by projecting the ultrasound puncture tract onto fluoroscopic images. Materials and Methods: The system consists of a computer and a localizer allowing spatial localization of the position of the various instruments. Without any human intervention, the ultrasound nephrostomy tract is superimposed in real time onto fluoroscopic images acquired in various views. Results: We tested our approach by laboratory experiments on a phantom. Also, after approval by our institution's Ethics Committee, we validated this technique in the operating room during PCNL in one patient. Conclusion: Our system is reliable, and the absence of image-processing procedures makes it robust. We have initiated a prospective study to validate this technique both for PCNL specialists and as a learning tool.

physics.med-ph↗