Biomedical subjects

Robert Rohling

Publications and source records attributed to Robert Rohling.

12 recordsLinked to original sources

PubMed2007

Microdevice-based delivery of gene products using sonoporation.

This paper presents a proof-of-concept miniature device for delivery of antisense oligonucleotides (ASO). A piezoelectric, lead zirconate titanate (PZT) plate (0.5 cm(2) x 0.75 mm) is used to transfect cells using cavitation-induced sonoporation. Both human umbilical vein endothelial cells (HUVEC) and human prostate cancer cells (PC3) are investigated in vitro. Preliminary results show that after sonication, the transfection rate for HUVEC increases by 96% compared to controls (p < 0.01). For PC3, the transfection rate increases by 31% compared to controls (p < 0.02). This research can potentially be applied in realizing a microelectromechanical system (MEMS)-based device for gene therapy in cancer treatment.

Cell Line, Tumor↗

PubMed2006

Anatomical structure modeling from medical images.

Some clinical applications, such as surgical planning, require volumetric models of anatomical structures represented as a set of tetrahedra. A practical method of constructing anatomical models from medical images is presented. The method starts with a set of contours segmented from the medical images by a clinician and produces a model that has high fidelity with the contours. Unlike most modeling methods, the contours are not restricted to lie on parallel planes. The main steps are a 3D Delaunay tetrahedralization, culling of non-object tetrahedra, and refinement of the tetrahedral mesh. The result is a high-quality set of tetrahedra whose surface points are guaranteed to match the original contours. The key is to use the distance map and bit volume structures that were created along with the contours. The method is demonstrated on computed tomography, MRI and 3D ultrasound data. Models of 170,000 tetrahedra are constructed on a standard workstation in approximately 10s. A comparison with related methods is also provided.

Algorithms↗

PubMed2006

Identifying the mechanical properties of tissue by ultrasound strain imaging.

A new elastography method is presented that images the mechanical properties of soft tissue. The tissue is externally vibrated over a range of frequencies simultaneously and the resulting displacement is recorded at multiple locations and time instants with a sequence of ultrasound images. Two methods are proposed for estimating the mechanical properties from the recorded data. In the first method, equations of motion are written for a tissue model of masses, springs and dampers. The equations are solved to identify the model parameters and construct an image. The second method performs a transfer function analysis of the tissue motion. The tissue properties are identified from the shape the of transfer function. Simulations show good performance of the new method compared with static elastography. Initial experimental results from homogeneous and layered tissue phantoms also demonstrate the ability quantitatively to image tissue stiffness. Preliminary results are obtained for viscosity and density estimation. Further work is needed to extend the formulation to 3-D and improve robustness of the viscosity and density estimates.

Algorithms↗

PubMed2005

3D needle-tissue interaction simulation for prostate brachytherapy.

This paper presents a needle-tissue interaction model that is a 3D extension of a prior work based on the finite element method. The model is also adapted to accommodate arbitrary meshes so that the anatomy can effectively be meshed using third-party algorithms. Using this model a prostate brachytherapy simulator is designed to help medical residents acquire needle steering skills. This simulation uses a prostate mesh generated from clinical data segmented as contours on parallel slices. Node repositioning and addition, which are methods for achieving needle-tissue coupling, are discussed. In order to achieve realtime haptic rates, computational approaches to these methods are compared. Specifically, the benefit of using the Woodbury formula (matrix inversion lemma) is studied. Our simulation of needle insertion into a prostate is shown to run faster than 1 kHz.

Brachytherapy↗

PubMed2005

A hand-held probe for vibro-elastography.

Vibro-elastography is a new medical imaging method that identifies the mechanical properties of tissue by measuring tissue motion in response to a multi-frequency external vibration source. Previous research on vibro-elastography used ultrasound to measure the tissue motion and system identification techniques to identify the tissue properties. This paper describes a hand-held probe with a combined vibration source and ultrasound transducer. The design uses a vibration absorption system to counter-balance the reaction forces from contact with the tissue. Simulations and experiments show a high level of vibration absorption. The first elastograms from the probe are also shown.

Computer-Aided Design↗

PubMed2005

Spectral clustering algorithms for ultrasound image segmentation.

Image segmentation algorithms derived from spectral clustering analysis rely on the eigenvectors of the Laplacian of a weighted graph obtained from the image. The NCut criterion was previously used for image segmentation in supervised manner. We derive a new strategy for unsupervised image segmentation. This article describes an initial investigation to determine the suitability of such segmentation techniques for ultrasound images. The extension of the NCut technique to the unsupervised clustering is first described. The novel segmentation algorithm is then performed on simulated ultrasound images. Tests are also performed on abdominal and fetal images with the segmentation results compared to manual segmentation. Comparisons with the classical NCut algorithm are also presented. Finally, segmentation results on other types of medical images are shown.

Algorithms↗

PubMed2005

Ultrasound image segmentation using spectral clustering.

Segmentation of ultrasound images is necessary in a variety of clinical applications, but the development of automatic techniques is still an open problem. Spectral clustering techniques have recently become popular for data and image analysis. In particular, image segmentation has been proposed via the normalized cut (NCut) criterion. This article describes an initial investigation to determine the suitability of such segmentation techniques for ultrasound images. The adaptation of the NCut technique to ultrasound is described first. Segmentation is then performed on simulated ultrasound images. Tests are also performed on abdominal and fetal images with the segmentation results compared to manual segmentation. The success of the segmentation on these test cases warrants further research into NCut-based segmentation of ultrasound images.

Computer Simulation↗

PubMed2005

A needle tracking device for ultrasound guided percutaneous procedures.

A novel tracking device is proposed for measuring the position and orientation of a needle with respect to an ultrasound probe. This device is intended to guide an operator during a percutaneous needle insertion so that the needle trajectory can be visually aligned with the target before insertion. The tracking device uses a pair of cameras to track the needle location so that a standard needle can be used without attaching a separate sensor to the needle. The main challenge is to calibrate the tracking system with sufficient accuracy. Calibration methods are described for each of the system parameters. A series of tests show that an overall error of 3.1 +/- 1.8 mm is achieved with two commercial cameras and an error of 6.5 +/- 5.7 mm is achieved with two inexpensive consumer cameras. An analysis of the source of errors reveals that the errors arise from all of the calibration steps. Overall system accuracy is therefore determined by both the quality of the cameras and the performance of calibration.

Biopsy, Needle↗

PubMed2005

Automatic detection of fiducial markers in fluoroscopy images for on-line calibration.

Calibrated C-arm fluoroscopy is used for a variety of medical procedures where objects and anatomical structures need to be located in space. Calibration is often based on imaging a grid of fiducial markers and using the C-arm image's geometrical measurements (radius and center) together with the positions of the markers. An on-line technique is developed to automatically locate the fiducial markers and validated on 97 images. The success rate of the detection algorithm is 96.28% with an average error of 0.46 mm and a standard deviation of 0.32 mm.

Algorithms↗

PubMed2004

iScout: an intelligent scout for accessing and navigating large image sets in a PACS.

A new software tool for PACS, called iScout (intelligent scout), has been developed and optimized for a radiology workstation. The purpose of iScout is to display an overview of a large image series, allowing the user to select images for priority downloading from a PACS server to a PACS workstation. This allows radiologists to reduce the delays that are associated with downloading hundreds or even thousands of images. Several schemes that semiautomatically manage the download process are presented along with tests to measure performance. The results of the tests confirm that priority downloading provides faster access to images in large image series and that the time savings increase in proportion to the study size.

Computer Systems↗

PubMed2004

Enhancement of needle visibility in ultrasound-guided percutaneous procedures.

The visibility of a needle in ultrasound (US)-guided percutaneous procedures is often limited by dispersion of the needle's reflections away from the probe. A needle enhancement algorithm is developed that maximizes the received reflections by steering the US beam precisely perpendicular to the needle. The resulting image clearly depicts the needle as a bright line. The key is to automatically detect the needle in the image and maintain the appropriate beam steering angle during the procedure. The brightened needle in the steered image is then fused with the original image to produce an improved image. Implementation of the needle-enhancement algorithm was made possible by using the programmable ultrasound platform and interface library (PUPIL). PUPIL is capable of acquiring digital images, processing the images in real-time, controlling the beam angle, and displaying the fused image. The results demonstrate significantly improved needle visibility in both breast phantoms and turkey breast samples.

Algorithms↗

PubMed2004

Automatic measurements of image geometry for online calibration of C-arm fluoroscopy.

Calibrated C-arm fluoroscopy is used for a variety of surgical procedures where surgical tools and anatomical structures need to be located in space. Calibration can be performed online by combining measurements of the geometry of the image (center and radius) with measurements of a grid of fiducial markers. This article focuses on the first aspect--image geometry--and describes a method to perform the geometry measurements automatically. The accuracy, robustness, and speed of the method are validated on 100 images obtained from several hospitals with different C-arm scanners. All 100 images were successfully measured with an average error of 0.8 mm for the center and 0.8 mm for the radius. The execution time is less than one second per image.

Algorithms↗