Showing papers by "Septimiu E. Salcudean published in 2010"

Sub-sample displacement estimation from digitized ultrasound RF signals using multi-dimensional polynomial fitting of the cross-correlation function

Abstract: A widely used time-domain technique for motion or delay estimation between digitized ultrasound RF signals involves the maximization of a discrete pattern-matching function, usually the cross-correlation. To achieve sub-sample accuracy, the discrete pattern-matching function is interpolated using the values at the discrete maximizer and adjacent samples. In prior work, only 1-D fit, applied separately along the axial, lateral, and elevational axes, has been used to estimate the sub-sample motion in 1-D, 2-D, and 3-D. In this paper, we explore the use of 2-D and 3-D polynomial fitting for this purpose. We quantify the estimation error in noise-free simulations using Field II and experiments with a commercial ultrasound machine. In simulated 2-D translational motions, function fitting with quartic spline polynomials leads to maximum bias of 0.2% of the sample spacing in the axial direction and 0.4% of the sample spacing in the lateral direction, corresponding to 38 nm and 1.31 μm, respectively. The maximum standard deviations were approximately 1% of the sample spacing in both the axial and the lateral directions, corresponding to 193 nm axially and 4.43 μm laterally. In simulated 1% axial strain, the same function fitting leads to mean absolute displacement estimation errors of 255 nm in the axial direction and 4.77 ?m in the lateral direction. In experiments with a linear array transducer, 2-D quartic spline fitting leads to maximum bias of 458 nm and 6.27 μm in the axial and the lateral directions, respectively. These results are more than one order of magnitude smaller than those obtained with separate 1-D fit when applied to the same data set. Simulations and experiments in 3-D yield similar results when comparing 3-D polynomial fitting with 1-D fitting along the axial, lateral, and elevational directions.

A high-frame-rate ultrasound system for the study of tissue motions

Abstract: In this article, a technique for measuring fast periodic motion is proposed. The sequencing used in this technique is similar to the one used in conventional color Doppler systems. However, a phase correction algorithm is introduced which compensates for the acquisition delays. Criteria for the types of motion which could be detected correctly by the system are developed and presented. Effective frame rates of several hundred hertz to a few kilohertz have been achieved with the system. Applications of the system in tissue elastography are presented together with experimental results from tissue mimicking phantoms.

Detection of Brachytherapy Seeds Using 3-D Transrectal Ultrasound

Abstract: Detection of brachytherapy seeds plays a key role in dosimetry for prostate brachytherapy. However, seed localization using B-mode transrectal ultrasound (TRUS) still remains a challenge for prostate brachytherapy, mainly due to the small size of brachytherapy seeds in the relatively low-quality B-mode TRUS images. In this paper, we propose a new solution for brachytherapy seed detection using 3-D ultrasound. A 3-D reflected power image is computed from ultrasound RF signals, instead of conventional B-mode images. Then, implanted seeds are segmented in 3-D local search spaces that are determined by a priori knowledge, e.g., needle entry points and seed placements. Needle insertion tracks are also detected locally by the Hough transform. Experimental results show that the proposed solution works well for seed localization in a prostate phantom implanted according to a realistic treatment plan with 136 seeds from 26 needles.

2-D high-frame-rate dynamic elastography using delay compensated and angularly compounded motion vectors: Preliminary results

Abstract: This paper describes a new ultrasound-based system for high-frame-rate measurement of periodic motion in 2-D for tissue elasticity imaging. Similarly to conventional 2-D flow vector imaging, the system acquires the RF signals from the region of interest at multiple steering angles. A custom sector subdivision technique is used to increase the temporal resolution while keeping the total acquisition time within the range suitable for real-time applications. Within each sector, 1-D motion is estimated along the beam direction. The intraand inter-sector delays are compensated using our recently introduced delay compensation algorithm. In-plane 2-D motion vectors are then reconstructed from these delay-compensated 1-D motions. We show that Young's modulus images can be reconstructed from these 2-D motion vectors using local inversion algorithms. The performance of the system is validated quantitatively using a commercial flow phantom and a commercial elasticity phantom. At the frame rate of 1667 Hz, the estimated flow velocities with the system are in agreement with the velocity measured with a pulsed-wave Doppler imaging mode of a commercial ultrasound machine with manual angle correction. At the frame rate of 1250 Hz, phantom Young's moduli of 29, 6, and 54 kPa for the background, the soft inclusion, and the hard inclusion, are estimated to be 30, 11, and 53 kPa, respectively.

3D ultrasound to stereoscopic camera registration through an air-tissue boundary

Abstract: A novel registration method between 3D ultrasound and stereoscopic cameras is proposed based on tracking a registration tool featuring both ultrasound fiducials and optical markers. The registration tool is pressed against an air-tissue boundary where it can be seen both in ultrasound and in the camera view. By localizing the fiducials in the ultrasound volume, knowing the registration tool geometry, and tracking the tool with the cameras, a registration is found. This method eliminates the need for external tracking, requires minimal setup, and may be suitable for a range of minimally invasive surgeries. A study of the appearance of ultrasound fiducials on an air-tissue boundary is presented, and an initial assessment of the ability to localize the fiducials in ultrasound with sub-millimeter accuracy is provided. The overall accuracy of registration (1.69 ± 0.60 mm) is a noticeable improvement over other reported methods and warrants patient studies.

Prostate brachytherapy postimplant dosimetry: automatic plan reconstruction of stranded implants.

Abstract: Purpose: Plan reconstruction for permanent implant prostate brachytherapy is the process of determining the correspondence between planned and implanted seeds in postimplant analysis. Plan reconstruction informs many areas of brachytherapy quality assurance, including the verification of seed segmentation, misplacement and migration assessment, implant simulations, and the dosimetry of mixed-activity or mixed-species implants. Methods: An algorithm has been developed for stranded implants which uses the interseed spacing constraints imposed by the suture to improve the accuracy of reconstruction. Seventy randomly selected clinical cases with a mean of 23.6 (range 18-30) needles and mean density of 2.0 (range 1.6-2.6) 2.0 (range 1.6-2.6) seeds/cm{sup 3} were automatically reconstructed and the accuracy compared to manual reconstructions performed using a custom 3D graphical interface. Results: Using the automatic algorithm, the mean accuracy of the assignment relative to manual reconstruction was found to be 97.7{+-}0.5%. Fifty-two of the 70 cases (74%) were error-free; of seeds in the remaining cases, 96.7{+-}0.3% were found to be attributed to the correct strand and 97.0{+-}0.3% were correctly connected to their neighbors. Any necessary manual correction using the interface is usually straightforward. For the clinical data set tested, neither the number of seeds or needles, average density, nor the presence ofmore » clusters was found to have an effect on reconstruction accuracy using this method. Conclusions: Routine plan reconstruction of stranded implants can be performed with a high degree of accuracy to support postimplant dosimetry and quality analyses.« less

4-D x 3-D ultrasound: real-time scan conversion, filtering, and display of displacement vectors with a motorized curvilinear transducer

Abstract: Recent research in the field of elastography has sought to expand displacement tracking to three dimensions. Once the 3-D volumes of displacement data have been obtained, they must be scan converted so that further processing, such as inversion methods to obtain tissue elasticity, can take place in Cartesian coordinates. This paper details an efficient and geometrically accurate algorithm to scan convert 3-D volumes of displacement vectors obtained from a motorized sector transducer. The proposed algorithm utilizes the physical scan geometry to convert the 3-D volumes of displacement data to both Cartesian coordinates and Cartesian displacements. Spatially varying filters are also proposed to prevent aliasing while minimizing data loss. Validation of the system has shown the algorithm to be correct to floating point precision, and the 3-D scan conversion and filtering can be performed faster than the native rate of data acquisition for the motorized transducer.

On the controllability of dynamic model-based needle insertion in soft tissue

Abstract: Soft tissue needle guidance and steering for clinical applications has been an active topic of research in the past decade. Although dynamic feedback control of needle insertion systems is expected to provide more accurate target tracking, it has received little attention due to the fact that most available models for needle-tissue interaction do not incorporate the dynamics of motions. In this paper, we study the controllability of rigid or flexible needles inside soft tissues using mechanical-based dynamic models. The results have significant implications on the design of suitable feedback controllers for different types of needle insertion systems.

Apparatus for clamping an organ during surgery

Abstract: This invention is a surgical clamp for the purpose of occluding the kidney or other organ and thereby obtaining a bloodless surgical field, while allowing the majority of the organ to remain normally perfused. Previous approaches are limited in ability to provide sufficient clamping force without damaging the oran. The invention comprises a first and second jaw, wherein the proximal ends of the two jaws, and the distal ends of the two jaws are connected by a strap, such that applying tension to the strap results in moving the relative positions of the jaws in a substantially parallel motion, which provide a clamping force to the organ. The jaws can be attached with a flexibly joint to a hollow shaft, such that a cable inside the shaft can be used to apply tension to the strap while maintaining the ability to pivot the jaws relative to the shaft.

Prostate brachytherapy seed reconstruction using c-arm rotation measurement and motion compensation

Abstract: During prostate brachytherapy, C-arm flouroscopy images are used for a qualitative assessment of the procedure. Three dimensional reconstruction of the implanted seeds can be used for intraoperative dosimetry and quantitative assessment. Accurate C-arm pose estimation is necessary for 3D localization of the seeds. We propose to measure the C-arm rotation angles and computationally compensate the inevitable C-arm translational motion to estimate the pose. We compensate the oscillation, sagging and wheel motion of the C-arm using a three-level optimization algorithm, without which the reconstruction can fail. We validated our approach on simulated and 10 data sets from 5 patients and gained on average 99.1% success rate, 0.33mm projection error and computation time of less than one minute per patient, which are clinically excellent results.

Haptic simulator for prostate brachytherapy with simulated ultrasound

Abstract: This paper presents a medical simulator for prostate brachytherapy procedure. Needles are inserted in deformable tissue models using a haptic device while the force feedback computed using a needle-tissue interaction model is rendered on the user's hand. Transrectal ultrasound images of the region of interest are also displayed in real-time using an interpolation scheme accounting for the mesh-based tissue deformation. Employing a 3D ultrasound volume data reconstructed a priori, this simulation method achieves realistic ultrasound feedback coupled with immediate tissue deformation. Models for simulating tissue deformation using the finite element method are obtained by segmented the relevant anatomy on MR slices. These models are rigidly registered to the ultrasound voxel volume using the prostate surface. The presented simulation system is suitable for brachytherapy training using haptic control/feedback. It can also be used for treatment planning.

Dynamic elastography using delay compensated and angularly compounded high frame rate 2D motion vectors

Abstract: This paper describes a new ultrasound-based system for high frame rate measurement of periodic motion in 2D for tissue elasticity imaging. The system acquires the RF signals from the region of interest from multiple steering angles in order to reconstruct the 2D motion from 1D estimation along each angle. To increase the temporal resolution, the acquisition area is divided into groups of scan lines called sectors. Each sector is acquired multiple times before moving onto the next sector. Following the data acquisition, 1D motions are estimated along the beam direction from the sequences of echo signals. Using a recently introduced delay compensation algorithm, the intra- and inter-sector delays in the motion estimates are compensated to create high frame rate images. In-plane 2D motion vectors are then reconstructed from these delay compensated 1D motions. Finally, modulus images are estimated from these 2D motion vectors using planar algebraic inversion of the Helmholtz equation. The performance of the system is validated quantitatively using a commercial elasticity phantom. At frame rate of 1250 Hz, phantom Young's moduli of 29kPa, 6kPa, and 54 kPa for the background, the soft inclusion, and the hard inclusion of a phantom, are estimated to be 30 kPa, 11kPa, and 53kPa, respectively, for an excitation frequency of 150 Hz.

Automatic prostate segmentation using fused ultrasound B- mode and elastography images

Abstract: In this paper we propose a fully automatic 2D prostate segmentation algorithm using fused ultrasound (US) and elastography images We show that the addition of information from mechanical tissue properties acquired from elastography to acoustic information from Bmode ultrasound, can improve segmentation results Gray level edge similarity and edge continuity in both US and elastography images deform an Active Shape Model Comparison of automatic and manual contours on 107 transverse images of the prostate show a mean absolute error of 26±09 mm and a running time of 179±122 s These results show that the combination of the high contrast elastography images with the more detailed but low contrast US images can lead to very promising results for developing an automatic 3D segmentation algorithm

Real time ultrasound needle image simulation using multi- dimensional interpolation

Abstract: In this paper, we propose an interpolation-based method for simulating needle images in B-mode ultrasound.We parametrize the needle image as a function of needle position and orientation. We collect needle images under various spatial configurations in a water-tank using a guidance robot. Then we use multi-dimensional tensor-product interpolation to simulate images of needles with arbitrary poses and positions using the collected images. Interpolated needle images are superimposed on top of phantom image backgrounds. The similarity between the simulated and the real images is measured using a correlation metric. A comparison with in-vivo images is also performed. The simulation procedure is demonstrated using transverse needle images and extended to sagittal needle images and brachytherapy seed images. The proposed method could be used in clinical procedure training simulators.

Soft Tissue Characterization Using One Dimensional Lumped Mass-Spring-Damper Model

Abstract: The characterization of tissue mechanical properties, such as its elasticity and viscosity, has proven to be useful in numerous clinical applications. For this reason, several techniques have been suggested in the literature to provide non-invasive estimates of these properties. Common to all these technique, an external or internal source is used to deform the tissue. The response of the tissue to this deformation is then measured and used to estimate its mechanical properties.Copyright © 2010 by ASME

A Curl-Based Approach to Ultrasound Elastography

Abstract: The past two decades have witnessed the development of a new medical imaging modality: tissue elastography. The contrast in the images produced by an elastography system is based on the tissue elasticity, hence these images are called elastograms. Tissue elasticity is of clinical interest, because it is often correlated with pathology [1]. Different approaches to tissue elastography have emerged [2, 3]. In this article we report a tissue elastography system and its implementation on an ultrasound machine which provides consistent elastograms of a commercial quality assurance elastography phantom. The system uses our previously developed high frame rate sequencing and phase compensation techniques to measure axial and lateral motions at a typical frame rate of 1.25 kHz [4]. The system uses the curl of the displacements in a direct inversion algorithm to reconstruct elasticity. The most important benefit of this method is that the obtained elastograms are not dependent on the boundary conditions or the shape, size or position of the exciter, and as a result, the elastograms have fewer artifacts originating from these factors. The curl of the displacement has been used in magnetic resonance elastography (MRE) before, together with the direct inversion of the wave equation [5] and promising results have been obtained.Copyright © 2010 by ASME

Ultrasound segmentation based on statistical unit-root test of B-scan radial intensity profiles

Abstract: Delineation of the perimeter of hollow structures, such as veins and arteries, from ultrasound images is an important step in US-based medical interventions. A simple and efficient approach is proposed for edge detection in ultrasound images. The technique examines the radial edge profiles for unit root based on the Dickey-Fuller test. The existence of the unit root is a sign of a trend, and hence nonstationarity, in the statistics of the edge profile. The method is applied to simulated data and clinical images of human arteries and veins. The outcomes are validated based on the average of the Hausdorff distance between the automatically derived vessel contours and vessel contours marked by five experts. The proposed edge detection method provides accurate segmentations (average Hausdorff distance from expert segmentation of 1.5 mm in vessel images. and 0.4 mm in simulated data).

Brachytherapy strand visibility in reflected power ultrasound images: Comparison of EchoStrand vs. regular strands using 3D visibility profiles

Abstract: Poor visibility of the implanted brachytherapy seeds in ultrasound images is an obstacle for real time ultrasound-based dosimetry. A common practice in brachytherapy is to encapsulate the seeds in a structure called strand, manufactured from a synthetic bioabsorbable polymer. A possible solution to the visibility problem of the brachytherapy seeds is to localize the strand polymers, as opposed to the seeds, by using an echogenic strand polymer as in the EchoStrand product from BrachySciences. We extract and compare the 3D visibility profiles of EchoStrand with those of regular strands, at different angles between the ultrasound probe and the strand. The results show that the ultrasound visibility of both strand types decreases when the angle of orientation between the ultrasound transducer and the strand increases. However, at non-parallel orientations, the EchoStrand is significantly (p-value < 0.03) more visible compared to regular strands.