3D Ultrasound Reconstruction Research Articles

3D intra-operative ultrasound and MR image guidance: pursuing an ultrasound-based management of brainshift to enhance neuronavigation.

Brainshift is still a major issue in neuronavigation. Incorporating intra-operative ultrasound (iUS) with advanced registration algorithms within the surgical workflow is regarded as a promising approach for a better understanding and management of brainshift. This work is intended to (1) provide three-dimensional (3D) ultrasound reconstructions specifically for brain imaging in order to detect brainshift observed intra-operatively, (2) evaluate a novel iterative intra-operative ultrasound-based deformation correction framework, and (3) validate the performance of the proposed image-registration-based deformation estimation in a clinical environment. Eight patients with brain tumors undergoing surgical resection are enrolled in this study. For each patient, a 3D freehand iUS system is employed in combination with an intra-operative navigation (iNav) system, and intra-operative ultrasound data are acquired at three timepoints during surgery. On this foundation, we present a novel resolution-preserving 3D ultrasound reconstruction, as well as a framework to detect brainshift through iterative registration of iUS images. To validate the system, the target registration error (TRE) is evaluated for each patient, and both rigid and elastic registration algorithms are analyzed. The mean TRE based on 3D-iUS improves significantly using the proposed brainshift compensation compared to neuronavigation (iNav) before (2.7 vs. 5.9mm; [Formula: see text]) and after dural opening (4.2 vs. 6.2mm, [Formula: see text]), but not after resection (6.7 vs. 7.5mm; [Formula: see text]). iUS depicts a significant ([Formula: see text]) dynamic spatial brainshift throughout the three timepoints. Accuracy of registration can be improved through rigid and elastic registrations by 29.2 and 33.3%, respectively, after dural opening, and by 5.2 and 0.4%, after resection. 3D-iUS systems can improve the detection of brainshift and significantly increase the accuracy of the navigation in a real scenario. 3D-iUS can thus be regarded as a robust, reliable, and feasible technology to enhance neuronavigation.

First trimester three-dimensional ultrasound diagnosis of iniencephaly. A case report with review of literature

Iniencephaly is a rare neural tube defect, characterized by the classical triad of extreme retroflexion of the head, occipital bone defect and variable rachischisis. Its etiology is not fully understood: it might arise due to anomalies of genes controlling the planar cell polarity pathway, affecting the dorso-ventral orientation of the body axis. Risk factors include low socio-economic status and lack of folic acid supplementation. In up to 90% of cases involves female gender. We report a case diagnosed prenatally at 13 weeks by ultrasonography. It was characterized by abnormal shape of the fetus, with no distinct separation between the head and the body, extreme retroflexion of the fetal head, significant shortening of the spine, hypotelorism and holoprosencephaly. Three-dimensional (3D) ultrasound reconstruction evidenced the occiput absence and the same marked retroflexion with lordotic cervical spine, but with clear, distinct, un-fussed vertebrae. The parents opted to have an elective termination of pregnancy. Pathological examination confirmed the diagnosis, showing a perfect correlation with the ultrasound findings. The anomaly is incompatible with life, and early antenatal ultrasound diagnosis is advisable. Suggestive 3D images were helpful for illustrating these issues to the parents during prenatal counseling.

A novel Bayesian-based nonlocal reconstruction method for freehand 3D ultrasound imaging

Freehand three-dimensional (3D) ultrasound imaging is an important medical imaging modality in computer-assisted clinical diagnosis and image-guided intervention. In this paper, we present a novel Bayesian-based nonlocal method for the accurate volume reconstruction of freehand 3D ultrasound imaging with irregularly spaced B-scans. In the algorithm, each pixel is represented as the Gamma distribution which corresponds to the speckle noise generated by the interaction of the acoustic wave with the tissues. The variational reconstruction functional is associated with a nonlocal denoising term and a nonlocal inpainting term. To suppress speckle noise in the ultrasound image, the observed data is filtered via nonlocal total variation method firstly. The nonlocal denoising model is adapted to the speckle noise by substituting the Pearson distance-based weight function for the Gaussian weight function. To interpolate the missing data, a new inpainting scheme derived from the nonlocal means filter and its implementation based on fast marching method are introduced to fill the empty regions. This makes interpolation of missing data more accurate and effective. The Pearson distance function derived from the Bayesian estimator is not only used for speckle reduction, but also serves as weight function for building nonlocal means-based inpainting algorithm. Experimental results on synthetic cube data, in-vitro ultrasound abdominal phantom and in-vivo liver of human subject and comparisons with some classical and recent algorithms are used to demonstrate its improvement in both speckle suppression and edge preservation in 3D ultrasound reconstruction.

Reconstruction of freehand 3D ultrasound based on kernel regression.

IntroductionFreehand three-dimensional (3D) ultrasound has the advantages of flexibility for allowing clinicians to manipulate the ultrasound probe over the examined body surface with less constraint in comparison with other scanning protocols. Thus it is widely used in clinical diagnose and image-guided surgery. However, as the data scanning of freehand–style is subjective, the collected B-scan images are usually irregular and highly sparse. One of the key procedures in freehand ultrasound imaging system is the volume reconstruction, which plays an important role in improving the reconstructed image quality.System and methodsA novel freehand 3D ultrasound volume reconstruction method based on kernel regression model is proposed in this paper. Our method consists of two steps: bin-filling and regression. Firstly, the bin-filling step is used to map each pixel in the sampled B-scan images to its corresponding voxel in the reconstructed volume data. Secondly, the regression step is used to make the nonparametric estimation for the whole volume data from the previous sampled sparse data. The kernel penalizes distance away from the current approximation center within a local neighborhood.Experiments and resultsTo evaluate the quality and performance of our proposed kernel regression algorithm for freehand 3D ultrasound reconstruction, a phantom and an in-vivo liver organ of human subject are scanned with our freehand 3D ultrasound imaging system. Root mean square error (RMSE) is used for the quantitative evaluation. Both of the qualitative and quantitative experimental results demonstrate that our method can reconstruct image with less artifacts and higher quality.ConclusionThe proposed kernel regression based reconstruction method is capable of constructing volume data with improved accuracy from irregularly sampled sparse data for freehand 3D ultrasound imaging system.

An accurate and effective FMM-based approach for freehand 3D ultrasound reconstruction

Freehand three-dimensional ultrasound imaging is a highly attractive research area because it is capable of volumetric visualization and analysis of tissues and organs. The reconstruction algorithm plays a key role to the construction of three-dimensional ultrasound volume data with higher image quality and faster reconstruction speed. However, a systematic approach to such problem is still missing. A new fast marching method (FMM) for three-dimensional ultrasound volume reconstruction using the tracked and hand-held probe is proposed in this paper. Our reconstruction approach consists of two stages: bin-filling stage and hole-filling stage. Each pixel in the B-scan images is traversed and its intensity value is assigned to its nearest voxel in the bin-filling stage. For the efficient and accurate reconstruction, we present a new hole-filling algorithm based on the fast marching method. Our algorithm advances the interpolation boundary along its normal direction and fills the area closest to known voxel points in first, which ensure that the structural details of image can be preserved. Experimental results on both ultrasonic abdominal phantom and in vivo urinary bladder of human subject and comparisons with some popular algorithms are used to demonstrate its improvement in both reconstruction accuracy and efficiency.

Threedimensional imaging of carotid arteries: Advantages and pitfalls of ultrasound investigations

Summary Objectives To describe normal and pathological findings with three-dimensional (3D) ultrasound of the carotid bifurcation. Methods Patients admitted to our ultrasound laboratory for vascular screening were submitted to standard carotid duplex and to 3D ultrasound reconstruction of the carotid bifurcation. Volume 3D scans were performed manually, on the axial plane, and the software presented the volume rendering from the inward blood flow signal detected with the Power Color Mode. Results Forty normal subjects, 7 patients with caliber alterations (4 carotid bulb ectasia and 3 internal carotid lumen narrowing), 45 patients with course variations (tortuosities and kinkings) and 35 patients with internal carotid artery stenosis of various degrees have been investigated. Conclusions 3D ultrasound is a feasible technique. It can improve carotid axis general imaging through a global image presentation “at a glance”, visualizing caliber variations and vessels course. Imaging of stenosis from inward flow can be provided, but complete stenosis characterization requires the assessment of plaque morphology and vessel wall.

Agenesis of the ductus venosus: three-dimensional power Doppler reconstruction

The ductus venosus (DV) is an important fetal vascular structure that connects the umbilical venous system to the inferior vena cava (IVC) near its insertion point into the right atrium1. It allows 20–30% of the umbilical blood to bypass the liver in utero and reach the heart rapidly, thus increasing the flow of well-oxygenated blood to the cephalic and coronary circulation. The DV therefore plays a key role in increasing the shunt of oxygenated blood to the heart and decreasing placental return during hypoxemia and hypovolemia1,2. For several years, improvements in ultrasound techniques, such as two-dimensional (2D) and threedimensional (3D) ultrasound reconstruction, have made it possible to identify numerous malformations that were previously undetectable antenatally, including agenesis of the DV3, which is associated with various morphological and cytogenetic abnormalities. Examination of the DV has been used in referral centers to refine diagnoses involving cardiac, extracardiac and chromosomal anomalies2 as well as in first-trimester screening for Down syndrome in the high-risk population4. The DV pulsatility index for veins can be used as a continuous variable, in combination with nuchal translucency (NT) measurement, to increase specificity in the identification of congenital heart defects5. We report here the case of a 31-year-old primigravida, referred at 35 weeks of gestation to our prenatal center after the abnormal finding at third-trimester ultrasound of a highly dilated IVC (4.1 mm) and umbilical vein. Firstand second-trimester findings had been unremarkable. Combined marker screening in the first trimester indicated a 1/554 risk for Down syndrome, with NT on the 60th percentile. The only morphological abnormalities found during the third-trimester examination were the dilated IVC and umbilical vein. Suspecting agenesis of the DV, we performed a color Doppler ultrasound examination. Looking for an abnormal course or flow in the umbilical vein, we found that it was connected directly to the IVC and the flow velocity was high. To clarify the situation, 3D volume datasets were acquired with transverse and sagittal sweeps over the abdominal region. The umbilical vein and IVC were reconstructed using the glass-body rendering (angiographic) mode to optimize examination of these vessels. To highlight their abnormal connection, we then used the Magicut postprocessing application (Figure 1). This 3D power Doppler reconstruction demonstrated the anomalous course of the dilated umbilical vein, which was connected directly to the dilated subdiaphragmatic IVC and bypassed the liver. Fetal echocardiography showed substantial disproportion in the diameters of the IVC and superior vena cava at the points of insertion into the heart: 4.1 mm vs 1.2 mm. No features of cardiac decompensation or morphological abnormality were seen. The patient was offered amniocentesis for karyotype determination because agenesis of the DV is associated with a high rate (17%) of chromosomal abnormalities2; the karyotype was normal. The remainder of the pregnancy and delivery were uneventful, and the child appeared healthy. Little is known about the consequences and clinical implications of agenesis of the DV6. This anomaly affects approximately 6/1000 fetuses in a high-risk population. The few reports in the literature of an absent DV are associated with three different abnormal patterns: the umbilical vein may bypass the liver and then connect to the subdiaphragmatic IVC or to the iliac or renal veins, it may connect directly to the right or left atrium, or it may connect directly to the portal vein without giving rise to the DV2,7. DV agenesis is associated with congenital morphological abnormalities in approximately 65% of cases and with cytogenetic abnormalities in 17%2,8. The cardiac anomalies associated with DV agenesis, which occur in 48% of cases, include atrial and ventricular septal defects, tricuspid atresia, double outlet right ventricle, pulmonary atresia and transposition of the great arteries7,9. Other common associated anomalies involve the gastrointestinal system (duodenal atresia and tracheoesophageal fistula), the genitourinary system (bilateral hydronephrosis and ectopic kidney) and the musculoskeletal system

A Fast Slam Approach to Freehand 3-D Ultrasound Reconstruction for Catheter Ablation Guidance in the Left Atrium

We present a method for real-time, freehand 3D ultrasound (3D-US) reconstruction of moving anatomy, with specific application towards guiding the catheter ablation procedure in the left atrium. Using an intracardiac echo (ICE) catheter with a pose (position/orientation) sensor mounted to its tip, we continually mosaic 2D-ICE images of a left atrium phantom model to form a 3D-US volume. Our mosaicing strategy employs a probabilistic framework based on simultaneous localization and mapping (SLAM), a technique commonly used in mobile robotics for creating maps of unexplored environments. The measured ICE catheter tip pose provides an initial estimate for compounding 2D-ICE image data into the 3D-US volume. However, we simultaneously consider the overlap-consistency shared between 2D-ICE images and the 3D-US volume, computing a “corrected” tip pose if need be to ensure spatially-consistent reconstruction. This allows us to compensate for anatomic movement and sensor drift that would otherwise cause motion artifacts in the 3D-US volume. Our approach incorporates 2D-ICE data immediately after acquisition, allowing us to continuously update the registration parameters linking sensor coordinates to 3D-US coordinates. This, in turn, enables real-time localization and display of sensorized therapeutic catheters within the 3D-US volume for facilitating procedural guidance.

Interactive computing and measurement in three dimensional ultrasound fetal volumetric reconstruction using visualization toolkit

We have proposed the generic computing of 3D ultrasound volumetric reconstruction and measurement using visualization toolkit (VTK) open source computing approach. In present research, we have investigated the extent of voxel conversion from two dimensional image pixels to three dimension volume spacing. This is essentially important to analyze that the measurement on 3D volumetric possesses higher impact and accuracyvis-a-vis 2D image measurement. For that reason, we have developed measurement algorithm in 3D spaces via the expansion of Euclidean equation. Simulated results on ultrasound fetal training phantom indicate that the measurements are promising and consistent. Key words: Ultrasound, three dimension, volumetric, rendering, measurement, Euclidean, distance, Visualization toolkit (VTK).

Advantages and Pitfalls of Three-Dimensional Ultrasound Imaging of Carotid Bifurcation

Objectives: Several specialists use three-dimensional (3D) ultrasound as adjuvant imaging technique in their clinical practice. It has been applied to study carotid plaque morphology, surface and volume during atherosclerosis progression. Nonetheless, no papers have so far described the use of this technique in conditions different than carotid stenosis, such as bifurcation anatomy changes of the caliber and vessel course modifications. Methods: Patients admitted to our ultrasound laboratory for vascular screening were submitted to standard carotid duplex and to 3D ultrasound reconstruction of the carotid bifurcation. Results: Forty normal subjects, 7 patients with caliber alterations (4 carotid bulb ectasia and 3 internal carotid lumen narrowing), 45 patients with course variations (tortuosities and kinking) and 35 patients with internal carotid artery stenosis of various degrees have been investigated. Conclusions: 3D ultrasound is a feasible technique. It can improve carotid axis imaging through a better presentation of caliber variations and vessel course ‘at a glance’. 3D ultrasound from the inward flow can provide imaging of the stenosis, but stenosis quantification should always take into account the assessment of plaque morphology and vessel wall.

Methodological approach to the 3D ultrasound reconstruction of human fetal thymus: a preliminary study

The aim of this preliminary study is to propose a new methodological approach to the study of thymic morphology and volume in human fetus by ultrasound, using mathematical three-dimensional (3D) models and comparing them to the volumes obtained by Virtual Organ Computer-aided (VOCAL). Thymic volume and morphology of two fetuses at 21 and at 28 weeks of gestational age were reconstructed using VOCAL system and two different 3D models of fetal thymus were created with a CAD 3D software by an addition of geometrical solids: a conical model for the 21 weeks thymus; an elliptical model for the 28 weeks thymus. We believe that dysmorphism, volume and involution of fetal thymus should be investigated by this method during pregnancy. The relationship between the volumes obtained by VOCAL and those obtained with 3D models should be confirmed by further studies.

Methodological approach to the 3D ultrasound reconstruction of human fetal thymus: a preliminary study

The aim of this preliminary study is to propose a new methodological approach to the study of thymic morphology and volume in human fetus by ultrasound, using mathematical three-dimensional (3D) models and comparing them to the volumes obtained by Virtual Organ Computer-aided (VOCAL). Thymic volume and morphology of two fetuses at 21 and at 28 weeks of gestational age were reconstructed using VOCAL system and two different 3D models of fetal thymus were created with a CAD 3D software by an addition of geometrical solids: a conical model for the 21 weeks thymus; an elliptical model for the 28 weeks thymus. We believe that dysmorphism, volume and involution of fetal thymus should be investigated by this method during pregnancy. The relationship between the volumes obtained by VOCAL and those obtained with 3D models should be confirmed by further studies.

3D ultrasound reconstruction algorithms from analog and digital data

Freehand 3D ultrasound is increasingly being introduced in the clinic for diagnostics and image-assisted interventions. Various algorithms exist for combining 2D images of regular ultrasound probes to 3D volumes, being either voxel-, pixel- or function-based. Previously, the most commonly used input to 3D ultrasound reconstruction has been digitized analog video. However, recent scanners that offer access to digital image frames exist, either as processed or unprocessed data. To our knowledge, no comparison has been performed to determine which data source gives the best reconstruction quality. In the present study we compared both reconstruction algorithms and data sources using novel comparison methods for detecting potential differences in image quality of the reconstructed volumes. The ultrasound scanner used in this study was the Sonix RP from Ultrasonix Medical Corp (Richmond, Canada), a scanner that allow third party access to unprocessed and processed digital data. The ultrasound probe used was the L14-5/38 linear probe. The assessment is based on a number of image criteria: detectability of wire targets, spatial resolution, detectability of small barely visible structures, subjective tissue image quality, and volume geometry. In addition we have also performed the more “traditional” comparison of reconstructed volumes by removing a percentage of the input data. By using these evaluation methods and data from the specific scanner, the results showed that the processed video performed better than the digital scan-line data, digital video being better than analog video. Furthermore, the results showed that the choice of video source was more important than the choice of tested reconstruction algorithms.

Three-dimensional ultrasound diagnostics of tongue posture in children with unilateral posterior crossbite

Incorrect tongue posture on the mouth floor is considered an important factor in the etiology of unilateral posterior crossbite. The aim of this study was to objectively assess tongue posture in children with unilateral posterior crossbite and those with normal deciduous dentition by using 3-dimensional (3D) ultrasonography. First, referential 3D ultrasound images for differently postured tongues were acquired and reconstructed in 10 adults. Second, 27 children with unilateral posterior crossbite (mean age, 5.4 ± 1 years) and 23 children with normal deciduous dentition (mean age, 6.2 ± 0.4 years) were examined by using the 3D ultrasound technique. The referential 3D ultrasound reconstructions were used for the assessment of tongue posture in each child. The characteristic 3D reconstruction of the tongue postured on the palate displays distinctive convexity of the tongue dorsum, whereas, in the 3D reconstruction with the tongue postured on the mouth floor, the dorsum is characterized by a central groove and expressed concavity. Posture on the mouth floor was demonstrated by 81.5% of the children with unilateral posterior crossbite and by only 34.8% of those with normal deciduous dentition. The difference was statistically significant (Fisher exact test: P = 0.0012). Three-dimensional ultrasonography enables objective assessment of tongue posture and could become in the future an important part of functional diagnostics before, during, and after orthodontic treatment.

Reconstruction of 3D ultrasound images based on Cyclic Regularized Savitzky–Golay filters

This paper presents a new three-dimensional (3D) ultrasound reconstruction algorithm for generation of 3D images from a series of two-dimensional (2D) B-scans acquired in the mechanical linear scanning framework. Unlike most existing 3D ultrasound reconstruction algorithms, which have been developed and evaluated in the freehand scanning framework, the new algorithm has been designed to capitalize the regularity pattern of the mechanical linear scanning, where all the B-scan slices are precisely parallel and evenly spaced. The new reconstruction algorithm, referred to as the Cyclic Regularized Savitzky–Golay (CRSG) filter, is a new variant of the Savitzky–Golay (SG) smoothing filter. The CRSG filter has been improved upon the original SG filter in two respects: First, the cyclic indicator function has been incorporated into the least square cost function to enable the CRSG filter to approximate nonuniformly spaced data of the unobserved image intensities contained in unfilled voxels and reduce speckle noise of the observed image intensities contained in filled voxels. Second, the regularization function has been augmented to the least squares cost function as a mechanism to balance between the degree of speckle reduction and the degree of detail preservation. The CRSG filter has been evaluated and compared with the Voxel Nearest-Neighbor (VNN) interpolation post-processed by the Adaptive Speckle Reduction (ASR) filter, the VNN interpolation post-processed by the Adaptive Weighted Median (AWM) filter, the Distance-Weighted (DW) interpolation, and the Adaptive Distance-Weighted (ADW) interpolation, on reconstructing a synthetic 3D spherical image and a clinical 3D carotid artery bifurcation in the mechanical linear scanning framework. This preliminary evaluation indicates that the CRSG filter is more effective in both speckle reduction and geometric reconstruction of 3D ultrasound images than the other methods.

An Improved Olympic Hole-Filling Method for Ultrasound Volume Reconstruction of Human Spine

Hole-filling in ultrasound volume reconstruction using freehand three-dimensional ultrasound estimates the values for empty voxels from the unallocated voxels in the Bin-filling process due to inadequate sampling in the acquisition process. Olympic operator, as a neighbourhood averaging filter, can be used to estimate the empty voxel. However, this method needs improvement to generate a closer estimation of the empty voxels. In this paper, the authors propose an improved Olympic operator for the Hole-filling algorithm, and apply it to generate the volume in a 3D ultrasound reconstruction of the spine. The conventional Olympic operator defines the empty voxels by sorting the neighbouring voxels, removing the n% of the upper and lower values, and averaging them to attain the value to fill the empty voxels. The empty voxel estimation can be improved by thresholding the range width of its neighbouring voxels and adjusting it to the average values. The method is tested on a hole-manipulated volume derived from a cropped 3D ultrasound volume of a part of the spine. The MAE calculation on the proposed technique shows improved result compared to all tested existing methods.

A survey of freehand 3D ultrasound reconstruction algorithms

A survey of freehand 3D ultrasound reconstruction algorithms

An ultrasound-directed robotic system for microwave ablation of liver cancer

SUMMARYHepatocellular carcinoma (HCC), which leads to more than one million deaths every year in the world, is the second most common malignancy in China. As microwave ablation (MWA) is an effective method for the treatment of liver cancer, an ultrasound-directed (US-directed) robotic system was designed to assist surgeons on positioning the needle. This interventional robotic system includes a 5-DOF needle-guiding robot, a conventional 2D ultrasound device, a workstation for path planning and image processing and an electromagnetic tracking device. In clinical environments, we first use real-time freehand 3D ultrasound reconstruction and image analysis methods to attain tumour position, and then manipulate the guiding hole of the robot to position the needle affirmed by the surgeon. Finally, the feasibility of the interventional robotic system are validated by experimental results.

An open-source real-time ultrasound reconstruction system for four-dimensional imaging of moving organs

Four-dimensional imaging is a necessary step in computer-assisted interventions (CAI) performed on moving surgical targets, such as those located within the beating heart or influenced by respiratory motion. Ultrasound (US) is often the best imaging modality for this application, as it provides good contrast and spatial resolution while remaining simple to integrate into the operating room. However, conventional 2D US imaging is often insufficient for preoperative planning and surgical guidance, real-time 3D ultrasound imaging using matrix array probes has a smaller field of view and lower spatial resolution, and 3D volumes created using 3D US reconstruction suffer from motion artifacts. As an alternative, gated 4D ultrasound reconstruction using a tracked 2D US probe is a promising technology. In this paper, we present SynchroGrab4D to the open-source community. SynchroGrab4D performs 3D and 4D US reconstruction in real-time while visualizing the output volume(s) within an OpenIGTLink-compliant CAI system, such as 3D Slicer. Also included are VTK classes that perform ECG-gating and that interface with several commercial tracking systems, as well as a 4D Imaging module in 3D Slicer. Our open-source imaging system can be used to collect the 4D image data required for computer-assisted surgical planning and intraoperative guidance for a variety of moving organs.

A probabilistic framework for freehand 3D ultrasound reconstruction applied to catheter ablation guidance in the left atrium

The catheter ablation procedure is a minimally invasive surgery used to treat atrial fibrillation. Difficulty visualizing the catheter inside the left atrium anatomy has led to lengthy procedure times and limited success rates. In this paper, we present a set of algorithms for reconstructing 3D ultrasound data of the left atrium in real-time, with an emphasis on automatic tissue classification for improved clarity surrounding regions of interest. Using an intracardiac echo (ICE) ultrasound catheter, we collect 2D-ICE images of a left atrium phantom from multiple configurations and iteratively compound the acquired data into a 3D-ICE volume. We introduce two new methods for compounding overlapping US data-occupancy-likelihood and response-grid compounding-which automatically classify voxels as "occupied" or "clear," and mitigate reconstruction artifacts caused by signal dropout. Finally, we use the results of an ICE-to-CT registration algorithm to devise a response-likelihood weighting scheme, which assigns weights to US signals based on the likelihood that they correspond to tissue-reflections. Our algorithms successfully reconstruct a 3D-ICE volume of the left atrium with voxels classified as "occupied" or "clear," even within difficult-to-image regions like the pulmonary vein openings. We are robust to dropout artifact that plagues a subset of the 2D-ICE images, and our weighting scheme assists in filtering out spurious data attributed to ghost-signals from multi-path reflections. By automatically classifying tissue, our algorithm precludes the need for thresholding, a process that is difficult to automate without subjective input. Our hope is to use this result towards developing 3D ultrasound segmentation algorithms in the future.