Three-dimensional ultrasound imaging

Three-dimensional contrast-enhanced ultrasonography of intraductal papillary mucinous neoplasms of the pancreas: a comparison with magnetic resonance imaging

OBJECTIVES

The objective of this study was to prospectively compare the diagnostic accuracy of 3-dimensional contrast-enhanced ultrasonography (3D-CEUS) with that of magnetic resonance imaging (MRI) in the study of intraductal papillary mucinous neoplasms (IPMNs) of the pancreas.

METHODS

Thirty consecutive patients with IPMN were studied.

RESULTS

Three patients (10.0%) did not undergo diagnostic 3D-CEUS because of technical problems. Three dimensional CEUS identified 12 (44.4%) main-duct IPMNs versus no cases by MRI (P < 0.001). Intraductal papillary mucinous neoplasm localization showed poor agreement between 3D-CEUS and MRI (κ = 0.058), whereas good agreement was found in detecting the pancreatic calcifications (κ = 1.000). Significant differences between 3D-CEUS and MRI were found regarding the number of lesions detected (1.4 ± 0.8 vs 3.8 ± 3.6; P < 0.001), the detection of mucinous plugs (3.7% vs 50.0%; P < 0.001), chronic pancreatitis (7.4% vs 26.7%; P = 0.031), pancreatic atrophy (0% vs 50.0%; P < 0.001), thick septa (22.2% vs 53.3%; P = 0.004), and mural nodules (25.9% vs 3.3%; P = 0.016). Three dimensional CEUS showed similar results as compared with MRI in evaluating IPMNs smaller than 1 cm of diameter or greater than 2 cm.

CONCLUSIONS

Even if MRI remains the criterion standard technique for the diagnosis of IPMNs, 3D-CEUS can be safely used to follow patients with IPMNs of less than 1 cm.

Reference ranges and distribution of placental volume by 3-dimensional virtual organ computer-aided analysis between 11 weeks and 13 weeks 6 days

OBJECTIVES

The purpose of this study was to determine the feasibility, reproducibility, and distribution of placental volume measurements according to the crown-rump length between 11 weeks and 13 weeks 6 days.

METHODS

Images were acquired in 128 pregnancies followed in Burgundy during first-trimester screening sonography using an abdominal 3-dimensional transducer. The placental volume was then calculated by the virtual organ computer-aided analysis method with a rotation angle of 30° by a single operator.

RESULTS

Placental volumes ranged from 33.3 to 107.6 cm(3) with a mean ± SD of 62.3 ± 14.8 cm(3); the 5th and 10th percentiles were 38.0 and 44.20 cm(3), respectively, whereas the 90th and 95th percentiles were 80.25 and 86.68 cm(3). An exponential relationship was found between placental volume and crown-rump length: ln placental volume = 0.018 × crown-rump length + 2.93425; ln SD = 0.15; r(2) = 0.58. Finally, the mean placental quotient, defined as the ratio of placental volume to crown-rump length, was 1 ± 0.1 cm(3)/mm; the respective percentile values were 0.74, 0.81, 1.18, and 1.29 cm(3)/mm. No associations were found between parity or smoking and the placental quotient or between obesity and the placental quotient. Intraobserver reproducibility was good, with a mean difference of 0.2 cm(3).

CONCLUSIONS

Measurement of placental volume between 11 weeks and 13 weeks 6 days is reliable and reproducible and correlates strongly with crown-rump length.

Three-dimensional ultrasound as a predictor of pregnancy in patients undergoing ART

Different ultrasound parameters have been used to assess endometrial receptivity during ART treatment, including endometrial thickness, endometrial pattern, endometrial volume, Doppler of uterine arteries and endometrial blood flow. However, conflicting results have been reported with regard to their role in the prediction of pregnancy in ART treatment. The 3D ultrasound with power Doppler provides a unique tool with which to examine the blood supply of the whole endometrium and subendometrial region. Volume assessment can also be precisely performed by 3D ultrasound. Based on a med-line research and on our experience, the clinical use of 3D ultrasound is discussed in this review article.

Creating a collimated ultrasound beam in highly attenuating fluids

We have devised a method, based on a parametric array concept, to create a low-frequency (300-500 kHz) collimated ultrasound beam in fluids highly attenuating to sound. This collimated beam serves as the basis for designing an ultrasound visualization system that can be used in the oil exploration industry for down-hole imaging in drilling fluids. We present the results of two different approaches to generating a collimated beam in three types of highly attenuating drilling mud. In the first approach, the drilling mud itself was used as a nonlinear mixing medium to create a parametric array. However, the short absorption length in mud limits the mixing length and, consequently, the resulting beam is weak and broad. In the second improved approach, the beam generation process was confined to a separate "frequency mixing tube" that contained an acoustically non-linear, low attenuation medium (e.g., water) that allowed establishing a usable parametric array in the mixing tube. A low-frequency collimated beam was thus created prior to its propagation into the drilling fluid. Using the latter technique, the penetration depth of the low frequency ultrasound beam in the drilling fluid was significantly extended. We also present measurements of acoustic nonlinearity in various types of drilling mud.

Effect of malaria on placental volume measured using three-dimensional ultrasound: a pilot study

BACKGROUND

The presence of malaria parasites and histopathological changes in the placenta are associated with a reduction in birth weight, principally due to intrauterine growth restriction. The aim of this study was to examine the feasibility of studying early pregnancy placental volumes using three-dimensional (3D) ultrasound in a malaria endemic area, as a small volume in the second trimester may be an indicator of intra-uterine growth restriction and placental insufficiency.

METHODS

Placenta volumes were acquired using a portable ultrasound machine and a 3D ultrasound transducer and estimated using the Virtual Organ Computer-aided AnaLysis (VOCAL) image analysis software package. Intra-observer reliability and limits of agreement of the placenta volume measurements were calculated. Polynomial regression models for the mean and standard deviation as a function of gestational age for the placental volumes of uninfected women were created and tested. Based on these equations each measurement was converted into a z -score. The z-scores of the placental volumes of malaria infected and uninfected women were then compared.

RESULTS

Eighty-four women (uninfected = 65; infected = 19) with a posterior placenta delivered congenitally normal, live born, single babies. The mean placental volumes in the uninfected women were modeled to fit 5th, 10th, 50th, 90th and 95th centiles for 14-24 weeks' gestation. Most placenta volumes in the infected women were below the 50th centile for gestational age; most of those with Plasmodium falciparum were below the 10th centile. The 95% intra-observer limits of agreement for first and second measurements were ± 37.0 mL and ± 25.4 mL at 30 degrees and 15 degrees rotation respectively.

CONCLUSION

The new technique of 3D ultrasound volumetry of the placenta may be useful to improve our understanding of the pathophysiological constraints on foetal growth caused by malaria infection in early pregnancy.

Doppler imaging in the diagnosis of ovarian disease

INTRODUCTION

Pelvic ultrasonography remains the non-invasive imaging modality of choice for detecting and characterising adnexal masses. The use of Doppler ultrasound has improved the differential diagnosis of ovarian disease and helped to widen the understanding of the aetiology and possible pathophysiology of the various underlying conditions with an aim of improved diagnosis and management.

AREAS COVERED

This review describes the basis of different Doppler techniques and their application in ovarian disease. The present evidence is critically analysed in an attempt to define the current role of Doppler ultrasound of the ovaries. The technique holds promise in certain ovarian diseases but remains controversial in others.

EXPERT OPINION

Doppler ultrasound has a role in both the clinical and research settings. Clinically, it can be used to differentiate benign and malignant disease and help confirm diagnoses suggested on grey-scale imaging giving the user more confidence. Its use here, however, is generally restricted to a subjective impression of colour flow rather than a quantitative analysis of vascularity or blood flow velocity. These measures are more relevant in the research setting where quantitative Doppler is being used to clarify the possible underlying aetiology of various ovarian diseases such as polycystic ovarian syndrome and benign cysts. Doppler ultrasound has also been used in various models to evaluate the response to ovarian stimulation and the effect of surgery on the ovary.

Non-invasive portography: a microbubble-induced three-dimensional sonogram for discriminating idiopathic portal hypertension from cirrhosis

OBJECTIVES

The aim of this prospective study was to elucidate the efficacy of contrast-enhanced three-dimensional (3D) ultrasound with Sonazoid(®) (GF Healthcare, Oslo, Norway) as a non-invasive tool to discriminate idiopathic portal hypertension (IPH) from cirrhosis by demonstration of portal vein structure.

METHODS

There were 16 patients: 11 with biopsy-proven cirrhosis and 5 with biopsy-proven IPH. Intrahepatic right portal vein images were taken by 3D ultrasound from 1 min after the injection of Sonazoid (0.0075 ml kg(-1)). Portal vein appearances were compared between 3D ultrasound and percutaneous transhepatic portography (PTP) by four independent reviewers. Sensitivity, specificity and area under the receiver operating characteristic curve (Az) of the images were used for the diagnosis of cirrhosis/IPH, and interimaging, inter-reviewer and interoperator agreement were examined.

RESULTS

Sensitivity, specificity and Az of PTP for the diagnosis of cirrhosis/IPH were 63.6%/100%, 100% and 0.9 (0.71-1.0) by Reviewer I and 90.9%/100%, 100% and 1.0 by Reviewer III, respectively. Similarly, sensitivity, specificity and Az of 3D ultrasound for diagnosis of cirrhosis/IPH were 54.5%/80%, 100% and 0.96 (0.84-1.0) by Reviewer II and 72.7%/80%, 100% and 0.97 (0.9-1.0) by Reviewer IV, respectively. Diagnostic agreement between PTP and 3D ultrasound was good between Reviewers I and II (κ=0.793) and good between Reviewers III and IV (κ=0.732). Inter-reviewer agreement was good between Reviewers I and III for PTP diagnosis (κ=0.735), and good between Reviewers II and IV for 3D ultrasound diagnosis (κ=0.792). Interoperator agreement of diagnostic results was good (κ=0.740).

CONCLUSION

Non-invasive visualisation of intrahepatic portal vein structure by contrast-enhanced 3D ultrasound with Sonazoid may have the potential to discriminate IPH from cirrhosis.

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.

Vibro-acoustography and B-mode integration for 3D imaging

Tridimensional representation of vibro-acoustography images based on the topology acquired by B-mode acquisitions is proposed for the evaluation of bone and implant surfaces. A tridimensional evaluation of the implant coverage used in a total hip arthroplasty procedure was performed to show the feasibility of this approach. A vibro-acoustography image of the uncovered area of the implant was acquired and represented in planar representation. However, tridimensional representation of the exposed surface area is necessary for proper evaluation of the stability of the implant. Hence, the topologies of the implant and the bone region around it were determined by acquiring 280 B-mode images. The B-scan images were processed in order to reconstruct the tridimensional surface of the objects. Finally, the vibro-acoustography image and the B-mode-based surface were aligned for the tridimensional visualization. The B-mode tridimensional representation of the bone and implant was improved by the enhancement of contrast and resolution provided by the vibro-acoustography image. The final tridimensional image presented a resolution of 0.25 mm. The topological correction based on B-mode slices allowed an accurate evaluation of the surface area.

3-D ultrasound volume reconstruction using the direct frame interpolation method

A new method for 3-D ultrasound volume reconstruction using tracked freehand 3-D ultrasound is proposed. The method is based on solving the forward volume reconstruction problem using direct interpolation of high-resolution ultrasound B-mode image frames. A series of ultrasound B-mode image frames (an image series) is acquired using the freehand scanning technique and position sensing via optical tracking equipment. The proposed algorithm creates additional intermediate image frames by directly interpolating between two or more adjacent image frames of the original image series. The target volume is filled using the original frames in combination with the additionally constructed frames. Compared with conventional volume reconstruction methods, no additional filling of empty voxels or holes within the volume is required, because the whole extent of the volume is defined by the arrangement of the original and the additionally constructed B-mode image frames. The proposed direct frame interpolation (DFI) method was tested on two different data sets acquired while scanning the head and neck region of different patients. The first data set consisted of eight B-mode 2-D frame sets acquired under optimal laboratory conditions. The second data set consisted of 73 image series acquired during a clinical study. Sample volumes were reconstructed for all 81 image series using the proposed DFI method with four different interpolation orders, as well as with the pixel nearest-neighbor method using three different interpolation neighborhoods. In addition, volumes based on a reduced number of image frames were reconstructed for comparison of the different methods' accuracy and robustness in reconstructing image data that lies between the original image frames. The DFI method is based on a forward approach making use of a priori information about the position and shape of the B-mode image frames (e.g., masking information) to optimize the reconstruction procedure and to reduce computation times and memory requirements. The method is straightforward, independent of additional input or parameters, and uses the high-resolution B-mode image frames instead of usually lower-resolution voxel information for interpolation. The DFI method can be considered as a valuable alternative to conventional 3-D ultrasound reconstruction methods based on pixel or voxel nearest-neighbor approaches, offering better quality and competitive reconstruction time.

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.

Three-dimensional ultrasound imaging

This review is about the development of three-dimensional (3D) ultrasonic medical imaging, how it works, and where its future lies. It assumes knowledge of two-dimensional (2D) ultrasound, which is covered elsewhere in this issue. The three main ways in which 3D ultrasound may be acquired are described: the mechanically swept 3D probe, the 2D transducer array that can acquire intrinsically 3D data, and the freehand 3D ultrasound. This provides an appreciation of the constraints implicit in each of these approaches together with their strengths and weaknesses. Then some of the techniques that are used for processing the 3D data and the way this can lead to information of clinical value are discussed. A table is provided to show the range of clinical applications reported in the literature. Finally, the discussion relating to the technology and its clinical applications to explain why 3D ultrasound has been relatively slow to be adopted in routine clinics is drawn together and the issues that will govern its development in the future explored.

An X-Ray computed tomography/positron emission tomography system designed specifically for breast imaging

Mammography has served the population of women who are at-risk for breast cancer well over the past 30 years. While mammography has undergone a number of changes as digital detector technology has advanced, other modalities such as computed tomography have experienced technological sophistication over this same time frame as well. The advent of large field of view flat panel detector systems enable the development of breast CT and several other niche CT applications, which rely on cone beam geometry. The breast, it turns out, is well suited to cone beam CT imaging because the lack of bones reduces artifacts, and the natural tapering of the breast anteriorly reduces the x-ray path lengths through the breast at large cone angle, reducing cone beam artifacts as well. We are in the process of designing a third prototype system which will enable the use of breast CT for image guided interventional procedures. This system will have several copies fabricated so that several breast CT scanners can be used in a multi-institutional clinical trial to better understand the role that this technology can bring to breast imaging.

Real-Time Three-Dimensional Ultrasound for Guiding Surgical Tasks

OBJECTIVE

As a stand-alone imaging modality, two-dimensional (2D) ultrasound (US) can only guide basic interventional tasks due to the limited spatial orientation information contained in these images. High-resolution real-time three-dimensional (3D) US can potentially overcome this limitation, thereby expanding the applications for US-guided procedures to include intracardiac surgery and fetal surgery, while potentially improving results of solid organ interventions such as image-guided breast, liver or prostate procedures. The following study examines the benefits of real-time 3D US for performing both basic and complex image-guided surgical tasks.

MATERIALS AND METHODS

Seven surgical trainees performed three tasks in an acoustic testing tank simulating an image-guided surgical environment using 2D US, biplanar 2D US, and 3D US for guidance. Surgeon-controlled US imaging was also tested. The evaluation tasks were (1) bead-in-hole navigation; (2) bead-to-bead navigation; and (3) clip fixation. Performance measures included completion time, tool tip trajectory, and error rates, with endoscope-guided performance serving as a gold-standard reference measure for each subject.

RESULTS

Compared to 2D US guidance, completion times decreased significantly with 3D US for both bead-in-hole navigation (50%, p = 0.046) and bead-to-bead navigation (77%, p = 0.009). Furthermore, tool-tip tracking for bead-to-bead navigation demonstrated improved navigational accuracy using 3D US versus 2D US (46%, p = 0.040). Biplanar 2D imaging and surgeon-controlled 2D US did not significantly improve performance as compared to conventional 2D US. In real-time 3D mode, surgeon-controlled imaging and changes in 3D image presentation made by adjusting the perspective of the 3D image did not diminish performance. For clip fixation, completion times proved excessive with 2D US guidance (> 240 s). However, with real-time 3D US imaging, completion times and error rates were comparable to endoscope-guided performance.

CONCLUSIONS

Real-time 3D US can guide basic surgical tasks more efficiently and accurately than 2D US imaging. Real-time 3D US can also guide more complex surgical tasks which may prove useful for procedures where optical imaging is suboptimal, as in fetal surgery or intracardiac interventions.

Treatment response evaluation with three-dimensional contrast-enhanced ultrasound for liver cancer after local therapies

OBJECTIVE

To investigate the potential usefulness of three-dimensional contrast-enhanced ultrasound (3D-CEUS) in evaluating the treatment response for liver cancer after local therapies.

METHODS

A total of 107 lesions in 95 consecutive patients with liver cancer underwent local therapies and thereafter received low acoustic power 3D-CEUS examination. The LOGIQ 9 ultrasound scanner and a volume transducer were used and the ultrasound contrast agent was SonoVue. The image quality of 3D-CEUS images was evaluated and the influence of 3D-CEUS to clinical outcome was investigated.

RESULTS

The image quality of 3D-CEUS was defined as high in 102 (102/107, 95.3%) lesions and common in 5 (5/107, 4.7%) lesions. 3D-CEUS did not change the diagnosis in any patient compared with 2D-CEUS. However, 3D-CEUS changed the management in 3 (2.8%) of 107 lesions, increased confidence but made no change in diagnosis in 85 (79.5%) lesions, added some information but did not change management or diagnosis in 15 (14.0%), and made no change in 4 (3.7%), respectively, in comparison with 2D-CEUS.

CONCLUSION

3D-CEUS enhances the diagnostic confidence in the majority of the patients and even changes the management in some patients. 3D-CEUS has potential usefulness in evaluating treatment response for liver cancer after local therapies.

Three-dimensional contrast-enhanced ultrasound of the liver: experience of 92 cases

Three-dimensional contrast-enhanced ultrasound (3D-CEUS) is a combination of three-dimensional ultrasound (3DUS) and contrast-enhanced ultrasound (CEUS). To evaluate the feasibility of 3D-CEUS in liver imaging, investigate possible influencing factors to its image quality, and evaluate the influence of 3D-CEUS to clinical outcome, low acoustic power (mechanical index, 0.08-0.13) 3D-CEUS was carried out in 102 focal liver lesions in 92 patients by using the LOGIQ 9 ultrasound scanner and a volume transducer (frequency range, 2-5 MHz; focusing ability, 2-25 cm in depth; azimuth aperture 5.9 cm). The lesions were classified into two groups: group 1 (n=51) for characterization and group 2 (n=51) for local treatment response evaluation. The factors that influenced the image quality of 3D-CEUS were analyzed. The image quality and usefulness of 3D-CEUS between the two groups were compared by using the chi(2)-test. The results showed that the lesion diameter, location, and scanning route had no significant influence on the image quality in both groups, whereas interfering factors damaged the image quality in group 1. In group 1, during arterial phase, high image quality was more frequently found in hyperenhanced and hypo- or non-enhanced lesions compared with isoenhanced lesions. In group 2, interfering factor and local treatment response had no obvious influence on the image quality. The visualization rate of high image quality was 94.1% (48/51) in group 2 vs. 72.6% (37/51) in group 1 (P=0.012). The investigators found that 3D-CEUS improved confidence but made no change in diagnosis in 19 (37.3%) of 51 lesions in group 1, whereas 41 (80.4%) of 51 lesions in group 2 (P=0.000). 3D-CEUS tends to obtain better image quality and lead to higher diagnostic confidence in the lesions for local treatment response evaluation, and perhaps is more useful in this aspect in future clinical settings.

Sonographic Assessment of the Neonatal Spine and the Potential for New Technologies to Aid in Diagnoses

Many spinal disorders, whether congenital or acquired, are likely to have an improved outcome if they are promptly identified. A rapid diagnosis may eliminate progressive sequela and provide insight to possible treatment plans. Although there are various medical imaging modalities for evaluating the neonatal spine, diagnostic medical sonography provides a safe (no exposure to ionizing radiation), quick, and inexpensive approach. Spinal diagnostic medical sonography can be performed in neonates as long as the vertebral column is not completely ossified. Diagnostic medical sonography is a valuable technique that, in addition to 2D imaging, provides 3D, extended field of view (EFOV), and M-mode imaging. Diagnostic medical sonography can identify normal spinal anatomy and variants, congenital malformations, and acquired diseases subsequent to birth-related trauma and lumbar punctures. This article discusses the normal embryology of the spine. Indications for neonatal spinal diagnostic medical sonography are reviewed along with a description of sonographic examination techniques. A review of spinal pathology and their embryological origin will be outlined as well as normal variants seen with sonography. A detailed literature review is provided evaluating case studies and their findings.

A new adaptive interpolation algorithm for 3D ultrasound imaging with speckle reduction and edge preservation

Conventional interpolation algorithms for reconstructing freehand three-dimensional (3D) ultrasound data always contain speckle noises and artifacts. This paper describes a new algorithm for reconstructing regular voxel arrays with reduced speckles and preserved edges. To study speckle statistics properties including mean and variance in sequential B-mode images in 3D space, experiments were conducted on an ultrasound resolution phantom and real human tissues. In the volume reconstruction, the homogeneity of the neighborhood for each voxel was evaluated according to the local variance/mean of neighboring pixels. If a voxel was locating in a homogeneous region, its neighboring pixels were averaged as the interpolation output. Otherwise, the size of the voxel neighborhood was contracted and the ratio was re-calculated. If its neighborhood was deemed as an inhomogeneous region, the voxel value was calculated using an adaptive Gaussian distance weighted method with respect to the local statistics. A novel method was proposed to reconstruct volume data set with economical usage of memory. Preliminary results obtained from the phantom and a subject's forearm demonstrated that the proposed algorithm was able to well suppress speckles and preserve edges in 3D images. We expect that this study can provide a useful imaging tool for clinical applications using 3D ultrasound.

Automatic guidance of an ultrasound probe by visual servoing based on B-mode image moments

We propose a new visual servo approach to automatically control in real-time the full motion of a 2D ultrasound (US) probe held by a medical robot in order to reach a desired image of motionless soft tissue object in B-mode ultrasound imaging. Combinations of image moments of the observed object cross-section are used as feedback information in the visual control scheme. These visual features are extracted in real-time from the US image thanks to a fast image segmentation method. Simulations performed with a static US volume containing an egg-shaped object, and ex-vivo experiments using a robotized US probe that interacts with a motionless rabbit heart immersed in water, show the validity of this new approach and its robustness to different perturbations. This method shows promise for a variety of US-guided medical interventions that require real-time servoing.

Role of endoluminal sonography in evaluation of obstruction of the ureteropelvic junction

OBJECTIVE

The objective of this study was to evaluate the clinical feasibility of the use of 2D and 3D endoluminal sonography during endourologic procedures on patients with an obstructed ureteropelvic junction (UPJ).

SUBJECTS AND METHODS

In 45 patients with an obstructed UPJ undergoing endoscopic procedures, a 6.2-French catheter-based ultrasound probe (12.5 or 20 MHz) was inserted under endoscopic guidance into the upper urinary tract for acquisition of 2D images for evaluation of UPJ structures and construction of 3D volume images with a computer workstation. The role of 3D in addition to 2D imaging for identification of abnormalities at the UPJ was evaluated.

RESULTS

Both 2D and 3D images depicted crossing vessels at the UPJ in 24 of 43 patients (55.8%) and a ureteral septum in 14 of 43 patients (32.6%), and endoscopic incisions were successfully made with sonographic guidance. The anatomic structures of the UPJ associated with abnormalities (e.g., crossing vessels, septum, calculi, tumors, and strictures) were appreciated and evaluated more fully on 3D than on 2D images. The endoluminal sonographic findings helped rule out or modify the interventional procedure (endopyelotomy or balloon ureteroplasty) in the cases of eight of 43 patients (18.6%).

CONCLUSION

Three-dimensional endoluminal sonography clearly displays diagnostic information that complements 2D imaging findings and enhances the assessment of normal and abnormal structures at the UPJ for endourologic surgery.

Rotational motion in sensorless freehand three-dimensional ultrasound

Freehand three-dimensional ultrasound is usually acquired with a position sensor attached to the ultrasound probe. However, position sensors can be expensive, obtrusive and difficult to calibrate. For this reason, there has been much research on alternative, image-based techniques, with in-plane motion tracked using conventional image registration methods, and out-of-plane motion inferred from the decorrelation between nearby B-scans. However, since out-of-plane motion is not the only source of decorrelation, image-based positions determined in this way suffer from cumulative drift errors. In this paper, we consider the effect of probe rotation on correlation and how this affects the position estimates. We then present a novel technique to compensate for out-of-plane rotations, by making use of orientation measurements from an unobtrusive sensor. Using simulations and in vitro experiments, we demonstrate that the technique is able to reduce the drift error in elevational positioning by 57% on average.

Volume reconstruction of freehand three-dimensional ultrasound using median filters

OBJECTIVES

This paper aims to apply median filters for reducing interpolation error and improving the quality of 3D images in a freehand 3D ultrasound (US) system.

BACKGROUND AND MOTIVATION

Freehand 3D US imaging has been playing an important role in obtaining the entire 3D impression of tissues and organs. Reconstructing a sequence of irregularly located 2D US images (B-scans) into a 3D data set is one of the key procedures for visualization and data analysis.

METHODS

In this study, we investigated the feasibility of using median filters for the reconstruction of 3D images in a freehand 3D US system. The B-scans were collected using a 7.5 MHz ultrasound probe. Four algorithms including the standard median (SM), Gaussian weighted median (GWM) and two types of distance-weighted median (DWM) filters were proposed to filter noises and compute voxel intensities. Qualitative and quantitative comparisons were made among the results of different methods based on the image set captured in freehand from the forearm of a healthy subject. A leave-one-out approach was used to demonstrate the performance of the median filters for predicting the removed B-scan pixels.

RESULTS

Compared with the voxel nearest-neighbourhood (VNN) and distance-weighted (DW) interpolation methods, the four median filters reduced the interpolation error by 8.0-24.0% and 1.2-21.8%, respectively, when 1/4 to 5 B-scans was removed from the raw B-scan sequence.

CONCLUSIONS

In summary, the median filters can improve the quality of volume reconstruction by reducing the interpolation errors and facilitate the following image analyses in clinical applications.

Interferometric Synthetic Aperture Microscopy: Computed Imaging for Scanned Coherent Microscopy

Three-dimensional image formation in microscopy is greatly enhanced by the use of computed imaging techniques. In particular, Interferometric Synthetic Aperture Microscopy (ISAM) allows the removal of out-of-focus blur in broadband, coherent microscopy. Earlier methods, such as optical coherence tomography (OCT), utilize interferometric ranging, but do not apply computed imaging methods and therefore must scan the focal depth to acquire extended volumetric images. ISAM removes the need to scan the focus by allowing volumetric image reconstruction from data collected at a single focal depth. ISAM signal processing techniques are similar to the Fourier migration methods of seismology and the Fourier reconstruction methods of Synthetic Aperture Radar (SAR). In this article ISAM is described and the close ties between ISAM and SAR are explored. ISAM and a simple strip-map SAR system are placed in a common mathematical framework and compared to OCT and radar respectively. This article is intended to serve as a review of ISAM, and will be especially useful to readers with a background in SAR.

An Ultrasound Probe Holder for Image-Guided Surgery

Automating image-guided therapy and registering a medical image to a patient require knowledge of the locations of both the medical image source (e.g., ultrasound) and the surgical tool with respect to a global coordinate system that is known relative to the patient. Also, sturdiness of the medical instrumentations is essential. A novel compact stabilizer-tracker integrated assembly is designed to serve as a holder that can be used to support, manipulate in six degrees-of-freedom, and firmly lock-in-place ultrasound imaging probes and other instruments for use in image-guided surgery as well as to provide the position and orientation of the probe in 3D space with respect to a known reference origin. The stabilizer’s configuration allows a clinician to easily manipulate an ultrasound probe in 3D space, and demonstrate improved sturdiness when locked. A reliable validation technique using forward kinematics was used to evaluate the performance of the holder. Performance tests show that the tracker assembly can acquire the position and orientation of the ultrasound probe with an average displacement accuracy of 0.66mm and roll, pitch, and yaw angular accuracies of 0.24deg, 0.38deg, and 0.19deg, respectively. The improved sturdiness demonstrated by the compact-sized stabilizer and the high accuracy of the tracking mechanism make the integrated holder mechanism well suited for use in image-guided robot-assisted brachytherapy. It is anticipated that this will lead to improvement in accuracy and clinical outcomes for the procedure. The novel tracker can also be used to acquire the positions and orientations of other passive mechanisms of complex designs.

Current role of ultrasound for the management of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) has a decisive influence on the prognosis of cirrhotic patients. Although α-fetoprotein (AFP) is a known and specific tumor maker for HCC, it is not suitable for the screening and surveillance of HCC because of its poor predictive value and low sensitivity. The use of imaging modalities is essential for the screening, diagnosis and treatment of HCC. Ultrasound (US) plays a major role among them, because it provides real-time and non-invasive observation by a simple and easy technique. In addition, US-guided needle puncture methods are frequently required for the diagnosis and/or treatment process of HCC. The development of digital technology has led to the detection of blood flow by color Doppler US, and the sensitivity for detecting tumor vascularity has shown remarkable improvement with the introduction of microbubble contrast agents. Moreover, near real-time 3-dimensional US images are now available. As for the treatment of HCC, high intensity focused ultrasound (HIFU) was developed as a novel technology that provides a transcutaneous ablation effect without needle puncture. These advancements in the US field have led to rapid progress in HCC management, and continuing advances are expected. This article reviews the current application of US for HCC in clinical practice.

Calibration of an orientation sensor for freehand 3D ultrasound and its use in a hybrid acquisition system

BACKGROUND

Freehand 3D ultrasound is a powerful imaging modality with many potential applications. However, its reliance on add-on position sensors, which can be expensive, obtrusive and difficult to calibrate, is a major drawback. Alternatively, freehand 3D ultrasound can be acquired without a position sensor using image-based techniques. Sensorless reconstructions exhibit good fine scale detail but are prone to tracking drift, resulting in large scale geometrical distortions.

METHOD

We investigate an alternative position sensor, the Xsens MT9-B, which is relatively unobtrusive but measures orientation only. We describe a straightforward approach to calibrating the sensor, and we measure the calibration precision (by repeated calibrations) and the orientation accuracy (using independent orientation measurements). We introduce algorithms that allow the MT9-B potentially to correct both linear and angular drift in sensorless reconstructions.

RESULTS

The MT9-B can be calibrated to a precision of around 1 degrees . Reconstruction accuracy is also around 1 degrees . The MT9-B was able to eliminate angular drift in sensorless reconstructions, though it had little impact on linear drift. In comparison, six degree-of-freedom drift correction was shown to produce excellent reconstructions.

CONCLUSION

Gold standard freehand 3D ultrasound acquisition requires the synthesis of image-based techniques, for good fine scale detail, and position sensors, for good large scale geometrical accuracy. A hybrid system incorporating the MT9-B offers an attractive compromise between quality and ease of use. The position sensor is unobtrusive and the system is capable of faithful acquisition, with the one exception of linear drift in the elevational direction.

Stereoscopic evaluation of fetal bony structures

OBJECTIVE

The purpose of this study was to assess the performance of stereoscopic compared with conventional viewing of 3-dimensional ultrasound (3DUS) data for evaluation of fetal bony structures.

METHODS

A series of 47 human fetuses were evaluated with conventional 3DUS scanning systems. Twenty-five volumes of the fetal head, thorax, and abdomen were acquired. Volume-rendered images of the fetal cranium and spine were displayed interactively on a real-time stereoscopic graphics workstation. Visualization parameters were interactively optimized. Both conventional and stereoscopic images were evaluated for the clarity of structure visualization (0, nonvisualized; 1, nondiagnostic; 2, adequate; and 3, excellent), the ability to identify key anatomic landmarks (eg, sutures, palate, vertebrae, and ribs), artifacts, and evaluation time.

RESULTS

Fetal bony structures, especially high-contrast structures, were readily identified with both conventional and stereoscopic. Overall, stereoscopic viewing provided a statistically significant improvement compared with conventional viewing (P < .01), improved conspicuity of complex bony structures, and added structural detail information that assisted in identification of complex anatomy in 14% of the fetal skull and 26% of the fetal spine cases. Overlapping structures were better identified on the volume-rendered stereoscopic display, with stereoscopic viewing improving differentiation of near and far structures. An interactive display and inclusion of a planar slice review further assisted in identification of structures. The evaluation times were comparable for the two methods.

CONCLUSIONS

The stereoscopic display of rendered 3DUS data adds valuable information that assists in identification of fetal bony structures, such as cranial sutures and spinal vertebrae, particularly in complex formations. The increasing availability of stereoscopic visualization workstations will offer an additional tool for fetal diagnosis and evaluation.

High-resolution real-time three-dimensional acoustic imaging system with a reflector

PURPOSE

We propose an acoustic real-time three-dimensional (3-D) diagnostic imaging system based on a hybrid array-reflector configuration that realizes high time and spatial resolutions with a modest computational load.

METHODS

All the elements on a small dense array were excited with proper time delays to transmit a broad beam similar to that of a single transmitter element. The echo was gathered by a concave reflector and received by the dense array. The image of the target was reconstructed by numerical back projection from the defocused image distributed on the array. With this scheme, images of the whole measurement area can be reconstructed from a single transmit and receive event.

RESULTS

The number of elements can be reduced to about 1/8.2 that of a dense 2-D array of a digital beamforming system having the same spatial resolution. By weighting individual elements, the sidelobe level could be suppressed to less than -21 dB. The maximum theoretical frame rate is 5000 3-D images/s. This method has a higher signal-to-noise ratio than that of defocused multi-element digital beamforming methods, overcoming conventional phased array performance.

CONCLUSION

The proposed scheme is suited for purposes that require high time and spatial resolutions, such as cardiology.

Freehand 3D ultrasound reconstruction algorithms--a review

Three-dimensional (3D) ultrasound (US) is increasingly being introduced in the clinic, both for diagnostics and image guidance. Although dedicated 3D US probes exist, 3D US can also be acquired with the still frequently used two-dimensional (2D) US probes. Obtaining 3D volumes with 2D US probes is a two-step process. First, a positioning sensor must be attached to the probe; second, a reconstruction of a 3D volume can be performed into a regular voxel grid. Various algorithms have been used for performing 3D reconstruction based on 2D images. Up till now, a complete overview of the algorithms, the way they work and their benefits and drawbacks due to various applications has been missing. The lack of an overview is made clear by confusions about algorithm and group names in the existing literature. This article is a review aimed at explaining and categorizing the various algorithms into groups, according to algorithm implementation. The algorithms are compared based on published data and our own laboratory results. Positive and practical uses of the various algorithms for different applications are discussed, with a focus on image guidance.

Prenatal three-dimensional ultrasound: perception of sonographers, sonologists and undergraduate students

OBJECTIVE

To assess the perception of non-pregnant sonographers, sonologists and undergraduate students on the use of three-dimensional (3D) ultrasound technology in fetal medicine.

METHODS

This was a study of two groups of non-pregnant subjects. Group I included 520 (305 female, 215 male) medical professionals who completed a questionnaire after attending a lecture on 3D imaging. Factors such as gender, career and having children were analyzed with respect to the attendee's responses about use of 3D ultrasound for medical purposes and for reassurance. Group II included 137 (75 female, 60 male, two unknown) undergraduate students from bioengineering, psychology and physiology classes who completed a questionnaire after attending a brief presentation on two-dimensional and 3D fetal imaging. Factors such as gender and area of educational interest were analyzed with respect to the students' responses about the use of 3D ultrasound for medical purposes and for parental-fetal attachment.

RESULTS

In Group I, 63% said that they would like to have a 3D ultrasound examination in the future, while 14% said that they would not. Common reasons given for wanting a 3D ultrasound exam in the future were for medical purposes (39%) or reassurance (18%). The main differences perceived between two-dimensional (2D) and 3D ultrasound were medical advantages (65%) and parental reassurance (28%). 62.4% of Group I thought 3D technology should be in wide use in obstetric ultrasound and 73.6% thought that 3D ultrasound would reassure parents carrying normal fetuses. Gender, age and career did not have a significant influence on perception of 3D ultrasound. In Group II, the majority (91%) said they could see a remarkable difference between 2D and 3D ultrasound. 83% responded that they would like to have a 3D ultrasound examination of their own baby in the future for the following reasons: 34% for the detailed picture, 31% for increased abnormality detection, 13% for reassurance or curiosity; 8% thought it would be unnecessary or a negative experience. Concerning parental-fetal attachment, 72% thought 3D ultrasound would have a positive effect. The majority of Group II (93%) thought 3D ultrasound would be valuable and 56% thought 3D ultrasound would assist in diagnosing fetal abnormalities. There was no significant relationship between gender, age or area of interest and the perception of 3D ultrasound.

CONCLUSIONS

Responses by sonographers and physicians suggest that 3D ultrasound will have a role in the future for medical indications and in reassuring patients carrying normal fetuses. Our results also suggest that undergraduate students believe that 3D ultrasound will be a valuable technique in obstetrics and that it will have a positive effect on parental-fetal attachment.

Blood flow in its context: combining 3D B-mode and color Doppler ultrasonic data

Visualization of volumetric multicomponent data sets is a high-dimensional problem, especially for color data. Medical 3D ultrasound (US) technology has rapidly advanced during the last few decades and scanners can now generate joint 3D scans of tissues (B-mode) and blood flow (power or color Doppler) in real time. Renderings of such data sets have to comprehensively convey both the relevant structures of the tissues that form the context for blood flow, as well as the distribution of blood flow itself. The narrow field of view in US data, which is often used to make real-time imaging possible, complicates volume exploration since only parts of organs are usually visible; that is, clearly defined anatomical landmarks are scarce. In addition, the noisy nature and low signal-to-contrast ratio of US data make effective visualization a challenge, whereby there are currently no convincing solutions for combined US B-mode and color Doppler data rendering. Therefore, displaying 2D slices out of the 3D data is still often the preferred visualization method. We present new combinations of photorealistic and nonphotorealistic rendering strategies for combined visualization of B-mode and color Doppler data, which are straightforward to implement, flexible, and suited for a wide range of US applications.

Sensorless reconstruction of unconstrained freehand 3D ultrasound data

Freehand 3D ultrasound can be acquired without a position sensor by finding the separations of pairs of frames using information in the images themselves. Previous work has not considered how to reconstruct entirely freehand data, which can exhibit irregularly spaced frames, intersecting frames, nonmonotonic out-of-plane probe motion and significant in-plane motion. This paper presents reconstruction methods that overcome these limitations and are able to robustly reconstruct unconstrained freehand data. The methods are assessed on freehand data sets and compared with reconstructions obtained with a position sensor.

Median filters used for volume reconstruction in freehand 3-d ultrasound

Freehand 3-D ultrasound imaging has been playing an important role in obtaining entire 3-D impression of tissues and organs. Reconstructing a sequence of irregularly located B-scan images into a volume data set with regular voxel arrays is one of key procedures for visualization and data analysis. In this study, we investigated the feasibility of median filters for volume reconstruction in freehand systems. Three median filters were proposed to filter noises and obtain voxel intensities. Qualitative and quantitative comparison results were presented to demonstrate the performance of median filters for volume reconstruction. Compared with conventional distance weighted (DW) interpolation, the three median filters were able to preserve more image details and reconstruct volume data with better quality.

Recent applications of ultrasound: diagnosis and treatment of hepatocellular carcinoma

Ultrasound (US) has the advantages of real-time observation, simple technique, and a noninvasive procedure compared to other imaging modalities. The recent development of digital technologies has enabled the observation of sonograms with improved signal-to-noise ratio, penetration, and spatial and contrast resolutions. Furthermore, microbubble contrast agents have increased the diagnostic ability of US examination, and the use of three-dimensional sonograms is now not unusual. These advances have furthered the usefulness of US for liver tumors in clinical practice. This article reviews the recent applications of US in the diagnosis and treatment of hepatocellular carcinoma.

Three-dimensional ultrasonography of the urinary bladder: preliminary experience of assessment in patients with haematuria

OBJECTIVE

To assess the value of three-dimensional (3D) vs two-dimensional (2D) ultrasonography (US) in the diagnostic evaluation of the urinary bladder in patients with haematuria.

PATIENTS AND METHODS

In all, 42 patients with painless haematuria and/or irritative voiding symptoms were examined with 2D- and 3D-US. US was done with an Acuson Sequoia unit (Siemens Medical Sol. Mountain View, CA, USA) and the Perspective(R) 3D technique, to assess the presence of bladder lesions, including bladder cancer, bladder wall hypertrophy with trabeculation and diverticula, mucosal bladder folds or re-growth of the prostate mimicking a bladder tumour. The imaging findings were compared with cystoscopy and/or bladder biopsy.

RESULTS

In 21 of the 42 patients (50%) cystoscopy with bladder biopsy revealed bladder cancer. Overall, 3D-US gave a correct diagnosis for 36 of 42 patients (86%). All 21 bladder cancers were correctly diagnosed, and 15 (71%) of the 21 benign bladder lesions were correctly identified. By contrast, 2D-US findings gave suspected bladder cancer in all patients.

CONCLUSIONS

3D-US is significantly more accurate than standard 2D-US in the diagnostic evaluation of patients with haematuria. Thus, this diagnostic technique might be useful for routine evaluation of the urinary bladder.

Two- or three-dimensional ultrasonography to predict pulmonary hypoplasia in pregnancies complicated by preterm premature rupture of the membranes

OBJECTIVES

The purpose of this study was to compare 3D lung volume measurements with 2D biometric parameters in predicting pulmonary hypoplasia in pregnancies complicated by preterm premature rupture of the membranes (PPROM).

METHODS

In this prospective study, 18 pregnancies complicated by PPROMs at a mean 21 weeks' gestation (range 14-32 weeks) were examined. The 3D lung volume measurements and the following 2D biometric parameters were measured: thoracic circumference (TC) versus gestational age or femur length (FL), the TC/abdominal circumference (AC) ratio and the thoracic area/heart area (TA/HA) ratio. The sensitivity, specificity, positive and negative predictive value of each measurement to diagnose pulmonary hypoplasia were compared. Pulmonary hypoplasia was diagnosed on the basis of clinical, radiological and/or pathologic criteria.

RESULTS

The incidence of pulmonary hypoplasia was 33.3%. The best diagnostic accuracy for predicting pulmonary hypoplasia was achieved using the 3D lung volume measurements versus gestational age (sensitivity 83%, specificity 100%, positive predictive value 100% and negative predictive value 92%).

CONCLUSIONS

Three-dimensional lung volume measurements seem to be promising in predicting pulmonary hypoplasia prenatally in pregnancies complicated by PPROM.

An adaptive squared-distance-weighted interpolation for volume reconstruction in 3D freehand ultrasound

Volume reconstruction is a key procedure in 3D ultrasound imaging. An algorithm named as squared-distance-weighted (SDW) interpolation has been earlier proposed to reduce the blurring effect in the 3D ultrasonic images caused by the conventional distance weighted (DW) interpolation. However, the SDW parameter alpha, which controls the weight distribution, is a constant assigned by operators so that the interpolation effect is invariant for both sharp edges and speckle noises. In this paper, we introduced a new adaptive algorithm based on SDW interpolation for volume reconstruction of 3D freehand ultrasound. In the algorithm, the local statistics of pixels surrounding each voxel grid were used to adaptively adjust the parameter alpha in SDW. The voxel grids with a higher ratio of local variance and mean in their neighbourhoods would have a smaller alpha to make the image details sharper, while the voxel grids locating in regions with a lower ratio of local variance and mean would have a larger alpha to smooth image content in homogeneous regions, where speckle noise is usually observed and damages the image quality. By comparing the simulation results using the SDW and new adaptive algorithm, it was demonstrated that this new algorithm worked well in both edge preservation and speckle reduction.

Ultrasound imaging

Ultrasound imaging is now in very widespread clinical use. The most important underpinning technologies include transducers, beam forming, pulse compression, tissue harmonic imaging, contrast agents, techniques for measuring blood flow and tissue motion, and three-dimensional imaging. Specialized and emerging technologies include tissue characterization and image segmentation, microscanning and intravascular scanning, elasticity imaging, reflex transmission imaging, computed tomography, Doppler tomography, photoacoustics and thermoacoustics. Phantoms and quality assurance are necessary to maintain imaging performance. Contemporary ultrasonic imaging procedures seem to be safe but studies of bioeffects are continuing. It is concluded that advances in ultrasonic imaging have primarily been pushed by the application of physics and innovations in engineering, rather than being pulled by the identification of specific clinical objectives in need of scientific solutions. Moreover, the opportunities for innovation to continue into the future are both challenging and exciting.

Sensorless freehand 3D ultrasound in real tissue: Speckle decorrelation without fully developed speckle

It has previously been demonstrated that freehand 3D ultrasound can be acquired without a position sensor by measuring the elevational speckle decorrelation from frame to frame. However, this requires that the B-scans contain significant amounts of fully developed speckle. In this paper, we show that this condition is rarely satisfied in scans of real tissue, which instead exhibit fairly ubiquitous coherent scattering. By examining the axial and lateral correlation functions, we propose an heuristic technique to quantify the amount of coherency at each point in the B-scans. This leads to an adapted elevational decorrelation scheme which allows for the coherent scattering. Using the adapted scheme, we demonstrate markedly improved reconstructions of animal tissue in vitro.