Three-dimensional ultrasound imaging

Normal fetal lung volume measured with three-dimensional ultrasound

OBJECTIVES

To construct reference intervals for fetal lung volumes measured longitudinally using three-dimensional (3D) ultrasound, and to evaluate the effect of gender on lung size.

METHODS

This was a prospective, longitudinal study in the obstetric outpatient department of the VU University Medical Center, Amsterdam. Seventy-eight women with uncomplicated pregnancies were scanned three to four times at gestational ages of 18-34 weeks. 3D models of the lung were constructed using the ultrasound machine's software. After the infants were delivered the entire group was reanalyzed with regard to fetal gender. Centiles for the lung volumes of the entire group and for each gender separately were estimated using multilevel modeling.

RESULTS

Charts and tables of right and left fetal lung volumes, using gestational age and estimated fetal weight as the independent variables, are presented. There was a significant difference in lung volume between male and female fetuses at each gestational age. Charts and tables of right and left fetal lung volumes for each gender at gestational ages of 18-34 weeks are also presented.

CONCLUSIONS

We present valid references for volumetric measurements of the right and left fetal lungs in male and female fetuses. The feasibility and reliability of fetal lung volume measurements using 3D ultrasound is good.

Various issues relating to computational fluid dynamics simulations of carotid bifurcation flow based on models reconstructed from three-dimensional ultrasound images

Computational fluid dynamics (CFD) flow simulation techniques have the potential to enhance understanding of how haemodynamic factors are involved in atherosclerosis. Recently, three-dimensional ultrasound has emerged as an alternative to other three-dimensional imaging techniques, such as magnetic resonance angiography (MRA). The method can be used to generate accurate vascular geometry suitable for CFD simulations and can be coupled with Doppler ultrasound to provide physiologically realistic flow boundary conditions. However, there are various ways to utilize the flow data acquired, possibly leading to different results regarding both flow and wall shear stress patterns. A disadvantage of three-dimensional ultrasound for imaging the carotid bifurcation has been established as being the scanning limitation of the jawbone position. This may make artificial extensions of the internal and/or external carotid arteries necessary, which in turn may influence the predicted flow patterns. Flow simulations were carried out for three outflow calculation schemes as well as four geometries with different extensions to the carotid daughter vessels. It was found that variation of flow patterns was more strongly influenced by the outflow conditions than by the extensions of the daughter vessels. Consequently, it is recommended that for future CFD simulations of carotid flow using three-dimensional ultrasound data, the outflow boundary conditions should rely on the most accurate measurement available, and flow data recorded in the common and internal carotid are considered more reliable than data from the external carotid. Even though the extended lengths of the daughter vessels have insignificant effects on the predicted haemodynamic parameters, it would be a safer option to extend the internal carotid by approximately three times the diameter of the common carotid artery.

3-D measurement of body tissues based on ultrasound images with 3-D spatial information

In this study, we developed a new method to perform 3-D measurements between the recorded B-scans using the corresponding spatial location and orientation of each B-scan, without the need to create a 3-D volume. A portable ultrasound (US) scanner and an electromagnetic spatial locator attached to the US probe were used. During data collection, the US probe was moved over the region-of-interest. A small number of B-scans containing interesting anatomical information were captured from different body parts and displayed in a 3-D space with their corresponding locations recorded by the spatial locator. In the B-scan planes, the distance between any two points, as well as the angle between any two lines, could be calculated. In validation experiments, three distances and three angles of a custom-designed phantom were measured using this method. In comparison with the results measured by a micrometer, the mean error of distance measurement was -0.8 +/- 1.7 mm (-2.3 +/- 3.6%) and that of angle measurement was -0.3 +/- 2.9 degrees (-0.1 +/- 4.1%). The lengths of the first metatarsals and the angles between the first metatarsals and the middle part of the tibias of three subjects were measured in vivo using magnetic resonance imaging (MRI) and the US method by two operators before and after MRI scanning. The overall percentage differences of the length and angle measurements were 0.8 +/- 2.2% and 2.5 +/- 3.6%, respectively. The results showed that this US method had good repeatability and reproducibility (interclass correlation coefficient values > 0.75). We expect that this new method could potentially provide a quick and effective approach for the 3-D measurement of soft tissues and bones in the musculoskeletal system.

Moderne Ultraschalltechniken und ihre Anwendungen am kindlichen Harntrakt

In children ultrasound plays a central role in the diagnostic imaging of the urinary tract. It is used most frequently and as a primary diagnostic option. Consequently, innovations in ultrasound technology and ultrasound contrast media have major impact on pediatric urosonography. Harmonic imaging is a modality that produces artifact-free images with high resolution. It has been shown that harmonic imaging is superior to fundamental mode in many urosonographic indications. Color Doppler is an established imaging modality, but its application for diagnosis of stones in the urinary tract, especially in children, is relatively new. The so-called twinkling sign, a color Doppler artifact at the site where one normally expects the acoustic shadow to be, enhances the conspicuity of the stone. A further development is three-dimensional (3D) ultrasound. It offers better volume measurement of the bladder and kidneys than 2D ultrasound. Contrast-enhanced voiding urosonography has already proven to be a valuable alternative in the diagnosis of vesicoureteral reflux. Thus, a significant decrease of radiation exposure has become possible as it replaces the radiological methods. With the introduction of contrast-specific ultrasound imaging modalities, further improvements in voiding urosonography are emerging.

Speckle classification for sensorless freehand 3-D ultrasound

Despite being a valuable tool for volume measurement and the analysis of complex geometry, the need for an external position sensor is holding up the clinical exploitation of freehand 3-D ultrasound. Some sensorless systems have been developed, using speckle decorrelation for out-of-plane distance estimation, but their accuracy is still not as good as that of sensor-based systems. Here, we examine the widely held belief that accuracy can be improved by limiting the distance measurements to patches of ultrasound data containing fully developed speckle. Without speckle detection, we observe that scan separation is systematically underestimated by 33.1% in biological tissue. We describe a number of speckle detectors and show that they reduce the underestimate to about 25%. We conclude that speckle classification can improve the quality of distance estimation, but not sufficiently to achieve accurate, metric reconstruction of the insonified volume.

Endocavitary Three-dimensional Ultrasonographic Assistance for Transvaginal or Transrectal Drainage of Pelvic Fluid Collections

PURPOSE

Determine the feasibility of using three-dimensional ultrasonography (3D US) to assist in planning and performing endocavitary drainage of deep pelvic fluid collections.

MATERIALS AND METHODS

Retrospective review of images and medical records of 16 patients in whom endocavitary 3D US was used during transvaginal or transrectal drainage of 17 deep fluid collections. 3D US was assessed regarding its ability to display the relevant structures, whether new information was provided compared with pelvic computed tomography (CT) and conventional two-dimensional US (2D US) displays, and whether this information altered drainage techniques.

RESULTS

Targeted fluid collections were visualized in all patients. 3D US added information in 11 of 16 patients (69%) that, in turn, resulted in adjustment of interventional technique in eight of 16 patients (50%). Specific features of 3D US that provided new information included the simultaneous display of three orthogonal US images, display of reconstructed US image plane orientations not possible with 2D US, and the ability to interactively scroll images through complex structures to assess for communication between the loculations. An attached needle guide was used in 15 of 16 patients to improve the precision of needle placement.

CONCLUSION

Endocavitary 3D US is feasible for assistance in transvaginal and transrectal drainage procedures, usually adds new information, frequently alters interventional technique, and permits precise access needle placement.

Building three-dimensional images using a time-reversal chaotic cavity

The design of two-dimensional (2-D) arrays for three-dimensional (3-D) ultrasonic imaging is a major challenge in medical and nondestructive applications. Thousands of transducers are typically needed for focusing and steering in a 3-D volume. In this article, we propose a different concept allowing us to obtain electronic 3-D focusing with a small number of transducers. The basic idea is to couple a small number of transducers to a chaotic reverberating cavity with one face in contact with the body of the patient. The reverberations of the ultrasonic waves inside the cavity create at each reflection virtual transducers. The cavity acts as an ultrasonic kaleidoscope multiplying the small number of transducers and creating a much larger virtual transducer array. By exploiting time-reversal processing, it is possible to use collectively all the virtual transducers to focus a pulse everywhere in a 3-D volume. The reception process is based on a nonlinear pulse-inversion technique in order to ensure a good contrast. The feasibility of this concept for the building of 3-D images was demonstrated using a prototype relying only on 31 emission transducers and a single reception transducer.

Prenatal diagnosis of musculoskeletal anomalies

Musculoskeletal anomalies are not uncommon in prenatal life. They can be either sporadic or part of chromosomal syndromes causing prenatal morbidity and mortality. The prenatal diagnosis of musculoskeletal anomalies is based on information assembled from various imaging modalities and from biochemical and genetic workups. The prenatal diagnosis can serve as a prognostic tool and in counseling the parents. Among the imaging methods, ultrasonography is the most popular and cost effective in observing and following fetal development from the very early stages of gestation. Transvaginal sonography can detect and identify most of the normal and the specific pathologic changes very close to the stage of their embryogenic development. From a practical point of view, early detailed transvaginal sonography screening at 14 to 15 weeks of gestation is very useful while late detection at 20 to 23 weeks of gestation may provide some additional information in low-risk pregnancies. Very early screening, even during the ninth week, may be indicated in high-risk pregnancies. Additional genetic counseling is recommended when abnormal findings are suspected. We summarize the diagnostic approach and the information available for the most common musculoskeletal anomalies.

A review of calibration techniques for freehand 3-D ultrasound systems

Three-dimensional (3-D) ultrasound (US) is an emerging new technology with numerous clinical applications. Ultrasound probe calibration is an obligatory step to build 3-D volumes from 2-D images acquired in a freehand US system. The role of calibration is to find the mathematical transformation that converts the 2-D coordinates of pixels in the US image into 3-D coordinates in the frame of reference of a position sensor attached to the US probe. This article is a comprehensive review of what has been published in the field of US probe calibration for 3-D US. The article covers the topics of tracking technologies, US image acquisition, phantom design, speed of sound issues, feature extraction, least-squares minimization, temporal calibration, calibration evaluation techniques and phantom comparisons. The calibration phantoms and methods have also been classified in tables to give a better overview of the existing methods.

A new scanning approach for limb extremities using a water bag in freehand 3-D ultrasound

3-D ultrasound (US) can significantly improve the visualization of musculoskeletal tissues, such as residual limbs, feet and hands. Traditionally, mechanical scanning is normally required to obtain the entire volume of these limb extremities. In this paper, a new scanning approach using a water bag was described to collect the complete volume of various tissues surrounding bones. The water bag was used to contain the limb extremity and the scanning was conducted on its external surface from different directions. The recorded 2-D US images containing complete anatomic information surrounding the bones from different directions were used to form full 3-D volumes of the limb extremities. A plastic auxiliary apparatus was designed to hold the water bag and support the subject's limb part with an armrest. A corresponding algorithm was proposed to remove invalid image information within each sweep by a separating plane defined semiautomatically. Two phantoms were used to test the repeatability and accuracy of the imaging. The distance between two plastic bands attached to a plastic tube filled with US gel measured by a micrometer and from the four reconstructed volumes were 39.03 +/- 0.36 mm and 39.2 +/- 0.5 mm, respectively. The diameter, height and volume of a silicone cylinder phantom measured for the 10 reconstructed volumes were 40.2 +/- 1.4 mm, 12.9 +/- 1.0 mm and 16400 +/- 1600 mm(3), respectively. They agreed with the corresponding results obtained by the micrometer, which were 41.29 +/- 0.13 mm, 12.98 +/- 0.17 mm and 17370 +/- 140 mm(3), respectively. The reconstructed volumes of the two phantoms, a chicken leg in vitro, and human fingers in vivo were also reported. The preliminary results obtained in this study demonstrated that this new scanning approach should have potential for the 3-D US imaging of musculoskeletal extremities using freehand scanning.

Processing and visualizing three-dimensional ultrasound data

This paper describes techniques for the visualization and processing of three-dimensional (3D) ultrasound data. The nature of such data demands specialized algorithms, which differ from those employed for other medical imaging modalities. In this paper, the emphasis is placed on generic processing techniques, which are relevant across a wide range of 3D ultrasound application domains.

Development and validation of an in vivo analysis tool to identify changes in carotid plaque tissue types in serial 3-D ultrasound scans

We have developed a three-dimensional (3-D) B-mode acquisition system suitable for imaging carotid plaques in vivo. A texture classification system using 157 statistical and textural algorithms, previously developed in our laboratory and shown to predict the contents of in vitro carotid plaques, was applied to in vivo 3-D image sets obtained from patients with both symptomatic and asymptomatic carotid artery plaques. Delineation of plaque boundaries is more difficult using in vivo images than in vitro images of excised plaques embedded in agar. This study has examined inter- and intraobserver variability studies to assess the degree of selectivity of the plaque region-of-interest (ROI) and assess the degree of repeatability for potential use in comparing serial scans. An interobserver limit of agreement of +/-12.9% and an intraobserver limit of repeatability of <2% were obtained. These results show that the plaque ROI selection is subjective, but is repeatable within acceptable limits.

A review of calibration techniques for freehand 3-D ultrasound systems

Three-dimensional (3-D) ultrasound (US) is an emerging new technology with numerous clinical applications. Ultrasound probe calibration is an obligatory step to build 3-D volumes from 2-D images acquired in a freehand US system. The role of calibration is to find the mathematical transformation that converts the 2-D coordinates of pixels in the US image into 3-D coordinates in the frame of reference of a position sensor attached to the US probe. This article is a comprehensive review of what has been published in the field of US probe calibration for 3-D US. The article covers the topics of tracking technologies, US image acquisition, phantom design, speed of sound issues, feature extraction, least-squares minimization, temporal calibration, calibration evaluation techniques and phantom comparisons. The calibration phantoms and methods have also been classified in tables to give a better overview of the existing methods.

Redundant system of passive markers for ultrasound scanhead tracking

Scanhead tracking by opto-electronic (OE) systems allows high accuracy in three-dimensional (3-D) freehand ultrasound imaging. In this paper, a new set of methods is proposed and compared with the standard approach [Gram-Schmidt method (GS)]. Three redundancy-based algorithms are introduced to compensate for possible loss of markers during data acquisition: regression plane (RP), multiple Gram-Schmidt (MGS), and center of mass least square (CMLS). When combined with the ultrasound instrument, the root-mean-squared (RMS) uncertainty in locating target points, over a working volume of 420 mm x 490 mm x 100 mm, improved by 7% and 24% using MGS and CMLS method respectively, compared to GS. A lower improvement was obtained with RP methods (5%), using the best marker configuration. In conclusion, CMLS method provides a robust and accurate procedure for 3-D freehand ultrasound scanhead tracking, able to manage possible loss of markers, with interesting perspectives for image fusion and body referenced 3-D ultrasound.

3-D ultrasonographic imaging of the cerebral ventricular system in very low birth weight infants

The purpose of the study was to assess reference ranges for lateral ventricular volume of very low birth weight (VLBW) infants using 3-D ultrasound (US). A total of 108 patients with birth weights < or =1500 g or mother's postmenstrual age < or =32 weeks were examined prospectively in a longitudinal study. Infants in conditions considered being potential confounders such as intraventricular haemorrhage (IVH) and periventricular leukomalacia (PVL) were not included in the calculations. Hence, 77 subjects remained for final statistical analysis. Mean postmenstrual age at birth was 194.5 (27 weeks and 5.5 days) +/- 14 SD days, mean birth weight was 972.5 +/- 236.3 SD g. Reference ranges for lateral ventricle volume were established from serial images. The exponential regression analyses revealed a weekly increase in volume of 6.3% (95% CI 4.4%-8.3%) and 6.6% (95% CI 4.7%-8.6%) in respect to the left and the right ventricle (p < 0.001). Postmenstrual age correlated significantly (p < or = 0.015) with ventricle volume. No significant association to head circumference could be determined. Establishment of reference values for the lateral ventricle volume of VLBW infants should facilitate application of 3-D US in routine diagnostics in neonatal intensive care units and detection of ventricular enlargement as a prediction of risk for poor neurodevelopmental outcome in high-risk cohorts.

Development of a portable 3D ultrasound imaging system for musculoskeletal tissues

3D ultrasound is a promising imaging modality for clinical diagnosis and treatment monitoring. Its cost is relatively low in comparison with CT and MRI, no intensive training and radiation protection is required for its operation, and its hardware is movable and can potentially be portable. In this study, we developed a portable freehand 3D ultrasound imaging system for the assessment of musculoskeletal body parts. A portable ultrasound scanner was used to obtain real-time B-mode ultrasound images of musculoskeletal tissues and an electromagnetic spatial sensor was fixed on the ultrasound probe to acquire the position and orientation of the images. The images were digitized with a video digitization device and displayed with its orientation and position synchronized in real-time with the data obtained by the spatial sensor. A program was developed for volume reconstruction, visualization, segmentation and measurement using Visual C++ and Visualization toolkits (VTK) software. A 2D Gaussian filter and a Median filter were implemented to improve the quality of the B-scan images collected by the portable ultrasound scanner. An improved distance-weighted grid-mapping algorithm was proposed for volume reconstruction. Temporal calibrations were conducted to correct the delay between the collections of images and spatial data. Spatial calibrations were performed using a cross-wire phantom. The system accuracy was validated by one cylinder and two cuboid phantoms made of silicone. The average errors for distance measurement in three orthogonal directions in comparison with micrometer measurement were 0.06+/-0.39, -0.27+/-0.27, and 0.33+/-0.39 mm, respectively. The average error for volume measurement was -0.18%+/-5.44% for the three phantoms. The system has been successfully used to obtain the volume images of a fetus phantom, the fingers and forearms of human subjects. For a typical volume with 126 x 103 x 109 voxels, the 3D image could be reconstructed from 258 B-scans (640 x 480 pixels) within one minute using a portable PC with Pentium IV 2.4 GHz CPU and 512 MB memories. It is believed that such a portable volume imaging system will have many applications in the assessment of musculoskeletal tissues because of its easy accessibility.

Real time computation and temporal coherence of opacity transfer functions for direct volume rendering of ultrasound data

Opacity transfer function (OTF) generation for direct volume rendering of medical image data is an intensely discussed subject. Several automatic methods exist for CT and MRI data, which are not apt for ultrasound data, mainly due to its low signal-to-noise ratio. Furthermore, ultrasound (US) imaging is able to produce time-varying 3D datasets in real time thus opening the door to 4D visualization. However, OTF design for 4D datasets has not been exhaustively discussed until now. We present an efficient solution to generate an optimized OTF for a given 3DUS dataset in real time. Our method results in excellent visualization which we demonstrate using 3D fetus datasets. Finally, we discuss the applicability of our method to 4DUS visualization.

Display of 3-dimensional ultrasonographic images for interventional procedures: volume-rendered versus multiplanar display

OBJECTIVE

The goal of this project was to assess the display of 3-dimensional ultrasonographic images as used for interventional procedures, particularly the conspicuity of various targets and interventional devices, comparing volume-rendered (VR) versus multiplanar reformatted (MPR) display approaches.

METHODS

A series of ultrasonographic phantoms were made from a petroleum gel with cornstarch used to vary the echo texture. Three-dimensional ultrasonographic target and device conspicuity were judged with a 5-point visual rating scale. The MPR image was considered the reference standard. Volume-rendered image conspicuity was judged for combinations of 7 different postprocessing display parameters and compared with MPR images.

RESULTS

Definite visualization of the embedded objects occurred in 92% of MPR and 13% of VR test situations (P < .0001). Volume-rendered display was associated with a mean conspicuity degradation of 2.6 on a scale of 0 through 4 (P < .0001) compared with MPR methods. The proportion of satisfactory VR images was greatest in test situations with a large degree of difference of echogenicity between the background medium and the embedded object. The transparent-type postprocessing rendering modes were superior to the surface-type rendering modes (P < .0001).

CONCLUSIONS

Current 3-dimensional ultrasonographic MPR imaging display in a solid organ environment provides better visualization performance of target and needle conspicuity than VR image display when there are not large differences in the signal levels of targeted structures and devices compared with surrounding tissues. The difficulty in viewing both target and device with VR imaging may restrict its ability to guide interventional procedures in some clinical situations.

Quo vadis medical ultrasound?

The last three decades of development in diagnostic ultrasound imaging and technology are briefly reviewed and the impact of the crucial link between the two apparently independent research efforts, which eventually facilitated implementation of harmonic imaging modality is explored. These two efforts included the experiments with piezoelectric PVDF polymer material and studies of the interaction between ultrasound energy and biological tissue. Harmonic imaging and its subsequent improvements revolutionized the diagnostic power of clinical ultrasound and brought along images of unparalleled resolution, close to that of magnetic resonance imaging (MRI) quality. The nonlinear propagation effects and their implications for both diagnostic and therapeutic applications of ultrasound are also briefly addressed. In diagnostic applications, the impact of these effects on image resolution and tissue characterization is reviewed; in therapeutic applications, the influence of nonlinear propagation effects on highly localized tissue ablation and cauterization is examined. Next, the most likely developments and future trends in clinical ultrasound technology, including 3D and 4D imaging, distant palpation, image enhancement using contrast agents, monitoring, and merger of diagnostic and therapeutic applications by e.g. introducing ultrasonically controlled targeted drug delivery are reviewed. Finally, a possible competition from other imaging modalities is discussed.

Ultrasonic biomedical technology; marketing versus clinical reality

Clinical ultrasound imaging is the most frequently used imaging modality in the world accounting for almost 25% of all imaging studies performed. Hence, manufacturers of commercial ultrasound equipment are committing significant engineering resources to advance the technology behind the modality and to improve the diagnostic capabilities of ultrasound imaging. Consequently, new imaging technologies are constantly being introduced to the market under a host of different trademarked names. Hence, this paper will review many of the recent advances in ultrasound imaging and try to differentiate between developments aimed at marketing and those providing real clinical improvements. In particular, we will describe the technologies behind concepts such as coded ultrasound imaging, real time spatial compounding, tissue harmonic imaging, extended field of view imaging as well as 3D and 4D (i.e., real time 3D) imaging. Some of the latest advances in blood flow imaging e.g., B-flow, advanced dynamic flow (ADF) and automatic optimization methods will also be described.

Three-dimensional ultrasonography for volume measurement of thyroid nodules in children

OBJECTIVE

The aim of this study was to compare the accuracy of thyroid nodule volume measurements performed by 2- and 3-dimensional ultrasonography and to evaluate the dependence of volume measurement results on nodule size and echographic characteristics.

METHODS

Results of multiple 2- and 3-dimensional ultrasonographic volume measurements of thyroid nodules in 102 children with different variants of thyroid nodular disease were reviewed retrospectively. The standardized difference, within-observer variability, and repeatability were estimated for both 2- and 3-dimensional ultrasonography. The mean age of the patients +/- SD in the examined group was 14.9 +/- 2.8 years; the mean volume of thyroid nodules was 0.78 +/- 0.13 mL.

RESULTS

The SD of the normalized difference for 3-dimensional ultrasonography (2.8%) showed the clear superiority of its accuracy over 2-dimensional ultrasonography (15.9%; F test, P < .01). Intraobserver variability and repeatability for both examined methods had significant dependence on the nodule outline. For 2-dimensional ultrasonography, the intraobserver variability increased from 14.0% in nodules with a regular outline to 24.5% in those with an irregular outline (P < .001), and for 3-dimensional ultrasonography, it increased from 5.1% to 9.3% (P < .001). Intraobserver repeatability dropped from 85.4% in regular nodules to 74.6% in irregular nodules (P < .001) for 2-dimensional ultrasonography and from 94.7% to 90.4% (P < .001) for 3-dimensional ultrasonography.

CONCLUSIONS

Volume measurements by 3-dimensional ultrasonography are more accurate, showing lower intraobserver variability and higher repeatability, than those made by 2-dimensional ultrasonography with less dependence on nodule size and echographic characteristics.

Diagnosing breast lesions with contrast-enhanced 3-dimensional power Doppler imaging

OBJECTIVE

To compare mammography with contrast-enhanced 2- and 3-dimensional power Doppler imaging for the diagnosis of breast cancer.

METHODS

Fifty-five patients, who underwent breast biopsies with histopathologic assessment, participated in a study of mammography and contrast-enhanced sonography. Levovist (Berlex Laboratories, Montville, NJ) and Optison (Mallinckrodt, St Louis, MO) were administrated to 22 and 33 patients, respectively. Precontrast and postcontrast 2-dimensional power Doppler data of the lesion were obtained with an HDI 3000 system (Philips Medical Systems, Bothell, WA), and 3-dimensional data were acquired with an LIS 6000A system (Life Imaging Systems Inc, London, Ontario, Canada). Two independent and blinded readers assessed diagnosis. Receiver operating characteristic curves were computed individually and in combination for mammography and 2- and 3-dimensional sonography (before and after contrast). Histopathologic and imaging parameters were compared by Mann-Whitney statistics.

RESULTS

Mammographic findings were available for 50 patients, biopsy for 54, and 2- and 3-dimensional sonographic images for 53 and 52, respectively. Of the 50 patients who had all 4 measures, 15 (30%) had malignancies. The areas under the receiver operating characteristic curve for the diagnosis of breast cancer were 0.51 for 2-dimensional contrast-enhanced imaging, 0.60 for 3-dimensional power Doppler imaging, and 0.76 for 3-dimensional contrast-enhanced imaging (P < .01). Mammography produced an area of 0.86, which increased when combined with 3-dimensional contrast-enhanced imaging to 0.90 and with all sonographic modalities to 0.96 (P < .001). The histopathologic diagnosis of benign or malignant correlated with the presence or absence of anastomoses and with the degree of vascularity assessed with contrast-enhanced 3-dimensional power Doppler imaging (P = .007 and .02).

CONCLUSIONS

Contrast-enhanced 3-dimensional power Doppler imaging increases the ability to diagnose breast cancer relative to conventional 2- and 3-dimensional sonographic imaging.

Clinical application of surface mode on three-dimensional ultrasonography: a preliminary study

To investigate the methology and evaluate the clinical value of surface mode on three-dimensional ultrasonography (3DUS) in static anatomical structures, 62 patients with various diseases were studied. The equipment used here was Voluson 530D 3DUS imaging system and 3D volume transducer with frequency being 3.0-5.0 MHz. The 3DUS rendering method was surface mode. The results showed that: 1) Surface mode of 3DUS could demonstrate clearly the anatomical characteristics of the region-of-interest (ROI) and the inner wall of lesions or organs that contained fluid. The anatomic details, such as location, size, shape, and number of the ROI, could be visualized intuitively; 2) The outer anatomic features (e.g. contour, edge, configuration, etc.) of some organs or lesions surrounded by fluid could be displayed clearly. It could be concluded that surface mode on 3DUS could provide more diagnostic information than two-dimensional ultrasonography (2DUS) in some cases and could served as a beneficial supplement to 2DUS in clinical practice.

Visualisation of 4-D colour and power Doppler data

Mechanically scanned, cardiac-gated, 4-D colour Doppler and power Doppler data were acquired and rendered using multiplanar slice display, surface-fitting (S-F) and direct volume rendering (DVR), with interactive viewpoint control or tool command language (Tcl)-scripted generation of animation sequences across the cardiac cycle. S-F applied the marching cubes algorithm within a YCbCr colour space to extract time-varying Doppler regions; supplementally generated surfaces enclosed all regions across the full cardiac cycle, partially to alleviate the problem of incomplete vessel filling. DVR used integrated intensity, maximum intensity and front-to-back projection; the latter applied an opacity function to the Cb, Cr and Y colour channels to control the appearance of the blood flow signal relative to the background B-mode image. Our most detailed display was a hybrid approach that combined multiplanar slicing and DVR.

Choledochal cysts in children: evaluation with three-dimensional sonography

In this report, we describe the application of 3-dimensional (3D) sonography for diagnosing choledochal cysts in 3 girls who were 18 months, 2 years, and 11 years old. The 3D images that were obtained during the sonographic examination revealed that all 3 patients had a type I choledochal cyst and also demonstrated dilatation of the biliary tracts. The 3 patients then underwent surgical excision of their cysts, cholecystectomy, and hepaticojejunostomy. Besides its other clinical applications, 3D sonography promises to be a valuable adjunct to conventional 2-dimensional imaging for the evaluation of choledochal cysts in pediatric patients.

Three-dimensional power Doppler imaging in depicting vascularity in hepatocellular carcinoma

OBJECTIVE

To assess the ability of three-dimensional power Doppler imaging to depict vascularity in hepatocellular carcinoma.

METHODS

Forty-three patients with hepatocellular carcinomas were subjected to two- and three-dimensional power Doppler imaging, and 14 of them also underwent angiography. The delineated amounts of intratumoral Doppler signals were compared between 2 methods of power Doppler imaging in 43 patients. In the 14 patients who also underwent angiography, the patterns of blood supply depicted by 2 methods of power Doppler imaging were compared with that depicted by angiography, and the intratumoral vascularity on three-dimensional projection images and angiograms was also quantitatively assessed by calculating the vascularity-area ratio with graphics software.

RESULTS

In comparison with two-dimensional power Doppler imaging, three-dimensional power Doppler imaging was subjectively determined as showing more intratumoral Doppler signals in 32 (74.4%) of the 43 lesions. The accuracies in depicting vascular patterns were 64.3% (9 of 14) for three-dimensional projection images and 14.3% (2 of 14) for two-dimensional slices compared with the results of angiography. The vascularity-area ratios on three-dimensional power Doppler imaging projections and angiograms were 46.0% +/- 25.6% and 48.5% +/- 22.5% (mean +/- SD), respectively (P > .05). Three-dimensional projection images correlated significantly with angiograms in quantifying the vascularity (gamma = 0.87; P < .001).

CONCLUSIONS

A three-dimensional power Doppler projection image gives a better overall picture of vascular distribution than a two-dimensional slice and correlates with angiography significantly for delineating vascularity in hepatocellular carcinoma.

Rapid registration for wide field of view freehand three-dimensional ultrasound

A freehand scanning protocol is the only way to acquire arbitrary large volumes of three-dimensional ultrasound (US) data. For some applications, multiple freehand sweeps are required to cover the area of interest. Aligning these multiple sweeps is difficult, typically requiring nonrigid image-based registration as well as the readings from the spatial locator attached to the US probe. Conventionally, nonrigid warps are achieved through general elastic spline deformations, which are expensive to compute and difficult to constrain. This paper presents an alternative registration technique, where the warp's degrees of freedom are carefully linked to the mechanics of the freehand scanning process. The technique is assessed through an extensive series of in vivo experiments, which reveal a registration precision of a few pixels with comparatively little computational load.

Usefulness of three-dimensional sonography in procedures of ablation for liver cancers: initial experience

OBJECTIVE

To investigate the usefulness of three-dimensional sonography in procedures of ablation for liver cancers.

METHODS

Two- and three-dimensional sonography were used in guiding 18 chemical ablation procedures (7 with boiling carboplatin ablation and 11 with ethanol ablation) and 21 radio frequency ablation procedures for treatment of liver cancers. The applicator conspicuity depicted by the 2 imaging modalities, the confidence level of the operator in determining the position relationship between the applicator and the tumor using the 2 imaging modalities, and the alteration of ablation procedures were evaluated.

RESULTS

Three-dimensional sonography was better than two-dimensional sonography in delineation of multitined, expandable electrode tips in radio frequency ablation procedures, whereas the 2 modalities were equal in depicting percutaneous transhepatic cholangiography needle tips in chemical ablation procedures. Three-dimensional sonography significantly enhanced the confidence level in defining the spatial relationship between applicator and tumor in comparison with two-dimensional sonography (P < .01). Suboptimal applicator placement was detected in 6 (15%) of 39 ablation procedures on three-dimensional sonography: 3 chemical ablation procedures and 3 radio frequency ablation procedures. Applicator adjustment was required in 3 chemical ablation procedures. In 15 (38%) of 39 procedures, three-dimensional sonography allowed better visualization of the position relationship between the applicator and adjacent critical structures.

CONCLUSIONS

Three-dimensional sonography was useful in delineation of expandable radio frequency electrodes, improvement of operator confidence level, determination of applicator placement, and visualization of the position relationship between the applicator and adjacent critical structures during procedures of liver cancer ablation under image guidance.

A robust and automatic method for evaluating accuracy in 3-D ultrasound-based navigation

We present a robust and automatic method for evaluating the 3-D navigation accuracy in ultrasound (US) based image-guided systems. The method is based on a precisely built and accurately measured phantom with several wire crosses and an automatic 3-D template matching by correlation algorithm. We investigated the accuracy and robustness of the algorithm and also addressed optimization of algorithm parameters. Finally, we applied the method to an extensive data set from an in-house US-based navigation system. To evaluate the algorithm, eight skilled observers identified the same wire crosses manually and the average over all observers constitutes our reference data set. We found no significant differences between the automatic and the manual procedures; the average distance between the point sets for one particular volume (27 point pairs) was 0.27 +/- 0.17 mm. Furthermore, the spread of the automatically determined points compared with the reference set was lower than the spread for any individual operator. This indicates that the automatic algorithm is more accurate than manual determination of the wire-cross locations, in addition to being faster and nonsubjective. In the application example, we used a set of 35 3-D US scans of the phantom under various acquisition configurations. The US frequency was 6.7 MHz and the average target depth was 6 cm. The accuracy, represented by the mean distance between automatically-determined wire-cross locations and physically measured locations, was found to be 1.34 +/- 0.62 mm.

Prostate boundary detection from ultrasonographic images

OBJECTIVE

Prostate diseases are very common in adult and elderly men, and prostate boundary detection from ultrasonographic images plays a key role in prostate disease diagnosis and treatment. However, because of the poor quality of ultrasonographic images, prostate boundary detection still remains a challenging task. Currently, this task is performed manually, which is arduous and heavily user dependent. To improve the efficiency by automating the boundary detection process, numerous methods have been proposed. We present a review of these methods, aiming to find a good solution that could efficiently detect the prostate boundary on ultrasonographic images.

METHODS

A full description of various methods is beyond the scope of this article; instead, we focus on providing an introduction to the different methods with a discussion of their advantages and disadvantages. Moreover, verification methods for estimating the accuracies of the algorithms reported in the literature are discussed as well.

RESULTS

From the investigation, we summarize several key issues that might be confronted and project possible future research.

CONCLUSIONS

Those model-based methods that minimize user involvement but allow for interactive guidance of experts will likely be most immediately successful.

Estimation of liver tumor volume using a three-dimensional ultrasound volumetric system

The usefulness of a new three-dimensional ultrasound (3DUS) volumetric system developed recently was validated in volume measurement of liver tumor in the present study. The system was used to estimate the volumes of 22 regular phantoms, 25 irregular phantoms and 37 liver tumors from 33 patients. The results showed that the consumed time of measurement with the system ranged from 1 to 15 min, depending on different rotation angles. The measured volumes at different rotation angles all significantly correlated with the true volumes and there were no significant differences among measured volumes at different angles. The measurement error of 3DUS was 0.3% +/- 3.3% in regular phantoms, -0.4% +/- 3.7% in irregular phantoms and 0.9% +/- 11.3% in liver tumors, respectively, as compared with -5.3 +/- 9.4%, 13.6 +/- 28.0% and 15.3 +/- 37.3% for two-dimensional ultrasound, respectively (all p < 0.05). The volume estimation with 3DUS also had significant intraobserver and interobserver reproducibility both in vitro and in vivo. It can be concluded that the new system that we used can greatly reduce the consumed time and manual labor for volume measurement with high accuracy and reproducibility. 3DUS volumetry using the new system is more acceptable and valuable in clinical practice and is expected to be useful for evaluation of the efficacy of tumor therapy in situ in patients with hepatic tumors.

3-D US frame positioning using speckle decorrelation and image registration

In this paper, a new positioning system is proposed for the 3-D ultrasound (US). This system combines the image registration technique and speckle decorrelation algorithm to accurately position sequential ultrasonic images without any additional positioning hardware. The speckle decorrelation algorithm estimates the relative distance of two neighboring frames and the image registration technique gets the range of the whole 3-D ultrasonic data set and makes slight modification on each frame's position. The image registration technique is based on the reference image, which is perpendicular to the 3-D ultrasonic data set. This reference image intersects each frame of the 3-D ultrasonic data set in a line. For each frame, the intersectional line is first found and then the location in the reference image can be used to estimate the position of this frame. This system uses the data set of consecutive 2-D freehand-scanned US B-mode images to construct the 3-D US volume data, and it can be integrated into the 3-D US volume rendering system.

Angiographic assessment of coronary stenoses: a review of the techniques

This article reviews the fundamental techniques to quantify the physiological severity of (coronary) stenoses. Although a wide survey of different techniques and applications is provided, the focus of this review is on: 1) the assessment of the immediate effect of the stenoses on blood flow (i.e., the hemodynamic severity), and not on the assessment of the pathology of the vessel itself; 2) the flow reserve methods to defining the physiological severity of stenoses; and 3) the determination of blood flow and tissue perfusion by X-ray angiography (a short survey of other imaging modalities is provided as well). Although the practical implementation of the techniques is illustrated by applying them to coronary stenoses, most of the issues involved are of interest in other application areas (using other imaging modalities) as well. This review consists of four parts. The first part deals with the definition of stenoses severity; the second part with tracer kinetic theory necessary to determine flows by imaging; the third part focusses on (cardiac) imaging modalities, with an emphasis on X-ray angiography; and the last part illustrates the practical implementation of the techniques in cardiology.

Accuracy and reproducibility of CFD predicted wall shear stress using 3D ultrasound images

Computational fluid dynamics (CFD) flow simulation techniques have the potential to enhance our understanding of how haemodynamic factors are involved in atherosclerosis. Recently, 3D ultrasound has emerged as an alternative to other 3D imaging techniques, such as magnetic resonance angiography (MRA). The method can be used to generate realistic vascular geometry suitable for CFD simulations. In order to assess accuracy and reproducibility of the procedure from image acquisition to reconstruction to CFD simulation, a human carotid artery bifurcation phantom was scanned three times using 3D ultrasound. The geometry was reconstructed and flow simulations were carried out on the three sets as well as on a model generated using computer aided design (CAD) from the geometric information given by the manufacturer. It was found that the three reconstructed sets showed good reproducibility as well as satisfactory quantitative agreement with the CAD model. Analyzing two selected locations probably representing the 'worst cases,' accuracy comparing ultrasound and CAD reconstructed models was estimated to be between 7.2% and 7.7% of the maximum instantaneous WSS and reproducibility comparing the three scans to be between 8.2% and 10.7% of their average maximum.

Comparison of three- and two-dimensional sonography in diagnosis of gallbladder diseases: preliminary experience

OBJECTIVE

To compare three-dimensional sonography with two-dimensional sonography for diagnosis of gallbladder diseases.

METHODS

Sixty-three patients with gallbladder diseases were examined with two- and three-dimensional sonography. The morphologic features presented on both modalities were analyzed, and the diagnostic accuracies of both modalities were evaluated and compared.

RESULTS

Both two- and three-dimensional sonography facilitated correct diagnosis in all patients with gallstones. Three-dimensional sonography had no influence on the diagnosis of gallstones compared with two-dimensional sonography. Three-dimensional sonography showed the granular surfaces in 18 (81.8%) of 22 cases of polypoid lesions and the pedunculated fundus in 19 (86.4%) of 22, whereas two-dimensional sonography displayed them in 10 (45.5%) and 3 (13.6%) of 22, respectively (P < .05 and .001). Three- and two-dimensional sonography made correct differential diagnoses between non-neoplastic and neoplastic polyps in 20 (90.9%) and 12 (54.5%) of 22, respectively (P < .05). In gallbladder carcinoma, both three- and two-dimensional sonography accurately showed all the associated gallstones and intrahepatic bile duct dilatation. Two-dimensional sonography could not correctly define the locations of the lesions in 2 (28.6%) and tumor extension in 1 (14.3%) of 7 cases with pathologically proved gallbladder cancer, whereas three-dimensional sonography improved the diagnosis in these cases.

CONCLUSIONS

Three-dimensional sonography adds no advantages for diagnosis of gallstones compared with two-dimensional sonography, but it is better than two-dimensional sonography for differential diagnosis of gallbladder polyps and may improve the localization and staging for gallbladder carcinoma; however, additional studies are needed for further determination.

A high frequency amplitude-steered array for real-time volumetric imaging

Real-time three-dimensional acoustic imaging is difficult in water or tissue because of the slow speed of sound in these media. Conventional pulse-echo data collection, which uses at least one transmit pulse per line in the image, does not allow for the real-time update of a volume of data at practical ranges. Recently, a linear amplitude-steered array was presented that allows the collection of a plane of data with a single transmit pulse by spatially separating frequencies in the lateral direction. Later, by using a linear array with frequency separation in the vertical direction and rotating the array in the horizontal direction, volumetric data were collected with a small number of transmit pulses. By expanding the linear array to a two-dimensional array, data can now be collected for volumetric imaging in real time. In this study, the amplitude-steered array at the heart of a real-time volumetric sonar imaging system is described, giving the design of the array and describing how data are collected and processed to form images. An analysis of lateral resolution in the vertical and horizontal directions shows that resolution is improved in the direction of frequency separation over systems that use a broad transmit beam. Images from simulated data are presented.

Approach to 3-d ultrasound high resolution imaging for mechanically moving large-aperture transducer based upon Fourier transform

A new three-dimensional (3-D) acoustic image formation technique is proposed that is based on the transmission of wide bandwidth pulse signals and the application of the 3-D fast Fourier transform. A solution to the Helmholz wave equation has been obtained using the Born approximation. The solution contains analytical expressions for the spatial spectra of the transmit and receive radiation patterns for transducers of various geometries with lenses of fixed focal distances. It has been shown that the proposed algorithms allow for radiation patterns with constant widths at depths both behind and in front of the focal point, starting practically from the plane of the transducer. The theoretical and experimental investigations and computer simulation for both spherical and rectangular transducer shapes have been performed. The results were used to estimate the beamwidths and the side lobe levels. A variant of the linear array has been studied for cylindrical lens of a fixed focal distance moving in a lateral direction. It has been shown that, in this case, a high resolution (of the order of a few wavelengths) can be achieved along all three Cartesian coordinates at a very high scanning velocity. The influence of the moving scatterers' velocity in inhomogeneous medium on the spatial radiation pattern characteristics has been estimated.

Comparison of two-dimensional and three-dimensional sonography in evaluating fetal malformations

PURPOSE

We assessed the differences between 2-dimensional (2D) and 3-dimensional (3D) sonography (US) in evaluating fetal malformations.

METHODS

Both 2D US and 3D US were used to examine pregnant women whose fetuses had malformations. The diagnostic information provided by the modalities was evaluated and compared.

RESULTS

A total of 62 malformations were confirmed by postnatal or postmortem follow-up in 41 fetuses of 40 pregnant women. 2D US made a definite and correct diagnosis of 49 malformations (79%), whereas 3D US definitely diagnosed 58 malformations (94%) (p < 0.01). 3D US definitely diagnosed all the abnormalities in 38 fetuses (93%), whereas 2D US did so in only 32 fetuses (78%) (p < 0.05). In 35 (60%) of the 58 malformations revealed by both 3D US and 2D US, the former provided more diagnostic information than the latter. 3D US was particularly superior to 2D US in evaluating fetal malformations of the cranium and face, spine and extremities, and body surface.

CONCLUSIONS

In comparison with 2D US, 3D US improves the diagnostic capability by offering more diagnostic information in evaluating fetal malformations, particularly in displaying fetal malformations of the cranium and face, spine and extremities, and body surface. 3D US is a valuable adjunct to 2D US in prenatal diagnosis.

The influence of maternal hematocrit on placental development from the first to the second trimesters of pregnancy

OBJECTIVES

To study the influence of maternal hematocrit (Ht) and hemoglobin (Hb) levels on placental size and growth in the first and mid-second trimesters of pregnancy.

SUBJECTS/METHODS

This was a prospective study performed at the fetal medicine unit of a university hospital. One hundred and eighty-one women with a singleton pregnancy were recruited at 11-14 weeks' gestation. For each case three scans of the placenta were performed, the first at recruitment and the following two at 3-week intervals. The volume of the placenta was measured at each visit using a three-dimensional ultrasound scanner. The maternal Hb and Ht were measured within 2 weeks of the first scan.

RESULTS

The placental growth during the second trimester was inversely related to the Ht levels (r = -0.29, P = 0.001). It was also related to the Hb level (r = -0.20, P = 0.021). An increase of 0.1 units of Ht was associated with 38% less growth of the placenta (95% confidence interval: 18-54% less growth).

DISCUSSION

This study demonstrates the effects of maternal environment on placental growth. Our data suggest that the levels of Ht appear to affect the placental growth during the second trimester. Further studies on the factors that regulate placental growth are needed to elucidate the pathophysiology of these interactions and their effect on pregnancy outcome.

Three-dimensional gray scale volume rendering of the liver: preliminary clinical experience

OBJECTIVE

To investigate the potential clinical usefulness of three-dimensional gray scale volume rendering in the liver.

METHODS

Sixty-two patients were enrolled in the study and categorized into 2 groups: group I with ascites and group II without. Two types of volume-rendering modes, i.e., surface and transparent, were used to obtain the three-dimensional images. The data were reviewed to identify the differences between two- and three-dimensional images of the liver in each subject.

RESULTS

In group I, three-dimensional sonography was superior to two-dimensional sonography in terms of surface features, edges, overall three-dimensional impression, image clarity, and structural relationships. However, it seemed that three-dimensional sonography in the surface mode was inferior to two-dimensional sonography in showing intrahepatic structures, because it had decreased resolution. In group II, three-dimensional sonography was superior to two-dimensional sonography with respect to the continuity of intrahepatic vessels, overall three-dimensional impression of the vessels, image clarity, and the relationship between lesions and neighboring vessels. However, the resolution of the lesions was decreased in 7 cases of hepatocellular carcinoma.

CONCLUSIONS

Our experience suggests that three-dimensional gray scale volume rendering of the liver provides more diagnostic information than two-dimensional sonography; however, further studies are needed to evaluate its clinical importance.

Future directions for cryosurgery computer treatment planning

Computer treatment planning for cryosurgery is an area of research and development that will greatly assist the practicing physician and will promote improved quality assurance for clinical procedures. Good planning and precision image-guided treatment delivery are complementary in achieving an optimal treatment outcome. State-of-the-art cryosurgery treatment planning systems are at an early stage of development in comparison with radiation treatment planning systems for external beams. Using 30 years of progress in the area of radiation treatment planning as a guide, this article presents a summary of the avenues for research and development in cryosurgery treatment planning that are likely to accelerate the practical application of precision cryosurgery to a broad spectrum of anatomical sites. Emphasis is placed on prostate cryosurgery, imaging techniques, and recommendations for manufacturers of these systems. Optimization of the clinical procedure in the planning stage using mathematical algorithms to define the positioning and operation of cryoprobes is discussed.

Prenatal diagnosis of fetal multicystic dysplastic kidney with two-dimensional and three-dimensional ultrasound

Fetal multicystic dysplastic kidney (MCDK) may have grave prognosis and prenatal diagnosis of MCDK by ultrasound (US) is very important. Traditionally, MCDK is diagnosed by 2-D US. Recently, 3-D US has emerged, and may overcome the weakness of 2-D US. In this series, we retrospectively analysed the cases of MCDK diagnosed by prenatal 2-D and 3-D US from November 1995 to March 2002 to evaluate the prenatal sonographic characteristics of this disease and to compare the efficacy of 2-D and 3-D US. The 2-D assessment included the lesion of MCDK, the amniotic fluid volume and associated anomalies. The 3-D assessment included three-orthogonal multiplanar views and various rendering modes of reconstruction of MCDK. In total, 28 cases were diagnosed by prenatal 2-D and 3-D US. Within the study period, 2-D US detected 100% of MCDK, as did 3-D US, and revealed that left, right and bilateral MCDK were in 46.4%, 28.6%, and 25% of cases, respectively. Oligohydromnios was present in 6 cases (21.4%). In addition, 3-D US showed fetal MCDK vividly and provided a whole view of the disease that assisted comprehension of the severity and extent better than 2-D US. In conclusion, although 2-D US detected all the cases of fetal MCDK in utero as did 3-D US, the 3-D images generated by various rendering modes can further assist in evaluating the severity and extent of MCDK, with a novel view that substantially aids the medical team in prenatal management and the parents in genetic consultation.

Contrast enhanced vascular three-dimensional ultrasound imaging

In other imaging modalities three-dimensional (3D) data displays are well established; not so in ultrasound. Due to the real-time requirements of ultrasound the time available to compute 3D displays is limited, particularly when flow data is acquired with Doppler techniques. Consequently, it is only recently that improvements in computer processing power have resulted in useful vascular 3D ultrasound scans. Many manufacturers have now implemented free-hand 3D power Doppler capabilities on their scanners. However, to obtain flow signals from smaller vessels associated e.g., with tumor neovascularity, may very well require the introduction of a microbubble based ultrasound contrast agent into the blood stream. Given the up to 30 dB enhancement of Doppler signals produced by the contrast microbubbles quite spectacular vascular 3D images are feasible. Moreover, new contrast imaging techniques, such as harmonic imaging, have now permitted 3D vascular information to be acquired and displayed in grayscale with the associated improvement in resolution. In this paper we will review different aspects of contrast enhanced vascular 3D ultrasound imaging including implementation, contrast specific techniques and in vivo imaging.

Ultrasound imaging in lower limb prosthetics

The biomechanical interaction between the residual limb and the prosthetic socket determines the quality of fit of the socket in lower limb prosthetics. An understanding of this interaction and the development of quantitative measures to predict the quality of fit of the socket are important for optimal socket design. Finite-element modeling is used widely for biomechanical modeling of the limb/socket interaction and requires information on the internal and external geometry of the residual limb. Volumetric imaging methods such as X-ray computed tomography, magnetic resonance imaging, and ultrasound have been used to obtain residual limb shape information. Of these modalities, ultrasound has been introduced most recently and its development for visualization in prosthetics is the least mature. This paper reviews ultrasound image acquisition and processing methods as they have been applied in lower limb prosthetics.

Image-guided acoustic therapy

The potential role of therapeutic ultrasound in medicine is promising. Currently, medical devices are being developed that utilize high-intensity focused ultrasound as a noninvasive method to treat tumors and to stop bleeding (hemostasis). The primary advantage of ultrasound that lends the technique so readily to use in noninvasive therapy is its ability to penetrate deep into the body and deliver to a specific site thermal or mechanical energy with submillimeter accuracy. Realizing the full potential of acoustic therapy, however, requires precise targeting and monitoring. Fortunately, several imaging modalities can be utilized for this purpose, thus leading to the concept of image-guided acoustic therapy. This article presents a review of high-intensity focused ultrasound therapy, including its mechanisms of action, the imaging modalities used for guidance and monitoring, some current applications, and the requirements and technology associated with this exciting and promising field.

Tissue motion and elevational speckle decorrelation in freehand 3D ultrasound

3D positioning is essential for quantitative volume analysis in 3D ultrasound. Particularly for freehand scanning without an external positioning device, such information must be estimated by analyzing the original 2D images prior to 3D reconstruction. Previous work on freehand 3D positioning has focused on elevational displacement estimation using speckle decorrelation for linear scans. However, the effects of other types of motion have been ignored. Given that all types of motion potentially introduce speckle decorrelation, the accuracy of the elevational displacement estimation is likely to be diminished by the presence of motions of other types. In the present study, simulations were performed to probe the effects of various motions on elevational displacement estimation. In particular, the effects of rotational motions on image correlation are investigated in detail. It is found that these motions significantly affect the estimation results and thus should be taken into account when reconstructing the 3D image. In addition, speckle variations also affect the estimation even when only elevational motion is present. Finally, full motion analysis in freehand scanning may not be possible by only using speckle correlation analysis unless speckle variations can be reduced and the correlation distribution under complex motion can be obtained.

Three-dimensional intraoperative ultrasound of vascular malformations and supratentorial tumors

The benefits and limits of a magnetic sensor-based 3-dimensional (3D) intraoperative ultrasound technique during surgery of vascular malformations and supratentorial tumors were evaluated. Twenty patients with 11 vascular malformations and 9 supratentorial tumors undergoing microsurgical resection or clipping were investigated with an interactive magnetic sensor data acquisition system allowing freehand scanning. An ultrasound probe with a mounted sensor was used after craniotomies to localize lesions, outline tumors or malformation margins, and identify supplying vessels. A 3D data set was obtained allowing reformation of multiple slices in all 3 planes and comparison to 2-dimensional (2D) intraoperative ultrasound images. Off-line gray-scale segmentation analysis allowed differentiation between tissue with different echogenicities. Color-coded information about blood flow was extracted from the images with a reconstruction algorithm. This allowed photorealistic surface displays of perfused tissue, tumor, and surrounding vessels. Three-dimensional intraoperative ultrasound data acquisition was obtained within 5 minutes. Off-line analysis and reconstruction time depends on the type of imaging display and can take up to 30 minutes. The spatial relation between aneurysm sac and surrounding vessels or the skull base could be enhanced in 3 out of 6 aneurysms with 3D intraoperative ultrasound. Perforating arteries were visible in 3 cases only by using 3D imaging. 3D ultrasound provides a promising imaging technique, offering the neurosurgeon an intraoperative spatial orientation of the lesion and its vascular relationships. Thereby, it may improve safety of surgery and understanding of 2D ultrasound images.

Freehand three-dimensional Doppler demonstration of monochorionic vascular anastomoses in vivo: a preliminary report

OBJECTIVES

To demonstrate the three-dimensional vascular anatomy of monochorionic placental anastomoses in vivo, both arterioarterial and arteriovenous.

DESIGN

Two-dimensional placental mapping techniques were used to locate arterioarterial and arteriovenous anastomoses. A freehand sweep was performed across the anastomotic site, and multiple images were stored to disk, at 17 Hz. These were then segmented to show only color information (vascular flow) using purpose-designed software (CQ analysis) and the files reconstructed into a three-dimensional volume, for multidirectional viewing and movie generation.

RESULTS

Both arterioarterial and arteriovenous anastomoses could be visualized in detail. Reconstruction of a dual volume of gray-scale and segmented color images allowed recreation of the vascular anatomy within the placental substance, as well as retention of the original directional flow information.

CONCLUSIONS

Detailed anastomotic anatomy can be demonstrated three dimensionally in vivo. Given the increasing evidence implicating various anastomotic configurations in pathological intertwin transfusion, this technique may prove useful in the antenatal assessment and treatment of monochorionic twin pregnancies.