Minimally-compressive, three- and four-dimensional ultrasound imaging of the clitoris: a feasibility study

There has been no objective means for imaging the three-dimensional (3D) morphology of the clitoris-a poorly understood, complex structure. A Live 3D ultrasound system with a matrix-array transducer was used for data acquisition from eight women. The transducer was positioned in front of and about 3 cm away from the clitoris, with a gel pad or water pad being placed in between. The pads allowed the delicate structures to be imaged without noticeable deformation. Quality images could be obtained with use of a water pad in all patients. The imaging volume was big enough to cover the clitoral glans and body simultaneously, allowing real-time 3D visualisation. To cover the entire clitoris, the probe was moved from one side of the crus to the other, or a four subvolume scan was performed. 3D clitoral anatomy was depicted from 71% of 51 water pad data-sets. The study demonstrates the feasibility of obtaining 3D clitoral ultrasound images. This will improve scientific and clinical understanding of the clitoral role in sexual activity. The minimally-compressive scanning offers an opportunity to visualise dynamic 3D (4D) morphology of other deformable body parts.     

Ultrasound imaging in three and four dimensions

Three-dimensional (3D) reconstruction of ultrasound images was first demonstrated nearly 15 years ago, but only now is becoming a clinical reality. In the meantime, methods for 3D reconstruction of CT and MRI images have achieved an advanced state of development, and 3D imaging with these modalities has been applied widely in clinical practice. 3D applications in ultrasound have lagged behind CT and MRI, because ultrasound data is much more difficult to render in 3D, for a variety of technical reasons, than either CT or MRI data. Only in the past few years has the computing power of ultrasound equipment reached a level adequate enough for the complex signal processing tasks needed to render ultrasound data in three dimensions. At this point in time, the clinical application of 3D ultrasound is likely to advance rapidly, as improved 3D rendering technology becomes more widely available. This article is a review of the present status of 3D ultrasound imaging. It begins by comparing the characteristics of CT, MRI, and ultrasound image data that either make these data amenable or not amenable to 3D reconstruction. The article then considers the technical features involved with acquiring an ultrasound 3D data set and the mechanisms for reconstructing the images. Finally, the article reviews the literature that is available regarding clinical application of 3D ultrasound in obstetrics, ultrasound, the abdomen, and blood vessels.     

A cognitive engineering framework for the specification of information requirements in medical imaging: application in image-guided neurosurgery

Purpose

This study proposes a framework coming from cognitive engineering, which makes it possible to define what information content has to be displayed or emphasised from medical imaging, for assisting clinicians according to their level of expertise in the domain.

Method

We designed a rating scale to assess visualisation systems in image-guided neurosurgery with respect to the depiction of the neurosurgical work domain. This rating scale was based on a neurosurgical work domain analysis. This scale has been used to evaluate visualisation modes among neurosurgeons, residents and engineers. We asked five neurosurgeons, ten medical residents and ten engineers to rate two visualisation modes from the same data (2D MR image vs. 3D computerised image). With this method, the amount of abstract and concrete work domain information displayed by each visualisation mode can be measured.

Results

A global difference in quantities of perceived information between both images was observed. Surgeons and medical residents perceived significantly more information than engineers for both images. Unlike surgeons, however, the amount of information perceived by residents and engineers significantly decreased as information abstraction increased.

Conclusions

We demonstrated the possibility of measuring the amount of work domain information displayed by different visualisation modes of medical imaging according to different user profiles. Engineers in charge of the design of medical image-guided surgical systems did not perceive the same set of information as surgeons or even medical residents. This framework can constitute a user-oriented approach to evaluate the amount of perceived information from image-guided surgical systems and support their design from a cognitive engineering point of view.     

Three-dimensional ultrasound in the evaluation of fetal anomalies.

OBJECTIVES: To determine the additional information and clinical impact provided by three-dimensional ultrasound (3D US) imaging of fetal anomalies compared to conventional 2-dimensional ultrasound (2D US). MATERIALS AND METHODS: Sixty-three patients with 103 anomalies were scanned prospectively with both 2D and 3D US. Each anomaly was reviewed by one or more fetal imaging specialists to determine whether the 3D US data were advantageous, equivalent, or disadvantageous when compared with 2D US images. Clinical impact and pathologic or clinical outcome were determined in all cases. RESULTS: The 3D US images provided additional information in 53 anomalies (51%), were equivalent to 2D US images in 46 anomalies (45%), and were disadvantageous in four anomalies (4%). The 3D US was most helpful in evaluating fetuses with facial anomalies, hand and foot abnormalities and axial spine and neural tube defects. Planar images derived from 3D US volume data sets generally were more helpful for diagnostic purposes, whereas rendered 3D US images were more useful as a point of reference and were better appreciated by patients in understanding fetal abnormalities. Additional information provided by 3D US images impacted clinical management in 5% of patients. The 3D US images were disadvantageous in two fetuses with multiple anomalies and two with cardiac anomalies. CONCLUSION: The 3D US offered diagnostic advantages in about one-half of the selected cases studied and had effect on patient management in 5% of cases. This modality can be a powerful adjunctive tool to 2D US in providing a more comprehensible, 3D US impression of congenital anomalies. Thus, 3D US is currently most helpful as a targeted study complementing 2D US.     

Filtering and segmentation of 3D angiographic data: Advances based on mathematical morphology

In the last 20 years, 3D angiographic imaging has proven its usefulness in the context of various clinical applications. However, angiographic images are generally difficult to analyse due to their size and the complexity of the data that they represent, as well as the fact that useful information is easily corrupted by noise and artifacts. Therefore, there is an ongoing necessity to provide tools facilitating their visualisation and analysis, while vessel segmentation from such images remains a challenging task. This article presents new vessel segmentation and filtering techniques, relying on recent advances in mathematical morphology. In particular, methodological results related to spatially variant mathematical morphology and connected filtering are stated, and included in an angiographic data processing framework. These filtering and segmentation methods are evaluated on real and synthetic 3D angiographic data.     

Real-time stereo 3D ultrasound

Real-time 3D ultrasound was developed at Duke University in 1991 and has since been used with a variety of transducers and shown effectiveness in clinical applications and in vivo animal imaging studies. Methods for displaying the 3D pyramid of data acquired by the system include selecting 2D image slices or integrating data into a volume rendered view. A third method, real-time stereo 3D imaging, is discussed here. The clinical commercial 3D system has been modified in our laboratory to display a real-time stereo image pair on the scanner display to be viewed through a stereoscope. This merges the pair into a single image, with a sensation of depth. Stereoscopic displays have previously been demonstrated to provide benefits, including improved depth judgments and increased perception of image quality in other applications. Previously-saved volumes of ultrasound data are shown in stereo 3D using the new system.     

High Frame Rate Contrast-Enhanced Ultrasound Imaging for Slow Lymphatic Flow: Influence of Ultrasound Pressure and Flow Rate on Bubble Disruption and Image Persistence

Contrast-enhanced ultrasound (CEUS) utilising microbubbles shows great potential for visualising lymphatic vessels and identifying sentinel lymph nodes (SLNs) which are valuable for axillary staging in breast cancer patients. However, current CEUS imaging techniques have limitations that affect the accurate visualisation and tracking of lymphatic vessels and SLN. (i) Tissue artefacts and bubble disruption can reduce the image contrast. (ii) Limited spatial and temporal resolution diminishes the amount of information that can be captured by CEUS. (iii) The slow lymph flow makes Doppler-based approaches less effective. This work evaluates on a lymphatic vessel phantom the use of high frame rate (HFR) CEUS for the detection of lymphatic vessels where flow is slow. Specifically, the work particularly investigates the impact of key factors in lymphatic imaging, including ultrasound pressure and flow velocity as well as probe motion during vessel tracking, on bubble disruption and image contrast. Experiments were also conducted to apply HFR CEUS imaging on vasculature in a rabbit popliteal lymph node (LN). Our results show that (i) HFR imaging and singular value decomposition (SVD) filtering can significantly reduce tissue artefacts in the phantom at high clinical frequencies; (ii) the slow flow rate within the phantom makes image contrast and signal persistence more susceptible to changes in ultrasound amplitude or mechanical index (MI), and an MI value can be chosen to reach a compromise between images contrast and bubble disruption under slow flow condition; (iii) probe motion significantly decreases image contrast of the vessel, which can be improved by applying motion correction before SVD filtering; (iv) the optical observation of the impact of ultrasound pressure on HFR CEUS further confirms the importance of optimising ultrasound amplitude and (v) vessels inside rabbit LN with blood flow less than 3 mm/s are clearly visualised.     

Role of imaging end points in atherosclerosis trials: focus on intravascular ultrasound

Increasing attention has been focused on the appropriate role of surrogate markers in the development of novel anti-atherosclerotic therapies. Technological advances in imaging modalities allow for visualisation of the entire arterial wall. Intravascular ultrasound (IVUS) has been increasingly employed to precisely quantify the extent of coronary atherosclerosis. Use of IVUS has provided a number of important insights into the natural history of atherosclerosis and the remodelling changes of the arterial wall in response to plaque accumulation. More recently, clinical trials have employed serial evaluations of arterial segments by IVUS to assess the impact of medical therapies.     

Use of three-dimensional ultrasound imaging in the diagnosis of prenatal-onset skeletal dysplasias.

OBJECTIVE: Recognition of prenatal-onset skeletal dysplasias has improved with advances in ultrasound imaging. Skeletal abnormalities can be recognized by two-dimensional (2D) ultrasound, but generating a precise diagnosis can be challenging. We aimed to determine whether three-dimensional (3D) imaging conferred any advantages over 2D imaging in these cases. METHODS: We studied five women with fetuses of 16-28 gestational weeks referred for abnormal ultrasound skeletal findings. First 2D and then 3D sonography was performed and the results compared. RESULTS: The pregnancies resulted in the following skeletal dysplasias: thanatophoric dysplasia, achondrogenesis II/hypochondrogenesis, achondroplasia, chondrodysplasia punctata (rhizomelic form) and Apert's syndrome. For all five fetuses, the correct diagnosis was made in the prenatal period by analysis of the 2D images. In each case the 3D images confirmed the preliminary diagnosis and for many findings it improved the visualization of the abnormalities. CONCLUSION: The 3D imaging had advantages over the 2D imaging when it came to evaluation of facial dysmorphism, relative proportion of the appendicular skeletal elements and the hands and feet. Most importantly, the patient and referring physician appreciated the 3D images of the abnormal findings more readily which aided in counseling and management of the pregnancy.     

A 20-MHz ultrasound system for imaging the intestinal wall

An ultrasound system has been developed which uses high-frequency (20 MHz) ultrasound to provide high-resolution images of tissue. The system provides 0.21-mm range and 0.65-mm lateral resolution. The transducer aperture size is 1.8 mm maximum. Miniature probes have been developed which can image via the biopsy channels of standard fiberoptic endoscopes as well as probes for imaging in vitro. A commercially available video "frame grabber" is used in conjunction with a standard microcomputer for image acquisition. This allows images to be displayed and recorded on standard television equipment and be stored and manipulated digitally. The features of the system allow in vivo imaging, in vitro imaging after resection, and histological images of the same tissue region to be acquired and compared. This method is particularly useful in learning how to correctly interpret ultrasonic images of the intestinal wall. The use of 20 MHz is advantageous in achieving excellent resolution and small size probes. The system provides a unique approach to imaging the intestinal wall.     

Imaging artifacts of medical instruments in ultrasound-guided interventions.

OBJECTIVE: Real-time 3-dimensional (3D) ultrasound imaging has the potential to become a dominant imaging technique for minimally invasive surgery. One barrier to its widespread use is that surgical instruments generate imaging artifacts, which can obfuscate their location, orientation, and geometry and obscure nearby tissue. The purpose of this study was to identify and describe the types of artifacts which could be produced by metallic instruments during interventions guided by 3D ultrasound imaging. METHODS: Three imaging studies were performed. First, imaging artifacts from stainless steel rods were identified in vitro and acoustically characterized. Second, 3 typical minimally invasive instruments were imaged (in vitro and in vivo), and their artifacts were analyzed. The third study compared the intensity of imaging artifacts (in vitro and in vivo) from stainless steel rods with rods composed of 3 different materials and stainless steel rods with roughened and coated surfaces. RESULTS: For the stainless steel rods, all observed artifacts are described and illustrated, and their physical origins are explained. Artifacts from the 3 minimally invasive instruments are characterized with the use of the artifacts observed with the rods. Finally, it is shown that artifacts can be greatly reduced through the use of alternate materials or by surface modification. CONCLUSIONS: Instrument artifacts in 3D ultrasound images can be more confusing than those from the same instruments imaged in 2 dimensions. Real-time 3D ultrasound imaging can, however, be used effectively for in vivo imaging of minimally invasive instruments by using artifact mitigation techniques, including careful selection of probe and incision locations, as well as by instrument modification.     

Effect of irradiation distance on image contrast in epi-optoacoustic imaging of human volunteers

In combined clinical optoacoustic (OA) and ultrasound (US) imaging, epi-mode irradiation and detection integrated into one single probe offers flexible imaging of the human body. The imaging depth in epi-illumination is, however, strongly affected by clutter. As shown in previous phantom experiments, the location of irradiation plays an important role in clutter generation. We investigated the influence of the irradiation geometry on the local image contrast of clinical images, by varying the separation distance between the irradiated area and the acoustic imaging plane of a linear ultrasound transducer in an automated scanning setup. The results for different volunteers show that the image contrast can be enhanced on average by 25% and locally by more than a factor of two, when the irradiated area is slightly separated from the probe. Our findings have an important impact on the design of future optoacoustic probes for clinical application.OCIS codes: (170.5120) Photoacoustic imaging, (170.7170) Ultrasound, (170.3880) Medical and biological imaging     

Endoscopic ultrasonography

Endosonography is primarily a diagnostic imaging modality, but new therapeutic applications are being developed. Miniprobe technology (ultrasound catheter probes) has led to new clinical applications. The staging of gastrointestinal cancers remains the major accepted indication for endosonography. Other conditions, such as chronic pancreatitis, portal hypertension, and inflammatory bowel diseases, are also being evaluated with endosonographic imaging.     

Ultrasound virtual endoscopic imaging

Volume data acquisition, three dimensional (3D) imaging, and multiplanar reformatting have become widely used for computed tomography (CT) and magnetic resonance imaging (MRI). As an extension of this technology, virtual endoscopic visualization of hollow organs has become a reality that is now finding its way into clinical CT practice. The same methods of computer processing as are used for CT and MRI can be applied to an ultrasound (US) volume image data set with the same potential output; namely, 3D, multiplanar, and virtual endoscopic images. The use of this image processing technology for US applications has lagged behind the CT and MRI applications, but considerable progress in applying these methods to US has occurred in recent years. As a result, US virtual endoscopic imaging now can be performed on a clinical basis by using standard US instruments and commercially available computer software. The use of newer US imaging methods, such as tissue harmonic and power Doppler imaging, has enhanced the potential for US virtual endoscopy. This article reviews the technology of US virtual endoscopy. In addition, our preliminary experience of using this method for abdominal and vascular diagnosis is described. Finally, we speculate on technical improvements and potential applications that are likely in the future.     

Modeling geometric artefacts in intravascular ultrasound imaging.

A model has been developed for estimating the geometric distortions in intravascular ultrasound (IVUS) imaging caused by the position of the ultrasound catheter within the artery. Geometric distortion causes degradation on cross-sectional images of the vessel wall where, for characteristic positioning of the transducer within the vessel, a circular artery is seen on IVUS images as a noncircular vessel represented by more or less complex shapes. Artefacts, therefore, have a clinical impact on the accuracy of qualitative and quantitative intravascular analyses. The main distortions are due to the inclination and the off-centered position of the transducer within the vessel. These effects are increased by two factors: first, the point of origin of the ultrasound beam does not coincide with the rotation axis of the catheter; second, in the case of a mechanical rotating transducer, the ultrasound beam is not perpendicular to the long axis of the catheter, but has an inclination such that the transducer looks forward from the emitting point. All these parameters are taken into account in the three-dimensional (3-D) geometric model developed in this paper. The model was formulated to predict the geometric deformation for artery contour of various shapes and can model artefacts during stent implantation (Finet et al. 1998). Simulations were made for various geometric configurations and compared to in vitro and in vivo IVUS images. The model results are consistent with the experimental results. Finally, the model was used for estimating the values of the geometric parameters that cause distortions on ultrasonic images.     

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.     

CREANUIS: A Non-linear Radiofrequency Ultrasound Image Simulator

Nonlinear ultrasound methods are widely used in clinical applications for tissue or contrast harmonic imaging. Accurate non-linear imaging simulation tools are required in research studies for the development of new methods. However, in existing simulators, the possible inhomogeneity of the coefficient of non-linearity, which is generally observed in tissue and in particular when contrast agents are involved, has not yet been implemented. This article describes a new ultrasound simulator, called CREANUIS, devoted to the computation of B-mode images where both linear and non-linear propagation in media is considered, with a possible inhomogeneous coefficient of non-linearity. The resulting fundamental images, based on a spatially variant and non-linear point spread function, are in accordance with those obtained through the reference linear FieldII simulator, with computation time reduced by a factor of at least 1.8. Non-linear images of media exhibiting inhomogeneous coefficients of non-linearity are also provided. The simulation software can be freely downloaded from our website.     

Standardization of three-dimensional images in obstetrics and gynecology: consensus statement.

Standardization of the display of ultrasound images has so far only been achieved in transabdominal two-dimensional (2D) sonography. In contrast, there is a lack of uniformity in the demonstration of transvaginal 2D ultrasound images. The described non-uniformity frequently leads to confusion in the assessment of an image, in particular with regard to the accurate anatomical assignment of left/right and dorsal/ventral. Three-dimensional (3D) sonography offers a unique opportunity to avoid this confusion in the interpretation of ultrasound images, because, independent of primary volume acquisition, the volume can always be rotated so that the stored object can at all times be visualized in a known anatomical position, rendering it of no importance whether the image acquired transvaginally is demonstrated from above or from below. This will also be important in allowing fusion of ultrasound image data with computed tomographic, magnetic resonance and/or positron emission tomography images. In this article we suggest that standardization of transabdominal and transvaginal 3D images does not only provide the inexperienced physician/sonographer with a guide to spatial orientation, but also serves to avoid erroneous topographical interpretations.     

Three-dimensional ultrasound in small parts: is it just a nice picture?

For longer than 40 years, ultrasound (US) has been a widely used imaging tool in medical practice, which has proved helpful for the diagnosis and staging of diseases. Although three-dimensional ultrasound (3D) US has been available for more than 10 years, it was only through the development of the most recent computer technologies and its adaptation to ultrasound systems, that 3D US has become able to achieve the high level of sensitivity and performance necessary to be considered seriously in clinical practice. 3D US is rapidly turning into a technology with an ever-increasing range of applications in numerous fields because, among other reasons, it helps overcome some of the key limitations related to two-dimensional imaging. 3D US can be used in ultrasonography for small parts, among other medical areas. The assessment of the testicle, parotid, thyroid and parathyroid glands is properly achieved. The multiplanar presentation and niche mode are quite useful to determine the extension--inside or outside the organs-, of nodules, cysts or tumors. The volume measurement is better assessed with 3D US and given this, we can perform studies that follow growth in order to decide medical or surgical treatment. The VOCAL makes it possible to obtain a proper after-treatment follow-up of focal disorders in these small organs. Neovascularization is clearly viewed with 3D US and probably can suggest malignant origin of a neoplasm. 3D US offers a more comprehensive image of anatomical structures and pathological conditions and also permits to observe the exact spatial relationships. We are aware more studies are needed to demonstrate specificity and sensibility of 3D US in particular clinical conditions, not only in small parts but also is some other non-Ob/Gyn applications.