Thomas R. Nelson

Three-dimensional ultrasound imaging

The objective of this article is to provide scientists, engineers and clinicians with an up-to-date overview on the current state of development in the area of three-dimensional ultrasound (3-DUS) and to serve as a reference for individuals who wish to learn more about 3-DUS imaging. The sections will review the state of the art with respect to 3-DUS imaging, methods of data acquisition, analysis and display approaches. Clinical sections summarize patient research study results to date with discussion of applications by organ system. The basic algorithms and approaches to visualization of 3-D and 4-D ultrasound data are reviewed, including issues related to interactivity and user interfaces. The implications of recent developments for future ultrasound imaging/visualization systems are considered. Ultimately, an improved understanding of ultrasound data offered by 3-DUS may make it easier for primary care physicians to understand complex patient anatomy. Tertiary care physicians specializing in ultrasound can further enhance the quality of patient care by using high-speed networks to review volume ultrasound data at specialization centers. Access to volume data and expertise at specialization centers affords more sophisticated analysis and review, further augmenting patient diagnosis and treatment.

Dedicated Breast CT: Initial Clinical Experience

PURPOSE To prospectively and intraindividually compare dedicated breast computed tomographic (CT) images with screen-film mammograms. MATERIALS AND METHODS All patient studies were performed according to protocols approved by the institutional review board and Radiation Use Committee; informed consent was obtained. A breast CT scanner prototype was used to individually scan uncompressed breasts in 10 healthy volunteers (mean age, 52.1 years) and 69 women with Breast Imaging Reporting and Data System category 4 and 5 lesions (mean age, 54.4 years). In women with lesions, breast CT images were compared with screen-film mammograms by an experienced mammographer and ranked with a continuous scale of 1-10 (score 1, excellent lesion visualization with CT and poor visualization with mammography; score 5.5, equal visualization with both modalities; and score 10, poor visualization with CT and excellent visualization with mammography). A Wilcoxon signed rank procedure was used to test the null hypothesis that ratings were symmetric at about a score of 5.5 for the entire group and for distinguishing microcalcifications versus masses and other findings and benign versus malignant lesions and for effect of breast density on lesion visualization. Women were asked to compare their comfort during CT with that during mammography on a continuous scale of 1-10. With a Wilcoxon signed rank procedure, the null hypothesis that comfort ratings were symmetric about a score of 5.5 (equal comfort with CT and mammography) was tested. RESULTS Overall, CT was equal to mammography for visualization of breast lesions. Breast CT was significantly better than mammography for visualization of masses (P = .002); mammography outperformed CT for visualization of microcalcifications (P = .006). No significant differences between CT and mammography were seen among benign versus malignant lesions or for effect of breast density on lesion visualization. Subjects found CT significantly more comfortable than mammography (P < .001). CONCLUSION Some technical challenges remain, but breast CT is promising and may have potential clinical applications.

Three-dimensional ultrasound

The papers in this issue show that the feasibility of three-dimensional ultrasound methods in the clinical setting using commercially available equipment is nearby. Their results demonstrate some of the advantages compared to two-dimensional ultrasound and other diagnostic modalities, including reduced scanning times that will offer more cost-effective use of equipment and sonographer time. Other benefits of three-dimensional ultrasound include allowing the physician: to evaluate arbitrary planes not available with two-dimensional ultrasound due to patient body habitus; to measure organ dimensions and volumes; to obtain anatomic and blood flow information; to improve assessment of complex anatomic anomalies; to confirm normalcy; to standardized the ultrasound exam procedures; to enhance the understanding of physicians in primary care facilities and communicate volume data over networks for consultation at tertiary facilities. Standardization of the ultrasound examination protocols can lead to uniformly high-quality examinations and decreased health care costs. Ultimately, three-dimensional ultrasound imaging will make it easier for primary care physicians to understand complex patient anatomy. Tertiary care physicians specializing in ultrasound can further enhance the quality of patient care by using high-speed computer networks to review volume or dynamic data at specialization centers with primary care physicians. Access to volume data at specialization centers affords more sophisticated analysis and review, further augmenting patient diagnosis and treatment and reducing health care costs.

Distance and volume measurement using three-dimensional ultrasonography.

The purpose of this study was to assess the accuracy of distance and volume measurements obtained by three‐dimensional ultrasonography. A tissue‐mimicking phantom was scanned using a prototype three‐dimensional sonographic imaging system to verify distance measurements. Measurements were taken from the reconstructed three‐dimensional sonographic data and compared to the real distances. Volume measurements were obtained by scanning 30 balloons of various shapes, sized 23 ml to 2400 ml. Each balloon was scanned twice in two orientations; three different masks were accomplished for each volume. Each volume measurement of 180 three‐dimensional sonographic measurements was compared to conventional two‐dimensional ultrasonographic volume estimates and to the actual, measured balloon size. Distance measurements had a mean error of 0.02 +/‐ 3.65% (range, ‐4.27 to 7.18%). Two‐dimensional sonographic volume estimates using traditional scanner based methods had a mean error of 13.7 +/‐ 10.1%. Three‐dimensional sonographic volume measurements had a mean error of 2.2 +/‐ 2.9% for regular and irregular objects over the entire range of volumes. The masking required 10 to 30 min. The field of view varied from 10 to 24 cm with a mean object depth of 9.8 cm. Three‐dimensional ultrasonographic methods can provide accurate volume measurements of regular and irregular objects and offer improved accuracy compared to traditional two‐dimensional methods.

Visualization of 3D ultrasound data

It is suggested that ultrasound data acquisition will play an increasing role in the future of medical imaging. Unlike magnetic resonance imaging (MRI) and computerized tomography (CT), ultrasound offers interactive visualization of underlying anatomy in real time. Additionally, ultrasound equipment costs far less and does not use ionizing radiation or require specialized facilities. The different methods for multidimensional medical imaging and scientific visualization are reviewed. Several volume visualization algorithms are discussed. They are multiplexer slicing, surface fitting, volume rendering, data classification, and viewing and shading. Three-dimensional ultrasound data display methods are also discussed.<<ETX>>

Ultrasound Biosafety Considerations for the Practicing Sonographer and Sonologist

The purpose of this article is to present the practicing sonographer and sonologist with an overview of the biohazards of ultrasound and guidelines for safe use.

In vivo three-dimensional sonographic measurement of organ volume: validation in the urinary bladder.

The purpose of this study was to assess the accuracy of in vivo measurement of organ volume using 3DUS and compare the results to 2D sonographic methods using the urinary bladder as the target organ and voided urine volume for validation. Fifty normal volunteers were studied. 2D volume measurements were based on length, width, and depth data and assumed a regular geometric model. 3D volume measurements were based on masked slices with the voxels integrated over the entire bladder. Voided urine volumes ranged from 35 ml to 701 ml. Residual urine volume was present in 48% of the subjects and ranged from 1% to 14% of the voided volume. 2D volume estimates for all 50 subjects had a mean absolute value of the error of 27.5% +/‐ 17.8%. 3D volume measurements had a mean absolute value of the error of 4.3% +/‐ 3.7% (transverse) and 5.6% +/‐ 3.8% (longitudinal). 3DUS provided more accurate volume measurements than 2DUS, particularly for irregularly shaped organs.

Technique factors and their relationship to radiation dose in pendant geometry breast CT

The use of breast computed tomography (CT) as an alternative to mammography in some patients is being studied at several institutions. However, the radiation dosimetry issues associated with breast CT are markedly different than in the case of mammography. In this study, the spectral properties of an operational breast CT scanner were characterized both by physical measurement and computer modeling of the kVp-dependent spectra, from 40 to 110 kVp (Be window W anode with 0.30 mm added Cu filtration). Previously reported conversion factors, normalized glandular dose for CT-DgN(ct), derived from Monte Carlo methods, were used in concert with the output spectra of the breast scanner to compute the mean glandular dose to the breast based upon different combinations of x-ray technique factors (kVp and mAs). The mean glandular dose (MGD) was measured as a function of the compressed breast thickness (2-8 cm) and three different breast compositions (0%, 50%, and 100% glandular fractions) in four clinical mammography systems in our institution. The average MGD from these four systems was used to compute the technique factors for breast CT systems that would match the two-view mammographic dose levels. For a 14 cm diameter breast (equivalent to a 5 cm thick compressed breast in mammography), air kerma levels at the breast CT scanners isocenter (468 mm from the source) of 4.4, 6.4, and 9.0 mGy were found to deliver equivalent mammography doses for 0%, 50%, and 100% glandular breasts (respectively) at 80 kVp. At 80 kVp (where air kerma was 11.3mGy∕100mAs at the isocenter), 57 mAs (integrated over the entire scan) was required to match the mammography dose for a 14 cm 50% glandular breast. At 50 kVp, 360 mAs is required to match mammographic dose levels. Tables are provided for both air kerma at the isocenter and mAs for 0%, 50%, and 100% glandular breasts. Other issues that impact breast CT technique factors are also discussed.

Three- and 4-Dimensional Ultrasound in Obstetrics and Gynecology Proceedings of the American Institute of Ultrasound in Medicine Consensus Conference

The American Institute of Ultrasound in Medicine convened a panel of physicians and scientists with interest and expertise in 3‐dimensional (3D) ultrasound in obstetrics and gynecology to discuss the current diagnostic benefits and technical limitations in obstetrics and gynecology and consider the utility and role of this type of imaging in clinical practice now and in the future. This conference was held in Orlando, Florida, June 16 and 17, 2005. Discussions considered state‐of‐the‐art applications of 3D ultrasound, specific clinical situations in which it has been found to be helpful, the role of 3D volume acquisition for improving diagnostic efficiency and patient throughput, and recommendations for future investigations related to the utility of volume sonography in obstetrics and gynecology.

Interactive acquisition, analysis, and visualization of sonographic volume data

This article discusses the design features of an interactive system for acquiring, analyzing, and displaying volume sonographic patient data. Methods for reprojection of two‐dimensional (2D) sonographic image data into a volume matrix are discussed. We describe an intuitive, easy‐to‐use graphical user interface that facilitates physician operation of a system incorporating an interactive volume renderer for optimization of viewing orientation and data presentation and incorporates stereoscopic viewing. Visualization methods are described that permit the operator interactively to extract tissues or organs of interest from the rest of the volume scanned. Selected examples of clinical images are given to demonstrate system capability. The system represents a cost‐effective 3D ultrasound system integrating clinical scanners and graphics workstations.