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.

Three-dimensional ultrasound imaging

3-D freehand ultrasound is a new imaging technique that is rapidly finding clinical applications. A position-sensing device is attached to a conventional ultrasound probe so that, as B-scans are acquired, they can be labelled with their relative positions and orientations. This allows a 3-D data set to be constructed from the B-scans. A key requirement of all freehand imaging systems is calibration; that is, determining the position and orientation of the B-scan with respect to the position sensor. This is typically a lengthy and tedious process that may need repeating every time a sensor is mounted on a probe. This paper describes a new calibration technique that takes only a few minutes to perform and produces results that compare favourably (in terms of both accuracy and precision) with previously published alternatives.

Rapid calibration for 3-D freehand ultrasound

INTRODUCTION History Role of Ultrasound in Medical Imaging Purpose of the Book Reference Further Reading FUNDAMENTALS OF ACOUSTIC PROPAGATION Stress and Strain Relationships Acoustic Wave Equation Characteristic Impedance Intensity Radiation Force Reflection and Refraction Attenuation, Absorption, and Scattering Nonlinearity Parameter B/A Doppler Effect References ULTRASONIC TRANSDUCERS AND ARRAYS Piezoelectric Effect Piezoelectric Constitutive Equation Ultrasonic Transducers Mechanical Matching Electrical Matching Transducer Beam Characteristics Arrays References GRAY-SCALE ULTRASONIC IMAGING A (Amplitude)-Mode and B (Brightness)-Mode Imaging M-Mode and C-Mode Ultrasound Computed Tomography (CT) Coded Excitation Imaging Compound Imaging Synthetic Aperture Imaging References DOPPLER FLOW MEASUREMENTS Nondirectional CW Flow Meters Directional Doppler Flow Meters Pulsed Doppler Flow Meters Clinical Applications and Doppler Indices Potential Problems in Doppler Measurements Tissue Doppler and Multigate Doppler References FLOW AND DISPLACEMENT IMAGING Color Doppler Flow Imaging Color Doppler Power Imaging Time-Domain Flow Estimation Elasticity Imaging B-Flow Imaging References CONTRAST MEDIA AND HARMONIC IMAGING Contrast Agents Nonlinear Interactions Between Ultrasound and Bubbles Modified Rayleigh-Plesset Equation for Encapsulated Gas Bubbles Solutions to Rayleigh-Plesset Equation Harmonic Imaging Native Tissue Harmonic Imaging Clinical Applications of Contrast Agents and Harmonic Imaging References INTRACAVITY AND HIGH-FREQUENCY (HF) IMAGING Imaging Intravascular Imaging High-Frequency Imaging Acoustic Microscopes References MULTIDIMENSIONAL IMAGING Parallel Processing Multidimensional Arrays Three-Dimensional Imaging References BIOLOGICAL EFFECTS OF ULTRASOUND Acoustic Phenomena at High-Intensity Levels Ultrasound Bioeffects Mechanical Effects and Index References METHODS FOR MEASURING SPEED, ATTENUATION, ABSORPTION, AND SCATTERING Velocity Attenuation Scattering References INDEX

Diagnostic Ultrasound: Imaging and Blood Flow Measurements

A method for real-time three-dimensional (3-D) ultrasound imaging using a mechanically scanned linear phased array is proposed. The high frame rate necessary for real-time volumetric imaging is achieved using a sparse synthetic aperture beamforming technique utilizing only a few transmit pulses for each image. Grating lobes in the two-way radiation pattern are avoided by adjusting the transmit element spacing and the receive aperture functions to account for the missing transmit elements. The signal loss associated with fewer transmit pulses is minimized by increasing the power delivered to each transmit element and by using multiple transmit elements for each transmit pulse. By mechanically rocking the array, in a way similar to what is done with an annular array, a 3-D set of images can be collected in the time normally required for a single image.

Real-time 3-D ultrasound imaging using sparse synthetic aperture beamforming

Real-time ultrasonic imaging systems have been available for more than thirty years. During this time much has occurred to the basic architecture and functions of these clinical systems and their beamformers, which are, in many ways, the most important components of these systems. This talk will review some of the changes that have occurred and will discuss current trends in beamformer design. Throughout most of the 30 years of real time imaging, analog beamformers have been the mainstay of all instruments. The common methods for the implementation of analog beamformers for annular, linear/curved arrays, and phased arrays will be reviewed and the distinguishing characteristics identified. At the present time the industry is undergoing a major shift toward digital beamformation with the introduction of several commercial systems. Given that the earliest digital systems were available roughly 15 years ago, it is fair to say that the introduction of digital beamformers has been relatively slow. Today this shift seems to be gaining momentum. Some of the factors causing these shifts will be reviewed along the the common types of designs and implementations. The ongoing search for improved imaging performance will continue to introduce new challenges for beamformer designers. Among already proposed imaging methods and techniques are elevation focusing (1.5D arrays), synthetic apertures, 2D and sparse arrays, phase aberration correction, and others. The most common complication introduced by these is a significant increase in channel count. Further, there will also be beamformer design issues related to signal processing. These include not only Doppler processing but also the processing of signals due to novel contrast agents. Finally, with advances in computer and microelectronics technologies, the way we view beamformation may have to undergo sizeable changes. These topics will be reviewed not only as technical challenges but also in light of the constraints introduced by today's marketplace.

Evolution of ultrasound beamformers

An ultrasonic transducer assembly is disclosed having both transmit and receive circuitry integral to the transducer assembly for generating and receiving ultrasonic pulses. The ultrasonic transducer array which is integral with the transducer assembly preferably includes multi-layer transducer elements as transmit elements of the array and may include single layer transducer elements as receive elements. Also disclosed is an ultrasonic scanner utilizing the transducer assembly with integral transmit and receive circuitry to reduce the amount and complexity of interconnections between the transducer assembly and a scanner rack.

Ultrasound transducer array with transmitter/receiver integrated circuitry

http://transducers.bme.duke.edu/pubs/ui_1998_1-16.pdf

Progress in Two-Dimensional Arrays for Real-Time Volumetric Imaging

https://orbit.dtu.dk/files/111862993/84710091.pdf

Two-Dimensional Random Arrays for Real Time Volumetric Imaging

The development of 2-D array transducers has received much recent interest. Unfortunately, fabrication of high density 2-D arrays is difficult due to the large number of electrical interconnections which must be made to the back side of the elements. A typical array operating at 2.2 MHz may have 256 or more connections within a 16.4 mm circular footprint. Interconnection becomes even more challenging as operating frequencies increase. To solve this problem, we have developed a multilayer flexible (MLF) circuit interconnect consisting of a polyimide dielectric with inter-laminar vias routing signals vertically and etched metal traces routing signals horizontally. A transducer is fabricated from an MLF by bonding a PZT chip to its surface and dicing the chip into individual elements, with the saw kerf extending partially into the top polyimide layer to ensure physical and electrical isolation of the elements. The KLM model was used to compare the performance of an MLF 2-D array to a conventional hand wired 2-D array. MLF and wire guide transducers were fabricated, each with 256 active elements, 0.4 mm interelement spacing, and 2.2 MHz center frequency. Vector impedance, pulse length, bandwidth, angular response, and cross-coupling were found to be comparable in both types of arrays. Using the MLF, however, fabrication time was reduced dramatically. More importantly, MLF technology may be used to increase 2-D array connection density beyond the limitations of current of hand wired fabrication techniques. Thus MLF circuits provide a means for the interconnection of current and future high frequency 2-D arrays.

Two-dimensional arrays for medical ultrasound using multilayer flexible circuit interconnection

l 1/2 -D and 2-D arrays offer a myriad of new imaging modalities and benefits when compared to the linear array. However, with added benefits come many problems and challenges and l 1/2 -D and 2-D arrays are no exception. The authors give possible solutions to a number of these challenges. The increase in transducer channels needed in a 1 1/2 -D and 2-D array can be reduced using a sparse periodic or sparse random array. The complexity of the fabrication is overcome using a multilayer flexible connector designed and fabricated using microelectronic techniques. The low SNR of 1 1/2 -D and 2-D arrays can be circumvented with the application of multi-layer ceramic elements to optimize the SNR given a specific transmit and receive configuration. In addition, optoelectronic transmitters allow for the reduction in size and increase in flexibility of the transducer cable because of the use of fiber optics. With the reduction in the number of channels, improvement in transducer fabrication, and increase in transducer SNR, l 1/2 -D and 2-D arrays will be accepted as viable replacements for the linear arrays of today.

R.E. Davidsen

Papers

Ultrasound transducer array with transmitter/receiver integrated circuitry

Progress in Two-Dimensional Arrays for Real-Time Volumetric Imaging

Two-Dimensional Random Arrays for Real Time Volumetric Imaging

Two-dimensional arrays for medical ultrasound using multilayer flexible circuit interconnection

Update on 2-D array transducers for medical ultrasound