Digital Scan Converter Research Articles

RETRACTED ARTICLE: FPGA logic design method based on multi resolution image real time acquisition system

Medical imaging techniques are mostly generated by human tissue echoes and received by the transducer which is converted to electrical signals, after amplification, extraction, processing, and then signals are converted by the digital scan converter for standard video signal, finally displayed by the display. We propose a scheme of real-time and multi resolution image acquisition system by FPGA control logic design based on the real-time data acquisition, beam forming, processing, acquisition and transmission to ARM embedded video signal processing system with high real-time requirements, so we choose FPGA and SRAM real-time acquisition system which can meet the above requirements in speed and capacity. According to the problems encountered in the process of high speed acquisition, a reasonable timing optimization and RTL level synthesis is designed. The experimental results show that the design and implementation of the image acquisition system is not only stable, but also significantly improve the overall performance of the image processing system.

High-speed digital scan converter for high-frequency ultrasound sector scanners

This paper presents a high-speed digital scan converter (DSC) capable of providing more than 400 images per second, which is necessary to examine the activities of the mouse heart whose rate is 5–10 beats per second. To achieve the desired high-speed performance in cost-effective manner, the DSC developed adopts a linear interpolation algorithm in which two nearest samples to each object pixel of a monitor are selected and only angular interpolation is performed. Through computer simulation with the Field II program, its accuracy was investigated by comparing it to that of bilinear interpolation known as the best algorithm in terms of accuracy and processing speed. The simulation results show that the linear interpolation algorithm is capable of providing an acceptable image quality, which means that the difference of the root mean square error (RMSE) values of the linear and bilinear interpolation algorithms is below 1%, if the sample rate of the envelope samples is at least four times higher than the Nyquist rate for the baseband component of echo signals. The designed DSC was implemented with a single FPGA (Stratix EP1S60F1020C6, Altera Corporation, San Jose, CA) on a DSC board that is a part of a high-speed ultrasound imaging system developed. The temporal and spatial resolutions of the implemented DSC were evaluated by examining its maximum processing time with a time stamp indicating when an image is completely formed and wire phantom testing, respectively. The experimental results show that the implemented DSC is capable of providing images at the rate of 400 images per second with negligible processing error.

X-band wideband experimental airborne radar for SAR, GMTI and maritime surveillance

Defence Research and Development Canada - Ottawa has completed Phase I in the development of a new multimode X-band wideband experimental airborne radar (XWEAR) to support studies in synthetic aperture radar (SAR) imaging, inverse SAR (ISAR), ground moving target indication (GMTI) radar and maritime surveillance radar with particular focus on small target detection and long-range surface surveillance. Specific areas of interest include research into SAR imaging techniques for fixed and moving targets, time–frequency analysis of ocean and land moving targets, space–time adaptive processing for application to GMTI, investigation into the electromagnetic backscatter properties of the ocean surface, generation of signatures for automatic target recognition and feature extraction, and analysis on the immunity of wide bandwidth systems against electronic countermeasures. Phase I culminated with the flight trialling of the SAR and maritime surveillance modes. Phase II will see the trialling of the wide area surveillance GMTI (WAS GMTI) and integrated SAR–GMTI modes. A description of the experimental radar is given along with an overview of its data collection capability. Distinguishing features include operation at X-band, single-channel operation for SAR and maritime surveillance, and two-channel operation for WAS-GMTI and integrated SAR–GMTI. The new radar maximises the use of an existing digital scan converter as a controller, and commercially available components including the transmitter, A/D converters and computer boards. The timing circuitry, waveform generator, single- and dual-channel receivers are custom built.

A study of the display pixel-based focusing method in ultrasound imaging.

This paper presents a new beamforming technique, in which ultrasound waves are focused at the display pixels on the Cartesian coordinates, rather than sampling points located on the uniformly-separated scanlines on either the polar or Cartesian coordinates. Consequently, this method does not require a digital scan converter (DSC) and therefore completely eliminates the distortions due to the DSC. A new imaging system based on the proposed method is also presented, which is advantageous over conventional systems in hardware complexity, especially when high-density imaging is required. The new method can also be used effectively to achieve high frame rates for real-time 3D imaging and cardiac applications. To verify the proposed method, we modified a commercial ultrasound scanner and performed experiments with a 3.5 MHz convex array and a 7.5 MHz linear array. The experimental results with in vivo and in vitro data show that the proposed technique provides much smoother and finer images than the conventional dynamic focusing methods.

Detection of renal stones with real-time sonography: effect of transducers and scanning parameters.

Three experiments with a variety of transducers and scanning parameters were designed to investigate if renal stones could be detected with greater certainty by using particular transducers or scanning parameters. First, the lateral resolution, derived from the -6-dB size of the beam profile, was measured at various depths for five transducers commonly used for renal sonography. Second, an in vitro test object was constructed from bovine liver, porcine kidneys, and two renal calculi to access gray-scale map effects on shadow visibility before and after storage in the digital scan converter. The third experiment combined 15 lithotripsy patients with known renal stones with 16 patients in whom the results of renal sonography and other radiographic procedures suggested renal calculi. The group of 15 patients was scanned several times with the transducers and gray-scale maps studied earlier, and the group of 16 patients was scanned only with one transducer and one gray-scale map. On radiographs, 12 of the 16 patients did not have renal calculi. Sonograms of the test object showed that low-contrast images were best for detection of posterior shadows. Three radiologists interpreted the 31 sonograms with a sensitivity of 81% and a specificity of 86% for detecting renal stones. For the 15 cases of renal stones scanned with a variety of transducers, the three radiologists found that annular-array transducers depicted stone shadowing with less ambiguity than mechanical sector transducers did 81% of the time.

Computer Fundamentals in Diagnostic Ultrasound Imaging

With the incorporation of the digital scan converter in real-time instruments, the computer has assumed an expanding role in diagnostic ultrasound imaging. A knowledge of computer fundamentals is essential for understanding the operation of present day scanners. The concepts of binary notation, memory capacity, analog-to-digital conversion, and the matrix format in digital imaging are discussed in detail. The accuracy of the analog-to-digital conversion is addressed with multiple illustrative examples. Data base management as a practical tool in the clinical environment is introduced.

A new time-gain correction method for standard B-mode ultrasound imaging

A method used to provide gain variation with received echo range to compensate for tissue attenuation in standard B-mode ultrasound imaging systems achieves signal multiplication by first logarithmically compressing the complete dynamic range of the received echo. The time-gain correction method described here is a modification of this method. It performs the time-gain correction operation digitally between the digital scan converter and the display. The overall system transfer function can be specified by means of a software interface without changing the characteristics of the analog front end. This interface can be automated to almost any degree, and it can include preset settings for typical imaging requirements. This method also allows the gain function to be changed even when new images are not being generated.

A new scan conversion algorithm for ultrasound compound scanning.

An improved scan conversion algorithm for ultrasound compound scanning is proposed. In this algorithm, the input data in the spatial domain is sampled by the concentric square raster sampling (CSRS) method, and the display pixel data are filled by one-dimensional linear interpolation. The reconstruction error of the proposed algorithm is much smaller than that of other algorithms, because only one-dimensional, rather than two-dimensional, interpolation is involved. This algorithm greatly simplifies implementation of a real-time digital scan converter (DSC) for spatial compounding of ultrasound images.

A new scan conversion algorithm for ultrasound compound scanning

An improved scan conversion algorithm for ultrasound compound scanning is proposed. In this algorithm, the input data in the spatial domain is sampled by the concentric square raster sampling (CSRS) method, and the display pixel data are filled by one-dimensional linear interpolation. The reconstruction error of the proposed algorithm is much smaller than that of other algorithms, because only one-dimensional, rather than two-dimensional, interpolation is involved. This algorithm greatly simplifies implementation of a real-time digital scan converter (DSC) for spatial compounding of ultrasound images.

Airport surface detection equipment

A special-purpose, high-resolution, radar that maps the airport surface has proved a useful tool to monitor aircraft movements under conditions of poor visibility. Such radars are referred to as ASDE (Airport Surface Detection Equipment). The rationale for the design and critical parameter selection for the ASDE-3 is presented. Key features of the chosen design are a rotodome with variable focus antenna, frequency-agile TWT transmitter, and a digital scan converter. Each feature brought specific and significant improvement to the system performance and these improvements, are discussed in some depth.

Improved technique of combined ultrasonotomographic and urodynamic monitoring: Simultaneous displaying and videotaping of ultrasonotomography and urodynamic data in color

AbstractWe have previously reported a new method of video urodynamic examination combining urodynamic and ultrasonotomographic monitoring. A modified version of this combined urodynamic and ultrasonotomographic monitoring method is presented herein. Simultaneous ultrasonotomographic images and urodynamic data can be displayed in color on a color display monitor and videotaped with a video recorder, using a display controller, digital scan converter, and color encorder.

Overcoming memory contention in a digital scan converter

The problem of memory contention in digital scan converters (DSC) is discussed. The role of the microprocessor in DSC design is examined, and the importance of uninterrupted display in the development and use of image-processing algorithms is stressed. The drawbacks inherent in interrupt and in direct memory access are pointed out and an elegant scheme using the CPU ‘READY’ feature is suggested as an alternative, cycles during which memory contention could occur are predictable, and during these cycles the CPU is prevented from addressing the store. A specific implementation is described using the TMS9900 microprocessor in a DSC displaying sector-scanned sonar images. Timing problems are discussed in detail.

Texture analysis of ultrasonic signals — A comparison of the use of radiofrequency and demodulated A-scan data

Previous work by our group has shown that the application of texture analysis to digitally recorded radiofrequency ultrasonic signals can provide useful diagnostic information in diffuse liver disease. It has now been investigated whether similar information can be obtained with demodulated signal data and established that reduced diagnostic accuracy due to an increased false negative rate results. From this study it would seem unlikely that ultrasonic image data stored in a digital scan converter could provide results as good as those obtainable from the analysis of radiofrequency signals.

An artificial cognitive map system

A blueprint for a geometric information processor is described. The system essentially combines a digital scan converter with a digital flight simulator. The latter's ‘local’ (Poincaréan) rather than standing (helmholtzian) display may have advantages in 3-dimensional diagnostic imaging. At the same time, the system provides a technologically realizable abstract model in terms of which to express (and perhaps eventually explain) the experimental results of O'Keefe and Nadel on the functioning of the hippocampus in the mammalian brain.

Digital ultrasonic imaging with microprocessor manipulation.

The author describes the development of a digital scan converter system which accepts ultrasonic B-scans in "oscilloscope" format and displays them in video format. The system involves the use of a microprocessor, the function of which is outlined in the paper. A brief comparison with a system employing a scan converter tube is given.

Digital solid-state scan-converter with unusual display capabilities

A digital solid-state scan-converter has been developed and used with an integrating silicon vidicon imaging system. The device will store a 256 x 256 picture-element image indefinitely with a resolution of 32 gray levels. Various display modes are available. These include plots of intensity vs position, as well as direct images.

Increasing the measurement accuracy of digital automatic scan converter compensators

On the basis of what has been proposed it is possible to conclude that the allowable errors in comparisons of two time functions do not depend on the levels of the switching thresholds of balance indicators. It is possible to design digital measuring instruments having high measurement sensitivity and accuracy by using ordinary balance indicator circuits. The methods considered permit us to take instruments of certain accuracy classes, and, without reducing the quality of their information indicators, reduce the number of quantization steps with respect to level and thereby increase, by many times, the measurement speed with the same response speed of the commutation elements.