High Frame Rate Imaging Research Articles

Logic design and implementation of FPGA for a high frame rate ultrasound imaging system

Recently, a method has been developed for high frame rate medical imaging [Jian-yu Lu, ‘‘2D and 3D high frame rate imaging with limited diffraction beams,’’ IEEE Trans. Ultrason. Ferroelectr. Freq. Control 44(4), 839–856 (1997)]. To realize this method, a complicated system [multiple-channel simultaneous data acquisition, large memory in each channel for storing up to 16 seconds of data at 40 MHz and 12-bit resolution, time-variable-gain (TGC) control, Doppler imaging, harmonic imaging, as well as coded transmissions] is designed. Due to the complexity of the system, field programmable gate array (FPGA) (Xilinx Spartn II) is used. In this presentation, the design and implementation of the FPGA for the system will be reported. This includes the synchronous dynamic random access memory (SDRAM) controller and other system controllers, time sharing for auto-refresh of SDRAMs to reduce peak power, transmission and imaging modality selections, ECG data acquisition and synchronization, 160 MHz delay locked loop (DLL) for accurate timing, and data transfer via either a parallel port or a PCI bus for post image processing. [Work supported in part by Grant 5RO1 HL60301 from NIH.]

Echocardiographic assessment of cardiac structure and function in rats

Background: Echocardiography is used in humans to characterise the structure and function of the heart, yet is relatively uncommon in studies on the rat, the most commonly used model of human cardiovascular disease. The aim of this study was to show that echocardiography in rats provides useful information on cardiac changes occurring in thyroid dysfunction and can also be used to characterise cardiac abnormalities. Methods: Transthoracic echocardiography and Doppler techniques with high frequency, high frame rate imaging were used to define cardiac dimensions and function in 240 Wistar rats and cardiac abnormalities in Wistar and spontaneously hypertensive rats (SHR). Results: Echocardiographic assessment of left ventricular dimensions and function and aortic flows was technically feasible in almost all adult Wistar rats and SHR, including those with thyroid dysfunction and cardiac abnormalities. Pulsed-wave Doppler profiles of mitral inflows to estimate diastolic function were less reliably obtained. Conclusions: Echocardiography is a powerful technique for non-invasive and serial determination of cardiac structure and function in rat models of human cardiovascular disease.

Strain rate imaging using two-dimensional speckle tracking.

Strain rate images (SRI) of the beating heart have been proposed to identify non-contracting regions of myocardium. Initial attempts used spatial derivatives of tissue velocity (Doppler) signals. Here, an alternate method is proposed based on two-dimensional phase-sensitive speckle tracking applied to very high frame rate, real-time images. This processing can produce high resolution maps of the time derivative of the strain magnitude (i.e., square root of the strain intensity). Such images complement traditional tissue velocity images (TVI), providing a more complete description of cardiac mechanics. To test the proposed approach, SRI were both simulated and measured on a thick-walled, cylindrical, tissue-equivalent phantom modeling cardiac deformations. Real-time ultrasound images were captured during periodic phantom deformation, where the period was matched to the data capture rate of a commercial scanner mimicking high frame rate imaging of the heart. Simulation results show that SRI with spatial resolution between 1 and 2 mm are possible with an array system operating at 5 MHz. Moreover, these images are virtually free of angle-dependent artifacts present in TVI and simple strain rate maps derived from these images. Measured results clearly show that phantom regions of low deformation, which are difficult to identify on tissue velocity-derived SRI, are readily apparent with SRI generated from two-dimensional phase-sensitive speckle tracking.

Charge transfer in a multi-implant pinned-buried photodetector

This work presents a charge transfer model for a multi-implant (graded) pinned-buried photodetector for high frame rate imaging applications. The model takes into account the initial charge of each implanted region which is divided into a large number of small areas and the maximum effective transit length of the far and near electrons by taking into account the fringing field effect due to graded implants under uniform illumination condition. The model predicts 1.5 /spl mu/s for a single-implant and 500 ns for a three-implant photodetector for collection of 90% of the initial charge. The computed values agree well with the experimental results for a three-implant 70 /spl mu/m/spl times/45 /spl mu/m photodetector measured at a rate of 10/sup 6/ frames/s with uniform illumination by 100 ns LED pulses.

A high frame rate image acquisition system for dynamic centrifuge tests

A high frame rate image acquisition system for dynamic centrifuge tests developed at Public Works Research Institute is described. The image acquisition and processing technique provide not only residual deformations but also the cyclic component of deformation. In order to verify the performance of the developed system a dynamic centrifuge test was conducted where both the high frame rate image recording and displacement measurements were made. The results of this calibration test showed that the deformation of target markers derived from image analysis compared fairly well with that obtained from direct measurement by displacement transducers.

A High Frame Rate Image Acquisition System for Dynamic Centrifuge Tests

A High Frame Rate Image Acquisition System for Dynamic Centrifuge Tests

Use of high-frame rate imaging and doppler tissue echocardiography in the diagnosis of fetal ventricular tachycardia

Ventricular tachycardia has rarely been diagnosed in the fetus. We describe a 31-week-old fetus with ventricular tachycardia and severely depressed ventricular function. M-mode and 2-dimensional Doppler tissue echocardiography were used in this study to assess the nature of the arrhythmia. The complete atrioventricular dissociation inherent to the diagnosis of ventricular tachycardia was particularly easy to detect with M-mode Doppler tissue echocardiography. Moreover, the onset and the pattern of propagation of the ventricular arrhythmia could be easily identified with 2-dimensional Doppler tissue echocardiography. Doppler tissue echocardiography facilitates the diagnosis of ventricular tachycardia and adds new information that is not available by other techniques. (J Am Soc Echocardiogr 2001;14:149-51.)

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan IT-CCD image sensor

A 30 frames/s 2/3-in 1.3 M-pixel progressive scan interline-transfer charge-coupled device (IT-CCD) image sensor has been developed for video and digital still-camera applications. To obtain high frame-rate images, a 49-MHz driving horizontal CCD (H-CCD) was developed. An 8-phase drive for vertical CCDs (V-CCDs) makes it possible to operate in a variety of modes, such as 1050 line progressive scan mode and 1049 line wide dynamic range interlaced scan mode. For digital still camera use, removing residual charges stored in the V-CCDs before exposure is essential, therefore new narrow-channel barrier over-flow drain (NCB-OFD) attached under the H-CCD was developed. The NCB-OFD automatically drains out extra charges and has the advantages of requiring neither an over-flow control gate nor any additional masks.

Increasing field of view of high frame rate ultrasonic imaging

A high frame rate imaging method has been developed recently based on the theory of limited diffraction beams for medical diagnosis. This method constructs images in a direction normal to the transducer surface. In this report, the high frame rate method is extended so that it will not only construct images in the normal direction, but also in any oblique directions. This increases the image construction area because images from several oblique angles can be combined. A new equation has been derived for this extension. A computer simulation was performed. Results show that the field of view of images constructed with the extended method is increased from about 15.74 deg to about 96.57 deg with a linear array of a width (foot print) of about 18.288 mm after combining images from only seven angles (the depth of the images is assumed to be 66.12 mm). This work is significant because a large field of view with a small transducer footprint is desirable for high frame rate heart imaging. [Work supported in part by Grant No. HL60301 from NIH.]

Effects of phase aberration on high frame rate imaging

A high frame-rate (HFR) imaging method (about 3750 frames/s for imaging of biological soft tissues at a depth of 200 mm) has been developed recently with limited diffraction beams. This method uses the fast Fourier transform (FFT) and inverse fast Fourier transform (IFFT) to construct images, and can be implemented with simple and inexpensive hardware, compared to the conventional delay-and–sum method where a digital beam former is usually used. In this paper, phase aberration effects are studied for both the high frame rate and the conventional methods by adding random phase shifts to echo signals obtained from an experiment. In the study, two broadband linear arrays were used to construct images of an ATS 539 tissue-equivalent phantom that has a frequency-dependent attenuation of about 0.5 dB/MHz/cm. The first array has 48 elements, a central frequency of 2.25 MHz, an aperture of 18.288 mm, and a width of 12.192 mm in elevation. The second has 64 elements, a central frequency of 2.5 MHz, and a dimension of 38.4 mm × 10 mm. The-6dB pulse-echo bandwidth of both arrays is about 40% of their center frequencies. Radiofrequency (RF) signals were digitized at 20 mega samples/s at a 12-bit resolution to construct images. Results show that phase aberration has about the same effect on both methods in terms of image resolution and contrast, although the high frame-rate method can be implemented with a simpler system.

High frame rate imaging with a small number of array elements

Recently, a high frame rate imaging method has been developed to construct either 2-D or 3-D images (about 3750 frames or volumes/s at a depth of about 200 mm in biological soft tissues because only one transmission is needed). The signal-to-noise ratio (SNR) is high using this method because all array elements are used in transmission and the transmit beams do not diverge. In addition, imaging hardware with the new method can be greatly simplified. Theoretically, the element spacing (distance between the centers of two neighboring elements) of an array should be lambda/2, where lambda is the wavelength, to avoid grating lobes in imaging. This requires an array of a large number of elements, especially, for 3-D imaging in which a 2-D array is needed. In this paper, we study quantitatively the relationship between the quality of images constructed with the new method and the element spacing of array transducers. In the study, two linear arrays were used. One has an aperture of 18.288 mm, elevation dimension of 12.192 mm, a center frequency of 2.25 MHz, and 48 elements (element spacing is 0.381 mm or 0.591 lambda). The other has a dimension of 38.4 mmx10 mm, a center frequency of 2.5 MHz, and 64 elements (0.6 mm or 1.034 lambda element spacing). Effective larger element spacings were obtained by combining signals from adjacent elements. Experiments were performed with both the new and the conventional delay-and-sum methods. Results show that resolution of constructed images is not affected by the reduction of a number of elements, but the contrast of images is decreased dramatically when the element spacing is larger than about 2.365 lambda for objects that are not too close to the transducers. This suggests that an array of about 2.365 lambda spacing can be used with the new method. This may reduce the total number of elements of a fully sampled 128x128 array (0.5 lambda spacing) from 16384 to about 732 considering that the two perpendicular directions of a 2-D array are independent (ignoring the larger element spacing in diagonal directions of 2-D arrays).

Smart CMOS focal plane arrays: a Si CMOS detector array and sigma-delta analog-to-digital converter imaging system

This paper evaluates the potential for the real-time utilization of high frame rate image sequences using a fully parallel readout system. Multiple readout architectures for high frame rate imaging are compared. The application domain for a fully parallel readout system is identified, and the design for a fully parallel, monolithically integrated smart CMOS focal plane array is presented. This focal plane image processing chip, with an 8/spl times/8 array of Si CMOS detectors each of which have a dedicated on-chip current input first-order sigma-delta analog-to-digital converter front end, has been fabricated, and test results for uniformity and linearity are presented.

A new time-domain narrowband velocity estimation technique for Doppler ultrasound flow imaging. II. Comparative performance assessment

For pt.I see ibid., vol.45, no.4, pp.939-54 (1998). The statistical performance of the new 2-D narrowband time-domain root-MUSIC blood velocity estimator described previously is evaluated using both simulated and flow phantom wideband (50% fractional bandwidth) ultrasonic data. Comparisons are made with the standard 1-D Kasai estimator and two other wideband strategies: the time domain correlator and the wideband point maximum likelihood estimator. A special case of the root-MUSIC, the "spatial" Kasai, is also considered. Simulation and flow phantom results indicate that the root-MUSIC blood velocity estimator displays a superior ability to reconstruct spatial blood velocity information under a wide range of operating conditions. The root-MUSIC mode velocity estimator can be extended to effectively remove the clutter component from the sample volume data. A bimodal velocity estimator is formed by processing the signal subspace spanned by the eigenvectors corresponding to the two largest eigenvalues of the Doppler correlation matrix. To test this scheme, in vivo common carotid flow complex Doppler data was obtained from a commercially available color flow imaging system. Velocity estimates were made using a reduced form of this data corresponding to higher frame rates. The extended root-MUSIC approach was found to produce superior results when compared to both 1- and 2-D Kasai-type estimators that used initialized clutter filters. The results obtained using simulated, flow phantom, and in vivo data suggest that increased sensitivity as well as effective clutter suppression can be achieved using the root-MUSIC technique, and this may be particularly important for wideband high frame rate imaging applications.

Experimental study of high frame rate imaging with limited diffraction beams

Limited diffraction beams have a large depth of field and have many potential applications. Recently, a new method (Fourier method) was developed with limited diffraction beams for image construction. With the method and a single plane wave transmission, both 2D (two-dimensional) and 3D (three-dimensional) images of a very high frame rate (up to 3750 frames/s for a depth of 200 mm in biological soft tissues) and a high signal-to-noise ratio (SNR) can be constructed with relatively simple and inexpensive hardware. If limited diffraction beams of different parameters are used in both transmission and reception and transducer aperture is shaded with a cosine function, high-resolution and low-sidelobe images can be constructed with the new method without montage of multiple frames of images [the image quality is comparable to that obtained with a transmit-receive (two-way) dynamically focused imaging system]. In this paper, the Fourier method was studied with both experiment and computer simulation for 2D B-mode imaging. In the experiment, two commercial broadband 1D array transducers (48 and 64 elements) of different aperture sizes (18.288 and 38.4 mm) and center frequencies (2.25 and 2.5 MHz) were used to construct images of different viewing sizes. An ATS539 tissue-equivalent phantom of an average frequency-dependent attenuation of 0.5 dB/MHz/cm was used as a test object. To obtain high frame rate images, a single plane wave pulse (broadband) was transmitted with the arrays. Echoes received with the arrays were processed with both the Fourier and conventional dynamic focusing (delay-and-sum) methods to construct 2D B-mode images. Results show that the quality (resolution and contrast) of constructed images is virtually identical for both methods, except that the Fourier method is simpler to implement. Both methods have also a similar sensitivity to phase aberration distortions. Excellent agreement among theory, simulation, and experiment was obtained.

Image compression sensor based on column parallel architecture

We propose a novel image sensor which has compression function on its sensor plane. The image compression sensor can significantly reduce the amount of pixel data output from the sensor. The proposed sensor is intended to overcome the communication bottle neck for high pixel rate imaging such as high frame rate imaging and high resolution imaging. The compression algorithm is based on conditional replenishment. It detects motion and encodes only the pixels in moving areas. We have been investigating pixel parallel and column parallel architectures of the image compression sensor. In this paper, we present the column parallel architecture of the proposed sensor. In this architecture, fill factor and power dissipation are comparable to conventional MOS sensors in spite of integration of the processing circuits. We have fabricated a prototype chip based on the column parallel architecture. We describe the circuit and layout design and the results of some experiments using the prototype.

2D and 3D high frame rate imaging with limited diffraction beams

A new 2D (two-dimensional) and 3D (three-dimensional) pulse-echo imaging method (Fourier method) has been developed with limited diffraction beams. In this method, a plane wave pulse (broadband) is used to transmit and limited diffraction beams of different parameters are used to receive. Signals received are processed to obtain spatial Fourier transform of object functions and images are constructed with an inverse Fourier transform. Because only one transmission is required to construct images, this method may achieve a high frame rate (up to 3750 frames/s for biological soft tissues at a depth of 200 mm). To demonstrate the efficacy of the method, both 2D C-mode and 3D images have been simulated using conditions that are typical for medical ultrasound. Results show that images of high resolutions (about 6 wavelengths at 200 mm) and low sidelobes (around -60 dB) can be constructed over a large depth of interest (30 to 200 mm) with a 50 mm diameter aperture. Experiments with the new method have also been carried out. 2D B-mode images have been constructed with conventional linear arrays. In the experiment, an ATS 539 tissue-equivalent phantom and two linear arrays were used. The first array had a center frequency of 2.25 MHz, dimension of 18.288 mm/spl times//spl times/12.192 mm, and 48 elements. The second had a center frequency of 2.5 MHz, 38.4 mm/spl times/10 mm in dimension, and 64 elements. Images of different fields of views were constructed from RF data acquired with these arrays using both the new and conventional dynamic focusing (delay-and-sum) methods. Results show that qualities of images constructed are almost identical with the two methods in terms of sidelobes, contrast, and lateral and axial resolutions. Phase aberration has also been assessed for the two methods, and results show that its influence is about the same on both methods. In addition, a practical imaging system to implement the new method is suggested and potential applications of the method are discussed.

360×360 element three-phase very high frame rate burst image sensor: design, operation and performance

Design, fabrication, operation and performance are described for a 360/spl times/360 element very high frame rate (VHFR) image sensor that can capture images at a frame rate of up to 10/sup 6/ frames/s. This VHFR imager has 50/spl times/50 /spl mu/m macropixels, each consisting of a high-speed zero-lag photodetector with a 13.5% fill factor and 30 stages of serial-parallel type buried-channel CCD registers for storage and readout of the last 30 image frames acquired. Readout of this imager is similar to a frame transfer CCD consisting of four quadrants. Each quadrant contains one million pixels, readout at a relatively slow rate compatible with low readout noise, and PC class microcomputer-based data acquisition and storage. This imager is designed using SiO/sub 2//Si/sub 3/N/sub 4/ gate dielectric, four levels of polysilicon, three levels of metal, eight implants, 21 photo masks using 1.5-/spl mu/m design rules, and it has four output ports. The high-speed photodetector is designed in the form of a graded three-potential-level pinned-buried BCCD structure. This 33-/spl mu/m long photodetector can achieve complete readout of photogenerated electrons in less than 0.1 /spl mu/s.

Computational image sensor for on sensor compression

We propose a novel integration of image compression and sensing in order to enhance the performance of an image sensor. By integrating a compression function onto the sensor focal plane, the image signal to be read out from the sensor is significantly reduced and the pixel rate of the sensor ran consequently be increased. The potential applications of the proposed sensor are in high pixel-rate imaging, such as high frame-rate image sensing and high-resolution image sensing. The compression scheme we employ is a conditional replenishment, which detects and encodes moving areas. In this paper, we introduce two architectures for on-sensor compression; one is the pixel parallel approach and the other is the column parallel approach. We prototyped a VLSI chip of the proposed sensor based on the pixel parallel architecture. We show the design and describe the results of the experiments obtained by the prototype chip.

A high frame-rate digital subtraction angiography imaging technique for evaluation of aortofemoral runoff.

Intravenous digital subtraction angiography was used to obtain a complete aortofemoral runoff examination of high diagnostic quality in a single patient session in eight patients. Using a 9-inch (22.9-cm) image intensifier, oblique and posteroanterior projections were obtained from the level of the aortic bifurcation to the tibial artery trifurcation. This technique is based upon the administration of one-half of the usual dose of contrast agent combined with a high frame-rate imaging technique and postacquisition integration to increase the signal-to-noise ratio. It is easily performed on an outpatient basis, lowers patient risk, and allows a significant savings of time, film, and cost compared with the conventional intra-arterial aortofemoral runoff examination.