Aiman Albert Abdel-Malek

Enhanced method for reducing ultrasound speckle noise using wavelet transform

This paper presents the results of the development of an adaptive method for reducing signal-dependent noise, such as speckle noise, in a coherent imaging system signal, such as in medical ultrasound imaging. Speckle noise is filtered using nonlinear adaptive thresholding of received echo wavelet transform coefficients. Filtering speckle noise in ultrasound imaging enhances the resultant image by improving the signal-to-noise ratio. This method includes the steps of transforming the imaging system signal using discrete wavelet transformation to provide wavelet transform coefficients for each of the wavelet scales having different levels of resolution ranging from a finest wavelet scale to a coarsest wavelet scale; deleting the wavelet transform coefficients representing the finest wavelet scale; identifying, for each wavelet scale other than the finest wavelet scale, which of the wavelet transform coefficients are related to noise and which are related to a true signal through the use of adaptive nonlinear thresholding; selecting those wavelet transform coefficients which are identified as being related to a true signal; and inverse transforming the selected wavelet transform coefficients using an inverse discrete wavelet transformation to provide an enhanced true signal with reduced noise. This method is shown to improve the signal-to-noise ratio by 2 - 5 dB in digital ultrasound images of real and phantom objects for a range of thresholding levels while preserving the contrast differences between regions and maintaining feature edges. The filtered images have an enhanced apparent contrast resulting from the reduction in the speckle noise and the preservation of the contrast differences.

Feature cueing in the discrete cosine transform domain

The demand for fast and cost-effective access to multiple compressed data sources is imminent. An interactive link between a distant user and the compressed data is needed such that data transmission is constrained to only a small subset of the compressed data that possesses specific features of interest to the user, hence avoiding transmission and decompression of other noninteresting data sources. We present the first step toward developing this user-compressed data link. We show that oriented line features can be detected in data that are transformed, prior to being quantized and coded, using the discrete cosine transform (DCT). Our work is based on the DCT performed on block sizes of 32 x 32 pixels. The choice of this particular block size is due to proprietary constraints imposed by the specific problem we were commissioned to solve. It involves a proprietary database structure. The DCT is the basis of many established image compression standards such as the Joint Photographic Experts Group (JPEG) and the Motion Picture Experts Group (MPEG). These standards are based on block sizes of 8 x 8 pixels. We also show that the effect we report is exploitable with this more familiar block size. Theoretical proof of the DCT line-feature detector and experimental results are provided. An extension of the approach for logical inference of the existence of specific objects of interest is also outlined. When used as a feature analytical tool in conjunction with its compression role, the DCT may serve as a smart compression procedure for intelligent data archiving, abstraction, and transmission.

An adaptive gating approach for X-ray dose reduction during cardiac interventional procedures

The increasing number of cardiac interventional procedures has resulted in a tremendous increase in the absorbed X-ray dose by radiologists as well as patients. A new method is presented for X-ray dose reduction which utilizes adaptive tube pulse-rate scheduling in pulsed fluoroscopic systems. In current pulsed systems, the X-ray tube is pulsed at a fixed rate of 30 pulses/sec (or higher) and an image is formed at the end of each pulse. In the proposed system, pulse-rate scheduling depends on the heart muscle activity phase determined through continuous guided segmentation of the patients electrocardiogram (ECG). Displaying images generated at the proposed adaptive nonuniform rate is visually unacceptable; therefore, a frame-filling approach is devised to ensure a 30 frame/sec display rate. The authors adopted two approaches for the frame-filling portion of the system depending on the imaging mode used in the procedure. During cine-mode imaging (high X-ray dose), collected image frame-to-frame pixel motion is estimated using a pel-recursive algorithm followed by motion-based pixel interpolation to estimate the frames necessary to increase the rate to 30 frames/sec. The other frame-filling approach is adopted during fluoro-mode imaging (low X-ray dose), characterized by low signal-to-noise ratio images. This approach consists of simply holding the last collected frame for as many frames as necessary to maintain the real-time display rate. Results of simulated system performance on an image sequence from a diagnostic study of left ventricular volume produced an average of approximately 3:1 dose reduction without compromising the diagnostic quality of the generated images. The adaptive pulsed-progressive system concept is viewed as the next evolutionary step in X-ray fluoroscopic systems.

Medical image sequence interpolation via hierarchical pel-recursive motion estimation

Reduction of exposure in a pulsed cardiac X-ray fluoroscopy system may be accomplished by interrupting exposure during slower phases of the cardiac cycle and filling in the missing frames by interpolation to restore the full frame rate. The authors present a novel interpolation method whereby the collected frames are decomposed into a multiresolution hierarchy and a pixel-recursive algorithm is employed from the lowest to highest resolution in the hierarchy to obtain estimates of the pixel displacements. The intensity changes between corresponding pixels are then interpolated to fill in the missing frames. The authors show a computer simulation of the method, where only 11 of the original 29 frames produce a natural, nearly artifact-free rendition of the sequence.<<ETX>>

Image segmentation via motion vector estimates

In the visual world moving edges in the periphery represent vital pieces of information that directs the human foveation mechanism to selectively gather information around these specific locations. This computationally efficient approach of allocating resources at key locations has inspired computer visionists to develop new target detection and hacking algorithms based on motion detection in image sequences. In this study we implemented a recursive algorithm for estimating motion vector fields for each pixel in a sequence of Digital Subtraction Angiography (DSA) images. Velocity information is used to segment the image and perform linear quadratic and acceleration-based frame interpolation to produce an apparent frame rate increase. Our results demonstrate the feasibility of low-rate digital fluoroscopy hence less exposure risks while preserving image quality. Furthermore the technique can be useful in the medical Picture Archival and Communication Systems (PACS) where image data can be compressed by storing and transmiting only the motion fields associated with the moving pixels. 1.© (1990) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Visually optimized image reconstruction

Exploiting human visual limitations in image reconstruction significantly reduces computational complexity. Based on a multiresolution pyramid image representation, direct and indirect exploitation of these limitations are attainable. In this study, direct exploitation of the variable acuity feature of the human visual system is achieved through tracking the viewers fovea. Multiresolution images are reconstructed such that high resolution is assigned to a rectangular region, centered at the fovea, with spatial resolution dropping gradually with eccentricity. Indirect exploitation makes use of the human visual sensitivity to abrupt intensity changes (edges) in the image. Accordingly, high resolution need only be preserved within 2X2 pixel neighborhood around the detected edges while low resolution is assigned elsewhere. The amount of savings in the number of pixels rendered could be as high as 98% for the direct exploitation and may exceed 50% (depending on image edge density) for the indirect application.

Satellite teleradiology test bed for digital mammography

Teleradiology offers significant improvement in efficiency and patient compliance over current practices in traditional film/screen-based diagnosis. The increasing number of women who need to be screened for breast cancer, including those in remote rural regions, make the advantages of teleradiology especially attractive for digital mammography. At the same time, the size and resolution of digital mammograms are among the most challenging to support in a cost effective teleradiology system. This paper will describe a teleradiology architecture developed for use with digital mammography by GE Corporate Research and Development in collaboration with Massachusetts General Hospital under National Cancer Institute (NCI/NIH) grant number R01 CA60246-01. The testbed architecture is based on the Digital Imaging and Communications in Medicine (DICOM) standard, created by the American College of Radiology and National Electrical Manufacturers Association. The testbed uses several Sun workstations running SunOS, which emulate a rural examination facility connected to a central diagnostic facility, and uses a TCP-based DICOM application to transfer images over a satellite link. Network performance depends on the product of the bandwidth times the round- trip time. A satellite link has a round trip of 513 milliseconds, making the bandwidth-delay a significant problem. This type of high bandwidth, high delay network is called a Long Fat Network, or LFN. The goal of this project was to quantify the performance of the satellite link, and evaluate the effectiveness of TCP over an LFN. Four workstations have Suns HSI/S (High Speed Interface) option. Two are connected by a cable, and two are connected through a satellite link. Both interfaces have the same T1 bandwidth (1.544 Megabits per second). The only difference was the round trip time. Even with large window buffers, the time to transfer a file over the satellite link was significantly longer, due to the bandwidth-delay. To compensate for this, TCP extensions for LFNs such as the Window Scaling Option (described in RFC1323) were necessary to optimize the use of the link. A high level analysis of throughput, with and without these TCP extensions, will be discussed. Recommendations will be made as to the critical areas for future work.

Experience with a proposed teleradiology system for digital mammography

Teleradiology offers significant improvement in efficiency and effectiveness over current practices in traditional film/screen-based diagnosis. In the context of digital mammography, the increasing number of women who need to be screened for breast cancer, including those in remote rural regions, make the advantages of teleradiology especially attractive for digital mammography. At the same time, the size and resolution of digital mammograms are among the most challenging to support in a cost effective teleradiology system. This paper describes a teleradiology architecture developed for use with digital mammography by GE Corporate Research and Development in collaboration with Massachusetts General Hospital under National Cancer Institute (NCI/NIH) grant number R01 CA60246-01. Experience with a testbed prototype is described. The telemammography architecture is intended to consist of a main mammography diagnostic site serving several remote screening sites. As patient exams become available, they are forwarded by an image server to the diagnostic site over a WAN communications link. A radiologist at the diagnostic site views a patient exam as it arrives, interprets it, and then relays a report back to the technician at the remote site. A secondary future scenario consists of mobile units which forward images to a remote site, which then forwards them to the main diagnostic site. The testbed architecture is based on the Digital Imaging and Communications in Medicine (DICOM) standard, created by the American College of Radiology (ACR) and National Electrical Manufacturers Association (NEMA). A specification of vendor-independent data formats and data transfer services for digital medical images, DICOM specifies a protocol suite starting at the application layer downward, including the TCP/IP layers. The current DICOM definition does not provide an information element that is specifically tailored to mammography, so we have used the DICOM secondary capture data format for the mammography images. In conclusion, experience with the testbed is described, as is performance analysis related to selection of network components needed to extend this architecture to clinical evaluation. Recommendations are made as to the critical areas for future work.

MOBILE BREAST CARE USING DICOM SATELLITE TELEMAMMOGRAPHY PROMPT-INTERPRETATION SYSTEM

The NCI 1989–1993 data on deaths from breast cancer showed that age-adjusted mortality fell 6% for white women, while age-adjusted mortality rose 1% for African-American women1. Minority women present later in the course of the disease for diagnosis and treatment. Thus there is a real need to increase access of minority, elderly, low income, rural and other under-served populations to high-quality breast care and clinical trials.

Effect of on-board compression on stereo and classification

Application-specific metrics for measuring effect of lossy compression on imagery are defined. Experimental results reveal that even small information loss, as measured by mean- square error, may result in large errors in classification and stereo extraction.