Extreme Compression for Extreme Conditions: Pilot Study to Identify Optimal Compression of CT Images Using MPEG-4 Video Compression

This study aims to evaluate the utility of compressed computed tomography (CT) studies (to expedite transmission) using Motion Pictures Experts Group, Layer 4 (MPEG-4) movie formatting in combat hospitals when guiding major treatment regimens. This retrospective analysis was approved by Walter Reed Army Medical Center institutional review board with a waiver for the informed consent requirement. Twenty-five CT chest, abdomen, and pelvis exams were converted from Digital Imaging and Communications in Medicine to MPEG-4 movie format at various compression ratios. Three board-certified radiologists reviewed various levels of compression on emergent CT findings on 25 combat casualties and compared with the interpretation of the original series. A Universal Trauma Window was selected at −200 HU level and 1,500 HU width, then compressed at three lossy levels. Sensitivities and specificities for each reviewer were calculated along with 95 % confidence intervals using the method of general estimating equations. The compression ratios compared were 171:1, 86:1, and 41:1 with combined sensitivities of 90 % (95 % confidence interval, 79–95), 94 % (87–97), and 100 % (93–100), respectively. Combined specificities were 100 % (85–100), 100 % (85–100), and 96 % (78–99), respectively. The introduction of CT in combat hospitals with increasing detectors and image data in recent military operations has increased the need for effective teleradiology; mandating compression technology. Image compression is currently used to transmit images from combat hospital to tertiary care centers with subspecialists and our study demonstrates MPEG-4 technology as a reasonable means of achieving such compression.     

Medical ultrasound image compression using contextual vector quantization

With ever increasing use of medical ultrasound (US) images, a challenge exists to deal with storage and transmission of these images while still maintaining high diagnostic quality. In this article, a state-of-the-art context based method is proposed to overcome this challenge called contextual vector quantization (CVQ). In this method, a contextual region is defined as a region containing the most important information and must be encoded without considerable quality loss. Attempts are made to encode this region with high priority and high resolution (low compression ratio and high bit rate) CVQ algorithm; and the background, which has a lower priority, is separately encoded with a low resolution (high compression ratio and low bit rate) version of the CVQ algorithm. Finally both of the encoded contextual region and the encoded background region is merged together to reconstruct the output image. As a result, very good diagnostic image quality with lower image size and enhanced performance parameters including mean square error (MSE), pick signal to noise ratio (PSNR) and coefficient of correlation (CoC) are gained. The experimental results show that the proposed CVQ methodology is superior as compared to other existing methods (general methods such as JPEG and JPEG2K, and ROI based methods such as EBCOT and CSPIHT) in terms of measured performance parameters. This makes CVQ compression method a feasible technique to overcome storage and transmission limitations.     

A compression and transmission system of ultrasonic image sequence for telemedicine.

OBJECTIVE: A newly developed compression and transmission system of ultrasound image sequence for telemedicine is proposed for transmitting ultrasonic image sequence in real time via IP-connected computers for telemedicine. MATERIALS AND METHODS: In the compression method, the characteristics of ultrasound images were taken into account. Only sound data were essential, and the histogram of the images had two narrow distributions around black-and-white areas. The sound data, therefore, were run length encoded and then transmitted. In the transmission, UDP/IP was employed with a time weight insertion among the packets so as not to overflow the data buffers of computers in this system to derive the maximum transmission performance up to the network capacity. The decompression method was the same as the generation of the sector scan images from the sound data, so that natural ultrasound image sequence could be obtained. RESULTS: This system was evaluated by transmitting the ultrasonic image sequence of the heart via ISDN (1. 5 mbps). Although this system completely specialized in compression and transmission of the ultrasound sector scan image sequence, a relatively good performance in the frame rate and the image quality was achieved, compared with the previous systems (H.260, JPEG, and MPEG-1).     

Displaying radiologic images on personal computers: Image storage and compression—Part 2

This is part 2 of our article on image storage and compression, the third article of our series for radiologists and imaging scientists on displaying, manipulating, and analyzing radiologic images on personal computers. Image compression is classified as lossless (nondestructive) or lossy (destructive). Common lossless compression algorithms include variable-length bit codes (Huffman codes and variants), dictionary-based compression (Lempel-Ziv variants), and arithmetic coding. Huffman codes and the Lempel-Ziv-Welch (LZW) algorithm are commonly used for image compression. All of these compression methods are enhanced if the image has been transformed into a differential image based on a differential pulse-code modulation (DPCM) algorithm. The LZW compression after the DPCM image transformation performed the best on our example images, and performed almost as well as the best of the three commercial compression programs tested. Lossy compression techniques are capable of much higher data compression, but reduced image quality and compression artifacts may be noticeable. Lossy compression is comprised of three steps: transformation, quantization, and coding. Two commonly used transformation methods are the discrete cosine transformation and discrete wavelet transformation. In both methods, most of the image information is contained in a relatively few of the transformation coefficients. The quantization step reduces many of the lower order coefficients to 0, which greatly improves the efficiency of the coding (compression) step. In fractal-based image compression, image patterns are stored as equations that can be reconstructed at different levels of resolution.     

ECG signal compression by multi-iteration EZW coding for different wavelets and thresholds

The modified embedded zero-tree wavelet (MEZW) compression algorithm for the one-dimensional signal was originally derived for image compression based on Shapiro's EZW algorithm. It is revealed that the proposed codec is significantly more efficient in compression and in computation than previously proposed ECG compression schemes. The coder also attains exact bit rate control and generates a bit stream progressive in quality or rate. The EZW and MEZW algorithms apply the chosen threshold values or the expressions in order to specify that the significant transformed coefficients are greatly significant. Thus, two different threshold definitions, namely percentage and dyadic thresholds, are used, and they are applied for different wavelet types in biorthogonal and orthogonal classes. In detail, the MEZW and EZW algorithms results are quantitatively compared in terms of the compression ratio (CR) and percentage root mean square difference (PRD). Experiments are carried out on the selected records from the MIT-BIH arrhythmia database and an original ECG signal. It is observed that the MEZW algorithm shows a clear advantage in the CR achieved for a given PRD over the traditional EZW, and it gives better results for the biorthogonal wavelets than the orthogonal wavelets.     

A method for splitting digital value in radiological image compression

A new decomposition method using image splitting and gray-level remapping has been proposed for image compression, particularly for images with high contrast resolution. The effects of this method are especially evident in this radiological image compression study. In these experiments, the impact of this decomposition method was tested on image compression by employing it with two coding techniques on a set of clinically used CT images and several laser film digitized chest radiographs. One of the compression techniques used as zonal full-frame bit-allocation in the discrete cosine transform (DCT) domain, which is an enhanced full-frame DCT technique that has been proven to be an effective technique for radiological image compression. The other compression technique used was vector quantization with pruned tree-structured encoding, which through recent research has also been found to produce a low mean-square error and a high compression ratio. The parameters used in this study were mean-square error and the bit rate required for the compressed file. In addition to these parameters, the differences between the original and reconstructed images were presented so that the specific artifacts generated by both techniques could be discerned through visual perception.     

基于ISA-DWT的MR图像压缩新算法

本研究提出一种新的ISA-DWT（整数到整数的形状自适应离散小波变换）的核磁共振（MR）图像压缩算法,对变换后的系数采用适合于形状自适应离散小波变换的修改的SPIHT算法进行编码,并增加上下文自适应算术编码以提高其压缩性能.本研究算法可将前景区域和背景区域生成的压缩码流完全分离,且小波域的系数个数和图像域的个数相同.实验结果表明,对于MR图像,本研究算法的压缩性能明显优于JPEG2000中的最大位移算法.     

Development of a PC-based Radiological Imaging Workstation

Low-cost image processing systems which can provide convenient access to image processing and analysis techniques hold great potential as diagnostic and research tools in medical imaging. At the University of Washington, we have developed a PC-based medium performance image processing system for use as an experimental radiological workstation. The workstation uses a standard IBM PC/AT personal computer augmented with a custom designed image processor implemented on two IBM PC/AT prototyping boards. Features of the system include up to 52 512 × 512 × 8 bit frame buffers (4 on the image processor board and up to 48 in the host computer memory) and a 512 × 512 × 4 bit graphics overlay memory, hardware zoom, pan and scroll, pseudo coloring, and a 60 Hz noninterlaced display. Many image processing and analysis functions are provided in this workstation, and all user requests are supported in an interactive fashion. For example, arithmetic and logical point operations between two 512 × 512 frame buffers require approximately 170 ms, while computationally intensive functions such as an 11 × 11 convolution or a full screen geometric transformation (warping) can be completed in less than 10 seconds. A full screen 2-D Fast Fourier Transform (FFT) and Inverse FFT (IFFT) based on the row-column method can be completed in less than 20 seconds. The developed system can easily be configured into a DIN/PACS workstation or a biological imaging system. Hardware and software details of this workstation as well as user interface functions implemented will be discussed in the paper. Copyright © 1988 by the International Society for Optical Engineering. Proc. SPIE 914:1257-1264, 1988. Reprinted with permission.     

Contrast-enhanced, real-time volumetric ultrasound imaging of tissue perfusion: preliminary results in a rabbit model of testicular torsion

Contrast-enhanced ultrasound (US) imaging is potentially applicable to the clinical investigation of a wide variety of perfusion disorders. Quantitative analysis of perfusion is not widely performed, and is limited by the fact that data are acquired from a single tissue plane, a situation that is unlikely to accurately reflect global perfusion. Real-time perfusion information from a tissue volume in an experimental rabbit model of testicular torsion was obtained with a two-dimensional matrix phased array US transducer. Contrast-enhanced imaging was performed in 20 rabbits during intravenous infusion of the microbubble contrast agent Definity? before and after unilateral testicular torsion and contralateral orchiopexy. The degree of torsion was 0° in 4 (sham surgery), 180° in 4, 360° in 4, 540° in 4, and 720° in 4. An automated technique was developed to analyze the time history of US image intensity in experimental and control testes. Comparison of mean US intensity rate of change and of ratios between mean US intensity rate of change in experimental and control testes demonstrated good correlation with testicular perfusion and mean perfusion ratios obtained with radiolabeled microspheres, an accepted 'gold standard'. This method is of potential utility in the clinical evaluation of testicular and other organ perfusion.     

Evaluation of the Effect of Varying MPEG-2 Compression Ratios on Digital Coronary Angiographic Assessment of Stenosis Severity

The purpose of this study is to evaluate the influence of MPEG-2 compression scheme on coronary angiography and to search the highest compression ratio at which no significant effect to accuracy of assessment of stenosis severity occurs. Forty-Four digital cine angiographies were used. Three cardiologists participated in a subjective study in which they read both uncompressed images and compressed images. Furthermore, an objective study was carried out to measure vessel stenosis ratio by using software. The influence of compression was evaluated by kappa statistics in case of subjective study and by both systematic error and random error in case of objective study. Kappa statistics between uncompressed image and compressed image at a ratio of 80:1 was significantly lower than that of other compression ratios such as 40:1. Similar results were obtained in objective evaluation. In this report, the authors provide the baseline for further studies on observer performance for motion images.     

整型提升小波变换的块编码在医学图像压缩中的应用

提出一种基于整型提升小波变换的图像块压缩编码方法.整型提升小波变换具有计算快速、能实现任意图像尺寸的小波算法、能在当前位置完成小波变换、节省内存等特点,而且该提升算法能同时对图像进行有损或无损压缩,因而更适应于远程医疗系统和医学图像压缩系统.基于图像块压缩编码方法不仅可以实现比特率控制,还可以实现SNR(信噪比)可缩放性,支持图像的渐进传输.     

Lossless Compression on MRI Images Using SWT

Medical image compression is one of the growing research fields in biomedical applications. Most medical images need to be compressed using lossless compression as each pixel information is valuable. With the wide pervasiveness of medical imaging applications in health-care settings and the increased interest in telemedicine technologies, it has become essential to reduce both storage and transmission bandwidth requirements needed for archival and communication of related data, preferably by employing lossless compression methods. Furthermore, providing random access as well as resolution and quality scalability to the compressed data has become of great utility. Random access refers to the ability to decode any section of the compressed image without having to decode the entire data set. The system proposes to implement a lossless codec using an entropy coder. 3D medical images are decomposed into 2D slices and subjected to 2D-stationary wavelet transform (SWT). The decimated coefficients are compressed in parallel using embedded block coding with optimized truncation of the embedded bit stream. These bit streams are decoded and reconstructed using inverse SWT. Finally, the compression ratio (CR) is evaluated to prove the efficiency of the proposal. As an enhancement, the proposed system concentrates on minimizing the computation time by introducing parallel computing on the arithmetic coding stage as it deals with multiple subslices.     

Radiologist evaluation of a multispectral image compression algorithm for magnetic resonance images

With the advent of teleradiology and picture archiving and communication systems (PACS), the expense and time required for image transmission and long term image archiving become important. The use of validated image compression algorithms can greatly reduce these costs. A lossy, multispectral image compression scheme at compression ratios (CR) of 25∶1 and 32∶1 was used for a set of 26 different patient MR exams. The original and compressed/decompressed (CD) image sets were evaluated in a blinded fashion by four radiologists in two phases. The main objective was to determine whether radiologic interpretation would vary between the two types of CD image sets and the corresponding originals. In general, the compression algorithm caused a slight decrease in image quality; however, the interpretation of pathology did not change between the original and CD image sets. In only one case at the maximum CR=32 did one of four radiologists change the interpretation of pathology after CD. In this study, lossy multispectral image compression of MR images at CR=25 maintained diagnostic integrity. This could play a significant role in image storage and communications.     

Optimization of block size for DCT-based medical image compression

In view of the increasing importance of medical imaging in healthcare and the large amount of image data to be transmitted/stored, the need for development of an efficient medical image compression method, which would preserve the critical diagnostic information at higher compression, is growing. Discrete cosine transform (DCT) is a popular transform used in many practical image/video compression systems because of its high compression performance and good computational efficiency. As the computational burden of full frame DCT would be heavy, the image is usually divided into non-overlapping sub-images, or blocks, for processing. This paper aims to identify the optimum size of the block, in reference to compression of CT, ultrasound and X-ray images. Three conflicting requirements are considered, namely processing time, compression ratio and the quality of the reconstructed image. The quantitative comparison of various block sizes has been carried out on the basis of benefit-to-cost ratio (BCR) and reconstruction quality score (RQS). Experimental results are presented that verify the optimality of the 16 x 16 block size.     

Optimization of block size for DCT-based medical image compression

In view of the increasing importance of medical imaging in healthcare and the large amount of image data to be transmitted/stored, the need for development of an efficient medical image compression method, which would preserve the critical diagnostic information at higher compression, is growing. Discrete cosine transform (DCT) is a popular transform used in many practical image/video compression systems because of its high compression performance and good computational efficiency. As the computational burden of full frame DCT would be heavy, the image is usually divided into non-overlapping sub-images, or blocks, for processing. This paper aims to identify the optimum size of the block, in reference to compression of CT, ultrasound and X-ray images. Three conflicting requirements are considered, namely processing time, compression ratio and the quality of the reconstructed image. The quantitative comparison of various block sizes has been carried out on the basis of benefit-to-cost ratio (BCR) and reconstruction quality score (RQS). Experimental results are presented that verify the optimality of the 16 × 16 block size.     

Colorectal cancer screening of African Americans by internal medicine resident physicians can be improved with focused educational efforts

Colorectal cancer causes significant morbidity and mortality in the United States. African Americans are disproportionately affected by this malignancy. There is evidence to suggest that resident physicians inconsistently screen for colorectal cancer in African Americans, perhaps because of a deficiency in knowledge and limited resources. This study evaluated internal medicine resident physicians' colorectal screening practices in African Americans prior to and following a focused educational intervention. A medical record review of internal medicine resident physicians' adherence to colorectal cancer screening recommendations was conducted. Physicians' performance of rectal exams, fecal occult blood testing, flexible sigmoidoscopy and colonoscopy was evaluated for six months prior to and six months following an educational intervention that focused upon issues related to racial disparities in colorectal cancer. Statistical significance was assessed using Fischer's exact test. There were 116 patients included in the preintervention assessment and 132 patients included in the postintervention assessment. There was no statistical significance in the rate at which rectal exams (p=0.6605) and fecal occult blood testing (p=0.7748) were performed prior to and following the educational initiative. However, there was a statistically significant difference in the rate at which endoscopic assessments (p<0.0001) were performed. Educational interventions that are focused upon racial disparity in colorectal cancer may improve resident physicians' performance of endoscopic exams in African Americans. Continued effort to enhance resident physicians' colorectal cancer screening practices in African Americans is important.     

一种基于改进零树小波算法的选择性医学图像压缩技术

针对传统零树编码的三个不足，利用游程编码结合人眼视觉特性，对其进行了改进，在此基础上根据医学图像压缩的特点，探讨了选择性医学图像压缩技术，并将其和小波压缩算法结合。实验结果表明，改进方法减少了编码比特率和编码时间，达到了较好的压缩效果。     

Medical image compression based on a morphological representation of wavelet coefficients.

Image compression is fundamental to the efficient and cost-effective use of digital medical imaging technology and applications. Wavelet transform techniques currently provide the most promising approach to high-quality image compression which is essential for diagnostic medical applications. A novel approach to image compression based on the wavelet decomposition has been developed which utilizes the shape or morphology of wavelet transform coefficients in the wavelet domain to isolate and retain significant coefficients corresponding to image structure and features. The remaining coefficients are further compressed using a combination of run-length and Huffman coding. The technique has been implemented and applied to full 16 bit medical image data for a range of compression ratios. Objective peak signal-to-noise ratio performance of the compression technique was analyzed. Results indicate that good reconstructed image quality can be achieved at compression ratios of up to 15:1 for the image types studied. This technique represents an effective approach to the compression of diagnostic medical images and is worthy of further, more thorough, evaluation of diagnostic quality and accuracy in a clinical setting.     

医学超声图像低码率环境下的编码技术研究

针对医学超声视频的结构和特点,并结合小波变换压缩编码技术,实现了低比特率环境下医学超声旬序列的渐近式传输,实验结果证明这种编码方法是有效的,可行的。