Sacrificing Image Quality Research Articles

Benefits of minimum-variance beamforming in medical ultrasound imaging

Recently, significant improvement in image resolution has been demonstrated by applying adaptive beamforming to medical ultrasound imaging. In this paper, we have used the minimum-variance beamformer to show how the low sidelobe levels and narrow beamwidth of adaptive methods can be used, not only to increase resolution, but also to enhance imaging in several ways. By using a minimum-variance beamformer instead of delay-and-sum on reception, reduced aperture, higher frame rates, or increased depth of penetration can be achieved without sacrificing image quality. We demonstrate comparable resolution on images of wire targets and a cyst phantom obtained with a 96-element, 18.5-mm transducer using delay-and-sum, and a 48-element, 9.25-mm transducer using minimum variance. To increase frame rate, fewer and wider transmit beams in combination with several parallel receive beams may be used. We show comparable resolution to delay-and-sum using minimum variance, 1/4th of the number of transmit beams and 4 parallel receive beams, potentially increasing the frame rate by 4. Finally, we show that by lowering the frequency of the transmitted beam and beamforming the received data with the minimum variance beamformer, increased depth of penetration is achieved without sacrificing lateral resolution.

Do we need to consider motion artefacts other than swallowing in carotid artery imaging?

Recent advances in carotid artery wall imaging have seen a transition from 2D to more efficient 3D imaging [1] without sacrificing image quality [2]. A disadvantage of 3D scans is their longer time to complete the acquisition, making them more susceptible to motion artefacts, particularly swallowing [3] and bulk head motion during the long 3D acquisition time. Respiratory movement artefact is controversial [4], but Boussel [5] demonstrated its detrimental effect on carotid wall imaging, using real-time transaxial cines. However, during quiet supine respiration, breathing is predominantly diaphragmatic resulting in the greatest carotid movement in the head-foot direction. We used a novel high temporal resolution interleaved approach to study carotid artery movement in all directions, over the typical 3D scan duration, for a true representation of the potential problem for 3D imaging.

Fast Fine Granularity Scalability Decoding Scheme for Low-Delay Scalable Video Coding Applications

The Fine Grain Scalability (FGS) technique used in SVC codec encodes and decodes the quantization error of QBL (quality base layer) along the cyclic scanning path. The FGS technique provides the scalability property to the compressed bit stream. However, the cyclic scanning procedure of FGS method may require a huge computing time. In this paper, we propose a fast FGS decoding scheme, which has a lower decoding complexity without sacrificing image quality.

In Vivo 3D Comprehensive Microscopy of the Human Esophagus for the Management of Barrett's Patients

Optical coherence tomography (OCT) provides high-resolution (∼10 μm resolution) cross-sectional images of esophageal microstructure and in recent years has been shown to accurately differentiate specialized intestinal metaplasia (SIM) from gastric cardia at the squamocolumnar junction for screening, and diagnose dysplasia and cancer in patients with SIM for surveillance of Barrett's esophagus. The clinical utility of this technology has however been restricted due to limitations in imaging speed and optical probe design. Optical frequency domain imaging (OFDI) is a new imaging technology that is capable of improving imaging speed over traditional OCT techniques by orders of magnitude without sacrificing image quality. We have developed a balloon catheter (2.5 cm dia.) based OFDI system that acquires comprehensive three-dimensional microscopic images of the entire distal esophagus (∼6.0 cm) with resolution in cylindrical coordinates of 20 μm (φ) × 8 μm (r) × 50 μm (z) in < 2 mins. Comprehensive microscopy of the distal esophagus was performed in over 40 patients with the OFDI system and balloon catheter. The acquired volumetric OFDI datasets were assessed and correlated to histopathological findings. For the 40 patients, we achieved satisfactory imaging in 37 patients (92%) and an average of over 90% surface area coverage per patient. Based on these early results, we anticipate that comprehensive volumetric microscopy with OFDI will provide a minimally invasive means for screening the entire distal esophagus for intestinal metaplasia, dysplasia, and adenocarcinoma.

Variable resolution reconstruction for cartesian data acquired with nonconstant sampling density in phase‐encoding direction

The variable-kernel extent technique is applied for providing local high-resolution images from k-space data sampled on a Cartesian sampling grid with gradually decreasing sampling density in the phase-encoding direction. The approach is based on a variable spatial resolution reconstruction technique providing gradually decreasing resolution in the phase-encoding direction with increasing distance to the image center, while preserving full spatial resolution in a narrow slab centered in spatial domain. Reconstruction is performed by a variable convolution kernel gridding technique. The convolution kernel width is chosen proportional to the k-space sampling spacing to utilize the respective apodization in the image for reduction of the aliasing artifacts. Application of this technique to carotid artery wall imaging shows the potential of the technique for a significant reduction of image acquisition time without sacrificing image quality in the region of the carotid arteries.

Steganography using overlapping codebook partition

A tradeoff between the hiding capacity of a cover image and the quality of a stego-image in steganographic schemes is inevitable. This paper presents overlapping codebook partitioning to challenge this tradeoff. The codewords in a codebook are grouped into sub-clusters, according to similarity. Any size sub-cluster is allowed; moreover, a sub-cluster is permitted to overlap with sub-clusters to increase hiding capacity without sacrificing image quality. As a result of this improved scheme, the hiding capacity of a cover image increases, whereas the quality of a stego-image stays the same.

3D Echocardiography: A Review of the Current Status and Future Directions

Ultrasound technology has improved markedly in the past 10 to 15 years, prompting echocardiographers to extend its use in studying cardiac structure and function. New ultrasound equipment and techniques offer superior image quality, greater accuracy, and expanding capabilities. As a result, more and improved imaging modalities are available for evaluating cardiac anatomy, ventricular function, blood flow velocity, and valvular diseases. Threedimensional (3D) echocardiography offers the ability to improve and expand the diagnostic capabilities of cardiac ultrasound. However, as with any emerging technology, the enthusiasm to embrace a new technique must be tempered by a critical appraisal of the evidence supporting its use. It is essential to assess the limitations as well as the unique capabilities it provides. Cardiac imaging should be safe, accurate, versatile, comprehensive, and cost-effective, while providing important clinical information. Criteria for appropriate utilization should be based on current evidence and updated as new information becomes available. To justify the use of a new 3D modality, its unique contribution to clinical practice must be critically analyzed. In this article we review the status of 3D echocardiography, examine the evidence for its use in various clinical situations, and propose guidelines for appropriate application of this technique based on available evidence.

Artifact-free black-blood cine cardiac imaging in a single breath-hold

Fast imaging using the STimulated Echo Acquisition Mode (STEAM) sequence can produce cine images of the heart with black-blood contrast. Nevertheless, correction of deformation-related artifacts is required in order to maintain myocardial signal throughout the cardiac cycle. Recent work by our group has eliminated this artifact by combining two STEAM sequences acquired with two different demodulation gradients. Unfortunately, these two STEAM sequences were acquired on two separate breath-holds; thus, scan time doubled. In this work, we present a technique to reduce the total scan time by one half, without sacrificing image quality. The technique is based on interleaving two demodulations within one acquisition in order to obtain quality cine images of the heart in a single breath-hold. The technique was tested on animal models and human subjects, and the impact of interleaved acquisition on image quality was studied using quantitative and qualitative measures.

The ALARA concept in pediatric cardiac catheterization: techniques and tactics for managing radiation dose

The cardiac catheterization laboratory plays an important role in the management of children with congenital heart disease by not only enabling diagnosis but, in many cases, providing definitive therapy. The goal of the ALARA (As Low as Reasonably Achievable) concept as it applies to cardiac catheterization is to provide maximal diagnostic and therapeutic benefit while requiring the lowest possible radiation dose. A number of specific challenges unique to the setting of pediatric cardiac catheterization, such as higher heart rates, smaller cardiovascular structures, smaller body size, and wider variety of unusual anatomic variants with the potential need for relatively lengthy and complex studies, result in relatively high radiation doses (to the patient and, consequently, to laboratory personnel). In addition, the improved survival of patients with complex anatomy (e.g., palliated single ventricle anatomies) implies that many such children with chronic cardiac disease require frequent catheterizations within the first few years of life. These factors, coupled with the increased radiosensitivity of children and a longer lifespan ahead of them in which to possibly develop radiation-related sequelae, converge to create potentially ominous consequences. Attention to basic rules of radiation safety is, therefore, of tremendous importance in the pediatric cardiac catheterization laboratory. This review focuses on the importance of adequate planning of the study, optimizing image formation, management of fluoroscopy and cine angiography parameters, and the use of certain equipment features that might allow the cardiologist to lower the radiation dose without sacrificing image quality.

An efficient scheme for motion estimation using multireference frames in H.264/AVC

The multiple reference frame motion compensation (MRMC) supported by H.264 makes use of the redundancy which is between multiple frames to enhance the coding efficiency over a scheme using the single reference frame motion compensation (SRMC) in which motion vectors are searched over a single reference frame. And, the technique using multiple reference frames can combat the channel errors efficiently. However, searching the motion vectors in multiple frames may require a huge computing time. This paper proposes a novel motion estimation procedure, which has a lower search complexity without sacrificing image quality. To reduce the complexity of motion estimation procedure, we use a temporary motion vector generated with little computation. The temporary motion vector is calculated from the motion vector map composed of motion vectors between successive frames, and used to predict the optimal motion vector for a reference frame. The proposed scheme requires the lower complexity than conventional schemes by using the temporary motion vector and refinement process over a narrow search range around the temporary predictive motion vector. Since the temporary predictive motion vector effectively chases the optimal motion vector for each reference frame, the encoded image quality by proposed scheme is very similar to that of full search algorithm. The proposed motion estimation process consists of three phases: 1)making a vector map between two consecutive frames, where the vector map is constructed by copying motion vectors which have been estimated in first reference frame, 2) composing a temporary motion vector with element vectors which are in the vector map, and 3) finally, the temporary predictive motion vector is refined over a narrow search range. We show experimental results which demonstrate the effectiveness of the proposed method. To compare the proposed motion estimation algorithm with the conventional schemes, we check the CPU times consumed by ME module in H.264 encoder using the proposed scheme. In the results, CPU time consumed by the proposed scheme has been reduced significantly without additional distortion of the encoded video quality.

Optimization of MDCT of the Wrist to Achieve Diagnostic Image Quality with Minimum Radiation Exposure

This study tests various acquisition and reconstruction protocols for MDCT of the wrist to determine the optimal protocol for obtaining diagnostic image quality with minimal radiation exposure. Thirty anatomic specimens were examined with an MDCT collimation of 4.0 x 1.0 mm and 2.0 x 0.5 mm (80, 120, and 140 kV; 80, 100, 130, 160, and 200 mA; rotation time, 0.5 0.75, 1.0 sec; pitch, 1.0, 1.3, 1.5, and 2.0). Coronal images were reconstructed using a slice thickness of 0.5, 1.0, and 2.0 mm with 60% overlap. Three observers evaluated all images independently for gross and fine anatomic detail. Diagnostic confidence was tested using Shrout-Fleiss intraclass correlation coefficients. Interobserver agreement was assessed by Kappa statistics and the Kruskal-Wallis test. Fine anatomic detail was best presented in 0.5-mm or 1.00-mm reconstructions based on a 2.0 x 0.5 mm acquisition. A rotation time of > or = 0.75 sec resulted in fewer artifacts; a significant dose reduction was achieved with 80 kV and 100 mA at the expense of somewhat increased noise, but without significant loss of anatomic detail in bone presentation. Artifacts were tolerable with a pitch of 1.5 or less. MDCT at the described optimal settings allows significant dosage reduction without sacrificing image quality. An acquisition and reconstruction thickness of 0.5 mm results in the best depiction of anatomic detail. A reconstruction thickness of 1.0 mm with a reconstruction interval of 0.5 mm represents a good trade-off between noise and resolution when using low-dose protocols.

MO-B-I-618-01: Recent Advances and State-Of-The-Art in Screen-Film Receptors and Film Processing

Purpose: This presentation discusses recent advances in film/screen radiography. These include a high-resolution high-contrast film/screen system for mammography, as well as a high-speed high-resolution film/screen system that provides improved image quality and opportunities for dose reduction, compared to an existing state-of-the-art, general purpose film/screen system. A description of the technical aspects and system design of these new systems is given. The new film features novel silver-halide microcrystals and is dual coated using a split E-layer coating format featuring gradient crossover control. Without sacrificing image quality, the new system can be exposed with existing intensifying screens and provides significant dose reductions. Method and Materials: This paper describes details of the system's design and performance. The film includes: 1) a dual-layer coating structure that provides high-speed and high-resolution imaging of chest and orthopedic imaging; 2) high sensitivity silver-halide microcrystals that provide high contrast and high resolution. Modulation transfer function (MTF) measurements were used to describe the resolution of various film/screen combinations using this new radiographic film and they are compared to existing state-of-the-art film/screen systems. Results: Inverse square sensitometry and MTF measurements, as well as phantom and clinical radiographs using this new film/screen system, demonstrate several benefits. A significant dose reduction is possible without reducing image quality by using standard intensifying screens. In addition, significant image quality improvements are possible in orthopedic imaging using high-resolution extremity-intensifying screens at conventional radiation doses. Conclusions: We have designed, built, and implemented a novel film/screen system for general-purpose radiography that provides high-resolution images with a potential for dose reduction or MTF improvement. Initial clinical evaluation of the system demonstrates a 2X reduction in dose without sacrificing image quality. In addition, significant resolution improvements are possible at the conventional radiation doses.

High Speed High Image Quality Printing on Plain Paper Using Symmetrically Arranged Color Bubble Jet Print Head

To date, printer manufacturers have faced an ongoing dilemma: How to increase printing speed without sacrificing image quality, and vice versa. The new bi-directional printing system that utilizes the New &#x201C;MicroFine Droplet Technology&#x201D; has proposed to overcome the problem.In conventional color printing, simple bi-direction printing leads to inconsistency in color produced between forward printing and backward printing due to the difference of color placement order within each printing direction. With the new bi-directional printing system, however, two groups of ink nozzle rows with cyan, magenta and yellow are arranged symmetrically to eliminate the inconsistency of color produced between different printing directions. The result of this work is Canon's S750 and i850 bubble jet printer. The key technologies that enabled this new nozzle arrangement without sacrificing the cost and the size of the print head will be described in this paper.

Schemes for the optimization of chest radiography using a computer model of the patient and x-ray imaging system.

A computer program has been developed to model chest radiography. It incorporates a voxel phantom of an adult and includes antiscatter grid, radiographic screen, and film. Image quality is quantified by calculating the contrast (deltaOD) and the ideal observer signal-to-noise ratio (SNR(I)) for a number of relevant anatomical details at various positions in the anatomy. Detector noise and system unsharpness are modeled and their influence on image quality is considered. A measure of useful dynamic range is computed and defined as the fraction of the image that is reproduced at an optical density such that the film gradient exceeds a preset value. The effective dose is used as a measure of the radiation risk for the patient. A novel approach to patient dose and image quality optimization has been developed and implemented. It is based on a reference system acknowledged to yield acceptable image quality in a clinical trial. Two optimizations schemes have been studied, the first including the contrast of vessels as measure of image quality and the second scheme using also the signal-to-noise ratio of calcifications. Both schemes make use of our measure of useful dynamic range as a key quantity. A large variety of imaging conditions was simulated by varying the tube voltage, antiscatter device, screen-film system, and maximum optical density in the computed image. It was found that the optical density is crucial in screen-film chest radiography. Significant dose savings (30%-50%) can be accomplished without sacrificing image quality by using low-atomic-number grids with a low grid ratio or an air gap and more sensitive screen-film system. Dose-efficient configurations proposed by the model agree well with the example of good radiographic technique suggested by the European Commission.

Dose reduction in computed tomography by attenuation-based on-line modulation of tube current: evaluation of six anatomical regions

This study investigated the potential of attenuation-based on-line modulation of tube current to reduce the dose of computed tomography (in milliamperes) without loss in image quality. The dose can be reduced for non-circular patient cross-sections by reducing the tube current at the angular positions at which the diameter through the patient diameter is smallest. We investigated a new technical approach with attenuation-based on-line modulation of tube current. Computed tomographic projection data were analyzed to determine the optimal milliampere values for each projection angle in real time, instead of performing prior measurements with localizer radiographs. We compared image quality, noise pattern, and dose for standard scans and for scans with attenuation-based on-line modulation of tube current in a group of 30 radiation therapy patients. Six different anatomical regions were examined: head, shoulder, thorax, abdomen, pelvis, and extremities (knee). Image quality was evaluated by four radiologists in a blinded fashion. We found the dose to be reduced typically by 15-50 %. In general, no deterioration in image quality was observed. Thus the dose in computed tomography be reduced substantially by technical measures without sacrificing image quality. Attenuation-based on-line modulation of tube current is an efficient and practical means for this.

MR fluoroscopy using projection reconstruction multi-gradient-echo (prMGE) MRI.

A projection reconstruction multi-gradient-echo (prMGE) technique is presented. The introduced technique is an extension of a standard projection reconstruction steady-state gradient-echo technique allowing for the acquisition of several gradient echoes after each excitation of the spin system. Each echo train is used for acquiring data of a certain angular segment of k-space. By use of echo trains consisting of up to four echoes, the overall acquisition time for a 128(2) image can be reduced to 150 ms without sacrificing image quality. Results are presented for cardiac fluoroscopy, for the visualization of swallowing, and for the visualization of joint motion. For all investigated applications promising results have been obtained. Especially in parts of the body where motion on an even shorter time scale than the acquisition process or significant in-plane or through-plane flow are within the field of view, the introduced technique appears to be a promising technique for MR fluoroscopy. Magn Reson Med 42:324-334, 1999.

RADIOGRAPHIC TRENDS OF DENTAL OFFICES AND DENTAL SCHOOLS

A survey of private practice facilities in the United States that perform dental radiography was conducted in 1993 and repeated in dental schools in 1995-1996. Both surveys were conducted as part of the Nationwide Evaluation of X-ray Trends, or NEXT, survey program. A representative sample of dental facilities from each participating state were surveyed, and data on patient radiation exposure, radiographic technique, film-image quality, film-processing quality and darkroom fog were collected. The authors found that dental schools use E-speed film more frequently than do private practice facilities. The use of E-speed film and better film processing by dental schools resulted in lower patient radiation exposures without sacrificing image quality. The authors also found that dental school darkrooms had lower ambient fog levels than did those of private practice facilities. The distribution for the 1993 NEXT survey facilities was greater than that observed for dental schools for radiation exposure, film-processing quality and darkroom fog. Dental schools, in general, had better film quality and lower radiation exposures than did private practice facilities. Facilities need to emphasize better quality processing and the use of E-speed film to reduce patient exposure and improve image quality.

Radiance interpolants for accelerated bounded-error ray tracing

Ray tracers, which sample radiance, are usually regarded as offline rendering algorithms that are too slow for interactive use. In this article we present a system that exploits object-space, ray-space, image-space, and temporal coherence to accelerate ray tracing. Our system uses per-surface interpolants to approximate radiance both interactive and batch ray tracers. Our approach explicity decouples the two primary operations of a ray tracer—shading and visibility determination—and accelerates each of them independently. Shading is accelerated by quadrilinearily interpolating lazily acquired radiance samples. Interpolation error does not exceed a user-specified bound, allowing the user to control performance/quality tradeoffs. Error is bounded by adaptive sampling at discontinuities and radiance nonlinearities. Visibility determination at pixels is accelerated by reprojecting interpolants as the user's viewpoint changes. A fast scan-line alogoithm then achieves high performance without sacrificing image quality. For a smoothly varying viewpoint, the combination of lazy interpolants and projection substantially accelerates the ray tracer. Additionally, an efficient cache management algorithm keeps the memory footprint of the system small with negilgible overhead.

Color images in telepathology: How many colors do we need?

It is generally assumed that for telepathology, accurate depiction of microscopic images requires the use of “true color” (ie, 24 bits, eight bits each for red, green, and blue) in the digitized image used for transmission. If such a 24-bit color image file, which provides a palette of 16.7 million colors, could be reduced in size by decreasing the possible numbers of colors displayed in the image to 8 bits (palette of 256 colors), the image files would require less storage space, could be transmitted more rapidly, and would require less telecommunications bandwidth. However, such color reduction must not result in detectable image degradation, especially if the images are to be used for diagnosis. Therefore, we performed a carefully controlled study to determine whether pathologists could detect differences in the quality of microscopic images that were reduced from 24 to 8 bits of color. Thirty pathologists were each asked to view a set of 30 image pairs displayed on a computer monitor. Each image pair consisted of the original 24-bit color version and an 8-bit color-reduced version, derived using an adaptive color reduction algorithm with diffusion dithering. Observers were asked whether they could detect any difference in quality between the image pairs. Then, regardless of their answer, they were asked to choose the better quality image of the pair. Overall, there was not a statistically significant ability to consciously detect differences between the image pairs ( P < .750). However, when forced to choose, there was a significant preference for the 8-bit images as being of “better quality” ( P < .005). We conclude that telepathology applications may be able to take advantage of adaptive color reduction algorithms to reduce image file size without sacrificing image quality. Additional studies must be performed to determine the minimal image requirements for accurate diagnosis by telepatholgy.

A wavelet representation of reflectance functions

Analytical models of light reflection are in common use in computer graphics. However, models based on measured reflectance data promise increased realism by making it possible to simulate many more types of surfaces to a greater level of accuracy than with analytical models. They also require less expert knowledge about the illumination models and their parameters. There are a number of hurdles to using measured reflectance functions, however. The data sets are very large. A reflectance distribution function sampled at five degrees angular resolution, arguably sparse enough to miss highlights and other high frequency effects, can easily require over a million samples, which in turn amount to over four megabytes of data. These data then also require some form of interpolation and filtering to be used effectively. We examine issues of representation of measured reflectance distribution functions. In particular, we examine a wavelet basis representation of reflectance functions, and the algorithms required for efficient point-wise reconstruction of the BRDF. We show that the nonstandard wavelet decomposition leads to considerably more efficient algorithms than the standard wavelet decomposition. We also show that thresholding allows considerable improvement in running times, without unduly sacrificing image quality.