How to improve microscopic images obtained with consumer-type digital cameras

AIM: Digital imaging is useful in conventional photography because it immediately provides images, and the image quality can be improved afterwards by the use of computer programs. The major disadvantages of consumer-type digital cameras mounted on microscopes are (i) unequal illumination through the image, and (ii) a coloured background. A computer program was specifically adapted and refined to improve images obtained with consumer-type digital cameras mounted on microscopes. METHODS AND RESULTS: An approach using a division operation between the specimen image and a background image leads to homogeneous illumination throughout the image, with automatically corrected brightness and white background. The correct colour spectrum is preserved by correction of the histogram. This approach was obtained from the freeware computer program 'Image Arithmetic'. In a test, three different consumer-type digital cameras (Sony, Nikon, Olympus) on different microscopes were used to obtain images of different types of histological specimens (cervical smear, bone marrow biopsy, and colonic biopsy). The computer program dramatically improved the quality of images obtained with all tested cameras. CONCLUSION: Using this approach, even low-cost digital cameras mounted on microscopes produce brilliant images with homogeneous illumination and a white background, the image quality being comparable with expensive cameras especially designed for microscopes.     

Comparison of radiographic image quality from four digitization devices as viewed on computer monitors

The objective of this study was to compare the quality of radiographic images digitized from commercial-grade and consumer-grade digital cameras and scanners as viewed on computer monitor. Radiographic images were digitized from hardcopy film using a commercial-grade laser scanner, a consumer-grade desktop flatbed scanner, a commercial-grade digital camera, and a consumer-grade digital camera. The quality of images without and with grayscale histogram adjustment was evaluated subjectively by 10 board-certified radiologists. Optical density response was evaluated objectively using a grayscale test pattern. There was no significant difference in subjective quality among images digitized with the commercial scanner, consumer scanner, and commercial camera. The quality of images digitized with the consumer camera was lower than the other 3. Objective tests showed the commercial scanner to have the most linear optical density response. For the purpose of viewing images on a computer monitor, a consumer-grade desktop scanner can produce images of similar quality to those produced by more expensive laser commercial-grade scanners and digital cameras and provides cost-efficient means to digitize radiographic plain films. A consumer-grade camera may not be optimal for use in this setting.     

Comparison of radiographic image quality from four digitization devices as viewed on computer monitors

The objective of this study was to compare the quality of radiographic images digitized from commercial-grade and consumer-grade digital cameras and scanners as viewed on computer monitor. Radiographic images were digitized from hardcopy film using a commercial-grade laser scanner, a consumer-grade desktop flatbed scanner, a commercial-grade digital camera, and a consumer-grade digital camera. The quality of images without and with grayscale histogram adjustment was evaluated subjectively by 10 board-certified radiologists. Optical density response was evaluated objectively using a grayscale test pattern. There was no significant difference in subjective quality among images digitized with the commercial scanner, consumer scanner, and commercial camera. The quality of images digitized with the consumer camera was lower than the other 3. Objective tests showed the commercial scanner to have the most linear optical density response. For the purpose of viewing images on a computer monitor, a consumer-grade desktop scanner can produce images of similar quality to those produced by more expensive laser commercial-grade scanners and digital cameras and provides cost-efficient means to digitize radiographic plain films. A consumer-grade camera may not be optimal for use in this setting.     

The use of digital images in pathology

Digital images are routinely used by the publishing industry, but most diagnostic pathologists are unfamiliar with the technology and its possibilities. This review aims to explain the basic principles of digital image acquisition, storage, manipulation and use, and the possibilities provided not only in research, but also in teaching and in routine diagnostic pathology. Images of natural objects are usually expressed digitally as ‘bitmaps’—rectilinear arrays of small dots. The size of each dot can vary, but so can its information content in terms, for example, of colour, greyscale or opacity. Various file formats and compression algorithms are available. Video cameras connected to microscopes are familiar to most pathologists; video images can be converted directly to a digital form by a suitably equipped computer. Digital cameras and scanners are alternative acquisition tools of relevance to pathologists. Once acquired, a digital image can easily be subjected to the digital equivalent of any conventional darkroom manipulation and modern software allows much more flexibility, to such an extent that a new tool for scientific fraud has been created. For research, image enhancement and analysis is an increasingly powerful and affordable tool. Morphometric measurements are, after many predictions, at last beginning to be part of the toolkit of the diagnostic pathologist. In teaching, the potential to create dramatic yet informative presentations is demonstrated daily by the publishing industry; such methods are readily applicable to the classroom. The combination of digital images and the Internet raises many possibilities; for example, instead of seeking one expert diagnostic opinion, one could simultaneously seek the opinion of many, all around the globe. It is inevitable that in the coming years the use of digital images will spread from the laboratory to the medical curriculum and to the whole of diagnostic pathology. © 1997 John Wiley & Sons, Ltd.     

A Comparative Study of Conventional Mammography Film Interpretations with Soft Copy Readings of the Same Examinations

An acceptable mammography film digitizer must provide high-quality images at a level of diagnostic accuracy comparable to reading conventional film examinations. The purpose of this study was to determine if there are significant differences between the interpretations of conventional film-screen mammography examinations and soft copy readings of the images produced by a mammography film digitizer. Eight radiologists interpreted 120 mammography examinations, half as original films and the other half as digital images on a soft copy work station. No radiologist read the same examination twice. The interpretations were recorded in accordance with the Breast Imaging Reporting and Data System and included other variables such as perceived image quality and diagnostic difficulty and confidence. The results provide support for the hypothesis that there are no significant differences between the interpretations of conventional film-screen mammography examinations and soft copy examinations produced by a mammography film digitizer. The study was conducted primarily at the Johns Hopkins Medical Institutions in Baltimore, MD where all of the authors except Dr. Chad Mitchell are located. He is a Naval Officer at the Uniformed Services University of the Health Sciences in Bethesda, MD.     

Critical comparison of 31 commercially available digital slide systems in pathology

Advances in new technologies for complete slide digitization in pathology have allowed the appearance of a wide spectrum of technologic solutions for whole-slide scanning, which have been classified into motorized microscopes and scanners. This article describes technical aspects of 31 different digital microscopy systems. The most relevant characteristics of the scanning devices are described, including the cameras used, the speed of digitization, and the image quality. Other aspects, such as the file format, the compression techniques, and the solutions for visualization of digital slides, (including diagnosis-aided tools) are also considered. Most of the systems evaluated allow a high-resolution digitization of the whole slide within about 1 hour using a x40 objective. The image quality of the current virtual microscopy systems is suitable for clinical, educational, and research purposes. The efficient use of digital microscopy by means of image analysis systems can offer important benefits to pathology departments.     

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.     

Image compression techniques for medical diagnostic imaging systems

As a result of recent technological advances, a significant (and increasing) number of the images in a typical radiology department are represented in digital form. This includes images that have been captured using digital imaging modalities such as computed tomography and magnetic resonance imaging as well as images that have been digitally converted from film originals as in computed radiography. To provide economical storage of such images and to allow for their efficient transmission over various networks, it becomes necessary to consider digital image compression techniques. In this article, the fundamental concepts of several popular reversible and nonreversible image compression schemes are reviewed. In addition, the performance of the schemes in terms of compression ratio and reconstructed image quality as applied to medical diagnostic images is investigated.     

Thick-section histometry of porous hydroxyapatite implants using backscattered electron imaging

A histometry system has been developed to measure bone ingrowth into porous hydroxyapatite implants utilizing the backscattered electron image of thick sections. The system consists of a scanning electron microscope (SEM) with backscattered electron detector, digital beam controller, minicomputer based image digitization, and microcomputer based image processing, point counting, and lineal analysis. The SEM backscattered electron imaging mode yields high tissue contrast and sharp tissue boundaries, substantially reducing the lost cap and projection effect errors of thick sections. High-resolution digitization of the image substantially reduces the standard error of the estimates. By using the digitized image the tedious process of filtering artifacts and recording actual point counts, intersections, and intercept lengths is delegated to computer software. Performance of this system in a recent study demonstrated substantial ease of operator use and speed of measurement. In the absence of a digital beam controller an inexpensive video digitizer circuit board may be used to digitize photographic prints of the SEM images. The combination of increased accuracy, precision, operator ease, and speed suggests that this system can be useful for soft tissue-bone-implant histometry.     

Novel MOS prediction models for compressed medical image quality

This paper presents the development of novel models which can be potentially useful in determining the upper limit of image compression thresholds, to preserve diagnostically relevant information in compressed medical images. These models were developed by evolving the correlation between the theoretically computed objective (peak signal-to-noise ratio and structural similarity) and subjective mean opinion score (MOS) quality parameters. The developed models were validated by comparing the model generated MOS with the corresponding experimental MOS of six independent observers considering joint photographic experts group (JPEG), JPEG2000 and set partitioning in hierarchical trees (SPIHT) compressions of computed tomography (CT) scan images. It is found that the correlation between the model generated and experimental MOS and PRD are ≥0.87 and ≤13% respectively for the compression range 0.05–2.0 bits/pixel of the CT scan images. Therefore our models can be potentially useful for observer-independent MOS prediction and quality assessment of reconstructed medical images. In addition this also avoids the need for exhaustive and time-consuming experimental MOS and thus it can be more suitable for teleradiology applications.     

Novel MOS prediction models for compressed medical image quality

This paper presents the development of novel models which can be potentially useful in determining the upper limit of image compression thresholds, to preserve diagnostically relevant information in compressed medical images. These models were developed by evolving the correlation between the theoretically computed objective (peak signal-to-noise ratio and structural similarity) and subjective mean opinion score (MOS) quality parameters. The developed models were validated by comparing the model generated MOS with the corresponding experimental MOS of six independent observers considering joint photographic experts group (JPEG), JPEG2000 and set partitioning in hierarchical trees (SPIHT) compressions of computed tomography (CT) scan images. It is found that the correlation between the model generated and experimental MOS and PRD are ≥0.87 and ≤13% respectively for the compression range 0.05-2.0 bits/pixel of the CT scan images. Therefore our models can be potentially useful for observer-independent MOS prediction and quality assessment of reconstructed medical images. In addition this also avoids the need for exhaustive and time-consuming experimental MOS and thus it can be more suitable for teleradiology applications.     

Characterization of color CRT display systems for monochrome applications

Soft-copy presentation of medical images is becoming more and more important as medical imaging is strongly moving toward digital technology, and health care facilities are converting to filmless hospital and radiological information management. Although most medical images are monochrome, frequently they are displayed on color CRTs, particularly if general-purpose workstations or PCs are used for medical viewing. In the present report, general measurement and modeling procedures for the characterization of color CRT monitors for monochrome presentation are introduced. The contributions from the three color channels (red, green, and blue) are weighted according to the spectral sensitivity of the human eye for photopic viewing. The luminance behavior and the resolution capabilities of color CRT monitors are analyzed with the help of photometer and charge-coupled device (CCD) camera measurements. For the evaluation of spatial resolution, a two-dimensional Fourier analysis of special test images containing white noise (broadband response) is employed. A stage model for a color CRT monitor is developed to discuss the effects of scanning and dot sampling. Furthermore, display intrinsic veiling glare and reflectivity of typical color CRT monitors are measured and compared with those of monochrome CRT monitors. The developed methods and models allow one to describe the image quality aspects of color monitors if they are applied for medical monochrome image presentation. Particularly, because of the reduced luminance and dynamic range of color monitors, the calibration and control of their luminance curves is a very important task. For present color CRT monitors, 1,280 x 1,024 turns out to be an intrinsic limit for the displayable matrix of medical images.     

Digital image capture applied to electron microscopic examination of renal biopsies

AIMS: Digital image capture systems to replace traditional film cameras are now available for most electron microscopes. For a diagnostic electron microscope laboratory the test of this new technology is in its application to the examination of renal biopsy specimens. METHODS: A long-term comparison is made between the work procedures employed with conventional film photography versus digital image capture in routine renal biopsy examination. RESULTS: Digital image capture has lead to a reduction in turnaround time and allows for more images to be collected per case, providing more diagnostic information. Ultrastructural measurement is made easier, accuracy of patient records is improved and electronic communication of results is more accessible. Significant operational cost savings are also possible. CONCLUSION: A quicker and more comprehensive assessment of renal biopsy specimens is possible using digital image capture for ultrastructural examination.     

Detection of Artificial Occlusal Caries in a Phosphor Imaging Plate System with Two Types of LCD Monitors Versus Three Different Films

The aim of this study was to determine diagnostic performance of a storage phosphor plate system Digora® Optime (Soredex, Helsinki, Finland) with two types of LCD monitor in the detection of artificial caries when compared to Ultraspeed (D), Ektaspeed Plus (E), and Insight (F) radiographic films. Seventy extracted human molars—with artificial caries—were radiographed under identical standardized conditions using (1) a storage phosphor plate system Digora (Soredex, Helsinki, Finland), (2) Insight, (3) Ektaspeed Plus, and (4) Ultraspeed (Carestream Health Inc, Rochester, NY). All digital images and radiographs were examined by three observers for the presence or absence of artificial caries using a five-point confidence scale. Digital images were evaluated both on a LCD computer monitor (Philips 170S, Holland) and medical monitor—3 megapixel monochrome display (Me355i2, Totoku, Tokyo)—with brightness and contrast enhancement. Observer responses were evaluated using ROC analysis and other measurements for diagnostic accuracy. Storage phosphor images with medical monitor demonstrated higher mean A_z values (0.70 ± 0.08) than digital images with computer monitor and conventional films. Storage phosphor images with medical monitor presented the highest score, 0.97, 0.90, 0.94, for each observer, respectively. Also, true positive observations (0.82) and positive likelihood ratios (2.71) were higher in enhanced storage phosphor images with medical monitor. Caries detection of mechanically created lesions by experienced radiologists is roughly comparable when examining D-speed film images and Digora images on both the computer and medical LCD monitors, and appears to be poorer on E- and F-speed film images.Key words: Diagnostic evaluation, digital display, digital imaging     

Vector quality measure of lossy compressed medical images

A numerical measure, which is able to predict diagnostic accuracy rather than subjective quality, is required for compressed medical image assessment. The objective of this study is to present a proposal for a new vector measure of image quality, reflecting diagnostic accuracy. Construction of such measure includes the formation of a diagnostic quality pattern based on the subjective ratings of local image features playing an essential role in the detection and classification of any lesion. Experimental results contain the opinions of 9 radiologists: 2 test designers and 7 observers who rated digital mammograms. The correlation coefficient between the numerical equivalent of the vector measure and subjective pattern is over 0.9.     

“Evaluation of a Very Low-Cost and Simple Teleradiology Technique”

This paper describes and analyzes a proposed solution of fundamental limitative factor of teleradiology to overcome the teleradiology usages problems in underdeveloped and developing countries. The goal is to achieve a very simple and cost-efficient way to take advantage of teleradiology in anywhere even in remote and rural areas. To meet the goal of this study, the following methodology which is consists of two main procedures was done: (1) Using a digital camera in order to provide a digital image from radiographs. (2) Using an image compression tool in order to compress digital images. The results showed that there is no significant difference between digital images (non-compress and compress images) and radiographic films. Also, there was a logic relationship between the diagnostic quality and diagnostic accuracy. Since the maximum percent of diagnostic accuracy can be seen among “Good” quality images and the minimum to was related “Poor”. The results of our study indicate that a digital camera could be utilized to capture digital images from radiographic films of chest x-ray. To reduce the size of digital images, a lossy compression technique could be applied at compression percent of 50 or less without any significant differences. The compressed images can be sent easily by email to other places for consultation and also they can be stored with a smaller size.     

Adaptive compression algorithm from projections: Application on medical greyscale images

Image compression plays a crucial role in medical imaging, allowing efficient manipulation, storage, and transmission of binary, grey-scale, or colour images. Nevertheless, in medical applications the need to conserve the diagnostic validity of the image requires the use of lossless compression methods, producing low compression factors. In this paper, a novel near-lossless compression algorithm from projections, which almost eliminates both redundant information and noise from a greyscale image while retaining all relevant structures and producing high compression factors, is proposed. The algorithm is tested on experimental medical greyscale images from different modalities and different body districts and results are reported.     

Displaying radiologic images on personal computers: Image storage and compression: Part 1

This is the third article of our series for radiologists and imaging scientists on displaying, manipulating, and analyzing radiologic images on personal computers. Part 1 of this article discusses image storage and reviews the basic concepts of information theory and image compression; part 2 will discuss specific methods of image compression. There are a wide variety of removable storage devices available to users who need to archive radiologic images on their personal computers. Tape drives have potentially very large storage capacity but slow performance. Removable SyQuest (SyQuest Technology, Femont, CA) and Bernoulli disks have near hard disk performance and can store from 100 to 150 Mbytes. Magneto-optical drives can store nearly 1 Gb on a 5.25″ disk, with somewhat slower performance. Selecting the most appropriate storage solution requires a careful balance of the user's requirements, including performance, storage needs, cost and compatibility with other users. Despite the advances in low cost high capacity storage technology, image compression remains a crucial technology for modern diagnostic radiology because digital images require such large amounts of storage. Image compression is possible because radiologic images have relatively low entropy (high information content) compared with random noise. Image compression is classified as lossless (nondestructive) or lossy (destructive). Lossless image compression commonly achieve compression ratios of 1.5:1 to 3:1 (33% to 67%), whereas lossy compression can compresses images from 3:1 to 30:1 (67% to 97%). Many lossless compression methods are enhanced by first creating a difference image using discrete pulse code modulation. All compression methods are adversely affected by image noise.     

A comparison of wavelet and Joint Photographic Experts Group lossy compression methods applied to medical images

This presentation focuses on the quantitative comparison of three lossy compression methods applied to a variety of 12-bit medical images. One Joint Photographic Exports Group (JPEG) and two wavelet algorithms were used on a population of 60 images. The medical images were obtained in Digital Imaging and Communications in Medicine (DICOM) file format and ranged in matrix size from 256 × 256 (magnetic resonance [MR]) to 2,560 × 2,048 (computed radiography [CR], digital radiography [DR], etc). The algorithms were applied to each image at multiple levels of compression such that comparable compressed file sizes were obtained at each level. Each compressed image was then decompressed and quantitative analysis was performed to compare each compressed-thendecompressed image with its corresponding original image. The statistical measures computed were sum of absolute differences, sum of squared differences, and peak signal-to-noise ratio (PSNR). Our results verify other research studies which show that wavelet compression yields better compression quality at constant compressed file sizes compared with JPEG. The DICOM standard does not yet include wavelet as a recognized lossy compression standard. For implementers and users to adopt wavelet technology as part of their image management and communication installations, there has to be significant differences in quality and compressibility compared with JPEG to justify expensive software licenses and the introduction of proprietary elements in the standard. Our study shows that different wavelet implementations vary in their capacity to differentiate themselves from the old, established lossy JPEG.