Digital Images PDF

# IMAGE PROCESSING AND VIEWING Regardless of the type of digital radiographic hardware selected, the electronic data are processed by a computer before the final image file is created and displayed. Image file processing and modification occur at a number of points and can be broken down into prepr...

# IMAGE PROCESSING AND VIEWING Regardless of the type of digital radiographic hardware selected, the electronic data are processed by a computer before the final image file is created and displayed. Image file processing and modification occur at a number of points and can be broken down into preprocessing, processing, and postprocessing steps. ## Preprocessing, Processing and Postprocessing - **Preprocessing** is usually beyond the control of the user. Manufacturers apply various corrections to the raw image data to accommodate such things as inhomogeneity in light collection, image distortion by focusing lenses in CCD systems, nonfunctional or dead pixels in the detector, and variation in efficiency between individual detector elements. - **Processing** is aimed at converting the corrected raw image data to a usable radiographic image. These manipulations, also done on the raw image data, can be controlled to some extent by the user and are aimed at optimizing image contrast, edge enhancement, minimizing image noise, and optimizing other aspects of image presentation. - **Postprocessing** represents one of the major advantages of digital radiography and is 100% user controlled. DICOM viewers allow images to be magnified and rotated, and the image blackness and contrast can be adjusted independently. Other features are also available, such as viewing multiple images simultaneously and obtaining quantitative measures of area and length. ## Ambient Lighting and Monitor Quality - Ambient lighting and monitor quality are two important considerations when optimizing image viewing. - As ambient light increases, the perceived difference between light and dark on a monitor decreases, and this can affect image interpretation negatively. - Viewing of digital radiographs in a completely dark room with no light other than the monitor light also reduces accuracy. - For this reason, computers used for primary image interpretation should be in a room with adjustable, or permanently dimmed, lighting but not in total darkness. ## Monitor Quality - Monitor quality is another factor that influences the accuracy of interpretation of digital radiographic images. Both monochrome (black and white) and color liquid-crystal display (LCD) monitors are available, and their technical specifications are highly variable, leading to a wide range of image display quality. - Ideally, radiographic images are best viewed on a dedicated medical-grade monochrome LCD monitor. Such monitors are characterized by superior brightness, contrast ratio, and resolution. - Monitor brightness relates to how bright a white screen is, and a brighter display enables the user to resolve more shades of gray. - Contrast ratio is a measure of the monitor’s ability to display true black as black and true white as white. - Medical-grade monochrome LCD monitors typically have 3 megapixel resolution or higher. - Medical-grade monochrome LCD monitors are expensive, and their routine use throughout the veterinary imaging environment cannot be justified financially. - Consumer-grade color LCD monitors are improving continuously. - Regardless, given the substantial investment that occurs when deploying a digital radiography system, an additional investment to acquire at least one medical-grade monochrome monitor for the primary interpretation of digital radiographic images is justifiable. ## Monitor Calibration - It is important to ensure that monitors are calibrated correctly. - Medical-grade monochrome LCD monitors should be calibrated using the DICOM grayscale display function standard. - LCD monitors lose brightness over time, with consumer-grade monitors affected more rapidly than medical-grade monitors, so brightness should be periodically measured. ## Advantages of Digital Imaging - The advantages of digital imaging are quite far reaching. - Advantages of digital radiography are: - Reduced expendable supply cost and elimination of darkroom - Contrast optimization and exposure latitude - Image postprocessing, ability to adjust image blackness and contrast after exposure - Improved image accessibility and consolidated image storage - Enhanced portability enables consultation - Use of artificial intelligence - An opportunity to change the imaging paradigm. ## Reduced Expendable Supply Cost and Elimination of Darkroom - In a digital imaging environment, the requirement for purchasing x-ray film, film-filing envelopes, darkroom chemistry, and other related supplies is eliminated. - Darkroom errors, such as outdated chemicals, incorrect temperature settings, chemical spills and splashes, and safelight fog or other light leaks, make up a substantial fraction of errors that compromise analog image quality. - Additionally, there are increasingly more stringent local government requirements in ensuring personnel safety with respect to darkroom chemicals and fumes and also in the safe disposal of exhausted darkroom chemicals ## Contrast Optimization and Exposure Latitude - Contrast optimization, also termed contrast resolution, is a feature of digital radiography that is related to the bit depth of each pixel and the processing software that accompanies the digital-imaging system. - The processing software can assign a gray shade to a pixel in a digital image that would have been either black or white in an analog image. - With radiographic film, radiographic contrast is associated rigidly with the relationship between kilovoltage peak (kVp) and mas, as discussed in Chapter 1. - With digital radiography, however, the computer can compensate for the wide range of thickness of the patient by assigning a suitable gray shade to pixels in the thick lumbosacral and thin stifle regions, as well as in the caudal abdomen. - What this means in practical terms is that in digital imaging, opacity differences associated with variation in thickness are much lower than in analog radiographs (Fig. 2.12). ## Terminology - The terminology used to describe this contrast optimization feature of digital radiographic systems can be confusing. - The term dynamic range has also been used to describe the low dependence of digital-imaging plates on absolute x-ray exposure (kVp and mas), which in this chapter we call exposure latitude. - To avoid this confusion, we recommend use of contrast resolution or contrast optimization to define the ability of an imaging system to display thick and thin regions, and regions of low and high atomic number, suitably in one image, and the term exposure latitude to define the ability of digital plates to compensate for either high or low kVp-to-mAs combinations that would result in overexposure or underexposure, respectively, in an analog system. ## Inherent Spatial Resolution - Because an antiscatter grid can improve both spatial resolution and image contrast, it is worth commenting specifically on their use in digital radiography. - Although antiscatter grids can be used in digital radiography, some manufacturers have incorporated a scatter-correction algorithm into the image-processing software that makes grid use unnecessary (Fig. 2.11). - Implementation of an antiscatter algorithm avoids the higher milliampere second (mAs) values that are needed to compensate for the presence of an actual grid in the x-ray beam. - Whether or not the end user will be satisfied with the quality of the antiscatter image-processing algorithm will be a matter of individual preference, and the functionality of this feature should be evaluated in any digital system prior to purchase. ## Exposure Latitude - The magnitude of the range of radiographic exposures (i.e., the radiographic technique) that can be used to create a diagnostic radiographic image is called exposure latitude. - With analog radiography, there is only a narrow range of kVp and mas combinations that will result in satisfactory film blackness, and even then, there will usually be regions of the film image that are too white or too black (see Figs. 2.12, 2.13, and 2.14). - One potential disadvantage of the wide exposure latitude that characterizes digital-imaging plates is exposure creep where unnecessarily high exposure factors are not recognized as they would be when using an analog system as overexposure is corrected by the image-processing software. - Most digital radiography manufacturers have incorporated an exposure index (EI) metric that enables the user to evaluate the amount of incident radiation that strikes the plate (i.e., the exposure factors). - The El is a measure of radiation striking the relevant image region in a receptor, and an approximate indicator of the x-ray “signal” detected by the digital radiography unit. - The El can be used to judge whether radiographic techniques are too high or too low. However, the El is only useful if it is monitored routinely. - The transition to digital radiography has led to a dramatic reduction in the number of retakes, especially those related to errors in radiographic exposure. - However, the wide exposure latitude that characterizes digital radiography does not mean that underexposure or overexposure is not a problem; these problems still occur, but only at the extremes of exposure factors. - With underexposure, the overall image quality may appear satisfactory from a global perspective, but a low EI should prompt a closer inspection of the image which will demonstrate a “grainy” appearance, also known as “quantum mottle.” - This grainy appearance is caused by high image noise relative to low x-ray signal, created by statistical uncertainty in computer assignment of a gray shade to underexposed regions of the image. - This grainy appearance will be obvious on close inspection and could interfere with detection of a subtle lesion, especially those affecting the trabecular pattern of bone. - Underexposure requires a repeat radiograph with increased exposure factors. - Image noise is particularly responsive to changes in mAs, so if excessive quantum mottle is detected, mAs can be increased until attaining an appropriate EI and satisfactory image noise levels. - Overexposure of digital radiographs does not result in overall film blackening, as with film. - The detector elements and processing software are able to compensate electronically for overexposure (excessive x-ray signal), up to a point at which the detector becomes saturated and cannot respond to additional exposure. - At saturation, the computer assigns the maximum pixel value, black, to the pixels that are saturated. - This results in some parts of the image being absent or having an abnormal gray shade assignment. - Because only portions of the image are overexposed, as compared to the entire image, the overexposed region can be misinterpreted easily as a lesion. ## Image Postprocessing - Despite the tremendous contrast resolution of digital radiographs, there is sometimes a desire to make some regions of the final processed image blacker or whiter to facilitate interpretation. - Modifying the image blackness and contrast is accomplished easily with DICOM viewing software, and magnification of regions of the image can also be very useful in detecting small lesions that would be overlooked in an unmagnified digital image or in an analog film image not viewed with a magnifying glass. - Most inexperienced interpreters fail to take advantage of the full range of manipulations provided by DICOM viewing software. ## Improved Image Accessibility and Consolidated Image Storage - The full advantages of digital imaging are best realized when digital imaging is incorporated into the global practice environment. - This means integrating image acquisition and management with the hospital’s electronic medical record. - In a fully integrated system, radiographic studies are ordered in the electronic medical record. - Selecting the study to be performed from a list of the examinations requested for the day eliminates data entry errors that might result from having to reenter all patient information and improves workflow. - When the study has been acquired, appropriate charges are posted automatically in the medical record, and the images are sent to a local server for distribution and archiving. - Images are viewable through the electronic medical record using either DICOM viewing software, or through an Internet browser. ## Picture Archiving and Communication System (PACS) - Picture archiving and communication system (PACS) refers to the host of technologies that contribute to the creation, distribution, and archiving of digital images. - The basic components of a PACS that might be found in a private veterinary practice are: - The device, the x-ray machine and the CR or DDR radiography system - A server that acts as the local image archive - Workstations that can retrieve images from the server for remote viewing - A local area network for data transfer - An image communication protocol (the DICOM standard) - Off-site or cloud-based secure image storage - When purchasing a digital-imaging system, there is often little attention paid to integration of the radiographic hardware and software into the overall hospital environment. - This can result in functionality problems that compromise the advantages of transitioning to digital imaging. ## DICOM Images - Traditionally, DICOM images have been viewed on a DICOM workstation software that is loaded on the client computer. - The images are "downloaded" to the workstation using software that is installed onto the local device, whether it is a MAC or PC operating system. - DICOM images can also be transferred using browser-based technology, and this enhances image portability, particularly when accessing images beyond the local area network. ## HTML5 - The demand for enhanced image portability with minimal delays in transmission is increasing. - With the development of the hypertext markup language 5 (HTML5) standard for web browsers has come a tremendous opportunity to develop browser-based medical image viewers that do not require complex browser plug-ins or programs that need to be installed locally on the client computer (so called thick client configuration). - These new viewers, known as zero footprint viewers, require only an HTML5-compatible browser, and many of these viewers have all the functionality of dedicated DICOM workstation software. - These viewers are browser and operating system agnostic, meaning that they work equally as well in any of the modern browses, running on modern Windows or Apple operating systems and also on iOS and Android devices. - In addition to being browser based, they may also be a mobile device "app." ## Vendor Neutral Archives (VNAs) - Whereas historically, medical image archives have been limited to the DICOM file format, modern medical archives are designed to archive all types of file formats in addition to DICOM. - Typical file formats for such medical data include .tiff, .jpeg, .pdf, and .mp4. - With the advent of vendor neutral archives (VNAs), all images related to a medical record can be archived in one resource whether they were acquired by diagnostic imaging, or any other service. ## Off-Site Image Archiving - It is not adequate because the hard drive can fail. Also, any other component of the server can also fail and lead to corrupt data, or the server can be destroyed during a physical disaster, an unprotected power surge, or corruption through a computer virus. - The best solution is redundant off-site duplication and storage where digital radiographic data are duplicated and transferred to an off-site computer on a regular basis, preferably daily, for safe storage. - Cloud storage is commonplace in today’s environment and while it is common to have a small image archive in the house, most PACS are configured such that either the primary archive is cloud-based or all studies are sent to the cloud for backup and disaster recovery. ## Enhanced Portability Enables Consultation - It is difficult for most practicing veterinarians to become totally competent in radiographic interpretation. - Analog film images were either hand-carried to a specialist, if one was lucky enough to be sufficiently close, or sent to the expert by mail or courier. - With the explosion of digital radiography in veterinary medicine, veterinary teleradiology was born. - Teleradiology is a type of telemedicine that involves the electronic transmission of radiological images from one location to another for the purposes of interpretation and/or consultation with a specialist. - Veterinary teleradiology was first introduced commercially in the early 1990s with limited success, mostly influenced by slow Internet speeds and large file sizes, but has grown dramatically in recent years, reflecting the recent growth of the broader veterinary telemedicine market. - It is worth noting that while telemedicine is a valuable tool that augments patient care, it does not replace the patient-client relationship, and should be viewed as a supplemental service. - DICOM files are large, and transmission as an email attachment can be problematic. - Currently, the practice of teleradiology in veterinary medicine is widespread because of the availability of broadband Internet connections, image compression, and economically priced PACS and DICOM software. - There are many teleradiology service providers throughout the world who have teleradiographic interpretation as their primary mission. - These advancements have made turnaround time very short and STAT interpretations possible. ## Artificial Intelligence - Artificial intelligence (AI) is a broad term that describes a situation where a computer system performs tasks that mimic human intelligence or serves an analytical role typically satisfied by humans. - The field of AI has rapidly progressed in the last 20 years and has now entered the veterinary market, with vendors actively advertising AI systems that provide interpretation input on radiographs in dogs and cats. - In human medicine, AI imaging interpretation is bound by FDA regulations, and implementation must include strict proof of design and accuracy. . - AI imaging interpretation tends to be narrow-focus and task specific, and often provides computer-aided diagnosis or computer-aided detection tools, rather than all-encompassing or definitive image interpretation. ## AI in Veterinary Medicine - There is no regulatory framework limiting AI in veterinary medicine. - Proof of efficacy is not required before a veterinary vendor can offer an AI tool. - AI provides great promise and likely will result in eventual improvements in veterinary practice, the benefits of AI and proof of efficacy are not currently known. - The quality of an AI model is heavily influenced by the quality of AI training and validation data used to build the AI model. - This type of information is not readily available for commercially available veterinary AI products. - The individual veterinary practitioner who implements these tools should be aware of these limitations when evaluating a potential AI interpretation tool. - Research publications evaluating AI tools in veterinary medicine have begun to appear, but more are necessary before evidence of efficacy is available. ## An Opportunity to Change the Imaging Paradigm - Veterinary medicine can be a competitive enterprise, especially in times of economic downturn. - Pet owners are highly educated and have a wealth of information at their fingertips that they use to help make decisions regarding medical care for their pet. - Being perceived as having a modern contemporary practice environment can help maintain and increase a healthy client base regardless of economic and client-education factors. - Having digital radiography is one way that practices are viewed as being progressive, and being able to provide high-quality radiographic services can bolster one's professional persona. ## Darkroom Errors - The transition to digital radiography can help alleviate problems with radiographic exposure, and darkroom errors are also eliminated. ## Radiographic View Positioning - Positioning and selecting the correct radiographic views will not be solved automatically by the transition to digital radiography, but with a digital system, the economic cost of making these modifications is insignificant. - With film imaging, many veterinarians were reluctant to obtain all needed views routinely, three projections of the thorax for example, because of the increased cost of expendable supplies required to do so. ## Radiographic Fee Structure - Radiographic studies should be priced on an examination basis, not on a per-image or per-view basis. - The fee should be set such that the practice makes a profit, all necessary views are included, and the quality standards are acceptable. ## Teleradiology Consultation - Similarly, offering teleradiology consultation signals that a veterinary practice has adopted modern medical technology services. - Telemedicine benefits all parties; the improved diagnostic ability improves quality of care for the owner and pet and is an additional service that can be advertised and charged by the veterinarian. - The benefits of teleradiology can only be realized if high-quality, well-positioned radiographs are submitted for evaluation. - Even the most experienced radiologist cannot provide meaningful consultation if the radiographs are marred by artifact, are poorly positioned, or do not focus on the area of interest. ## Artifacts - As with all medical-imaging modalities, there is potential for digital radiographic imaging artifacts. - An artifact is an unwanted, usually non-patient-related anomaly in the image that may or may not compromise image interpretation. - These occur in both CR and DDR systems and are unique from those encountered in analog film radiography. - Overexposure and underexposure and how these differ in appearance from exposure errors in analog radiography were described previously. - The discussion of other imaging artifacts that are observed in digital radiography is beyond the scope of this chapter, but excellent references are available. <start_of_image> Diagrams: <start_of_image> Diagrams are not included in the markdown. Refer to the original document to see the diagrams in detail. Please note: this document contains a very large number of diagrams.