Capturing and Using Image Files
Capturing and Using Image Files |
|
Richard H. Wiggins, III, MD has reported no financial interest, arrangement or affiliation with a commercial organization that may have a direct or indirect influence in the subject matter of this presentation.
Objectives
Introduction
The ability to digitally acquire, transfer, and display radiologic images at the workstation has resulted in a complete redesigning of the radiologic workflow. The entire process from ordering studies to the distribution of reports has evolved with these technology changes. Although most technology vendors focus on the clinical workflow, there are other important aspects of radiology, which must similarly evolve in the digital arena. It is vital that these issues are considered when evaluating systems such as Picture Archiving and Communication Systems (PACS), Teleradiology systems, and Radiology Information Systems (RIS). Similar to voice recognition, there is an initial decrease in radiologist productivity when converting from a film-based practice to PACS. The ability to perform clinical work, find digital assistance with a diagnosis, create and/or edit articles, and to contribute to, edit, and display Digital Teaching Files (DTFs) at the PACS workstation all greatly increase the efficiency of the radiologist. The evolution of DTFs has progressed from hard copy films with organizations based on countless schemes:
to laser disc projects:
and then to CD-ROMs:
and hierarchal divisions existing on networks, such as on a Network Attached Storage (NAS) device. These different types of media for DTF use all have at some level considered the implications of how deal with image file formats, and what steps need to be followed to create the system. There are four significant steps in digital imaging: acquisition, storage, manipulation, and presentation.
Acquisition
The acquisition of the image can be the most important step in digital imaging, and it is often imperative to consider the final step, presentation, when acquiring the image itself. If the image is going to be used for a digital purpose, such as PowerPoint the color depth. [1] Usually the image file formats are divided into two groups: vector and raster. The vector type images are those that are referred to as "object-oriented". These are "spatial resolution independent", because they can be resized without a loss of resolution. These can be thought of as having the elements of the image defined as equations; as a result, this image file format type may be better used for line diagram type illustrations:
Examples of vector image file formats include Encapsulated PostScript (EPS, .eps) and Scalable Vector Graphics (SVG, .svg).
The raster, or bitmap, type of image files can be defined as individual dots, or picture elements, known as "pixels". Examples of bitmap images are Graphic Interchange Format (GIF, .gif), JPEG File Interchange Format (JFIF, .jff), Portable Network Graphics (PNG, .png), and Tag(ged) Image File Format (TIFF, .tif). The Joint Photographic Experts Group (JPEG) is the image compression algorithm used with the JFIF image file format, and is the common name, for JFIF image files. Digital Imaging and Communications in Medicine (DICOM) is another type of bitmap, or raster, image file format. The DICOM standard itself includes the image data and multi-layered communications and networking protocols, so these image file sizes are usually considered too large for fast DTF work, outside of PACS integration. GIF is the oldest web-based image file format, but is limited by a maximum of 256 colors. The JPEG image file format has good contrast resolution, with 24-bit color, but a lossy compression algorithm. It is important to remember that every time you open, edit, and save a JPEG file, you are loosing some resolution, because of this lossy compression algorithm. The TIFF file format was created to allow image file formats to move between devices, such as printers and scanners without significant loss of resolution, but the "tagged" architecture usually makes these images larger than the other image file formats. The PNG image file format is relatively new, and including a lossless compressions algorithm, and an inherent gamma correction, which allows more standardization of image views when moving between computer platforms, an attractive feature to those creating web-based DTF systems. The PNG and TIFF image file formats have a higher contrast resolution than JPEG, with 48-bit color. [1 and 2]
There are numerous methods of acquiring an image. If the image is in a PACS, then the user may be limited as to their options for exporting the image based on the functions inherent to the system. Most modern PACS have the ability to export an individual image, usually as a TIFF or JPEG. If the PACS are Windows-based, one option is to utilize the clipboard for transfer of the image directly into presentation software, like PowerPoint. Another option is to use a Web-based client, which can usually interact with the main archive of the PACS to pull over an image, and then various "right mouse click" pop-up window options are usually available to export a particular image. Another option is to use a DICOM viewer to push a DICOM data set from a PACS to a particular computer, and export the image through the viewer. [2 and 3]
If the analog image is on a slide, the best results are usually obtained with a dedicated slide scanner:
A flatbed scanner with a transparency adapter can be used with unreliable results. A hard-copy film can be acquired with a full sheet digitizer. These images can be viewed on a PACS workstation, and acquired, but it may be at a lower resolution, due to a decrease window/level capability with scanned images. The hard-copy film can be scanned with a scanner with a transparency adapter. It is also feasible to hang the film on a view box and take a picture with a digital camera:
with relatively good results. Digital cameras are outstanding tools for acquiring images in various locations. [4]
Storage
There are many options for storage of the images, and it is preferable to store the image at the highest spatial and contrast resolution available, for possible future work. It is important to compression algorithm (lossy or lossless) and metadata, or data about data. The media used for storage is also a significant consideration, especially for a low budget DTF system. Fortunately, storage space is inexpensive, so most institutions will be able to add a NAS device to a network, for DTF use, allowing the user to take advantage of the hierarchical folder system to create an expansive anatomy and pathology based schema. This will be an attractive option as recordable DVDs decrease in price, similar to how CDR has widely replaced the ZIP disks, which were so widespread just a few years ago:
Manipulation
While no manipulation may be necessary for some images, most will need some "idealizing" prior to presentation. Because of HIPAA, it is more important than ever to be certain that no patient specific data is included in images used outside of one's own institution. PhotoShop is an excellent tool for removing text data. Using the PhotoShop image file format in between edits allows the flexibility of the software, while using a lossless image file format, with multiple "undos" in the newer versions. When editing an image in PowerPoint, it is important to keep in mind that the data can be "unedited". If you are using PowerPoint to simply crop off the patient's name and medical record number, remember that the data is still there, and can be seen by others, by simply "uncropping" the image. [4]
Presentation
It is important to consider this final step when acquiring the image. The acquisition of an image for use in a digital format, such as a Web-based DTF or LCD projection, will require different attributes than an analog presentation format, such as for a print journal. For a digital presentation, an 800 X 600 JPEG image should be more than adequate. For an analog media format, a higher resolution is required, such as a 1600 X 1200 TIFF or PNG image. Publishers often prefer TIFF images, as it has a better ability to transfer between devices without loss of image accuracy. Most journals include instructions for the image file format and resolution required for digital submission. [5 and 6]
A first-rate presentation tool should be reliable and inexpensive. One of the most basic is a default image-viewing program. A web browser can easily display any JPEG or GIF image. Computers also include default image viewing software, such as Imaging for Windows, and QuickTime. Another option is Microsoft Word, and AppleWorks, these are word processing software packages allow integration of text and images into a single file for easy presentation. There are many Web-based options for DTFs, which can be complicated and time-intensive, often requiring assistance from an experienced programmer. [4 and 7]
Conclusion
The increasing use of technology will support new teaching methods, and an understanding of these steps is vital to surviving in the digital arena. Digital image purposes are significantly different from those for analog media, and must be taken into account when acquiring images. With PowerPoint, a lower resolution image is often adequate, but the hardware and software must be in place for this transition to occur. PACS can not only enhance the clinical workflow, but also the academic activities of a radiology department, A PACS deployment must include plans for conferences such as tumor boards, and radiologic/pathologic meetings, as well as for teaching purposes, and should include wireless technology. Future systems will integrate wireless technology in addition to handheld computing for greater flexibility and mobility in academia. [8 and 9]
References:
Copyright © 2004 American Society of Neuroradiology, www.asnr.org