Richardson Electronics
As diagnostic imaging departments convert to filmless operation, the workstation has become a critical piece of equipment. Whether adding additional workstations to an existing PACS network, purchasing them independently for clinical hospital areas that require soft-copy imaging, or implementing a completely modular PACS using various vendors, workstations can't be overlooked in planning.
The imaging workstation consists of the central processing unit (CPU), display controller card, display (CRTs or flat-panel displays), and the viewing software. For those who intend to purchase a completely bundled solution from an OEM manufacturer, or create their own workstation(s) by combining components, the product selection process can be simplified by using the following guidelines.
Choosing the computer
The viewing software chosen by the hospital will be the primary factor in determining the general specifications of the computer itself. Under most circumstances, the PACS vendor will provide predetermined specifications to act as a guideline. This doesn't mean the workstation must be built exactly as specified, but it does provide a good starting point.
When reviewing the guidelines provided by the PACS vendor, it's important to take the time to compare the specifications against current technology, as older specifications can reduce performance and lead to early obsolescence. Generally speaking, workstations with higher-speed processors and more RAM are more capable of performing large-matrix image reviews than models that meet dated specifications. Dual-processor, RAM-heavy workstations have become very popular in the last 12 months, and unit costs are quite reasonable.
If the hospital's information services department is going to configure the workstation onsite, it’s wise to procure detailed installation and troubleshooting instructions from each vendor in order to limit delays. Consulting with the IS department on the specifications and features of these workstations before purchasing will also often ensure smooth installation and set-up.
CRTs
Medical displays come in a variety of resolutions, brightness levels, and orientations. Generally speaking, there are two types of workstations: clinical review and diagnostic review. A quick discussion with the radiologists in the department can often help determine how many of each type will be necessary.
Clinical-review monitors can be further broken down into grayscale and color models. Clinical-review grayscale monitors have a standard resolution of 1600 x 1280 and can be either portrait or landscape in orientation. Landscape displays are often used to review different types of images (such as CT, MRI, ultrasound, R/F, angiography, cardiology, etc.), while portrait displays are primarily used to view general radiographic images.
Clinical-review monitors come in a peak brightness range of 65 to 200 foot-Lamberts (fl). When choosing a particular monitor, the peak brightness should be considered against local ambient light conditions and the desired longevity of the monitor. For example, if the standard operating brightness of a display has been determined to be 50 fl for a particular application, a monitor with a peak brightness of 65 fl will have a limited life cycle, as the monitor will be set near its maximum. On the other hand, a monitor with a peak brightness of 125 fl will be able to operate at 50 fl for a much longer period.
Clinical-review grayscale monitors are primarily chosen in combination with DICOM-compliant display controllers and calibration software. While the images displayed on clinical-review workstations are restricted by the native resolution of the monitors themselves, they can provide the clinician with a high-quality image that is as close to the captured image as possible.
Color monitors can be employed for primary diagnosis of small-matrix (less than 1024 x 1024 pixels) color images. These monitors do not normally offer brightness of 50 fl or the image quality and spot size of many grayscale monitors.
Diagnostic-review grayscale monitors have been defined by the American College of Radiology as requiring a minimum brightness of 50 fl. Product selection is limited to a few specialized manufacturers, providing general characteristics of resolutions ranging from two megapixel (1 MP = 1024 x 1024 pixels) to 5 MP in either landscape or portrait orientation, and a brightness specification of 65 to 200+ fl.
These monitors are typically used to perform primary diagnosis. To maintain image integrity, they must be driven by a DICOM-compliant display card and be capable of generating up to 5-MP resolution. Considering their cost, hospitals should ensure they have an adequate workload for the number of diagnostic workstations they plan to purchase.
Color and grayscale LCD flat panels
Over the past 12 to 18 months, LCD flat-panel displays have become a hot topic of discussion in the medical imaging community. The monitors are being deployed in medical imaging workstations for clinical review (both color and grayscale panels) and diagnostic review (grayscale) around the world. LCD panels offer a variety of benefits, but there are important issues to consider when contemplating a flat-panel display.
- Ensure that the LCD panels come equipped with a set of DICOM-compliant look-up tables (LUTs) and that backlight stability controls have been included in the design of the LCD. Having a DICOM-compliant LUT allows the LCD panel to display grayscale images appropriately.
- If the panels are capable of operating in a portrait orientation, check with the manufacturer to see if the image needs to be rotated by some type of pivot software. Even so, image load and window/level times can be slowed by the use of such software, decreasing radiologist productivity. The rotation should be performed by the hardware within the LCD panel itself.
- To take full advantage of the benefits of existing flat-panel technology, select an LCD panel capable of directly interfacing with a digital display controller. Digital interfacing provides better image quality, less signal noise, and is much better suited for medical imaging than analog interfacing.
- The 3-MP grayscale products are sold as systems that include the LCD panels, display controller, cables, and drivers. One important question is how much after-sales support is provided for each of the components, as well as the calibration software.
Uses for smaller-sized 15-inch and 18-inch LCD panels include patient-monitoring applications, clinical review in operating rooms, and other areas with space restrictions. Standard desktop LCD panels are excellent for use in some areas of a hospital, but they do not have the necessary safety approvals to be deployed in areas where patients are near electrical devices.
Generally speaking, if a staff member can touch the patient and the LCD panel at the same time, or if the panel is to be placed within close proximity of the patient, the panel may need to meet a special standard before it can be employed. These standards, UL2601-1 (developed by Underwriters Laboratories) or IEC 60601-1 (developed by the International Electrotechnical Commission), provide for the safety of all medical electrical equipment used by or under the supervision of qualified personnel in the general medical and patient environment.
These standards also contain certain requirements for reliable operation to ensure safety. Buyers should consult with appropriate engineering staff personnel in the hospital before ordering products that may be employed under the above circumstances.
Another current technology restriction of LCD panels is pixel response time, which is the amount of time required for a pixel to change from fully lit or exposed to fully closed, or shut and vice versa. While LCD manufacturers publish pixel response times between 25 and 30 ms, this can be somewhat misleading. If the department is planning to review any type of grayscale image stack, cine or video streams using an LCD panel, it's important to confirm this performance. Some panels may not be able to produce a clean-flowing series of grayscale images, and image distortion and lag due to slow pixel response may occur.
Display controllers
The display controller or graphics card is the interface between the viewing software and the monitors or LCDs. For clinical- or preliminary-review workstations using color monitors, commercially available graphics cards can be utilized instead of high-resolution medical display controllers.
This ultimately offers cost savings to the department, but does have some drawbacks for review of large-matrix images. Most of these controllers have image quality and DICOM conformance limitations compared with high-end cards, but proper quality assurance software can improve image quality and produce a suitable rendering of the captured images.
For diagnostic or primary review of images, a high-end medical display controller should be employed, as it will ensure display optimization in accordance with part 14 of the DICOM 3.0 standard. These display controllers should be purchased with QA software from the display controller vendor.
Using this type of display controller will ensure that pixel values sent to the display are closely matched to the original values generated by the imaging modality. In addition, these high-end display controllers contain static gray software drivers to allow for the full dynamic range of an image to be displayed.
For clinical-review applications, display controllers are designed to support 2-MP displays with a maximum output resolution of 1600 x 1280 in either portrait or landscape orientation. In diagnostic-review applications, display controllers are manufactured to support 3-MP, 4-MP, and 5-MP displays in either portrait or landscape orientation. Most display cards can be purchased in either single- or dual-head configurations.
Viewing software can determine the type of display controller used with the workstation. The PACS vendor should be asked whether the viewing software has been certified for use with the display controller and the operating system chosen to run the workstation. Nearly all PACS vendors will ensure compatibility with available grayscale display controllers running on Windows NT and 2000.
Calibration hardware and software
As with most equipment, grayscale monitors and LCD panels degrade over time. This natural phenomenon leads the display response to shift away from the DICOM curve. Calibration software packages are critical to ensure consistent and accurate images as the display ages. The software packages available should be quoted or included with any grayscale or color workstation the department is purchasing.
By Harley FirthAuntMinnie.com contributing writer
May 22, 2002
Harley Firth is a district sales manager in the display systems group of Richardson Electronics, a provider of high-resolution monochrome LCD flat-panel and CRT displays, medical display controllers, quality assurance software, workstations, film digitizers, and mounting hardware.
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