Softcopy
viewing of medical images require that the display tools perform day
in, day out at an optimum level, and not just in radiology, but
throughout the entire healthcare enterprise where primary reading
stations are needed. Quality control fundamentally improves image
quality and the consistency in which images are displayed. To be
optimized, QC programs must be non-intrusive to radiologists,
manageable for the QA administrator to carry out, consistent throughout
the enterprise, and of course, cost-effective. Automatic and remote
monitoring tools are making this possible, in addition to increasing
productivity gains and streamlining QC programs.
The University of Pittsburgh Medical Center, which is on its
second-generation PACS, has 400 primary reading workstations installed
throughout the integrated healthcare system's multi-center campus.
Prior to the availability of automatic and remote calibration tools,
two IT personnel manually performed QA (quality assurance) on each
display to determine if it was compliant with DICOM (digital imaging
and communications in medicine) part 14 grayscale standard display
function (GSDF). Traveling to more than 17 hospitals, evaluating each
workstation - which could take up to 30 minutes - and
coordinating a time that was non-intrusive to radiologist workflow
proved to be almost impossible.
This list of problems is exactly why quality control (QC) programs are
often neglected at many hospitals, especially in lieu of large PACS
deployments that consume a lot of resources. But without QC, image
quality of the display can degrade over time, opening up the
possibility of improper diagnosis or interpretation of a softcopy image.
With advancements in calibration software, QC does not have to be as
ominous as once perceived. A well-planned and executed QC program with
the help of emerging calibration tools can alleviate the arduous nature
of display calibration, lower administrative costs and ensure excellent
image quality for interpreting physicians. UPMC realized this as it
moved to the next wave in display calibration - remote monitoring.
The elements
As radiologists make life-critical decisions on medical imaging
displays - be it LCD-based (liquid crystal display) or CRT (cathode
rode tube) - QA checks and re-calibration is fundamental to ensure
optimal image viewing.
Research attests that LCD-based displays are typically more stable and
require less frequent calibration than their CRT counterparts, making
them the standard of choice for new PACS rollouts and monitor
replacements. Despite their advantages, an LCD's brightness will
degrade over time. The most influencing parameter aside from lighting
conditions is backlight degradation. Brightness decreases as the
phosphors used in the fluorescent backlights of LCDs age. If the
backlight is not monitored and re-calibrated, it could fail to be
DICOM-compliant over time.
"DICOM calibration is a fundamental requirement for displays used in
medical imaging," says Matt Harris, vice president, marketing and
corporate development for Planar Systems Inc. "The reason why? The
DICOM curve is really meant to represent how the human eye perceives
shades of gray. The human eye can better perceive differences at low
gray levels than at high gray levels. So the DICOM calibration
function, used in LCD displays, is created to mimic the sensitivity of
the human eye."
Harris explains that the typical response curve of an LCD looks nothing
like that of a DICOM curve. "What DICOM calibration really does is
change the response curve of an LCD into that of a DICOM curve, and it
allows a much higher degree of gray level separation at low gray
levels," he says. In a healthcare enterprise and distributed PACS
environment, this ensures that softcopy images look the same when
viewed on different workstations at different times.
LCD calibration
There are three modes of display calibration for flat panels, Harris
explains. The first - factory calibration - ensures that the graphic
board has been adjusted prior to shipment so that the display renders
DICOM-calibrated images. An acceptance test upon arrival of the new
monitor must take place to confirm the display is DICOM compliant.
The second way to calibrate uses an external photometer (sometimes
referred to as a puck) to reset the display to the DICOM GSDF curve.
"From time to time, the medical imaging display should be manually
calibrated," says Harris. "The external photometer works with
calibration software to update the calibration of the display,
especially the backlight brightness."
The third uses a built-in calibrator that continuously corrects
short-term and long- term instabilities, particularly the backlight.
The internal sensor measures the output of the backlight and talks with
the software on a continuous basis to make continuous calibration
checks. Depending on the vendor, luminance sensors are placed in the
center of the display or are otherwise corner-based. Some monitors also
are packaged with integrated fast-feedback backlight sensors that
control and adjust the luminance and whitepoint.
These systems automatically perform QA checks and DICOM calibrations on
a regular basis without user interaction. QC of medical imaging
displays is not eliminated, but is less frequent.
Remote monitoring software allows administrators and service
technicians to access the status of networked displays through a web
interface. (See chart on previous page.) The software allows
calibration to be managed remotely via a WAN or LAN. Features include
scheduling for calibration as well as history and alert tracking.
Administrators can monitor all the displays within the enterprise,
launch calibration, and receive alerts if an LCD falls out of
calibration or if calibration is unable to be completed.
A centralized management tool for QC helps PACS to achieve its potential in a hospital's distributed environment.
Putting standards to the test
In the Diagnostic Imaging Division at the University of Texas M.D.
Anderson Cancer Center, all medical images acquired, with the exception
of some mammograms, are transmitted and stored electronically.
Physicians read the images at 50 PACS workstations dispersed throughout
the facility.
QC starts from the very beginning. "The QC program needs to address
initially the basic performance characteristics of the monitor," says
Jeff Shepard, senior medical physicist, Imaging Physics Department.
"You must perform an acceptance test when a monitor first comes in
order to verify that it functions the way the manufacturer claims or
the way you have required in your purchase specifications."
The displays are equipped with software for calibration, automatically
monitoring their light output in 20-minute intervals. On a monthly
basis, the imaging physics department will perform a visual assessment
on each PACS display using a new test pattern purposed by the American
Association of Physicists in Medicine Task Group 18 (TG 18).
Similar to a SMPTE (Society of Motion Pictures and Television
Engineers) test pattern, Shepard says the guidelines are under review
and not yet published. "It has several different patches of gray
in it that you can look at it, and there are lines through it to
measure geometric uniformity," explains Shepard. "In each one of the
gray steps, there are very small objects of low contrast, so that you
can evaluate your ability to resolve subtle contrast in every
brightness level in the image. If your display is calibrated properly
with the right look up table (LUT), you can see those subtle contrast
objects in all of those steps."
AAPM TG 18 developed a document that provides guidelines to medical
physicists and engineers for the evaluation of electronic display
devices intended for medical use, but Shepard says this was prior to
the availability of calibration software. "At M.D. Anderson, we are
finding that we don't need to check calibration on our brand of
self-calibrating monitors more than once a year," he says.
Before selecting which displays and calibration software will be
deployed for softcopy viewing, Shepard suggests a test drive of some
sort. "If you know what the performance trade offs are, you can start
looking at the real value of the product based on its price," he says.
"The differences are in the subtle details," opines Shepard. "When you
are making a purchase decision, you really need to have an opportunity
to spend some time with a monitor and evaluate how well it works. Look
into different parameters, implement them, and try to see what sort of
problems you run into."
The wave of the future Image Systems Corp. announced at RSNA in November that UPMC is in the
initial stages of replacing their grayscale CRTs with its grayscale
LCDs and remote monitoring tools. The first hospital to implement the
technology is UPMC's Northwest facility, which Jeff Roberts, UPMC's
radiology informatics project manager, says is a completely digital
facility.
"With Image Systems' CFS [calibration feedback system], we use a
service called SNMP [simple network management protocol]," explains
Roberts. "It's a network-driven software tool that communicates with
CFS and allows IT to remotely monitor, control and schedule the
calibration checks." SNMP is a commonly used protocol that makes
integrating software into existing networks relatively easy.
CFS can be used to adjust the backlight, generate a new DICOM
correction LUT, as well as provide reporting tools that monitor the
lifetime of the display. This is beneficial not only for legal reasons
but also budget allocation, indicates Roberts.
These tools will be used, but UPMC is still in the "getting-to-know"
stages of the implementation. "One of the things that we are working on
is developing standards for the CFS - how often do we have the CFS
check the LCD, and what are the controls and settings that we are going
to use for the check that we do," poses Roberts. "For example, you
define the standards that you want checked, and for whenever they are
scheduled to take place, the display will automatically perform the
check. What is the luminance level? Is it out? If it is out, by what
percentage? And if we don't want to be out by more than 2 percent, and
it's out by 3 percent, can we set up the CFS to notify IT via a page or
email."
"This is going to allow UPMC to effectively perform the QA/QC process
remotely and automatically on its 400-plus PACS workstations with
minimal man hours ... which will let me sleep better at night,"
continues Roberts. "It also is ensuring that radiologists are seeing
the best images possible."
REMOTE MONITORING: Who's Got What Planar Systems | Dome Dashboard
Functions with Dome CXtra calibration software on Planar's Dome Cx, Qx
and Px lines. The Cx line for primary reading (C5i, C3i and C2) has a
built-in photometer in the center of the display, behind the glass.
National Display Systems | Integrity
QA for the new AXIS series uses SNMP (simple network management
protocol) to track networked displays for status, prompt for service by
e-mail/pager and verification of proper function. Integrity runs in the
background in combination with MD-Cal software on each workstation.
NEC-Mitsubishi Electronics Display of America | GammaComp MD Administrator
Centralized control and management software available on NEC's
MultiSync MD series, which in addition to GammaComp MD calibration
software, features X-Light technology that controls and adjusts the
luminance and whitepoint via an internal backlight sensor.
Siemens Display Technologies | SMfit ACT Remote
Remote access management tool that allows access from one central
workstation out to all systems on a network. Siemens' ACT Calibration
software can be used on any Siemens CRT or LCD. Siemens has a front
sensor on its high-end 5MP display but utilizes an internal backlight
sensor to control panel stability on its other monitors.
Image Systems Corp. | Calibration Feedback System (CFS)
Remote capability for 2MP, 3MP and 5MP grayscale displays. The displays
operate with a backlight sensor to monitor and maintain brightness
stability along with an in-bezel, retractable front sensor that
measures and calibrates the display.
Barco | MediCal Administrator
Remote QA checks and DICOM calibration on Coronis displays. A new
feature allows management of these tasks via a PDA. Barco's Coronis
line - including 1MP, 2MP, 3MP, 5MP, color Coronis and Coronis 5MP
Mammo - features an I-Guard front sensor and Medical Pro calibration/QA
software.
Quest | PM Medivisor
Remote monitoring software for all Totoku monitors. Installed in each
workstation, the software agents collect data such as luminance,
operating hours, calibration accuracy, on each monitor and reports to a
central server, permitting the health of every monitor on the network
to be observed from one location.
Double Black Imaging | LumiCal Administrator
Allows scheduling for calibration history and alert tracking. An
administrator can monitor all the displays within the enterprise,
launch calibration and receive alerts. In addition to LumiCal Agent
software, DBI's LCDs feature 3 sensors; two in the front retractable
module and one on the backlight.
Eizo Nanao | RadiNet Pro
A network of up to 8,000 RadiForce monitors can be managed, ranging
from monitors for diagnostic imaging in reading and modality rooms to
HIS/RIS monitors handling reference images and electronic diagnostic
chart monitors in clinics.
Softcopy
viewing of medical images require that the display tools perform day
in, day out at an optimum level, and not just in radiology, but
throughout the entire healthcare enterprise where primary reading
stations are needed. Quality control fundamentally improves image
quality and the consistency in which images are displayed. To be
optimized, QC programs must be non-intrusive to radiologists,
manageable for the QA administrator to carry out, consistent throughout
the enterprise, and of course, cost-effective. Automatic and remote
monitoring tools are making this possible, in addition to increasing
productivity gains and streamlining QC programs.