Advantages of High Bright Color LCDs for PACS

Table of Contents

1.Preface ..................................................................... 1
2.The trend of color imaging and advantages of high-brightcolor LCD ....................................................................... 1
2-1.Overview of LCDs used with today’s PACS ................ 1
2-2.Demands and advantages of color LCDs ................... 2
3.Technology behind the high-bright color LCD ................ 4
3-1.Mechanism of color LCDs ........................................... 4
3-2.Challenges and solutions of delivering high-brightcolor............................................................................. 5
3-2-1.Heat dissipation design ............................................ 5
3-2-2.Highly accurate brightness stabilizing circuit ........... 6
3-2-3.Light condensing lenses .......................................... 7
4.Summary ........................................................................ 7

JVC White Paper

Advantages of High Bright Color LCDs for PACS

1.Preface
The picture Archive and Communication System (PACS) introduced in the early 1990’a, was acomputer system designed to provide aid in diagnostic image reading and data management, inthe world of conventional X-ray films. Initially, these systems were handling monochrome images
generated from Ultrasound, CT and MRI. As the technology of diagnostic devices and IT
advanced, the use of color images has become more prominent.
This advance in technology is driving increased demand for PACS monitors capable of diagnostic
color image reading. Commercially available color LCDs are not adequate for diagnostic readingof grayscale images because both the brightness and the contrast levels are too low compared tomonochrome displays. Therefore, a mix of color and monochrome LCDs is a common
configuration for today's PACS to support reading different applications.
It is evident that there is strong demand from the medical facilities for a single monitor that is
capable of reading both greyscale and color applications. To meet such a demand, JVC hasdeveloped the high-bright, high-resolution color monitors of “i3 series”.
This white paper describes the trend of color imaging in the medical field, the advantages of thehigh-bright color LCD, and technologies supporting our high-bright color LCD.

2.The trend of color imaging and advantages of high-bright color LCD
2.1 Overview of LCDs used with today’s PACS
A typical configuration in today's PACS workstation consists of a mix of displays; somemonochrome LCDs for medical imaging and some color LCDs for multi modality imaging. There
are two types of color LCDs available: the general purpose commercial color LCD that are usuallyused with PCs, and the medical LCD used for medical image display that support DICOM
calibration capabilities. Commercial color LCDs are not considered adequate for diagnostic
reading because these types of displays do not feature brightness stabilization systems and are
difficult to maintain the display quality. Display quality is required by the DICOM Grayscale
Standard Display Function (GSDF), so commercial units are mainly used in PACS/RIS
operations. The color LCDs used for medical image displays are generally equipped with both abrightness stabilization system and calibration capability, and also comply with the DICOM GSDF.
However, most are still inadequate for diagnostic image reading due to a low brightness setting in
the 180-240cd/m2 range and the inability to maintain brightness stability for a long period of time.
A guideline concerning medical display devices, AAPM-TG18 (American Association of
Physicists in Medicine Task Group 18) recommends a minimum brightness of 250cd/m2 for
medical image diagnostic reading. Brightness less than the minimum recommended level is too
low to obtain JNDs (Just Noticeable Differences) necessary for diagnostic reading.
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Advantages of High Bright Color LCDs for PACS

Thus, today's typical PACS workstations are configured with a mix of displays, somemonochrome monitors for medical image displays and some color displays in order to support
different applications.

2.2 Demands and advantages of color LCDs
This section describes why JVC has developed the high-bright color displays for today’s PACS
environment.
First, the use of color data in the medical field has become prominent over the past 10 years. Two
different types of color images displayed on a PACS system are as follows:
One type of image starts as a monochrome image when captured and is colorized during
subsequent processes by the diagnostic equipment. Examples are 3D rendering of CT, MRI,
Doppler ultrasound, and Computer Aided Diagnosis (CAD). The other type is where the color
image is natively generated by the diagnostic devices, resulting in color from the start. Some
examples are the Single Photon Emission Computed Tomography (SPECT) images and the
Positron Emission Tomography (PET) images used in the areas of nuclear medicine, ultrasound,and endoscopic images. At large hospitals, implementation of PACS is growing beyond theradiology departments and expanding to internal medicine, orthopedics, ophthalmology, and thedermatology departments. These new applications create more diversity and frequency of color
images.
In summary, this trend in medical color imaging is driving an increasing demand for color displaysthat are suitable for diagnostic reading and use as the primary monitor with workstations. To date,color displays have been mainly used as secondly monitors.
Let's look at how users would benefit from the high-bright color monitors:
With the availability of high-bright color displays capable of use with all applications, the PACS
workstation can be simpler to configure or configured with more flexibility according to theapplications. As long as monochrome displays are still superior providing higher brightness andcontrast, not all displays can be replaced with high-bright color monitors (CT and Mammography
as an example). However, making the color displays available for diagnostic reading is asignificant step forward.
A high bright color display offering allows the end user the option of deploying a true “multi-use”
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Advantages of High Bright Color LCDs for PACS

workstation within their facility. This workstation may view both color and grayscale images froma variety of modalities, without the need for multiple displays. The use of a high bright color LCD
display helps contribute to PACS cost reduction, wherever a color and grayscale Workstation canbe combined. This solution not only reduces cost, but also reduces the physical footprint of theworkstation.
When you consider the impact of possible implementation of acceptance and constancy test for
all medical monitors, a reduction in the total number of monitors makes QA control easier. In
summary, the users will benefit with the reduction of Total Cost of Ownership (TCO).
As imaging technology advances, we expect to see color integrated into predominantly grayscale
environments, similar to what happened with ultrasound in the past decade. Facilities who ownhigh resolution color display systems, will be compatible with future diagnostic equipment
improvements.
PACS graphical user interfaces designed and displayed in color are more intuitive and easier touse. The color diagnostic display takes advantage of this fact, making the user interface easier touse. Colors may be used to group icons depending on function, or icons may be made to change
colors registering state. PACS workstation users also often run Radiology Information System(RIS) applications and web browsers, and it is obvious that the color displays deliver better
performance than monochrome for such applications.
To benefit from the advantages mentioned above, the high-bright color monitors have to be able
to offer grayscale display capabilities comparable to conventional monochrome displays, meetingthe DICOM and exceeding the ACR standards. The high-bright color monitors developed by JVC
feature a maximum brightness of 1300cd/m2 or more, and are able to set the brightness to410-600cd/m2 when users require brightness stability for a long period of time. With advancing
technologies offering such high brightness as well as the grayscale display capabilities
comparable to the medical monochrome displays, we are bringing a new future for the color LCD.
Our high-bright color LCDs offer a significant increase in perceivable shades compared tocommercially available LCDs; the number of JNDs is increasing in higher input level. (See Figure
1).
As mentioned above, the most important challenge in developing color monitors adequate for
medical systems including PACS is achieving higher brightness. The next section describes thetechnical aspects of our high-bright color technology.

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Advantages of High Bright Color LCDs for PACS

2M color, 410 cd/m2

2M color, 200 cd/m2

700

600

Number of JND

500

400

300

200

100

0
0

15

30

45

60

75

90

105

120

135 150

165 180

195 210225 240255

Input level

Figure 1. Relationship between JNDs and Input level

3.Technology behind the high-bright color LCD
This chapter describes the technical background; how color LCDs work and why color LCD’s
brightness is generally lower than the monochrome LCD, and tells how we overcame thechallenge to develop our high-bright color monitors.

3.1Mechanism of color LCDs
The LCD panel displays images by passing light through from a light source (backlight), placedin the rear of the panel. As the light transmits through the liquid crystal cells (pixels), the amountof light penetration is controlled. Each pixel of the color LCD panel is made up of three sub-pixels,
red, green and blue, with polarizing filters (Figure 2), and as the light penetrates through thesethree sub-pixels and reaches the human eyes, additive colors form images.
Brightness
Control Circuit
Backlight

LCD PanelPower Supplyof Backlight

Color Filter

Figure 2. LCD Panel Construction Details
As shown in Figure 2, because the color LCD panels select colors using the white backlight which

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Advantages of High Bright Color LCDs for PACS

penetrates through three color filters, the transmission factor of light is lower than that of themonochrome LCD panels. The transmission factor of color LCD glass is about one-fifth of
monochrome LCD glass; color LCD is 3-6% and monochrome LCD is 15-30%. This means thatthe color LCD panels have to be five times brighter to achieve the same brightness as
monochrome LCD panels. However, simply increasing brightness alone will cause otherproblems such as a shorter life of the backlight and an increase in temperature causing unstablebrightness.
The higher the resolution, the more difficult it is to achieve higher brightness. This is because theapertures of the cells (pixel fill factor) get smaller as the resolution gets higher; assuming thepanel size is constant.

3.2 Challenges and solutions of delivering high-bright color
How did we overcome the challenges mentioned above? The JVC high-bright color LCDs weremade possible with our advanced design technology and implementation of the most effective
materials. Specifically, we have optimized the backlight and the circuits, improved the heatdissipation design accordingly, and integrated a highly accurate brightness stabilizing circuit andlight condensing lenses. The details of each item are described below:

3.2.1 Heat dissipation design
Making the backlight brighter raises the internal temperature of the display. This causes heatstress to individual parts in the display, preventing the secure stability of internal circuits of themonitor which are crucial for display stability. Overheating could also contribute to shortening of
the product life. While cooling fans are effective in lowering the internal temperature, the noise
generated by the fans are undesirable for image reading.
We have achieved a precise heat dissipation design by utilizing our unique simulation techniquewhich has been developed over many years. With this design, natural heat dissipation is sufficientand there is no need to run cooling fans under normal temperature; only when the room
temperature is 30℃ or higher, will the fans be activated to force cooling. We have achieved theinitial design goal of a stabilized display by managing heat with minimum fan cooling.
Simulations were performed analyzing the mechanisms of the monitor’s interior and its heat

Figure 3. Heat dissipation simulation test results

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Advantages of High Bright Color LCDs for PACS

source parts. As a result, we were able to optimize locations of the heat source parts, theventilation opening space, and location for heat exhaust slit, as well as the position of the cooling
fan and its capacity. Additionally, the medical displays may be used in both landscape and portrait
orientations. Recognizing that changing LCD orientation affects the internal temperature status,
the simulations were performed in both orientations.

3.2.2 Highly accurate brightness stabilizing circuit
The characteristic of the panel’s brightness changes remarkably when the internal temperaturechanges, as shown in Figure 4. Thermal stability is required for diagnostic image review.
Our high-bright color LCDs are equipped with a sensor in front of the panel connected to abrightness stability feedback loop to control not only the backlight but also the entire LCD panel
and its driver circuit based on the measured brightness values by the sensor.
The brightness feedback system is optimized to measure the light transmitted through the liquid
crystal cells by using the “sensor elements,” the “micro current amplification circuit,” and its“firmware,” then realizes the high accurate brightness stability for the entire grayscale range fromminimum to maximum luminance based on measured data by the sensor.

Relative brightness (%)

120
100
80
60
40
20
0

0

10

20

30

40

50

60

Sorrounding temperature (℃)

Figure 4. Relationship between relative brightness and ambient temperature

Monitor

Signal Processing Circuit
Computer

Measured Dataof panelbrightness

Built-in Sensor

Built-in sensor
correction table

Backlight
power source

External Luminance Sensor

Gamma correction
lookup table

LCD panel
driving circuit

During Normal Operation
During Calibration

Figure 5. Brightness detection feedback loop

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Advantages of High Bright Color LCDs for PACS

3.2.3 Light condensing lenses
As mentioned in the previous section, the higher the resolution, the more difficult it is to increasebrightness. We overcame this challenge by using light condensing lenses for our 3Mega
high-bright color LCDs. As shown in Figure 6, the light condensing lenses work as
micro-convex-lens films which are placed at each of the RGB cells behind a liquid crystal cell
layer. This diffracts the backlight towards the opening of the cells to transmit the light otherwise
absorbed in the black strips. This effective use of the backlight achieves higher brightness.
As mentioned above, the simple solution of stronger output of backlight to achieve higher
brightness would cause the instability of operation. The use of light condensing lenses resulting inhigher display brightness without changing the backlight output itself was an ingenious
achievement.
Penetrated light
Glass

Light gathering lens
Backlight

Figure 6. Diagram of light condensing lenses

4.SummaryThis document described the trend in color imaging and the advantages of the high-bright color
LCDs and the supporting technologies. JVC high-bright color LCD monitor is a breakthrough in
the industry and its impact in the medical information systems including PACS is expected to offer
many advantages to the users.
*“i3 series” models: CL-S1200, CL-S600, CL-S500, CL-S500 Dualstand, CL-S300, CL-S200,
MS-S500 Dualstand, MS-S500, MS-S300, MS-S200 (As of March, 2022)7