Comparison of Monitors for Digital Diagnosis of Medical Images
1
MIEW KEEN CHOONG, 1RAJASVARAN LOGESWARAN, 2ZAHARAH MUSA, 1AZIAH ALI
1
Faculty of Engineering
Multimedia University
Persiaran Multimedia, 63100 Cyberjaya
MALAYSIA
2
Diagnostic Imaging Department
Selayang Hospital
68100 Batu Caves
MALAYSIA
Abstract: - Radiology departments have been using monitors as the display medium for several modalities for
some time now. Radiologists make their diagnosis based on the images displayed on these monitors. This article
studies the diagnostic difference of 15 inch, 20 inch, 21 inch high quality CRT monitor, and 15 inch LCD
monitor. A number of images from different modalities were used, and five radiologists were involved in the
study. Blind testing was done where radiologists had to diagnose the images, and state their confidence level.
Results show that there is no significant diagnostic difference when using the different monitors. The
non-high-quality monitor may act as a low-cost solution especially for medical posts in remote and less affluent
communities. The findings also indicate that portable notebooks are viable mobile tools for use in medical image
diagnosis.
Key-Words: - Monitors, Medical Images, ROC analysis, Diagnostic quality, MRI, CT, X-ray.
1 Introduction
Display is an important link in the imaging chain.
With medical images increasingly digitally stored,
monitors have become dominant in image display.
Reporting and viewing radiological images on
monitors has become common practice in medicine
[1]. Thus, the quality of the monitors used must be
good. One of the advantages of digital medical
images is that the data can be sent directly from the
console via modem to any workstation for
interpretations in a telemedicine environment. In the
case where a study needs to be sent to the
radiologists’ home or office workstation for
emergency interpretation, the image would be
viewed on a normal user monitor [2]. Besides,
non-high-quality monitors are commonly used by
referring physicians and clinicians. Thus, it would be
necessary to compare the quality of the normal user
monitors and high quality monitors used for
diagnosis. Specifically, the quality of the monitor
chosen must not lead to wrong interpretation and
mis-diagnosis. Since images that score high on
objective quality scales are not necessarily ranked
equally high by human viewers, a randomized
double-blind trial closely resembling actual clinical
practice has to be done. The results have to be graded
to allow statistical analysis [2].
2 Methodology
This study was designed as multiobserver, reader
performance (receiver operating characteristic
(ROC)) [3] study in which observer performance was
measured for four different types of monitors.
Participating radiologists rated each image with
regards to the likelihood that abnormality was
present.
A total of 25 (18 X-rays, 4 CT, and 3 MRI) images
were used. The images consist of acquisitions from a
variety of body parts such as ankle joint, foot,
abdomen, skull, pelvis, chest, hand, wrist, humerus,
cervical spine, shoulder, brain, and lumbar spine.
These images were chosen by the Head of Radiology
of the collaborating medical institution such that it
contained a combination of some with lesions and
some without. The X-ray radiographs were archived
with minimum 1576 x 1976 pixel resolution and a
10-bit depth; CT (Computed Tomography) images
were stored with 512 x 512 pixel resolution and a
12-bit depth; whereas MRI (Magnetic Resonance
Image) were stored with 256 x 256 pixel resolution
and a 12-bit depth. All the images used were stored in
American College of Radiology (ACR) and the
National Electrical Manufacturers Association
(NEMA) defined standard - DICOM (Digital
Imaging and Communication in Medicine) format
[4-5]. This standard is a framework for
medical-imaging communication.
Diagnostic experiments were done using different
monitors, namely the conventional 15 inch CRT
(Cathode Ray Tube) office computer monitor, 20
inch CRT, and 21 inch CRT high quality monitor
(SMM2183L, Siemen Simomed HM 1.8 MP
(high-contrast)). The 21 inch CRT monitor is the
default monitor used with the Picture Archiving
Communication System (PACS) in the Hospital
Information System (HIS) at the medical institution
for diagnosis purposes. As such, this monitor will be
considered as the ‘golden standard’ in this
experiment. Taken into account that LCD (Liquid
Crystal Displays) monitors are becoming gradually
more important [1], and portable computers (eg.
laptop) are becoming more powerful and possess the
additional advantage of mobility in second opinion
consultation, evaluation was also done with a 15 inch
laptop LCD monitor.
Table 1 shows the comparison among the
monitors. The viewing software used was Siemens
MagicView 1000 [6] for SMM2183L, and Siemens
MagicView 300 [6] for the 15 inch, 20 inch and LCD
monitors. The MagicView 1000 is the high end
reporting workstation and is the default software used
by the PACS for medical image display; whereas
MagicView 300 is a clinician viewing workstation.
The display resolutions chosen for the monitors are
indicated by the ‘matrix used’ row in the table.
Resolution and refresh rates were as the
recommended for standard usage of the monitors.
Table 1: The different monitors used for the
experiment
model
max.
matrix
matrix
used
refresh
rate (Hz)
CRT
15”
Compaq
v55
1024
x 768
1024
x 768
47.5
– 125
CRT
20”
Compaq
v1000
1800
x 1440
1024
x 768
48 -160
CRT
21”
SMM
2183L
1600
x 1200
1280
x 1024
50
-120
LCD
Compaq
LCD 15”
1024 x
768
1024 x
768
60
Five radiologists were involved in the study. Blind
tests were done where radiologists had to identify
which images had lesions and those without.
Interpretations of the selected images were
performed individually in four separate sessions at
1-week intervals. Using first the lower quality 15
inch monitor, the radiologists were shown the 25
images (one at a time) at a room condition which was
similar to the real diagnostic environment. The
radiologists were asked to detect if there were any
lesions and state their confidence level (1-not
confident to 6-very confident). They were also asked
to rate the diagnostic quality of the images shown
(1-poor to 6-good). After one week, the same
radiologists re-examine the images using the 20 inch
monitor. The process is repeated a week later with the
high quality 21 inch monitor. The evaluation of
different monitors was done with an interval of at
least one week so that the radiologists conducted
their analysis based on the images presented to them
and not from memory.
From the data collected, statistical tests of the
possible effects of using different monitors were
conducted.
3 Results
A powerful Multi-Reader Multi-Case statistical
method – receiver operating characteristic (ROC)
curves [7] is used to analyse the results. The ROC
curve is a plot of sensitivity versus 1-specificity,
where “sensitivity” is the proportion of the abnormal
cases correctly identified as such by the diagnostic
test, and “specificity” is the proportion of the normal
cases correctly identified as such by the diagnostic
test.
ROC analysis was performed on the confidence
levels to measure diagnostic accuracy when different
monitors were used. The area under the ROC curve
was analysed as it is the average sensitivity over all
possible specificities [8-10]. The calculation of areas
under the ROC curves was done using the Analysis-it
software
(available
at
http://www.analyse-it.com/download/dl.asp). It uses
a non-parametric method for constructing curves
[11], and the Hanley and McNeil method [12] for
comparing the curves.
Table 2 summarises the area under the ROC
curves for abnormality detection by each radiologist
(R1-R5) with the different monitors.
Table 2: Area under the ROC curve for detection
of abnormalities by individual radiologists for the
different monitors
R1
CRT
15”
0.781
CRT
20”
0.943
CRT
21”
0.917
LCD
0.833
0.877
0.921
0.895
0.912
0.991
0.789
0.842
0.991
1.000
0.746
0.816
0.886
0.978
0.978
0.842
0.930
A plot of the mean area under the ROC curve is
presented in Fig. 1. The error bars are the standard
deviation of mean for all the trials. The differences in
the mean area under the ROC are very small. Thus, it
supports the earlier observation that there were no
significant differences in diagnostic accuracy by
using the different monitors.
Fig.2 shows the mean of the diagnostic quality of
the 25 images shown on different monitors. Overall
the images were highly rated when the 21 inch
SMM2183L was used. SMM2183L is used as the
radiologists’ daily diagnostic monitors and this may
cause a bias by the radiologists. For the 15” CRT and
LCD monitors, the rating is quite low, and this may
be caused by the perception of the participating
radiologists that smaller monitors display lower
quality images.
Based on the statistical results in Table 1 and Fig.
1, however, it is proven that this bias is faulty.
Instead, the results recommend that the diagnostic
quality of low-cost monitors is comparable to
high-quality monitors. As such, smaller low-cost
monitors may be an economical and convenient
solution for displaying medical images.
Area under ROC curve
Mean area under ROC curve with different monitors
1
0.9
0.8
0.7
0.6
0.5
CRT 15"
CRT 20"
CRT 21"
LCD
Type of monitors
Fig. 1: Percentage of correct selections based on
radiologists
Diagnostic quality of different monitors
diagnostic quality value
R2
R3
R4
R5
7
6
R1
5
R2
4
R3
3
R4
2
R5
1
0
15 "
20"
21"
LCD
types of monitors
Fig. 2: Diagnostic quality of images shown on
different monitors rated by the different radiologists
4 Discussion
In this study, ambiguity occurs because no patient
history was provided, and radiologists were not sure
what abnormalities they were searching for. As such,
diagnosis results were gained purely on the
interpretation of the results presented on the
monitors. It is found that referring physicians and
clinicians may use non-high-quality monitors in their
respective clinics without any risks. In addition,
non-high-quality monitors (eg. v55 and v1000) may
be a low-cost solution particularly in rural areas
where cost and availability are pertinent factors. LCD
monitors may be higher in price than the 15” CRT
monitors, but still cheaper than high-quality monitor
may act as a low-cost mobile solution. With the price
of monitors decreasing and the quality improving, it
is worth keeping an eye on the market for a low-cost
good-quality monitors for medical displays.
As the results show that there is generally no
diagnostically significant difference in using
high-quality or non-high-quality monitors, the
question lies on factors such as display performance
and user behaviors. Display performances are
measured by luminance, gray scale and contrast,
resolution, veiling glare, and linearity, just to name a
few [13-14]; user behaviors includes characteristic
such as search behaviors, viewing time, and
experience as radiologists [14]. These factors are
needed for a more thorough evaluation of the
displays used in radiology department, should a
technical analysis be desired to support the results
presented here.
This article aims to provide a preliminary study
targeted at subjective diagnosis evaluations by
medical experts in a workplace environment. This is
important as technical specifications of hardware are
not necessarily reflected in the day-to-day operations
of the biological human visualisation system and
experience. Based on the results, and with the
availability of good quality LCD monitors/screens on
modern notebook PC, further work should be
undertaken to investigate the viability of using such a
mobile platform for medical diagnosis. The results
presented here may be extended for monitor selection
in other applications as well.
5 Conclusion
No obvious trend is observed in the results presented,
indicating that there was no significant preference to
any particular monitor in the detection of
abnormalities by the radiologists (each radiologist
had the best results using different monitors).
However, there was a trend in higher confidence in
using larger monitors which the users have prior
experience with. As such, some amount of training
and exposure may be required in confidence building
when migrating to using lower quality and smaller
less costly monitors. The results on LCD are
important as it supports the use of notebook PC in
conducting diagnosis. Furthermore, the findings may
prove beneficial in a more cost-effective
telemedicine environment.
Acknowledgement:
This paper reports a collaborative study conducted
with images and medical expertise (Dr Noriza Ismail,
Dr Wan Zainab Hayati Wan Mokhtar, Dr
Faizatuddarain Mahmood, Dr S. Sivalingam, and Dr
Shahrina Man Harun) from Selayang Hospital,
Malaysia. The authors would also like to
acknowledge Michel Bister (formerly of Multimedia
University) for his contributions toward this project.
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