Summary: In the past three decades, the practice of radiology in general, and
pediatric radiology in particular, has been transformed by imaging
technology. Ultrasound, computed tomography (CT), and magnetic resonance imaging
(MRI) have all contributed immensely to the care of children and led to a
deeper understanding of both normal anatomy and disease processes.
However, there has been no greater impact on pediatric radiology than
the development of digital radiography (DR).
Dr. Towbin is Radiologist-in-Chief, and Mr. Owen is PACS Administrator, Department of Radiology, Phoenix Children’s Hospital, Phoenix, AZ.
the past three decades, the practice of radiology in general, and
pediatric radiology in particular, has been transformed by imaging
technology. Ultrasound, computed tomography (CT), and magnetic resonance
imaging (MRI) have all contributed immensely to the care of children
and led to a deeper understanding of both normal anatomy and disease
processes. However, there has been no greater impact on pediatric
radiology than the development of digital radiography (DR).
radiography has evolved considerably over the past 20 years. Film
screen radiography was the standard—the diagnostic centerpiece—of
radiology departments for decades. By today’s standards, the technology
was not too expensive and was able to create diagnostic images of good
to excellent quality. But as technology advanced it became clear that
there were several issues, including the need for film processing with
the associated processing equipment, a dark room, chemicals and
dedicated darkroom personnel. As a result, throughput was slow, repeat
rates at times exceeded 10%, and the pressure was on the technologists
to restrain, position, and make exposures that minimized motion
artifacts in children who could be crying and/or unwilling to cooperate.
In 1985, computed radiography (CR) was introduced, providing an
alternative to film-screen radiography. CR was able to use existing
x-ray equipment to create and retain an image on a phosphor plate. Once
exposed, the CR cassette was put into a reader, where a laser scanned
the plate and converted the analog (A) image into a digital (D) format.
This A-to-D conversion changed plain film radiography. The digital image
could be fed into a computer and displayed on a PACS for review and
interpretation. This simplified and decreased the expense of the entire
process, since no photographic development was needed; film processors,
dark rooms and associated personnel also were no longer necessary. This
technology was widely accepted and utilized by radiology departments
around the world. Once in a digital format, the images could be
post-processed in a variety of ways to improve the diagnostic abilities
of the radiologist and to promote rapid distribution of the imaging
study to be immediately available to local and wide-area networks. In
addition, once digitized, the images were immediately available on PACS
and could be reviewed by the pediatric radiologist, who could assist the
technologist with difficult cases and more rapidly provide a final
reading to physicians caring for the child. The shortened turnaround
time from image production to final reading improved patient care and
radiology workflow, leading to customer satisfaction and potentially
Definitions of “DR”
The term ‘DR’ has two meanings in medical imaging. The first is
“digital radiography,” which includes all methods of image acquisition,
resulting in an image that can be displayed in a digital format. The
hierarchy of digital radiography is divided into two major categories
usually abbreviated as ‘CR’ and ‘DR’. This second use of the
abbreviation ‘DR’ refers to ‘direct radiography,’ and it includes any
system in which the image is created directly from a receptor. In direct
radiography systems, the image is sent directly from the receptor for
processing. Computed radiography is also referred to as indirect
radiography because the image is read off the imaging plate through a
discrete acquisition process. Generally speaking, techniques used in CR
imaging can be compared to a 200 speed film/screen system while DR
techniques may be compared to a 400 speed or higher film/screen system.1,5 Essentially, a DR system requires approximately 50% or less technique than a CR system to produce a comparable image.
radiography was introduced in the late 1990s. The substantial impact of
DR on daily practice is multifaceted, and related in part to the high
percentage of case volume represented by plain radiography. In our
practice, and that of most departments, plain film radiography accounts
for more than 50% of total imaging volume. As a result, this section of
the department employs the most technologists. The high efficiency and
rapid turnaround time [TAT] of digital radiography often lead to a
reduction in the number of technologists by significantly increasing the
number of studies performed per technologist. To better understand the
effect of direct radiography in the pediatric radiology setting, we did a
time-motion study that contrasted film screen radiography (FSR) and DR.
We found that the average TAT for a 3-view skeletal examination was
approximately 12 minutes for FSR and 3 minutes for DR. The effect on
exam completion was more dramatic when all or part of an examination
needed to be repeated. Other authors have documented similar
experiences. An unanticipated outcome of the faster TAT was demonstrated
in the relationship between radiology and clinical services. For
example, with FSR or CR, the TAT was too slow to keep up with a busy
orthopedic clinic, resulting in tension between the two groups. In
contrast, with DR, the TAT is fast enough to keep up with the demands of
“herd-type” scheduling and multiple orthopedists seeing patients
simultaneously. This has dramatically improved relations between the two
The Phoenix Children’s experience
be configured using single or dual detector systems. While both
configurations work well and add efficiency at lower radiation doses,
the technologists in our department prefer the dual-detector
configuration because it is easier to position patients and requires
fewer steps to complete a study with >2 views. However, this is not
always a practical solution, since it is more costly—about $100,000. In
2011 Phoenix Children’s Hospital opened a new hospital building that
included a new radiology department fitted with Philips imaging
equipment. We made a commitment to use DR only and installed three DR
units, one with a dual-detector system and two with single detectors. In
addition, our satellites feature combination RF/DR rooms with single
As a children’s hospital, our facility is a strong advocate of the Image Gently®
movement with the goal of producing diagnostic studies at the lowest
possible radiation dose. Our DR equipment supports these efforts by
using lower mAs in most studies1 and reducing the repeat
rate. Other positive features of DR include faster TAT, more flexibility
of the imaging device making it easier for the technologist to position
the child resulting in shorter imaging times in our experience and that
reported in the literature.2,3 Compared to film/screen
imaging, digital imaging systems are very forgiving of both under- and
overexposure. Severely underexposed digital images can be grainy and
unacceptable even after post-processing. In contrast, overexposed
digital images can appear as if a correct technique had been used. This
is a double-edged sword, since it eliminates a second exposure but may
lead to exposure creep, one of the major problems of DR. Exposure creep
is a tendency to increase technique to ensure that all images are
diagnostic. Studies have shown DR images with exposure rates of 500% to
1000% can still produce a diagnostic quality image.4 Thus, a
quality-assurance program that regularly monitors the technical output
of DR to ensure the highest-quality imaging at the lowest possible dose
is very important.
At Phoenix Children’s, the prevention of
exposure creep has been addressed through two simple but effective
measures: Technique charts and a film review program. Technique charts
that build in substantive reductions in dose are employed in all our
imaging systems. Coupled with the technique charts is a regular review
of randomly selected studies to ensure compliance with the charts. A few
examples of DR techniques include: a neonatal chest radiograph was
typically obtained with CR using 58 Kvp and 2.0 mAs. With DR, the same
examination is performed using 56 Kvp and 1.0-1.25 mAs. A 3-view ankle
scan on a teenager (15-19 years old) on a CR system used 60 kVp at 4
mAs. The same study on DR uses 55 kVp at 1.5 mAs. An AP chest technique
for a 6-month-old using CR required 70 kVp at 2-3 mAs. The same study on
our DR system uses 60 kVp at 0.8 mAs. All examples show a reduction
equal to or greater than 50% of patient dose.
In most CR systems,
technique tracking can only be achieved through exposure indicators in
the DICOM header. There is not an accurate way to track kVp, mA, or
time. This is because a CR cassette has no connectivity to the x-ray
generator. Consequently, there is no way to transfer study information
from the x-ray generator to the CR cassette. CR system exposure
indicators can be problematic. Every CR system manufacturer has a
different methodology and scale to designate exposure indicator values.
In addition, exposure indicators are a reference value representing the
relative amount of radiation hitting the plate. Direct radiography
systems do have the ability to track technique factors. With DR, the
x-ray generator and receptor are part of a single, fully integrated
system. Technique factors [mA, kVp, time] from the x-ray generator
component of the DR system are included in the DICOM header. Patient and
study information from the work list also becomes part of the DICOM
The pros and cons of DR and CR are summarized in Table 1.
conclusion, DR has had a substantial positive impact on pediatric
imaging by reducing radiation dose, imaging costs, and patient
turnaround times. As a result of the image-acquisition advantages,
post-processing toolbox, and cost savings, we anticipate that over time,
DR will replace all other forms of plain film pediatric imaging.
- Seibert JA. Medical Radiation Exposure Requirements for Digital Radiography. Presented: Digital Imaging Summit and Workshop for Veterinary Radiologists. San Luis Obispo, Calif. May 29-31, 2008.
Hermann T. Computed radiography and digital radiography: A comparison
of technology, functionality, patient dose, and image quality.
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Accessed September 1, 2012.
- Reiner Bruce I, et al. Multi-institutional analysis of computed and direct radiography: Part I. Technologist, Productivity, Radiology. 2005;236:413-419. Epub 2005 Jun 21.
J. The standardized exposure index for digital radiography: An
opportunity for optimization of radiation dose to the pediatric
population. Pediatr Radiol. 2011;41: 573–581. Published online 2011 April 14. doi: 10.1007/s00247-010-1954-6.
- Willis, C. Computed radiography: A higher dose? SPR Seminar in Radiation Dose Reduction 2002. Ped Radiol. 2002;32:745-750.