The use of helical computed tomography (CT) is particularly important in children, but posses some unique challenges to the radiologist to optimize scan quality while minimizing risk to the child. This article presents current pediatric body helical CT techniques, including the issues of sedation, use of contrast materials, and scan parameters.
Dr. Hollingsworth is a Clinical Associate and Dr. Frush is
an Associate Professor in the Division of Pediatric Radiology,
Duke University Medical Center, Durham, NC. Dr. Donnelly is an
Associate Professor in the Department of Radiology, Children's
Hospital Medical Center, Cincinnati, OH.
Since its advent more than 25 years ago, computed tomography
(CT) has become a well-established and increasingly utilized
diagnostic tool. During the past decade, helical technology has
accelerated this trend with a dramatic further reduction in time
necessary for data acquisition of volume data sets. Familiarity
with this pervasive technology is particularly important in
children to optimize scan quality and minimize risk.
Although current literature abounds with information pertaining
to current techniques and evolving applications for adult helical
CT, information regarding the optimization of helical CT in infants
and children is sparse.
This is true despite the fact that many more variables must be
addressed in the pediatric population. These include techniques for
intravenous (IV) and oral contrast material administration,
including variable delays in onset of scanning. Although successful
helical CT data acquisition in children is complex and often
requires attention to each individual child rather than adherence
to protocol, diagnostic scanning can be achieved. To this end, the
following material reviews contemporary pediatric body helical CT
As CT scanning has become faster, the need for sedation has
decreased. For example, the frequency of sedation dropped from 18%
to 10% in young children as helical CT became available.
Introduction of even faster multidetector scanners has further
decreased the frequency of sedation in children <6 years of age
to as low as 3%.
Even with these reductions, the issue of safe and effective
sedation remains an integral aspect of cross-sectional imaging in
children. General guidelines and regulations concerning safe
practice parameters for pediatric sedation have been published
and support the basic principle of protecting the welfare of the
child. Importantly, a minimal set of standards, including
pre-sedation evaluation, selection of appropriate sedative agents,
procedural monitoring, and implementation of specific discharge
criteria, is essential.
Once the decision to sedate a child for the purpose of
cross-sectional imaging has been made, there is a multitude of
sedative agents from which to choose. Unfortunately, there is no
singularly perfect agent. In general, successful, safe sedation
stems from a limited group of drugs with which the radiologist is
familiar (Table 1). Chloral hydrate and sodium pentobarbital are
two of the most widely used sedative agents for pediatric
diagnostic imaging purposes. Chloral hydrate, an oral medication
given in doses of 50 to 100 mg/kg body weight (maximum dose of 2.0
grams) is most successful in children under about 15 kg.
Intravenous administration of sodium pentobarbital in titrated
doses of 1.0 to 3.0 mg/kg body weight with a total dose of 6.0 to
8.0 mg/kg (maximum dose of 200 mg) can also be safe and effective.
When necessary, IV fentanyl citrate can be administered in
conjunction with sodium pentobarbital in titrated doses of 1.0
µg/kg body weight (maximum dose of 4.0 µg/kg). This combination of
drugs acts synergistically and is helpful when the child requires
pain relief as well as sedation during a radiologic
Oral contrast material
Although the use of oral contrast material in abdominal and
pelvic CT examinations in children has become, for the most part,
routine, its use has benefits and disadvantages. Oral contrast
material is helpful in identification of the course and caliber of
bowel, in distinction of bowel from adjacent solid structures or
organs, and in determining luminal and mural abnormalities. The
temporal information related to how far anterograde the contrast
has passed can also be helpful in diagnosing bowel obstruction.
However, certain clinical situations and diagnostic questions can
be addressed in the absence of oral contrast material. In fact, the
routine administration of gastrointestinal contrast material has
and is not used routinely anymore at some institutions. Dense
iodinated contrast may mask subtle mucosal enhancement
abnormalities and may make detection of intraluminal or submucosal
lesions difficult. Evaluation of the solid organs is usually not
affected by the presence or absence of oral contrast material,
particularly in a follow-up examination. In the setting of trauma,
the use of oral contrast material is generally considered safe
; however, there is a risk of significant aspiration. The
radiologist must take an active role in deciding the relative
necessity of oral contrast material and must be prepared to handle
any adverse outcome related to its use.
The issue of administration of oral contrast material to young
children who require sedation prior to their examination is also
controversial as oral intake of fluids increases the risk of
Oral contrast material is usually administered an hour or so prior
to scanning, which interferes with most general nothing-by-mouth
guidelines of 2 to 6 hours depending on the size of the child
undergoing the examination and the liquid or solid nature of the
ingested material. At our institution, oral contrast material may
be administered up to the point the child is sedated for
examinations for which contrast enhancement is believed necessary,
such as cases of suspected bowel or mesenteric pathology (i.e.,
abscess) or in blunt abdominal trauma. We recently reviewed safety
issues regarding our past 5 years of experience with administering
oral contrast before sedation. In 337 consecutive cases, there were
no instances of vomiting with aspiration (LF Donnelly, unpublished
Agents used for standard opacification of the gastrointestinal
tract usually contain water-soluble contrast diluted with liquids,
such as fruit drink or soda. However, agents composed of dilute
barium are also available. Table 2 presents appropriate amounts of
oral contrast material given age- or weight-based considerations.
Coaxing very young or sick children to drink enough oral contrast
material is difficult. At our institution, adequate intraluminal
contrast has been achieved by encouraging children to drink liquids
(such as juice, water, or carbonated drinks) without contrast
media. Figure 1 illustrates opacification of the gastrointestinal
tract with juice in a child who refused to drink liquids containing
iodinated contrast material.
IV contrast material
The issue of appropriate administration of IV contrast is
perhaps the most challenging and most important aspect of
successful CT scanning in children. Multiple parameters that must
be addressed include type of contrast, volume administered,
location and caliber of intravenous access, method of contrast
administration (manual injection versus power injection), and delay
from time of injection to the initiation of scanning. Although the
task may seem daunting, attention to these variables can lead to
optimal contrast enhancement in most instances.
Generally, low-osmolar, nonionic IV contrast material is
recommended in children.
However, the use of specific contrast agents should be based on
either individual or institutional standard of practice. The
standard dose of IV contrast material for abdomen scanning is 2.0
mL/kg, not to exceed an adult dose of approximately 150 mL. When
scanning the chest or performing CT angiography with a goal of
vascular opacification instead of organ enhancement, 1.5 mL/kg is
With both single- and multidetector CT technology, CT angiography
can be performed successfully, even in infants with relatively slow
rates of administration and small volumes of IV contrast media
Administration of IV contrast may be through a peripheral
catheter or central venous catheter. Methods of administration
include manual (hand) bolus and power injector. Although for years
manual injection has been standard practice in pediatric patients,
power injectors have been used successfully with increasing
frequency. This practice has been found to be safe.
We use power injection through peripheral angiocatheters as small
as 24 gauge, providing that the catheter functions well.
Contraindications to the use of power injectors include absence of
blood return through the catheter and inability to flush the
Use of power injectors with central lines is controversial.
Although this practice is probably more widespread than reports in
the literature indicate,
this practice is not sanctioned by the manufacturers.
Suggested rates of intravenous contrast administration are 1.0
to 1.5 mL/sec for 24-gauge angiocatheters and 1.5 to 2.0 mL/sec for
However, rates as low as 0.5 mL/sec have been used with acceptable
Generally speaking, target rates should be between 1.2 and 2.5
mL/sec to provide optimal vascular and solid organ enhancement. We
use rates as high as 3.0 mL/sec for CT angiography despite the size
of the child. Although manual injection of contrast material is
regarded as safe and has provided quality scans for many years, the
true rate of injection is imprecise. The rates vary between 1.0 and
3.0 mL/sec with an average rate of just under 2.0 mL/sec.
Complications are no more common with power injection than with
manual injection, provided that the catheter functions properly and
is monitored during injection.
The timing of scanning onset in relation to IV contrast
administration (often referred to as scan delay) has changed with
the advent of helical CT. In conventional slice-by-slice abdominal
CT scanning, scanning was initiated after approximately one-half of
the contrast bolus was administered. Recommendations for helical CT
in children are to delay scanning of the abdomen until completion
of IV contrast material administration. Reported delays from the
end of contrast administration to the onset of diagnostic scanning
vary from approximately 5 to 30 seconds.
We have found that delays for abdominal scanning of 20 to 25
seconds, and 10 to 15 seconds for chest scanning, are reliable for
both single and multislice helical CT. Chest scanning can also
follow abdominal scanning with excellent enhancement of the
With multidetector technology, neck, chest, abdomen, and pelvis
scanning can be performed sequentially without the traditional
splitting of IV contrast material.
Multidetector helical technology allows even more rapid image
acquisition, placing new demands on appropriate utilization and
timing of IV contrast material administration. Using multislice
equipment for abdominal imaging, we commonly use a 20-second delay
in scanning initiation after completion of contrast administration.
This allows for fairly consistent portal venous phase of contrast
enhancement of the liver and parenchymal renal enhancement.
In addition to these empiric delays, bolus tracking can also be
used to determine scan onset, thus individualizing each CT. This is
especially useful in pediatric body CT, where contrast material
administration is complex. This technology confers only a slight
increase in radiation dose to the patient. Although the usefulness
of bolus tracking in adults is debatable,
it has been found to be quite useful when scanning children
In addition to the complexities surrounding issues of sedation
and appropriate use of IV and oral contrast material in children,
several other technical parameters deserve careful attention. These
include tube current (milliampere [mA]), kilovoltage (kVp), table
speed and slice thickness ("pitch"), and gantry rotation cycle
time. These parameters are important since they determine image
quality and radiation exposure. Despite this importance, specific
recommendations and even general guidelines are lacking for
pediatric helical CT. In general, investigators have recommended
size-based adjustments in tube current (Table 3), and scanning at
pitches of 1.5 to 2.0.
These adjustments provide acceptable image quality while reducing
radiation for general body indications. While lowering the kVp will
also reduce radiation, there are no clinical guidelines for
application of data that support sized-based kVp adjustments.
In general, scanning should be performed using the fastest table
speed and largest slice thickness indicated. This will, of course,
depend on individual preferences, scan indication, and scanner
manufacturer. A few studies support the use of low (or lower) tube
current scanning in the chest
The issue of radiation and CT is a timely topic.
Computed tomography radiation can be considered a public health
concern for the following reasons. First, CT accounts for up to 65%
of medical radiation, and children account for approximately 11% of
all CT examinations.
Moreover, the rate of CT scans is increasing. Importantly, it has
been shown that scanning is often obtained using adult technique
(average pediatric mA was about 200), exposing the children to
This is important because children are more radiosensitive to the
same organ dose than adults, and because a child's longer life
could allow radiation-induced malignancies to develop. We now
realize that the relationship between low-level (CT) radiation and
cancer is much closer than previously thought.
Together, these facts mandate that radiation be minimized.
Strategies include using other modalities that can provide
sufficient diagnostic information, using sized-based scanning, and
changing the paradigm of image quality from optimal (high dose) to
acceptable (figures 2 and 3).
Helical CT scanning has become an invaluable tool for imaging
children, although scanning children often presents unique
challenges. Despite these challenges, diagnostic scanning can be
achieved. Even in the most complex circumstances, attention to the
individual child and addressing the diagnostic question with
appropriate scan techniques can provide excellent results while