This publication was supported by an educational grant from
Amersham Health, Princeton, NJ. The opinions expressed in this
publication are those of the authors and not necessarily those of
Dr. Bae reports relationships with Tyco Healthcare and
Mallinckrodt through patent agreements and as a consultant. Dr.
Fishman reports relationships with Siemens Medical Solutions and
Amersham Health as a consultant. Dr. Foley reports a relationship
with GE Medical Systems through an investigator agreement. Dr.
Naidich reports a relationship with Siemens Medical Solutions
through its Advisory Board and as a consultant. Dr. Saini reports a
relationship with GE Medical Systems through research support. Dr.
Becker, Dr. Sahani, Dr. Siegel, Dr. Tahktani, and Dr. Zinreich
report that no such relationships exist.
is a Professor of Radiology and Pediatrics at the Mallinckrodt
Institute of Radiology, Washington University School of Medicine,
St. Louis, MO.
Multidetector computed tomography (CT) offers the same
advantages in children as it does in adults. These advantages
include faster scan acquisition, increased resolution, and optimal
three-dimensional (3D) processing. The implications of
multidetector technology are often different in pediatric patients,
Faster scanning improves contrast enhancement in any population.
But in children, it also reduces the need for sedation. With
single-slice scanners, sedation is needed in 40% to 100% of
pediatric patients. Early experience with 16-row multidetector
scanners suggests that although sedation cannot be completely
eliminated, it is now needed in <5% of pediatric patients. In
addition, respiratory artifacts have nearly been eliminated.
Improvements in resolution and 3D reconstructions offer
additional advantages. Together they make CT an excellent
alternative to magnetic resonance (MR) imaging. Although exposure
to ionizing radiation puts CT at a relative disadvantage when
compared with MR, newer techniques are reducing the radiation dose.
More important, children under 5 years of age require sedation
during hour-long MR examinations. The risks of sedation are real,
and in some instances they may exceed the risks of exposure to
At our institution, CT angiography (CTA) is beginning to replace
conventional catheter angiography for evaluation of cardiac
It is associated with a radiation dose at least 2 to 3 times lower
than that of conventional angiography. This estimate is based on
older radiographic parameters, including a kV of 140 and an mA of
up to 400. With more contemporary radiographic settings
(80 kV and mA adjusted for weight), the radiation dose is likely to
be much lower, perhaps 8 to 10 times lower than that of
Achieving the best result
Optimizing CTA in children requires attention to scanner design.
It is possible to perform CTA using a 4-row scanner, but a 16-row
scanner is preferred. Patient preparation is also important. We
place the intravenous (IV) line before the patient arrives in the
imaging suite. Waiting to place the IV line until the child is on
the CT table is likely to result in an uncooperative child.
We use the largest-gauge catheter possible, generally a
22-gauge, and insert it in the antecubital region if possible. Some
patients arrive with an IV line already placed in a scalp vein or a
catheter in the foot, however. For an abdominal scan, oral contrast
must be administered before the study.
Table 1 outlines technical factors to consider in CTA of
pediatric patients. The selection of slice width usually represents
a compromise. With our 4-row Siemens scanner (Siemens Medical
Solutions, Iselin, NJ), detector collimation thickness can range
from 1 to 5 mm, or greater. A slice width of 1 mm will produce
images of superb resolution but at an excessively high radiation
dose. A slice width of
5 mm will reduce the radiation dose, but resolution may be
unacceptable. A slice width of 2.5 mm represents a reasonable
compromise. Table speed is as fast as possible, 15 to 20 mm/sec,
also with the goal of reducing radiation exposure. Scan speed is
With our Siemens 16-row scanner, slice width can be 0.75 or 1.5
mm. We use the larger width to reduce radiation exposure. Table
speed is 24 to 36 mm/sec, and scan speed is 0.5 seconds. With both
4- and 16-row scanners, the slice reconstruction thickness is 3 to
5 mm for routine viewing.
It is important to tailor the selection of radiographic
parameters to patient size, as shown in Table 2. In the case of a
neonate, whose weight is <15 kg, the maximum allowable mA in the
chest is approximately 25, and in the abdomen, approximately 30.
These limits gradually increase until the patient reaches
approximately 50 kg, when it becomes possible to use adult
radiographic standards. Another factor to consider is kVp. In a
child of <50 kg, we successfully use a kVp of 80. In a child who
weighs >50 kg, we increase the kVp to 100 to 120.
The multidetector CT study itself is very short. We do not
routinely perform multiphasic imaging. In the chest, we usually
acquire images in the arterial phase, and in the abdomen, the
portal venous phase. Our approach varies with the clinical
indication; however, this topic is beyond the scope of this
Multiphasic imaging is justified under certain circumstances. In
complicated cases of congenital heart disease, it may be helpful to
do both arterial- and venous-phase imaging. In evaluating hepatic
tumors, we perform dual-phase imaging as well.
The key issues of contrast administration are similar in
children and adults: contrast volume, flow rate, and the timing of
image acquisition. We use nonionic contrast media and a standard
concentration of 300 mgI/mL. In the past, the typical contrast dose
in children was 2 mL/kg, but faster scanners permit a reduction to
1.5 mL/kg. The maximum contrast dose in children is the lesser of 4
mL/kg or 125 mL. In our experience with faster scanners, it is very
rare to need more than 2 mL/kg.
If the patient has a peripheral IV or a central line, we inject
contrast by hand, delivering the dose as quickly as we can. In such
cases, the speed of injection will vary by the location of the
access line and the caliber of the needle.
If it has been possible to insert a 22-gauge or larger catheter in
the antecubital space, we use a power injector to deliver contrast
material at a flow rate of 1.5 to 2 mL/sec. With a 20-gauge
catheter, the injection rate can be increased to 2 to 3 mL/sec.
With a 24-gauge catheter or a central line, contrast is injected at
The timing of image acquisition is the final and critical step
in optimizing contrast delivery. One of the biggest problems with
smaller-caliber needles is that the scan may be completed before
all of the contrast has been injected. Therefore, when imaging
vascular structures in the chest in children weighing <10 kg, we
use a scan delay of 12 to 15 seconds.
In larger children, we sometimes use a scan delay of 20 to 25
seconds for imaging vascular structures in the chest. We prefer to
use automated scan initiation or bolus tracking, however. In
smaller children, this approach is not sufficiently reliable. With
a contrast volume of only 4 to 8 mL, it can be difficult to achieve
the enhancement threshold necessary to trigger the scan, 100 HU in
We sometimes use electrocardiographic gating in adolescent
patients, particularly if we suspect a very small lesion, such as a
septal defect, or some type of a postoperative small conduit, such
as the baffle or Fontan grafts. We seldom use ECG gating in
neonates because the heart rate is so fast, and gating increases
For CTA of the abdomen in neonates weighing <10 kg, the scan
delay typically is 10 to 15 seconds for image acquisition during
the arterial phase, and approximately 45 seconds for image
acquisition during the venous phase. In infants and children
weighing >10 kg, scan delays of 20 to 25 seconds for the
arterial phase, and 50 to 55 seconds for the venous phase are
typical. It is also possible to use bolus tracking and trigger
scanning at approximately 50 HU, but usually an empiric delay works
well in abdominal studies.
We use a two-dimensional (2D) multiplanar technique because it
is easy and can be done at the console, where clinicians can also
look at images quickly. This technique provides substantial
information about the vasculature, but it lacks depth. Therefore,
we prefer to use 3D volume rendering for postprocessing of data
from CTA studies.
Volume rendering enables the visualization of both vessels and
Vascular lesions in children are often associated with airway
abnormalities, and volume rendering affords the option to study
both. We also find that some of the maximum intensity projections,
particularly the thick slabs, are useful for looking at
intraparenchymal vessels and for examining arteriovenous
In reviewing volume-rendered datasets, it is important to use a
workstation with real-time, interactive capabilities. It remains
essential to review the axial images, as they often provide
diagnostic information that is complementary to that derived from
3D images. In some cases, a diagnosis can be made only on the basis
of either a 2D or a 3D image.
The vascular applications of pediatric CTA include the diagnosis
of congenital abnormalities of the thoracic vessels, and vessel
mapping for tumor staging and surgical planning. Examination for
coarctation of the aorta, or a double aortic arch, are common. We
also evaluate abnormalities of pulmonary venous return and
Figure 1 depicts a 10-day-old infant girl with congestive heart
failure. The most likely cause is coarctation of the aorta. CTA was
performed using 8 mL of contrast and a 12-second scan delay. It is
difficult to make a diagnosis on the axial view. On the multiplanar
sagittal view and the 3D reconstruction, a very tight high-grade
stenosis is evident, indicating the need for surgical repair.
Figure 2 illustrates the use of CTA to differentiate extra-lobar
sequestration from neuroblastoma. In this newborn,
8 mL of contrast was slowly injected through an existing IV line in
the scalp. The axial images, though not optimal, demonstrate a tiny
vessel arising from the aorta. A tiny vein draining the
sequestration was recognizable only in retrospect. On multiplanar
3D images, the arterial feeder that characterizes sequestration is
easily visualized, however. An unusual vein providing drainage to
the portal vein is also evident. This case demonstrates that even
with a very small amount of contrast injected through a peripheral
IV line, CTA produces clinically useful images.
Examination of sacrococcygeal teratoma in a neonate represents
another vascular application of CTA, in this case for tumor
staging. Often the axial view will easily show the tumor, but the
vessels may be barely visible. By comparison, on the 3D
reconstruction, a feeder vessel may be evident coming off the
middle sacrococcygeal artery.
One of the most exciting uses of CTA is in cardiac applications,
including the diagnosis of congenital shunt lesions and the
evaluation of postoperative anatomy, including palliative shunts
and complex heart disease.
Figure 3 presents the example of a 2-week-old infant who was
cyanotic and thought to have congenital heart disease. CTA,
accomplished with 8 mL of contrast material and mAs of 30, clearly
demonstrates a right hemitruncus, in which one pulmonary artery
arises from the aorta and the other from a pulmonary trunk.
Another cardiac application of CTA, the postoperative assessment
of a patient with a history of teratology of Fallot, is depicted in
Figure 4. A surgically placed shunt between the subclavian artery
and the pulmonary artery has thrombosed, as shown on both axial
images and multiplanar reconstruction.
Finally, Figure 5 shows the postoperative evaluation of a
patient who, as a neonate, underwent repair of transposition of the
great vessels. CTA easily reveals a 5-mm graft between the right
atrium (RA) and left ventricle, as well as a small septal defect
between the right and left ventricles.
CTA has many exciting applications in pediatric patients, and
many advantages. The use of 16-slice CTA offers the opportunity to
eliminate the long periods of sedation associated with MR, and
reduces the radiation exposure associated with conventional
The benefits of accurate diagnosis alone generally outweigh the
risks associated with CTA. Nonetheless, care must be taken to
reduce unnecessary risks, as children <10 years of age are more
sensitive to the effects of radiation than are middle-aged adults.
To reduce radiation exposure, the CTA protocol and technical
settings must be optimized. The tube current and kVp must be as low
as possible, the table feed as fast as possible, the number of
contrast-enhanced phases must be minimized, and automated dose
reduction technology should be used, if it is available.
Inappropriate referrals to CT must also be eliminated.
As CT technology advances, it is having an increasingly profound
impact on the care and imaging of children. When performing CTA in
children, study design and execution are critical. Even with small
volumes of contrast and very small anatomy, CTA is successful if
performed with an attention to detail. Patient preparation is
crucial, as are the proper selection of technical factors and
optimal delivery of contrast material. Data processing,
particularly the creation of 3D volume renderings, is often
essential in making a diagnosis.
Aortic coarctation in a 10-day-old girl with congestive heart
failure (8 mL contrast, 12-second delay time). (A) The diagnosis
of coarctation of the aorta is difficult on the axial view, but
on (B) the multiplanar sagittal view and (C) the 3D
reconstruction, a very tight high-grade stenosis is evident
(arrow in B), indicating the need for surgical repair.
Differentiation of extralobar sequestration from neuroblastoma in
a newborn (slow scalp vein injection, 8 mL contrast). (A and B)
Axial images demonstrate a tiny feeding artery (arrow in A). A
tiny draining vein (arrow in B) was recognizable only in
retrospect. (C, D, and E) On multiplanar 3D images, the arterial
feeder that characterizes sequestration is visualized easily. An
unusual vein providing drainage to the portal vein is also
(A and B) CTA provides the diagnosis for a right hemitruncus in a
2-week-old infant (30 mAs, 8 mL contrast). One pulmonary artery
[PA] arises from the aorta [A] and the other from a pulmonary
Postoperative assessment of a palliative shunt in an adolescent
patient using bolus-tracking technique. In this patient with a
history of tetralogy of Fallot, a surgically placed shunt
(arrows) between the subclavian artery and the pulmonary artery
has thrombosed, as shown on both (A and B) axial images and (C)
Postoperative assessment of a patient with repaired transposition
of the great vessels. (A) CTA easily reveals a 5-mm graft between
the right atrium [RA] and the left ventricle (arrow), as well as
(B) the shunting of contrast from the right to the left ventricle
through a tiny residual ventricular septal defect (arrow).
ELLIOT K. FISHMAN, MD:
KYONGTAE T. BAE, MD, PhD:
You use pretty much the same delay for CTA of the chest and
MARILYN SIEGEL, MD:
Yes. Chest CTA is initiated at 12 to 15 seconds in very small
patients and at 20 to 25 seconds with an automated program in
larger patients. The major role of CTA in the abdomen is in the
evaluation of the liver. The timing of the arterial phase is at 12
to 15 seconds in small patients and 20 to 25 seconds in larger
patients. It works.
So 16-slice CT hasn't really changed the timing.
No, the time delay for CTA of the chest and abdomen remain
Pediatric patients are obviously unique, in terms of selection of
contrast concentration or types of contrast. Are there specific
rules you recommend?
We still use concentrations of 280 to 320 mgI/mL. This results in
excellent vascular opacification as long as the catheter is of
adequate size to sustain a fast flow rate.
DAVID P. NAIDICH, MD:
Are kidneys in neonates more vulnerable?
Yes. Stasis nepropathy is a problem in the neonate. This is the
result of the accumulation of glycoproteins (the principal one
being the Tamm-Horsfall protein) within the tubules, leading to
temporary oliguria. The use of intravenous contrast material has
been associated with the precipitation of excess amounts of
Tamm-Horsfall protein. Stasis nephropathy is transient and
generally resolves within the first week.
Do you think using a higher concentration gives you more of a
window doing a successful CTA? If you are looking at vessels or the
hepatic artery or renal arteries, would a higher concentration give
you more leeway in terms of finding a higher sweet spot or a wider
sweet spot, or would it make a difference?
If one were injecting through a very small needle, then a higher
concentration of iodine might be beneficial. However, experience
using higher concentrations of contrast material in children has
not yet been reported in large series. As noted above, excellent
contrast enhancement can generally be achieved as long as the
catheter caliber is large enough to allow a fast flow rate. It also
helps to have the catheter in an upper extremity, particularly in
an antecubital location.
W. DENNIS FOLEY, MD:
I think the answer to that question is that if your iodine load is
the same, and your injection rates are the same, and one contrast
agent is more concentrated than the other, then your imaging window
is just going to vary in time. It's not going to have any wider
temporal window. In other words, with a higher concentration under
those circumstances, the number of iodine atoms going into the
circulation is going in faster per second.
Can you check creatinine in this population, then administer
Yes, but the volume of fluid that can be given to a neonate is
We're using iopromide, which is 370 mgI/mL, as a routine for
pulmonary artery CT. It seems empirically that going from 300 to
370 mgI/mL has reduced the number of indeterminate CT studies that
we've had. I appreciate that it's a large iodine load; but just the
opposite of where you're leading with your question, I think we're
still relatively safe with using a higher, rather than a lower,
dose of iodine. It would be nice to reduce it, but I don't see, at
this point, that we could do that.
All right, thanks very much, Marilyn.