The advent of spiral CT scanning has provided the opportunity
for optimization of CT data sets by coupling fast scanning with
rapid contrast delivery. Spiral CT scanning provides the ability to
acquire volumetric CT data in a single breath-hold acquisition.
Current scanners allow single acquisitions in the 40 to 50 second
range, as well as the ability to acquire back-to-back spiral scans
with minimal interscan delay time (generally less than 10 seconds).
This rapid scanning stresses the importance of coordinating
contrast administration and scanning to maximize the detection of
Traditional methods for timing contrast delivery include the
test bolus technique, which is time consuming, or the use of
standard set scan delay intervals, which ignores individual
variations in circulation time and contrast enhancement. There is
increased need for easy to use programs that promise individualized
control of the timing of contrast administration and data
GE previously introduced SmartPrepTM (General Electric Medical
Systems, Milwaukee, WI), an automated computer technique designed
to tailor scans for the individual patients. Published results have
been encouraging.4-6 We recently tested an even newer program
called the C.A.R.E. Bolus (Combined Application to Reduce
Exposure). This software program allows the physician to monitor an
individual patient's contrast enhancement curve over a region of
interest, and then it automatically initiates the spiral scan when
a predetermined threshold enhancement level is reached. Herein, we
report our initial experience with this new technique.
Materials and methods
C.A.R.E. Bolus is a commercially available software upgrade for
the Siemens Plus CT Scanner. This program allows the operator to
chose a contrast enhancement threshold for a region of interest,
which will then automatically trigger the data acquisition once the
preselected density threshold is reached.
The program is fairly straight forward. The operator first
selects an appropriate level on the initial scout topogram (figure
1A) and obtains a single low-dose axial scan using mAs 90, kVp 120
and a collimation equal to the collimation for the subsequent
spiral CT scan (typically 3 to 5 mm). A region of interest is then
chosen (i.e. the aorta) for contrast flow and density monitoring
(figure 1B). If monitoring of different vascular structures or
organs is desired, a maximum of four regions of interest can be
placed; however, only one of the regions of interest can be used to
trigger the scan mode. Next, the user enters a threshold value
(i.e. 150 HU) as the trigger for the initiation of the spiral scan
(figure 1C). A sampling start time and rate, which specifies when
and how often monitoring scans and contrast density plots will be
displayed, also can be set for the area of interest. The frequency
can be selected for up to 10 monitoring scans. Once the selected
threshold is crossed, the system automatically begins scanning at
the pre-selected start point (figure 1D). There is a delay of
approximately 3 to 7 seconds from the time the threshold is crossed
until the data acquisition starts. The three second delay is
standard if the region of interest is selected as either the upper
or lower border of the subsequent scan. If necessary, the trigger
threshold can be adjusted, either higher or lower, during the
In our initial protocol, we selected the aorta as the region of
interest. Our sampling scans and plots were set to begin at 20
seconds after initiation of contrast injection and to continue at 5
second intervals until the threshold trigger was reached and the
data acquisition automatically started. We discovered that an
aortic threshold trigger of 150 Hounsfield units was most useful,
as this represents a midpoint on the upward density curve and
allows for the short delay (3 to 5 seconds) between the threshold
trigger and the start of the scan. However, the sampling can occur
as early as the specific clinical application might dictate.
Patients chosen for evaluation included those with thoracic or
abdominal pathology where arterial phase imaging was desirable.
Our initial experience with the C.A.R.E. Bolus has been
promising. The program is easy to use, flexible, and allows each
scan to be tailored to a patient's unique contrast enhancement
profile. This program should be especially useful for CT
angiography or in any study where arterial phase imaging is
More controlled studies are needed to determine the best
utilization of these new computer programs in order to maximize the
detection of pathology by individualizing the timing of rapid
contrast administration and scanning. AR
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Dr. Horton, Dr. Urban, and Dr. Fishman are with Johns Hopkins
Hospital in Baltimore, MD; Dr. Starr is with Siemens Medical
Systems in Iselin, NJ, where Dr. Fishman is a consultant and a
member of the CT Advisory Board.