AJR 2001; 176:454-456
© American Roentgen Ray Society
Biphasic and Discontinuous Injection of Contrast Material for Thin-Section Helical CT Angiography of the Whole Aorta and Iliac Arteries
Yeon Hyeon Choe1,
Lae Hyun Phyun and
Boo-Kyung Han
1
All authors: Department of Radiology, Samsung Medical Center, Sungkyunkwan
University School of Medicine, 50 Ilwon-dong, Kangnam-ku, Seoul, 135-710
Korea.
Received April 10, 2000;
accepted after revision July 31, 2000.
Presented at the annual meeting of the American Roentgen Ray Society, New
Orleans, 1999.
Address correspondence to Y. H. Choe.
Introduction
As a result of recent developments in technology, helical CT is now used
for evaluation of patients with aortic disease
[1,2,3,4].
However, the imaging area during one scanning session using single-detector
helical CT is still limited because of the low scan speed, patient intolerance
of long breath-hold time, and overheating of the CT tube. If the slice
thickness is reduced to 3 mm to obtain high-quality images from the aortic
arch to the iliac arteries, it is impossible to scan the entire area during a
single breath-hold. As a result, the patient must rest before the radiologist
can continue to scan the abdominal aorta and iliac arteries.
We designed a split-bolus injection technique to eliminate wasting contrast
material during the pause for respiration between the two scan clusters and to
secure optimal aortic enhancement in the abdominal aorta and iliac arteries.
With this technique, the amount of contrast material is divided and then
injected biphasically.
Subjects and Methods
Eighty-four consecutive patients (41 men and 43 women; age range, 26-84;
mean age, 57.4 years) in whom aortic disease was suspected were included in
this study. The diagnoses included acute or chronic aortic dissection in 51
patients, no known aortic abnormality in 25 patients, and aortic aneurysm in
eight patients. The patients were chosen randomly, and all underwent CT with
either a split- or single-bolus injection technique. The mean body weight of
the patients was 55 kg (range, 50-85 kg). Examinations of all patients had a
scan delay time of 15-30 sec as determined by a test scan and time-attenuation
curve analysis.
All studies were performed on a single-detector helical CT scanner (HiSpeed
Advantage; General Electric Medical Systems, Milwaukee, WI). In both patient
groups, 120 mL of a nonionic contrast material (Iopromide 300 mg I/mL;
Schering, Berlin, Germany) was injected at a speed of 3 mL/sec through an 18-
or 20-gauge IV catheter using a power injector (Microprocessor CT Injector
System; Medrad, Pittsburgh, PA). In both groups, the thoracic aorta, abdominal
aorta, and iliac arteries were scanned using a thickness of 3 mm and a pitch
of 2.0.
The split-bolus technique was performed as shown in
Figure 1. The duration of the
interbolus pause was the same as the duration of the interscan pause. The
single-bolus injection technique entailed injecting 120 mL of contrast
material at one time, scanning the thorax for 30 sec after a time delay, and
then scanning the abdominal aorta and iliac arteries after an 8-sec interscan
pause.
We compared the length of the aorta measured on CT for both groups and
performed statistical analysis using the Student's t test. Two
radiologists evaluated, in consensus by visual assessment, the degree of
aortic attenuation from the origin of the ascending aorta to the bifurcation
of the iliac arteries on CT images. For quantitative analysis of vascular
attenuation, one radiologist measured the CT numbers of the vascular lumens at
eight anatomic locations from the aortic arch to the iliac bifurcation at the
picture archiving and communication system workstation. The region of interest
covered the entire area of the vascular lumen (250-1750 mm2 for the
aorta and 12-42 mm2 for the iliac artery). In cases of aortic
dissection, the attenuation was measured in the true lumen. We also performed
the Student's t test to compare the aortic attenuation at each
anatomic location for the two patient groups.
Results
The average length from the aortic arch to the aortic bifurcation was
comparable in the two groups (p < 0.05). The average scan delay
time for the two groups was not significantly different; using the split-bolus
technique it was 22.3 sec (range, 16-27 sec), and using the single-bolus
technique it was 21.5 sec (range, 15-28 sec).
On visual assessment, the degree of aortic attenuation gradually decreased
from the point of the aortic arch to the distal abdominal aorta and iliac
arteries using the single-bolus technique. Images of most patients showed a
grainy pattern of aortic enhancement because of the decreased attenuation in
the distal abdominal aorta. In the split-bolus technique group, aortic
attenuation gradually decreased from the aortic arch to the descending
thoracic aorta and increased at the upper abdominal aorta (Fig.
2A,2B,2C,2D).
On visual assessment, the second attenuation peaks were seen in the aorta
around the gastroesophageal junction in 76.2% (32/42) of the
split-bolus-technique group. No patients in the single-bolus-technique group
showed second attenuation peaks. The average step-up in attenuation number in
the aorta around the second attenuation peaks was 78±29 H.
View larger version (122K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2A. —52-year-old woman with interposition graft of ascending aorta
and remaining dissection in descending thoracic aorta and abdominal aorta. CT
angiograms using split-bolus technique show uniform enhancement of whole aorta
and iliac arteries.
|
|
View larger version (168K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2B. —52-year-old woman with interposition graft of ascending aorta
and remaining dissection in descending thoracic aorta and abdominal aorta. CT
angiograms using split-bolus technique show uniform enhancement of whole aorta
and iliac arteries.
|
|
View larger version (125K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2C. —52-year-old woman with interposition graft of ascending aorta
and remaining dissection in descending thoracic aorta and abdominal aorta. CT
angiograms using split-bolus technique show uniform enhancement of whole aorta
and iliac arteries.
|
|
View larger version (69K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 2D. —52-year-old woman with interposition graft of ascending aorta
and remaining dissection in descending thoracic aorta and abdominal aorta.
Three-dimensional image using maximal-intensity-projection technique reveals
aneurysm of suprarenal aorta, left renal artery arising from false lumen, and
patent iliac and common femoral arteries.
|
|
By quantitative measurement, the degree of attenuation between the single-
and split-bolus techniques showed no significant difference in the thoracic
aorta. However, the split-bolus technique yielded a significantly higher mean
attenuation from the upper abdominal aorta to the iliac arteries (Student's
t test, p < 0.005)
(Fig. 3).
View larger version (15K):
[in this window]
[in a new window]
[as a PowerPoint slide]
|
Fig. 3. —Graph shows mean attenuation values of anatomic locations of
aorta and iliac artery according to two bolus-injection techniques:
split-bolus technique (solid line) and single-bolus technique
(dashed line). Error bars represent range (mean ± 1 SD) of
attenuation. Anatomic locations: 1, aortic arch; 2, thoracic aorta at level of
main pulmonary artery; 3, thoracic aorta at level of aortic valve; 4,
abdominal aorta at level of gastroesophageal junction; 5, abdominal aorta at
level of celiac axis; 6, abdominal aorta at level of left renal artery; 7,
aortic bifurcation; 8, iliac bifurcation.
|
|
Discussion
To obtain high-quality CT angiograms, timing of the CT examination during
the transit of contrast material and adequate concentration in the aorta are
important. Mean aortic attenuation of approximately 200 H or higher is ideal
for the diagnosis of aortic diseases. The faster injection rate of 4 mL/sec
produces 10-15% greater aortic enhancement, which occurs earlier than with the
slower injection rate of 3 mL/sec
[5,
6]. A disadvantage of the
faster injection rate is reduction of the optimal scan window for a given
amount of contrast material. Evaluation of the entire aorta and the iliac
arteries is necessary in patients with various aortic diseases. To evaluate
the entire aorta during one scanning session, the scan range should be wider
(70-85 sec) than that in focused CT angiography. A pause between the two scan
clusters is inevitable for patients and cooling of the X-ray tubes of the CT
scanner. Aortic attenuation in the mid to distal abdominal aorta and iliac
arteries was low using the single-bolus technique as a result of the waste of
contrast material during scan pauses, whereas aortic attenuation in the same
anatomic levels was good, approximately 190 H, using our new technique.
The doses of the first and second bolus were determined both theoretically
and empirically in our study. According to Kim et al.
[7], peak enhancement in their
study was achieved at 38 sec after injection of 90 mL of contrast material
(Iomeprol 300 mg I/mL; Eisai, Tokyo, Japan). They used the same amount of
contrast material as that of the first bolus in our study. Their study showed
that aortic enhancement was greater than 200 H at 24-44 sec after contrast
injection and greater than 150 H at 20-50 sec after contrast injection.
Therefore, an additional dose of contrast material is necessary to overcome
the fall in aortic attenuation after 44-50 sec. Because we require 50 sec for
scanning the thoracic aorta after initiation of the contrast injection, at
least 90 mL of contrast material is necessary for a 30-sec injection at a rate
of 3 mL/sec. The effect of the second bolus, although it was only 30 mL, was
beneficial in increasing the attenuation number of the mid to distal abdominal
aorta and the iliac arteries. Larger volumes of contrast material (
150 mL)
or a slower injection rate (
2.5 mL/sec) with a longer duration of
injection may increase the aortic attenuation to greater than 200 H in the
abdominal aorta even with the conventional bolus-injection technique. The
split-bolus technique allowed us to perform thin-section CT angiography of the
whole aorta and iliac arteries with a relatively small amount of contrast
material.
In conclusion, the split-bolus technique is useful in evaluating the aorta
and iliac arteries at one time when a single-detector helical CT system is
used with a low total volume of contrast material. The aorta and iliac
arteries maintain a higher concentration of contrast material during CT with
this technique than with the conventional single-bolus technique. Therefore,
we recommend using the split-bolus injection technique as the standard
protocol for aortic helical CT angiography.
Acknowledgments
We wish to acknowledge the editorial assistance of Bonnie Hami, Department
of Radiology, University Hospitals of Cleveland, Cleveland, OH.
References
-
Rubin GD, Dake MD, Napel SA, McDonnell CH, Jeffrey RG. Abdominal
spiral CT angiography: initial clinical experience.
Radiology
1993;186:147
-152[Abstract/Free Full Text]
-
Rubin GD. Helical CT angiography of the thoracic aorta.
J Thorac Imaging
1997;12:128
-149[Medline]
-
Bluemke DA, Chambers TP. Spiral CT angiography: an alternative to
conventional angiography. Radiology
1995;195:317
-319[Free Full Text]
-
Zeman RK, Baron RL, Jeffrey RB Jr, Klein J, Siegel MJ, Silverman
PM. Helical body CT: evaluation of scanning protocols.
AJR
1998;170:1427
-1438[Free Full Text]
-
Platt JF, Reige KA, Ellis JH. Aortic enhancement during abdominal
CT angiography: correlation with test injections, flow rates, and patient
demographics. AJR
1999;172:53
-56[Abstract/Free Full Text]
-
Bae KT, Heiken JP, Brink JA. Aortic and hepatic peak enhancement at
CT: effect of contrast material injection rate—pharmacokinetic analysis
and experimental porcine model. Radiology
1998;206:455
-464[Abstract/Free Full Text]
-
Kim T, Murakami T, Takahashi S, et al. Effects of injection rates
of contrast material on arterial phase hepatic CT. AJR
1998;171:429
-432[Abstract/Free Full Text]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati What's this?
This article has been cited by other articles:
|
|
|
|
 
J. M. Kerl, J. G. Ravenel, S. A. Nguyen, P. Suranyi, C. Thilo, P. Costello, W. Bautz, and U. J. Schoepf
Right Heart: Split-Bolus Injection of Diluted Contrast Medium for Visualization at Coronary CT Angiography
Radiology,
May 1, 2008;
247(2):
356 - 364.
[Abstract]
[Full Text]
[PDF]
|
|
|
Top
Introduction
Subjects and Methods
