Feasibility of Low-volume Injectionsof Contrast Material with a Body

Weight–Adapted Iodine-DoseProtocol in 320-Detector Row

Coronary CT Angiography

Fuminari Tatsugami, MD, Mitsuru Matsuki, MD, Yuki Inada, MD, Shuji Kanazawa, MD, Go Nakai, MD,

Yoshihiro Takeda, MD, Hideaki Morita, MD, Haruhiko Takada, RT, Kenji Ashida, RT,Shushi Yoshikawa, RT, Katsunori Fukumura, RT, Yoshifumi Narumi, MD

Ac

FrS.O86co

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Rationale and Objectives: To investigate the feasibility of low-volume injections of contrast material with a body weight-adapted iodine-

dose protocol in computed tomography coronary angiography (CTCA) using a 320-detector row scanner.

Materials and Methods: Ninety-eight patients who underwent CTCA in a single heartbeat with electrocardiogram-gating were divided

into two groups, receiving 0.8 mL/kg of contrast material injected at a fixed duration of 12 seconds (A; n = 48) or 0.7 mL/kg of contrast

material injected at a fixed duration of 10 seconds (B; n = 50); all patients then received 20 mL of saline. Contrast densities were assessedfor the ascending aorta, left ventricle, right coronary artery (RCA), and left main coronary artery (LMA).

Results: The mean flow rate was 4.00� 0.56 mL/second in group A and 4.06� 0.57 mL/second in group B (P = .51). There were no signif-

icant differences in the mean enhancement values of the ascending aorta, LMA and proximal RCA between the two groups. Also, there wasno significant difference between the mean enhancement values at the three different levels of the RCA (proximal, middle, and distal

segments) (group A; P = .27, group B; P = .07).

Conclusion: The use of 0.7 mL/kg of contrast material injected at a fixed duration of 10 seconds was feasible for CTCA using 320-detectorrow CT, with a sufficient and reliable contrast enhancement in the ascending aorta and coronary artery.

Key Words: Cardiac CT; CT coronary angiography; contrast material; injection method; 320-detector row CT.

ªAUR, 2010

Computed tomography coronary angiography

(CTCA) has become a standard in the noninvasive

assessment of coronary arteries in the past few years

(1–4). In CTCA, high and consistent vascular enhancement

is a prerequisite for sufficient evaluation (5–8). Recently, it

has been reported that a patient weight–adapted iodine-dose

protocol with fixed injection duration yielded significantly

better image quality than the fixed-dose protocol in

64-detector row CTCA (9). An injection volume of 1.0

mL/kg body weight of contrast material (370 mgI/mL) is

necessary to achieve a sufficient contrast enhancement, and

ad Radiol 2010; 17:207–211

om the Departments of Radiology (F.T., M.M., Y.I., S.K., G.N., H.T., K.A.,Y., K.F., Y.N.), Internal Medicine I (Y.T.), and Internal Medicine III (H.M.),saka Medical College, 2-7 Daigaku-machi, Takatsuki City, Osaka 569-86, Japan. Received May 7, 2009; accepted August 19, 2009. Addressrrespondence to: F.T. e-mail: sa104@rg8.so-net.ne.jp

AUR, 2010i:10.1016/j.acra.2009.09.010

injection duration of 15 seconds is recommended in 64-

detector row CTCA (9).

Very recently, 320-detector row CT scanner has been devel-

oped with a z-coverage value of 160 mm; thus, the entire heart

can be scanned in a single rotation and within a single heartbeat

with a minimum temporal resolution of 175 ms (10,11). The

data acquisition time for 320-detector row CTCA is less

than 3 seconds, which is quite short compared with

64-detector row CTCA at less than 10 seconds. Because this

shorter scan time permits a decrease in the contrast dose or

the injection duration at CTCA (8,9), contrast material proto-

cols must be adjusted and optimized as CT technology evolves.

To our knowledge, no study has evaluated the optimal dose

of contrast material on the basis of patient body weight for

a reliable vessel enhancement in 320-detector CTCA. The

purpose of this study is to compare contrast injection proto-

cols with different volume of contrast material and to investi-

gate the feasibility of low-volume injections of contrast

material with a body weight–adapted iodine-dose protocol

in 320-detector row CTCA.

207

TATSUGAMI ET AL Academic Radiology, Vol 17, No 2, February 2010

MATERIALS AND METHODS

Patients

Initially, 106 patients who were scheduled to undergo 320-

detector row CTCA were recruited in this study. Patients

who had previous allergic reaction to iodinated contrast mate-

rial, severe heart failure, valvular heart disease, or elevated serum

creatinine level (>1.5 mg/dL) were excluded, along with

women who were potentially pregnant. Patients were referred

because of suspected coronary artery disease (CAD) (n = 92)

based on the following symptoms such as dyspnea (n = 11), atyp-

ical chest pain (n = 48), pathological exercise test or electrocar-

diogram (n = 25), or high cardiovascular risk factors (n = 8).

Fourteen patients with known CAD were referred for stent

control. However, eight patients were excluded because of

severe calcification of the coronary arteries (n = 3) or manifest

arrhythmia (n = 5). The final study group consisted of 98

patients (57 men, 41 women) who were 37–84 years old

(mean, 69.0 � 9.3 years) with a body weight of 41–77 kg

(mean, 58.6 � 8.4 kg). This study was performed according

to the principles of the Declaration of Helsinki, and approved

by our institutional review board. Informed consent was

obtained from all patients before the CTexamination.

CT Scanning

CT was performed using a 320-detector row scanner (Aqui-

lion ONE, Toshiba Corporation Medical Systems, Tokyo,

Japan). Patients with a prescan heart rate of 65 beats per

minute (bpm) or higher were given 20–60 mg of metoprolol

(Selokeen; AstraZeneca, Zoetermeer, Netherlands) orally 1

hour before scanning. The scan parameters were a collimation

of 320 � 0.5 mm, a voltage of 120 kV, a tube current of 450–

580 mA, and a rotation time of 0.35 or 0.375 seconds. The

patient’s electrocardiogram was digitized and monitored

continuously during image acquisition.

The volume of contrast material was adapted to the patient’s

body weight. Patients were divided into two groups, receiving

0.8 mL/kg of nonionic contrast material (Iomeprol, Iomeron

350 mgI/mL; Eisai, Tokyo, Japan) injected at a fixed duration

of 12 seconds (group A; n = 48) or 0.7 mL/kg of contrast

material injected at a fixed duration of 10 seconds (group B;

n = 50). In both protocols, contrast administration was fol-

lowed by 20 mL of 0.9% saline solution injected at the same

flow rate as the contrast material. Using a dual shot injector

(Nemoto Kyorindo, Tokyo, Japan), the contrast material

and saline solution were injected through a 20-gauge intrave-

nous injection catheter (Termo, Tokyo, Japan) inserted into

the antecubital vein.

The scan delay was set with the use of automatic bolus-

tracking technology (Real Prep technique; Toshiba Corpora-

tion Medical Systems, Tokyo, Japan). As soon as the single

density level in the ascending aorta reached 150 Hounsfield

units, the patient was instructed to take a deep breath and

hold it. Five seconds after triggering, the contrast-enhanced

CT scan was performed. The phase window during which

208

the patient was exposed was limited to 70%–80% of the R-

R interval for all patients with a heart rate <60 bpm, to

65%–85% of the R-R interval for patients with a heart rate

60–65 bpm and to 30%–90% of the R-R interval for patients

with a heart rate >65 bpm. However, patients who required

visualization of the myocardial or valve motion throughout

the cardiac cycle were imaged with a dose modulation. The

effective radiation dose of CTCA was calculated as the

product of the dose-length product times a conversion coeffi-

cient for the chest (k = 0.017 mSv/mGy�cm) (12).

For evaluation of the coronary arteries, data was recon-

structed at 75% of the R-R interval with a slice thickness of

0.5 mm and a reconstruction interval of 0.25 mm. If motion

artifacts were still present in this phase, images were recon-

structed at each 2% interval around the 5% intervals with fewest

motion artifacts at the midlevel of the heart. The reconstructed

image data was transferred to a computer workstation (ZIO

Station System 610, Ziosoft, Tokyo, Japan) for postprocessing.

Methods of Evaluation

One observer (F.T., with 7 years of experience in cardiovas-

cular radiology) collected all the measurements using

a circular region of interest (ROI) cursor. First, four represen-

tative slice levels were selected in each patient; level 1 was the

origin of the left main trunk, level 2 the origin of the RCA,

level 3 the center of the left ventricle, and level 4 the hori-

zontal part of the distal RCA (9). Examples of selected slices

and ROIs are shown in Figure 1. Next, enhancement values

for the ascending aorta, pulmonary artery trunk and left main

coronary artery were measured at level 1 (Fig 1a), for the

proximal RCA at level 2 (Fig 1b), for the right and left

ventricle and the middle RCA at level 3 (Fig 1c), and for

the distal RCA at level 4 (Fig 1d) (9). ROIs for the coronary

arteries were plotted on a cross-sectional image at each slice

level (Fig 1). Calcifications, coronary artery stents, and soft

plaques were carefully excluded from the ROI measure-

ments.

Statistical Analyses

SPSS software (version 17.0, SPSS) was used for statistical

testing. Patients’ ages, body weights, the heart rate during

acquisition of CT scans, injection rate, and iodine delivery

rate were compared between the two groups with a one-

way analysis of variance. The quantitative results for the two

groups were compared using the Mann-Whitney U test.

The quantitative results for the three different levels of the

RCA were compared using the Kruskal-Wallis test. All data

were expressed as means � SD, and differences were consid-

ered to be statistically significant at P < .05.

RESULTS

CT was successfully performed without complications on all

98 patients, of whom 30 were smokers (31%), 23 had diabetes

Figure 1. Enhancement values for the

ascending aorta (black line), pulmonary artery

trunk (white line), and left main coronary artery(a), for the proximal right coronary artery (b),for the right ventricle (dotted white line), left

ventricle (dotted black line), and the middle right

coronary artery (c), and for the distal right coro-nary artery (d) were measured using a circular

region of interest (ROI) cursor. Enhancement

values for the coronary arteries were measured

on a cross-sectional image at each slice levelusing an ROI cursor (dotted line).

Academic Radiology, Vol 17, No 2, February 2010 INJECTION PROTOCOL IN 320-SLICE CORONARY CT

(23%), 24 had a positive family history for CAD (24%), 32 had

dyslipidemia (33%), and 49 were hypertensive (50%). CTCA

revealed significant coronary artery stenosis (lumen obstruc-

tion of $50%) in 24 patients (24%).

All the examinations were performed within a single heart-

beat with electrocardiogram-gating. Forty-one of the 98

patients were imaged with a dose modulation, and the remain-

ing patients (n = 57) were imaged with prospective gating.

The phase windows for these 57 patients were 70%–80%

(n = 12), 65%–85% (n = 29), and 30%–90% (n = 16). The

mean estimated effective doses for the patients with dose

modulation and prospective gating were 14.7 � 4.6 mSv

and 8.0 � 2.2 mSv, respectively. The mean data acquisition

time was 1.54 � 0.26 seconds.

There were no statistically significant differences in age,

body weight, mean heart rate during acquisition of CT scans,

mean flow rate, and the mean iodine delivery rate between the

two groups (Table 1). The mean total dose of contrast material

was 47.5� 7.4 mL in group A and 41.5� 5.5 mL in group B.

The mean enhancement values of the pulmonary artery trunk

and right ventricle for group A were significantly higher than

those for group B (P < .01); however, there were no signifi-

cant differences in the mean enhancement values of the

ascending aorta, left ventricle, and coronary arteries between

the two groups (Table 2). Also, there was no statistically signif-

icant difference between the mean enhancement values at the

three different levels of the RCA (group A; P = .27, group B;

P = .07).

DISCUSSION

This is the first study to investigate the feasibility of low-

volume injections of contrast material with a body weight–

adapted iodine-dose protocol in 320-detector row CTCA.

The use of 0.7 mL/kg of contrast material injected at 10

seconds resulted in sufficient and steady enhancement in the

ascending aorta and coronary artery.

In CTCA, high and consistent vascular enhancement is

a prerequisite for sufficient evaluation (5–8), and an optimal

enhancement value in the coronary arteries is considered to

be more than 300–350 Hounsfield units (13). For this purpose,

a high concentration of nonionic contrast material, such as

350–400 mg of iodine/mL, should be injected at a fast injection

rate of 3.5–5 mL/second (6–8). Most investigators used a fixed

dose of contrast material, such as 60–80 mL, administered at

a fixed injection rate in 64- or 320-detector row CTCA

(7,10,11,13). However, an increase in the patient’s body weight

can lead to lower contrast enhancement, and therefore the

contrast material volume should be adjusted for the patient’s

body weight in CTCA (8,13,14). Recently, Nakaura et al

reported that the patient weight–adapted iodine-dose protocol

with a fixed injection duration yielded significantly better

image quality than the fixed-dose protocol using a 64-detector

row CTCA (9). In that report, 1.0 mL/kg body weight of

contrast material (370 mgI/mL) was useful to achieve a suffi-

cient contrast enhancement, and injection duration of 15

seconds was recommended for use in 64-detector row CTCA.

209

TABLE 2. The Mean Enhancement Values in Each Portion

Group A Group B P

Ascending aorta 452.9 � 50.4 450.7 � 49.1 .83

Pulmonary artery trunk 188.7 � 63.7 130.8 � 31.6 <.01

Right ventricle 146.0 � 45.4 106.2 � 27.3 <.01

Left ventricle 414.9 � 46.4 402.9 � 49.5 .21

Left main coronary artery 410.6 � 47.9 416.8 � 52.6 .52

Proximal right coronary

artery

374.6 � 43.7 384.2 � 49.8 .38

Middle right coronary artery 361.6 � 47.0 364.4 � 48.8 .98

Distal right coronary artery 357.8 � 51.6 361.2 � 46.1 .79

Data are the mean � SD.

TABLE 1. Patient Characteristics and contrast Dose at EachGroup

Group A Group B P

Age (y) 69.8 � 9.8 68.7 � 9.0 .39

Weight (kg) 59.3 � 8.4 58.0 � 8.1 .34

Heart rate (beats/min) 57.1 � 9.7 58.8 � 6.4 .14

Flow rate (mL/sec) 4.00 � 0.56 4.06 � 0.57 .51

Iodine rate (gI/sec) 1.40 � 0.20 1.42 � 0.20 .50

Data are the mean � SD.

TATSUGAMI ET AL Academic Radiology, Vol 17, No 2, February 2010

In 320-detector row CTCA, the entire heart can be

scanned in a single rotation and within a single heart beat

with a minimum temporal resolution of 175 ms (10,11).

Because a shorter scan time permits a decrease in the contrast

dose or the injection duration at CTCA (8,9), we chose the

contrast dose of 0.8 mL/kg (group A) and 0.7 mL/kg body

weight of contrast material (group B), which is smaller dose

than previous report (1.0 mL/kg) (9). On the other hand, it

is reported that the optimal duration for the injection of

contrast material in the weight-adapted iodine-dose protocol

is the sum of the delay time from triggering at bolus tracking

and the time necessary for scanning the whole heart (9). With

our CT scanner, the delay time from triggering at bolus

tracking is less than 6 seconds and the scan time for the whole

heart is 1–3 seconds, depending on the heart rate. Therefore,

it is considered that the injection duration could be shortened

to around 10 seconds in 320-detector row CTCA. Consid-

ering these advantages of this scanner, we compared two

protocols in this study: the use of 0.8 mL/kg of contrast mate-

rial injected at a fixed duration of 12 seconds and 0.7 mL/kg of

contrast material injected at a fixed duration of 10 seconds.

The most important factor in determining arterial

enhancement is the iodine delivery rate (15). In this study,

the mean iodine delivery rate was 1.40 g/second in group A

and 1.42 g/second in group B, which were both almost equal

to the duration reported by Nakaura (1.47 g/second) (9).

It is reported that aortic enhancement is closely related to

injection duration when the contrast material dose is deter-

mined according to patient weight, and shorter injection

duration contributes to higher aortic enhancement (16, 17).

In this study, there were no significant differences in the

mean enhancement value in the ascending aorta and coronary

arteries between groups A and B, and the enhancement value

in the ascending aorta and coronary arteries were reliable in

both groups. This indicates that a short injection duration of

contrast material allows a reduction in the total volume of

contrast material from 0.8 mL/kg to 0.7 mL/kg for the assess-

ment of coronary arteries.

It was a 12.8% reduction in the total volume of contrast

material from 47.6 mL (0.8 mL/kg) to 41.5 mL (0.7 mL/

kg) in this study. It is necessary to reduce the total volume

of contrast material injected for patients with congestive heart

failure or renal impairment, especially when that impairment

is due to diabetic nephropathy (18), to lower the risk of

contrast material–induced nephropathy (19). Therefore, the

210

use of 0.7 mL/kg body weight of contrast material injected

at 10 seconds is recommended for these patients to reduce

the total injection volume of contrast material.

In this study, the use of contrast material with a body

weight–adapted iodine-dose protocol resulted in sufficient

and reliable contrast enhancement of the ascending aorta,

left main coronary artery, and proximal RCA. Moreover,

contrast enhancement of the middle and distal RCA were

also sufficient, and there was no statistically significant differ-

ence between the mean enhancement values at the three

different levels of the RCA. In 320-detector row CTCA,

the entire heart is scanned in a single rotation and a single heart

beat, so the entire coronary artery is imaged simultaneously.

Our study suggests that a consistent and homogeneous

enhancement of the coronary artery from the proximal to

distal segment is obtained with this scanner.

We acknowledge the following limitations in this study.

First, the mean body weight of patients examined in this study

is 30%–35% smaller than those of average American and

European subjects. If our protocol is adopted in such a popu-

lation, the contrast material will have to be injected at flow

rate that is higher than our result. Some investigators have

reported contrast injection rate of 6–8 mL/second, and they

have not observed any side effects associated with the high

flow rate (20–22). In those reports, an 18-gauge intravenous

injection catheter was used to prevent an extravasation

when the contrast material was injected. Therefore, it is

considered that the use of an 18-gauge catheter enables the

patients of body weight up to 115 kg to be adopted to our

protocol; further studies are required to determine whether

our results also apply to heavier patients. Second, patients

who had congestive heart failure or valvular heart disease

were excluded from this study. However, these patients repre-

sent an important subset of patients who are referred for

CTCA in clinical practice. The data for patients with such

conditions might be different from the results obtained in

this study. Third, enhancement for distal segments of the left

coronary artery were not evaluated, because the small diame-

ters of distal segments of the left coronary artery do not allow

the placement of an ROI without including parts of the vessel

wall and adjacent tissue thus causing partial volume effects.

Academic Radiology, Vol 17, No 2, February 2010 INJECTION PROTOCOL IN 320-SLICE CORONARY CT

In conclusion, the use of 0.7 mL/kg of contrast material

injected at a fixed duration of 10 seconds was feasible for

CTCA performed with a 320-detector row CT scanner and

a sufficient and reliable contrast enhancement was maintained

in the ascending aorta and coronary artery.

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