AJR:195, December 2010 1347
evaluating absorbed radiation doses of spe-
cific organs that may be affected by primary
beam or scatter radiation caused by the
MDCT angiography examination [5–7].
Parameters such as the maximum tube
voltage, retrospective image acquisition,
heart rate (HR), and tube current time–prod-
uct significantly affect the absorbed radiation
dose associated with MDCT angiography [8,
9]. In addition, the effect of maximum tube
voltage variation on radiation dose depends
on the type of CT scanner because of indi-
vidualized internal scanner filtrations and
geometry. Also, results of maximum tube
voltage variations have generally been evalu-
ated for the CTDI or CTDI
w
, but not as they
pertain to specific organ doses [10]. Another
parameter that influences absorbed radiation
dose associated with MDCT angiography
is HR. The objectives of this study were
to measure the absorbed radiation dose in
Absorbed Radiation Dose in
Radiosensitive Organs During
Coronary CT Angiography
Using 320-MDCT: Effect of
Maximum Tube Voltage and
Heart Rate Variations
Boris Nikolic
1
Faisal Khosa
1
Pei-Jan Paul Lin
1
Atif N. Khan
1
Sheryar Sarwar
1
Chun-Shan Yam
1
Laurence E. Court
2
Vassilios Raptopoulos
1
Melvin E. Clouse
1
Nikolic B, Lin PP, Khosa F, et al.
1
Department of Radiology, Beth Israel Deaconess
Medical Center, 1 Deaconess Rd., W/CC 308A, Boston,
MA 02215. Address correspondence to M. E. Clouse
(mclouse@bidmc.harvard.edu).
2
Department of Radiation Oncology, Brigham and
Women’s Hospital, Boston, MA.
MedicalPhysicsandInformatics•OriginalResearch
AJR 2010; 195:1347–1354
0361–803X/10/1956–1347
© American Roentgen Ray Society
R
adiation dose has been the single
most significant concern in the
context of widespread clinical
applications of MDCT angiogra-
phy. As a reference for radiation exposure, it
should be noted that, in the general popula-
tion, background exposure accounts for 82%
and artificial exposure accounts for 18% of
the total annual radiation exposure. Artificial
exposure includes diagnostic x-ray studies,
such as CT of the chest and abdomen, and the
use of MDCT angiography [1]. Previous stud-
ies using 16- and 64-MDCT scanners often
have not focused on absorbed radiation dose
to radiosensitive organs but have used the
dose–length product or weighted CT dose in-
dex (CTDI
w
) and its derivatives, which are
displayed by the equipment, for evaluation of
radiation doses [2–4]. In addition to consid-
erable doubts about the accuracy of these dis-
plays, these parameters are not suitable for
Keywords: 320-MDCT, absorbed radiation dose, cardiac
imaging, cardiac MDCT, CT dose index, dose–length
product, metal oxide semiconductor field effect
transistor dosimetry
DOI:10.2214/AJR.10.4333
Received January 25, 2010; accepted after revision
April 19, 2010.
B. Nikolic and F. Khosa contributed equally to this work.
OBJECTIVE. The purpose of this article is to estimate the absorbed radiation dose in ra-
diosensitive organs during coronary MDCT angiography using 320-MDCT and to determine
the effects of tube voltage variation and heart rate (HR) control on absorbed radiation dose.
MATERIALS AND METHODS. Semiconductor field effect transistor detectors were
used to measure absorbed radiation doses for the thyroid, midbreast, breast, and midlung in an
anthropomorphic phantom at 100, 120, and 135 kVp at two different HRs of 60 and 75 beats per
minute (bpm) with a scan field of view of 320 mm, 400 mA, 320 × 0.5 mm detectors, and 160
mm collimator width (160 mm range). The paired Student’s t test was used for data evaluation.
RESULTS. At 60 bpm, absorbed radiation doses for 100, 120, and 135 kVp were 13.41 ±
3.59, 21.7 ± 4.12, and 29.28 ± 5.17 mGy, respectively, for midbreast; 11.76 ± 0.58, 18.86 ± 1.06,
and 24.82 ± 1.45 mGy, respectively, for breast; 12.19 ± 2.59, 19.09 ± 3.12, and 26.48 ± 5.0 mGy,
respectively, for lung; and 0.37 ± 0.14, 0.69 ± 0.14, and 0.92 ± 0.2 mGy, respectively, for thyroid.
Corresponding absorbed radiation doses for 75 bpm were 38.34 ± 2.02, 59.72 ± 3.13, and 77.8 ±
3.67 mGy for midbreast; 26.2 ± 1.74, 44 ± 1.11, and 52.84 ± 4.07 mGy for breast; 38.02 ± 1.58,
58.89 ± 1.68, and 78 ± 2.93 mGy for lung; and 0.79 ± 0.233, 1.04 ± 0.18, and 2.24 ± 0.52 mGy
for thyroid. Absorbed radiation dose changes were significant for all organs for both tube volt-
age reductions as well as for HR control from 75 to 60 bpm at all tube voltage settings ( p < 0.05).
The absorbed radiation doses for the calcium score protocol were 11.2 ± 1.4 mGy for midbreast,
9.12 ± 0.48 mGy for breast, 10.36 ± 1.3 mGy for lung, and 0.4 ± 0.05 mGy for thyroid.
CONCLUSION. CT angiography with 320-MDCT scanners results in absorbed radia-
tion doses in radiosensitive organs that compare favorably to those previously reported. Sig-
nificant dose reductions can be achieved by tube voltage reductions and HR control.
Nikolic et al.
Radiation Dose in 320-MDCT
Medical Physics and Informatics
Original Research
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