Three-Dimensional Rotational Angiography in Congenital Heart Disease: Estimation of Radiation Exposure

doi:10.4236/ojrad.2013.33020

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Open Journal of Radiology, 2013, 3, 124-129

http://dx.doi.org/10.4236/ojrad.2013.33020 Published Online September 2013 (http://www.scirp.org/journal/ojrad)

Three-Dimensional Rotational Angiography in Congenital

Heart Disease: Estimation of Radiation Exposure

Gloria Reinke1, Julia Halbfaß1, Sven Dittrich1, Rosemarie Banckwitz2, Christoph Köhler2,

Stephan Achenbach3, Oliver Rompel4, Martin Glöckler1*

1Department of Pediatric Cardiology, University Hospital Erlangen, Erlangen, Germany

2Siemens Medical Solutions, Forchheim, Germany

3Department of Cardiology, University Hospital Erlangen, Erlangen, Germany

4Division of Pediatric Radiology, Department of Radiology, University Hospital Erlangen, Erlangen, Germany

Email: *[email protected]

Received June 1, 2013; revised July 1, 2013; accepted July 9, 2013

which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

ABSTRACT

Objectives: There is an increasing use of three-dimensional rotational angiography (3D-RA) during catheterization of

congenital heart disease. Dose-area-product (DAP) measured by the angiography system and computed-tomography

dose index (CTDI) do not appear practical for dose assessment. Hence, we performed real dose measurements in an-

thropomorphic phantoms. Methods: Three different anthropomorphic phantoms (10 kg, 19 kg and 73 kg bodyweight)

equipped with thermoluminescent dosimeters (TLD) were used. We used a typical standard diagnostic program and a

low-dose program. The effective dose (ED) was calculated according to the International Commission on Radiological

Protection (ICRP) 103. The 3D distribution of radiation in the body was assessed. Results: ED for the male 10 kg

phantom was 0.192 mSv in the diagnostic program and 0.050 mSv (male) in the low-dose program. The 19 kg phantom

received an ED of 0.205 mSv (male) in the diagnostic program. In the low-dose program the ED reached 0.058 mSv

(male). The male adult 73 kg phantom was exposed with an ED of 0.730 mSv in the diagnostic program and 0.282 mSv

in the low-dose program. ED for the female phantoms was slightly higher for both acquisition-programs. Dose distribu-

tion was inhomogeneous with a dose maximum in the esophageal region behind the heart, whereas in the brain, intes-

tine and gonads we found nearly no radiation. Conclusions: 3D-RA imaging in the interventional catheter laboratory is

possible with an effective dose lower than 1 mSv. With its potential to reduce fluoroscopic time and the number of con-

trol angiographies in catheterization and intervention in complex anatomy, it can decrease the radiation dose.

Keywords: Effective Dose; Radiation Exposure; Anthropomorphic Phantom; Rotational Angiography

1. Introduction

The emerging technique of three-dimensional rotational

angiography (3D-RA) in congenital heart disease has a

high impact on the workflow of pediatric cardiologists.

The 3D-RA is a flat-detector computer tomography (FD-

CT) with continuous contrast admission in the volume of

interest (VOI) during a typical acquisition time of 5 sec.

The flat-detector is mounted on the c-arm of the angio-

graphy-system and moves once over 180˚ plus fan angle

around the patient. It provides accurate diagnostic infor-

mation exceeding conventional biplane angiography. The

main advantages of this new imaging modality include

the unlimited views on the high resolution three dimen-

sional (3D) vascular models for surgical planning and the

use of 3D models in interventions. These 3D models can

be used for 3D navigation in catheter interventions. There-

fore, models from high resolution 3D-RA as well as im-

ages from former magnetic resonance imaging (MRI) or

computed tomography (CT) studies are acquired. MRI

and CT images can be implemented by merging them

with an actual low-dose 3D-RA dataset [1-4].

Image acquisition for 3D-RA is performed by a single

run of the c-arm equipped with a flat detector around the

patient. These FD-CT scanners provide an irradiation

field in cranio-caudal z-direction of typically up to 200

mm. Consequently, resulting radiation doses should be

determinable in a reliable way. In standard CT, dosi-

metry is based upon the concept of the computed to-

mography dose index (CTDI) as a dose descriptor. In its

current definition it is characterized by an integration

*Corresponding author.

G. REINKE ET AL. 125

length of 100 mm. Therefore CTDI100 is inadequate for

dose assessment in wide beam CT-scanners such as C-

arm FD-CT [5]. Moreover, these scanners utilize the

so-called partial scanning (angular range < 360˚), which

is expected to cause inhomogeneous dose distribution

within the patient and consequently makes the use of

CTDI even more questionable. Kyriakou et al. emphasize

that the use of CTDI100 may strongly underestimate pa-

tient’s dose acquired during FD-CT examination. As a

practical solution they recommend Monte Carlo simula-

tion-based radiation dose calculations [5]. On the other

hand, dose estimations solely based on the dose-area pro-

duct (DAP) also have to be scrutinized critically, be-

cause the used conversion factors derive from single in-

cidence imaging and have never been validated for FD-

CT. This clearly leads to underestimation of dose asses-

sment, too [6]. To estimate the organ and the total dose

phantom measurements have to be performed in large

phantoms with respect to the large z-coverage. Therefore,

humanlike anthropomorphic phantoms equipped with

multiple thermoluminescent dosimeters (TLD) seem to

be a reliable method to estimate the effective dose (ED).

2. Methods

In our catheterization laboratory we exposed the phan-

toms to a biplane angiography system equipped with two

20 × 20 cm2 flat panel detectors (Axiom Artis, syn-

goDynaCT, Siemens Healthcare, Forchheim, Germany).

Two different imaging protocols were used: First, a di-

agnostic program (5sDRc) with 30 images per second,

scanning time 5 sec, a fixed tube voltage of 90 kV and

automatically adapted tube current. Second, a low-dose

program which is in use for registration of prior high

resolution datasets from MRI or CT. The low-dose pro-

gram (5sDR-L) also uses 30 images per second and a 5

second-scanning time but 0.2 mm copper filtration and a

tube voltage of 70 kV. To achieve enough radiation ex-

posure for the TLDs we always exposed the phantom

three times with the same program in the same position.

Three different anthropomorphic phantoms were exa-

mined:

1. A 10 kg model “Clifford” representing children with

an age of 0.5 - 3 years.

2. A 19 kg model “Braden” representing children with

an age of 3 - 7 years.

3. A 73 kg model “Alderson” representing an adult

person.

We exposed the Clifford- and the Braden-model se-

parately with the two different programs and in addition

separately with and without anti scatter grid in the diag-

nostic program. The adult Alderson model also under-

went both programs, always using the anti-scatter grid.

The models are composed of transversal slices with

2.5 cm thickness including drilled holes in which the

lithium fluoride TLDs were placed (TLD-100 rods, 1 × 1

× 6 mm; The Harshaw Chemical Company, Chrystal and

Electronics Products Department, Solon, Ohio, USA).

There are always 3 TLDs for one anatomic structure to

get an averaged dose value. For the male gonads we used

sachets.

Before starting the irradiation the TLDs were cali-

brated. The TLDs of one series were always used to-

gether for a measuring cycle to guarantee equal quality.

Thus, they were irradiated, read and regenerated. There-

fore, they were divided in two fractions: fraction 1 was

used for the calibration and for the determination of the

calibration factor. It was irradiated by a definitive dose of

1Gy. Fraction 2 then underwent the real examination

after the calibration factor had been transferred to the

TLDs.

The readout was performed according to a standard

procedure [7]. The organ doses result from the mean value

of 3 TLDs. To estimate the organ equivalent dose the di-

rectly and indirectly weighted organ dose were added.

The effective dose was calculated by summarizing the

weighted organ doses according to the guidelines of the

International Commission on Radiological Protection

(ICRP) 103 [8].

To illustrate the measured organ doses, we created de-

lineations with slices in frontal, sagittal and transversal

direction. To visualize the amount and the distribution of

the organ doses a color scale represented in spectral col-

ors was designed with the dimension of 0 mSv to 8.5

mSv. Then the organs and tissues were dyed referring to

the dose values on the scale (image editing software

GIMP 2.1.11; GNU imaging manipulation program; Free

Software Foundation, Boston, MA USA).

3. Results

We found an inhomogeneous dose distribution. The

highest dose was registered anterior the spine behind the

heart, measured by TLDs in the esophagus (Alderson:

8.43 mSv). In all three phantoms the maximal organ dose

is located in the thorax (Alderson: esophagus, Braden:

left lung, Clifford: right lung). Concerning the head and

abdominal region, especially the brain (≤0.06 mSv), the

intestine (≤0.04 mSv), the urinary bladder (≤0.01 mSv)

and the gonads (≤0.02 mSv), we detected only little ra-

diation. No radiation measured by the testis sachets. We

noticed higher dose values in the posterior part of the

body than in the front (lung, esophagus > thymus, ster-

num). There was a slightly higher dose registered on the

patient’s left side compared to the right in the Alderson

phantom. Figure 1 illustrates the organ doses and their

distribution in the phantom bodies.

The effective gender-specific dose of the different pro-

grams and phantoms are represented in Table 1. De-

pending on the acquisition-program, the phantom and

G. REINKE ET AL.

126

(a) (b) (c)

Figure 1. (a) “Clifford”, 10 kg bodyweight anthropomorphic model representing children with an age of 0.5 - 3 years. (b)

“Braden”, 19 kg bodyweight anthr opomorphic model representing children with an age of 3 - 7 years. (c) “Alderson”, 73 kg

bodyweight anthropomorphic model representing an adult. Slices in frontal (A), sagittal (B) and transversal direction(C) are

shown to visualize the amount and the distribution of the organ doses. The color scale on the left side (D) represents the di-

mension of 0 mSv to 8.5 mSv in spectral colors. The organs and tissues are dyed referring to the dose values on the scale.

Table 1. Effective dose.

the gender the effective whole-body dose ranged from

0.05 mSv (male Clifford phantom; Low dose program) to

0.73 mSv (adult Alderson phantom; diagnostic program

with grid). The effective dose values of the female phan-

toms were higher for all acquisition-programs.

Programs

5sDRc without

grid 5sDRc with grid

Low Dose

5sDR-L 0.2Cu

(with grid)

male femalemale female male female

Clifford 0.1920.2720.219 0.326 0.0500.072

Braden 0.2050.2720.315 0.392 0.0580.068

Alderson 0.730 0.282

Table 2 shows the organ equivalent doses (ICRP103)

of the different programs for all three models in mSv.

4. Discussion

Since there is a special responsibility towards children’s

health, radiation dose in pediatric radiology has to be

reduced to a minimum. Therefore the technical progress

developing new X-ray systems are one of the major cri-

teria. As far as we know only few studies exist which

examined radiation exposure using 3D-RA in pediatric

catheter laboratories [1,2]. Because CTDI and DAP are

neither practicable nor reliable to estimate effective dose

[5,6,9] we equipped three different anthropomorphic

phantoms with several TLDs to determine organ and

effective dose as well as dose distribution in their bodies

depending on program, phantom and gender.

a. The effective dose according to ICRP103 separate for each program,

phantom and gender. The values are given in milli Sievert (mSv). Clifford

and Braden are hermaphrodite, Alderson is a male phantom. Alderson did

not undergo the 5sDRc diagnostic program without grid.

of 6.6 ± 1.8 mSv according to ICRP103 using 3D-RA

[10,11]. However, we did not include patient individual

factors, especially the use of contrast dye, which could

increase radiation dose. However, Wielandts et al. (2010)

only examined adult computer-simulated models whereas

we performed real dose measurement in different sized

phantoms. This is a more reliable method to evaluate

radiation dose and leads to more exact results than simu-

lated calculations. Moreover, Wielandts et al. (2010)

performed image acquisition with a dose of 0.54 μGy per

frame (60 frames per second) which is a higher mean

dose compared to ours (0.36 μGy per image in the diag-

nostic programs, 0.1 μGy in the low dose program; al-

ways 30 images per second). The higher dose and frame

rate could possibly explain the elevated EDs measured

y Wielandts et al. Another publication by Glatz et al.

The lowest effective dose was achieved using the low

dose program for all phantoms, followed by the diagnos-

tic program without grid. The highest effective dose

emerged using the diagnostic program with grid. Our

calculated effective doses ranged from 0.05 mSv up to

0.73 mSv. Compared to Wielandts et al. (2010) our re-

sults show lower doses [10]. They estimated a mean ef-

fective dose in computer-simulated phantoms (PCXMC) b

G. REINKE ET AL. 127

Table 2. Organ equivalent doses.

Clifford Braden Alderson

organ/

5sDRc

without grid

5sDRc with

Low Dose

5sDRc

without grid

5sDRc with

Low Dose

5sDRc with

Dose

tissue grid

5sDR-L

0.2Cu (with

grid)

grid

5sDR-L

0.2Cu (with

grid)

grid

Low

5sDR-L

0.2Cu (with

grid)

brain 0.04 0.03 0.01 0.02 0.00 0.00 0.00 0.01

thyroid 0.75 0.33 0.19 0.06 0.08 0.03 0.08 0.01

lung 0.87 1.19 0.23 0.89 1.28 0.23 2.87 1.21

red bone rrow

0 0.

adrd

urinder

remairgans

ma0.09 0.12 0.02 0.31 0.47 0.09 1.29 0.51

esophagus 0.78 0.60 0.20 1.06 1.50 0.32 3.86 1.24

thymus 0.87 1.10 0.22 0.90 1.25 0.25 1.03 0.45

breast 0.65 0.88 0.19 0.64 0.83 0.15 - -

liver 0.03 0.03 0.01 0.03 0.08 0.00 .1706

tomach0.03 0.04 0.01 0.02 0.08 0.00 0.18 0.07

spleen 0.06 0.10 0.02 0.02 0.06 0.00 0.11 0.02

enal glan0.07 0.09 0.02 0.03 0.06 0.00 0.19 0.07

pancreas 0.05 0.12 0.02 0.01 0.08 0.00 0.16 0.05

left kidney0.03 0.06 0.00 0.02 0.03 0.00 0.09 0.05

mall intestine0.02 0.03 0.01 0.00 0.02 0.00 0.00 0.00

colon 0.01 0.02 0.00 0.00 0.04 0.00 0.01 0.00

ovary 002 0.02 0.00 0.00 0.00 0.00 0.00 0.00

testis 0.00 0.00 0.00 0.00 0.00 0.07 0.00 0.00

uterus 0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00

ary blad0.01 0.01 0.00 0.00 0.00 0.00 0.00 0.00

bone surface 0.05 0.17 0.02 0.00 0.01 0.00 0.99 0.38

skin 0.05 0.17 0.02 0.00 0.00 0.00 0.98 0.38

nder o0.15 0.20 0.04 0.12 0.19 0.03 0.20 0.07

a.the len. The we organ equt dose is giilli Sievor the rogramch phantomrson

.5 mSv

program) than in the children phantoms Braden (EDmax

Organs are listed in ft columightedivalenven in mert (mSv) fdifferent ps of ea. Alde

has no values for the breast because it represents a male phantom.

0) reported effective doses <0.1 mSv to 3(201

using 3D-RA [1]. They also used phantom testing with a

dose of 0.17 μGy per frame (60 frames per second), but

calculated the radiation dose leading to less correct val-

ues than measured in our direct dose assessment.

With the use of the anti-scatter grid the dose increases

according to Partridge et al. (2006) and Justino et al.

(2006) [12,13]. Indeed, we also registered higher radia-

tion doses when using the program with grid. Neverthe-

less, we found the difference in radiation doses between

the diagnostic program with and without grid is minimal.

Studies examining the relation between phantom size

(age) and radiation dose for 3D-RA are scarce. Increased

ED with decreasing age of the patients is reported for

biplane catheterization units [14]. Our results are com-

parable to those published by Glatz et al. (2010): total

effective dose increased with older age [1]. We detected

higher ED in the adult phantom (0.730 mSv in the diag-

nostic program with grid, 0.282 mSv in the low dose

0.392 mSv) and Clifford (EDmax 0.326 mSv) both in the

diagnostic program with grid. We also observed a higher

radiation dose in the adult phantom (organ dose maxi-

mum 8.43 mSv in the esophagus) than in the children

phantoms (organ dose maximum Braden: 1.86 mSv left

lung; Clifford: 1.69 mSv right lung) for all acquisi-

tion-programs. Comparing our organ doses to those es-

timated by Wielandts et al. (2010), most of the organ

doses are stated to be a lot higher in their study [10]. Or-

gans such as the lungs, the esophagus, the breasts and the

thymus show higher radiation doses (up to 23.35 mGy)

in their study [10], whereas organs such as the brain, the

urinary bladder and the gonads are evaluated as low

(<0.03 mGy) as our organ dose values (<0.04 mSv, Al-

derson even <0.01 mSv). The advantage of our dose as-

sessment based on real phantom measurement compared

to the computer-simulated method has already been men-

tioned. Moreover, our phantoms were equipped with an

G. REINKE ET AL.

128

extraordinarily large number of accurately calibrated

TLDs (up to 141 TLDs). In addition, we always used

three TLDs for one anatomic structure to guarantee a

high quality of our measurements and to get an averaged

dose value.

In our current study we demonstrated an inhomoge-

neous dose distribution. The highest doses were meas-

ured in the thorax region and the posterior parts of the

body where the X-ray tube rotates. This is similar to the

0.04 mSv) compared t

erable to

dergoing one of the exam-

factors, such as the BMI, t

onal pediatric catheter laboratory can be per-

formed with an effective dose less than 1 mSv. The tech-

is imaging method leads to a reduce-

c CT Imaging in the Cardiac

Catheterization Laboratory for Congenital Heart Di-

sease,” JACC g, Vol. 3, No. 11,

2010, pp. 1149g.2010.09.011

sults shown by Kalender and Kyriakou et al. (2007)

and Kyriakou et al. (2008) [5,6]. In the evaluation of our

organ doses visualized by the phantom drawings, some

dose values seem to differ from the expected distribution:

In the fourth transversal section of phantom Clifford we

measured a higher dose in both lungs than in the eso-

phagus. In the third transversal section of the Alderson

phantom a higher dose was registered in the thymus than

in the lungs. Reasons for these aberrations could be the

attenuation of the radiation by bones and the spine, the

particular wave angle and the radiation sensitivity of the

organ, respectively. These observations can not be found

in computer-simulated phantom studies. Therefore, an-

thropomorphic phantoms as we used are necessary to

notice scattered radiation. The female phantoms received

a slightly higher radiation dose compared to the male

ones which is due to the breast tissue and its high con-

version factor [10,15,16].

Nearly no radiation was measured in the brain with all

programs in each phantom. However, the children phan-

toms, especially the smallest, received a slightly in-

creased brain dose (up too the

ult phantom. This observation may be important since

small children still have a weak skullcap. Consequently,

it could be assumed that there is even more radiation

exposure to the brain than was measured in our study.

3D-RA leads to an increase of the skin dose due to its

rotation around the patient compared to fixed tubes. Even

though the region of interest is still the heart, the skin

dose is no longer concentrated on the thoracic skin region

but evenly spread over the whole skin surface. In conse-

quence, less radiation injuries can be observed.

5. Study Limitations

Since we exposed anthropomorphic phantoms of normal

weight in this study, the results are only transf

normal weighted persons un

ined programs. Individual he

application of contrast dye, the radiation sensitivity and

the DNA repair capacity were not taken into account

[17-20].

6. Conclusion

In our study we showed that 3D-RA imaging in the

interventi

nical progress in th

tion of fluoroscopic time resulting in a reduced radiation

dose due to high image quality and decreasing number of

control angiographies. However, due to our responsibil-

ity towards children’s health, further methods to reduce

radiation in children during diagnostic and interventional

procedures need to be found. Further studies, especially

biological dose assessments are necessary to consider

individual factors and to receive more information about

the direct effects of irradiation in children’s bodies dur-

ing diagnostic procedures and interventions in the pediat-

ric catheterization laboratory.

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