THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
Analyzis of Computed Tomography Dose Index (CTDI)
Value towards X-ray Tube Current and Voltage Variations
of Computed Tomography Scanner (CT Scan)
by using PPMA Phantom
Syamsir Dewang1*, Bualkar Abdullah1, Bannu1, Nur Hasanah1, Suryaningsih1,
and Satrial Male2
1. Physics Department, Hasanuddin University, Makassar.
2. Department of Radiology, Hasanuddin University Hospital
* Email: dewang1163@gmail.com
Abstract. Medical physics gave the contribution in the field of health, especially for developing of radio
diagnostics and radiotherapy. The applying of radiography machine is intended to diagnoses of disease,
which is needed by patient for detecting their sickness. There were measured the X-ray radiations using a
simulator computed tomography Scanner (CT scan). The CT scan is the radiology checkup to describe
internal body structure by multislice CT scan (MSCT scan). It was observed the influence of expose
variations such as X-ray tube voltage (kV), and X-ray current tube (mA) toward Volume Computed
Tomography Dose Index (CTDIvol) value for investigating using head and body of Polymethyl
Methacrylic (PPMA) phantom. Diameters of head and body phantom are 16 and 32 cm, respectively.
Radiation output was observed by using a set of CT Dose profiler. Utilization of voltage variations
between 80-135 kV and tube current between 50-200 mA. For the head phantom obtained, the value of
CTDI100 and CTDIVol are 7- 43 mGy, and 10-32 mGy, respectively. This value is greater than CTDI100
value of 0.9-4.8 mGy and CTDIVol 0.9 - 4 mGy by current variations. As for the body phantom, the CTDI
values of the voltage variation were also obtained greater than with the current. The high difference
indicates that the value of the CTDI estimation using the voltage would be appropriate for an object or
solid organs such as bone, while the variation of the current tube is more suitable for object softer organs.
Furthermore, the CTDI value have a linear relationship between tube voltage (kV) and current flow (mA)
of the X-ray machine.
Keywords: CTDI , CT scan, X-ray, phantom, voltage, and tube current .
PACS: 87.57.qp
1. INTRODUCTION
The use of Computed Tomography Scan (CT
Scan) has gave a great contribution to medicine for
patients to detect disease. With the development of
technology, every hospital in the capital city of each
province in Indonesia have had a CT Scan equipment.
Through the use of CT Scan will make it easier for
doctors to detect the inner structure of the body and
disease for the patient. This is because the Xray
radiation with a wavelength about 10-100 nm, so It
has the strong power and intensity of light to penetrate
body tissue.
Operating the CT Scan machine has several
physical parameters which can be regulated to obtain
the radiation dose received by patients include: X-ray
tube voltage (kV), X-ray tube current, and rotation
time (mAs)[1]. The method used to determine the dose
received by the patient on a CT scan is Computed
Tomography Dose Index (CTDI).
This research uses the object of Polymethyl
Methacrylic (PPMA) Phantom of head and body as a
substitute for the human body. The aim of research is
to determine the effect of factors expose produced by
radiation dose of Simulator CT scan and the spread of
radiation dose in the phantom. Furthermore, analyzing
the relatiaon between the change in value expose
Volume Computed Tomography Dose Index
(CTDIvol), which represents the radiation dose received
by the patient in the checkup of the head and body.
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
2. THEORY AND METHOD
CTDI is an integral dose profile D (z) along the
axis of rotation, perpendicular to the plane of the scan
for one time rotation or a single axial tomographic
slice divided by the number (N) and nominal slice
width (T) of X-ray beam. Profile CTDI value
represents the average absorbed dose along the z axis,
as shown in Figure 1 below:
CTDIw
. . . . . . (4)
CT pitch factor
∆d
With CT pitch factor = , where ∆d is the distance in
NT
mm movement of the patient table during the process
of scanning, and NT is the total width of collimation
that amount multiplied by the width tomographic slice
collimation. CTDIVol value measurement in this study
is done by setting the tube voltage (kV) and tube
current (mA).
CTDIvol =
2.1. RESEARCH PROCEDURE
Figure 1. Radiation dose profile
Analitical calculation of CTDI values can be
formulated as follows:
+∞
1
CTDI=
∫ D(z)dz
......
(1)
N∙T -∞
Where D (z) is profile of absorbed dose (mGy). To
provide a standard of measurement based on the length
of objects introduced CTDI100. Measurements with the
use of a pencil ionization chamber CTDI100 used,
length 100 mm with 3 cm3 active volume and use
standard acrylic phantom CTDI. The value of CTDI100
by using the ion chamber is:
CTDI100 =
+50 mm
1
∫
D(z)dz … … … . (2)
N T -50 mm
Where pencil ionization with 100 mm lengths insert to
hole of PPMA phantom. We took center position then
obtained by calculating the integral upper limit +50
mm, -50 mm and the lower limit.
To calculate the approximate average value of CTDI,
we define CTDIw in the measurement using a phantom
object. The calculation ⅓ CTDI100 measured at the
middle of the phantom coupled with ⅔ CTDI100 values
measured at the edge of the phantom. The value
CTDIw can be written as follows:
1
2
3
3
CTDIw = CTDI100, C + CTDI100,P . . . . . . . . . . (3)
Furthermore, for the calculation on a particular
examination protocol that is used CTDIvol, which is
counting on a volume CTDIw at a volume calculation.
CTDIvol determined on spiral CT scans, where the ratio
of the time table for the one-time movement of
rotation of 360 ° and the nominal beam width (NT) are
referenced as Pitch. So CTDIvol such as follows:
This research was observed in Hasanuddin
University Hospital by using simulator computed
tomography Scanner (CT scan). The equipments used
in this measuremen are a Simulator CT scan machine
of Toshiba-Alexion 16 Slic brand, phantom CT 007
model. Diameter of head and body phantom is 16 and
32 cm, respectively. CT dose profiler for measuring
the radiation released by the CT scan, the Barracuda as
a dose detector, bluetooth adapters, software and CT
dose ocean profiler analyzer. The procedure of this
experiment is CT scan turned on, then connect the CT
dose profiler and barracuda detector bluetooth on.
Prepare PPA phantom objects on the table the patient.
Perform scanning of CT with rotating 360 degrees,
while the object moves in the horizontal axis by
default. Profiler CT dose phantom inserted into the
hole located at the center and at the edges. After that,
eksposi done in accordance with the parameters of the
tube voltage (kV) and variations that have been
determined. Computer and panels are placed outside
the control panel will receive the data through
bluetooth network. The CT Scan data acquisition
process is done on two parts i.e. tube voltage (kV)
vatiations and tube current (mA) settings for data
phantom head and the body, respectively.
Left and right side are a
Head and body phantom
Figure 2 left side. Phantom looks forward with a hole
for the pencil ionization chamber at the center position
C, the edge side P1 in 12 O.clock, P2 in 3 o'clock, P3
in 6 o'clock, and P4 in 9 o'clock, respectively. Right
side, PPMA Phantom side view with a pencil
ionization chamber
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
35
a. Measurement CTDI100 and CTDIvol values with
Tube Voltage Variation
30
The CTDI100 values for phantom head and the body
were observed by each point of C, P1, P2, P3, and P4,
respectively, with some variation of tube voltage.
Figure 3 shows measuring of sample dose rate profile
of head phantom with positioning the ion chamber at
the center point C with 80 kV tube voltage settings.
We can see that maximum dose rate is 3.5 mGy/s at
80-100 mm axis on time exposure 6-8 second.
CTDI vol (mGy)
4. RESULTS AND DISCUSSION
25
y = 7.1323x + 3.5117
R² = 0.9895
20
15
10
5
80
100
120
135
Tube Voltage of X-ray (kV)
Figure 5. Relationship CTDIvol (mGy) of head
phantom against X-ray tube voltage.
Here are the measurements on a body phantom with a
tube voltage variations, such as in Figure 6.
Figure 3 Profile of the dose rate for phantom head at
the center point C with 80 kV tube voltage settings.
CTDI100 (mGy)
25
20
C
15
P1
10
P2
5
P3
0
P4
80
CTDI100 (mGy)
45
C
P1
P2
P3
P4
35
25
15
5
80
100
120
135
Tube Voltage of X-ray (kV)
Figure 4 graphs the relationship value of the X-ray
tube voltage vs. the CTDI100 value of head phantom at
position of ion chamber for each hole of C, P1, P2, P3
and P4.
The CTDI100 value will increase when operating the
greater tube voltage. The higher and the lowest value
of CTDI100 are in point P1 about 43 mGy at 135 kV and
P3 about 7 mGy at 80 kV, respectively. By using
equation (3) to find the CTDIw value, and equation (4)
to find the CTDIvol. We can calculate the volume of
CTDIvol that is illustrated in graph, such as in Figure 5.
The CTDIvol value of head phantom increases with the
increase in X-ray tube voltage. The maximum value is
32 mGy at 135 kV and minimum value at 80 kV is 10
mGy. We find linear realtionship betwen CTDIVol with
the tube voltage variation.
Figure 6 Relationship X-ray tube voltage to the value
of CTDI100 body CTDI
Similar to the head phantom, the CTDI100 value
obtained greater when increase tube voltage, the
lowest value in point C is 2.5 mGy at 80 kV, and
highest value P3 in 23 mGy of CTDI100 at 135 kV .
This is because the X-ray absorption center C
distributed throughout the phantom body that is larger
than the value of phantom heads so CTDI100 on the
few holes at point P is higher than from point C
20
CTDIvol (mGy)
Furthermore, the result of CTDI100 (mGy) value for
head phantom in each position of C, P1, P2, P3, and P4
such as in Fig. 4.
100
120
135
X-rayTube Voltage (kV)
y = 3.4725x + 0.9975
R² = 0.9984
15
10
5
0
80
100
120
X-ray Tube Voltage (kV)
135
Figure 7. Relationship X-ray tube voltage against
CTDIvol values.
From the above chart CTDIvol values increased linearly
along with the increase of the X-ray tube voltage, the
higher selection of X-ray tube voltage, giving the
higher value of CTDIvol obtained. We can see the
higher and lower value were 15 and 5 mGy, in 135 kV
and 80 kV, respectively.
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
b. Measurement of CTDI100 and CTDIvol values
with Current Tube Variation
P1
P2
1
P3
4
C
3
2
P4
0
50
P1
100
150
200
Tube Current of X-ray (mA)
P2
1
P3
0
50
100
150
Tube Current of X-ray (mA)
200
P4
Figure 8 Relationship X-ray tube current to the value
of head phantom CTDI100.
From the chart above in Figure 8. CTDI100 on
the current value of 50 mA almost have the same value
as the absorption evenly throughout the phantom head.
There is a similar trend, namely CTDI100 value
increases linearly along with the increase in the value
of the X-ray tube current. CTDI100 highest value on the
P1 is 4.8 mGy of 200 kV and the lowest on the P3 is
0.9 mGy in 50 kV.
4
CTDIvol (mGy)
C
2
y = 0.9999x - 0.1831
R² = 0.9917
3
2
Figure 10. Relationship X-ray tube current to the value
of body phantom CTDI100.
From the picture 10 above, at the observation
point at P1 the value obtained CTDI100 highest in 2.5
mGy and lowest is 0.2 mGy in C point . CTDI100
value that was obtained in line with the increase in the
flow tube. Similar to the phantom head, CTDIvol
values increased linearly along with the increase of
the X-ray tube current. In figure 11, the maximun
CTDIVol is 1.5 mGy at 200 mA, and minimum value
is 0.5 mGy at 50 mA.
2.0
y = 0.3622x + 0.055
R² = 0.9999
CTDIVol (mGy)
CTDI100 (mGy)
5
CTDI100 (mGy)
The CTDI100 value measurement on phantom
head and the body is done with some variation of the
X-ray tube current and other parameters remain at all
measurement points C, P1, P2, P3, and P4.
3
1.5
1.0
0.5
0.0
50
1
0
50
100
150
200
Tube Current of X-ray (mA)
Figure 9 Relationship of CTDIVol value of head
phantom vs. X-ray tube current
Calculation CTDIVol for head on current variation
measurement values obtained 4 mGy at 200 mA and
0.9 mGy at 50 mA. This result can be shown that both
CTDI value for CTDI100 and CTDIVol for head to the
measurement of the voltage variation has a higher
value than the measurement of the current variation.
The results observation of CTDI100 values for voltage
variation at the body phantom can be shown in Figure
10 as follows:
100
150
Tube Current of X-ray (mA)
200
Figure 11. Relationship of CTDIVol value of body
phantom vs. X-ray tube current
Similar to the phantom head, value of CTDI100 and
CTDIvol increased linearly with the increase of the Xray tube current. However CTDIVol value is always
lower than the value CTDI100, this is because CTDIVol
calculate the radiation absorbed on the dimensions of
the volume are scattered in the phantom while CTDI100
calculate radiation absorbed by ion chamber in the
phantom along the 100 mm.
The results generally show that the value CTDI100
and CTDIVol have a higher value by measuring the
voltage variation compared with the variation of the
current tube. So for the purposes of solid objects
expose require higher CTDI values such as bone, it is
suitable to use a voltage variation, while for soft
objects more suitable for measuring the current
variation.
THE 4th INTERNATIONAL CONFERENCE ON THEORETICAL AND APPLIED PHYSICS (ICTAP-2014)
16-17 October 2014, Denpasar-Bali, Indonesia
5. CONCLUSIONS
REFERENCES
Several conclusions from this research can be written
as follows:
1. The results of the measurement value CTDI
(Computed Tomography Dose Index) on the
Simulator CT scans have a linear relationship
between the value CTDI100 and CTDIVol in (mGy)
with a tube voltage (kV) and tube current (mA) of
the X-ray machine.
2. The results for the value of CTDI phantom head
and body have been obtained values for phantom
head using voltage variation between 80-135 kV.
CTDI100 values derived of 7- 43 mGy, and CTDIVol
of 10-32 mGy. As for the body phantom, the
CTDI100 value is 2.5 - 23 mGy, and CTDIVol of 515 mGy. Further measurements for phantom head
with current between 50-200 mA has been
estimated of 0.9-4.8 mGy for CTDI100 and CTDIVol
is 0.9 - 4 mGy. Further to the phantom body CTDI
values procured for 0.2- CTDI100 is 0.2 to 2.5 mGy
and CTDIVol is 0.5 - 1.5 mGy. The high difference
in CTDI values for voltage than the current flow
indicates that analyzing using voltage would be
appropriate for an object or a sample of solid
organs such as bone, while the variation of the tube
current is more suitable for object softer organs.
3. The result value of CTDI for head phantom at
voltage and current flow was obtained greater than
the value for the CTDI body phantom. This result
is gained because of the smaller size of the head
from the body phantom, so that the absorption of
radiation received by the head phantom will be
higher, while for the body phantom can absorb Xray radiation is distributed uniformly with a larger
volume CTDI, so that it would be small compared
to the head phantom.
ACKNOWLEDGEMENTS
The writer wishes many thanks to
Hasanuddin University, and chairman
center, Hasanuddin University for the
using operational funding for State
(BOPTN), 2014.
Rector of
of research
sponsorship
University
1. Siemens. (2010). Easy Guide to Low Dose.
Siemens AG. Medical Solution.
2. International Atomic Energy Agency. (2009). Dose
Reduction in CT while Maintaining Diagnostic
Confidence: A Feasibility/Demonstration Study.
IAEA.
3. Siemens Medical. (2007). Somatom Sensation
40/60 Application Guide. Siemens AG Medical
Solution.
4. Bauhs, J.A., J. Vrieze, T., N. Primak, A.,
Bruesewitz, M.R., H. McCollough, C. (2008). CT
Dosimetry:
Comparison
of
Measurement
Techniques and Devices.
5. AAPM. (2007). AAPM Report No.96, The
Measurement, Reporting, and Management of
Radiation Dose in CT. Collage Park, American
Association of Physicists in Medicine.
6. Bushberg, J Harold. (2002). The Essential of
Medical Imaging Second Edition. Philadelphia:
Lippincott Williams & Wilkins.
7. Bongartz G., Golding S.J. et al. (2004).
European Guidelines for Multislice Computed
Tomography 2004 CT Quality Criteria.