Textbook 3Rd International Conference On Radiation Safety Security in Healthcare Services R Zainon Ebook All Chapter PDF
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R. Zainon Editor
3rd International
Conference on
Radiation Safety
& Security in
Healthcare Services
Proceedings of the Thirs, ICRSSHS,
Dewan Budaya USM, Penang, Malaysia
Lecture Notes in Bioengineering
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R. Zainon
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Editor
R. Zainon
Advanced Medical and Dental Institute
Universiti Sains Malaysia
Kepala Batas, Penang
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Preface
v
vi Preface
vii
The Influence of Pitch Factor in
Reducing Computed Tomography Head
Dose Exposure: Single–Centre Trials
Abstract Computed tomography (CT) is mainly associated with high radiation dose
exposure to patient and potential for increased risk of cancer. The increasing number
of CT head examinations worldwide shows the need for optimization and strategy for
dose reduction technique. Thus, the aim of this study is to evaluate the influence of
pitch factor in reducing CT dose particularly CT head examination. In this study, the
scan acquisition parameter and the CT dose parametric information were collected
retrospectively from 16-slice CT scanner (Toshiba Activion) console display. Effec-
tive dose (E) was estimated using effective dose per dose-length product (E/DLP)
conversion factor, k 0.0021 mSv/mGy.cm. This experiment involved two sets of
study, the pre-intervention (n 163, 58 ± 18 years, 120 kV, 200 mAs, pitch 0.688)
and post-intervention (n 165, 57 ± 19 years, 120 kV, 200 mAs, pitch 0.938) on
January 2017 and March 2017, respectively. The mean CTDIvol values recorded for
pre- and post-intervention were 70.00 ± 8.84 mGy and 51.30 ± 0.72 mGy, respec-
tively. Generally, the mean E value for pre-intervention and post-intervention were
2.75 ± 0.35 mSv and 2.16 ± 0.17 mSv, respectively. It is interesting to note that by
increasing the pitch factor in CT head examination has significantly reduced the CT
head dose exposure without adversely affecting image quality. The mean DLP value
for post-intervention is 1030.10 mGy.cm and has been set as institutional DRL. In
conclusion, it is recommended for radiology personnel especially radiographer and
radiologist to be aware certain acquisition parameters i.e. pitch factor that work for
the optimization process.
1 Introduction
CT has developed diagnostic decision making as it provides fast and accurate three
dimensional data as compared to other medical imaging tools, hence allowing better
patient management [1]. The rapid increase in CT scan examinations is alarming as it
is associated to relatively high radiation dose and potential increased risk of cancer.
Although it comprises approximately 17% of all medical imaging procedures, it
produces approximately half of the population’s medical radiation exposure [2].
The increasing number of CT head examinations worldwide shows the need for
optimization and strategy for dose reduction technique. Pitch factor is one of the
factors affecting CT dose to the patient in the institutional since helical scanning is
used as the standard protocol for routine CT head examination. Pitch factor can be
defined as the ratio of table translation per 360° tube rotation relative to the nominal
beam width in helical CT. A higher pitch indicates faster table translation, and thus
larger volume coverage per unit time. Therefore, a higher pitch results in lower
radiation dose to the patient, if other parameters including tube current, and kV are
kept the same, at the price of lower image quality.
To our knowledge, currently there is no study done on the effect of pitch factor
on CT dose for CT head examination. Thus, the aim of this study is to evaluate the
influence of pitch factor in reducing CT dose particularly CT head examination.
2 Methodology
The methodology used in this study can be explained under the subtopic CT system,
CT dose quantities and data collection.
2.1 CT System
The study involved 16-slice CT scanner (Toshiba Activion). It is the only CT scanner
unit available in the institution which has been installed in 2010. The CT scanner was
evaluated and tested for quality assurance and quality control protocols regularly for
CT Dose Index volume (CTDIvol ) and dose-length product (DLP).
CTDIvol which is a measure of the energy output administered to a single axial “slice”
of a patient, and DLP which is an estimation of the total dose administered over the
The Influence of Pitch Factor in Reducing … 3
entire scan range (z-axis) were collected retrospectively as displayed in the patient
protocol on the console display.
All examination data for consecutive CT head examination in adult (age > 16 years)
performed between January 2017 to April 2017 were extracted from INFINITT
PACS system which enable the user to extract data such as patient gender, age,
scan protocol, CTDIvol and DLP. The experiment involved two sets of study; pre-
intervention and post-intervention. Both studies using fixed 120 kV and 200 mAs. The
intervention used in this study was the increment of pitch factor from 0.688 to 0.938
(36%) as shown in Table 1. Imaging quality was found to be acceptable following
discussion with the radiologists. In order to decrease beam-hardening artefacts, an
overlapping pitch (p < 1) is used in helical CT head [3]. CT head examination under
trauma protocol or contrast-enhanced were excluded from the study.
Based on Eq. 1, effective dose (E) was estimated using effective dose per dose-
length product (E/DLP) conversion factor, k 0.0021 mSv/mGy.cm [4]. Pre- and
post-intervention data were analysed using Microsoft Excel 2010. The institutional
DRL presented in this study are based on mean value (50th percentile) of the dose
spread from all patients.
E DL P × k (1)
3 Results
There were 328 adult CT head examinations that were evaluated from January
2017 to April 2017. Table 2 shows the comparison of mean CTDIvol , mean DLP
and mean E for pre- and post-intervention. The mean CTDIvol for pre- and post-
intervention were 70.00 ± 8.84 mGy and 51.30 ± 0.71 mGy, respectively. Generally,
the mean E value for pre-intervention and post-intervention were 2.75 ± 0.35 mSv
and 2.16 ± 0.17 mSv, respectively. The mean DLP value for post-intervention is
1030.10 mGy.cm and has been set as institutional DLP as recommended by ICRP
Publication 103. The institutional DRL was found not to exceed the national DRL,
that is 1050 mGy.cm.
4 N. E. Ismail et al.
4 Discussion
It is interesting to note that by increasing the pitch factor by 36% in CT head exam-
ination has significantly reduced the CTDIvol by 27%, reduced the DLP and E by
21% without adversely affecting the image quality. The qualitative assessment of the
image quality is difficult to be made as the study involved patients with inconsistent
patient positioning and patient’s head size. It was understood that by increasing the
pitch increases the potential for artefacts due to data insufficiency. In this study, the
post-intervention CT head images were diagnostically acceptable after discussion
with the radiologists.
The reduction of CT head dose exposure in this study leads to the establishment
of institutional DRL, which observed to be lower than Canada and Japan DRL as
shown in Table 3. However, based on the definition of DRL given by ICRP which
is ‘a form of investigation level, applied to an easily measured quantity, usually the
absorbed dose in air or tissue-equivalent material at the surface of a simple standard
phantom or a representative patient’ recommends that DRL should be implemented
as a benchmark to help operators for optimisation of radiation doses, rather than dose
limit.
A process of continuous audit is recommended to guide the appropriateness of
institutional scanning parameters and to avoid unnecessarily high doses being deliv-
ered to the patient. It is also important to ensure that similar diagnostic quality images
are being produced and the DRL produced are within institutional and national limits.
5 Conclusion
Increasing pitch factor in CT head examination was found to reduce the CT head
dose by 21%. In conclusion, it is recommended for radiology personnel especially
radiographer and radiologist to be aware certain acquisition parameters such as pitch
factor that work for the optimization process.
References
Abstract This main goal of this study was to evaluate image quality in single-energy
(SE) and dual-energy (DE) CT imaging with the presence of barium and iodine. A
fabricated polymethyl methacrylate abdomen phantom with 32 cm diameter size was
used to mimic human abdomen. Two different contrast agents: barium and iodine,
were scanned separately. The imaging parameters for SECT were set at tube voltage
80, 120 and 140 kV while the imaging parameters for DECT were set at fixed tube
voltage 80/140 kV. Both scan modes were set at the different pitch: 0.6 and 1.0 mm,
and the slice thickness was set at 3.0 and 5.0 mm with automatic exposure control
for the tube current. The CT images obtained from both scanning were analysed to
evaluate the signal-to-noise ratio (SNR). Barium and iodine gave highest SNR of
39.30 and 182.68, respectively, at a tube voltage of 140 kV, a pitch of 1 and a slice
thickness of 3 mm for SECT. In DECT mode, the highest SNR for barium and iodine
were 36.74 and 112.15 respectively at pitch 1 and slice thickness of 3 mm. There
was no significant difference between SNR of barium and iodine obtained with both
CT imaging modes with p-values of 0.75 and 0.12, respectively.
1 Introduction
The application of the contrast agent has been widely used in clinical work to improve
the image quality. Each contrast agent has a different atomic number which influ-
ences the attenuation that occurred during the computed tomography (CT) scanning.
Contrast agents with the high atomic number are preferable in CT imaging. This is
due to their K-edge energy which is within the effective x-ray energies [1–3]. More-
over, the photon starvation effect from the high atomic number of contrast agent is
not severe [4]. The widespread use of the contrast agents in the clinical application
are barium and iodine with atomic number (Z) of 56 and 53, respectively. Their
K-edge energy is 37.4 and 33 keV, respectively, which is within the effective x-ray
energy. Thus, barium and iodine have high attenuation at low tube voltage either
at 80 or 100 kVp [5–7]. However, more noise produced at low tube voltage which
causes low image quality [8–10].
CT tube voltage, slice thickness and pitch are factors that affect the CT image
quality [11]. By increasing the tube voltage, the photon numbers will be increased
which contribute to high signal-to-noise ratio (SNR). Increasing the slice thickness
will increase the number of the photon captures in each voxel; thus, more SNR will
be calculated, but it will deduct the CT image resolution. The SNR decreases with
the increment of the pitch. Pitch is the table movement per 360˚ rotation divided by
the slice thickness [12].Thus, more noise will be obtained when applying high pitch.
Therefore, this study was performed to evaluate the CT image quality with the
presence of contrast agents (barium and iodine) in both SECT and DECT imaging.
The effect CT imaging parameters on the CT image quality will be investigated in
both scan modes.
The clinical contrast agents of barium (E-Z-CAT) and iodine (IOMERON 350) were
used in this study with concentration of 4.9187% w/v (4.6% w/w) and 350 mg
iodine/ml, respectively. A single source with dual detector arrays CT scanner
(SOMATOM Definition AS, Siemens) was used to scan both contrast agents for
SECT and DECT scanning.
The CT imaging parameters were set at various tube voltages (80, 120, and 140 kV)
for single-energy CT (SECT) while 80 and 140 kV was set for dual-energy CT
(DECT). Different pitch and slice thickness were applied for both scanning modes
at pitch of 0.6 and 1, and slice thickness of 3.0 and 5.0 mm with automatic exposure
control (AEC).
Weasis software was used to analyse the CT images obtained from both scan
modes and three regions of interest (ROI) were drawn on the CT images to analyse
the image quality. The ROIs were drawn within the contrast agent region and water
region as the background to get the average mean CT number as shown in Fig. 2.
The SNR was calculated as shown in Eq. 1. The SA , SB , and σB is the mean CT value
of contrast agent (HU), mean CT value of background (HU), and standard deviation
of background, respectively.
|S A − S B |
SN R (1)
σB
The CT images of barium and iodine were analysed in both SECT and DECT modes.
The effect CT imaging parameters on the CT image quality was investigated in
both scan modes. Analysis CT number of both contrast agents obtained at different
tube voltage in SECT mode was shown in Fig. 3. Results show that barium has
highest attenuation at low tube voltage (80 kV). Similar profile of CT attenuation
was observed at different pitch and slice thickness. This is due to more CT attenuation
occurs at lowest tube voltage compared to high tube voltage.
10 J. Zukhi et al.
Fig. 2 Three ROIs were drawn on the CT contrast agent image for image quality evaluation
(a)
1200 1013.16 1015.40
1011.00 1009.48
1000
CT Number, HU
800 588.53
587.62
587.10
590.24 495.76 511.41
Pitch 0.6, Slice thickness 3 mm
600 497.20 513.18
Pitch 0.6, Slice thickness 5 mm
400
Pitch 1, Slice thickness 3 mm
200
Pitch 1, Slice thickness 5 mm
0
80 120 140
Tube voltage, kV
2259.82
2500 2215.07
1757.30
2000 1840.54 Pitch 0.6, Slice thickness 3 mm
1500 Pitch 0.6, Slice thickness 5 mm
Fig. 3 The CT number of (a) barium and (b) iodine at different tube voltage in SECT mode
Image Quality Evaluation in Contrast Agents … 11
160
150
140
130
120
110
100 Ba, SECT
SNR
90
80 Ba, DECT
70 I, SECT
60
50 I, DECT
40
30
20
2 3 4 5 6
Slice thickness, mm
Fig. 4 The SNR of barium and iodine at different slice thickness for both SECT and DECT scan
modes at pitch of 1 and tube voltage of 120 kV
The highest attenuation of iodine was observed at 120 kV as shown in Fig. 3b.
The K-edge energy of iodine is at 33.0 keV and it is within the low tube voltage
energy range. However, iodine gave highest attenuation at 120 kV. This is due to the
use of high concentration of iodine in this study that affects the attenuation of iodine.
This study found that CT attenuation is also affected by the concentration and the
atomic number of contrast agent used in this study. Results obtained in this study
is similar to previous studies which found that concentrated iodine gave the highest
attenuation at 120 kV [13, 14]. The CT attenuation of iodine gives similar trend at
different pitch and slice thickness.
The SNR of both contrast agents at different slice thickness was also investigated.
Figures 4 shows the SNR of barium and iodine at different slice thickness from
both scan modes at pitch of 1 and tube voltage at 120 kV. Results shows that the
SNR increases with the increment of slice thickness. With the use of thicker slices,
the number of photons captured in each voxel is high. Thus, more signals were
obtained and this factor influences the SNR value for barium and iodine at different
slice thickness. Result in this study shows that the SNR of iodine is higher than
barium even though its atomic number is smaller than barium. This is due to iodine
concentration used in this study is concentrated than barium. The concentration of
the contrast agent affects the CT attenuation and, thus, it affects the SNR [15].
This study also found that there was no significant difference in SNR of both
contrast agents for SECT and DECT scan mode. This finding is in-line with Zhu
and his colleagues, and Yu et al., results where there was no significant difference
between SECT and DECT in SNR [16, 17]. The insignificant result is because the
SNR of the fused image that obtained from DECT scanning was assumed similar
with the 120 kV tube voltage of SECT scanning [18].
Figure 5 shows the SNR of barium and iodine at different pitch value for both
scan modes. The SNR decreases with the increment of pitch. Pitch is the table move-
ment per 360˚ rotation divided by the slice thickness. The image noises obtained
12 J. Zukhi et al.
140
130
120
110
100
90 Ba, SECT
SNR
80
70 Ba, DECT
60 I, SECT
50 I, DECT
40
30
20
0.4 0.6 0.8 1 1.2
Pitch
Fig. 5 The SNR of barium and iodine at different pitch for SECT and DECT scan modes
were affected by pitch. Increasing the pitch will cause less projection on the object.
Therefore, more noise was obtained on the CT image [12, 19]. On the same note,
the SNR is inversely proportional to the noise captured on the CT image. Thus, the
higher pitch used gave lower SNR in this study because of more noise were pro-
duced. There was no significant difference in SNR of barium for both scan modes
at different pitch. However, there was a significant difference in SNR of iodine for
both scan modes at different pitch. This is due to the use of concentrated iodine that
affect the SNR value.
4 Conclusion
In conclusion, the attenuation of barium and iodine are higher when applying low
tube voltage. Barium has higher attenuation at 80 kV tube voltage. However, the
use of concentrated iodine makes it more attenuated at higher tube voltage. The CT
image quality is affected by a number of factors including the tube voltage, slice
thickness, pitch, atomic number and concentration of contrast agent. Increasing the
tube voltage and slice thickness will increase the SNR. The SNR decreases with the
pitch increment. The SNR obtained from SECT and DECT were not significantly
difference for barium when using different slice thickness and pitch. However, iodine
had statistically significant between SECT and DECT when applying different pitch
but not significantly different when applying different slice thickness. This funda-
mental knowledge is important to give a better understanding in improving the CT
image quality with the presence of multiple contrast agent in CT imaging.
Acknowledgements The authors would like to acknowledge the financial support from Ministry
of Higher Education through Fundamental Research Grant Scheme (FRGS).
Image Quality Evaluation in Contrast Agents … 13
References
Abstract The CT dose index (CTDI) and dose length product (DLP) are the most
frequently used indicators to represent radiation doses in CT examination. However,
the limitation of both is that they only estimate dose based on the scanner output infor-
mation for specific standardized condition and phantom sizes. This study was aimed
in evaluation of the radiation dose based on the SSDE method for adult abdomen CT
study at AMDI, Universiti Sains Malaysia, Penang. A total of 91 CT procedures were
selected consisting only adult patients undergo CT thorax-abdomen-pelvis (TAP)
examination. As recommended by American Association of Physicist in Medicine
(AAPM), the individual dimensions of each patient were determined. The conver-
sion factors for SSDE were multiplied with the displayed CTDIvol . The comparative
study between displayed CTDIvol with SSDE-calculated dose were done and percent-
age difference were then determined. From the results, significant differences were
observed between SSDE-calculated and displayed dose with variations of 3–47% for
method of AP and LAT summation, and 1.96–46% with method of effective diam-
eter. The SSDE calculated doses were significantly higher than the displayed dose
values by CT scanner. Therefore, evaluation of patient dose by individual specific
size is critical for optimization of radiation exposure in CT imaging.
N. M. Huzail
School of Physics, Universiti Sains Malaysia, 11800 Minden, Penang, Malaysia
e-mail: nurhanishuzail@gmail.com
M. A. A. M. Roslee
Imaging Unit, Advanced Medical and Dental Institute, Universiti Sains Malaysia, 13200 Kepala
Batas, Penang, Malaysia
e-mail: amirul.azrie@usm.my
N. S. M. Azlan
Faculty of Computer and Mathematical Sciences, Universiti Teknologi MARA, 15050, Kota
Bharu, Kelantan, Malaysia
e-mail: noorsyamimimuhamadazlan@gmail.com
N. D. Osman (B)
Oncological & Radiological Sciences, Advanced Medical and Dental Institute, Universiti Sains
Malaysia, Bertam, 13200 Kepala Batas, Penang, Malaysia
e-mail: noordiyana@usm.my
1 Introduction
Currently, the volumetric CTDI (CTDIvol ) and dose length product (DLP) values have
been employed to represent radiation doses from CT examination [1]. The CTDIvol
is defined for two standard polymethylmethacrylate (PMMA) phantoms; a diameter
of 32 cm to represent the patient’s body and 16 cm to represent the patient’s head [2,
3, 8]. However, both metrics are not considered to represent the actual patient dose
but only the measurement of machine output [1–5].
The main controversial issue with current dose metrics is the underestimation
of the patient dose by 40–70% for averaged-size adult and paediatric torsos [1,
5, 7]. This problem led to the beginning of new technique known as size-specific
dose estimate (SSDE) by American Association of Physicist in Medicine (AAPM).
AAPM introduced the conversion factors for an accurate dose estimation as proposed
in Report 204 [1–9]. This report combined four independent research teams that have
studied the potential of patient size-dependent factors to estimate the true patient dose
from the displayed CTDIvol [10]. Four different calculation methods were used to
represent the patient size such as the anteroposterior (AP) dimension, the lateral
(LAT), the sum of both dimensions (AP + LAT), and the effective diameter (Deff).
In this study, two different approaches to calculate SSDE were compared. The
calculated SSDE were derived from two conversion factors; one from the summation
of AP + LAT dimensions and another is the effective diameter. Both different methods
to determine individual patient’s diameter were compared.
2 Method
Institutional committee review for ethical approval on the clinical data study was
obtained (USM/JEPeM/17030180). All CT imaging performed at Imaging Unit,
AMDI USM, Penang, Malaysia were performed with dual-energy SOMATOM Def-
inition AS + CT scanner (Siemens Healthcare, Germany). This study involved a ret-
rospective survey on selected patient data that only included the patient dose received
from CT TAP study. This retrospective survey was carried out on patient data retrieved
from the Picture Archiving and Communication System (PACS) between the periods
of June 2016 until March 2017.
Study on Different Method to Determine the Individual Diameter … 17
The collected patient data consists of individual patient’s information such as age,
gender, examination date, CT procedure, CTDIvol , DLP, and scan parameters (kVp,
mAs, scan length and slice thickness). The individual AP and LAT diameters for each
patient were measured at similar anatomic landmark through the relatively largest
extent for a reliable result. The measurements were done at three sub regions, which
were mid spleen, mid kidney, sacral level by using digital caliper tool on the CT
workstation console.
Figure 1 shows the measured LAT and AP projections for three different anatomic
scan locations from the CT images. The LAT diameter was measured at the central
image as it is the widest region of lateral dimension. However, the measurement
of AP diameter was measured at the widest point of AP dimension. The diameter
measured for each different location were then compared.
The individual effective diameter (Deff ) of each patient was determined using
the root of the product of the AP and LAT patient measurements as defined by the
equation provided in AAPM Report 204 [5].
√
E f f ective diameter A P × L AT (1)
LAT
LAT
LAT
Fig. 1 The measurement of both lateral and AP dimensions at three different subregions: a mid
spleen, b mid kidney and c sacral region
18 N. M. Huzail et al.
SS D E C T D Ivol
32
× f si32ze (2)
3 Results
28
26
Mid spleen
Mid kidney
25 Sacral
24
23
21-30 31-40 41-50 51-60 61-70 71-80 81-90
Age (year)
Fig. 2 Relationship between effective diameter of each sub-level with patient age
Mean overall in the AP + LAT dimension was 52.0 cm ± 6.4, with a range of
38.9–69.8 cm and were corresponded with a range of conversion factor of 1.04 up to
1.87. The mean effective diameter computed from the AP thickness and LAT width
for each data series was 25.6 cm ± 3.2 and was ranged from 18.96 to 34.50 cm for
overall age groups.
Figure 3 shows the scatterplot that describe the distribution of measured individual
diameter using two different methods, which were the summation of AP + LAT
(Fig. 3a) and efective diameter (Fig. 3b) for both gender as a function of patient age.
From these figures, the slope of the line shows a very weak relationship between the
measured diameter and age for both female and male patients. For first method (AP +
LAT summation), results showed weak correlation between patient age and measured
diameter for both male and female with R2 value of 0.31% and 0.66%, respectively.
For AP + LAT method, the statistical analysis showed significant difference for both
gender, with p-value of 0.812 and 0.854, for both male and female respectively.
In Fig. 3b, the scatter plot shows the distribution of measured dose using Deff
dimension for both genders as a function of patient age. From the figure, it can be
observed that the relationship between patient size, Deff of both male and female
20 N. M. Huzail et al.
(a) 90
80 (Male) R² = 0.0031
70
AP + LAT (cm)
60
50
40
30 (Female) R² = 0.0066 Male
20 Female
Male
10
Female
0
0 10 20 30 40 50 60 70 80 90 100
Age group (years)
(b) 40
35 (Male) R² = 0.004
30
25
Deff (cm)
20
15 (Female) R² = 0.0054 Male
10 Female
Male
5
Female
0
0 10 20 30 40 50 60 70 80 90 100
Age group (years)
Fig. 3 The individual diameter determined from two different methods; a summation of AP + LAT
dimension and b the effective diameter is shown as a function of age for female and male patient
group
patient were very weak, since the value of R2 is 0.4% and 0.54%, respectively.
However, the statistical analysis showed significant difference between gender, with
p-value of 0.794 and 0.781, for both male and female respectively.
Based on the dose measurement among the 91 patients, the mean displayed CTDIvol
was 8.6 mGy ± 3.1, which is based on standard phantom size. However, the mean
SSDE-calculated dose derived from both AP + LAT and effective diameter calcu-
lations resulted in higher dose, which were 11.9 mGy ± 2.8 and 11.8 mGy ± 2.8,
respectively.
Study on Different Method to Determine the Individual Diameter … 21
14
12
10
CTDIvol (mGy)
CTDIvol
8 SSDE (LAT + AP)
SSDE (Deff)
6
0
21-30 31-40 41-50 51-60 61-70 71-80 81-90
Age group (years)
Fig. 4 The comparison of SSDE-calculated dose between two different methods for diameter
measurement and displayed dose for each age group
Figure 4 shows comparison of displayed CTDIvol and calculated-SSDE doses for both
methods as a function of patient age. For patients aged between 23 and 88 years,
the calculated-SSDEs were approximately a factor of 1.46 times greater than the
displayed CTDI32vol .
Besides, when the source of SSDEs was analysed, overall agreement of no more
than 50% were observed between the displayed and calculated dose. The variations
were slightly higher for dose derived from summation of AP and lateral dimensions
of 3–47%, compared with 1.96–46% when effective diameter was applied.
22 N. M. Huzail et al.
4 Discussion
SSDE conversion factors can be determined for a particular patient from the AP
thickness and LAT width from the table that has been provided in AAPM Report
204 [5]. Based on the report, the range of summation of the AP and LAT dimensions
based on the use of the 32 cm diameter PPMA phantom for CTDIvol is from 16 to
90 cm.
In the conditions that both AP and LAT dimensions of the patients are known,
these two dimensions were used to estimate the effective diameter. Alternatively,
calculated effective diameter values were also used to find the fsize that then multiplied
by CTDIvol , yields SSDE calculated dose. The range of effective diameter in the
Report 204 is limited from 8 to 45 cm. Meanwhile, ICRU Report 74 has provided the
option to estimate effective diameter as a function of patient age. The corresponding
effective diameter provided in the Report 74 can be further used to determine the
conversion factors, fsize in AAPM Report 204 [1, 5]. However, using the age only to
calculate SSDE were impossible in this study because of a lack of data published
in ICRU 74 for patients older than 18 years. In fact, as the Report 204 has provided
size-based variable, patients’ sizes are at an advantage to find the most appropriate
fsize .
Figure 4 demonstrated slightly differences between calculated SSDEs that come
from AP + LAT or effective diameter calculations due to the drawback of translating
three-dimensional object into two-dimensions [1]. These results give justification for
the combination of AP and LAT measurements, either as a summation or effective
diameter calculation is more preferable for calculating SSDE than either measure-
ment used individually similar to Braudy Kaufman et al suggested previously [1].
From Fig. 4, variability between displayed CTDIvol and calculated SSDEs for a
given patient size were observed because of the expected variability in patient size
as the reported CTDIvol is known to be based on the specific diameter of 32 cm
for body dosimetry phantom. Christner et al reported that the spread out in CTDIvol
for individual patient size was noticed even for patients of the same AP + LAT
dimension because of the expected variability in patient body habitus and selected
scan range [7]. Thus, by multiplying different CTDIvol values with the same fsize , the
computed SSDE would also differ.
Based on the Report 204, for patient’s diameter higher than 72 cm (for AP + LAT)
and 35 cm (effective diameter), the fsize is smaller than 1. Thus, the calculated SSDE
obtained by multiplying the CTDIvol with fsize will be smaller than the displayed
dose. This subsequently result in enlarge of SSDE for smaller-sized patients. In the
evaluation of the data sets studied, a range of patient sizes indicated by the AP
+ LAT measurements and effective diameter were smaller than 72 cm and 35 cm
respectively, thus the SSDE calculated dose derived were expected to be higher than
the displayed CTDIvol . It is therefore proved that patient size is more important in
CT acquisitions performed.
Our study has some limitations. The sample population in this study only included
91 adult patients that undergo TAP CT examinations and it may not the optimal
Study on Different Method to Determine the Individual Diameter … 23
sample size for SSDE calculations. Besides, because of individual habitus is differs,
consistent anatomical landmark is also difficult to be measured for each patient. In
this study, only patient age was used for correlation with the SSDE-calculated dose.
Patient age alone may not be the best variable to correlate with radiation dose.
5 Conclusions
Acknowledgements The authors would like to thank all radiographers and staff at Imaging Unit,
AMDI USM, Malaysia for their help and support throughout this work.
References
Language: English
F O R P R I VAT E FA M I L I E S
BY ELIZA ACTON
NEW EDITION
LONDON
LONGMANS, GREEN, READER, AND DYER
1882.
PREFACE.
Farce—forcemeat.
Fondu—a cheese soufflé.
Nouilles—a paste made of yolks of egg and flour, then cut small like
vermicelli.
Sparghetti—Naples vermicelli.
Stock—the unthickened broth or gravy which forms the basis of
soups and sauces.
Zita—Naples maccaroni.
TABLE OF CONTENTS.
CHAPTER I.
SOUPS.
Page