Radiation Dose Reduction Strategies for the Dose-Image Optimisation in Abdominal CT and a ...

341 Pages·2012·5.24 MB·English

Radiation Dose Reduction Strategies for the Dose-Image
Optimisation in Abdominal CT and a Demonstration of Validity
of Visual Grading Analysis

Submitted by
Myeongsoo Kim
BSc (Biology) (Kyung Hee University)
BMSc (Medical Imaging) (Charles Sturt University)

A thesis submitted for the requirement of the degree of

Doctor of Philosophy
Medical Radiation Science
Faculty of Science

Charles Sturt University
©2016
Table of contents

List of Figures .................................................................................................................................. vii
List of Tables ................................................................................................................................... xix
Certificate of Authorship ........................................................................................................... xxvi
Acknowledgements ................................................................................................................... xxvii
Radiation Safety Approval………………………………………………………………………..………………xxix
Human Research Ethic Approval……………………………………………………………………………….xxix
Institutional Review Board Approval…………………………………………………………………………xxix
Professional Editorial Assistance……………………………………………………………………….........xxix
Proceedings………………………………………………………………………………………………………………xxx
Statement from Presenters' Confirming……………………………………………………………........xxxi
Abstract .......................................................................................................................................... xxx

Chapter 1. INTRODUCTION ............................................................................................... 1
1.1 Background ........................................................................................................... 1
1.2 Computed Tomography and Radiation Doses ...................................................... 4
1.3 Problem in Optimisation....................................................................................... 6
1.4 Problems in Visual Grading scale .......................................................................... 9
1.5 Objectives of the Study ...................................................................................... 10
1.6 Structure of the Thesis ....................................................................................... 11
Chapter 2. REVIEW OF THE LITERATURE ......................................................................... 12
2.1 Introduction ........................................................................................................ 12
2.2 Dose Optimization on Computed Tomography .................................................. 13
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2.3 Image Quality and Radiation Dose ..................................................................... 18
2.4 Diagnostic Reference Levels (DRLs) .................................................................... 20
2.5 Subjective Image Quality Assessments .............................................................. 21
2.6 Patient Size and CTDI ....................................................................................... 25
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2.6.1 Cross-sectional Area (mm2) ...................................................................... 27
2.7 The Reference Man Models ............................................................................... 27
2.8 Radiation Protection in Computed Tomography ................................................ 29
2.9 Radiation Dose Units in CT ................................................................................. 32
2.9.1 Effective Dose Equivalent .......................................................................... 32
2.9.2 Overview of the CT Dose Index ................................................................. 34
2.9.3 CTDI , CTDI , and DLP ............................................................................. 35
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2.9.4 Dose Conversion Factor ............................................................................ 38
2.10 Dose Reduction Strategies ................................................................................ 41
2.10.1 Dose Management .................................................................................. 41
2.10.2 Operators Training .................................................................................. 42
2.10.3 Technological Advance in CT Scanner ..................................................... 43
2.11 Using AEC systems ............................................................................................ 47
2.11.1 Advanced AEC Techniques in CT systems ............................................... 47
2.11.2 Manufacturers and AEC systems ............................................................ 48
Chapter 3. METHODOLOGY ............................................................................................. 50
3.1 Introduction ........................................................................................................ 50
3.2 Practical Problems and Needs ............................................................................ 54
3.3 Study Instruments .............................................................................................. 55
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3.3.1 Instruments for the Dose-Image Quality Optimisation ............................ 56
3.3.2 Instruments for the comparison of visual grading study .......................... 60
3.4 Study Variables ................................................................................................... 61
3.5 Quantitative assessment Procedures ................................................................. 61
3.5.1 CT Imaging Systems .................................................................................. 62
3.5.2 Image Protocols for Abdominal CT ........................................................... 64
3.5.3 Dose Measurement .................................................................................. 65
3.5.4 Image Acquisition with Anthropomorphic Phantom ................................ 67
3.5.5 Image Noise Measurement ....................................................................... 69
3.5.6 Contrast-to-Noise Ratio Measurement .................................................... 72
3.5.7 Logistic Psychometric Function ................................................................. 73
3.5.8 Body Mass Index (BMI), Body Weight, and Cross-Sectional Area ............ 75
3.6 Qualitative assessment procedures ................................................................... 77
3.7 Institutional Review Board (IRB) and Ethics Approval ........................................ 77
3.8 Radiation Safety Issue ......................................................................................... 78
3.9 Statistic Procedure .............................................................................................. 79
Chapter 4. EVALUATION OF VGA IN CT ........................................................................... 80
4.1 Task Ⅰ; CT x-ray tube voltage optimisation and image reconstruction evaluation
using visual grading analysis ..................................................................................... 80
4.1.1 Introduction .............................................................................................. 80
4.1.2 Materials and methods ............................................................................. 83
4.1.3 Results ....................................................................................................... 92
4.1.4 Discussion ............................................................................................... 145
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4.1.5 Conclusion ............................................................................................... 147
4.2 Task Ⅱ; Studies of CT system performances using visual grading scaling: a
methodological comparison among visual grading characteristics, ordinal
regressions and visual grading psychometric functions. ........................................ 148
4.2.1 Introduction ............................................................................................ 148
4.2.2 Materials and methods ........................................................................... 150
4.2.3 Results ..................................................................................................... 152
4.2.4 Discussion ............................................................................................... 168
4.2.5 Conclusion ............................................................................................... 168
Chapter 5. DOSE REDUCTION AND DRLS IN ABDOMINAL CT ....................................... 169
5.1 Task Ⅰ; Feasibility study for using the 50th percentile levels in the DRLs estimated
by an evaluation of image noise, CNR, CTDI and VGA-Score .............................. 169
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5.1.1 Introduction ............................................................................................ 169
5.1.2 Materials and method ............................................................................ 171
5.1.3 Results ..................................................................................................... 178
5.1.4 Discussion ............................................................................................... 207
5.1.5 Conclusion ............................................................................................... 209
5.2 Task Ⅱ; The effectiveness of patient size indices to precise kVp selection: A
retrospective study using MDCT abdominal imaging under AEC systems ............. 210
5.2.1 Introduction ............................................................................................ 210
5.2.2 Materials and methods ........................................................................... 212
5.2.3 Results ..................................................................................................... 219
5.2.4 Discussion ............................................................................................... 243
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5.2.5 Conclusion ............................................................................................... 258
Chapter 6. CONCLUSION ............................................................................................... 259
REFERENCES .................................................................................................................. 261
APPENDICES .................................................................................................................. 279
Appendix 1 .............................................................................................................. 279
Appendix 2 .............................................................................................................. 280
Appendix 3 .............................................................................................................. 282
Appendix 4 .............................................................................................................. 284
Appendix 5…………………………………………………………………………………………………………286
Appendix 6…………………………………………………………………………………………………………300

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LIST OF FIGURES
CHAPTER 1
Figure 1-1 Comparison of total annual doses for Australia, the USA and the UK
Figure 1-2 Scan concept of single-slice detector and multi-slice detector system
Figure 1-3 Basic concept of protocol and dose-image quality optimisation

CHAPTER 2
Figure 2-1 Simplified qualitative relationship between physical image quality
and diagnostic performance
Figure 2-2 (a) 75th percentile for DRLs in survey of dose distribution
(Cordy,2011); & (b) Dose Length Production (DLP) dose distribution
for chest CT examination
Figure 2-3 Signal detection theory; the distance between signal (true-positive)
and noise (false-positive) can be affected by radiation dose in CT; the
area of triangle represents the error in the observer’s decision and
small radiation dose can lead to a short distance between both mean
values of signal and noise
Figure 2-4 Explanation of the basic concept of the ROC method with AUC. A high
percentile of AUC represents real validity of tested systems
Figure 2-5 Area under the curve (AUC ) statistically obtained from the VGC-
VGC
curve data presented in Table 2-3 and 2-4
Figure 2-6 Human body types with BMI classification
Figure 2-7 (a) Schematic drawing of a DNA molecule and damage that may
result from one X-ray photon. X-ray photons interact with water to
produce reactive free radicals and recoil electrons, which in turn
cause DNA damage. When ionising radiation breaks the double
stranded backbone (in dark grey) of the DNA in multiple places the
DNA cannot repair the damage itself. Such damage may lead to
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cancer. (b) Free radical damage causes inflammation and production
of antioxidants from the radiation exposure
Figure 2-8 Human exposure to ionising radiation in Australia
Figure 2-9 Auto-exposure control system and tube current selection. Average
tube current is used to calculate CTDI for automatic dose report
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by CT scanner

(a) A solid-state real-time dosimeter (arrow) is located in the core of
Figure 2-10
a head phantom to measure the CTDI . (b) The analogue signal
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data is transferred to a computer and used to depict dose profile.
Figure 2-11 The anterior-posterior (AP) and a lateral dimension, along with
effective diameter are illustrated in this figure. The lateral dimension
can determine from a PA or AP of CT radiograph, and a lateral CT
radiograph can identify the AP dimension. The effective diameter
corresponds to a circle having an area equal to that of the patient’s
cross section on a CT image.
Figure 2-12 The best-fit curve between normalised dose coefficient vs effective
diameter.

Figure 2-13 Photograph of multi-detector computed tomography (CT)
components.
Figure 2-14 (a) This illustration of dual-energy technique shows hypothetical
elements A and B, which have K edges of 90 keV and 190 keV,
respectively. The percentage of x-ray photon absorption is plotted as
a function of x-ray energy (in keV). (b) DSCT with two tubes running
at different voltages and corresponding detectors mounted
orthogonally in one gantry
Figure 2-15 Demonstration of the FBP algorithm
Figure 2-16 Adaptive statistical iterative reconstruction (ASIR) images by using
GE 750HD. (a) Filtered back projection image obtained at 120 kVp
and 300 mA at 11.3 mGy. (b) 60% ASIR image generated through
multiple iterations by noise reduction model rules
Figure 2-17 (a) The tube current may be modulated as a function of projection
angle, (b) longitudinal location. (c) x and y-axis combination

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CHAPTER 3
Figure 3-1 Example CT images with 100 kVp and tube currents from 10 to 580
mA; (a) 10 mA; (b) 50 mA; and (m)580 mA
Figure 3-2 Toshiba Aquilion ONETM 320 MDCT scanner
Figure 3-3 GE DiscoveryTM 750HD 64 MDCT scanner
Figure 3-4 Philips Ingenuity 64 MDCT scanner
Figure 3-5 CTDIvol summary; (a) Toshiba Aquilion ONETM 320 MDCT, (b) GE
DiscoveryTM 750HD 64 MDCT, and (c) Philips Ingenuity 64 MDCT
Figure 3-6 (a) Appearance of the PH-5 Abdominal CT phantom, (b) scout view
(120 kVp; 30 mA; CTDI 0.085mGy)
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Figure 3-7 Internal structures; (a) lungs and heart. (b) liver (include hepatic
veins, hepatic arteries, bile duct), stomach with gas, spleen, IVC, and
abdominal aorta, (c) pancreas, spinal column, (d) kidneys enhanced
with contrast media (Iodine)
Figure 3-8 Examples of characteristics of manual noise measurement; (a) two
typical homogeneous ROIs with air-space between the anatomical
structures in the CT image. (b) the magnified local area within ROI 1.
(C) magnified local area within ROI 2. (d) 3D surface plot of the ROI 1.
(e) 3D surface plot of ROI 2
Figure 3-9 Diameter measurement by using a “set scale” tool of Image J
computational programme

CHAPTER 4
Figure 4.1-1 Scout view and scan range
Figure 4.1-2 Example of FBP and iterative reconstruction images using the Toshiba
Aquilion OneTM 320 slices MDCT with 80 kVp, 400 mA, CTDI mGy;
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(a) FBP image, (b) AIDR Mild image, (c) AIDR STD image, (d) AIDR STR
image
Figure 4.1-3 Example of FBP and iterative reconstruction images using the GE
DiscoveryTM 750HD 64-slice MDCT with 80 kVp, 400 mA, CTDI mGy;
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(a) FBP image, (b) ASiR 20% image, (c) ASiR 40% image, (d) ASiR 60%
image
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Figure 4.1-4 Example of FBP and iterative reconstruction images using the Philips
Ingenuity (PI) 64-slice MDCT with 80 kVp, 400 mA, CTDI mGy; (a)
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FBP image, (b) iDOSE 20% image, (c) iDOSE 40% image, (d) iDOSE 60%
image
Figure 4.1-5 Graph of CTDI (mGy) values of 80, 100, and 120 kVp corresponding
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to 10-580mA using the Toshiba Aquilion OneTM
Figure 4.1-6 Graph of CTDI (mGy) values of 80, 100, and 120 kVp corresponding
vol
to 10-580mA using the GE DiscoveryTM 750HD
Figure 4.1-7 Graph of CTDI (mGy) values of 80, 100, and 120 kVp corresponding
vol
to 10-580mA using the Philips Ingenuity CT
Figure 4.1-8 Graph of Image noise (HU) values of FBP image, AIDR MILD, STD, and
STR images using 80 kVp corresponding to 10-580mA under the
Toshiba Aquilion OneTM
Figure 4.1-9 Graph of Image noise (HU) values of FBP image, AIDR MILD, STD, and
STR images using 100 kVp corresponding to 10-580mA under the
Toshiba Aquilion OneTM
Figure 4.1-10 Graph of Image noise (HU) values of FBP image, AIDR MILD, STD, and
STR images using 120 kVp corresponding to 10-580mA under the
Toshiba Aquilion OneTM
Figure 4.1-11 Graph of image noise (HU) values of FBP image, ASiR 20, 40, and 60%
images using 80 kVp corresponding to 10-580mA under the GE
DiscoveryTM 750HD
Figure 4.1-12 Graph of image noise (HU) values of FBP image, ASiR 20, 40, and 60%
images using 100 kVp corresponding to 10-580mA under the GE
DiscoveryTM 750HD
Figure 4.1-13. Graph of image noise (HU) values of FBP image, ASiR 20, 40, 60%
images using 120 kVp corresponding to 10-580mA under the GE
DiscoveryTM 750HD
Figure 4.1-14 Graph of image noise (HU) values of FBP image, iDOSE 20, 40, and
60% images using 80 kVp corresponding to 10-580mA under the
Philips Ingenuity CT
Figure 4.1-15. Graph of image noise (HU) values of FBP image, iDOSE 20, 40, and
60% images using 100 kVp corresponding to 10-580mA under the
Philips Ingenuity CT

Figure 4.1-16 Graph of image noise (HU) values of FBP image, iDOSE 20, 40, and
x