The Influence of Accurate Attenuation Correction

263 Pages·2013·2.84 MB·English

by  Heleln Blundell

The Influence of Accurate Attenuation Correction on
Quantitative Gamma Camera Imaging

by

Helen Louise Blundell

Cardiff University, School of Engineering

PhD Thesis

2012
DECLARATION
This work has not previously been accepted in substance fro any degree and is
not concurrently submitted in candidature for any degree.

Signed………………………….. (candidate) Date …………………

STATEMENT 1
This thesis is being submitted in partial fulfillment of the requirements for the
degree of PhD.

Signed …………………………. (candidate) Date …………………

STATEMENT 2
This thesis is the result of my own independent work/investigation, except when
otherwise stated. Other sources are acknowledged by explicit references.

Signed ………………………….. (candidate) Date ………………….

STATEMENT 3
I hereby give consent for my thesis, if accepted, to be available for photocopying
and for inter-library loan, and for the title and summary to be made available to
outside organizations.

Signed……………………….. (candidate) Date…………………..
Abstract

Gamma camera systems are used in a variety of diagnostic applications to image and in
some cases measure, the physiological uptake of a radioactive tracer within the body. A
number of factors, particularly attenuation and scatter of photons within the body tissues
can cause degradation of image quality and inaccuracies in the measurement of tracer
uptake. Single photon emission tomography (SPECT) systems which incorporate an x-
ray computed tomography (CT) facility have enabled accurate transmission images of
the patient to be obtained. These ‘attenuation maps’ can be used to correct the SPECT
images for the effects of attenuation.

The aim of this project was to investigate the use of an x-ray CT based attenuation
correction (AC) system in SPECT gamma camera imaging. The use of AC with other
physical parameters of the imaging process including scatter was firstly examined in
order to determine the optimum imaging parameters required to maximise image quality.
The influence of attenuation, scatter and other imaging parameters on the accuracy of
absolute and relative quantitative measurements was then investigated.

The methodology involved using the GE Millenium Hawkeye gamma camera system to
obtain images of a range of phantoms filled with various concentrations of radioactivity;
from simple point sources to phantoms which simulate organs of the body.
An attempt was made to establish SPECT sensitivity values that would allow accurate
determination of activity in a region of interest. These sensitivity values were applied to
all subsequent measurements and a measure made of quantitative accuracy.

The results showed that the sensitivity value used for quantitative SPECT
measurements must reflect the reconstruction method and corrections used in the
acquisition. Attenuation correction proved to be more significant than scatter correction
in quantitative accuracy, with activity results being within 30% of expected values in all
cases where AC was used.
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Acknowledgments

I am grateful to all in the Department of Medical Physics and Clinical
Engineering for allowing me to do this project, especially Professor Wil
Evans for much needed support and guidance. Thanks also to Professor
Peter Wells for helpful comments on my thesis.

With love and thanks to all my family and friends.
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Contents

Title page i
Declaration ii
Abstract iii
Acknowledgements iv
Contents v
List of abbreviations xii

Chapter 1 Introduction 1

1.1. Background 1
1.2. Quantification in nuclear medicine 2
1.3. Aim 5

Chapter 2 Planar and SPECT Gamma Camera Imaging 7

2.1.Introduction 7
2.2. Technetium-99m (Tc-99m) 8
2.3.Interaction of photons with matter 9
2.3.1 The photoelectric effect 12
2.3.2 Compton scattering 13
2.4.Gamma camera image formation 17
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2.4.1 The collimator 18
2.4.2 The scintillation crystal 19
2.4.3 The photomultiplier tubes 21
2.4.4 Signal processing 22
2.4.5 Energy discrimination 24
2.4.6 Linearity, energy and sensitivity corrections 26
2.4.7 Image display 26
2.5 Single photon emission computed tomography imaging 28
2.5.1. Backprojection and filtered backprojection 30
2.5.2. Iterative reconstruction techniques 35
2.6. Conclusions 39

Chapter 3 Corrections for Quantitative Gamma Camera Imaging

3.1. Introduction 40
3.2. Attenuation correction 41
3.3 Scatter correction 47
3.4 Correction for the partial volume effect 54
3.5 Correction for depth dependent collimator response 57
3.6 Incorporation of corrections in iterative reconstruction 62
3.7 Three dimensional (3D) reconstruction 67
3.8 Clinical applications of correction techniques 69
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3.8.1 Internal dosimetry for targeted radionuclide therapy 71
3.8.2 Myocardial perfusion imaging (MPI) 75
3.8.3 Skeletal studies 83
3.8.4 Renal studies 86
3.8.5 Lung studies 88
3.8.6 Thyroid studies 92
3.8.7 Brain studies 95
3.9 Conclusions 96

Chapter 4 Baseline Characteristics of the Gamma Camera 98

4.1 Introduction 98
4.2 Measurement of planar gamma camera performance
4.2.1 Method 100
4.2.1.1 Uniformity 100
4.2.1.2 Energy resolution 101
4.2.1.3 System spatial resolution 102
4.2.1.4 Sensitivity 103
4.2.2 Results 103
4.2.3 Planar quality control measurements 104
4.2.3.1 Method 104
4.2.3.2 Results 105
4.2.4 Investigation of change in planar spatial resolution
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with source-camera separation 108
4.2.5 Conclusion 111
4.3 CT performance measurements 111
4.3.1 Method 111
4.3.2 Results 113
4.3.3 Conclusions 116
4.4 SPECT reconstruction software performance 116
4.4.1 Method 116
4.4.2 Results 119
4.4.2.1 Uniform cylinder 119
4.4.2.2 Hot rods 119
4.4.2.3 Concentric rings 120
4.4.2.4 Spatial resolution with a line source 121
4.4.3 Conclusions 121
4.5 SPECT performance measurements 122
4.5.1 Centre of rotation offsets 122
4.5.1.1 Method 122
4.5.1.2 Results 123
4.5.2 SPECT performance phantom measurements 113
4.5.2.1 Conservation of counts measurements 125
4.5.2.2 Effect of FBP filters on conservation of counts 126
4.5.2.3 Cylindrical phantom uniformity measurements 126
4.5.2.4 Results 127
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4.5.3 Anthropomorphic phantom measurements 131
4.5.3.1 Method 131
4.5.3.2 Results 133
4.5.3.3 Conclusion 134
4.6 Discussion 135

Chapter 5 Validation of Method 138

5.1. Introduction 138
5.2.Use of positioning jig 139
5.2.1 Method 140
5.2.2 Results 142
5.3. Establishment of ROI 146
5.3.1 Method 147
5.3.2 Results 148
5.4 Repeat measurements for error analysis 149
5.4.1 Method 151
5.4.2 Results 151
5.5 Determination of rotational orientation 152
5.5.1 Method 152
5.5.2 Results- Symmetrical phantom 156
5.5.3 Results – Non-symmetrical phantom 163
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5.6 Discussion 175

6 Chapter 6 Quantitation Measurements 176

6.1 Introduction 176
6.2 Establishment of SPECT sensitivity 177
6.2.1 Method 177
6.2.2 Results 179
6.2.3 Calculated activities using point source sensitivity 180
6.2.4 Calculated activities using source A sensitivity 182
6.2.5 Calculated activities using source B sensitivity 184
6.3.1 Calculated activities using cylindrical phantom sensitivity
6.3.2 Discussion on sensitivity values 187
6.4 Effect of position on quantitation with a single phantom insert
6.3.1 Method 191
6.3.2 Results 192
6.4 Quantitation measurements with two sources 194
6.4.1 Method 194
6.4.2 Results – Symmetrical phantom 196
6.4.2.1 Variation in activity ratio 196
6.4.2.2 Variation in volume of cylindrical sources 199
6.4.2.3 Variation in background concentration 201
6.4.3 Results- Non-symmetrical phantom 205
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