effects of orthodontic appliances on diagnostic quality of mr images of the head

124 Pages·2015·2.26 MB·English

by  Dzmitry Zhylich

EFFECTS OF ORTHODONTIC APPLIANCES ON
DIAGNOSTIC QUALITY OF MR IMAGES OF THE
HEAD

By

Dzmitry Zhylich

A thesis submitted in conformity with the requirements
for the degree of Master of Science (Orthodontics)
Graduate Department of Dentistry
University of Toronto
© Copyright by Dzmitry Zhylich, 2015
EFFECTS OF ORTHODONTIC APPLIANCES ON DIAGNOSTIC QUALITY OF MR IMAGES OF THE
HEAD
Dzmitry Zhylich
MSc Degree, 2015
Discipline of Orthodontics, Faculty of Dentistry, University of Toronto
Toronto, Ontario, Canada

Abstract
Introduction: The influence of four common fixed orthodontic appliances on artifact formation and
diagnostic quality of head MR images produced by a 3 Tesla MR scanner was studied. Methods:
Stainless steel brackets, ceramic brackets, combination of ceramic brackets and steel molar tubes, and
multistranded steel mandibular lingual retainers were embedded into custom made Essix® trays for each
of 10 adult subjects. Head MR scans of nine regions were acquired for each subject wearing these trays.
Sagittal T1-weighted, axial T2-weighted, axial gradient-recalled, axial diffusion-weighted, non-contrast
axial MR angiography and axial fluid-attenuated inversion recovery MR sequences were included. Two
neuroradiologists evaluated image distortions and diagnostic qualities of the 13860 acquired images.
Results: Images were affected by appliance, head region and MR sequence. Conclusions: Head MR
images are differentially affected by the presence of orthodontic appliances. The appliance, region imaged
and MR sequence need consideration before imaging patients wearing different fixed orthodontic
appliances.

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Acknowledgments:
I would like to express my sincere gratitude to my primary supervisor Dr. Sunjay Suri for the
idea of the project and his great support and guidance through and through. I would also like to
thank my knowledgeable committee members: Dr. Bryan Tompson, Dr. Wendy Lou and Dr.
Andrea Doria for their advice and input during this study. I very much appreciate the work of the
radiologists Dr. Pradeep Krishnan and Prakash Muthusami who spent long hours reading
thousands of images as well as Dr. Manohar Shroff’s support and expertise.
My sincere thanks goes to very accommodating and professional MR technicians Ms. Tammy
Rayner-Kunopaski and Ms. Ruth Weiss.
I am very grateful to my patient colleagues who participated in the study.
Finally, I would like to thank my family, especially my wife Irina, son Antony and my mother
Safiya whose love and support gave me inspiration and strength to complete the project.

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Table of contents:
Chapter Page
1. Introduction 1
1.1 Orthodontic appliances and MRI 1
1.2 Current state of the literature on orthodontic appliances in MRI 3
1.3 Purpose and statement of the problem 4
1.4 Aims and objectives 4
1.5 Hypothesis 5
2. Materials and methods 6
2.1 Study sample 6
2.2 Consent 7
2.3 Appliances tested 7
2.4 Procedures 8
2.5 Pilot test 9
2.6 Main study 12
2.7 Statistical analysis 17
3. Results 18
3.1 Pilot test: assessment of MR image distortion produced by the Essix® tray 18
material
3.2 Main study: comparison of the distortion scores between different subjects 18
3.3 Comparison of the distortion scores between different anatomic regions 25
3.4 Comparison of the distortion scores between different MR sequences 31
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3.5 Comparison of the distortion scores of different orthodontic appliances 37
3.6 Calculation of inter and intrarater agreements 71
4. Discussion 73
4.1 Scientific novelty of the study 74
4.2. Explanation of findings 76
4.3 Recommendations for clinical practice. 80
4.4 Strengths and limitations of the study 82
4.5 Recommendations for future studies 84
5. Conclusions 86
6. Bibliography 87
7. Appendices 91
7.1 University of Toronto Research Ethics Board approval 91
7.2 The Hospital for Sick Children Research Ethics Board approval 93
7.3 Invitation letter to subjects for participation 94
7.4 Research consent form 98
7.5 MRI screening form 108
7.6 Case Report Form 109
7.7 Randomized order of the appliances for 10 subjects 110
7.8 Representative sagittal and axial images for scores 1 to 5 111

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List of figures:
Figure Description Page
1. Appliances tested 13
2. Complete sets of maxillary and mandibular appliances 14
3. Flowchart of image acquisition 16
4. Mean distortion scores by the appliance type for each subject 20
5. Diagnostic scores for stainless steel brackets and tubes for each subject 21
6. Diagnostic scores for ceramic brackets for each subject 22
7. Diagnostic scores for ceramic brackets and stainless steel buccal tubes for each 23
subject
8. Diagnostic scores for ceramic brackets for each subject 24
9. Mean diagnostic scores for different appliances for each anatomic region 26
10. Diagnostic scores for stainless steel brackets and tubes for each anatomic region 27
11. Diagnostic scores for ceramic brackets for each anatomic region 28
12. Diagnostic scores for ceramic brackets and stainless steel buccal tubes for each 29
anatomic region
13. Diagnostic scores for lingual retainer for each anatomic region 30
14. Diagnostic scores of different appliances for each sequence 32
15. Diagnostic scores for stainless steel brackets and tubes for each MR sequence 33
16. Diagnostic scores for ceramic brackets for each MR sequence 34
17. Diagnostic scores for ceramic brackets and stainless steel tubes for each MR 35
sequence
18. Diagnostic scores for lingual retainer for each MR sequence 36
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19. Mean diagnostic scores for different anatomic regions according to the MR 39
sequence for the appliance type: stainless-steel brackets and buccal tubes
20. Diagnostic scores for stainless steel brackets and tubes for sagittal T1 sequence 40
according to anatomic regions
21. Diagnostic scores for stainless steel brackets and tubes for axial T2 sequence 41
according to anatomic regions
22. Diagnostic scores for stainless steel brackets and tubes for axial gradient-recalled 42
sequence according to anatomic regions
23. Diagnostic scores for stainless steel brackets and tubes for axial diffusion-weighted 43
sequence according to anatomic regions
24. Diagnostic scores for stainless steel brackets and tubes for axial MRA sequence 44
according to anatomic regions
25. Diagnostic scores for stainless steel brackets and tubes for axial FLAIR sequence 45
according to anatomic regions
26. Mean diagnostic scores for different anatomic regions according to the MR sequence 47
for the appliance type: ceramic brackets
27. Diagnostic scores for ceramic brackets for sagittal T1 sequence according to 48
anatomic regions
28. Diagnostic scores for ceramic brackets for axial T2 sequence according to anatomic 49
regions
29. Diagnostic scores for ceramic brackets for axial gradient-recalled sequence 50
according to anatomic regions
30. Diagnostic scores for ceramic brackets for axial diffusion-weighted sequence 51
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according to anatomic regions
31. Diagnostic scores for ceramic brackets for axial MRA sequence according to 52
anatomic regions
32. Diagnostic scores for ceramic brackets for axial FLAIR sequence according to 53
anatomic regions
33. Mean diagnostic scores for different anatomic regions according to the MR 55
sequence for the appliance type: ceramic brackets and stainless steel buccal tubes
34. Diagnostic scores for ceramic brackets + steel buccal tubes for sagittal T1 56
sequence according to anatomic regions
35. Diagnostic scores for ceramic brackets + steel buccal tubes for axial T2 sequence 57
according to anatomic regions
36. Diagnostic scores for ceramic brackets + steel buccal tubes for axial 58
gradient-recalled sequence according to anatomic regions
37. Diagnostic scores for ceramic brackets + steel buccal tubes for axial 59
diffusion-weighted sequence according to anatomic regions
38. Diagnostic scores for ceramic brackets + steel buccal tubes for axial MRA 60
sequence according to anatomic regions
39. Diagnostic scores for ceramic brackets + steel buccal tubes for axial FLAIR 61
sequence according to anatomic regions
40. Mean diagnostic scores for different anatomic regions according to the MR 63
sequence for the appliance type: lingual retainer
41. Diagnostic scores for lingual retainer for sagittal T1 sequence according to anatomic 64
regions
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42. Diagnostic scores for lingual retainer for axial T2 sequence according to anatomic 65
regions
43. Diagnostic scores for lingual retainer for axial gradient-recalled sequence according 66
to anatomic regions
44. Diagnostic scores for lingual retainer for axial diffusion-weighted sequence according
66
to anatomic regions
45. Diagnostic scores for lingual retainer for axial MRA sequence according to anatomic 68
regions
46. Diagnostic scores for lingual retainer for axial FLAIR sequence according to 69
anatomic regions
47. Approximate relative distances from the orthodontic appliances to the anatomic 77
regions of the head assessed in the study

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List of tables:
Table Description Page
Table 1: Parameters of the MR sequences used 10
Table 2: Modified ROC (receiver operating characteristic) score system used for 11
MR image diagnostic quality determination
Table 3: Mean distortion scores with standard deviations (in brackets) by the 19
appliance type for each subject, overall mean distortion scores for each
appliance and pairwise comparisons with scores of ceramic brackets
Table 4: Mean distortion scores with standard deviations for different appliances 25
according to the anatomic regions
Table 5: Mean distortion scores with standard deviations for different appliances 31
according to the imaging sequence
Table 6: Mean diagnostic scores with standard deviations for different anatomic 38
regions according to the MR sequence for the appliance type: stainless steel
brackets and buccal tubes
Table 7: Mean diagnostic scores with standard deviations for different anatomic 46
regions according to the MR sequence for the appliance type: ceramic brackets
Table 8: Mean diagnostic scores with standard deviations for different anatomic 54
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