PhD Thesis Examination of Grey Value Accuracy and Improvement of Image Quality in Cone Beam Computed Tomography (CBCT) Mark Plachtovics, DMD 2015 Szeged, Hungary Examination of Grey Value Accuracy and Improvement of Image Quality in Cone Beam Computed Tomography (CBCT) PhD Thesis Mark Plachtovics, DMD Department of Oral Surgery Faculty of Dentistry University of Szeged Graduate School of Clinical Sciences Research in Dental Medicine Supervisor: Dr.Katalin Nagy, DMD, PhD, DDS, Professor Head of the Programme: Dr. János Minárovits, MD, DSc, Professor 2015 i Preliminary method oriented publications Plachtovics M. Digital Volume Tomography: Cone beam CT imaging in dentistry, oral and maxillofacial surgery (original article in Hungarian: A Digitális Volumentomográfia: Cone Beam CT-k a fogászatban, az arc-, állcsont- és szájsebészetben.) MRadiol 2009;83:254-262. Plachtovics M. Practical advice on the application of cone beam CT imaging in implantology I. (original article in Hungarian: Gyakorlati tanácsok a digitális volumentomográfia implantológiai alkalmazásához I.) Implantológia 2011;8:22-27. Plachtovics M. Practical advice on the application of cone beam CT imaging in implantology II. (original article in Hungarian: Gyakorlati tanácsok a digitális volumentomográfia implantológiai alkalmazásához II.) Implantológia 2012;9:30-38. Publications directly related to the dissertation I Paper 1: Plachtovics M, Patonay L, Kerenyi T. What Pal Szechenyi's tooth tells us: Modern investigation of a tooth with digital volume tomography. In Lilla Alida Kristof and Vilmos Toth (ed.): In honour of Archbishop Pal Szechenyi. Contribution for the path of life and the results of the study of the mummy of Nagycenk. (Original chapter and book in Hungarian: Amiről Széchényi Pál foga mesél. Korszerű fogvizsgálat DVT-vel. In: Széchényi Pál érsek emlékezete. Adalékok az életúthoz és a nagycenki múmia vizsgálatának eredményei.) Universitas-Győr Nonprofit Kft., 2012. Győr, Hungary. ISBN 978-963-9819- 95-5. pp. 136-141. II Paper 2: Plachtovics M, Goczán J, Nagy K. The effect of calibration and detector temperature on the reconstructed Cone Beam CT image quality. A study for the work-flow of the iCAT Classic equipment. Oral Surg Oral Med Oral Pathol Oral Radiol. 2015;119:473-480. doi: 10.1016/j.oooo.2014.12.009. Epub 2014 Dec 31. IF: 1.46 ii III Paper 3: Molnar G, Plachtovics M, Baksa G, Patonay L, Mommaerts MY. Intraosseous territory of the facial artery in the maxilla and anterior mandible: Implications for allotransplantation. J Craniomaxillofac Surg. 2012;40:180-184. doi: 10.1016/j.jcms.2011.03.019. Epub 2011 Apr 1. IF: 1.61 IV Paper 4: Plachtovics M, Bujtar P, Nagy K, Mommaerts MY. High-quality image acquisition by double exposure overlap in cone beam computed tomography. Oral Surg Oral Med Oral Pathol Oral Radiol. 2014;117:760-767. doi: 10.1016/j.oooo.2014.02.024. Epub 2014 Mar 13. IF: 1.46 Cumulative Impact Factor: 4.53 Additional publications Pataky L, Plachtovics M. About Cone Beam CT Imaging (original article in Hungarian: A Cone Beam CT-kről.) Dental Express 2006;9:3-6. Plachtovics M. Of additional interest from the world of Cone Beam CT Imaging (original article in Hungarian: További érdekességek a 3D CBCT világából.) Dental Hírek 2009;13:28-30. iii Abbreviations AD apparent density CBCT cone-beam computed tomography CCD charge-coupled device COLD COLD means that the CBCT acquisition was taken with no warming-up period and without calibration process of the flat panel detector. COLD+C COLD+C is the abbreviation for the scan taken directly after the start of the equipment with cold detector but after the calibration process. CP calibration process CT computed tomography DVT digital volume tomography EMI Electric and Musical Industries Ltd FOV field of view FPD flat panel detector GE General Electric HU Hounsfield unit ISI Imaging Sciences International LDPE low-density polyethylene MDCT multidetector computed tomography MRI magnetic resonance imaging MSCT multi slice computed tomography PET positron emission tomographic imaging RD raw data SCBCT sequential cone beam computed tomography SD standard deviation TLD thermoluminescent dosimeters US ultrasonography WARM The WARM operation mode represents that the CBCT machine was switched on for at least two hours before the scan but no detector calibration was performed. WARM+C WARM+C scan protocol is consistent with the cone beam computed tomography scan with the complete calibration sequence after the warming-up period. The two-hour warming-up period preceded the calibration process. WUP warming-up period 2D 2 dimensional 3D 3 dimensional iv TABLE OF CONTENTS 1 Historic Overview of Medical Imaging 1 1.1 Mapping-up the human body 1 1.2 Development of medical imaging 2 2 Introduction 8 2.1 Overview of the technical development of dentomaxillofacial X-ray imaging 8 2.2 Basic principles of Computed Tomography (CT) 15 2.3 Dental Cone Beam CT imaging 16 2.3.1 Nomenclature 16 2.3.2 Technical details 17 2.3.3 Advantages and disadvantages of dental CBCT 18 2.4 Various image artefacts in dental CBCT 20 2.4.1 Inherent artefacts 20 2.4.2 Procedure-related artefacts 22 2.4.3 Introduced artefacts 23 2.4.4 Patient motion artefacts 23 2.5 Quality improvement of images by post-processing methods 23 3 Aims 24 4 Materials and Methods 26 5 Results and Discussion 29 5.1 Focusing on X-ray scattering as the first basic problem 29 5.1.1 Examination of the magnitude of X-ray scattering on CBCT imaging 30 5.1.2 Examination of the possibility of mapping of dry soft tissue within a single tooth with the drastic reduction of X-ray scattering 32 5.2 Optimal density response for the dental CBCT imaging as the second basic problem; quality improvement by pre-processing and processing methods 34 5.2.1 Steady-state temperature and the calibration of the FPD as the result of the pre-processing work-flow 34 5.2.2 The calibration of the ideal concentration of the contrast material solution by mapping-up the angiosome of the human face 40 5.2.3 High-quality image acquisition in dental CBCT by using the concept of sequential cone beam computed tomography (SCBCT). The data collection as the third basic problem 44 6 Conclusions 48 7 Acknowledgments 50 8 References 51 9 Appendices A 1 1 Historic overview of medical imaging 1.1 Mapping-up the human body Throughout the ages, during different civilizations and various cultures, people were curious to know what is inside the human body. Although some of the driving force in this regard was related to medicine, there was nevertheless a recognizable quest for the development of anatomy. The first European attempt, in the 2nd century, was made by the Greek Galen of Pergamon (Figure 1) (Aelius Galenus or Claudius Galenus AD 129 – 216 [1]). A B Figure 1 A: Artist impression of Galen. B: The ruins of Pergamon. Galen’s principal interest was in human anatomy but, from about 150 BC [2], Roman law had prohibited the dissection of human cadavers. Because of this restriction, Galen performed anatomical dissections on living (vivisection) and dead animals, mostly focusing on pigs and primates [3]. This work was useful because the anatomical structures of these animals usually closely mirror those of humans. Galen clarified the anatomy of the trachea, and was the first to demonstrate that the larynx generates the voice [4,5]. In one experiment, Galen used bellows to inflate the lungs of a dead animal. In his work De motu musculorum, Galen explained the difference between motor and sensory nerves, discussed the concept of muscle tone, and explained the difference between agonists and antagonists [5,6]. Andreas Vesalius (Figure 2 A) (31 December 1514 – 15 October 1564) was a Brabantian (from what is modern-day Belgium) anatomist, physician, and author of the most influential seven-volume books on human anatomy, De humani corporis fabrica (On the Fabric of the Human Body). Vesalius is often referred to as the founder of modern human anatomy. His work Fabrica was in strong contrast to many previous anatomical models because the basis of Vesalius’s knowledge came from the anatomical dissection of the human 2 body. He was a professor at the University of Padua and later became Imperial Physician at the court of Emperor Charles V. A B C Figure 2 A: Portrait of Andreas Vesalius. B and C: Anatomic figures by Vesalius. Vesalius's Fabrica contained many intricately detailed drawings of human dissections, often in allegorical poses. Such pictures are shown in Figure 2 B and C. The Fabrica emphasized the priority of dissection and what has come to be called the ‘anatomical’ view of the body, seeing human internal functioning as an essentially corporal structure filled with organs arranged in three-dimensional space. This was in stark contrast to many of the anatomical models used previously, which had strong Galenic/Aristotelian elements as well as elements of astrology. This environment, which lasted from the second century (Galenius) to the sixteenth century (Vesalius), developed a strong desire to have the ability to see inside the human body [7]. 1.2 Development of medical imaging During many centuries the only way to visualize the inside of the human body was through dissection. With technical development, scientists had started to investigate the inside of the human body without its opening. In 1881, Alexander Graham Bell attempted to use magnets and sound waves to discover the location of the bullet that eventually killed U.S. President James A. Garfield [8]. After a lengthy period, during scientific experiments with various types of vacuum tube equipment, the discovery of X-rays in 1895, by the Bavarian physicist Conrad Röntgen, represented a major breakthrough (Figure 3 A). When X-rays were finally discovered, they found their way to medical applications within months [9]. 3 The original discovery by Röntgen, at the Physical Institute, Julius-Maximilian University, Würzburg, Germany, is recorded to be on 8 November 1895 [9-17]. During the discovery, he speculated that a new kind of ray might be responsible for the observation. Since 8th November was a Friday, instead of relaxing over the weekend, Röntgen took advantage of the time to repeat his experiments. In the following weeks he investigated many properties of the new rays he had temporarily termed ‘X-ray’. In fact, he virtually lived in his laboratory during that time. The new X-ray is called the ‘Röntgen ray’ in many languages [18]. A B C Figure 3 A: Wilhelm Conrad Röntgen (1845-1923). B: An artist’s impression of Röntgen’s work with Bertha Röntgen, his wife, producing the first medical X-ray image in early 1896. C: Hand with Rings: a print of one of the first of Wilhelm Röntgen's X-ray photographs. It shows the left hand of his wife [18]. Nearly two weeks after his discovery, he took the very first picture using X-rays of his wife Anna Bertha's hand. When she saw her skeleton she exclaimed ‘I have seen my death!’ (Figure 3 B and C) [10,18]. Röntgen receive the first Nobel Prize in Physics in 1901 [9,18]. The birthday of the Dental Radiograph is set at January 1896 by German dentist Otto Walkhoff (Figure 4 A) [9-11,16,17]. Needless to say, the world’s first dental radiograph had no diagnostic value (Figure 4 B). While it did prove that the X-ray could be used in dentistry, it was an overexposure (twenty-five minute exposure) [10,11,19] and also applied a high dose of radiation [11]. A B Figure 4 A: Otto Walkhoff (1860-1934) B: The first dental radiograph. 4 Professor József Iszlai (1840-1903) was the first dentist in Hungary to recognize the importance of the X-ray in dentistry (Figure 5A) [9]. In a book by Henrik Salamon [20] published in 1942, one can find a description of a certain piece of equipment called a ‘skiagram’. With this instrument, X-ray images could have been visualized directly without the use of a screen. At the beginning of the 20th century, in Hungary, the medical community had already recognized the importance and usage of dental X-ray imaging. Consequently, in the newly opened Stomatology Clinic (Mária street 52, Budapest, Hungary) on 14 February 1909, an independent dental X-ray laboratory was established on the first floor [20]. A B C Figure 5 A: Professor József Iszlai in 1902. B: Gusztáv Grossmann (1878-1957). C: Dr Hisatugu Numata [10,19,20]. William Herbert Rollins (1852-1929) was an American dentist and scientist who, in 1901, published the first paper about the dangers of X-ray radiation [19]. This publication was very timely because numerous irresponsible applications had appeared on the market (Figures 6 A and B) [10,11]. A B Figure 6 Illustrations of early irresponsible applications of radiation. A: ‘Biologically effective’ radioactive toothpaste. B: Photograph of a shoe-fitting test instrument. Public use prohibited in 1973 [10,11].