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Program Co-ordinator of Restorative Dentistry and Endodontics, Universitat Internacional de Catalunya, Barcelona, Spain

Consultant in Endodontics, Endodontic Postgraduate Unit, Guy’s and St Thomas’ NHS Foundation Trust, London, UK and Specialist practice, London, UK

Specialist Registrar in Dental and Maxillofacial Radiology, Guy’s and St Thomas’ NHS Foundation Trust, London, UK

Head of Operative Dentistry, National University of Malaysia, Kaula Lumpur, Malaysia

Consultant/Honorary Senior Lecturer in Endodontics, King’s College London Dental Institute, London, UK and Specialist practice, London, UK

Associate Professor and Chair, Division of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands

General Practitioner and Chairperson of Tsukiboshi Dental Clinic, Aichi, Japan and Clinical Professor, Tohoku University, Graduate School of Dentistry, Japan

Postgraduate in Endodontics, Division of Endodontology, Academic Centre for Dentistry Amsterdam (ACTA), Amsterdam, The Netherlands

Senior Lecturer/Honorary Consultant in Dental and Maxillofacial Radiology, King’s College London Dental Institute, London, UK

Berlin, Chicago, Tokyo, Barcelona, Bucharest, Istanbul, London, Milan, Moscow, New Delhi, Paris, Beijing, Prague, Riyadh, São Paulo, Seoul, Singapore, Warsaw and Zagreb

All rights reserved. This book or any part thereof may not be reproduced, stored in a retrieval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, or otherwise, without prior written permission of the publisher.

Acknowledgements

Francesco Mannocci, per i tuoi saggi consigli;
Andrew Dawood for being ahead of the game, and introducing me to the ‘third dimension’ in 2006;
The endodontic staff and postgraduate team at King’s College London Dental Institute.

Jackie Brown, Marta Varela, Eric Whaites and Georgina Harvey for their invaluable assistance.

JA Baart, Department of Maxillofacial Surgery, and JA Castelijns, Head and Neck Radiology, of the VU Medical Centre, Amsterdam, Netherlands.

Eilis Lynch at Ennis Periodontology and Implant Clinic, and my colleagues at Riverpoint Specialist Dental Clinic, Limerick.

Foreword

The primary objectives of Restorative Dentistry are to relieve pain, prevent tooth loss and restore lost oral and dental tissues to meet the aesthetic, psychological and functional needs of patients. These key objectives often require the coordination of multi-professional teams, which in the context of this book include Endodontists.

The use of cone beam computed tomography (CBCT) in dentistry, and specifically endodontics, is controversial, and although several position statements and guidance documents have been published in recent years, there remains a lack of knowledge and a degree of misunderstanding about the benefits and risks associated with this diagnostic tool. Without doubt, there has been a need for a comprehensive and authoritative textbook that covers all the elements of this subject in relation to diseases of the pulp and periapical region. Thus, this new book on CBCT and endodontics is timely, and provides a rich resource for specialists in Endodontology and Maxillofacial Radiology. It is also an excellent reference book for general dentists, trainees on clinical training pathways, as well as students on specialist postgraduate programmes and undergraduates using CBCT.

The book is user-friendly and is divided into two sections. The initial chapters (1–4) cover the important and essential aspects of radiology in relation to CBCT, which is an area that is often underemphasised and misunderstood. The remaining chapters (5–11) are dedicated to the various applications of CBCT in endodontics. An essential focus running throughout the book is the understanding that, as CBCT is associated with a higher effective patient radiation dose, the ALARA principles are paramount.

Each chapter is written by subject specialists who have a wealth of research and clinical experience. The book is extensively illustrated with conventional radiographic and CBCT images, all with comprehensive legends.

CBCT is a relatively modern imaging method that provides a substantial amount of clinically relevant information. The book provides an excellent review of the subject, emphasises case selection and is supported by key references to provide an evidence-based approach and a framework for the use of CBCT in endodontics.

Professor of Restorative Dentistry,
Dean of Education and Students, Cardiff University
Secretary of the European Society of Endodontology

Preface

Endodontics relies on radiographic imaging for diagnosis, treatment planning and the assessment of healing. However, conventional radiographic imaging has several well-documented limitations, which can result in an impaired diagnostic yield, and potentially influence treatment planning.

In recent years, cone beam computed tomography (CBCT) has become much more widely available and utilised in all aspects of dentistry, including endodontics. CBCT overcomes many of the limitations of conventional radiography and has been shown to be essential for the diagnosis and management of complex endodontic problems.

The editors of Cone Beam Computed Tomography in Endodontics are all experienced users of CBCT. In their clinical practice and academic/teaching roles, they recognised the need for a guide to illustrate the applications of CBCT in endodontics using the latest evidence and principles.

The aim of the book is two-fold; firstly, to give the reader a thorough account of the radiological aspects of CBCT; and secondly, to comprehensively illustrate the applications of CBCT in endodontics. The book emphasises the fact that, inherent in the responsible use of CBCT is the understanding that, as CBCT is associated with a higher effective patient radiation dose than conventional radiographic imaging, the prescription of CBCT must be justified, and the associated radiation exposure be kept as low as reasonably achievable.

This book gives the reader a sound foundation on small field of view, high resolution CBCT and its applications in endodontics. However, one cannot overemphasise the fact that dental radiology is continuously evolving. As such, it is essential that CBCT users keep abreast of developments in dental radiology and maintain a contemporaneous core knowledge of both dental radiology and of CBCT, specifically.

Chapter 1The Limitations of Conventional Radiography and Adjunct Imaging Techniques

The differences and similarities between multidetector computed tomography and cone beam computed tomography

Introduction

Radiographic assessment is essential in every aspect of endodontics, from diagnosis to the management and assessment of treatment outcome (Forsberg, 1987a, b; Patel et al, 2015). Intraoral periapical radiography has historically been accepted as the most appropriate imaging system in endodontics. However, conventional periapical images yield limited information, which can potentially have an impact on diagnosis and treatment planning.

The purpose of this chapter is to describe the limitations of conventional periapical radiography, and to discuss the relative advantages and disadvantages of alternative imaging techniques.

Limitations of conventional radiographic imaging

Superimposition of three-dimensional anatomy

Conventional radiography results in three-dimensional (3D) structures being superimposed and displayed as a two-dimensional (2D) image (Nance et al, 2000; Cohenca et al, 2007). The resulting image allows complex dentoalveolar anatomy to be visualised only in the mesiodistal (clinical) plane, and provides limited information of the dental anatomy in the buccolingual (non-clinical) plane.

Radiographic 2D images prevent accurate assessment of the spatial relationship of the roots, and associated periapical lesions, to the surrounding anatomy (Cotti and Campisi, 2004). In addition, the location, nature, and shape of variations within the root under investigation (e.g. root resorption) may be difficult to assess (Patel et al, 2007; Whaites and Drage, 2013a). Diagnostic information in the missing ‘third dimension’ is of relevance when planning for endodontic surgery (Velvart et al, 2001; Bornstein et al, 2011). Useful information may include the position and angulation of the root/s in relation to the cortical plate, the thickness of the cortical plate itself, and the relationship of the root/s to adjacent anatomical structures, such as the inferior alveolar nerve, mental foramen or maxillary sinus (Lofthag-Hansen et al, 2007).

Additional parallax radiographic images, taken by changing the horizontal and/or vertical angulation of the X-ray beam in relation to the area under examination (Figs 1-1 and 1-2), may be used to enhance assessment of the spatial relationships of the imaged anatomical structures (European Society of Endodontology, 2006; Davies et al, 2015). However, these additional images will still only provide limited information (Soğur et al, 2012; Kanagasingam et al, 2015).

Fig 1-1 Horizontal parallax. The right radiograph has a 10-degree shift to aid visualisation of the two separate canals, which allows the quality of the root canal fillings to be assessed more accurately in the mandibular central incisors.

Fig 1-2 Vertical parallax. A vertical beam shift (change in inclination) has caused the periapical lesions (red arrows) associated with all three roots of this maxillary right first molar to disappear with the change of angulation in the right radiograph. Note that the defective distal margin on the left radiograph (yellow arrow) is also no longer visible on the right radiograph.

Geometric distortion

Intraoral periapical radiographic images should ideally be taken with a paralleling technique. The use of a biteblock to ensure the tooth and image receptor are parallel with one another, as well as the use of a beam aiming device to ensure the X-ray beam meets the tooth and image receptor at right angles, has been proven effective at creating a geometrically accurate image (Forsberg, 1987a, b, c).

An accurate image is obtained when the image receptor (X-ray film or digital sensor) is parallel to the long axis of the tooth, and the X-ray beam is perpendicular to both the image receptor and the tooth undergoing examination (Fig 1-3). This may be readily achievable in certain regions of the oral cavity, but may not be possible in some patients with e.g. small mouths or pronounced gag reflexes, and/or where the image receptor is poorly tolerated. Anatomical limitations, such as a shallow palatal vault, prevent the ideal positioning of the intraoral image receptor, causing incorrect long-axis orientation—which in turn results in geometric distortion (poor projection geometry) of the radiographic image (Figs 1-3 and 1-4). The ideal positioning of solid-state digital sensors may be even more challenging due to their size and rigidity, compared with conventional radiographic films and phosphor plate digital sensors (Patel et al, 2009a; Whaites and Drage, 2013a).

Ideal positioning of the image receptor may be possible when, firstly, the roots being imaged are relatively straight and, secondly, when there is sufficient space to position the image receptor correctly. If these objectives are not achieved (Fig 1-5), there will be a degree of geometric distortion and magnification. This may be particularly relevant in the posterior maxilla (Lofthag-Hansen et al, 2007). Over- or underangulated radiographs may reduce or increase the ‘apparent’ radiographic root length of the tooth under investigation (White and Pharaoh, 2014), and increase or decrease the size, or even result in the disappearance, of periapical lesions (Bender and Seltzer, 1961a, b; Huumonen and Ørstavik, 2002). A minimum 5% magnification of the imaged structures will occur, even when a ‘textbook’ paralleling technique has been employed (Vande Voorde and Bjorndahl, 1969).

Anatomical noise

Anatomical features within or superimposed over the roots being examined may obscure the area of interest, thereby preventing a thorough assessment of the imaged region (Gröndahl and Huumonen, 2004). These anatomical structures vary in radiodensity, and may be radiopaque or radiolucent. This phenomenon is sometimes referred to as ‘anatomical noise’ (Fig 1-6). The more complex the anatomical noise, the greater the reduction in contrast within the area of interest. The resulting radiographic image may be more difficult to interpret.

Fig 1-3 Geometric distortion. Although it may be possible to position the image sensor holder (and image sensor) parallel with the long axis of the crown and mid-third of the root, it is not possible to obtain a parallel relationship of the long axis of the entire tooth and root with the image sensor. The sagittal reconstructed CBCT image shows a parallel (and accurate) relationship of the mid-third root (green line) and the image sensor, and perpendicular X-ray beam (blue arrow). However, the apical third (red line) is not parallel to the image sensor or perpendicular to the X-ray beam, resulting in geometric distortion of the apical third of the root canal.

Fig 1-4 Geometric distortion. A distolingual canal (yellow arrow) can be seen on the intraoral radiograph (left). A coronal reconstructed CBCT image (right) clearly demonstrates how the distolingual root cannot be accurately assessed in the radiographic image. Neither the coronal (red line) nor apical (green line) halves of this root canal are parallel to the image sensor (yellow arrow), or perpendicular to the X-ray beam (blue arrow). This results in significant geometric distortion in this region of the image.

Fig 1-5 Geometric distortion. It may not be possible to position the image sensor in the ideal position, resulting in distortion of the resulting image. When imaging these maxillary left premolar teeth, the anatomical constraints of a shallow palate have prevented a paralleled image from being obtained.

Fig 1-6 Anatomical noise. (a) A periapical radiolucency is clearly seen, and is associated with the maxillary left incisor (yellow arrow). (b) A second radiograph taken at a 10-degree horizontal shift reveals an additional periapical radiolucency (red arrow) associated with the maxillary left incisor. This ‘new’ radiolucency is the incisive foramen, which in this case creates radiolucent anatomical noise mimicking a periapical lesion.

Fig 1-7 Anatomical noise. The superimposition of anatomical structures prevents complete and accurate assessment of the imaged teeth. As demonstrated in these parallax periapical radiographs, the maxillary sinus and zygomatic buttress may often create anatomical noise, which prevents visualisation of the periapical regions of the maxillary premolar and molar teeth.

Brynolf (1967, 1970a, b) demonstrated that superimposition of the incisive canal over the apices of the maxillary central incisors may complicate radiographic interpretation, i.e. the incisive foramen (anatomical noise) mimicked periapical lesions in healthy teeth.

Several studies have shown that periapical lesions confined to the cancellous bone may not be detected with conventional radiographic imaging (Bender and Seltzer, 1961a, b). It has been suggested that periapical lesions may be successfully detected when confined to cancellous bone, provided the cortical bone is thin and the anatomical noise minimal. Such lesions may go undetected beneath a thicker cortex. Anatomical noise also accounts for some underestimation of periapical lesion size in radiographic images (Shoha et al, 1974; Marmary et al, 1999; Scarfe et al, 1999).

The maxillary molar region is a complex anatomical region with a number of closely related structures, which include the maxillary sinus and zygomatic buttress (Fig 1-7).

Anatomical noise is dependent on several factors that may include: overlying anatomy; the thickness of the cancellous bone and cortical plate; and the relationship of the root apices to the cortical plate. Brynolf (1967) compared the radiographic and histological appearance of 292 maxillary incisor teeth to assess whether there was a relationship between the radiographic and histological features of the periapical lesions. Overall, there was a high correlation between radiographic and histological findings; this conclusion may have been related to the lack of anatomical noise in the specific area being assessed. The root apices of maxillary incisors lie very close to the adjacent cortical plate, and therefore erosion of this cortex may often occur soon after periapical inflammation ensues. In other areas of the jaws with increased anatomical noise, e.g. the posterior mandible with its thicker cortical plate, the correlation between histological findings and radiographic appearance may be less interrelated (Patel et al, 2009b).

Follow-up radiographs

Sequential radiographic images, taken over a period of time, are required when determining endodontic treatment outcomes (European Society of Endodontology, 2006). An accurate comparison can only be made when these images have been standardised with respect to radiation geometry, density, and contrast. Poorly standardised radiographs may lead to misinterpretation of the disease status (Bender et al, 1961a, b).

The use of customised bite blocks may be helpful in obtaining standardised images, but even then, no two images will be identical.

Advanced radiographic techniques for endodontic diagnosis

In order to overcome the limitations of conventional intraoral radiographs, a number of alternative imaging techniques to complement periapical radiography have been suggested. These include:

Magnetic resonance imaging

Magnetic resonance imaging (MRI) is a specialised technique that utilises hydrogen atoms (one proton and one electron) and a magnetic field to produce an a magnetic resonance (MR) image. This imaging technique does not use ionising radiation.

For image acquisition, the patient is positioned within an MRI scanner that creates a strong magnetic field around the area being imaged (Fig 1-8a). Tissues that are composed of water contain protons (hydrogen atoms). Energy from the oscillating magnetic field is temporarily applied to the patient at the appropriate resonant frequency. This aligns the protons contained along the long axis of the magnetic field and the patient’s body. A pulsed beam of radio waves, with a similar frequency to the patient’s spinning hydrogen atoms, is then transmitted perpendicular to the magnetic field. This misaligns the hydrogen protons, resulting in an alteration of their axis of rotation from a longitudinal to a transverse plane (Fig 1-8b). The atoms behave like several mini bar magnets, spinning synchronously with each other. This generates a radio signal (resonance) that is detected by the receiver within the scanner (Fig 1-8c). Similar radio signals are detected as the hydrogen protons relax and return to their original (longitudinal) direction. A computer processes the receiver information, and an image is thereby produced (White and Pharaoh, 2014; Whaites and Drage, 2013b).

MRI has been used for the investigation of soft tissue lesions in salivary glands, the investigation of the temporomandibular joint, for tumour staging (Goto et al, 2007), and for the treatment planning of dental implants (Imamura et al, 2004; Monsour and Dhudia, 2008).

The MRI technique has been used to assess a cohort of patients with periapical disease. With MRI, it was possible to differentiate the roots of multirooted teeth, and smaller branches of the neurovascular bundle could be clearly identified entering apical foramina. The presence and nature of periapical lesions could also be determined, as could the remodelling of the cortical bone. An important advantage of MRI is that, unlike computed tomography (CT) imaging, it is not affected by artefacts caused by metallic restorations (Eggars et al, 2005).

There are several limitations to MRI, including poor resolution when compared with conventional radiographic images. The scanning times involved with the MRI technique are lengthy, and the cost and maintenance of the imaging hardware results in the scanners seldom being found anywhere but in dedicated radiology units. The dental hard tissues (e.g. enamel and dentine) cannot be differentiated from one another, or from metallic objects, as they all appear radiolucent. This currently limits the endodontic applications of MRI. Finally, MRI scanners need highly trained radiographers to take the image, and radiologists to interpret the resulting scan.

To make the MRI technique more applicable to the oral cavity, researchers have developed a technique that utilises an intraoral loop coil placed in the occlusal position. This technique has been shown to detect caries lesions in vivo (Tymofiyeva et al, 2009; Idiyatullin et al, 2011), and to differentiate between sound and carious dentine due to the porosity of the latter, which in turn has a higher water content (Tymofiyeva et al, 2009). Coil MRI has also been used to determine the distance from caries lesions to the pulp. While the potential applications of coil MRI show promise, problems are acknowledged due to patient movement and the effect of certain dental materials on image quality. However, it would seem that the MRI technique is less sensitive to dental materials than other techniques, such as CT imaging (Eggars et al, 2005).

Fig 1-8 (a) The magnetic resonance imaging (MRI) technique involves the formation of a magnetic field around the area being imaged. The protons within the magnetic field and body then become aligned along the long axis. (b) A pulsed beam of radio waves is transmitted perpendicular to the long axis of the magnetic field, causing the protons to be disrupted, and altering their axis of rotation. (c) The disrupted protons spin synchronously with one another, producing a faint radio signal, which in turn is sent back to a receiver. A computer processes the resulting signal and the image is produced.

One of the limitations of the conventional MRI technique is that the densely calcified dental tissues cause deterioration of the MRI signal before digitisation is achieved, which results in weakened or absent MRI signals. Thus, the majority of MRI studies in relation to dentistry have been on the dental soft tissues, including the pulp and periodontal ligament.

In addition to the limitations previously described, coil MRI lacks the ease of use of other imaging techniques. Furthermore, the costs involved with coil MRI are significant. As a result, access to suitable coil MRI scanning equipment is limited.

Fig 1-9 Ultrasound. An extraoral transducer probe emits and detects the ultrasound (US) signal. The US signal is created using the piezoelectric effect.

Fig 1-10 Ultrasound (US). (a) This patient presented with a large, fluctuant swelling palatal to the maxillary right anterior teeth. (b) Periapical radiographs demonstrated a large radiolucency encompassing the apices of the root-treated maxillary right central incisor, lateral incisor and canine teeth. Two-dimensional radiographs (b to d) fail to provide information on the depth of the lesion and the location of resorption of the respective buccal and palatal cortical plates. (e) A US scan of the area was conducted by placing a probe extraorally over the region of interest. The resultant scan images the relative hyperechoic and hypoechoic regions, demonstrating the buccolingual extent of the periapical lesion, as well as the locations where the cortical plates have been resorbed.

Ultrasound

The ultrasound (US) technique is based on the reflection (echoes) of US waves at the interface between tissues that have different acoustic properties (Gundappa et al, 2006). Ultrasonic waves are created using the piezoelectric effect via a transducer (probe). The beam of US energy is emitted and reflected back to the same probe (i.e. the probe acts as both emitter and detector). A transducer detects the echoes and converts them into an electrical signal (Fig 1-9). The resulting real-time image is composed of black, white, and shades of grey. As the probe is traversed across the area of interest, new images are generated in real time. The intensity or strength of the detected echoes is dependent on the difference between the acoustic impedance of two adjacent tissues. The greater the difference between the tissues, the greater the distinction in the reflected US energy, resulting in higher echo intensity. Tissue interfaces that generate high echo intensity are described as hyperechoic (e.g. bone and teeth). Anechoic tissues (e.g. fluid-filled cysts) are those that do not reflect US energy (Fig 1-10). Images consisting of varying degrees of hyperechoic and anechoic usually have a heterogeneous profile. The Doppler effect (the change of sound frequency reflected from a moving source) can be used to assess arterial and venous blood flow (Whaites and Drage, 2013b).

Fig 1-11 Tuned aperture computed tomography (TACT). With this technique, 8 to 10 digital radiographic images are taken at different defined projection geometries. The images are reconstructed to provide 3D data, which may be viewed slice by slice.

US has been used to diagnose the full nature of periapical lesions (Cotti et al, 2003). In this study, 11 periapical lesions of endodontic origin were assessed with US imaging. Provisional diagnoses were made according to the echo images (hyperechoic and hypoechoic). The evidence of vascularity within the lesions was determined using the colour laser Doppler effect. The provisional diagnoses (seven cysts, four granulomas) were successfully confirmed by histology in all 11 cases. A similar study also concluded that US was a reliable diagnostic technique for determining the pathological nature (granulomas versus cysts) of periapical lesions (Gundappa et al, 2006). However, in both of these studies the apical biopsies were not removed together with the root apices, therefore making it impossible to confirm whether the assessed lesions were true or pocket cysts. Furthermore, the lesions were not serially sectioned, making accurate histological diagnosis unreliable (Nair et al, 1996). Therefore, the ability of US to assess the true nature of periapical lesions is questionable.

Doppler flowmetry has also been used to assess the outcome of orthograde root canal treatment in maxillary anterior teeth (Maity et al, 2011). It was demonstrated that healing could be established earlier with the Doppler technique when compared with conventional radiographs. Evidence of healing was apparent in the majority of cases after just 6 weeks when assessed with Doppler flowmetry.

US energy is unable to penetrate bone effectively and is therefore only useful when assessing periapical lesions with little or no overlying cortical bone. While US may be used with relative ease in the anterior region of the mouth, the positioning of the probe is more difficult against the buccal mucosa of posterior teeth. In addition, the interpretation of US images is limited to radiologists who have received relevant training.

Tuned aperture computed tomography

Tuned aperture computed tomography (TACT) is based on the concept of tomosynthesis (Webber and Messura, 1999). A series of 8 to 10 radiographic images are exposed at different projection geometries using a programmable imaging unit with specialised software to reconstruct a 3D data set, which can then be viewed slice by slice (Fig 1-11).

The advantage of TACT over conventional radiographic imaging is that there is less superimposition of anatomical noise over the area of interest (Tyndall et al, 1997). The overall radiation dose of TACT is no greater than one to two times that of conventional periapical X-ray exposure, as the total dose is divided among the series of exposures (Nair et al, 1998; Nance et al, 2000). Additional advantages claimed for this technique include the absence of artefacts resulting from radiation interaction with metallic restorations (see later section on CT). The resolution is reported to be comparable to 2D radiographs (Nair and Nair, 2007).

TACT appears to have potential benefits that may make it useful in the future. For the time being, however, the technique for the imaging of dentoalveolar anatomy should be considered as a research tool.

Fig 1-12 Computed tomography (CT). (a) A large periapical radiolucency associated with the maxillary left lateral incisor and canine teeth is revealed following periapical radiographic examination. (b) The gantry of the CT scanner contains the X-ray source and the imaging detectors. The patient is advanced through a circular aperture in the centre of the scanner. The patient is thereby scanned ‘slice by slice’ while being advanced through the scanner. (c) The reconstructed slices can then be observed individually in the imaged plane. In this case, the width and depth of the periapical radiolucency can be assessed at each of the axial sections (red arrows).

Computed tomography

Computed tomography (CT) is an imaging technique that produces 3D radiographic images using a series of 2D sectional X-ray images. Essentially, CT scanners consist of a gantry that contains the rotating X-ray tube head and reciprocal detectors. In the centre of the gantry is a circular aperture through which the patient is advanced. The tube head and reciprocal detectors within the gantry either rotate synchronously around the patient, or the detectors take the form of a continuous ring around the patient and only the X-ray source moves within the detector ring (Fig 1-12a and b). The data from the detectors produces an attenuation profile of the particular slice of the body being examined. The patient is then moved slightly further into the gantry for the next slice of data to be acquired. The process is repeated until the area of interest has been fully scanned.

Fig 1-13 Multislice computed tomography (MSCT). To overcome the limitations of CT, the CT beam width is widened, and detectors are arranged in multiple rows, enabling the entire fan beam to be captured at any one time.

Early generation CT scanners acquired ‘data’ in the axial plane by scanning the patient ‘slice by slice’, using a narrow collimated fan-shaped X-ray beam passing through the patient to a single array of reciprocal detectors. The detectors measured the intensity of X-rays emerging from the patient.

Over the past three decades, there have been considerable advances in CT technology (Yu et al, 2009; Runge et al, 2015). To overcome the problems of conventional (single slice) medical CT imaging, which results in relatively poor image quality, the technique of multislice computed tomography (MSCT) was developed. Here, the CT beam is widened in the z-direction (beam width), and instead of a single detector, multiple detectors are arranged in parallel rows, so that a number of slices can be obtained by capturing the entire fan beam at any one time (Fig 1-13). This reduces the number of rotations of the X-ray tube and therefore the radiation dose. The number of detectors on MSCT scanners has increased, facilitating a greater number of simultaneously acquired images.

A number of researchers have evaluated MSCT and compared it to cone beam computed tomography (CBCT). One autopsy study demonstrated that the quality of small-volume CBCT scans might be better or at least equal to MSCT in assessing delicate anatomical structures, such as the periodontal ligament and bone trabeculae.

In addition to providing multiplanar 3D images, CT has several other advantages over conventional radiography. These include the elimination of anatomical noise and high contrast resolution, allowing differentiation of tissues with less than 1% physical density difference, compared with the 10% variation in physical difference that is required with conventional radiography (White and Pharaoh, 2014).

Acknowledgements

Foreword

Preface

Contents

Chapter 1

The Limitations of Conventional Radiography and Adjunct Imaging Techniques

Introduction

Limitations of conventional radiographic imaging

Superimposition of three-dimensional anatomy

Geometric distortion

Anatomical noise

Follow-up radiographs

Advanced radiographic techniques for endodontic diagnosis

Magnetic resonance imaging

Ultrasound

Tuned aperture computed tomography

Computed tomography