Atlas Of Cone Beam Imaging For Dental Applications 2nd Edition Dale A.Miles

Tôi choáng ngợp và có phần khiêm tốn trước sự thành công ngoài mong đợi của ấn bản đầu tiên của tập bản đồ này. Tôi cũng biết ơn sâu sắc nhiều đồng nghiệp đã tiếp cận tôi tại các cuộc hội thảo để nói với tôi rằng họ giữ cuốn sách này bên cạnh khi họ kiểm tra khối lượng chùm tia hình nón của họ cũng như nhiều người khác đã yêu cầu tôi ký vào bản sao của Ấn bản đầu tiên. Rõ ràng, cuốn sách đã tạo ra một tác động trong kỷ nguyên mới đầy thú vị của ngành Xquang răng hàm mặt và răng miệng. Trong ấn bản thứ hai được cập nhật này, tôi đã sử dụng thuật ngữ chụp cắt lớp vi tính chùm tia hình nón (CBCT) thay vì hình ảnh thể tích chùm tia hình nón (CBVI). Tôi vẫn tin rằng thuật ngữ đúng hơn cho phương thức này là hình ảnh thể tích. Tuy nhiên, như hầu hết các đồng nghiệp X quang của tôi đã chỉ ra, thuật ngữ CBCT được đặt trong các tài liệu nha khoa và y tế, vì vậy tôi đã quyết định, hơi miễn cưỡng, tự mình chấp nhận thuật ngữ này. Ngoài thay đổi nhỏ về tiêu đề, tôi đã thêm các trường hợp mới vào hầu hết các chương, phát triển một phần mới đề cập đến giải phẫu trong tập nhỏ và thêm ba chương mới để thảo luận về các ứng dụng cho CBCT trong nội nha, các rủi ro và trách nhiệm của CBCT, và các trường hợp được chọn từ thực hành X quang của tôi. Tôi tin rằng những bổ sung và cập nhật này đã củng cố cuốn sách và làm cho cuốn sách trở nên hữu ích hơn. Tôi đủ thông minh để biết những hạn chế của mình, và trong ấn bản này, tôi đã mời người đóng góp đầu tiên của tôi, Tiến sĩ Thomas McClammy , một nhà nội nha giỏi và một người bạn tuyệt vời. Ông đã viết chương 16 về việc sử dụng CBCT trong chuyên ngành nội nha. Là một người đầu tiên chấp nhận, Tiến sĩ McClammy đã đánh giá kỹ lưỡng, đau đớn trước quyết định mua một máy CBCT, và sau đó lao vào. Anh ấy giống như một đứa trẻ trong cửa hàng kẹo có ngôn ngữ, và sự nhiệt tình của anh ấy về phương thức này xuất hiện khi anh ấy giải thích tiện ích đáng kinh ngạc của nó trong thực hành nội nha. Cuối cùng, một số độc giả có thể đặt câu hỏi về một bác sĩ X quang đang cố gắng giải quyết các vấn đề trách nhiệm pháp lý phát sinh từ việc sử dụng CBCT. Tuy nhiên, tôi rất cảm thấy rằng một số đồng nghiệp đang chuẩn bị cho hành động pháp lý bằng cách kiên trì xem xét khối lượng CBCT chỉ để xác định vị trí cấy ghép phù hợp và bằng cách bỏ qua việc kiểm tra phần còn lại của dữ liệu hoặc giới thiệu đến bác sĩ chuyên khoa. Đây là tiêu chuẩn chăm sóc của nghề nghiệp khi một nhiệm vụ hoặc chẩn đoán nằm ngoài khả năng của chúng tôi. Hầu hết những gì tôi nêu trong chương 17 là lẽ thường. Tuy nhiên, tôi đang tự chấp nhận rủi ro này bằng cách trực tiếp giải quyết mối lo ngại này. Tôi làm điều đó vì sự an tâm của bản thân và để giáo dục đồng nghiệp. Tôi biết người đọc ấn bản thứ hai này sẽ thấy những phát triển này trong nội dung cuốn sách vừa cần thiết vừa thú vị. Thưởng thức và cảm ơn một lần nữa vì đã hỗ trợ

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Library of Congress Cataloging-in-Publication Data

© 2013 Quintessence Publishing Co, Inc

Quintessence Publishing Co, Inc

Editor: Bryn Grisham

Design: Ted Pereda

Production: Angelina Sanchez

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Table of Contents

Preface to Second Edition

Preface to First Edition

10 Orthognathic Surgery and Trauma Imaging

11 Paranasal Sinus Evaluation

12 Temporomandibular Joint Evaluation

13 Systemic Findings

14 Vertebral Body Evaluation

15 Selected Cases from Radiology Practice

16 Clinical Endodontics

17 Risk and Liability

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Preface to the Second Edition

I am overwhelmed and somewhat humbled by the unexpected success of thefirst edition of this atlas I am also deeply grateful to the many colleagueswho have approached me at seminars to tell me that they keep this bookbeside them when they are examining their cone beam volumes as well as tothe many others who have asked me to sign their copy of the first edition.Obviously, the book has made an impact in this exciting new era of oral andmaxillofacial radiology

In this updated second edition, I have used the term cone beam computed

tomography (CBCT) instead of cone beam volumetric imaging (CBVI) I still

believe that the more correct term for this modality is volumetric imaging.

However, as most of my radiology colleagues have pointed out, the term

CBCT is ensconced in the dental and medical literature, so I have decided,

somewhat reluctantly, to adopt the term myself In addition to the minor titlechange, I have added new cases to most chapters, developed a new section toaddress anatomy in the small volume, and added three new chapters todiscuss applications for CBCT in endodontics, the risks and liabilities ofCBCT, and selected cases from my radiology practice I believe that theseadditions and updates have strengthened the book and made it even moreuseful

I am smart enough to know my limitations, and in this edition, I haveinvited my first contributor, Dr Thomas McClammy*, a great endodontistand a great friend He has written chapter 16 about the use of CBCT in thespecialty of endodontics As an early adopter, Dr McClammy did his duediligence, agonized over the decision to purchase a CBCT machine, and thenplunged in He has been like a kid in the proverbial candy store, and hisenthusiasm about this modality comes through as he explains its incredibleutility in his practice of endodontics

Finally, some readers may question a radiologist attempting to addressliability issues arising from the use of CBCT However, I feel very stronglythat some colleagues are setting themselves up for legal action by persisting

in looking at the CBCT volumes only to determine a suitable implant site,and by neglecting the examination of the rest of the data or its referral to a

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specialist This is the profession’s standard of care when a task or diagnosis isbeyond our capability Most of what I state in chapter 17 is common sense.Nevertheless, I am taking this risk myself by addressing this concern directly.

I do it for my own peace of mind and to educate my colleagues

I know the reader of this second edition will see these developments inthe book’s content as both necessary and exciting Enjoy, and thanks againfor the support

* Thomas V McClammy, DMD, MS

Private Practice

Scottsdale, Arizona

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Preface to the First Edition

Like any innovation in the dental profession, the availability of cone beamvolumetric imaging (CBVI) has preceded the understanding of its use Ithappened with panoramic imaging as it did with digital radiographic imaging.The cone beam images in this atlas will educate dental professionals on how

to use CBVI technology to better visualize the diseases and disorders thatthey encounter with their patients

One aim of this atlas is to refresh the reader’s memory of anatomy Asdentists we never “worked” in the axial plane of section after our anatomytraining; we have lived our lives in a world of plain films or digital images,all in the format of 2D grayscale panoramic, intraoral, or lateralcephalometric images CBVI allows us to visualize patient anatomy andpathology like never before CBVI helps to reveal bony changes caused bypathology In addition, the level of anatomic detail in the 3D image setsmeans that clinicians placing implants no longer have to experience anxietyabout whether they are placed correctly CBVI allows us to determine theprecise location of the inferior alveolar nerve in relation to impactedmandibular third molars, which improves preoperative planning and reducespatient morbidity as well as our liability At last, we can see out patients’problems in a whole new manner—in 3D and color I hope this book willhelp you understand how CBVI can improve your clinical experiences andthe management of your patients’ treatment

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I am deeply appreciative to CyberMed USA and CyberMed International forallowing me to continue to test their software product and to use it in mypractice I happen to think that it is the premier software for examining conebeam computed tomography image data Mr Eusoon Han and the marketingteam at CyberMed USA work tirelessly to support the product and havehelped me understand the incredible tools within the software Thanks to all.Thanks once more to Prof C Young Kim, the CEO of CyberMedInternational for your product, your confidence, and your friendship Thisbook would not be possible without your product and support

A big thank you to Mr William Hartman of Quintessence for going theextra mile with my requests, and to Ms Lisa Bywaters and Ms Bryn Grishamfor their editorial support

Finally, love and special thanks to my wife, Kathryn, for her continuedsupport, love, confidence, sacrifice, and patience

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no resemblance to traditional medical computed tomography (CT) scansexcept in the display of the final product.

The process of image acquisition for CBCT machines is unlike traditionalmedical CT scanners in that the patient is not usually supine, the imagegathered is in a voxel (volume element) format, the x-ray dose absorbed bythe patient is substantially lower, appointment availability is much easier, and

it is less expensive In short, although this imaging modality producessignicant data volumes like medical CT, it is different and vastly superior totraditional CT data for specic dental applications

Dentists and dental specialists continue to be amazed at the incredibly preciseand profound information produced by CBCT scans, and they are realizingthat the data they receive will influence their treatment decisions like no otherimaging modality used in the profession in the past 100 years CBCT makesclinical decision making easier and more precise, patient treatment decisionsmore accurate, and visualization of the x-ray data more meaningful Dentistry

is moving away from “radiographic interpretation” and into “diseasevisualization,” and it could not have come at a better time

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Clinical Applications of CBCT

The applications for CBCT encompass most of the procedures cliniciansperform in their office Some applications for CBCT are listed in Box 1-1;examples of many of these applications are discussed in chapters 4 to 16.Additional applications will undoubtedly follow as clinicians learn about andbegin to appreciate the incredibly beneficial data this imaging modalitydelivers for improved treatment planning and clinical decision making

The evolution of implant technology, the technical skills and training ofdental professionals, and the patients’ desire for more permanent andpredictable restorative solutions to missing teeth all ensure that implantdentistry will remain the largest growth market for dental professionals andcommercial vendors for at least another decade Within 5 years, thereconstructed data in 2D/3D grayscale and color formats from CBCTmachines will become the standard of care for displaying patients’radiographic information for presurgical implant site assessment, implantplacement, and follow-up radiographic assessment CT, plain film imaging,and digital imaging modalities will probably become obsolete, at least forimplant dentistry applications

In recent years, the most rapid adoption of CBCT technology has been inthe endodontic community Manufacturers of limited field of vision (FOV)units have rigorously pursued the use of CBCT for endodontic imaging Inaddition, a position statement on the use of CBCT in endodontics wasdeveloped jointly by the American Association of Endodontists (AAE) andthe American Academy of Oral and Maxillofacial Radiology (AAOMR) andpublished in 2011.1,2 More clinicians are discovering that CBCT dataprovides tremendous advantages with its thin slices and precision inendodontic imaging For this application alone, sales of limited FOVmachines will continue to increase.

Another growing area for CBCT application is in the diagnosis andtreatment of obstructive sleep apnea (OSA) CBCT provides precision airwayassessment that can quantify the amount of airway opening as well as theeffects of different intraoral appliances Treatment of OSA improves patientquality of life while reducing the risk of cardiac complications related tohaving an obstructed airway This application of CBCT allows clinicians tosignificantly improve patient systemic health Construction of simpleintraoral appliances are essential for patients who have failed with continuouspositive airway pressure (CPAP) machines and have increased cardiac risk

Considerations for CBCT

The rapid rate of adoption of this technology has been surprising By thesummer of 2011, I had interpreted over 10,000 CBCT scans and the firstedition of this book was already out of print Now I spend close to 80% of myprofessional time interpreting CBCT scans and creating reports for clinicianswho use this technology I practice my specialty of oral and maxillofacialradiology both from my home in a dedicated radiology office environment aswell as while I travel to give lectures and consult I can operate just as mymedical radiology colleagues do and practice my specialty from virtuallyanywhere in the world because of global Internet access

Just as there are many different CBCT models available on the market, Ireceive the data volumes to interpret through many different avenues Goneare the days when we relied on 2D grayscale single images attempting torepresent 3D structures, viewed on light boxes under poor lighting

conditions, to help us make our clinical treatment decisions It is nowpossible to have 2D and 3D color “renderings” of each patient’s anatomy andsigns of clinical diseases/disorders.

Figure 1-1 shows this CBCT machine’s broad capabilities and power.Whether you are considering purchase of a machine for image acquisition inyour practice or simply accessing this technology by requesting a scan, youshould consider the following important questions:

1 How much data (number of images) do you need?

2 How large an area do you wish to evaluate?

3 Do you simply need 2D grayscale information for your decision?

4 Does the diagnostic task really require a CBCT?

5 Does every patient require this type of imaging?

6 Are you comfortable diagnosing all of the data in the volume?

7 What is your risk of missing an important occult finding?

Fig 1-1 This 3D color reconstruction is 42 mm thick and shows bilateral

calcification of the stylohyoid complex as well as the airway, the hyoidbone, and a cross section of the mandible

The data volume vs the single image

Before I address these questions, it is very important to understand the sizedifference between a data volume from a CBCT machine and traditional

static 2D grayscale images Each periapical image in a computer is about 300

kB in size, and three of these static intraoral images would fill a 1-MB floppydisk A digital panoramic image is about 5 to 7 MB, so approximately 100images could fit on a CD-ROM By contrast, each CBCT data volumeacquired for a single patient can range from 100 to 250 MB Only a fewpatient scans would fit on an 800-MB CD-ROM Even the so-called small-volume machines provide much more anatomical information than we havebeen accustomed to viewing and assessing (Fig 1-2)

Fig 1-2 Small-volume 3D color reconstruction of a 9-year-old patient with a

fractured mandible, rendered with Accurex (CyberMed International) Thefracture is easily identified in the anteroposterior view, and the 3D imagecan be rotated 360 degrees to see the fracture in any orientation

The impact of this data volume is huge, both literally and figuratively.Several large-capacity computers or servers are necessary to store thevolumes These data volumes should also be stored offsite via the Internet,which requires high-speed Internet connection

In addition, as a clinician, remember that you are responsible for all of the information in a volume, whether you order or acquire it, and whether it is

for your own use or for a referral client This tenet is still a source ofconfusion within the profession and is sometimes made more confusing byconflicting information provided by CBCT scanner manufacturers

Chapter 16 is new to this edition and discusses the risk and liability issuesspecific to CBCT volume data The chapter is illustrated with multiple

examples of occult findings from volume data that, if missed, would have led

to patient harm and delayed treatment Such oversights are unacceptable inthe dental profession, which has an implicit responsibility, like the medicalprofession, to do no harm No clinician can have a patient sign a formabsolving him/her from this important duty

The responsibility for looking at the entire data volume is analogous tolooking at a single panoramic radiograph No clinician would look at onlyhalf of a panoramic radiograph; clinicians must look at the entire image.CBCT data, although much more extensive, is no different, and if a cliniciancannot interpret the entire volume, referral to a specialist who can isnecessary Although this at first seems to represent a fundamental paradigmshift for all clinicians, it is really common sense and the standard of care that

we would use for any specialist referral When a clinician is in doubt about afinding, referral to a specialist is expected

In 1999 the American Dental Association’s house of delegates voted toaccept the application for specialty recognition from the AAOMR to createdentistry’s ninth specialty Now clinicians have specialists in oral andmaxillofacial radiology to whom they can refer difficult cases

In essence, this signals a move to the medical model of radiographicimaging; that is, we are shifting the responsibility for the overall imagefindings to a qualified radiologist after more than 100 years of cliniciansserving as their own radiology expert Plain films and digital intraoral andpanoramic images will still be used for some diagnostic procedures, butclinicians will probably need to enlist the services of an oral andmaxillofacial radiologist to look at patient CBCT data for occult pathology inless familiar anatomical regions It is both prudent and professional to do so

Table 1-1 shows the reportable findings in 381 CBCT cases in a 1-yearperiod (March 2005 to March 2006)

Common CBCT concerns

How much data do you need?

This is a very difficult question to answer Orthodontists or dentists who treatorthodontic problems in their patients require much more diagnosticinformation to assess a case and predict the outcome Currently, orthodonticassessment usually involves intraoral images; panoramic, cephalometric, andsometimes hand-wrist radiographs; and plaster casts Casts are mentionedbecause, in the future, clinicians will create 3D casts from the radiographicdata in the cone beam scan So the ability to acquire all the image data needed

in one single imaging procedure offers orthodontists a very distinct advantageover current methods Of course, the clinician does not always need all ofthose images on an 8-year-old patient at the initial record visit because it isunlikely that brackets will be placed on this patient until a few years later.Dentists should think about the information they need for each diagnostic

task before they take or order a CBCT scan This practice of applyingselection criteria is only now becoming standard practice.4

How large an area do you wish to evaluate?

Some CBCT machines acquire larger data volumes than others Dataacquisitions range from volumes of 4 x 4 cm2 to 22 x 22 cm2 Figure 1-3

demonstrates the differences in size and region of the head corresponding tothese volumes Not all clinicians need to see the entire skull or would wish to

be responsible for the occult pathology that might be encountered in the datavolume (slice) Radiologists and others wishing to assess the patient’s datavolume must scroll and be able to detect pathologic findings in as many as

512 slices (images) in three orthogonal planes (axial, sagittal, and coronal).Most clinicians are not comfortable with this task or do not have the time tolook at such a large amount of information

Fig 1-3 Comparison between the results from a small-volume machine

versus those from a large-volume machine (top) Axial slice of the middle of the condylar head (bottom) Larger area at approximately the same level.

Both volumes contain anatomical structures and cells, such as the middleear, mastoid cells, airway, and vertebral bodies, all of which would requireevaluation to determine whether pathology was present

Do you simply need 2D grayscale information for your decision?

It may not be necessary to have 3D color information for decision making atall The reconstruction of a panoramic image from a 250-MB data volumerequires anywhere from 4 to 70 times the amount of x-rays needed for atraditional panoramic film or digital image Therefore, a 2D digital panoramicradiograph from a full-featured panoramic machine can often suffice for thepreliminary visualization of the patient’s dentition, bone, condyles, andrelated anatomy (Fig 1-4)

Fig 1-4 Digital panoramic radiograph of a developing mixed dentition.

Except for the slightly ectopic resorption of the primary canine roots, thedentition is developing normally This child would not need a cone beamscan to make this determination The x-ray dose from the CBCT scan would

not be justified when this panoramic image would suffice.

Does the diagnostic task really require CBCT?

The clinician must determine if CBCT is even necessary for a particulardiagnostic task Applications and clinical indications to help with thisdetermination are discussed further in later chapters Detection of caries doesnot require a cone beam scan Periodontal bone loss can be evaluated bywell-positioned bitewing and periapical radiographs Some underestimation

of the alveolar architecture may occur in plain film or digital intraoralradiography, but this task again does not require CBCT’s thin slice data tosee bone problems If a patient exhibits systemic disease or a set of risk

factors that could accelerate the bone loss associated with periodontaldisease, a cone beam scan may be indicated to detect the disease earlier ormonitor the treatment success However, noninvasive, diagnosticimmunoassay tests performed on saliva could detect disease processes evenearlier without exposing the patient to any x-rays The clinician shouldcarefully consider the precise indications for this imaging modality and fullyexpect the images produced to result in a positive finding that could affect atreatment outcome Although x-ray doses are lower for any CBCT machinethan traditional medical CT, not every patient will require a CBCT scan.4

Does every patient require this type of imaging?

The short answer is an emphatic no Again, the clinician must consider the

application and prescribe this imaging test only for those patients who wouldactually benefit from a precise measurement for an implant site or a betteroutcome prediction based on the data volume acquired There are enoughreasons to use CBCT.5,6 Income generation is not one of them, nor is the

production of “prettier images.”

Are you comfortable diagnosing all of the data in the

volume?

Most clinicians are not comfortable with viewing radiographic data in anaxial plane We have rarely seen anatomical structures or pathology in a thinslice format that displays a plane of information of 1 mm (or less) Considerthe image in Fig 1-5 and ask yourself if you can identify the structureindicated by the white arrow

Fig 1-5 Try to identify the structure designated by the arrow, but do not be

surprised if you do not recognize it; most dentists have never seen thisstructure in this plane of section Note the total opacification of the rightmaxillary sinus As is conventionally done in medical CT and withpanoramic radiographs, we are viewing the patient from the foot end, so thepatient’s right side is the left side of the image The indicated structure is thecoronoid process

What is your risk of missing an important occult finding?

There is a lot of interest and some confusion about who is responsible for theimage data in the CBCT volume Is it the owner of the machine? Is it thereferring doctor? Is it the specialist whose office has the machine and

provides the radiographic data? The short answer is yes Everyone in these

various scenarios is liable The dentist, the dental specialist who onlyprovides images, and the radiographic imaging laboratory providing servicesfor the referring clinician would all be named in a lawsuit if a significantfinding were missed that resulted in harm to the patient The only solution is

to look at all the images in all planes of section and record any abnormality.Then refer this patient, with their images, for a consultation with theappropriate clinician If you do not feel capable of detecting and interpretingthe data, or if you do not have the time, you should probably consider using a

reading service, medical or dental, to review the image data set and report thefindings There are always many reportable findings in CBCT scans.1

References

1 American Association of Endodontists; American Acadamey of Oral andMaxillofacial Radiography AAE and AAOMR joint position statement.Use of cone-beam-computed tomography in endodontics Pa Dent J(Harrisb) 2011;78:37–39

2 American Association of Endodontists; American Academy of Oral andMaxillofacial Radiology Use of cone-beam computed tomography inendodontics Joint Position Statement of the American Association ofEndodontists and the American Academy of Oral and MaxillofacialRadiology Oral Surg Oral Med Oral Pathol Oral Radiol Endod2011;111:234–237

3 Miles DA Clinical experience with cone beam volumetric imaging: Report

of findings in 381 cases US Dent 2006;Sep:39–42

4 US Department of Health and Human Services, Public Health Service,Food and Drug Administration; American Dental Association, Council onDental Benefit Programs, Council on Dental Practice, Council onScientific Affairs The selection of patients for dental radiographicexaminations Revised 2004 Available at:

www.ada.org/sections/professionalResources/pdfs/-topics_radiography_examinations.pdf Accessed 14 March 2012

5 Ludlow JB, Davies-Ludlow LE, Brooks SL Dosimetry of two extraoraldirect digital imaging devices: NewTom cone beam CT and OrthophosPlus DS panoramic unit Dentomaxillofac Radiol 2003;32:229–234

6 Danforth RA, Miles DA Cone beam volume imaging (CBVI): 3Dapplications for dentistry Ir Dent 2007;10(9):14–18

Basic Principles of CBCT

The method of obtaining the patient’s data volume in cone beam computedtomography (CBCT) differs signicantly from that of conventional medicalcomputed tomography (CT) In medical CT scanning (previously termed

CAT [computed axial tomography]), the patient’s region of interest (ROI),

such as the head or abdomen or other body part, is selected As the x-raysource rotates around the ROI 60 times per minute, multiple sensors,consisting of either a gas or scintillator material (most commonly cesiumiodide), detect the x-ray beam The patient must be moved into the scanner aknown distance in the z-plane It is this distance—perhaps a centimeter, a halfcentimeter, or in cases where high resolution is required, as little as 1

millimeter—that determines the slice thickness This type of image

acquisition is very precise The data acquired are voluminous and, in turn, thepatient’s absorbed x-ray dose is also very large A typical CT scan for amaxillary implant site assessment may have a radiation dose as high as 2,100µSV, equivalent to the dose from about 375 panoramic lm or digital images.1

Image Acquisition

Unlike conventional CT, CBCT uses a narrow cone-shaped beam to rotate

194 to 360 degrees around the patient (Fig 2-1) The sensor is either an imageintensifier (II) that is coupled to either a charge-coupled device (CCD) (Fig 2-

2) or complementary metal oxide semiconductor (CMOS), or a thin filmtransistor (TFT) flat-panel type image receptor (Fig 2-3) The II is an oldertechnology that was developed to improve the viewing of fluoroscopicimages in the operating room during surgery In the past, the bright lights ofthe operating room made it a poor environment for surgeons to viewradiographic film, necessitating a device to “intensify” the resulting images.The major disadvantage of the II system is distortion at the periphery of itsimages The image pattern appears as a sphere or “ball” and thus the edgeregions are not ideal.

Fig 2-1 (left) Traditional medical CT detector array with x-ray source

rotates 360 degrees around the patient about 60 times per minute Thethickness of each image slice is determined by the distance (usually 1.0 to100.0 mm) the patient is moved through the gantry This exposes the patient

to a large dose of x-rays (right) A cone beam device, using the cone-shaped

beam, rotates around the patient The exposure factors are similar to thoseused for exposing traditional dental radiographs, so the x-ray dose to thepatient is substantially reduced

Fig 2-2a In the II system, a curved input phosphor, usually censium iodide,

introduces geometric distortion, which must be compensated for bysoftware The phosphor coating will degrade over time, so the II will have to

be replaced eventually—sometimes in as few as 3 or 4 years This olderimaging system is being replaced by flat-panel displays that offer the manyadvantages of a direct digital capture

Fig 2-2b This II system is stylish but large because of the II configuration.

The x-ray source is on the left of the patient The detector system is on theright side (Courtesy of Sirona USA.)

Fig 2-3a The flat-panel detector (FPD) system is a simple digital capture

system that uses only an x-ray source and a digital detector to capture theimage volume The devices made with this type of system are much lessbulky and therefore more ergonomic

Fig 2-3b This FPD system is the ProMax 3D (Courtesy of Planmeca USA.)

Flat-panel detectors (FPDs) are the newest image receptors for solid-statelarge-area arrays.2 These panels are expensive but offer some advantagesover the older II systems including less distortion, wider scale of contrast,and elimination of veiling glare

Compared with medical CT, CBCT doses are much lower, only about 40

to 500 µSv.1 The method of acquiring images is very different, and the

exposure factors (kV and mA) are much lower CBCT machines use either asingle FPD or an II (scintillator or phosphor screen) coupled to a series ofCCDs Table 2-1 illustrates the various current CBCT devices that areavailable More information about CCDs is available at the LearnDigitalwebsite.3

Several CBCT machines that were available in 2008, including the Iluma(Imtec) and the CBMercuRay (Hitachi), are no longer marketed in NorthAmerica However, manufacturers continue to introduce new machines andimprove their products For example, in North America, the supine units likethe original NewTom 9000 (QR Verona) have largely been replaced bymachines used in mobile CBCT units, such as the NewTom VGi (QRVerona) In addition, many manufacturers have introduced units with variablefields of vision (FOVs) or units with either an FPD or an II

Pixel vs Voxel Information

A pixel is a picture element It is a square that measures between 20 and 60

µm in size The size of the receptor area is the same whether it resides in anintraoral device, the TFT screen, or the II and solid-state combination device.CCDs and CMOSs for intraoral sensors are megapixel arrays, meaning thateach is one million pixels or more The larger flat panels, of course, use manymillions of pixels

A voxel is a volume element This describes a pixel that has a third side; it

is really a cubed array In CBCT this cube is made up of isotropic pixels with

equal sides In conventional medical CT, the pixel is nonisotropic, meaning

that two sides are equal, but the third (z-plane) is a selectable width,anywhere from 0.5 to 10 mm or more Figure 2-4 illustrates this difference

Fig 2-4 Traditional medical CT scanners use pixels The slice thickness is

determined by gantry movement The thickness, or z-plane, is determined

by the operator CBCT devices gather the volume information directly usingvoxels or cubes with known dimensions (typically 0.15 to 0.6 mm) AllCBCT slice thicknesses in the resulting image are much thinner than slicescreated by medical CT devices

Voxel Size and Image Resolution

Some manufacturers have touted voxel size as the sole measure of imageresolution and, by extension, image quality While voxel size is important, it

is not the only parameter that affects image quality Several studies have

addressed this point.6–8 Pauwels et al6 designed a cylindric prototype madefrom polymethyl methacrylate that could be scanned to assess the imagequality parameters of various CBCT machines In the results of the study, theauthor stated that “the voxel size itself provides only a crude prediction ofspatial accuracy.”6

Some types of assessment, like those for endodontic applications orimplant site assessment, may require the ability to select a very small voxelsize Implant site assessment necessitates image capture using a voxel size of0.2 mm or less On the other hand, orthodontic records, airway analysis, andtemporomandibular joint (TMJ) assessment do not usually require very smallvoxel sizes Regardless, almost every contemporary CBCT unit offersvariable voxel parameters so that operators can select a voxel size rangingfrom 0.076 to 0.125 mm

Factors affecting image quality and resolution

Clinicians must identify the particular diagnostic abilities that they need fromtheir CBCT units When planning to invest in a CBCT unit, clinicians mustconsider many parameters in addition to voxel size in order to select theCBCT unit that will best meet their needs:

• Detector type II versus FPD

• Head positioner The most stable is a three-point configuration seen in Fig2-3b

• Exposure factors The higher the milliamperage, the more photons available

to the detector However, the trade-off is a higher radiation dose

• Bit depth of the detector system Affects the quality of the imagereconstruction

• Reconstruction algorithm Inherited from the manufacturer

• Focal spot size at the anode Just like that found in standard intraoral x-raymachines

Radiation Dose

Although the dose from CBCT machines is significant, it is much less thanthat of traditional medical CT scans Recent data from Ludlow et al1estimates that the absorbed x-ray dose from a CBCT examination for aprocedure like an implant site assessment is between 1% and 25% the doseabsorbed from a medical CT scan This means that many dentally specificevaluations can be performed much more safely with CBCT than withmedical CT Thus, when a patient is being considered for any of theapplications cited in Box 1-1, a clinician cannot justify a medical CTprocedure since its radiation dose would greatly exceed that of a CBCTevaluation As more machines become available, more dose data are sure tofollow CBCT will become the imaging modality of choice for most dentaltasks requiring 2D/3D information for clinical decision making.

Legal Concerns

A few of my colleagues believe, or have been advised by CBCT machinemanufacturers, that they can simply have their patient sign a consent formstating that the dentist is not sufficiently trained to interpret the data beyondthe “dental bases” and is not to be held liable if a significant finding ismissed Actually, both the owner of the CBCT machine and the referringclinician have a co-responsibility to make sure the entire data volume isreviewed for occult pathology If they are not comfortable interpreting thevolume, it is up to them to make sure a qualified individual reads the volume

and reports the findings to them There is no ignoring this responsibility.

Consider a lawyer questioning a machine owner on a witness stand Here

is the hypothetic conversation, but I assure you it is a reasonable line ofinquiry

Lawyer: Doctor X, was Miss Y present in your office on June 30, 2006,

for an appointment to have a CBCT examination performed?

Doctor X: Yes.

Lawyer: Doctor X, what was the fee you charged Miss Y for said CBCT

examination?

Doctor X: Four hundred twenty-five dollars

Lawyer: Doctor X, did you collect that fee from Miss Y?

Doctor X: Yes

Lawyer: Well Doctor X, wouldn’t you call that “practicing dentistry”?

Doctor X: Yes, but …

Lawyer: Doctor X, just answer the question yes or no.”

Doctor X: Yes

As this fictional scenario demonstrates, when a clinician performs aprocedure, charges a fee, and collects that fee, it is considered practicingdentistry There is no other recourse than to ensure the images in the datavolume are reviewed— all 512 images in each of the three orthogonal planes:axial, sagittal, and coronal If a clinician does not feel qualified to do this, it isessential to have that volume read by an oral and maxillofacial radiologist or

a medical radiologist See chapter 17 for further discussion of risk andliability with cone beam imaging

References

1 Ludlow JB, Davies-Ludlow LE, Brooks SL Dosimetry of two extraoraldirect digital imaging devices: NewTom cone beam CT and OrthophosPlus DS panoramic unit Dentomaxillofac Radiol 2003;32:229–234

2 Floyd P, Palmer P, Palmer R Radiographic techniques Br Dent J1999;187:359–367

3 Miles DA LearnDigital website Available at: http://www learndigital.net.Accessed 19 March 2012

4 Hirsch E, Silva M Radiation doses from different conebeam-ct devices.Presented at the 11th Congress of the European Academy of Dento-Maxillo-Facial Radiology, Budapest, 27 Jun 2008

5 Brooks SL Answer to question #6120 submitted to “Ask the Experts.”

Health Physics Society website Available at:

http://hps.org/publicinformation/ate/q6120.html Accessed 19 March 2012

6 Pauwels R, Stamatakis H, Manousaridis G, et al Development andapplicability of a quality-control phantom for dental cone-beam CT J ApplClin Med Phys 2011;12:245–260

7 Loubele M, Jacobs R, Maes F, et al Image quality vs radiation dose offour cone beam computed tomography scanners Dentomaxillofac Radiol2008;37:309–318

8 Loubele M, Maes F, Schutyser F, et al Assessment of bone segmentationquality of cone-beam CT versus multislice spiral CT: A pilot study OralSurg Oral Med Oral Pathol Oral Radiol Endod 2006;102:225–234

Anatomical Structures in Cone Beam Images

To discern a potential problem in the cone beam computed tomography(CBCT) data volume, the clinician or radiologist must examine multipleslices in three planes of section: axial, sagittal, and coronal While cliniciansare quite familiar with many structures in the sagittal plane (since it is similar

to periapical, bitewing, panoramic, and cephalometric orientations), they arenot as familiar with these same structures as viewed in the coronal orespecially the axial plane To illustrate this point, I would ask you to lookback at Fig 1-5 and recall the difficulty of interpreting thin slice data in aplane of section most of us have not seen since dental school

This chapter presents many anatomical structures in the three planes ofsection as grayscale images, supported in most cases by thicker 3D slices,slabs or volume images to help the reader orient themselves and reconstructthe structures in the mind’s eye No attempt was made to illustrate allpossible just structures; the chapter instead focuses on those that arecommonly seen by dentists and dental specialists to help them relearnanatomical detail that may be long forgotten Because many of the structuresinvolve several bones, they are repeated in various views and planes ofsection

Maxillary structures should be very familiar to all of us, especially in thelateral or sagittal view Although these bones can be described separately, wewill see them in this chapter as they appear clinically—joined together tomake walls, spaces, and structures that we must recognize to understand the

3D changes one might encounter during an examination of CBCT volumedata When possible, these structures will be identied as they relate to oneanother.

The first part of this chapter illustrates anatomy as seen in a large old ofvision (FOV) The second part focuses on these same anatomical structures

as seen in a small FOV

Anatomy in the Large FOV

Structures identified in Figs 3-1 to 3-33 include the antra, incisive foramenand canal, nasal fossa, nasal conchae, nasolacrimal canal, pterygoidplates/processes, pterygoid hamulus, and styloid and mastoid processes Ineach section the structures are identified in the axial plane first (both thin andthick sections), followed by similar views in the sagittal and coronal planes

In some figures, we include all three planes to show the clinician and studenthow a specific structure or anomaly is oriented between the three planes Inmost instances, the images start with a section through a recognizable part ofthe anatomy such as the temporomandibular joint (TMJ) condyles

Fig 3-1 A 0.15-mm slice at the level of the mandibular fossa (top of

condyle)

Fig 3-2 A 1-mm slice at the level of the mandibular fossa (middle of

condyle)

Fig 3-3 A 21.5-mm slice from the palatal to midportion of condyle.

Fig 3-4 Same slice as shown in Fig 3-3, processed to show airwaystructures.

Fig 3-5 A 2.2-mm slice through the mandbiular fossa (middle of condyle).

Fig 3-6 A 0.15-mm slice through the mandibular fossa (medial pole of

condyle)

Fig 3-7 A 100-mm slab rendering (lateral pole of condyle).