16 Advanced Imaging Systems










185
16
Advanced Imaging Systems
EDUCATIONAL OBJECTIVES
Upon completing this chapter, the student will be able to:
1. Dene the key terms listed at the beginning of the chapter.
2. Describe the following related to computed tomography
(CT) scanning:
• ExplaintheprocedureforCTscanning.
• Describethefunctionsoftheaxial,coronal,andsagittal
planes of the human body.
• ListtheadvantagesanddisadvantagesofCTscanning.
3. Discuss the following related to cone beam computed
tomography (CBCT) imaging in dentistry:
• DescribetheroleofCBCTimagingindentistry.
• StatetheprocessforacquiringtheimageintheCBCT
technique.
• DiscusstheadvantageoftheCBCTprocedurewhen
compared with CT scanning in dental imaging.
• ListtheindicationsforuseofCBCTimagingindentistry.
4. Discussthemechanismofimageacquisitioninmagnetic
resonanceimaging(MRI)imaging,aswellastherolethat
MRI imaging plays in dentistry.
5. Dene nuclear medicine and discuss its role in medical
imaging.
KEY TERMS
axial plane
bone window
computed tomography (CT) scanning
cone beam computed tomography
(CBCT)
coronal plane
CT number
DICOM images
eld of view (FOV)
gamma camera
Hounseld unit
image acquisition
magnetic eld
magnetic resonance imaging (MRI)
matrix
multiplanar reconstructed (MPR)
images
radiofrequency
sagittal plane
scan
signal intensity
soft tissue window
software
target tissues
for such imaging, or copies of the images may be brought
to the oce by the patient for opinions and interpretation.
erefore, an overview of these imaging systems is included
in this chapter.
Although dierent sources of energy are used (x-radiation
in CT and radiofrequency energy in MRI), a common
theme in these imaging systems is the use of tomography
and the absence of lm as the sensing device and the use
of electronic detectors that send electrical impulses to a
computer, which then stores or generates an image on a
monitor.
As a result of the use of CBCT imaging in dentistry,
dental imaging is not limited to two-dimensional imaging
any longer. CBCT imaging provides a three-dimensional
(3D) view of the structures in the oral cavity. is imaging
technique furnishes more detailed information in formulat-
ing an enhanced and accurate interpretation of structures
in the oral cavity.
Introduction
With the introduction and now common use of advanced
imaging techniques, such as computed tomography (CT)
scanning, magnetic resonance imaging (MRI), cone
beam computed tomography (CBCT), positron emission
tomography (PET), and digital imaging (see Chapter 15),
the eld of dental radiology has greatly expanded. ese
new techniques can be used by dentists to image structures
in ways that were previously unavailable. e use of CBCT
scans for diagnosing lesions and planning implant cases
and the use of MRI to visualize soft tissue components of
the temporomandibular joint (TMJ) and assess pathologic
conditions are now accepted as standard procedures in
dental radiology. Although CT scanners and MRI units are
not found in most general dental oces except in the ever-
increasing dental radiology specialty practices, the dental
professional should have some familiarity with these newer
imaging systems, because patients may have to be referred

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18516 Advanced Imaging SystemsEDUCATIONAL OBJECTIVESUpon completing this chapter, the student will be able to:1. Dene the key terms listed at the beginning of the chapter.2. Describe the following related to computed tomography (CT) scanning:• ExplaintheprocedureforCTscanning.• Describethefunctionsoftheaxial,coronal,andsagittalplanes of the human body.• ListtheadvantagesanddisadvantagesofCTscanning.3. Discuss the following related to cone beam computed tomography (CBCT) imaging in dentistry:• DescribetheroleofCBCTimagingindentistry.• StatetheprocessforacquiringtheimageintheCBCTtechnique.• DiscusstheadvantageoftheCBCTprocedurewhencompared with CT scanning in dental imaging.• ListtheindicationsforuseofCBCTimagingindentistry.4. Discussthemechanismofimageacquisitioninmagneticresonanceimaging(MRI)imaging,aswellastherolethatMRI imaging plays in dentistry.5. Dene nuclear medicine and discuss its role in medical imaging.KEY TERMSaxial planebone windowcomputed tomography (CT) scanningcone beam computed tomography (CBCT)coronal planeCT numberDICOM imageseld of view (FOV)gamma cameraHounseld unitimage acquisitionmagnetic eldmagnetic resonance imaging (MRI)matrixmultiplanar reconstructed (MPR) imagesradiofrequencysagittal planescansignal intensitysoft tissue windowsoftwaretarget tissuesfor such imaging, or copies of the images may be brought to the oce by the patient for opinions and interpretation. erefore, an overview of these imaging systems is included in this chapter.Although dierent sources of energy are used (x-radiation in CT and radiofrequency energy in MRI), a common theme in these imaging systems is the use of tomography and the absence of lm as the sensing device and the use of electronic detectors that send electrical impulses to a computer, which then stores or generates an image on a monitor.As a result of the use of CBCT imaging in dentistry, dental imaging is not limited to two-dimensional imaging any longer. CBCT imaging provides a three-dimensional (3D) view of the structures in the oral cavity. is imaging technique furnishes more detailed information in formulat-ing an enhanced and accurate interpretation of structures in the oral cavity.IntroductionWith the introduction and now common use of advanced imaging techniques, such as computed tomography (CT) scanning, magnetic resonance imaging (MRI), cone beam computed tomography (CBCT), positron emission tomography (PET), and digital imaging (see Chapter 15), the eld of dental radiology has greatly expanded. ese new techniques can be used by dentists to image structures in ways that were previously unavailable. e use of CBCT scans for diagnosing lesions and planning implant cases and the use of MRI to visualize soft tissue components of the temporomandibular joint (TMJ) and assess pathologic conditions are now accepted as standard procedures in dental radiology. Although CT scanners and MRI units are not found in most general dental oces except in the ever-increasing dental radiology specialty practices, the dental professional should have some familiarity with these newer imaging systems, because patients may have to be referred 186 CHAPTER 16 Advanced Imaging Systems(Figs. 16.3 and 16.4). Fig. 16.5 is a diagram illustrating all of the orientation planes.e computer can generate an image based on the digi-tized data it has received. is image can be (1) displayed on a monitor, (2) reformatted into other planes in two or three dimensions (which cannot be done in digital dental radiography), (3) adjusted for optimum viewing of hard and soft tissue, (4) stored on a disk, (5) produced as a printout (hard copy), and (6) transmitted to other locations. Once the scan has been completed, the patient can be dismissed, because all subsequent image reconstruction manipulation can be done by the computer.Computed Tomography ScanningCT was introduced into the eld of radiology in the early 1970s. In contrast to conventional radiographic tech-niques in which lm or lm-screen combinations are used to produce images, CT images are computer generated. However, CT still uses ionizing radiation as the energy source.CT scanners produce digital data measuring the extent of the x-ray penetration through the patient. e image acquisition is done in a tomographic mode with the source of the radiation or the detectors traveling 360 degrees around the patient. Fig. 16.1 shows the comparison between tomography and CT scanning.In CT, a nely collimated x-ray beam is directed through the patient to a series of electronic detectors or sensors. ese detectors send electrical impulses that are digitized and stored by the computer. In medicine, this is called the scan, and it is usually done in the axial plane with the patient positioned in a large, doughnut-shaped unit that contains the x-ray tube and the sensors (Fig. 16.2). Originally, all scans were done in the axial plane, thus leading to the name computerized axial tomography (CAT) scan. e “A” has been dropped, because some initial scans are done in other planes than the axial plane (a plane that divides the body into inferior and superior regions). ese images can be reformatted and viewed in the coronal plane (a vertical plane that divides the body into anterior and posterior regions), sagittal plane (a vertical plane that divides the body into right and left regions), and axial plane BeamSensorsBABCABCA• Figure 16.1 A, Tomography. Note the lm as the image receptor. B, CT scan. Note the sensors as the image receptor. • Figure 16.2 Computed tomography (CT) scanning unit. Note the patient in the scanner, the technician at the computer, and the image on the screen. (Courtesy Philips Medical, Andover, MA.) 187CHAPTER 16 Advanced Imaging Systemstechnique. CT numbers range from +1000 to −1000, with 0 being water, bone being +1000, and air being −1000. For example, fat tissue is about 100 Hounseld units. Because the density of tissue has been assigned a number, one can narrow the densities that can be displayed. is is called using a window, and there can be either a bone window or a soft tissue window (Figs. 16.6 and 16.7). Box 16.1 presents the advantages and disadvantages of CT.e computer collects the x-ray beam penetration data in a grid pattern called a matrix, much like the digital imaging described in Chapter 15. Each square in the matrix is made up of pixels, which represent the density of a small volume of tissue. Because each pixel is digitized, it can be assigned a CT number, which represents the density of a particular area that has been penetrated by the x-ray beam. CT numbers are also called Hounseld units, in honor of one of the developers of this radiographic imaging • Figure 16.3 Computed tomography (CT) scan in the axial plane. Note the gray soft tissue imaging and the radiopaque bone. • Figure 16.4 Computed tomography (CT) scan in the axial plane. Note the gray soft tissue imaging and the radiopaque bone. CoronalSagittalAxial• Figure 16.5 All orientation planes. 188 CHAPTER 16 Advanced Imaging Systems• Figure 16.6 Computed tomography (CT) scan with a bone window. Decide which maxillary sinus is abnormal. • Figure 16.7 Computed tomography (CT) scan with a soft tissue window. • BOX 16.1 Advantages and Disadvantages of Computed TomographyAdvantages1. Eliminates the superimposition of images of structures supercial or deep to the area in question (tomography), which can be done in any plane. Images can be acquired in any plane, and the scan can reproduce images in any plane.2. A computed tomography (CT) scan can enable one to distinguish between tissue density that differs from 1% to 2%, whereas at least 10% is needed for conventional radiography.3. Images can be reformatted to another plane without the necessity of another scan. Some CT scanners can image the mandible and the maxilla on one scan.4. Density and contrast can be adjusted using the CT numbers to create a bone or soft tissue window.5. The enhanced image makes interpretation easier and more accurate.Disadvantages1. Increased radiation dose when compared with conventional lm. Some of the newer cone beam units can reduce radiation by 90% when compared with older-design CT units. Many special software programs have been written for CT scanners that are specic for dental use in implant planning (Fig. 16.8). This software directs the computer in obtaining the desired images in three planes so that the site of the implant xture can be determined. Not all CT units have implant software; thus, it is very important to ask whether the facility has the desired software program before referring a patient to a medical facility for an implant scan. However, cone beam computed tomography (CBCT) imaging is specically designed for use in dentistry and is therefore recommended for three-dimensional (3D) imaging of the oral cavity. The use of CT scanning in the evaluation and planning of implant sites and evaluation of bone density has become a common application in dentistry and is rapidly becoming the standard of care for implant planning. The American Academy of Oral and Maxillofacial Radiology (AAOMR) has stated in their position paper on the use of x-rays in implants that “some form of cross-sectional imaging be used for implant cases,” and CT is a form of cross-sectional imaging. Never before has it been possible to obtain multiple cross-sectional cuts with the speed and accuracy available now in implant evaluation.2. The cost to the patient for a CT scan is quite considerable in comparison to, for example, a panoramic radiograph.3. Signicant artifacts are produced by metallic objects that are in the plane being scanned, such as metal dental restorations. 189CHAPTER 16 Advanced Imaging SystemsCBCT and CBVT represents a new generation of U.S. Food and Drug Administration–approved dental scanners that generate signicantly less radiation than do traditional medical CT scanning devices. ese CBCT (CBVT) scan-ners deliver comparable diagnostic images while adhering to the ALARA (as low as reasonably achievable) principle of using the least amount of radiation to obtain a diagnostic image. CBCT scanners are cost-eective and more accurate than conventional medical CT scanners. CBCT technology has many benets, including reduced radiation exposure while creating 3D images of the anatomic structures of the mandible, maxilla, and related structures (Fig. 16.10). Given the fact that CBCT (CBVT) technology has greater accuracy than a dental periapical image, a panoramic projection, or even a medical CT scan, it is suggested that CBCT (CBVT) may be used in dentistry not only for dental implant planning, but also to evaluate impacted teeth, supernumeraries, oral pathologic conditions, and many more dental applications in multiple views (Fig. 16.11).Acquiring the ImageTo take a scan, the technician places the patient in position in the CT scanner and a preliminary scout image is exposed. is scout image helps the technician determine if the patient is positioned properly and calibrates the radiation dosage according to the hard and soft tissue densities. Once the head is in the correct position, the x-ray tube rotates 360 degrees once around the patient’s head to take the desired images, which is similar to the technique used in panoramic imaging. e image produced is a 3D image as opposed to the former two-dimensional images that were produced in the past.Cone Beam Computed TomographyA more recent means to acquire a CT image is by CBCT, also known as cone beam volumetric tomography (CBVT). Some of these CT scanners are dedicated to maxillofacial scans (NewTom 9000; Fig. 16.9A). e technique involves use of a round or rectangular cone-shaped x-ray beam on a two-dimensional x-ray sensor. is technique has the advantage of using less radiation, as well as less time acquir-ing the image as compared with medical CT scanning. e scanned series consists of 360 images, including transaxial, axial, and panoramic images. ese CBCT units allow the patient to either be in the supine or upright position for exposure (see Fig. 16.9B). is option allows patients to have dental scans exposed without having to lie down in a conned space.• Figure 16.8 Computed tomography (CT) scan using software designed specically for dental implant planning. A, Axial cut with numbered orientation planes that are seen in the corresponding vertical cuts in B. AB• Figure 16.9 The NewTom VGI evo cone beam computed tomog-raphy (CBCT) unit, ideal for imaging the maxillofacial region. (Courtesy NewTom by Cea s.c.) 190 CHAPTER 16 Advanced Imaging SystemsBA• Figure 16.10 A, Conventional computed tomography (CT) scan reformats a series of parallel helical slices, which incorporate small errors in nal scan. B, Cone beam volumetric tomography (CBVT) captures volumes of data taken in one 360-degree rotation about a patient’s head. Each volume “touches” adjacent volume to avoid distortion and error in reformatted studies. NOTEThe dental applications of cone beam computed tomography (CBCT) images include:• Implantplanning• Endodontics• Temporomandibularjoint(TMJ)disorders• Extractions• Locationofanatomicstructures,suchasthementalforamen and inferior alveolar nerve• Orthodontics• Trauma• Assessmentofabnormalitiesandlesions• Figure 16.11 A, Cone beam computed tomography (CBCT) axial view. B, Cone beam volumetric tomography (CBVT; CBCT) sagittal view. C, CBVT (CBCT) coronal view. Basic Information: Cone Beam Computed Tomographye patient’s maxillofacial area that is of interest when taking a CBCT image is known as the eld of view (FOV). e CBCT unit takes multiple images of the FOV in a single scan. e digital receptor receives the information generated by the radiation exposure. is raw data is 3D, goes through reconstruction, and forms a pile of images known as DICOM images. ese images are transferred to the software that allows the dental professional to view the area of interest (or FOV) in the axial, coronal, and sagittal planes. When these axial, coronal, and sagittal images are viewed simultaneously, they are referred to as multiplanar reconstructed (MPR) images.Radiation Dosagese average absorbed dose from a CBCT scanner is roughly 12.0 mSv (millisieverts), which is equivalent to or less than the radiation needed to take ve periapical radiographs utilizing conventional lm. is amount of radiation is similar to one-fourth of a typical panoramic machine. By comparison, medical CT scanners acquire images using eective doses 40 to 60 times these amounts; the radiation dose for medical CT scanners is based on the patient’s weight, bone density, and whether one jaw or two jaws is being studied. 191CHAPTER 16 Advanced Imaging Systemstissues). ese organ-specic compounds are injected into the patient, where they concentrate in the target tissue and are detected and imaged by a sensor called a gamma camera. In this manner, both the form and function of the target tissue can be studied. e injectable radiopharmaceutical material consists of an organic substance specic for a given tissue or structure and a nonspecic radionuclide (label). e image is recorded by a gamma camera, which detects the release of gamma rays in a given location and during a given period of time. e image is displayed on a cathode ray tube or stored in a computer. Radionuclide scanning is useful for examining bone and salivary gland tissue, as well as for investigating metabolic bone disorders, infection, and bone fractures.• Figure 16.12 Magnetic resonance image (MRI) of the temporo-mandibularjoint(TMJ).Locateandidentifythecondyle,articulardisc,and the muscles. Magnetic Resonance ImagingMRI does not use ionizing radiation as the energy source but rather another type of energy wave from the electro-magnetic spectrum, that is, radiofrequency energy (see Fig. 1.4). Because these wavelengths are long and cannot cause ionization, there is no radiation dose to the patient.e patient is placed in a large magnet that is 10,000 times more powerful than the earth’s magnetic eld. e eld is so powerful that all freestanding metal objects must be removed from the room, because they can become lethal objects if aected by the magnetic eld. e magnetic eld temporarily changes the alignment and orientation of the protons in the patient’s body. Radiofrequency waves are applied to the realigned protons, and this radiofrequency energy is absorbed. When the radiofrequency signal ends, the protons release the absorbed energy, which is received by a sensor, and the information is transmitted to a computer that generates an image. Because MRI is actually based on measurement of proton density and 70% of the human body is water, of which protons are the major component, MRI is better for visualization of soft tissues and not as good for viewing bone, which has very little water. e images produced show strong signal intensity (white area) for soft tissue with many water molecules and show a weak signal (black area) where there are few water molecules. is is the exact opposite of radiation-generated images, in which bone is white (radiopaque) and soft tissue is black (radiolucent).Presently, the main application of MRI in dentistry has been in imaging the articular brous disc of the TMJ and other soft tissue lesions (Fig. 16.12).Nuclear MedicineNuclear medicine (radionuclide scanning, bone scanning) is a diagnostic radiation procedure using radioactive com-pounds that have an anity for particular tissues (target Chapter Summary• CTscanningisusedindentistryto produceenhancedimages that makes interpretation easier and more accu-rate. e advantages of CT scanning include the elimina-tion of superimposed images, the ability to reformat images on other planes, and the option of adjusting the density and contrast of the CT image. e disadvan-tages of CT scanning include an increase in radiation dose, a considerable cost to the patient, and signicant artifacts caused by metallic objects in the patient’s oral cavity.• CBCT imaging is a type of CT scanning specicallyused in dentistry to produce 3D images that provides the dental professional with a dimensionally accurate view of the desired area.• MRIisusedindentistrytoevaluatethebrousarticulardisc of the TMJ. e images produced are more useful for soft tissue evaluation than for hard tissue evaluation.• Nuclearmedicineorradionuclidescanningisusefulforexamining salivary gland tissue and bony structures in dental imaging. 192 CHAPTER 16 Advanced Imaging SystemsChapter Review QuestionsMultiple Choice1. MRI is an eective means of visualizing: a. Bony structures b. Soft tissue c. Metallic objects d. Amalgam restorations e. e mandibular condyle2. A diagnostic radiation procedure that uses radioactive compounds is known as: a. CBCT imaging b. MRI imaging c. CT scanning d. PET scanning e. Nuclear medicine3. e plane that divides the body into superior and inferior regions is known as the: a. Coronal plane b. Cross-sectional plane c. Axial plane d. Sagittal plane e. Frontal plane4. e 3D raw data produced when a CBCT image is taken and reconstructed is known as: a. e FOV b. Spatial resolution c. Contrast resolution d. A DICOM image e. A voxel5. CBCT images can be used in dentistry: a. To evaluate lesions and abnormalities b. For implant planning c. To evaluate areas of trauma d. For endodontic assessment e. All of the aboveCritical Thinking Exercise1. A patient in your dental facility is referred for a CBCT to be utilized in the treatment plan for an implant procedure. Your task is to educate the patient about the CBCT particular to the patient’s treatment plan. Be sure to include the following in your information session: a. What is CBCT imaging? b. What is the advantage of a CBCT procedure when compared to a medical CT scan? c. What is the procedure for acquiring a CBCT image? d. Other than implant planning, what other dental applications can CBCT images be used for? e. Is the radiation dose from a CBCT procedure harmful to the patient? f. What is meant by the term 3D imaging?2. A patient in your oce is referred to a facial pain special-ist for an MRI depicting the brous articular disc of the TMJ. You are presented with the task of educating the patient about an MRI and why it is prescribed for TMJ evaluation. Be sure to include the following in your informative session: a. Does an MRI use x-radiation as the source of energy for image production? b. Why is the MRI unit referred to as a large magnet? c. Why is it recommended that all metal objects be removed from the area when an MRI is being taken? d. What does the “magnet” do to the human body? e. What happens during an MRI procedure, and why is there a loud banging noise heard during the procedure? f. Why is an MRI used to view soft tissue rather than bony structures? g. Which structures are represented as “white” images on an MRI and which are “black?” How does this visu-alization dier from images produced by x-radiation?BibliographyBrooks SL: Computed tomography, Dent Clin North Am 37:575–590, 1993.Iannucci JM, Howerton LJ: Dental radiography: Principles and tech-niques, ed 5, St Louis, MO, 2016, Elsevier Saunders.White SC, Pharoah MJ: Oral radiology: Principles and interpretation, ed 7, St Louis, MO, 2013, Mosby.Winter AA, Pollack AS, Frommer HH, et al: Cone beam volumetric tomography vs. medical CT scanners, NY State Dent J 71:28–33, 2005.

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