A Guide to Digital Radiographic Diagnosis

8/10/2019 A Guide to Digital Radiographic Diagnosis

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A Guide to Digital Radiographic Diagnosis:From Panoramic, to Periapicals, to Cone

Beam CTFeatured Article - By Edwin T. Parks, D.M.D., M.S.

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H ow to Ensure Excllence in Radiographic I nterpr etation

Primum non nocere , First do no harm, is a guiding p rinciple in all ofthe health professions. Patient care is predicated upon accurateassessment of clinical data, formulation of an appropriate treatment

plan and implementation of that plan. Inaccurate interpretation ofdiagnostic data can result in failure to diagnose and treat dental disease or it can generateunnecessary treatment. Neither of these scenarios embraces the concept of do no harm.Radiographic imaging provides a wealth of data that allows the clinician to generate the mostaccurate and complete treatment plan for each patient. Digital radiographic imaging has made theacquisition of radiographic information much easier for the clinician; however, the parametersthat affect film based imaging still have an impact on digital imaging . Additionally, digital

imaging systems provide numerous software tools that impact the ability to accurately interpretthe radiographic image.

Appropriate Survey

Selecting the appropriate imaging for each patient is essential for providing adequate diagnosticinformation. Caries experience, periodontal status, systemic health and current medications allfactor into the selection of appropriate radiographic images. Utilization of the above-mentionedfactors when determining the appropriate imaging is termed selection criteria. Selection criteriaguidelines were updated in 2004 .

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The new guidelines place more emphasis on panoramic imaging for new patients (Figure 1). Forexample, you dont need a full -mouth series on an 18 year-old who only has a few occlusalrestorations. Bitewings and a panoramic image would be sufficient. Conversely, an 18 year-oldwith rampant caries might require a full mouth survey and a panoramic image.

Use of vertical bitewings for patients with alveolar bone loss is another good example of the useof selection criteria. The advent of cone beam computed tomography (CBCT) has also affectedthe way that clinicians evaluate their patients (Figure 2). CBCT can provide three-dimensionalinformation that assists the clinician in evaluating potential implant sites, planning orthodontictreatment, localizing unerupted teeth or assessing the expansion of a pathologic entity. One of theadvantages of CBCT over conventional computed tomography is dose (Figure 3). The dose fromCBCT is slightly more than a conventional panoramic image as opposed to more than ten timesthe dose from conventional CT. While CBCT technology provides a wealth of information it isimportant to remember that the clinician is responsible for all of the information contained in thedata set, not just in a particular region of interest.
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Image Quality

The five factors of image quality apply to digital imaging as well as conventional imaging.Photons dont care about the type of receptor used. These factors are separated into visual andgeometric factors. Visual factors are density and contrast.

Visual Factors: Density is the overall darkness of a radiographic image and is controlled byexposure time. It is essential to assess the size of a patient before you expose the image. Large

patients require more exposure time. If the resultant image is too light, the clinician can darkenthe image electronically. Unfortunately, you cant enhance information that wasnt captured in

the first place. Conversely, a dark image can be electronically lightened (as long as the receptorisnt saturated). The linear relationship between exposure and density allows the clinician to alterdensity but it also can create an image that is too dark in the anterior region of the image or toolight in the posterior portion of the image (Figure 4). To allow optimum use of the image alwaysuse the exposure setting for the most posterior teeth in the image (e.g. use the molar exposuresetting for the premolar bitewing so that the molars will be of appropriate density and the densityof the premolars can be diminished).


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Contrast is defined as the difference in density visualized on an image. Contrast can only bemanipulated by altering kVp. Digital systems have the ability to manipulate the contrast of theoutput image by altering the slope of the exposure/density curve. Altering the slope of this curveallows the clinician to accentuate small density differences but again, if the subject contrast isntcaptured, it cant be enhanced. Geometric Factors

The three geometric factors of image quality are image unsharpness, magnification and imagedistortion. Image unsharpness and magnification both create a fuzzy image or penumbra becausethe object of interest is too far away from the image receptor. The impact of the object-receptordifference can be minimized by using a long target receptor difference or long cone technique.Image distortion is created when the alignment of the source, object of interest and imagereceptor is incorrect. The goal is to align the long axis of the object of interest parallel to theimage receptor and direct the center of the x-ray beam perpendicular to the long axes of theobject and the receptor.

Sound familiar? This is the description of the paralleling technique. Achieving these

relationships can be difficult with film based or phosphor plate imaging. Creating theserelationships with rigid sensors is even more challenging. It isnt a good idea to bend the cornerof a sensor so the clinician must utilize the space in the patients mouth to their advantage. The

palate is the deepest in the midline towards the posterior. Place the receptor towards the posteriorwhen taking anterior proj ections and there wont be a shadow of the soft tissue of the nosesuperimposed over the image. The floor of the mouth is deepest in the midline and towards the

posterior. Dont try to place the sensor right next to the posterior teeth, the patient wont b itedown and will turn their tongue into an immoveable mass of tense muscle. Projection geometryhas a huge impact on image quality and can affect multiple image enhancements if the principlesof parallelism are not applied.

Digital radiographic imaging provides both clinician and patient with the opportunity to viewlarger than life images of the dentition. Monitor placement can affect how well the image isdisplayed. Make sure that the monitor isnt in a brightly lit area of the operatory and that itsangulation can be changed to give the patient and the operator the best possible view.

Systematic approach

The best way to interpret radiographs is to use a systematic approach every time images areviewed. Regardless of the order, the following components should be included in theinterpretation: maxillofacial bone, alveolar bone, teeth, paranasal sinuses, structures outside the

jaws and the temporomandibular joint complex. The temptation is for the eye to be drawn to thelargest radiographic finding if a systemic approach isnt followed.

Maxillofacial Bone: Maxillofacial bone supports the alveolar bone. The overall density andtrabecular pattern of the bone should be evaluated. Any biological process that affects calciumhomeostasis (e.g. osteoporosis, Pa gets Disease of Bone) can affect the trabecular patterns in the

bone. The apical regions of the teeth should also be evaluated. Subtle changes in the density ofthe lamina dura or the periodontal ligament space provide an early warning system that the

pulpal tissues of the tooth are injured. Evaluation of the maxillofacial bone is necessary for the


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edentulous patient. As the alveolar bone resorbs, normal anatomic structures appear to change.The genial tubercles appear to become more prominent when in fact they just become morevisible. The mental foramina appear to migrate to the superior aspect of the residual ridge. Theforamina dont move, the bone just goes away.

Alveolar Bone: Periodontal disease affects the alveolar bone of almost every dental patient. Lossof alveolar bone height is a radiographic sign of periodontal disease. However, density changesin both cortical and trabecular bone occur prior to loss of bone height. Radiographic images aretwo dimensional representations of three-dimensional structures. Consequently, architecturalsubtleties may be obscured due to errors in projection geometry. Finally, radiographic imagesdemonstrate loss of alveolar bone but provide no information about disease activity. It isessential to correlate radiographic findings with the clinical examination when evaluating the

periodontal status of the patient. 1

Teeth: Radiographic imaging has long been the method by which dental caries are detected on proximal surfaces. Sufficient destruction of the dental hard tissues must occur before the lesioncan be radiographically detected. Carious lesions on the occlusal surfaces are less likely to bediscovered radiographically due to the amount of hard tissue destruction that must occur.Proximal caries present just gingival to the proximal contact regardless of the alignment of theteeth. Occlusal caries are found in dentin, apical to the deepest pits found on clinical examination(e.g. central pits of molars). Others conditions that increase the difficulty of caries detection areresin restorations, liners, cervical burnout and lesions of toothbrush abrasion. It is common to

find a radiolucent margin between the restoration and the tooth (Figure 5). Block out therestoration and determine if the radiolucency still exists. The mach effect is an optical illusionthat creates a distinct radiolucent edge at the junction of two dissimilar structures. Sometimes,the anatomy of the tooth causes an altered radiographic appearance. The fluting of the roots ofthe maxillary first premolars commonly generates a radiolucency that could be confused withdental caries. Finally, the ability to alter density and contrast can increase the likelihood ofcreating cervical burnout (Figure 6). Always correlate radiographic findings with the clinicalexamination.


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Paranasal Sinuses: The paranasal sinuses are airspaces that can be captured in dental imaging.The maxillary sinus can be seen in maxillary posterior periapicals and in panoramic imaging.The normal content of these sinuses is air and they appear radiolucent. Alterations in the contentsof the sinuses can be seen in many dental images. Cloudiness in the maxillary sinus suggests the

presence of fluid in the sinus. Long standing inflammation in the maxillary posterior teeth cancause thickening of the mucosal lining of the sinus. The antral pseudocyst can be easilyidentified in radiographic images.

Structures outside the Jaws: There are numerous radiographic entities that exist outside the jaws but are visible on panoramic imaging. Panoramic images can be used to evaluate air spaces,soft tissue calcifications, the stylohyoid and stylomandibular ligaments, and mastoid air-cells.Perhaps the most significant soft tissue one can find is the carotid artery calcification. Carotidartery calcifications can be found adjacent to the cervical spine. The presence of thesecalcifications is indicative of heart disease. It is the responsibility of the clinician to inform the

patient and the patients physician if these soft tissue calcifications ar e identified. There is noway to tell the amount of carotid artery occlusion from radiographic imaging so the patientshould be referred to their physician for further evaluation.


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Temporomandibular Joint Complex: The most common view of the temporomandibularcomplex is the panoramic view. The condylar head can have numerous appearances that arenormal due to patient positioning and the problems associated with three dimensional objectscaptured in a two dimensional image. The shape of the Glenoid Fossae and articular eminentiaeshould also be evaluated. The asymmetric slope of the Glenoid fossae can present as a deviation

on opening during the clinical examination. Radiographic imaging can tell the clinician a greatdeal about the bony components of the temporomandibular joint complex but photons are nomatch for the articular disc. The best method to evaluate the articular disc is with MagneticResonance Imaging (MRI). MRI evaluates the hydrogen content of tissues. Consequently, it is avery good method for evaluating soft tissues due to their water content (Figure 7).

Using enhancement tools

A systematic approach to image interpretation is essential for the development of a completetreatment plan and is applicable for either film- based or digital imaging. Lets look at some ofthe image enhancements available with digital imaging systems.

Numerous investigators have evaluated the effects of various enhancements on the diagnosticefficacy of digital images. The results are varied. Some authors report no benefit fromenhancements 2,3,4,5,6 some find increased diagnostic efficacy 7 and some state that the enhancedimage is less diagnostic than the unenhanced image 8. A global assessment of the literaturesuggests that the effects of image enhancement have more to do with the visual system of theoperator than with the digital information itself. Consequently, the benefit of the enhancementswill vary among individuals. The clinician must experiment with enhancements to determinewhat works and what doesnt work. The benefits will be dependent upon the operator and thetask.


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Density and Contrast Enhancement: These two enhancements have already been discussed.

There are obvious advantages to changing the density or contrast on the output image (Figures 8and 9). The ability to lighten, darken and accentuate contrast are valuable diagnostic tools. 3,9 It ishowever important to remember that you cant necessarily salvage a light image and that toomuch enhancement can produce distortions that can be misinterpreted as dental disease.

Measurement Tool: The ability to measure length in a radiographic image is a great advantageof digital imaging (Figure 10). 10,11 Most systems allow the clinician to calibrate this tool tomaintain the accuracy of measurements. The measurements are made of the image and are onlyas good as the projection geometry. A foreshortened image will not be measured with aforeshortened ruler. Adherence to the principles of the paralleling technique is essential foraccurate measurement.


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Flashlight: The flashlight tool is simply a histogram equalization performed on a specific regionof interest (Figure 11). Histogram equalization is a mathematical technique that evens out thedistribution of gray levels in a particular area. This enhancement accentuates the densitydifferences within a region of interest and affords the clinician a valuable diagnostic tool. 2,3,12,13

Image Inversion: Image inversion generates an image with the gray scale flipped (Figure 12).What used to be dark on the image is now light. This enhancement may have some utility incertain diagnostic tasks but is entirely dependent upon the visual system of the clinician. 14 This isone of the enhancements that must be evaluated by the individual clinician to determine the levelof benefit derived from the manipulation.


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Pseudocolor Enhancement: This enhancement has been studied by several investigators withvaried results. Pseudocolor enhancement has been reported to improve diagnosis of periapicaldefects5 but has impeded the diagnosis in a variety of other diagnostic tasks. 9,15 This is anotherenhancement tha ts utility is determined by the visual system of the clinician (Figure 13). Thereis no question that pseudocolor enhancement serves as a valuable patient education tool.

Now lets apply a systematic approach to evaluating the non -tooth bearing areas of the panoramic radiograph (Figure 14). There are five notable findings in this image. Figure 15displays the positive findings.


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Excellence in radiographic interpretation is essential for quality patient care. Selecting theappropriate imaging study with good image quality provides the clinician with the materials to

begin the interpretive process. A systematic approach coupled with judicious use of electronicimage enhancements will allow the clinician to derive the optimum amount of information fromthe radiographic data. The correlation of radiographic findings with the clinical examinationaffords the clinician to develop a complete and accurate treatment plan.

References

1. Kilic AR, Efeoglu E, Yilmaz S, Orgun T. The relationship between probing bone loss andstandardized radiographic analysis. Periodontal Clinical Investigations 1998; 20:25-32.

2. Dove SB, McDavid WD. A comparison of conventional intra-oral radiography and computerimaging techniques for the detection of proximal surface dental caries. Dentomaxillofac Radiol1992; 21:127-34.

3. Borg E. Some characteristics of solid state and photo-stimulable phosphor detectors for intra-oral radiography. Swed Dent J Supplement 1999; 139:1-67.

4. Moystad A, Svanaes DB, Risnes S, et al. Detection of approximal caries with a storage phosphor system. A comparison of enhanced digital images with dental x-ray film.Dentomaxillofac Radiol 1996;25:202-6.

5. Li G. Comparative investigation of subjective image quality of digital intraoral radiographs processed with 3 image-processing algorithms. Oral Surg Oral Med Oral Path Oral Radiol Endod2004; 97:762-7.

6. Moystad A. Svanaes DB, van der Stelt PF, Grondahl HG et al. Comparison of standard andtask-specific enhancement of Digora storage phosphor images for approximal caries diagnosis.Dentomaxillofac Radiol 2003; 32:390-6.


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7. Meier AW, Brown CE, Miles DA, Analoui M. Interpretation of chemically created periapicallesions using direct digital imaging. J Endod 1996;22:516-20.

8. Tyndall DA, Ludlow JB, Platin E, Nair M. A comparison of Kodak Ektaspeed Plus film andthe Seimans Sidexis digital imaging system for caries detection using receiver operating

characteristic analysis. Oral Surg Oral Med Oral Path Oral Radiol Endod 1998; 85:113-8.

9. Bragger U, Burgin W, Marconi M, et al. Influence of contrast enhancement and pseudocolortransformation on the diagnosis with digital subtraction images (DSI). J Perio Res 1994;29:95-102.

10. Wenzel A, Kirkevang LL. Students attitudes to digital radiography and measu rementaccuracy of two digital systems in connection with root canal treatment. European Journal ofDental Education 2004;8:95-102.

11. Woolhiser GA, Brand JW, Hoen MM, Geist JR, et al. Accuracy of film-based, digital and

enhanced digital images for endodontic length determination. Oral Surg Oral Med Oral Path OralRadiol Endod 2005; 99:499-504.

12. Chuang KS, Chen S, Hwang IM. Thresholding histogram equalization. J Digital Imaging2001;14:182-5.

13. Sund T, Moystad A. Sliding Window adaptive histogram equalization of intraoralradiographs: effect on image quality. Dentomaxillofac Radiol 2006;35:133-8.

14. Haak R, Wicht MJ. Grey-scale reversed radiographic display in the detection of approximalcaries. J Dent 2005; 33:65-71.

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A Guide to Digital Radiographic Diagnosis