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Radiology: Yesterday, Today and Tomorrow


October 21, 2010
by Rajinder Jain, DDS

There was a time when it took a few minutes to expose a tooth to get a diagnostic image, which meant that patience was a virtue for the patient as well as the clinician. All this was at the expense of the safety of the patient and in many cases the person who exposed the patient as well. When I did one of my early research projects comparing film speeds more than two decades ago, it earned me tenure at my present job. Today the outcome of such research seems miniscule compared to the sophisticated technology in front of us. Dentists and few other scientists like Albert G. Richards devised many techniques that changed the world of diagnostic radiology and set the stage for modern innovation. If films were the order of the day then, digital sensors occupy that space now. If transcranial and submento vertex views (try explaining the position to even an educated, cooperative patient) let you analyze temporomandibular joints then, try doing a Cone Beam computed tomography (CBCT) exam in a few seconds. Or better still explain the processes to the patient and let them pick. Yes, we are sitting at the helm of technology that has definitely changed not only the way we capture diagnostic radiographs but the information they provide.

Simply put, diagnostic intraoral radiographs changed the way dentists treated their patients. Today’s intraoral radiography options are superior to those of the past, primarily due to the development of digital radiography, beginning with Trophy Radiology’s introduction of the RVG sensor. Digital sensors in particular afford many clinical and pragmatic advantages over traditional film radiography. With the right digital sensors and proper techniques, the amount of radiation exposure to patients can be reduced. While film images have traditionally been of higher resolution, some modern digital intraoral radiography systems can generate film-quality images. Digital radiographs are generated faster, making image capture and processing much quicker and cleaner than with film. Sophisticated digital imaging software often includes a wide array of processing filters, highlighting anatomic features such as the dentin to enamel junction or periapical lesions. These filters enable clinicians from across different specialties to manipulate images for specific applications.

The widest application for intraoral radiography has long been and continues to be in identifying caries. In fact, the ever-increasing demand to detect and treat the disease in an early stage has probably sped the evolution of enhanced caries detection methods, including revolutionary software. For instance, Logicon caries detector software, which is used with the Kodak RVG 6100 digital radiography system, uses grayscale contrast to diagnose interproximal caries at an earlier stage while lowering the risk of false positives.1 So on one hand you have earlier detection and better treatment outcomes, and on the other hand you reduce unnecessary procedures. This sort of ‘win-win’ scenario is the ultimate goal of innovation, and I expect it will continue in the future.

Some seasoned clinicians have resisted the transition from film to digital radiography based on the perceived advantages and disadvantages to their practices -perhaps they are nearing retirement, believe that films are superior diagnostically, are in denial of the technology or some or all of the above in combination. However, I really can’t make a blanket statement that all practices should immediately switch to digital or anything along those lines. However, I can say with certainty that digital sensors have numerous advantages over film and that intraoral radiography is in the digital age.

I believe that extraoral radiography’s future is digital as well. But let us not forget that the advent of panoramic radiograph changed the way dentists viewed the oral cavity and for many clinicians defined the scope of their practice. While the oral surgeon looked at impacted third molars, the periodontist examined the height of the crestal bone; while the orthodontist evaluated the temporomandibular joint, the otolaryngologist sought to diagnose sinus pathology. Panoramic radiography had all of a sudden become a one-stop solution to all types of maxillofacial imaging needs.

It would probably be right to say that this modality remains to be the most abused, overused and under diagnosed imaging modality in dentistry because of its relatively low resolution coupled with limitations of projection geometry and magnification factors. Still, we cannot ignore the marked contribution of it to the world of extraoral imaging. Modern day panoramic radiography units emit about the same radiation as 4-16 periapical radiographs (Reference Table 1). As with intraoral radiography, digitization has brought gains in terms of dramatically shorter image acquisition times and the ability to manipulate images. Patient positioning is now more flexible, and some units like Morita’s Veraviewepocs house both cephalometric and panoramic imaging modalities in one body. The above unit and others like it also offer optional 3D imaging, which is arguably the most significant recent development in oral and maxillofacial radiography.

Before I delve too deeply into the ways 3D CBCT imaging has revolutionized the oral health field, I must take a moment to reflect on its ancestors. By using basic principles of projection geometry and knowledge of radiation physics, dentistry had the rare privilege of using lateral oblique views and analog tomography. The latter was so cumbersome we had a dedicated staff member for all such procedures in our institution. (I should mention that there were only about two or three procedures scheduled for the day!) And then came interpreting these images, which took even more time. Thankfully I was in academia which allowed me more time to evolve than in private practice. Today one might bump into a dinosaur before an analog tomography unit!

With the advent of CBCT the question of use and abuse also rises, and rightfully so. CBCT at present is indicated only for hard tissue imaging and is not to be used as a replacement for panoramic, cephalometric or intraoral radiography. CBCT has put our science in a new pedestal. I am not the only doctor who had to go back to the drawing board to learn about the clinical techniques, image properties, and potential applications associated with this technology. (However, I was privileged to work for an institution that acquired one of these units early, which certainly helped me learn these things faster.)

My younger colleagues salute this technology as the one that gave them their jobs and a reason to believe that innovation in diagnostic radiography still exists. Residents across different specialties at most institutions now use CBCT, a fact which will no doubt lead to the development and dissemination of this groundbreaking imaging modality and which will likely make 3D imaging an increasingly frequent occurrence.

The multiplanar views offered by CBCT allow dentists to view regions of interest in stunning detail and to effectively see through overlapping anatomic structures that otherwise obscured pathology. CBCT units come in various fields of view and with adjustable spatial and contrast resolution, revealing an unprecedented level of information. A patient’s bone volume and depth may now be accurately measured in 3D rather than in 2D. The alveolar nerve may be precisely visualized (Figure 1). Presence of any other occult pathology can be identified or ruled out. In essence, the additional clinical information has resulted in more comprehensive treatment planning and monitoring. I believe that the only factor limiting the potential of 3D is skepticism to new technology.

One sign of the primacy of 3D is the sheer number of available options. A practitioner must select the imaging system with the field of view that best
suits his or her practice. This in turn depends on that practice’s most common clinical procedures. Focused-field 3D systems are well-suited for endodontic and periodontic assessment and therapy, as well as evaluations of impacted teeth, pre-implant placement or post-placement complications in an individual quadrant or more. Medium-field systems are ideal for multiple implant placements, TMJ analyses and any procedures requiring dual jaw images (Figure 2). Large-field systems are good for planning requiring full craniofacial images, such as orthognathic surgery, multiple implant placements, pathology of jaws and trauma induced injuries to facial bone (Figure 3).

The benefits of CBCT are unquestionable. 3D images can be extremely high resolution – as sharp as 0.076mm voxels with the Kodak 9000 3D extraoral imaging system which are reconstructed within minutes. The patient dose is considerably lower than spiral/helical (medical) CT, and CBCT scans are typically much less expensive (Reference Table 1). The imaging software allows for a high degree of image manipulation and optimization and frequently contains helpful collaborative features. As with intraoral digital imaging systems, there are a host of compatible third party software applications such as NobelGuide and SureSmile.

With this great power comes great responsibility. The rise of CBCT means clinicians are now viewing a lot more information than before and can be held liable to identify and interpret such anatomical areas for the benefit of the patient. This liability issue along with use and abuse of this technology is still being debated in professional circles and has been addressed by organizations such as American Academy of Oral & Maxillofacial Radiography through official publications. I hope common sense and patient benefit prevails. There are two primary rules of thumb to address these liability concerns. First, clinicians should be wise enough to capture 3D images only when needed and to limit the field of view to only that which is necessary for clinical purposes. Second, clinicians may employ the services of an oral and maxillofacial radiologist to review patient volumes for signs of incidental findings that may require a higher level of interpretation.

Today the institution where I work has multiple CBCT units, multiple panoramic and cephalometric units, and an incredibly large number of intraoral units. All of this technology, combined with new age human skill and mountains of data gathered by oral and maxillofacial radiologists and scientists, has led to radiology taking significant strides through the years. There is good reason to think that progress will continue in the pursuit of patient health and favorable treatment outcomes. We’ve come a long way, and there’s a lot more in store. We should all be excited about the possibilities and opportunities. OH

 

References

1. Gakenheimer, David C. “The Efficacy of a Computerized Caries Detector in Intraoral Digital Radiography.” Journal of the American Dental Association 133 (2002): 883-890

Table 1.

Effective Dose from Diagnostic X-Ray Examinations and Equivalent Background Exposure.

Examination

Effective Dose (µSv)

Equivalent background exposure (days)

Intraoral

Rectangular collimation

   

Posterior bitewings – PSP or F-speed film

5.0

0.6

FMX – PSP or F-speed film

35

4

Round collimation

   

FMX – PSP or F-speed film

171

21

FMX – D-speed film

388

47

Extraoral

Panoramic

9-26

1-3

Cephalometric

3-6

0.5-1

Cone-beam imaging

   

3D Accuitomo

20

3

NewTom 3G

68

8

Gailieos

70

9

Next Generation i-CAT Landscape mode

74

9

PreXion

185

23

i-CAT-Extended Scan

235

29

CB Mercuray – Facial standard quality

569

69

Iluma

592

74

Promax 3D

599

75

Computed tomography

Somaton 64 MDCT

860

105

Head

2,000

243

Abdomen

10,000

3 years

Upper gastrointestinal tract

3,000

1 year

Barium enema

Plain films

7,000

2 years

Skull

70

9

Chest

20

2