3-D X-Ray: An Update
Allan G. Farman; Claudio M. Levato; William C. Scarfe
“A Primer on Cone Beam CT” was published in the January 2007 issue of Inside Dentistry. It was noted in that article that the application of cone beam computerized tomography (CBCT) has taken dentistry by storm. The purpose of this sequel is to provide an update on existing and emerging systems based upon exhibits shown at the 32nd International Dental Show (IDS), held in Cologne, Germany, March 20?24, 2007. The article will also provide a review of the imaging software and service add-ons that work with CBCT image data sets. There also has been development of a new international digital imaging and communications in medicine (DICOM) standard to specifically address communication interoperability for the 3-dimensional (3-D) image class encompassing CBCT. Potential 3-D imaging systems will also be discussed. In an attempt to keep the content as current as possible, this article is restricted to a relatively concise overview.
NEW CBCT SYSTEMS UNVEILED AT IDS
In the previous article, the systems discussed included: the NewTom 3G (Dent-X Visionary Imaging, Elmsford, NY), the 3D Accuitomo (J. Morita USA, Irvine, CA), i-CAT® (Imaging Sciences International, Inc, Hatfield, PA), CB MercuRay™ (Hitachi Medical Systems, Brisbane, CA), ILUMA™ Ultra Cone Beam CT Scanner (manufactured by IMTEC, Ardmore, OK, and distributed by Kodak Dental Systems, Atlanta, GA), and Galileos (Sirona Dental Systems, Charlotte, NC). In a footnote, the authors apologized for not detailing the Planmeca Promax 3D (Planmeca Oy, Helsinki, Finland) as its commercial release had come after the deadline for that article.
It is perhaps appropriate to update information on these previously mentioned systems before moving forward to look at entirely new potential entries into the marketplace.
Following three generations of NewTom CBCT systems in which the patient is supine, QR srl (the manufacturer of the first maxillofacial CBCT system) unveiled the NewTom VG dental volumetric tomograph for the seated or standing patient. This is under review for Food and Drug Administration (FDA) approval. It is intended as an alternative to the NewTom 3G rather than a replacement. The new system employs a high-frequency converter for constant potential x-ray generation at 110 kV, a 0.3-mm focal spot, and a 20-cm x 25-cm amorphous silicon flat panel. The exposure time is variable, with 24 seconds being typical. Scan dimensions are 14 cm (diameter) and a maximum of 10 cm (height). Reconstruction time is about 2 minutes and the output is 14-bit grayscale. System dimensions are 145 cm (depth), 110 cm (rotation width), and 230 cm (height). For more information, visit www.qrverona.it.
J. Morita USA is adding an alternative line to its 3D Accuitomo. The new entry unveiled at IDS is the Veraviewepocs® 3D, an update to a well-established top-of-the-line digital panoramic system that will retain its traditional panoramic and cephalogram functions in addition to adding limited volume CBCT. The Veraviewepocs 3D model X550 works at 100/110/120/220/230/230/240-V AC with a power consumption of 2 kVA. The x-ray tube operates at 60 kV to 90 kV with a tube current of 1 mA to 10 mA and an effective focal spot of 0.5 mm. The exposure time in the 3-D mode is 9.4 seconds and the imaging area has a diameter of 4 cm to 8 cm and height of 4 cm to 8 cm, depending on the 3-D digital cassette selected. Isotopic voxel resolution is 0.125 mm with adjustable slice width from 0.125 mm to 2 mm. The patient can be scanned standing or seated. The suggested space requirement is 2.25 square meters for a pano-ramic attachment or 3.45 square meters for a cephalometric attachment. A single cassette (40 mm x 40 mm) can be used to obtain panoramic images, as well as 3D images. Other cassette options include 80 mm x 80 mm for a larger 3D imaging area. Output is specified as DICOM. For more information, visit www.jmorita-mfg.com.
Imaging Sciences International (ISI)
In January 2007, ISI joined the Danaher Dental Group (Washington, DC) through acquisition. Advances in software now permit the i-CAT to provide greater spatial resolution with a maximum (ultra-high) resolution of 0.12 mm. This is possible with existing installations given sufficient computer memory to accommodate the greater computing demands involved. The Danaher Dental Group also includes KaVo Dental Corporation (Lake Zurich, IL). At IDS the KaVo 3D eXam system was demonstrated. This has many features in common with the i-CAT in terms of specifications and the look of the supplied proprietary software, though the software will be in German. However, the scan time has been cut in half and extended field-of-view scans can be performed in half the time and with half the radiation dose. The KaVo 3D eXam is expected to be available for distribution in Germany in late September 2007. For more information, visit www.kavo.com.
Hitachi Medical Systems
Hitachi did not exhibit at the IDS Congress; nevertheless, this company has released a smaller CBCT system specifically for the Japanese market, the CB Throne, while continuing to produce the larger CB MercuRay. Representatives from Hitachi indicated that the CB Throne has not been submitted for FDA approval and that there is presently no intent to enter the US market with this smaller CBCT system.
Imtec and Sirona
The Imtec/Kodak Iluma and Sirona Galileos were exhibited at the IDS Congress; however, the specifications had not changed since our previous article. Sirona has completed studies on radiation dose for the Galileos, with a resulting value of 29 µSv.
The Planmeca ProMax 3D is fully FDA-approved for sale in the United States through authorized dealers of PLANMECA USA, Inc. It is the first CBCT system in the US market to have interchangeable sensors for both CBCT and for traditional digital panoramic radiographs. It is possible to purchase a digital panoramic system, then upgrade to CBCT later. The Planmeca ProMax 3D generator has a fixed anode with a 0.5-mm effective focal spot. The detector is a CsI-coated CMOS flat panel. The resolution is 0.18-mm isotopic voxel. There is a single 194° rotation to acquire the image data with a 16- to 18-second pulsed exposure, with an effective radiation exposure time of only 6 seconds. Fields of view are 800 mm x 800 mm, 500 mm x 800 mm, and 500 mm x 400 mm. Reconstruction time is typically under 3 minutes. Image reconstructions for the jaws and tempo-romandibular joints using the Planmeca Promax are shown in Figure 1. For more information, visit www.planmeca.com.
OTHER COMPANIES ANNOUNCING POTENTIAL ENTRY TO THE CBCT MARKET
Soredex (Helsinki, Finland) announced the development of the Scanora® 3D CBCT system and exhibited the system at IDS. The Soredex system can use a traditional digital panoramic detector as well as a CBCT panel. This system is not yet approved for sale in Europe or the United States (FDA approval is pending). The system uses a CMOS flat panel detector with a receptor active area of 12.4 x 12.4 cm. The field of view is adjustable (6 x 6 cm; 7.5 x 10 cm; 7.5 x 14.5 cm) with scan times of 10 to 20 seconds and reconstruction time of 1 to 3 minutes. The patient is seated. The dimensions are 1.963 m height; 1.541 m width, and 1.1 m depth. The output is specified as DICOM. For more information, e-mail email@example.com.
At the IDS, E-Woo Technology (Giheung-gu, South Korea) Vatech (Seoul, South Korea) exhibited a series of three different CBCT systems: Picasso Pro, a standard dental CT unit with a 12 cm x 7 cm field of view; Picasso Master, with a field of view of either 20 cm x 19 cm or 10 cm x 15 cm; and Picasso Trio, combining a CBCT field of view of 12 cm x 7 cm or 8 cm x 5 cm with traditional digital panoramic and cephalograms functions. The CBCT exposure sequences are 12 to 24 seconds and the system uses a full 360° rotation. Image reconstruction time is 29 seconds for the Picasso Master and 15 seconds for the Picasso Pro. The x-ray system has an effective focal spot of 0.49 mm and operates at 40 kV to 90 kV and 2 mA to 10 mA. The detector for CBCT is a flat panel. FDA approval for sale in the United States is pending. The E-Woo Picasso systems are already being sold in various parts of Europe and Asia and there are plans to enter the US market soon. For more information, visit www.e-wootech.com.
MyRay Dental Imaging
MyRay (Imola, Italy) exhibited the concept of a C-arm based CBCT system at IDS in which the patient would be supine on a platform of similar dimensions to a dental chair (footprint 1.5 m x 2.4 m). The system uses a 6-inch detector providing 11 cm x 11 cm x 11 cm or 7 cm x 7 cm x 7 cm fields of view. Resolution is 0.14 mm or 0.2 mm isotopic voxel. The generator works at 90 kV with a variable current up to 10 mA, and a 0.5-mm effective focal spot. The detector is an image intensifier with a 1,000 x 1,000 charge-coupled device (CCD) camera. Exposure can be varied from 10 seconds to 20 seconds (15 seconds standard). Images are 12-bit and reconstruction time is less than 4 minutes. Release to the US market is not anticipated until 2008. For more information, visit www.my-ray.com.
TeraRecon (San Mateo, CA)did not exhibit at the IDS but has shown the TeraRecon at each of the last two Radiological Society of North America meetings in Chicago 2005 and 2006, and at the American Dental Association Annual Congress in Las Vegas in 2006. The TeraRecon system is a sit-down unit and is approved for sale in Japan. The system runs at 120 kV and up to 10 mA with a focal spot of 0.2 mm. The detector is a flat panel combined with CsI scintillator and a maximum field of view of 8.1 cm diameter and 7.4 mm height. Detector resolution is 0.2 mm. Scan time is 20 seconds and reconstruction time 30 seconds. FDA approval is pending. For more information, visit www.terarecon.com.
CBCT OPTIONS CONTINUE TO GROW
While not all of the systems listed are presently available in the US market, dentists, dental specialists, and imaging centers do have a growing selection of options with respect to CBCT. The trend is toward smaller footprints that are closer to those of a panoramic dental system. There are options for the supine, seated, or standing patient. There are options for systems that are stand-alone CBCT and those combined with traditional digital and panoramic radiographic sensors. There are systems that can accommodate much of the head for 3-D orthodontic and surgical/pathologic assessments. Some of these larger field-of-view systems can be collimated to a specific region, whereas other cannot. Some systems have smaller fields of view that are aimed principally at dental implant placement and evaluation of limited volumes. The choice of system depends on usage needs.
OTHER IMAGING ANNOUNCEMENTS AT THE 2007 IDS
Back to “Tomography” through Digital Tomosynthesis
At the IDS Congress, Instrumentarium Dental Inc (Milwaukee, WI) exhibited the volumetric tomography option for the Orthopantomograph® OP200D as “an advanced tool for implantology.” This provides for a field of view of 6 cm x 6 cm x 6 cm with a minimum slice thickness of 0.23 mm. The images have a similar appearance in terms of blur to traditional film-based linear tomographs that have traditionally been used for evaluation of dental implant sites. A separate exposure sequence is needed for each region to be examined. Magnification needs to be factored. This is certainly not CBCT; however, the cost is an order of magnitude less provided that the panoramic system is already owned. It probably has a place for practitioners placing a very limited number of implants per patient. Use is greatly facilitated by on-screen directions at the system controls. For more information, visit www.instrumentariumdental.com.
After-the-Fact Adjustable Panoramic Focal Trough
AJAT (Espoo, Finland) produces CdTe-CMOS x-ray detectors that can be applied to the PC1000 by Panoramic Corporation (Fort Wayne, IN) (Figure 2 and Figure 3), Orthoralix 9200 by Gendex (Lake Zurich, IL), Hanjin DigiPano, OP100 by Instrumentarium Dental, and Orthophos 3 by Sirona. Cadmium telluride provides direct conversion of x-ray energy without the need for a scintillator and provides direct electronic signals to the CMOS chip. Images are acquired at 300 frames per second. The digital sensor is unique in that the dentition can be artificially detected in the image and the focal trough selected for the individual patient. If there are discrepancies between the maxillary and mandibular arch, it is even possible to save separate focal layers for each. This technology can compensate for the lack of complex computer-controlled motions on less sophisticated panoramic machines, making high-quality images on the least sophisticated and least expensive basic panoramic system.
The system collects 500 megabytes of raw data for a 3-cm range in focal layer, with the choice to save all data or simply to save the 1% to 4% of the data used for the selected image. At this stage there is the ability to use 2-dimensional (2-D) rotation and tilting tools; however, as there is a collection of data for a 3-cm field in the shape of the dental arch, it does not need much imagination to see that some limited 3-D applications should be possible in the future using this technology. The cost of the add-on sensor is, again, an order of magnitude less than the price of a full CBCT system. However, this is a solution for provision of digital panoramic images and not a substitute for CBCT. For more information, visit www.ajat.fi.
APPLICATIONS USING CBCT IMAGE DATA SETS
There has been a relatively rapid growth of 3-D applications for orthodontics. Three-dimensional data sets can be used to provide traditional cephalograms in 2-D via a ray-sum approach. Alternatively, it is possible to simulate the human anatomy in high detail using a variety of orthodontic-centered products such as Dolphin 3D (Dolphin Imaging & Management Solutions, Chatsworth, CA). It is also possible to superimpose precise 3-D photographic images made using the Dolphin imaging system (Figure 4). An alternative photographic input is available from 3dMD (Atlanta, GA).
Surgical Planning(Third Molars)
The relationship of the mandibular canals to the roots of mandibular third molar teeth is of importance when attempting to minimize the likelihood of nerve damage that can, at worst, lead to permanent loss of sensation to one side to the lower lip. Traditional panoramic imaging is sufficient when the third molar is clear of the canal, but in the case of radiographic superimposition, it is advisable to use a 3-D imaging approach. This can be achieved at a comparatively low radiation dose using CBCT combined either with the proprietary software accompanying the imaging device, or exporting to other diagnostic software. One such add-on software approach is the one provided by the Materialise Simplant program (Materialise Dental Inc, Glen Burnie, MD) (Figure 5). For more information, visit www.materialise.com. Services are available directly from Materialise, and also from other vendors such as 3D Diagnostix Inc (Brighton, MA). These conversion services accurately transform multipart x-ray scan files into a single 3-D image that is readable by dental clinicians. Any artifacts are also removed and key features can be colorized. For more information, visit www.3ddx.com.
Perhaps the greatest impact of CBCT has been on the planning of dental implants. For this, a number of solutions exist, including add-on services to the CBCT system proprietary software based upon DICOM file set output. This can be achieved using Simplant (Figure 6) and also by using other systems including Procera/Noble Guide (Nobel Biocare, Yorba Linda, CA; www.nobelbiocare.com), iDent (Fort Lauderdale, FL; www.identsurgical.com), and Implant Logic Systems (Cedarhurst, NY; www.implantlogic.com). See Figure 7 through Figure 9 for examples of virtual implant placement. In most instances, a radiographic stent is made using standard impression models. This stent is worn at the time of CBCT exposure to provide a precise fiducial reference. The CBCT data set is then sent to the outside laboratory and an implant placement stent is provided for use at surgery. This facilitates the precise placement of implants and speeds completion of the case. This procedure is enabling dentists to carry out implant procedures that were previously beyond their scope of practice.
As technology changes, there is the need for standards to keep up to make interoperability more likely. At this point in time, CBCT data output has been largely kept to that used with standard multislice computed tomography. Earlier this year Supplement 116 (3-D x-ray) was added to the DICOM Standard to specifically accommodate CBCT usage in healthcare including dentistry. DICOM Working Group 22 (Dentistry) collaborated with working groups on angiography and mammography among others to develop this new supplement. The American Dental Association acts as secretariat to DICOM WG 22.
CBCT technology provides 3-D images that facilitate the transition of dental imaging from initial diagnosis to image guidance throughout the treatment phase. It provides the third dimension on dental imaging and is extending dental imaging from diagnosis to image guidance of operative and surgical procedures. The importance that industry places on CBCT can be gleaned from the rapid growth of this sector in terms of new devices being readied for the marketplace.