1997 - SIDEXIS, of Siemens (currently Sirona, Germany) offered a digital option for Ortophos Plus panoramic unit, DigiPan of Trophy Radiology (France) offered a digital option for the OP100 panoramic made by Instrumentarium (Finland).
1998-2004 - many panoramic manufacturers offered their own digital system.
Historical milestones for Digital Panoramic Systems
1995 - DXIS, the world wide first dental digital panoramic X-rays system available on the market, introduced by Signet (France). DXIS targets to retrofit all the panoramic models.
Forming the image
Normally, the person bites on a plastic spatula so that all the teeth, especially the crowns can be viewed individually. The whole orthopantomogram process takes about one minute.
Because the collimation, while rotating, the X-rays projects on the film only a limited portion of the anatomy, at every instant but, as the rotation progresses around the skull, the whole maxillo-facial block is scanned. While the arm rotates, the film moves in a such way that the projected partial skull image (limited by the beam section) scrolls over it and exposes it entirely. Because the beam travels across the skull, the partial image it projects on the film every instant contains all the anatomical elements it crossed in the skull, overlapped. Not all the overlapped element images projected on the film have the same magnification because the beam is divergent and the elements are at different distances from the generator focus. Also not all the element images move with the same velocity on the target film as some of them are far and other closer to the instant rotation center. The velocity of the film is controlled in such fashion to fit exactly the velocity of projection of the anatomical elements of the dental arch side which is closer to the film. Therefore they are recorded sharply while the elements in different places are recorded blurred as they scroll at different velocity.
The dental panoramic image suffers from important distortions because a vertical zoom and a horizontal zoom both varying differently along the image. The vertical and horizontal zooms are determined by the relative position of the recorded element versus film and generator. Closer to the generator means bigger vertical zoom. More, the horizontal zoom is also dependent on the relative position of the element to the focal path. Inside the focal path arch means bigger horizontal zoom and blurred, outside means smaller horizontal and blurred.
The result is an image showing sharply the section along the mandible arch and blurred the rest. For example, the more radio-opaque anatomical region, the cervical vertebras (neck), shows as a wide and blurred vertical pillar overlapping the front teeth. The path where the anatomical elements are recorded sharply is called "focal path".
Equipment
Dental panoramic radiography equipment consists of a horizontal rotating arm which holds an X-ray source and a moving film mechanism (carrying a film) arranged at opposed extremities. The patient's skull sits between the X-ray generator and the film. The X-ray source is collimated toward the film, to give a beam shaped as a vertical blade having a width of 4-7mm when arriving on the film, after crossing the patient's skull. Also the height of that beam covers the mandibles and the maxilla regions. The arm moves and its movement may be described as a rotation around an instant center which shifts on a dedicated trajectory.
The manufacturers propose different solutions for moving the arm, trying to maintain constant distance between the teeth to the film and generator. Also those moving solutions try to project the teeth arch as orthogonally as possible. It is impossible to select an ideal movement as the anatomy varies very much from people to people. Finally a compromise is selected by each manufacturer and results in magnification factors which vary strongly along the film (15%-30%). The patient positioning is very critical in regard to both sharpness and distortions.
Orthopantomogram
An Orthopantomogram (OPG), also known as an "orthopantogram" or "panorex", is a panoramic scanning dental X-ray of the upper and lower jaw. It shows a two-dimensional view of a half-circle from ear to ear.
Occlusal view
The occlusal view is indicated when there is a desire to reveal the skeletal or pathologic anatomy of either the floor of the mouth or the palate. The occlusal film, which is about three to four times the size of the film used to take a periapical or bitewing, is inserted into the mouth so as to entirely separate the maxillary and mandibular teeth, and the film is exposed either from under the chin or angled down from the top of the nose. Sometimes, it is placed in the inside of the cheek to confirm the presence of a sialolith in Stenson's duct, which carries saliva from the parotid gland. The occlusal view is not included in the standard full mouth series.
Bitewing view
The bitewing view is taken to visualize the crowns of the posterior teeth and the height of the alveolar bone in relation to the cementoenamel junctions, which are the demarcation lines on the teeth which separate tooth crown from tooth root. When there is extensive bone loss, the films may be situated with their longer dimension in the vertical axis so as to better visualize their levels in relation to the teeth. Because bitewing views are taken from a more or less perpendicular angle to the buccal surface of the teeth, they more accurately exhibit the bone levels than do periapical views. Bitewings of the anterior teeth are not taken.
The name bitewing refers to a little tab of paper or plastic situated in the center of the X-ray film, which when bitten on, allows the film to hover so that it captures an even amount of maxillary and mandibular information.
Periapical view
The periapical view is taken of both anterior and posterior teeth. The objective of this type of view is to capture the tip of the root on the film. This is often helpful in determining the cause of pain in a specific tooth, because it allows a dentist to visualize the tooth as well as the surrounding bone in their entirety. This view is often used to determine the need for endodontic therapy as well as to visualize the successful progression of endodontic therapy once it is initiated.
The name periapical is derived from the Latin peri, which means "around," and apical, which means "tip."
Panoramic films
Panoramic films are extraoral films, in which the film is exposed while outside the patients' mouth, and they were developed by the United States Army as a quick way to get an overall view of a soldiers' oral health. Exposing eighteen films per soldier was very time consuming, and it was felt that a single panoramic film could speed up the process of examining and assessing the dental health of the soldiers; soldiers with toothaches are not very effective. It was later discovered that while panoramic films can prove very useful in detecting and localizing mandibular fractures and other pathologic entities of the mandible, they were not very good at assessing periodontal bone loss or tooth decay.
Full mouth series
A full mouth series is a complete set of intraoral X-rays taken of a patients' teeth and adjacent hard tissue.[1] This is often abbreviated as either FMS or FMX. The full mouth series is composed of 18 films:
- four bitewings
- eight posterior periapicals
- two maxillary molar periapicals (left and right)
- two maxillary premolar periapicals (left and right)
- two mandibular molar periapicals (left and right)
- two mandibular premolar periapicals (left and right)
- six anterior periapicals
- two maxillary canine-lateral incisor periapicals (left and right)
- two mandibular canine-lateral incisor periapicals (left and right)
- two central incisor periapicals (maxillary and mandibular)
The Faculty of General Dental Practice of the Royal College of Surgeons of England publication Selection Criteria in Dental Radiography holds that given current evidence full mouth series are to be discouraged due to the large numbers of radiographs involved, many of which will not be necessary for the patient's treatment. An alternative approach using bitewing screening with selected periapical views is suggested as a method of minimising radiation dose to the patient while maximizing diagnostic yield.
Dental radiography
Dental X-rays are pictures of the teeth, bones, and surrounding soft tissues to screen for and help identify problems with the teeth, mouth, and jaw. X-ray pictures can show cavities, hidden dental structures (such as wisdom teeth), and bone loss that cannot be seen during a visual examination. Dental X-rays may also be done as follow-up after dental treatments.
A radiographic image is formed by a controlled burst of X-ray radiation which penetrates oral structures at different levels, depending on varying anatomical densities, before striking the film or sensor. Teeth appear lighter because less radiation penetrates them to reach the film. Dental caries, tooth decay, infections and other changes in the bone density, and the periodontal ligament, appear darker because X-rays readily penetrate these less dense structures. Dental restorations (fillings, crowns) may appear lighter or darker, depending on the density of the material.
Historical milestones for Digital Panoramic Systems
- 1995 - DXIS, the world wide first dental digital panoramic X-rays system available on the market, introduced by Signet (France). DXIS targets to retrofit all the panoramic models.
- 1997 - SIDEXIS, of Siemens (currently Sirona, Germany) offered for Ortophos Plus panoramic unit, DigiPan of Trophy Radiology (France) offered for the OP100 panoramic made by Instrumentarium (Finland).
- 1998-2004 - many panoramic manufacturers offered their own digital system.
- 2005 - SCAN300FP, of Ajat (Finland) is the last one offered. It shows the feature to acquire many hundreds of mega bytes of image information at high frame rate and to reconstruct the panoramic layer by intensive post acquisition computing like a computed tomography. The main advantage is the ability to reconstruct focused differently. The drawback is the low signal/noise ratio of primary information which involves much software work for correction. Also the ability to reconstruct various layers raises the importance of the geometrical distortions already high in dental panoramic radiography.
Currently there are several digital systems for panoramic digital radiology. Some of them are rebranded. Examples: SCAN300FP of Ajat was or is sold as SuniPan or RetroPan or Panoramic Corporation pan, DXIS of Signet was or is sold also as of LightYear, Sigma Biomedics, Panoramic Corporation, AFP Digital or Bluex, iPan of Schick was or is sold as of Bluex or Panoramic Corporation, I-MAX of Owandy sold as of Villa, etc.
Historical milestones for Digital Intraoral Sensors
1987 - RVG, the world wide first intraoral X-rays imaging sensor available on the market, introduced by Trophy Radiology (France) was very quickly and largely recognized by the European dental market. This company is owned actually by Kodak and continues to produce intraoral sensors.
1992 - Sens-a-Ray of Regam (Finland) is offered. They closed the business and their technology is currently owned by Dent-X (USA).
1993 - VisualX of Gendex-Italy (subsidiary of USA company).
1994 - CDR of Schick Technology (USA). Also Schick Technology introduced last years a wireless CDR version being the only supplier offering such feature. This company is owned actually by Sirona (Germany).
1995 - SIDEXIS of Sirona, DEXIS of ProVison Dental Systems, Inc. (renamed DEXIS, LLC following its acquisition by Danaher Corp.), DIGORA (PSP solution) of Soredex (Finland)
Today there are many other products available under a lot of different names (rebranding is quite usual for this type of product)
The manufacturers claim the resolution is between 12 to 25 LP/mm. A useful precise comparison is difficult because depends on many parameters including the post processing or imaging software.
Digital radiographic systems
One particular type of digital system uses a Memory Phosphor Plate (a.k.a. PSP -- Photostimulable Phosphor) in place of the film. After X-ray exposure the plate (sheet) is placed in a special scanner where the latent formed image is retrieved point by point and digitized, using laser light scanning. The digitized images are stored and displayed on the computer screen. This method is halfway between old film-based technology and current direct digital imaging technology. It is similar to the film process because it involves the same image support handling but differs because the chemical development process is replaced by the scanning process. This is not much faster than film processing and the resolution and sensitivity performances are contested. However, it has the clear advantage to be able to fit within any pre-existing equipment without modification because it replaces just the existing film.
Also, sometimes the term "Digital X-rays" is used to designate the scanned film documents which are handled by further computer processing.
Other types of digital imaging technologies use electronic sensors. A majority of them first convert the X-rays into visible light (using a GdO2S or CsI layer), which is further captured using a CCD or a CMOS image sensor. Some of them use a hybrid arrangement which first converts the X-rays into electricity (using a CdTe layer) and then captures this electricity as an image with a reading section based on CMOS technology.
Radiological examinations
Dental
The radiological examinations in dentistry may be classified in: intraoral - where the film or the sensor is placed in the mouth, the purpose being to visualize a limited region and extraoral where the film or the sensor is outside the mouth and the purpose is to visualize a wide region. In dentistry, extraoral imaging splits in: Panoramic X-ray (aka "panorex" or "pano") showing a section, curved following more or less mandible shape, of the whole maxillo-facial block and the Cephalometric X-ray showing a projection, as parallel as possible, of the whole skull.
Digital radiography
Digital radiography is a form of x-ray imaging, where digital X-ray sensors are used instead of traditional photographic film. Advantages include time efficiency through bypassing chemical processing and the ability to digitally transfer and enhance images. Also less radiation can be used to produce an image of similar contrast to conventional radiography.
Note: this term is restricted to flat, two-dimensional imaging. For more advanced forms of three-dimensional calculated images, see Computed tomography.
Disadvantages
- CR is still not an approved method for most higher quality radiologic applications (aerospace), due to the possibility of digital manipulation to the captured image, the inherent geometric unsharpness and resultant lower spatial resolution as compared to film (radiographic) images, SNR (signal vs. noise)issues and sensitivity to scattered radiation, and the general lack of procedural consensus among primes and OEM's.
- Imaging plates (IP's) are quite expensive and can be easily damaged, if the system being used requires manual handling of the IP's. Theoretically, IP's may be reused thousands of times, but constant use will always result in damage to the IP and image artifacts, eventually to the point of necessary replacement.
Advantages
- No silver based film or chemicals; instead a computer is used.
- Exposure times are a fraction of typical film exposures, which reduces occupational exposure to radiographers in field applications and is more economical.
- Image acquisition is much faster; commonly one minute instead of seven minutes, as with conventional radiography.
- By adjusting image brightness and/or contrast, a wide range of thicknesses may be examined in one exposure, unlike conventional film based radiography, which may require a different exposure or multiple film speeds in one exposure to cover wide thickness range in a component. Computed radiography often requires fewer re-shots due to under- or over-exposure.
- Images can be enhanced digitally to aid in interpretation.
- Images can be stored on disk or transmitted for off-site review.
- Ever growing technology makes the CR more affordable than ever today. With Chemicals, dark room storage and staff to organize them, you could own a CR for the same monthly cost while being environmentally conscious, depending upon the size of the Radiographic Operation.
Medical applications
- Computed Radiography systems are the most common in medical applications because of their low cost. (compared to other similar technologies)
Plate based DR usually starts at around $150,000.00, while CR starts at around $100,000.00. DR (plate detector) systems must be dedicated to a single X-ray Generator due to the detector to workstation interface. CR IP's can be used in multiple X-ray sites and the IP's processes through a single reader (scanner), similar to a film processor.
Industrial applications
Common applications for computed radiography include:
- corrosion surveys on pipes, often through insulation;
- Examination of valves for erosion;
- Information shots on industrial components; e.g. checking to see if a valve is closed properly, or checking for obstructions in valves and pipes;
- Examination of boiler water walls;
- Weld examination for certain ASME code applications
- Automotive casting inspection
- High pressure braze joint inspection (aerospace)
- Wax pattern core integrity verification in investment casting foundries
Imaging plate
The CR imaging plate contains photostimulable storage phosphors, which store the radiation level received at each point in local electron energies. When the plate is put through the scanner, the scanning laser beam causes the electrons to relax to lower energy levels, emitting light that is detected by a photo-multiplier tube, which is then converted to an electronic signal. The electronic signal is then converted to discrete (digital) values and placed into the image processor pixel map. Imaging plates can theoretically be re-used thousands of times if they are handled carefully, although handling under industrial conditions may result in damage after a few hundred uses. An image can be erased by simply exposing the plate to a room-level fluorescent light. Most laser scanners automatically erase the image plate after laser scanning is complete. The imaging plate can then be re-used. In the software, the scanned image is encrypted so that the original data is kept secure and can not be tampered with. Reusable phosphor plates are environmentally safe.
Differences from Direct Radiography
Computed radiography is commonly distinguished from Direct Radiography (DR). The difference is that after exposure a DR system will almost instantly display the image on the display in front of the radiographer, therefore removing any need for processing. Image processing or enhancement can of course be performed on DR images in the same way that CR images can due to the digital format of each. There are many different types of DR detectors in use in medicine and industry. Each type has its own merits and distinctions and may be applied to certain imaging requirements based on these attributes.
CR and DR should not be confused with Fluoroscopy, where there is a continuous beam of radiation, and the images appear on the screen like on a TV. This is the system many people are familiar with, where the image of the article being x-rayed is viewed in real time on a monitor or display. Many people think airports use Fluoroscopes for baggage inspection, when in fact LDA's (Linear Diode Arrays)are universally used to generate static images of luggage content. LDA's are also used in a wide variety of other screening and imaging applications, and are also presented in a digital format. Modern fluorosopes use a device called an image intensifier to enhance the analog output of the real time x-ray image, where it is picked up by either a video or CCD camera and digitally enhanced to reduce the noise inherent in the system.
What is Computed Radiography
Computed Radiography (CR) uses very similar equipment to conventional radiography except that in place of a film to create the image, an imaging plate is used. The imaging plate is placed under the object to be examined and the x-ray exposure is made. Hence, instead of taking an exposed film into a darkroom for developing in chemical tanks or an automatic film processor, the imaging plate is run through a special laser scanner to read and digitize the image. The digital image can then be viewed and enhanced using software that has functions very similar to other conventional digital image-processing software, such as contrast, brightness, filtration and zoom.
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