Digital Image Receptors

Digital Image Receptors

Panoramic x-ray systems are available that use either linear array charge-coupled device (CCD) or complementary metal oxide semi-conductor (CMOS) detectors as well as photostimulable phosphor plate (PSP) receptors. CCD/CMOS and PSP receptors are used for intraoral radiography as well but with altered sizes and receptor designs. The digital panoramic imaging method is comparable to film-based panoramic radiography but the receptor, processing, display, storage, and transmission capabilities differ. ^5,11 Both types of digital image receptors will produce diagnostic results when properly utilized and maintained.

Direct Digital Image Receptors

CCD/CMOS linear array designs arrange the detector in a grid with the same vertical dimension as panoramic film but only a few pixels wide. The vertical sensor is moved around the patient opposite to the x-ray source and captures the image one vertical line at a time. In the subsequent photographs, a CCD sensor system is used to capture the image. To initiate the process, a patient file must be created in the computer software system. (Figure 4) The patient is aligned in the same head positions as required in film-based panoramic x-ray machines.(Figure 5) The computer processes the image as it is acquired. Then, the image is displayed on the computer monitor in real time.(Figure 6) The image is archived in the patient database and electronic patient record. The acquired images can be viewed in diverse ways through the application of software enhancement tools.

Direct Digital Panoramic Imaging

Figure 4.

Figure 4.

Figure 5.

Figure 5.

Figure 6. Panoramic Image.

Figure 6. Panoramic Image.

Photostimulable Phosphor Plate (PSP)

PSP sensors consist of a rare earth phosphor, barium europium fluorohalide, coated onto a polyester base.(Figure 7) A PSP plate is inserted into a cassette just like film but without the intensifying screens. The image is captured on the phosphor plate, and the energy is stored on the plate until it released during a laser scanning process. When a helium-neon laser beam scans the PSP plate, the energy is released in the form of blue florescent light.¹¹ The emitted light is captured, intensified by a photomultiplier tube and converted into digital data. PSP plates are reusable but must be exposed to light to erase remnant energy. More recent developments include faster plate scanning and erasure of the plate during the scanning process. It is important to scan the exposed plate without delay as white light or delayed scanning can degrade the image result.^11,12 PSP imaging is considered an indirect digital imaging method because the data is captured in an analog format like film and then converted into digital data via the scanning process.

Figure 7. Photostimulable Phosphor Plate.
Emulsion or exposure side – Blue
Non-exposure side - Black

Figure 7. Photostimulable Phosphor Plate.
Emulsion or exposure side – Blue
Non-exposure side - Black

The obvious advantage of digital panoramic imaging, particularly direct digital panoramic imaging, is elimination of the darkroom, processing machine maintenance, and associated processing errors. Other advantages include timesaving, electronic image storage and transfer, the ability to enhance the captured image with various software tools (e.g. density, contrast, measurement, image reversal manipulations), and teleradiography capabilities for the purposes of consultation, insurance claims, or referral.

Image quality, regardless of receptor type, remains operator-dependent. The technical requirements of proper patient preparation, positioning, and exposure selection are essential to produce optimal results and to avoid retakes.