## 8 Newest Advances for PAN in a Digital Era  
Recently, advances in PAN have had a significant impact on improving image sharpness without neglecting any aspects related to patient health. The design of state-of-the-art dental panoramic units is based on multi-layer recording, flexible radiation beam collimation, quick scan modes, the correction of positioning errors and motion artefacts, and reductions in effective doses [27]. Multiple panoramic imaging generates a set of several parallel and thin layers within the focal trough so that manual or automatic image postprocessing enables one to choose the best segments of one-time registered layers and gather them in a high-quality PAN. This system makes it possible both to more accurately examine patients with malocclusion  
Figure 11: Motion artefact represented by the stepped-stairs effect on the mandibular lower edge below the left first molar due to the rapid (abrupt) movement of the patient before X-ray tube crosses over their back. Figure 12: Motion artefact. The movement of a young patient after X-ray tube crosses over their back can be observed as a blurred and distorted image on the mandibular canine/premolar area on the right side. or maxillofacial asymmetries and to correct positioning errors on the anteroposterior plane due to the incorrect location of incisors on the bite block [27]. Different radiation beam collimations allow one to acquire different kinds of PAN, including the orthogonal PAN that reduces crown overlapping of adjacent teeth, which provides a better periodontal analysis; selectable segmentation into two (hemi-panoramic) or four quadrants with optimized projections to reduce the radiation dose; and four-segment bitewing exposures that are limited to crowns, though this is an alternative technique to intraoral imaging and is prized by patients with strong gag reflexes when it comes to examining interproximal caries. In addition, specific protocols for pediatric patients are capable of limiting radiation doses by means of a reduction in exposure parameters and times. This is made possible because children have small mouths; therefore, the robotic C-arm in panoramic machines can carry out a rotation arch that is shorter than normal by removing the initial and final parts of the exposure [17; 37]. Some dental panoramic units automatically adjust the size of the field of view in relation to a patient's date of birth, while others implement technologies that recognize the individual dental arch morphology associated with the best focusing selection systems to optimize exposure and scan times for people of all ages. Modern machines may be also equipped with a quick scan mode. Regardless of exposure time, this is a high-speed scan option that enables the performance of a PAN in 7 to 10 s. The short scan time reduces the chance of movement in uncooperative patients such as small children, old adults, and people with motor disabilities. When associated with low exposure times, a fast PAN significantly reduces the delivered radiation dose; therefore, such scans should be used in children for primary investigations and in cases of multiple follow-ups [27]. Furthermore, algorithms compensating for a patient's movement may be available, making it possible to correct a limited range of movement (up to 1.5 cm). This option is not only useful for children but also for patients with involuntary movements, e.g., Parkinson's disease. Some dental panoramic units are fitted with cameras that enable the verification of both the choice of shape/size of dental arches that come closest to those of patients and their positioning by different colored lines corresponding to acceptable or incorrect localizations of horizontal and vertical reference planes. An image preview may be also visible live on the screen panel during the examination to verify potential patient movement.