Vertical magnification correction in vertical dual-exposure panoramic radiography.

PURPOSE: To clarify the magnification error caused by the degree of tilt of the incisor and the elevation of the X-ray focus position, and the verification effect of magnification correction when performing vertical dual-exposure panoramic radiography. METHODS: Panoramic radiographic images of a phantom embedding 26 steel balls were taken at different heights (0, 5, 10, 15, and 20 mm) and tilt angles (0°, 10°, 20°, and 30°) to evaluate vertical magnification in each condition. Error and correlation coefficients in the vertical magnifications were calculated between the measured and theoretical magnification values. RESULTS: The more the steel ball phantom was tilted, the more the images of the uppermost steel balls were laterally stretched. In the vertical direction, image magnification also influenced the tilt angle of the object in the incisal region. The range of error in vertical magnification was -0.35-0.30%. The Spearman's rank correlation coefficient between the measured and theoretical magnification value was 0.983. CONCLUSION: Vertical magnification correction has the potential to improve image quality when merging panoramic radiographs in vertical dual-exposure panoramic radiography.

Reduction of cervical vertebra ghost images in panoramic radiography using vertical dual exposure.

PURPOSE: To evaluate the image quality of vertical dual-exposure panoramic radiography (PR), which merges two PR images taken at different focus heights to reduce ghost images of cervical vertebrae (CV) and intervertebral spaces (IVS) in the incisor region. METHODS: PR images of an aluminum block, a CV phantom and a human head phantom were taken at 0 mm and merged with and subtracted from PR images taken at other heights (0, 5, 10, 15, and 20 mm) to create new images, e.g., Merg0 + 15 mm and Sub0 - 10 mm. The subtracted images were analyzed subjectively according to the uniformity on the line profile. Merged images were evaluated subjectively by six raters to determine the influence of the ghost images. RESULTS: Objective evaluation revealed a positional shift in the ghost images according to the height of the focus for both phantoms. In the subjective evaluation, the normal PR (Merg0 + 0 mm) showed the worst score, indicating strong influence of CV and IVS ghost images. CONCLUSION: The vertical dual-exposure PR method, which merges PR images taken at the normal position and a higher X-ray focus, can reduce CV and IVS ghost images in the incisor region.

Correction of intraoral radiography with dual imaging plates using enlargement of the horizontal direction with division into 12 blocks.

PURPOSE: The dual imaging plate (DIP) method, which synthesizes intraoral radiographs from a front imaging plate (FIP) and a back imaging plate (BIP), produces adequate image quality and allows the radiation dose to be reduced. However, there are slight errors in superimposition and alignment between the FIP and BIP. The aim of this study was to establish positional correction in the DIP method and evaluate the effect. METHODS: Six sets of two imaging plates were used for imaging a mesh plate and a porcine mandible phantom. Subtraction images between FIP and BIP images were synthesized in four steps: correcting horizontal and vertical direction, rotation, enlargement ratio, and enlargement ratio into 12 blocks. Variance of the pixel value on the subtraction images at each step was compared to evaluate the alignment of FIP and BIP images. RESULTS: The variance of the pixel values in the subtraction images was gradually and significantly decreased by each step of image processing (P < 0.01), indicating that the degree of alignment of FIP and BIP images improved during the image processing. CONCLUSION: The present study revealed that it is possible to synthesize more precise DIP images using an additional four-step image processing technique.

Reduction of scratch or dirt artifacts on intraoral radiographs using dual imaging plates in image processing.

OBJECTIVES: Artifacts including scratches and dirt artifacts on the digital intraoral radiographs finally contribute to making inaccurate diagnoses. The aim of this study was to reduce the incidence of artifacts using dual imaging plates (DIPs) in imaging processing. METHODS: Conventional X-rays were taken of a porcine mandible embedded in acrylic resin using a DIP which consists of a front IP (FIP) and a back IP (BIP) with some scratches and dirt. The two images of the FIP and BIP were then synthesized and averaged to obtain a conventional DIP image. The following image processing method was used to make a DIP with artifact reduction (DIP+AR) image. A subtraction image of the FIP and BIP was constructed and the standard deviation (SD) was calculated. If the pixel value was over 3SD on the subtraction images, the pixel value of the DIP was swapped with the value on the opposite side of the non-artifact pixel. The conventional and DIP+AR images were also subjectively evaluated. RESULTS: Image processing to create a DIP+AR image was able to reduce the number of artifacts. Medians of number of artifacts evaluated were 2.00 [interquartile range (IQR), 2.50] in DIP images and 0.67 (IQR, 1.29) in DIP+AR images, indicating a significant reduction of number of artifacts in DIP+AR images. CONCLUSIONS: DIP+AR image processing can reduce the incidence of artifacts caused by scratches and dirt, and could extend the lifespan of the IP and contribute accurate diagnosis in oral radiology.

Preliminary evaluation of dual imaging plate intraoral radiography.

PURPOSE: This study evaluated the contrast-to-noise ratio (CNR), spatial resolution, and subjective quality of dual imaging plates (DIP) intraoral radiography. METHODS: The DIP and conventional single IP (CSIP) methods both used YCR DT-1 imaging plates (Yoshida Co.). The DIP, comprising a front IP (FIP) and back IP (BIP), was constructed. DIP images were synthesized from the FIP and BIP images. An aluminum step phantom was used to measure the CNR. A line pair gauge was used to measure the spatial imaging resolution. A phantom comprising a porcine mandible embedded in acrylic resin was used for subjective evaluation. RESULTS: The CNR of the DIP image was 32% higher than that of the FIP image. The spatial resolution achieved using the FIP, DIP, and CSIP was highly comparable except above 4 line pairs/mm, where that of the CSIP was highest. In subjective evaluation, the noise in the DIP images was significantly lower than in those obtained using the FIP and CSIP. CONCLUSION: The CNR of the DIP was higher than that of the FIP. The decrease in spatial resolution of the DIP was limited. The subjective image quality of the DIP was higher than that of the FIP.