- Email: [email protected]
Effect of delayed scanning of storage phosphor plates
Vol. 99 No. 5 May 2005
ORAL AND MAXILLOFACIAL RADIOLOGY
Editor: Allan G. Farman
Effect of delayed scanning of storage phosphor plates B. Gu¨niz Akdeniz, DDS, PhD,a Hans-G€oran Gr€ondahl, DDS, PhD,b and Timur Kose, PhD,c Izmir, Turkey, and G€ oteborg, Sweden ¨ TEBORG UNIVERSITY EGE UNIVERSITY AND GO
Objective. To test longevity of image quality in storage phosphor plates (SPPs) at various exposure settings, storage conditions, and delays in scanning.
Study design. Fifteen Digora plates were exposed from 0.08 to 0.20 seconds and scanned immediately, 10, 30, and 60 minutes, and 24 hours after exposure. Plates were stored both in daylight and in a light-tight box. Mean gray values (MGVs) were compared using 2 3 5 3 5 factorial ANOVA. Interaction between variables was tested using Bonferroni/Dunn multiple comparisons test. Results. MGVs decreased with increase in exposure but increased with the scan delay. Only MGVs of plates scanned within 10 minutes after exposure were not significantly different from the ones scanned immediately (P [ .05). MGVs increased with scan delay for all exposure times no matter how the plates were stored (P \ .05). Conclusion. Based on the time delays examined, it is recommended to scan the Digora SPP no later than 10 minutes after exposure. Longer periods may cause loss of quality. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:603-7)
The storage phosphor system became a reality in intraoral digital imaging in the 1990s with the release of the Digora system by Soredex (Helsinki, Finland). The storage phosphor plate (SPP) has approximately the same size and flexibility as conventional film and the exposure latitude is wide.1-3 Studies comparing the image quality of phosphor plates to conventional film and charge-couple device (CCD) systems report similar or better image quality with the phosphor plate4,5 and a wider dynamic range.1,6 Subjective evaluation of different types of intraoral storage phosphor systems with regard to image quality pertaining to various clinical tasks has, in general, found the quality of Digora images to be high.7-9 a
Associate Professor, Department of Oral Diagnosis and Radiology, School of Dentistry, Ege University. b Professor and Chair, Oral and Maxillofacial Radiology, Faculty of Odontology, Sahlgrenska Academy, G€oteborg University. c Assistant Professor, Department of Computer Engineering, School of Engineering, Ege University. Received for publication Sep 30, 2004; returned for revision Nov 23, 2004; accepted for publication Dec 14, 2004. Available online 3 February 2005. 1079-2104/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.tripleo.2004.10.021
The photostimulable phosphor plates are normally sealed in a protective light-tight polymer bag, protecting them from contamination with saliva and surrounding light. It is generally recommended to scan the plate soon after exposure. However, this may not always be possible in busy dental clinics and hospitals. Sometimes, plates are exposed in different locations and then brought to the center where they are scanned, which may cause a considerable delay in scanning. Although Digora produces high-quality images of dental structures under ideal conditions, exposed-but-not-scanned SPPs may lose some of the information with time. Although the image quality of SPPs for various systems has been evaluated in many studies,4,9,10 how long it remains unaffected by delayed scanning of the image plate is still an unanswered question. The aim of this study was to determine the longevity of the image quality in storage phosphor plates of the Digora system at various exposure settings, storage conditions, and delays in scanning.
MATERIAL AND METHODS Fifteen blue Digora storage phosphor plates were used and scanned in the Digora FMX-scanner calibrated 603
604 Akdeniz, Gr€ ondahl, and Kose
OOOOE May 2005
Fig 1. Experimental set-up demonstrating the number of exposed plates.
for a highest exposure of 1.00 second. The plates were exposed with an x-ray unit (Anthos Ac, Anthos Company, Imola, Italy) with 2.5 mm aluminum (Al) equivalent total filtration at 65 kVp and 10 mA, using a focus-to-receptor distance of 20 cm. An optical bench was used to standardize geometric projection. The resulting images were transferred as 8-bit TIFF files to a personal computer (CM-1454NEL, Lite-On Technology Corp, Dong Guang, China) and analyzed with a software program (Image Tool 3.0 SDK; University of Texas Health Sciences Center, San Antonio, Texas) developed particularly for dental image analysis. Parameters of initial dose (exposure time), time after exposure (scan delay), and 2 different storage conditions were included in the statistical evaluation of possible image quality degradation. The effect of initial dose on the image quality was tested using an Al step-wedge made of 99.5% pure aluminum and with 5 2-mm incremental steps. The wedge was exposed at 5 time settings ranging from 0.08 to 0.20 seconds. In Fig 1 the experimental set-up is shown, demonstrating that a total of 135 exposures were made. Fifteen new plates were first cleared from any background effect by means of the strong light source built into the scanner and then reused throughout the experiment. The strong light removes any residual information still stored in the plates and thus brings the plates back to their original state leaving no memory of previous experiments behind. Plates were scanned immediately, 10, 30, and 60 minutes, and 24 hours after they were exposed. Mean gray values of the immediately scanned plates provided the gold standard values. Scanned plates were stored in their envelopes both in a room with daylight and in a light-tight box in order to evaluate the effect of different storage conditions. Each exposure was repeated 3 times for each parameter being included in the statistical analysis, that is, initial dose (5 settings), storage (2 conditions), and scanning delay (4 different). This results in 3 3 5 3 4 3 2 = 120 images. The remaining 15 images (135 ÿ 120) were
Fig 2. MGVs for various exposures and immediate scanning.
those that were scanned immediately and served as reference images. When all plates had been scanned, the gray-level information in each step of the Al wedge was sampled with 3 nonoverlapping (40 3 40 pixel) regions of interest (ROI). Black was assigned a value of 0 and white a value of 255. An average gray-level value for each step in each separate image was calculated from the 3 ROIs. Later on, mean gray values (MGVs) were determined for each step from the information in the 3 images obtained by repeat exposures. Contrast was measured as gray-level differences at various settings and conditions. Contrast was compared on the basis of gray-level differences between the highest and lowest gray values. The data were statistically analyzed using 2 3 5 3 5 factorial ANOVA (P \.05). Bonferroni/Dunn multiple comparison test was used to assess the difference between group means. RESULTS Mean gray values for each step of the Al step-wedge obtained from plates that were scanned immediately after being exposed are shown in Fig 2. Exposure of plates for 0.08 and 0.20 s produced pixel values between 148 and 242. Analysis of variance revealed that MGVs of plates exposed for 0.08 s and 0.10 s were not significantly different from each other. MGVs acquired for all other exposures were significantly lower (P \ .05). Figure 3 is an example showing the MGVs of all steps of the wedge in immediately scanned plates and in those scanned after delays of 10, 30, and 60 min and 24 h. In general, MGVs decreased with the increase in exposure time but increased with the scan delay. All results mentioned above were valid and
OOOOE Volume 99, Number 5
Akdeniz, Gr€ ondahl, and Kose 605
Fig 3. MGV changes for various scan delays for each step of Al step-wedge.
similar for each step of the wedge. Gray-level changes with regard to scan delay were higher for darker image areas (thinner steps) for all exposure times and scan delays used (P \.05). Figure 3 shows the change in contrast with regard to scan delays. Comparison of the contrast revealed that it decreased with increasing scanning delays. The decrease in contrast was larger for darker image areas than
for lighter ones. However, the relative change in contrast was nearly similar at different exposures and thus various gray levels. Statistical analysis indicated that MGVs of the plates scanned after 30 and 60 min and 24 h were significantly higher than those scanned immediately (P \ .05) whereas MGVs of plates scanned 10 min after exposure were not (P [.05). Furthermore, comparison of only
OOOOE May 2005
606 Akdeniz, Gr€ ondahl, and Kose
Fig 4. Pixel density differences due to different storage conditions of storage phosphor plates.
10, 30, and 60 min and 24 h delay values with each other revealed that only the MGVs of plates scanned 10 min after exposure were significantly different from the ones scanned 24 h later (P \.05). No significant differences were obtained between MGVs of plates with scan delay of 30 and 60 minutes. This pattern of increase in MGVs was observed for both storage conditions. However, MGVs of plates kept in daylight were significantly higher than those stored in light-tight environment (P \.05). The increase in pixel values with respect to scan delay exhibited a harmonious (symmetrical) ascending pattern for plates stored in a light-tight box but not for plates kept in daylight (Fig 4). The Bonferroni/Dunn test revealed significant interaction between the initial dose (exposure time) and delay in scan time for the plates stored in a light-tight environment (P = .0003). However no interaction between these 2 parameters were found for the plates stored in daylight. The other double or triple interactions of the parameters used in this study, namely storage conditions, exposure times, and scan delays, did not show any interaction with each other. DISCUSSION The increase in mean gray values with the scan delay signifies that time after exposure is 1 of the causes of fading of the latent image. The loss of image quality is due to the decay (loss of electrons from their traps in the higher energy states) that occurs with time or due to the ambient light (light leaking through the envelope).11 It is relevant that the amount of information lost is higher for darker image areas, because this leads to lower contrast.
According to the manufacturers of storage phosphor plates they start losing information within 5 minutes of image capture, and within the first hour close to 50% is lost.11 However, we found images of similar density and contrast up to 10 minutes after the initial exposure. The latent image started to fade away if the scanning was delayed more than 10 minutes with subsequent increase in MGVs. When the immediate scan (gold standard) values were left out of the comparison it was observed that only the plates scanned 10 minutes after exposure showed a significant difference to the ones scanned after 24 hours. Therefore, it is possible to recommend that storage phosphor plates should be scanned within 10 minutes after being exposed. However, scan delays up to an hour have a limited effect on the latent image stored in the plates. This finding partly corresponds to those of Martins et al11 but is somewhat different to the findings of a study by Hildebolt et al.12 The latter found that 25%-50% of the latent image stored in phosphor plates is lost within the first hour after exposure and that the relative rate of loss declines with time.12 Further research using shorter time intervals for the scan delays is needed to assess the threshold value for scan delay. Additionally, the clinical relevance of this loss remains to be analyzed because some compensation for it can be achieved by image processing.13,14 Once the phosphor plate is read, it is flooded with light to erase any remaining image and to prepare it for the next exposure. Since the latent image is erased by exposure to light, it is important to avoid exposing the phosphor plate to excessive amount of background light before it is scanned. The pattern of increase in mean gray values of plates stored in a light-tight environment
OOOOE Volume 99, Number 5
indicates that the information loss is due to an unforced return of the electrons to their original state.12 Random increases in mean gray values of plates kept in daylight indicate that light leakage through the plastic envelopes may be the cause. In the present study, mean gray values of plates increased as a function of exposure time and delayed scanning only if the plates were kept in darkness. Such an interaction could not be defined for the plates kept in daylight because abrupt increases in mean gray values were observed. If the findings of the present study are extrapolated into clinical settings where full mouth surveys are required, one may suggest that by the time the last plate is exposed, especially by a beginning student, the first plate may have lost a fair amount of its trapped electrons. In conclusion, although storage phosphor plates do not lose all their information for many days, it is recommended that they be scanned no later than 10 minutes after exposure to obtain best quality images. If plates cannot be scanned within 10 minutes they should be kept in a light-tight environment until scanned. REFERENCES 1. Wenzel A, Gr€ ondahl H-G. Direct digital radiography in the dental office. Int Dent J 1995;45:27-34. 2. Huda W, Rill LN, Benn DK, Pettigrew JC. Comparison of a photostimulable phosphor system with film for dental radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;83:725-31. 3. Wenzel A. Digital radiography and caries diagnosis. Dentomaxillofac Radiol 1998;27:3-11. 4. Borg E, Attaelmanan A, Gr€ondahl H-G. Subjective image quality of solid-state and photostimulable phosphor systems for digital intra-oral radiography. Dentomaxillofac Radiol 2000;29:70-5.
Akdeniz, Gr€ ondahl, and Kose 607 5. Moystad A, Svanaes DB, Risnes S, Larheim TA, Gr€ondahl H-G. Detection of approximal caries with a storage phosphor system. A comparison of enhanced digital images with dental x-ray film. Dentomaxillofac Radiol 1996;25:202-6. 6. Borg E, Gr€ondahl H-G. On the dynamic range of different x-ray photon detectors in intra-oral radiography. A comparison of image quality in film, charge-coupled device and storage phosphor systems. Dentomaxillofac Radiol 1996;25:82-8. 7. Hintze H, Wenzel A, Frydenberg M. Accuracy of caries detection with four storage phosphor systems and E-speed radiographs. Dentomaxillofac Radiol 2002;31:170-5. 8. Oliveira AE, de Almeida SM, Paganini GA, Haiter Neto F, Boscolo FN. Comparative study of two digital radiographic storage phosphor systems. Braz Dent J 2000;11:111-6. 9. Kitagawa H, Farman AG, Scheetz JP, Brown WP, Lewis J, Benefiel M, Kuroyanagi K. Comparison of three intra-oral storage phosphor systems using subjective image quality. Dentomaxillofac Radiol 2000;29:272-6. 10. Shearer AC, Mullane E, Macfarlane TV, Gr€ondahl H-G, Horner K. Three phosphor plate systems and film compared for imaging root canals. Int Endod J 2001;34:275-9. 11. Martins MGBQ, Haiter Neto F, Whaites EJ. Analysis of digital images acquired using different phosphor storage plates (PSPs) subjected to varying reading times and storage conditions. Dentomaxillofac Radiol 2003;32:186-90. 12. Hildebolt CF, Couture RA, Whiting BR. Dental photostimulable phosphor radiography. Dent Clin North Am 2000;44:273-97, vi. 13. Gotfredsen E, Wenzel A, Gr€ondahl H-G. Observers’ use of image enhancement in assessing caries in radiographs taken by four intra-oral digital systems. Dentomaxillofac Radiol 1996;25: 34-8. 14. Analoui M. Radiographic image enhancement. Part I: Spatial domain techniques. Dentomaxillofac Radiol 2001;30:1-9.
Reprint requests: B Gu¨niz Akdeniz Ege Universitesi, Dishekimligi Fakultesi Oral Diagnoz & Rad AD, Bornova, 35100 Izmir, Turkey [email protected]
ORAL AND MAXILLOFACIAL RADIOLOGY
Editor: Allan G. Farman
Effect of delayed scanning of storage phosphor plates B. Gu¨niz Akdeniz, DDS, PhD,a Hans-G€oran Gr€ondahl, DDS, PhD,b and Timur Kose, PhD,c Izmir, Turkey, and G€ oteborg, Sweden ¨ TEBORG UNIVERSITY EGE UNIVERSITY AND GO
Objective. To test longevity of image quality in storage phosphor plates (SPPs) at various exposure settings, storage conditions, and delays in scanning.
Study design. Fifteen Digora plates were exposed from 0.08 to 0.20 seconds and scanned immediately, 10, 30, and 60 minutes, and 24 hours after exposure. Plates were stored both in daylight and in a light-tight box. Mean gray values (MGVs) were compared using 2 3 5 3 5 factorial ANOVA. Interaction between variables was tested using Bonferroni/Dunn multiple comparisons test. Results. MGVs decreased with increase in exposure but increased with the scan delay. Only MGVs of plates scanned within 10 minutes after exposure were not significantly different from the ones scanned immediately (P [ .05). MGVs increased with scan delay for all exposure times no matter how the plates were stored (P \ .05). Conclusion. Based on the time delays examined, it is recommended to scan the Digora SPP no later than 10 minutes after exposure. Longer periods may cause loss of quality. (Oral Surg Oral Med Oral Pathol Oral Radiol Endod 2005;99:603-7)
The storage phosphor system became a reality in intraoral digital imaging in the 1990s with the release of the Digora system by Soredex (Helsinki, Finland). The storage phosphor plate (SPP) has approximately the same size and flexibility as conventional film and the exposure latitude is wide.1-3 Studies comparing the image quality of phosphor plates to conventional film and charge-couple device (CCD) systems report similar or better image quality with the phosphor plate4,5 and a wider dynamic range.1,6 Subjective evaluation of different types of intraoral storage phosphor systems with regard to image quality pertaining to various clinical tasks has, in general, found the quality of Digora images to be high.7-9 a
Associate Professor, Department of Oral Diagnosis and Radiology, School of Dentistry, Ege University. b Professor and Chair, Oral and Maxillofacial Radiology, Faculty of Odontology, Sahlgrenska Academy, G€oteborg University. c Assistant Professor, Department of Computer Engineering, School of Engineering, Ege University. Received for publication Sep 30, 2004; returned for revision Nov 23, 2004; accepted for publication Dec 14, 2004. Available online 3 February 2005. 1079-2104/$ - see front matter Ó 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.tripleo.2004.10.021
The photostimulable phosphor plates are normally sealed in a protective light-tight polymer bag, protecting them from contamination with saliva and surrounding light. It is generally recommended to scan the plate soon after exposure. However, this may not always be possible in busy dental clinics and hospitals. Sometimes, plates are exposed in different locations and then brought to the center where they are scanned, which may cause a considerable delay in scanning. Although Digora produces high-quality images of dental structures under ideal conditions, exposed-but-not-scanned SPPs may lose some of the information with time. Although the image quality of SPPs for various systems has been evaluated in many studies,4,9,10 how long it remains unaffected by delayed scanning of the image plate is still an unanswered question. The aim of this study was to determine the longevity of the image quality in storage phosphor plates of the Digora system at various exposure settings, storage conditions, and delays in scanning.
MATERIAL AND METHODS Fifteen blue Digora storage phosphor plates were used and scanned in the Digora FMX-scanner calibrated 603
604 Akdeniz, Gr€ ondahl, and Kose
OOOOE May 2005
Fig 1. Experimental set-up demonstrating the number of exposed plates.
for a highest exposure of 1.00 second. The plates were exposed with an x-ray unit (Anthos Ac, Anthos Company, Imola, Italy) with 2.5 mm aluminum (Al) equivalent total filtration at 65 kVp and 10 mA, using a focus-to-receptor distance of 20 cm. An optical bench was used to standardize geometric projection. The resulting images were transferred as 8-bit TIFF files to a personal computer (CM-1454NEL, Lite-On Technology Corp, Dong Guang, China) and analyzed with a software program (Image Tool 3.0 SDK; University of Texas Health Sciences Center, San Antonio, Texas) developed particularly for dental image analysis. Parameters of initial dose (exposure time), time after exposure (scan delay), and 2 different storage conditions were included in the statistical evaluation of possible image quality degradation. The effect of initial dose on the image quality was tested using an Al step-wedge made of 99.5% pure aluminum and with 5 2-mm incremental steps. The wedge was exposed at 5 time settings ranging from 0.08 to 0.20 seconds. In Fig 1 the experimental set-up is shown, demonstrating that a total of 135 exposures were made. Fifteen new plates were first cleared from any background effect by means of the strong light source built into the scanner and then reused throughout the experiment. The strong light removes any residual information still stored in the plates and thus brings the plates back to their original state leaving no memory of previous experiments behind. Plates were scanned immediately, 10, 30, and 60 minutes, and 24 hours after they were exposed. Mean gray values of the immediately scanned plates provided the gold standard values. Scanned plates were stored in their envelopes both in a room with daylight and in a light-tight box in order to evaluate the effect of different storage conditions. Each exposure was repeated 3 times for each parameter being included in the statistical analysis, that is, initial dose (5 settings), storage (2 conditions), and scanning delay (4 different). This results in 3 3 5 3 4 3 2 = 120 images. The remaining 15 images (135 ÿ 120) were
Fig 2. MGVs for various exposures and immediate scanning.
those that were scanned immediately and served as reference images. When all plates had been scanned, the gray-level information in each step of the Al wedge was sampled with 3 nonoverlapping (40 3 40 pixel) regions of interest (ROI). Black was assigned a value of 0 and white a value of 255. An average gray-level value for each step in each separate image was calculated from the 3 ROIs. Later on, mean gray values (MGVs) were determined for each step from the information in the 3 images obtained by repeat exposures. Contrast was measured as gray-level differences at various settings and conditions. Contrast was compared on the basis of gray-level differences between the highest and lowest gray values. The data were statistically analyzed using 2 3 5 3 5 factorial ANOVA (P \.05). Bonferroni/Dunn multiple comparison test was used to assess the difference between group means. RESULTS Mean gray values for each step of the Al step-wedge obtained from plates that were scanned immediately after being exposed are shown in Fig 2. Exposure of plates for 0.08 and 0.20 s produced pixel values between 148 and 242. Analysis of variance revealed that MGVs of plates exposed for 0.08 s and 0.10 s were not significantly different from each other. MGVs acquired for all other exposures were significantly lower (P \ .05). Figure 3 is an example showing the MGVs of all steps of the wedge in immediately scanned plates and in those scanned after delays of 10, 30, and 60 min and 24 h. In general, MGVs decreased with the increase in exposure time but increased with the scan delay. All results mentioned above were valid and
OOOOE Volume 99, Number 5
Akdeniz, Gr€ ondahl, and Kose 605
Fig 3. MGV changes for various scan delays for each step of Al step-wedge.
similar for each step of the wedge. Gray-level changes with regard to scan delay were higher for darker image areas (thinner steps) for all exposure times and scan delays used (P \.05). Figure 3 shows the change in contrast with regard to scan delays. Comparison of the contrast revealed that it decreased with increasing scanning delays. The decrease in contrast was larger for darker image areas than
for lighter ones. However, the relative change in contrast was nearly similar at different exposures and thus various gray levels. Statistical analysis indicated that MGVs of the plates scanned after 30 and 60 min and 24 h were significantly higher than those scanned immediately (P \ .05) whereas MGVs of plates scanned 10 min after exposure were not (P [.05). Furthermore, comparison of only
OOOOE May 2005
606 Akdeniz, Gr€ ondahl, and Kose
Fig 4. Pixel density differences due to different storage conditions of storage phosphor plates.
10, 30, and 60 min and 24 h delay values with each other revealed that only the MGVs of plates scanned 10 min after exposure were significantly different from the ones scanned 24 h later (P \.05). No significant differences were obtained between MGVs of plates with scan delay of 30 and 60 minutes. This pattern of increase in MGVs was observed for both storage conditions. However, MGVs of plates kept in daylight were significantly higher than those stored in light-tight environment (P \.05). The increase in pixel values with respect to scan delay exhibited a harmonious (symmetrical) ascending pattern for plates stored in a light-tight box but not for plates kept in daylight (Fig 4). The Bonferroni/Dunn test revealed significant interaction between the initial dose (exposure time) and delay in scan time for the plates stored in a light-tight environment (P = .0003). However no interaction between these 2 parameters were found for the plates stored in daylight. The other double or triple interactions of the parameters used in this study, namely storage conditions, exposure times, and scan delays, did not show any interaction with each other. DISCUSSION The increase in mean gray values with the scan delay signifies that time after exposure is 1 of the causes of fading of the latent image. The loss of image quality is due to the decay (loss of electrons from their traps in the higher energy states) that occurs with time or due to the ambient light (light leaking through the envelope).11 It is relevant that the amount of information lost is higher for darker image areas, because this leads to lower contrast.
According to the manufacturers of storage phosphor plates they start losing information within 5 minutes of image capture, and within the first hour close to 50% is lost.11 However, we found images of similar density and contrast up to 10 minutes after the initial exposure. The latent image started to fade away if the scanning was delayed more than 10 minutes with subsequent increase in MGVs. When the immediate scan (gold standard) values were left out of the comparison it was observed that only the plates scanned 10 minutes after exposure showed a significant difference to the ones scanned after 24 hours. Therefore, it is possible to recommend that storage phosphor plates should be scanned within 10 minutes after being exposed. However, scan delays up to an hour have a limited effect on the latent image stored in the plates. This finding partly corresponds to those of Martins et al11 but is somewhat different to the findings of a study by Hildebolt et al.12 The latter found that 25%-50% of the latent image stored in phosphor plates is lost within the first hour after exposure and that the relative rate of loss declines with time.12 Further research using shorter time intervals for the scan delays is needed to assess the threshold value for scan delay. Additionally, the clinical relevance of this loss remains to be analyzed because some compensation for it can be achieved by image processing.13,14 Once the phosphor plate is read, it is flooded with light to erase any remaining image and to prepare it for the next exposure. Since the latent image is erased by exposure to light, it is important to avoid exposing the phosphor plate to excessive amount of background light before it is scanned. The pattern of increase in mean gray values of plates stored in a light-tight environment
OOOOE Volume 99, Number 5
indicates that the information loss is due to an unforced return of the electrons to their original state.12 Random increases in mean gray values of plates kept in daylight indicate that light leakage through the plastic envelopes may be the cause. In the present study, mean gray values of plates increased as a function of exposure time and delayed scanning only if the plates were kept in darkness. Such an interaction could not be defined for the plates kept in daylight because abrupt increases in mean gray values were observed. If the findings of the present study are extrapolated into clinical settings where full mouth surveys are required, one may suggest that by the time the last plate is exposed, especially by a beginning student, the first plate may have lost a fair amount of its trapped electrons. In conclusion, although storage phosphor plates do not lose all their information for many days, it is recommended that they be scanned no later than 10 minutes after exposure to obtain best quality images. If plates cannot be scanned within 10 minutes they should be kept in a light-tight environment until scanned. REFERENCES 1. Wenzel A, Gr€ ondahl H-G. Direct digital radiography in the dental office. Int Dent J 1995;45:27-34. 2. Huda W, Rill LN, Benn DK, Pettigrew JC. Comparison of a photostimulable phosphor system with film for dental radiology. Oral Surg Oral Med Oral Pathol Oral Radiol Endod 1997;83:725-31. 3. Wenzel A. Digital radiography and caries diagnosis. Dentomaxillofac Radiol 1998;27:3-11. 4. Borg E, Attaelmanan A, Gr€ondahl H-G. Subjective image quality of solid-state and photostimulable phosphor systems for digital intra-oral radiography. Dentomaxillofac Radiol 2000;29:70-5.
Akdeniz, Gr€ ondahl, and Kose 607 5. Moystad A, Svanaes DB, Risnes S, Larheim TA, Gr€ondahl H-G. Detection of approximal caries with a storage phosphor system. A comparison of enhanced digital images with dental x-ray film. Dentomaxillofac Radiol 1996;25:202-6. 6. Borg E, Gr€ondahl H-G. On the dynamic range of different x-ray photon detectors in intra-oral radiography. A comparison of image quality in film, charge-coupled device and storage phosphor systems. Dentomaxillofac Radiol 1996;25:82-8. 7. Hintze H, Wenzel A, Frydenberg M. Accuracy of caries detection with four storage phosphor systems and E-speed radiographs. Dentomaxillofac Radiol 2002;31:170-5. 8. Oliveira AE, de Almeida SM, Paganini GA, Haiter Neto F, Boscolo FN. Comparative study of two digital radiographic storage phosphor systems. Braz Dent J 2000;11:111-6. 9. Kitagawa H, Farman AG, Scheetz JP, Brown WP, Lewis J, Benefiel M, Kuroyanagi K. Comparison of three intra-oral storage phosphor systems using subjective image quality. Dentomaxillofac Radiol 2000;29:272-6. 10. Shearer AC, Mullane E, Macfarlane TV, Gr€ondahl H-G, Horner K. Three phosphor plate systems and film compared for imaging root canals. Int Endod J 2001;34:275-9. 11. Martins MGBQ, Haiter Neto F, Whaites EJ. Analysis of digital images acquired using different phosphor storage plates (PSPs) subjected to varying reading times and storage conditions. Dentomaxillofac Radiol 2003;32:186-90. 12. Hildebolt CF, Couture RA, Whiting BR. Dental photostimulable phosphor radiography. Dent Clin North Am 2000;44:273-97, vi. 13. Gotfredsen E, Wenzel A, Gr€ondahl H-G. Observers’ use of image enhancement in assessing caries in radiographs taken by four intra-oral digital systems. Dentomaxillofac Radiol 1996;25: 34-8. 14. Analoui M. Radiographic image enhancement. Part I: Spatial domain techniques. Dentomaxillofac Radiol 2001;30:1-9.
Reprint requests: B Gu¨niz Akdeniz Ege Universitesi, Dishekimligi Fakultesi Oral Diagnoz & Rad AD, Bornova, 35100 Izmir, Turkey [email protected]