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Evaluation of a New Phosphor Plate Technology for Neonatal Portable Chest Radiographs
Evaluation of a New Phosphor Plate Technology for Neonatal Portable Chest Radiographs Mervyn Cohen, MB, ChB, MD, Donald Corea, DO, Matthew Wanner, MD, Boaz Karmazyn, MD, Richard Gunderman, MD, Kimberly Applegate, MD, Samuel G. Jennings, MD Rationale and Objectives: The aim of this study was to evaluate a new thick-needle phosphor plate for computed radiography. Materials and Methods: Two studies were performed. Patients acted as their own controls. In the first study, old powder and new needle phosphor plate technologies were compared. Twenty infants were identified who had undergone chest x-rays with both systems within 3 days of each other. Exposure factors were constant. In the second study, standard and reduced exposure techniques (tube current–time product reduced by 20%) using the needle phosphor technology were compared. Twenty babies who had been imaged with both standard and reduced exposures within 3 days of each other were evaluated. Results: There was a significant preference for images obtained with the new needle phosphor technology compared with the older powder technology (P < .01). Using the new needle phosphor plates, a dose reduction of 20% could be achieved without a significant detectable difference between the high-dose and low-dose images (P < .19). Conclusions: For the study comparing old and new phosphor plate technology at fixed exposure, images were better with the new technology. Using the new plate technology, dose can be decreased by $20%. Key Words: Radiation dose; computed radiography; neonatal chest imaging. ªAUR, 2011
T
here are many methods of reducing radiation exposure for chest imaging in the newborn nursery. With phosphor plate computer imaging, one approach is to use a different detector material in the phosphor plate. The Agfa Corporation (Mortsel, Belgium) has developed a new thick-needle phosphor plate technology to replace existing thin powder phosphor plates for computed radiography (1–3). Our purpose was to evaluate this new technology.
MATERIALS AND METHODS Two studies were performed. For each study, patients acted as their own controls. All images were routine clinical images ordered by the infants’ neonatologists. Institutional review board approval was obtained. In the first study, we compared the old powder and new needle phosphor plate technologies. Using our ‘‘standard’’ expo-
Acad Radiol 2011; 18:197–198 From the Department of Radiology, Riley Hospital for Children, 702 Barnhill Drive, Room 1053, Indianapolis, IN 46202. Received April 16, 2010; accepted September 20, 2010. Address correspondence to: M.C. e-mail: mecohen@ iupui.edu ªAUR, 2011 doi:10.1016/j.acra.2010.09.015
sure factors, 20 infants were identified who had undergone portable chest radiography with both the new and old systems within 3 days of each other. Exposure factors were kept constant for both images. In the second study, we compared standard and reduced exposure techniques (tube current–time product reduced by 20%) using only the needle phosphor technology. We identified radiographs of 18 babies who had been imaged with both standard and reduced exposures within 3 days of each other. Each image pair was from the same infant. For any image pair, the images were presented on the left and right picture archiving and communication system monitors. All images were blindly read by board-certified pediatric radiologists. All patient information and the dates of image acquisition were removed. Images were randomly presented with regard to the location of the first or second image of each pair being displayed on the left or the right monitor. The same scoring system was used for both studies. The readers were given the following instructions: ‘‘You are reading portable newborn chest radiographs. Indicate your overall preference, if any, for either the left or right image, using the following five-point scale: definitely prefer left image, possibly prefer left image, no preference, possibly prefer right image, definitely prefer right image.’’ 197
COHEN ET AL
Academic Radiology, Vol 18, No 2, February 2011
TABLE 1. Comparison of Old Powder Phosphor Versus New Needle Phosphor
Prefer Old Phosphor Technology
Possibly Prefer Old Phosphor Technology
10
8
No Preference
Possibly Prefer New Phosphor Technology
Prefer New Phosphor Technology
6
16
56
P < .01 (null hypothesis).
TABLE 2. Comparison of Standard Versus 20% Tube Current–Time Product Reduction with Needle Phosphor Plate Technology Prefer Higher Dose
Possibly Prefer Higher Dose
No Preference
Possibly Prefer Lower Dose
Prefer Lower Dose
29
8
14
11
18
P < .19 (null hypothesis).
RESULTS There was a significant preference for images obtained with the new needle phosphor technology compared with the older powder technology (Table 1). Using the new needle phosphor plates, a dose reduction of 20% could be achieved, without significant detectable difference between the high-dose and low-dose images (Table 2). DISCUSSION Readers were able to identify a significant preference for images obtained with the new needle phosphor plate technology compared with the old powder technology. Readers found no statistical difference in their preferences for images obtained at standard versus 20% reduced exposure factors, using only the needle phosphor plates. What represents adequate image quality is open for discussion (1). We believe that asking our reviewers for a preference, when presented with paired images, provides a simple, rapid method of evaluating overall image quality. Patient exposure depends on many variables, including tube voltage, tube current–time product, filtration, source-toimage distance, grid, and so on (1). Attempts to reduce patient radiation exposure by changing the detector are not new. Changing the speed of film-screen combinations allows for decreasing radiation dose by increasing the speed of the system (1). This has been done for many years. Patient exposure can also be reduced by increasing beam filtration (4). All of the above methods can be used with the new phosphor plate to further control patient radiation exposure. Computed radiography is a digital technology in which a storage phosphor plate is used to store a latent image (2).
198
Recently introduced needle phosphor technology has been shown to improved radiation capture compared to powder technology (2,3). A needle phosphor construction of the image plate leads to a better image because thicker phosphor layers lead to higher x-ray absorption by the phosphor (2,3). Also, the needles provide strong light forward scattering, reducing light spread in the lateral direction. Image sharpness is greater for equal phosphor thickness (2,3). The plate phosphor has no binder, giving maximum phosphor density (2,3).
CONCLUSIONS For the study comparing old and new phosphor plate technology at fixed exposure, subjects strongly preferred images obtained with the new needle phosphor plates. When dose was reduced using the new plate technology, subjects evinced a slight preference for the images obtained at the higher dose. The difference was not significant. Image dose can potentially be decreased with the new Agfa needle phosphor system.
REFERENCES 1. Schaetzing R. Management of pediatric radiation dose using Agfa computed radiography. Pediatr Radiol 2004; 34:S207–S214. 2. Leblanc P, De Winter B. Interview. Needle vs. powder image plate for computer radiography: image quality measurement—Agfa test results using IEC 62220 standard method. 3. Leblanc P, Struye L. New needle-crystalline CR detector. Proc SPIE 2001; 4320:59–67. 4. Slovis TL, Haller JO, Berdon WE, Baker DH, Joseph PM. Non-invasive visualization of the pediatric airway. Curr Prob Diagn Radiol 1979; 8: 1–67.
T
here are many methods of reducing radiation exposure for chest imaging in the newborn nursery. With phosphor plate computer imaging, one approach is to use a different detector material in the phosphor plate. The Agfa Corporation (Mortsel, Belgium) has developed a new thick-needle phosphor plate technology to replace existing thin powder phosphor plates for computed radiography (1–3). Our purpose was to evaluate this new technology.
MATERIALS AND METHODS Two studies were performed. For each study, patients acted as their own controls. All images were routine clinical images ordered by the infants’ neonatologists. Institutional review board approval was obtained. In the first study, we compared the old powder and new needle phosphor plate technologies. Using our ‘‘standard’’ expo-
Acad Radiol 2011; 18:197–198 From the Department of Radiology, Riley Hospital for Children, 702 Barnhill Drive, Room 1053, Indianapolis, IN 46202. Received April 16, 2010; accepted September 20, 2010. Address correspondence to: M.C. e-mail: mecohen@ iupui.edu ªAUR, 2011 doi:10.1016/j.acra.2010.09.015
sure factors, 20 infants were identified who had undergone portable chest radiography with both the new and old systems within 3 days of each other. Exposure factors were kept constant for both images. In the second study, we compared standard and reduced exposure techniques (tube current–time product reduced by 20%) using only the needle phosphor technology. We identified radiographs of 18 babies who had been imaged with both standard and reduced exposures within 3 days of each other. Each image pair was from the same infant. For any image pair, the images were presented on the left and right picture archiving and communication system monitors. All images were blindly read by board-certified pediatric radiologists. All patient information and the dates of image acquisition were removed. Images were randomly presented with regard to the location of the first or second image of each pair being displayed on the left or the right monitor. The same scoring system was used for both studies. The readers were given the following instructions: ‘‘You are reading portable newborn chest radiographs. Indicate your overall preference, if any, for either the left or right image, using the following five-point scale: definitely prefer left image, possibly prefer left image, no preference, possibly prefer right image, definitely prefer right image.’’ 197
COHEN ET AL
Academic Radiology, Vol 18, No 2, February 2011
TABLE 1. Comparison of Old Powder Phosphor Versus New Needle Phosphor
Prefer Old Phosphor Technology
Possibly Prefer Old Phosphor Technology
10
8
No Preference
Possibly Prefer New Phosphor Technology
Prefer New Phosphor Technology
6
16
56
P < .01 (null hypothesis).
TABLE 2. Comparison of Standard Versus 20% Tube Current–Time Product Reduction with Needle Phosphor Plate Technology Prefer Higher Dose
Possibly Prefer Higher Dose
No Preference
Possibly Prefer Lower Dose
Prefer Lower Dose
29
8
14
11
18
P < .19 (null hypothesis).
RESULTS There was a significant preference for images obtained with the new needle phosphor technology compared with the older powder technology (Table 1). Using the new needle phosphor plates, a dose reduction of 20% could be achieved, without significant detectable difference between the high-dose and low-dose images (Table 2). DISCUSSION Readers were able to identify a significant preference for images obtained with the new needle phosphor plate technology compared with the old powder technology. Readers found no statistical difference in their preferences for images obtained at standard versus 20% reduced exposure factors, using only the needle phosphor plates. What represents adequate image quality is open for discussion (1). We believe that asking our reviewers for a preference, when presented with paired images, provides a simple, rapid method of evaluating overall image quality. Patient exposure depends on many variables, including tube voltage, tube current–time product, filtration, source-toimage distance, grid, and so on (1). Attempts to reduce patient radiation exposure by changing the detector are not new. Changing the speed of film-screen combinations allows for decreasing radiation dose by increasing the speed of the system (1). This has been done for many years. Patient exposure can also be reduced by increasing beam filtration (4). All of the above methods can be used with the new phosphor plate to further control patient radiation exposure. Computed radiography is a digital technology in which a storage phosphor plate is used to store a latent image (2).
198
Recently introduced needle phosphor technology has been shown to improved radiation capture compared to powder technology (2,3). A needle phosphor construction of the image plate leads to a better image because thicker phosphor layers lead to higher x-ray absorption by the phosphor (2,3). Also, the needles provide strong light forward scattering, reducing light spread in the lateral direction. Image sharpness is greater for equal phosphor thickness (2,3). The plate phosphor has no binder, giving maximum phosphor density (2,3).
CONCLUSIONS For the study comparing old and new phosphor plate technology at fixed exposure, subjects strongly preferred images obtained with the new needle phosphor plates. When dose was reduced using the new plate technology, subjects evinced a slight preference for the images obtained at the higher dose. The difference was not significant. Image dose can potentially be decreased with the new Agfa needle phosphor system.
REFERENCES 1. Schaetzing R. Management of pediatric radiation dose using Agfa computed radiography. Pediatr Radiol 2004; 34:S207–S214. 2. Leblanc P, De Winter B. Interview. Needle vs. powder image plate for computer radiography: image quality measurement—Agfa test results using IEC 62220 standard method. 3. Leblanc P, Struye L. New needle-crystalline CR detector. Proc SPIE 2001; 4320:59–67. 4. Slovis TL, Haller JO, Berdon WE, Baker DH, Joseph PM. Non-invasive visualization of the pediatric airway. Curr Prob Diagn Radiol 1979; 8: 1–67.