138, 74-77 (1984)
Radiochemical Technique for Intensification of Underexposed Autoradiographs Azu
Department of Radiology, University of Rochester, School of Medicine and Dentistry, Rochester, New York 14627 Received July 22, 1983 A radiochemical technique has been used to recover images of underexposed and developed autoradiographs. The underexposed image was radioactivated in a solution of [%]thiourea, airdried, and reexposed to Kodak NMC film which was developed and processed in a Kodak X-Omat processor. Features which were not discernible in the underexposed autoradiographs were well distinguished in the intensified autoradiograph. KEY WORDS: autoradiography; Sulfur-35; thiourea; radioactivation; intensification.
Askins introduced the use of [35S]thiourea for the intensification of underexposed silver images ( 1,2). Vachon et al. have used the technique to recover silver images of both intentionally and accidentally underexposed radiographs (3). They also showed that treating the underexposed image in a solution of a subtractive photographic reducer (potassium ferricyanide and sodium thiosulfate mixture) before radioactivation with [35S]thiourea decreased the fog level and thereby increased the contrast of the intensified image (4). In this account, I will report on the application of this technique to the intensification of underexposed routine autoradiographs. MATERIALS
it in a Kodak X-Omat processor. This initial autoradiograph is the underexposed image. A similar underexposed autoradiograph was obtained of a section of the femoral head of a dog to which technetium-99m-labeled pyrophosphate had been intravenously injected. A subtractive photographic reducer was prepared by dissolving 100 g of potassium ferricyanide in 1 liter of distilled water and also 200 g of sodium thiosulfate (hypo) crystals in 1 liter of distilled water. Just prior to use, 5 ml of the potassium ferricyanide was mixed with 100 ml of sodium thiosulfate. [35S]Thiourea (sp act 402.8 mCi/mmol) was obtained from New England Nuclear. Stock solutions of the [35S]thiourea and sodium hydroxide were made by dissolving 10 mCi of [35S]thiourea and 4 g of sodium hydroxide in 500 ml and 1 liter of distilled water, respectively. The radioactivating solution was prepared by mixing 25 ml of [35S]thiourea (500 &i) and 25 ml of NaOH with 150 ml of distilled water just prior to use. The underexposed images were treated in the subtractive photographic reducer contained in a conventional photographic tray. The tray was manually agitated for 30 s. These images were placed in a processing drum (used for developing color prints) which contained the radioactivating solution. They were se-
Routine cellulose acetate electrophoresis was performed on a technetium-99m-labeled methylenediphosphonate-plasma protein mixture to separate the protein components. An autoradiograph of the fractions was obtained by exposing the electrophoretic pattern to Kodak NMC film for 6 h and developing ’ Present address: Department of Radiology and Nuclear Medicine, Faculty of Medicine, Kuwait University, P.O. Box 24923, Kuwait. 0003-2697/84 $3.00 Copyright 0 1984 by Academic Press. Inc. All rights of reproduction in any form reserved.
cured to the sides of the drum with a masking tape. The images were radioactivated by continuously rotating the drum on a sinusoidal agitator for 30 min. The activated images were washed in 20 and 50% water-methanol mixtures for 5 min, then rinsed in a running distilled water for 30 min and air-dried for at least 2 h. The underexposed and radioactivated images were then exposed to Kodak NMC film for 2 h. The films were developed and processed in a Kodak X-Omat processor. This second autoradiograph is the intensified image. RESULTS
The underexposed and intensified autoradiographs of the plasma protein electrophoretie separations are shown in Figs. 1 and 2, respectively. The protein bands are clearly visible in the intensified autoradiograph (Fig. 2) while they are barely discernible in the underexposed image (Fig. 1). The underexposed and intensified autoradiographs of the femoral head of the dog are shown in Figs. 3 and 4, respectively. It is obvious that while no features of the femoral head can be seen in the un-
derexposed image (Fig. 3) both the epiphysis and shaft can be clearly seen in the intensified images (Fig. 4). Comparison of Figs. 1 and 3 (the underexposed images) with Figs. 2 and 4 (the intensified images) indicate that the underexposed images of a routine autoradiograph can be intensified by radioactivating the underexposed image in a solution of [35S]thiourea and reexposing the radioactivated image to a second emulsion. The results of this experiment are consistent with those of Askins (1,2), Vachon (3), and Thackray (5,6). The procedure is fairly simple and easy to follow. Sulfur-35 has a half-life of 88 days which is long enough for the radioactivating solution to retain most of its radioactivity during normal usage and short enough to be stored locally until the radioactivity decays to background level when it can be disposed of as regular chemical waste. It is a low and pure p emitter of 167 keV maximum energy and 50 keV average energy. Its maximum particle range is 25 cm in air and 0.02 cm in glass. It does not require any special shielding and is easily monitored with a Geiger counter. One of the major disadvantages of the procedure is the fog level of the intensified image.
FIG. 1. The underexposed routine autoradiograph of a cellulose acetate electrophoretic mixture of technetium-99m-labeled methylenedisphosphonate and plasma protein.
2. The intensified image of an autoradiograph of a cellulose acetate electrophoretic mixture of methylenedisphosphonate and plasma protein.
133. 3. The underexposed routine autoradiograph of the fen moralhead of a dog injected with technetium-99mlab eled sodium pyrophosphate.
FIG. 4. The intensified image of an autoradiog svh of the femoral head of a dog injected with technetiumn-99mlabeled sodium pyrophosphate.
The fog problem is due to the concurrent intensification of nonimage with the image silver. The net effect is to decrease the contrast between the image and nonimage areas of the intensified autoradiographs. This problem is partially solved by treating the underexposed image in the subtractive photographic reducer (4) prior to radioactivation. The main significance of this technique is that because it can be used as a second stage image recovery process, the long exposure times of the initial autoradiograph can be considerably reduced.
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