Use of Micropulverized Barium Sulfate in X-Ray Diagnosis

In the routine use of powdered barium sulfate as a radiopaque material, the importance of a critical particle size range has not been reported, although it has long been known that the phenomenon of adsorption is intensified as particle size is decreased (1). Barium sulfate powder has been suspended in various colloidal substances to aid in “sedimentation of barium precipitate on the gastro-intestinal mucosa” (2, 3). Powdered barium sulfate has been mixed with tannic acid (4), gum acacia (5), and gelatin (6), the chief purposes of such mixtures being to obtain a preparation sufficiently radiopaque to permit fluoroscopic examination and to coat the intestinal mucosa with just enough adherent radiopaque material simultaneously to permit optimal x-ray visualization. Available preparations do not fulfill both criteria completely. The possible value of micropulverizing barium sulfate was suggested during inhalation studies with antibiotic dusts (7). Particles 0.2 to 2.0 micra in diameter suspended in air have been shown to penetrate the entire pulmonary tree, with retention of a large percentage in the lungs (8). Also, the covering property of paints and pigments is enhanced by reduction of the particle size (9). Particle Size Studies Preparations of barium sulfate were examined for particle size distribution by light and electron microscopy. Identical electron microscope examinations were made of five leading commercially available barium sulfate powders used for x-ray diagnosis. Figure 1A is an electron micrograph magnified approximately 2150 times of a typical commercial barium sulfate preparation. The particle size distribution in the same product before and after micropulverization by dry grinding is recorded in Table I and shown in Figures 1A and B. It is apparent that this milling process reduces the number of large particles (5 to 20 micra), and increases the concentration of small particles (.04 to .10 micron). Subsequently, particle size reduction has been accomplished more efficiently by wet grinding in a ball mill for several days (Fig. 3). Toxicity Studies The advantages of using micropulverized radiopaque preparations in the x-ray examination of the gastro-intestinal tract are being investigated. This modification of a well established technic must be studied thoroughly, particularly in respect to any possible harmful features, since it is known that there is a correlation between toxicity and particle size (10–15). In general, the finer the particle size the greater the absorbability and toxicity. No immediate or delayed toxic reactions were encountered in ten rabbits following the intravenous injection of aqueous suspensions of barium sulfate in the dosage of 0.5 gm. per kilo of body weight. Potential toxic properties of barium sulfate powders would probably relate only to the finest particles (0.04 to 0.1 micron), which by weight represent less than 0.0001 per cent of the total barium sulfate in suspension.