ORIGINAL Annals of Nuclear Medicine Vol. 3, No. 3, 143-147, 1989 Preparation of a fine powder of 2-deoxy-2-[18F]fluoro-D-glucose suitable for inhalation to diagnose lung diseases by means of PET Fumiyoshi OJIMA,* Tatsuo IDO,* Toshihiro TAKAHASHI,* Jun HATAZAWA,* Masatoshi ITO,* Hidetada SASAKI,** Masaru YANAI,** Takashi AIKAWA,** Tamotsu TAKISHIMA,** Kenji ABIKO*** and Masafumi AMANO*** *Cyclotron and Radioisotope Center, Tohoku University **First Department of Internal Medicine, Tohoku University School of Medicine ***MECT Corporation Fine 2-deoxy-2-[18F]fluoro-D-glucose (18FDG) powder was obtained by adding diethyl ether into a methyl alcohol solution of 18FDG and other sugar as seed. When micronized particles of sodium N-acetyl-neuraminate (Neu5Ac-Na) were used as seed crystals, particles containing 18FDG were obtained and 80 % of them were smaller than 10 /um in size. More than 60 %; of these crystals were 4-6 um in size. In a preclinical study of forced inhalation in a dog, the 18FDG fine powder was mainly distributed in the trachea. The radioactivity in the trachea then increased once and a gradual decrease followed. The radioactivity was transferred into the blood and radioactivity incorporation into the heart was observed. After a normal volunteer inhaled 18FDG dry powder aerosol, the radioactivity was found in the respiratory tract and the peripheral area of the lung by means of PET. Absorption and in vivo dynamics of the 18FDG were also analysed. Key words : PET study, 18FDG dry powder aerosol, Mucociliary clearance INTRODUCTION IT HAS BEEN RECOGNIZED that in the condition of the mucus on the inner surface of the air tract and clearance of mucociliary transport there are some differences between normals and patients who have chronic bronchitis, bronchial asthma and other lung diseases.1-3 Quantitative measurement of deposition, clearance of the air tract and absorption from the lung after inhalation of drugs is regarded as useful in diagnosing lung diseases. Noninvasive measurement of the mucociliary clearance by inhalation of 99mTc particles micronized with a nebulizer has been reported.4 This method made it possible to analyze the permeability of the alveolar membrane.5,6 Since the images are planar although the lung is three- Received June 2, 1989; revision accepted September 11 , 1989. For reprints contact : Tatsuo Ido, Cyclotron and Radio-isotope Center, Tohoku University, Aoba, Aramaki, Aoba-ku, Sendai 980, JAPAN. dimensional, the details of such regions as the main bronchi and alveoli are not separated. Positron emission tomography (PET) can analyze the deep areas of the whole body exactly and quantitatively and can distinguish the main bronchi and the alveoli. Clearance of the air tract and absorption can be analyzed by periodic measurement. Since 18F has a relatively long half-life among the positron emitting nuclides, it is suitable for obtaining chronological in-formation. 18FDG is frequently used to measure glucose metabolism in clinical studies. Since 18FDG is soluble in water, it is possibly absorbed from the alveoli into the blood. Therefore, by analyzing the in vivo dynamics of 18FDG, some lung diseases may be diagnosed. It is also assumed that analysis of the deposition on the inner surface of the respiratory tract of 18FDG particles inhaled as a dry powder aerosol will reveal the condition of the mucus. Since drugs in dry powder aerosol form have recently been developed, we examined their availability for ad-ministration. In the nebulizer, particle size primarily depends on the apparatus and temperature.7 How-ever, particles grow larger under such high humidity conditions as in the respiratory tract.8 The dry powder aerosols seems to be adequate for diagnosis. To examine the usefulness of dry powder aerosols in diagnosis of lung diseases, we investigated the 18FDG fine powder preparation suitable for inhalation. MATERIALS AND METHODS Materials 18FDG was synthesized from triacetylglucal and Ac018F by means of an automated synthesis system9. Usually, 5-6 mg of carrier FDG is provided with this system. Sodium-N-acetylneuraminate (Neu5Ac-Na), reported to be nontoxic when inhaled,10 was obtained from the MECT Corporation (Tokyo). Lactose was purchased from De Melkindustrie Veghel (DMV, Holland) and used after screening with 105 um mesh. Other reagents were all special grade. Preparation of 18FDGfine particles The incorporation yield of radioactivity into crystals and the particle size distribution of seed sugars and crystals including 18FDG were measured in this experiment. The peparation procedure is as follows. Diethyl ether was dropped into a methyl alcohol solution of 18FDG and about 20 mg of sugars (glucose, Neu5Ac-Na and lactose) with ultrasonication (200 W, 38 kHz). Methyl alcohol in the crystals was eliminated by washing twice with diethyl ether and the crystals were mixed with lactose as an additive and dried in a vacuum (60s, 10 min). Approximately 40 mg of the powder was put into hard gelatin Particle size distribution analysis The particle size of the crystals was measured with a centrifugal automatic particle analyzer (CAPA-300, Horiba Ltd.) with n-octyl alcohol as the suspension medium. Dispersion analysis of 18FDG dry powder aerosol A multistage liquid impinger11,12 (Fig. 1) was used for the dispersion test of the 18FDG dry powder aerosol at 60 l/min air flow for 3 sec. Effective cut-off diameters for 50 % collection efficiency (ECD50) in each stage of our apparatus are shown in Table I . Preclinical positron emission tomography (PET) study An adult dog (Beagle, 16 kg) was anesthetized with pentobarbital (25 mg/kg) and 0.47 mCi (17.39 MBq) of the 18FDG powder was inhaled by force with an air bag through intratracheal tubing and a modified Rotahaler (Fig. 2). Inhaled radioactivity was calculated after subtracting residual radioactivity in the inhaler and oral cavity from the total radioactivity in the capsule. Beginning immediately after forced inhalation, positron scans (ECAT II, EG & G, Ortec) and venous blood samples were taken periodically. In the normal volunteer study, 0.40 mCi (14.8 MBq) of the 18FDG dry powder aerosol was inhaled and two tomographic planes defined by means of X ray CT were imaged for a 46-0ld-male normal volunteer. One of the slices was an area which included the trachea and the other was primarily the bronchi area at the mid-heart level. Positron scans were done twice at O and 60 min. Venous blood samples were taken at 15, 30, 60, 90, 120, 150 and 180 min after inhalation. RESULTS AND DISCUSSION Deposition sites of inhaled particles are affected by many factors such as particle size, density, inertia, sedimentation and diffusion. In order to deliver the powder to near the alveoli, the particles must be smaller than about 6 um.13 With a pulverizer we could not obtain a powder suitable for inhalation. Crystallization of 18FDG by adding diethyl ether to the methyl alcohol solution was studied. Crystals of 18FDG could not be obtained by dropping diethyl ether into the methyl alcohol solution without any seeding with sugars. In the sugars employed, smaller particles were obtained when Neu5Ac-Na was used as a seed crystal rather than glucose. Twenty mg of Neu5Ac-Na and 18FDG were dissolved in 2 ml of methyl alcohol and then diethyl ether was dropped into this solution at the rate of 10ml/min under ultrasonication. More than 90 % of the crystals were smaller than 10um, but recovered radioactivity yield in the crystals was not high enough for our inhalation experiment. The relationship between the recovered radioactivity yield and the methyl alcohol volume during crystallization was then investigated (Table 2). When the volume of methyl alcohol was decreased to 0.1 ml, the recoved radioactivity yield increased by more than 60 % which was sufficient for the experiment. However, Neu5Ac-Na was not completely dissolved in the volume of methyl alcohol used. Since the crystals grew following the deposition of 18FDG on their surface, the particle size was affected by the diameter of the initial Neu5Ac-Na particles. Fig. 3 shows the particle size distribution for 3 experiments with 4-5 um Neu5Ac-Na as seed. Eighty percent of the crystals were particles smaller than 10 um. A dispersion test of the 18FDG powder prepared with micronized Neu5Ac-Na was carried out with the multistage liquid impinger and the results are shown in Table 3. Thirty percent of the radioactivity dispersed to stages 2, 3 and 4, which were assumed to be the trachea and the bronchi from the ECD50 in Table I . Examination with fine particles (median diameter, 4-5 um) of lactose in-stead of Neu5Ac-Na was carried out, but powder dispersible in the multistage liquid impinger test could not be obtained. Since there was a contamination of an inorganic salt (NaCl) from the ion exchange resinl4 in the synthesized 18FDG, 18FDG was extracted with a mixture of ethyl alcohol and diethyl ether before crystallization. The established preparation procedure for 18FDG dry powder aero-sol is shown in Fig. 4. It took about 100 min for the preparation procedure and three capsules of dry powder aerosol including about 2 mCi (74 MBq) of 18FDG were obtained from 50-60 mCi (1.85-2.22 GBq) of the initial 18FDG. Two capsules were used for the PET study and another capsule was used for the dispersion analysis. A preclinical study was carried out in a dog with forced inhalation of 18FDG dry powder aerosol. Just after administration of the powder, deposition of the radioactivity in the trachea was recognized. The radioactivity in the trachea increased once and then decreased with time (Fig. 5). The increase possibly reflects the mucociliary clearance of inhaled 18FDG from the deep area of the lung to the measurement site. Since the 18FDG was transferred to an upper site in the throat by mucociliary clearance, a decrease in radioactivity consequently occurred. The 18FDG dry powder aerosol permits measurement of mucociliary clearance in the air tract. Absorption of 18FDG was observed and incorporation into the myocardium was imaged. In a normal male volunteer, after inhalation of the 18FDG dry powder aerosol it was found that 18FDG was delivered to the trachea, bronchus and peripheral area containing the terminal bronchus and alveoli (Table 4. Figs. 6 and 7). The blood level and elimination of the radioactivity in two planes were measured (Fig. 8). The experiment was per-formed for up to 60 min and each region was analyzed. The blood level of 18FDG reached its plateau at from 60 min to 180 min. Both the mucociliary transport and absorption from the micro-capillaries in the lung could be analysed with this method . Further studies on lung diseases will be required. The 18FDG dry powder aerosol will be used in diag-nosing lung diseases and in revealing the condition of the mucus in the deposition sites in the air tract, since 18FDG is soluble in water. ACKNOWLEDGMENTS The authors wish to thank Dr. Koichiro Kawashima for his help in the PET study with the dog, and the members of the Cyclotron and Radioisotope Center for their cooperation. REFERENCES 1 . Hogg JC, Macklem PT, Thurlbeck WM : Site and nature of airway obstruction in chronic obstructive lung disease. New Engl J Med 278 : 1355-1360, 1968 2. Wanner A : Clinical aspects of mucociliary transport. Am Rev Respir Dis 116: 73-125, 1977 3. Goodman RM, Yergin BM, Landa JF, et al: Relationship of smoking history and pulmonary function tests to trachea mucous velocity in nonsmokers, young smokers, ex-smokers, and patients with chronic bronchitis. Am Rev Respir Dis 117 : 205-214, 1978 4. Isawa T, Teshima T, Hirano T, et al : Lung clearance mechanisms in obstructive airways disease. J Nucl Med 25 : 447-454, 1984 5. Rees PJ, Shelton D. Chan TB : Effects of histamine on lung permeability in normal and asthmatic subjects. Thorax 40 : 603-606, 1985 6. Kennedy SM, Elwood RK, Wiggs BJR, et al: In-creased airway mucosal permeability of smokers. Relationship to airway reactivity. Am Rev Respir Dis 129: 143-148, 1984 7. Pillay M, Akkermans JA, Cox PH : A high efficiency ultrasound nebuliser for radioaerosol studies of the lung. Eur J Nucl Med 13 : 331-334, 1987 8. Byron PR. Davis SS, Bubb MD, et al : Pharmaceutical implication of particle growth at high relative humidities. Pestic Sci 8 : 521-526, 1977 9. Iwata R, Ido T, Takahashi T, et al : Automated synthesis system for production of 2-deoxy-2-[18F] fluoro-D-glucose with computer control. Int J Appl Radiat Isot 35 : 445-454, 1984 10. Takahashi A, Hanabusa T, Mitomi M, et al : Acute inhalation toxicity of a dry powder aerosol sodium-5 - (acetoamino) - 3 , 5 - dideoxy - D-glycero-D-galacto-2-nonulosonate (KI-111) in rats. The Clinical Report 21 : 142-146, 1987 l I . Bell JH, Hartley PS, Cox JSG : Dry powder aerosols I : A new powder inhalation device. J Pharm Sci 60 : 1559-1564, 1971 12. May KR : Mutistage liquid impinger. Bacteriol Rev 30: 559-570, 1966 13. Landahl HD : On the removal of air-borne droplets by the human respiratory tract : I. The lung. Bul Math Biophys 12: 43-56, 1950 14. Reis ML, Draghetta W, Greene LJ : AG 11A8 ion-retardation resin : I. Separation of proteins from sodium chloride, buffer ions, and reagents used to deproteinize solutions. Anal Biochem 81: 346-357, 1977