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Production of [13N]NH3 with ultra-high specific activity
Applied Radiation and Isotopes PERGAMON
Applied Radiation and Isotopes 50 (1999) 497±503
Production of [13N]NH3 with ultra-high speci®c activity K. Suzuki a, b, *, Y. Yoshida a, c a
Division of Advanced Technology for Medical Imaging, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263, Japan b Subfemtomole Biorecognition Project, Japan Science and Technology Corporation, Osaka 565, Japan c Sumitomo Accelerator Service, 5-9-11 Kitashinagawa, Shinagawa-ku, Tokyo 141, Japan Received 23 February 1998
Abstract Aqueous solutions of [13 N]NH3 were synthesized according to well-known methods using the 16 O( p, a)13 N reaction under conditions rendering the smallest possible amount of nitrogen-contaminants. The speci®c activities and radiochemical yields were measured. Factors, aecting the speci®c activity of [13 N]NH3, were investigated using radio-ionchromatography. The achieved speci®c activities (GBq/mmol) and radiochemical yields (GBq) of [13 N]NH3 were 14 2 2.8 and 0.3 2 0.1 (TiCl3 method)*, 5902 200 and 5.42 1.1 (DeVarda's Alloy method), 55002 500 and 12.7 2 0.1 (ethanol method), and 62002 2700 and 2.8 2 0.3 (hydrogen method, 3 bar), respectively at 15 mA for 20 min irradiation (*; 5 mA, 5 min irradiation). More than 70% of the N-13 generated with the hydrogen method was of the chemical form [13 N]N2. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction N-13 (half life; 9.965 min, 100% b+decay) is one of the most important emitters of all the positron emitters, and has been used, mostly in the chemical form [13 N]NH3 (Wu et al., 1995; Yoshida et al., 1996) or [13 N]-amino acids (Knapp et al., 1988; Conlon et al., 1989; Cooper et al., 1996), in the ®eld of nuclear medicine. However, it is dicult to synthesize N-13 labeled compounds with a high enough speci®c activity and radioactivity to carry out receptor studies with PET, due to its short half-life and the ease of contamination by non-radioactive nitrogen compounds of N-13. N-13 is usually produced by the 16 O( p, a)13 N reaction and converted to [13 N]NH3 by in-target or classical reduction methods. With classical reduction methods, the [13 N]NOÿ x generated in irradiated water is reduced to [13 N]NH3 with TiCl3 (TiCl3 method) (Krizek et al., 1973; Ido and Iwata, 1981) or with DeVarda's alloy (DeVarda's alloy method) (Vaalburg et al., 1975; Suzuki and Tamate, 1984; Gatley and
* To whom all correspondence should be addressed.
Shea, 1991). With in-target reduction methods, the [13 N]NH3 generated directly in the target is prevented from being oxidized to [13 N]NOÿ x by addition of ethanol (ethanol method) (Tilbury and Dahl, 1979; Wieland et al., 1991; Berridge and Landmeier, 1993; Korsakov et al., 1995) or H2 (hydrogen method) (Mulholland et al., 1990; Berridge and Landmeier, 1993; Korsakov et al., 1995) to pure water as a scavenger of oxidizing radical OH (Tilbury and Dahl, 1979; Korsakov et al., 1992). In some cases, an aqueous solution of [13 N]NH3 has been used as a synthetic precursor in preparations of 13 N-labeled compounds (Irie et al., 1985; Tominaga et al., 1986, 1987; Helus et al., 1991; Watanabe et al., 1991; Suzuki et al., 1995). The importance of anhydrous [13 N]NH3 as a synthetic precursor was suggested by Tominaga et al. However, little eort has been made to achieve a higher speci®c activity of [13 N]NH3, since N-13 has been used in the chemical forms of amino acids and ammonia which exist abundantly in the living body (NH3 in human blood plasma; 11±35 mM, Merck and Co., 1987). Only a few papers have mentioned speci®c activity of 13 N-labeled compounds (Knapp et al., 1982;
0969-8043/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 9 8 ) 0 0 0 9 5 - 5
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K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
Lambrecht et al., 1986; Parks and Krohn, 1978; Gatley and Shea, 1991; Channing et al., 1994) and their values were quite low, compared to the theoretical value of N-13, i.e. 6.9 105 GBq/mmol. We measured the speci®c activity of N-13 ion species generated in water saturated with pure gases (O2, He, H2, N2) under ¯ow conditions and observed a remarkable decrease of speci®c activity of N-13 in N2 gas saturated water (Sasaki et al., 1995). The establishment of methods producing [13 N]NH3 with high speci®c activity would enable receptor studies with N-13 labeled compounds, if coupled with automated equipment (Suzuki et al., 1995), to allow for the quick production of such compounds. This paper reports on the speci®c activity and yield of [13 N]NH3 produced by well-known methods under conditions rendering the smallest possible amounts of nitrogen-contaminants. 2. Experimental 2.1. Chemicals The water used as a target material was prepared using the MilliQ SP Reagent Water System (Millipore, MA). Pure gases, O2 (purity; >99.9995%) and H2 (purity; >99.99999%), used to purge the air dissolved in the water, were obtained from Nippon Sanso (Tokyo). Sodium hydroxide was purchased from Nakarai Tesque (Kyoto, impurity; 0.001% as N), Fluka Chemie (Buchs, purity; >98%) and Aldrich Chemical (WI, purity; 99.99%). TiCl3 solution was obtained from Wako Pure Chemical (Osaka), Fluka and Aldrich. DeVarda's alloy was purchased from Wako (impurity; <0.003% as N), Fluka (impurity; 0.001% as N) and Aldrich. DeVarda's alloy and NaOH were dried at 3508C for 05 hours in vacuo. The target water was bubbled for 0one hour with pure O2 or H2 gas in a sealed bottle to purge dissolved gases. 2.2. Analysis Ionic species were analyzed by ion chromatography using DX-100 (Dionex, CA) and IC-7000 (Yokogawa Electric, Tokyo) coupled with a NaI(Tl) detector, respectively. Cation analysis was performed using an Ion Pac CS-14 column (4 mm b 250 mm, guard column; Ion Pac CS-14, 4 mm b 50 mm) with 10 mM methansulfonic acid as an eluent at 1.5 mL/min [Rt(NH+ 4 ), 3.3 min]. Anion analysis was performed using an ICS-A35 column (4.6 mm b 150 mm, guard column; ICS-A3G, 4.6 mm b 30 mm) with 5 mM Na2CO3+1.5 mM NaHCO3 as an eluent at 1 mL/min and 408C oven temperature [Rt(NOÿ 2 ), 6.6 min and Rt(NOÿ 3 ), 8.5 min]. Quanti®cation of trace ions was
carried out using calibration curves obtained with 10± 300 ppb solutions of the corresponding ions (NH+ 4 , ÿ NOÿ 2 , NO3 ). Gas chromatography was performed on a HP5890 gas chromatograph (Yokogawa, Tokyo) with a thermal conductivity detector and a NaI(Tl) detector. A glass column (2 mm b 2 m) packed with Molecular Sieve 5A (30/60 mesh) was used with a He gas ¯ow rate of 67 mL/min at 508C for identi®cation of radiolabeled gases [Rt(N2) = 1.2 min, Rt(O2) = 0.8 min]. 2.3. Determination of nitrogen in chemicals The amount of nitrogen contained in the reagents used in this study was determined by procedures similar to those used for [13 N]NH3 synthesis. Nitrogen contained in Devarda's alloy (10, 20, 40 mg) and NaOH (190 mg) was converted to ammonia in 4 ml of ultrapure water and distilled into a sealed plastic bottle in ice. The total volume was adjusted to 2 ml with ultrapure water. The amount of nitrogen in DeVarda's alloy was calculated from the slope of the straight line obtained by plotting the amount of NH+ 4 against the amount of DeVarda's alloy. A similar technique was applied for the determination of carrier nitrogen contained in other reagents, such as a solution of TiCl3 and NaOH pellets. 2.4. Production of [13 N]NH3 Fig. 1 is a block diagram of the systems used for the production of [13 N]NH3 solution. As can be seen, the tube through the 6- and 3-way valves from the target chamber is connected to one of the reduction vessels or a collection vial. Each component in the production lines is connected with thin tubes (SUS316 and PEEK tube; 1/16 inch o.d., 0.75 mm i.d.). The target chamber (21 mm i.d. 6 mm) was made of SUS-316 and window foils of 100 mm SUS-316 were welded on the chamber body by an electron beam in vacuo. All the parts, including the reaction vessel, the collection vial, the target chamber and the tube lines were cleaned thoroughly with ultra-pure water before the experiment. Before irradiation, the target water used in the N-13 production other than with the hydrogen method was bubbled with pure oxygen gas for 60 min, which was released through the relief valve kept at a constant pressure (1 bar), to replace the dissolved gas in the water with oxygen. With the hydrogen method, a pure hydrogen gas (1 or 3 bar) was used instead of oxygen. With the ethanol method, a 10 mM ethanol solution saturated with pure O2 gas was used. The water bubbled with pure gas was charged into the target chamber through a 6-way valve and pressurized by closing the 3-way valve at the exit. Irradiation was carried out with 18 MeV protons (15.7 MeV on target)
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
Fig. 1. Schematic diagram for the [13 N]NH3 production PG; pressure gauge.
; 2-, 3-way valves, w; thermocouple,
499
; radioactivity sensor,
from the NIRS cyclotron (HM18, Sumitomo Heavy Industries, Tokyo) at 15 mA for 20 min in a closed circuit (6-way valve; closed).
was monitored continuously to determine the end point of distillation by using a small Si detector (Oyokoken, Tokyo). The product was then analyzed.
2.4.1. Hydrogen and ethanol methods The irradiated water was transported into a collection vial equipped with a gas collection bag by He gas pressure. The He gas was allowed to bubble through the collected solution for 20 s to remove radioactive gas. The radioactive liquid and gas fractions were measured separately using a curiemeter IGC-3R (Aloka, Tokyo) and radio-ion/radio-gas chromatography systems.
2.4.3. TiCl3 method The irradiated water was introduced into a reaction vessel (maintained at 1008C) containing 1.2 g of NaOH (Fluka) and then 1 ml of 7.5% TiCl3 in hydrochloric acid (Fluka) was added. Distillation and analysis of the product were carried out in a similar manner as above.
2.4.2. Devarda's alloy method The irradiated water was introduced into a reaction vessel containing 5 mg of DeVarda's alloy (Fluka) and 20 mg of NaOH (Fluka), maintained at 1008C, by He gas pressure. Then, the temperature was increased to 3508C. The radioactivity distilled into a collection vial
3. Results and discussion The measured amounts of nitrogen in the reagents used in the present study are summarized in Table 1, where the amount of distilled ammonia is assumed to imply the amount of nitrogen in the reagents. The values in Table 1 do not refer to the total amount of
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K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
Table 1 Measured amount of nitrogen in the reagents (n = 3) Reagents
Nitrogen (nmol)
NaOH (Nakarai) NaOH (Fluka) NaOH (Aldrich) DeVarda's (Wako) DeVarda's (Fluka) DeVarda's (Aldrich) TiCl3 (Wako) TiCl3 (Fluka) TiCl3 (Aldrich)
0.06020.004* 0.02720.012* 0.02720.014* 0.4 20.1* 0.2 20.1* 0.3 20.1* 86 216$ 70 224$ 106 237$
* Values in 1 mg of the reagent. $ Values in 1 ml of the TiCl3/HCl solution.
nitrogen in the reagents since distillation eciency of ammonia and amount of nitrogen not-converted to ammonia were not taken into account. But, they do suggest the amount of nitrogen related strongly to the speci®c activity of [13 N]NH3 since the values were obtained employing the same procedure used for [13 N]NH3 production. The reagents from Fluka were used in the present study since they gave the smallest contamination of nitrogen. A relatively large amount of nitrogen was detected in a TiCl3 solution. The use of 1 ml of TiCl3 solution and 1.2 g of NaOH as in the
present study would increase the amount of ammonia by 70 nmol and 30 nmol, respectively and cause a remarkable decrease in the speci®c activity of [13 N]NH3. On the other hand, with DeVarda's alloy method, 1 nmol and 0.5 nmol of ammonia is generated in [13 N]NH3 production on using 5 mg of DeVarda's alloy and 20 mg of sodium hydroxide. Therefore, DeVarda's alloy method may be preferable to the TiCl3 method for high speci®c activity of [13 N]NH3, with the smallest amount of reagents which are within the limit which does not cause a remarkable decrease of [13 N]NH3 yield. Fig. 2 shows radiochromatograms of O2-saturated water irradiated at 15 mA for 20 min. The radioactive ÿ 18 peaks were identi®ed to be [13 N]NH+ 4 , [ F]F , ÿ 13 [13 N]NOÿ and [ N]NO on comparison with an auth2 3 entic sample solution. Table 2 summarizes the amount of nitrogen ion in the target solution recovered from the target chamber with or without irradiation. Without irradiation, only 0.1 2 0.01 nmol of NH+ 4 was ÿ detected, and ions NOÿ and NO were below the 2 3 detection limit in the water recovered from the target system according to the same procedure with actual [13 N]NH+ production. Obvious increases of nitrate 4 and nitrite ions were observed following irradiation. The tendency was increased with a higher beam current and longer irradiation particularly for NOÿ 3 . This
Fig. 2. Radio-ionchromatograms of the irradiated water. Upper and lower chromatogram in (a) and (b): Upper; radioactivity output, Lower; conductivity output. (a) anion chromatogram. Column; ICS-A35 + ICS-A3G, eluent; 5 mM Na2CO3+1.5 mM NaHCO3, ¯ow rate; 1 ml/min, oven temp.; 408C. (b) cation chromatogram. Column; IonPac CS-14, eluent; 10 mM methansulfonic acid, ¯ow rate; 1.5 ml/min.
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
501
Table 2 Amount of nitrogen ions (nmol) in the target solution with or without irradiation (n = 3) Ions
Without irradiation
NH+ 4 NOÿ 2 NOÿ 3
With irradiation
0.1020.01 <0.05 <0.08
5 mA, 5 min
15 mA, 25 min
0.1020.03 (1.020.8) 0.3720.01 (4.020.5) 1.0520.09 (94.026.0)
0.102 0.03 (0.720.6) 0.202 0.04 (3.320.7) 3.602 0.56 (93.523.2)
target: ultra-pure water saturated with a pure O2 gas. bracket: % of 13 N-radioactivity.
observation supports our previous result, where a marked increase of non-radioactive nitrogen ions, especially in the N2-saturated water target, was detected in the ¯ow target system on irradiation of water saturated by pure gas (N2, O2, He and H2) (Sasaki et al., 1995). To avoid the increase of nitrogen ions by irradiation, special attention was given to the following: (1) use of ultra-pure water, (2) purge of nitrogen gas from the water as suggested by Sasaki et al., (3) use of a target chamber welded by electron beam in vacuo, and (4) baking of the target chamber by repeated irradiation at high beam current for long periods. Nevertheless, an increase of nitrogen ions was observed as shown in Table 2, although the extent of this increase was not remarkable. The reason for the increase is still not clear. The purity of the material of the target chamber, especially the window, may be a factor. Table 3 shows the speci®c activity and radiochemical yield obtained in the [13 N]NH3 syntheses under conditions of 20 min irradiation at 15 mA. The highest speci®c activity, 62002 2700 GBq/mmol, of [13 N]NH3 was obtained with the hydrogen method (H2; 3 bar), but the yield, 2.82 0.3 GBq, was only about one fourth of that of the highest value (ethanol method), due to loss of radioactivity by [13 N]N2 gas evolution (70.82 12.3%). The speci®c activity and yield were Table 3 Results of
13
lower at 1 bar H2 gas pressure than at 3 bar. Higher yield of [13 N]NH3 may be achieved by the use of water saturated with a higher pressure H2 gas (Berridge and Landmeier, 1993). On the other hand, the ethanol method produced fairly high speci®c activity, 55002 450 GBq/mmol, and the highest radiochemical yield, 12.72 0.1 GBq. With this method, [13 N]NH3 with a radiochemical purity of >99% was obtained without any puri®cation. The above values of speci®c activity are higher than the reported values, 22 GBq/ mmol for [13 N]glutamate (Knapp et al., 1982), 7.4 GBq/mmol at EOB for [13 N]GABA (Lambrecht et al., 1986), 37 GBq/mmol for [13 N]NH3 (Parks and Krohn, 1978), >30 GBq/mmol for [13 N]NH3 (Channing et al., 1994) and 150 GBq/mmol at EOB for total [13 N]anions (Gatley and Shea, 1991). In the present study, 10 mM EtOH solution saturated with pure O2 gas was used as target material to achieve a higher speci®c activity for N-13 (Sasaki et al., 1995). Although a signi®cant decrease of the [13 N]NH3 yield was reported in an O2-saturated 5 mM EtOH solution for 0.83 mA h irradiation (Channing et al., 1994), we have found no decrease of the [13 N]NH3 yield under the present condition. The disagreement may be attributed to the dierences in ethanol concentration, material of the target chamber, beam pro®le on the target, etc., between the two production systems.
NH3 production by well-known methods (n = 3) Yield* (GBq)
Speci®c activity* (GBq/mmol)
Synthesis time (s)
Remarks
A
5.421.1
590 2200
220227
B
2.820.3
620022700
40
C D E
1.320.1 12.72 0.1 0.320.1
43002930 55002450 14.0 22.8
40 40 390228
purity; >99% 13 13 N2 70.8212.3%, 13 NOÿ NOÿ 2 0.822.0%, 3 2.02 0.6% 13 13 N2 78.123.0%, 13 NOÿ NOÿ 2 0.820.3%, 3 4.52 1.1% purity; >99% purity; >99%
A = DeVarda's alloy method, B = hydrogen method (3 bar), C = hydrogen method (1 bar) D = ethanol method (10 mM), E = TiCl3 method. Irradiation conditions: A, B, C, D = 15 mA/20 min, E = 5 mA/5 min. * Yield and speci®c activity of [13 N]NH3 at EOS.
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K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
By contrast, less speci®c activity of [13 N]NH3 was obtained using the DeVarda's alloy and TiCl3 methods, probably due to contamination from the reagents used in the reductive alkaline distillations after irradiation. The lowest speci®c activity was obtained with the TiCl3 method, the yield and speci®c activity of which should be multiplied by a factor 10 to correct for the low beam current and short period of irradiation. The use of a strongly acidic solution of TiCl3, which would absorb ammonia during storage, explains this ®nding. The yield of [13 N]NH3 produced by the DeVarda's alloy and TiCl3 methods was lower than that with the ethanol method. The dierence can be ascribed to the longer process time, incomplete reduction and distillation, and loss of radioactivity in the line due to the complexity of the production system. For clinical use, the [13 N]NH3 solution produced by the above classical methods can be directly applied, whereas a puri®cation process with an ion-exchange column or a distillation process would be required in the in-target reduction methods to remove undesirable radioactive/non-radioactive impurities. Based on these considerations, we believe the ethanol method to be the best choice for production of [13 N]NH3 as a synthetic precursor with high speci®c activity and high radiochemical yield under the studied conditions. Extremely high speci®c activity of aqueous [13 N]NH3 solution was obtained in the present study. Using the proposed technique, attempts to synthesize 13 N-labeled compounds with high speci®c activity employing automated equipment are underway.
Acknowledgements We are grateful to the sta of cyclotron for operating the NIRS cyclotron HM-18. This work was supported by the International Joint Research Program of Japan Science and Technology Corporation.
References Berridge, M. S., Landmeier, B. J., 1993. In-target production of [13 N]ammonia: Target design, products, and operating parameters. Appl. Radiat. Isot. 44, 1433±1441. Channing, M. A., Dunn, B. B., Kiesewetter, D. O., Plascjak, P., Eckelman, W. C., 1994. The quality of [13 N]ammonia produced by using ethanol as a scavenger. J. Label. Comp. Radiopharm. 37, 334±336. Cooper, A. L., Sheu, K. F., Blass, J. P., 1996. Normal glutamate metabolism in Alzheimer's disease ®broblasts de®cient in alpha-ketoglutarate dehydrogenase complex activity. Developmental Neuroscience 18, 499±504. Conlon, K. C., Bading, J. R., Diresta, G. R., Corbally, M. T., Gelbard, A. S., Brennan, M. F., 1989. Validation of transport measurements in skeletal muscle with N-13 amino
acids using a rabbit isolated hindlimb model. Life Sciences 44, 847±859. Gatley, S. J., Shea, C. 1991. Radiochemical and chemical quality-assurance methods for [13N]-ammonia made from small volume H216O target. Appl. Radiat. Isot. 42, 793± 796. Helus, F., Weber, K., Zeisler, S., Maier-Borst, W., 1991. An automatic system for the enzymatic synthesis of 13 N-glutamate. J. Radioanal. Nucl. Chem. Letters 155, 9±13. Ido, T., Iwata, R., 1981. Fully automated synthesis of 13 NH3. J. Labeled Comp. Radiopharm. 18, 244±246. Irie, T., Inoue, O., Suzuki, K., Tominaga, T., 1985. Labeling of 13 N-labeled adenosine and nicotinamide by ammonolysis. Int. J. Appl. Radiat. Isot. 36, 345±347. Knapp, W. H., Helus, F., Ostertag, H., Tillmanns, H., Kuebler, W., 1982. Uptake and turnover of L-[13 N]glutamate in the normal human heart and in patients with coronary artery disease. Eur. J. Nucl. Med. 7, 211±215. Knapp, W. H., Panzer, M., Helus, F., Layer, K., Sinn, H.-J., Ostertag, H., 1988. Eect of methotrexate on perfusion and nitrogen-13 glutamate uptake in the Walker-256 carcinosarcoma. J. Nucl. Med. 29, 208±216. Korsakov, M. V., Krasikova, R. N., Kuznetsova, O. F., Fedorova, O. S., Khorti, A. G., 1992. Reaction of recoil 13 N atoms in aqueous ethanol. Synthesis of [13 N]NH3. Radiokhimiya 34, 70±76. Korsakov, M. V., Krasikova, R. N., Fedorova, O. S., 1995. Reactions of recoil nitrogen-13 atoms in the ethanol±water system. Formation of [13 N]NH3 upon irradiation of water and dilute aqueous solutions of ethanol under a pressure of various gases. Radiokhimiya 37, 369±373. Krizek, H., Lembares, N., Dinwoodie, R., Gloria, I., Lathrop, K. A., Harper, P. V., 1973. Production of radiochemically pure 13 NH3 for biomedical studies using the 16 O( p, a)13 N reaction. J. Nucl. Med. 14, 629±630. Lambrecht, R. H. D., Slegers, G., Mannens, G., Claeys, A., 1986. Enzymatic synthesis of 13 N-labeled r-amino-butyric acid. J. Label. Comp. Radiopharm. 23, 1114±1115. Merck and Co. (1987) The Merck manual of diagnosis and therapy. Merck, Sharp and Dohme Research Laboratories, Rahway, NJ. Mulholland, G. K., Kilbourn, M. R., Moskwa, J. J., 1990. Direct simultaneous production of [15 O]water and [13 N]ammonia or [18 F]¯uoride ion by 26 MeV proton irradiation of a double chamber water target. Appl. Radiat. Isot. 41, 1193±1199. Parks, N. J., Krohn, K. A., 1978. The synthesis of 13 N labeled ammonia, dinitrogen, nitrite, and nitrate using a single cyclotron target system. Int. J. Appl. Radiat. Isot. 29, 754± 756. Sasaki, M., Haradahira, T., Suzuki, K., 1995. Speci®c activities of 13 N-chemical species generated by the 16 O( p, a)13 N reaction using an ultra pure water target saturated with gases. J. Label. Comp. Radiopharm. 37, 761±763. Suzuki, K., Shikano, N., Kubodera, A., 1995. Development of an automated synthesis apparatus for [13 N]-labeled compounds using anhydrous [13 N]ammonia. J. Label. Comp. Radiopharm. 37, 644±646. Suzuki, K., Tamate, K., 1984. Automatic production of 13 NH3 and L-(N-13) glutamate ready for intravenous injection. Int. J. Appl. Radiat. Isot. 35, 771±777.
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503 Tilbury, R. S., Dahl, J. R., 1979. 13 N species formed by proton irradiation of water. Radiat. Res. 79, 22±33. Tominaga, T., Inoue, O., Suzuki, K., Yamasaki, T., Hirobe, M., 1986. Synthesis of 13 N-labeled amines by reduction of 13 N-labeled amides. Appl. Radiat. Isot. 37, 1209±1212. Tominaga, T., Suzuki, K., Inoue, O., Irie, T., Yamasaki, T., Hirobe, M., 1987. [13 N]ammonia in organic solvents; a potent synthetic precursor for 13 N-labeling. Appl. Radiat. Isot. 38, 437±445. Vaalburg, W., Kamphuis, J. A. A., Beerling-Van Der Molen, H. D., Reiers, S., Rijskamp, A., Woldring, M. G. 1975. An improved method for the cyclotron production of 13Nlabeled ammonia. Int. J. Appl. Radiat. Isot. 26, 316±318. Watanabe, Y., Suzuki, K., Tsukada, H. et al, 1991. Synthesis of 13 N-labeled L-tyrosine. Acta Radiol. Suppl. 376, 110± 111.
503
Wieland, B., Bida, G., Padgett, H., Hendry, G., Zippi, E., Kabalka, G., Morelle, J.-L., Verbruggen, R., Ghyoot, M., 1991. In-target production of [13 N]ammonia via proton irradiation of dilute aqueous ethanol and acetic acid mixtures. Appl. Radiat. Isot. 42, 1095±1098. Wu, H. M., Hoh, C. K., Buxton, D. B., Kuhle, W. G., Schelbert, H. R., Choi, Y., Hawkins, R. A., Phelps, M. E., Huang, S. C., 1995. Quanti®cation of myocardial blood ¯ow using dynamic nitrogen-13-ammonia PET studies and factor analysis of dynamic structures. J. Nucl. Med. 36, 2087±2093. Yoshida, K., Mullani, N., Gould, K. L., 1996. Coronary ¯ow and ¯ow reserve by PET simpli®ed for clinical applications using rubidium-82 or nitrogen-13-ammonia. J. Nucl. Med. 37, 1701±1712.
Applied Radiation and Isotopes 50 (1999) 497±503
Production of [13N]NH3 with ultra-high speci®c activity K. Suzuki a, b, *, Y. Yoshida a, c a
Division of Advanced Technology for Medical Imaging, National Institute of Radiological Sciences, 4-9-1 Anagawa, Inage-ku, Chiba 263, Japan b Subfemtomole Biorecognition Project, Japan Science and Technology Corporation, Osaka 565, Japan c Sumitomo Accelerator Service, 5-9-11 Kitashinagawa, Shinagawa-ku, Tokyo 141, Japan Received 23 February 1998
Abstract Aqueous solutions of [13 N]NH3 were synthesized according to well-known methods using the 16 O( p, a)13 N reaction under conditions rendering the smallest possible amount of nitrogen-contaminants. The speci®c activities and radiochemical yields were measured. Factors, aecting the speci®c activity of [13 N]NH3, were investigated using radio-ionchromatography. The achieved speci®c activities (GBq/mmol) and radiochemical yields (GBq) of [13 N]NH3 were 14 2 2.8 and 0.3 2 0.1 (TiCl3 method)*, 5902 200 and 5.42 1.1 (DeVarda's Alloy method), 55002 500 and 12.7 2 0.1 (ethanol method), and 62002 2700 and 2.8 2 0.3 (hydrogen method, 3 bar), respectively at 15 mA for 20 min irradiation (*; 5 mA, 5 min irradiation). More than 70% of the N-13 generated with the hydrogen method was of the chemical form [13 N]N2. # 1999 Elsevier Science Ltd. All rights reserved.
1. Introduction N-13 (half life; 9.965 min, 100% b+decay) is one of the most important emitters of all the positron emitters, and has been used, mostly in the chemical form [13 N]NH3 (Wu et al., 1995; Yoshida et al., 1996) or [13 N]-amino acids (Knapp et al., 1988; Conlon et al., 1989; Cooper et al., 1996), in the ®eld of nuclear medicine. However, it is dicult to synthesize N-13 labeled compounds with a high enough speci®c activity and radioactivity to carry out receptor studies with PET, due to its short half-life and the ease of contamination by non-radioactive nitrogen compounds of N-13. N-13 is usually produced by the 16 O( p, a)13 N reaction and converted to [13 N]NH3 by in-target or classical reduction methods. With classical reduction methods, the [13 N]NOÿ x generated in irradiated water is reduced to [13 N]NH3 with TiCl3 (TiCl3 method) (Krizek et al., 1973; Ido and Iwata, 1981) or with DeVarda's alloy (DeVarda's alloy method) (Vaalburg et al., 1975; Suzuki and Tamate, 1984; Gatley and
* To whom all correspondence should be addressed.
Shea, 1991). With in-target reduction methods, the [13 N]NH3 generated directly in the target is prevented from being oxidized to [13 N]NOÿ x by addition of ethanol (ethanol method) (Tilbury and Dahl, 1979; Wieland et al., 1991; Berridge and Landmeier, 1993; Korsakov et al., 1995) or H2 (hydrogen method) (Mulholland et al., 1990; Berridge and Landmeier, 1993; Korsakov et al., 1995) to pure water as a scavenger of oxidizing radical OH (Tilbury and Dahl, 1979; Korsakov et al., 1992). In some cases, an aqueous solution of [13 N]NH3 has been used as a synthetic precursor in preparations of 13 N-labeled compounds (Irie et al., 1985; Tominaga et al., 1986, 1987; Helus et al., 1991; Watanabe et al., 1991; Suzuki et al., 1995). The importance of anhydrous [13 N]NH3 as a synthetic precursor was suggested by Tominaga et al. However, little eort has been made to achieve a higher speci®c activity of [13 N]NH3, since N-13 has been used in the chemical forms of amino acids and ammonia which exist abundantly in the living body (NH3 in human blood plasma; 11±35 mM, Merck and Co., 1987). Only a few papers have mentioned speci®c activity of 13 N-labeled compounds (Knapp et al., 1982;
0969-8043/99/$19.00 # 1999 Elsevier Science Ltd. All rights reserved. PII: S 0 9 6 9 - 8 0 4 3 ( 9 8 ) 0 0 0 9 5 - 5
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K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
Lambrecht et al., 1986; Parks and Krohn, 1978; Gatley and Shea, 1991; Channing et al., 1994) and their values were quite low, compared to the theoretical value of N-13, i.e. 6.9 105 GBq/mmol. We measured the speci®c activity of N-13 ion species generated in water saturated with pure gases (O2, He, H2, N2) under ¯ow conditions and observed a remarkable decrease of speci®c activity of N-13 in N2 gas saturated water (Sasaki et al., 1995). The establishment of methods producing [13 N]NH3 with high speci®c activity would enable receptor studies with N-13 labeled compounds, if coupled with automated equipment (Suzuki et al., 1995), to allow for the quick production of such compounds. This paper reports on the speci®c activity and yield of [13 N]NH3 produced by well-known methods under conditions rendering the smallest possible amounts of nitrogen-contaminants. 2. Experimental 2.1. Chemicals The water used as a target material was prepared using the MilliQ SP Reagent Water System (Millipore, MA). Pure gases, O2 (purity; >99.9995%) and H2 (purity; >99.99999%), used to purge the air dissolved in the water, were obtained from Nippon Sanso (Tokyo). Sodium hydroxide was purchased from Nakarai Tesque (Kyoto, impurity; 0.001% as N), Fluka Chemie (Buchs, purity; >98%) and Aldrich Chemical (WI, purity; 99.99%). TiCl3 solution was obtained from Wako Pure Chemical (Osaka), Fluka and Aldrich. DeVarda's alloy was purchased from Wako (impurity; <0.003% as N), Fluka (impurity; 0.001% as N) and Aldrich. DeVarda's alloy and NaOH were dried at 3508C for 05 hours in vacuo. The target water was bubbled for 0one hour with pure O2 or H2 gas in a sealed bottle to purge dissolved gases. 2.2. Analysis Ionic species were analyzed by ion chromatography using DX-100 (Dionex, CA) and IC-7000 (Yokogawa Electric, Tokyo) coupled with a NaI(Tl) detector, respectively. Cation analysis was performed using an Ion Pac CS-14 column (4 mm b 250 mm, guard column; Ion Pac CS-14, 4 mm b 50 mm) with 10 mM methansulfonic acid as an eluent at 1.5 mL/min [Rt(NH+ 4 ), 3.3 min]. Anion analysis was performed using an ICS-A35 column (4.6 mm b 150 mm, guard column; ICS-A3G, 4.6 mm b 30 mm) with 5 mM Na2CO3+1.5 mM NaHCO3 as an eluent at 1 mL/min and 408C oven temperature [Rt(NOÿ 2 ), 6.6 min and Rt(NOÿ 3 ), 8.5 min]. Quanti®cation of trace ions was
carried out using calibration curves obtained with 10± 300 ppb solutions of the corresponding ions (NH+ 4 , ÿ NOÿ 2 , NO3 ). Gas chromatography was performed on a HP5890 gas chromatograph (Yokogawa, Tokyo) with a thermal conductivity detector and a NaI(Tl) detector. A glass column (2 mm b 2 m) packed with Molecular Sieve 5A (30/60 mesh) was used with a He gas ¯ow rate of 67 mL/min at 508C for identi®cation of radiolabeled gases [Rt(N2) = 1.2 min, Rt(O2) = 0.8 min]. 2.3. Determination of nitrogen in chemicals The amount of nitrogen contained in the reagents used in this study was determined by procedures similar to those used for [13 N]NH3 synthesis. Nitrogen contained in Devarda's alloy (10, 20, 40 mg) and NaOH (190 mg) was converted to ammonia in 4 ml of ultrapure water and distilled into a sealed plastic bottle in ice. The total volume was adjusted to 2 ml with ultrapure water. The amount of nitrogen in DeVarda's alloy was calculated from the slope of the straight line obtained by plotting the amount of NH+ 4 against the amount of DeVarda's alloy. A similar technique was applied for the determination of carrier nitrogen contained in other reagents, such as a solution of TiCl3 and NaOH pellets. 2.4. Production of [13 N]NH3 Fig. 1 is a block diagram of the systems used for the production of [13 N]NH3 solution. As can be seen, the tube through the 6- and 3-way valves from the target chamber is connected to one of the reduction vessels or a collection vial. Each component in the production lines is connected with thin tubes (SUS316 and PEEK tube; 1/16 inch o.d., 0.75 mm i.d.). The target chamber (21 mm i.d. 6 mm) was made of SUS-316 and window foils of 100 mm SUS-316 were welded on the chamber body by an electron beam in vacuo. All the parts, including the reaction vessel, the collection vial, the target chamber and the tube lines were cleaned thoroughly with ultra-pure water before the experiment. Before irradiation, the target water used in the N-13 production other than with the hydrogen method was bubbled with pure oxygen gas for 60 min, which was released through the relief valve kept at a constant pressure (1 bar), to replace the dissolved gas in the water with oxygen. With the hydrogen method, a pure hydrogen gas (1 or 3 bar) was used instead of oxygen. With the ethanol method, a 10 mM ethanol solution saturated with pure O2 gas was used. The water bubbled with pure gas was charged into the target chamber through a 6-way valve and pressurized by closing the 3-way valve at the exit. Irradiation was carried out with 18 MeV protons (15.7 MeV on target)
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
Fig. 1. Schematic diagram for the [13 N]NH3 production PG; pressure gauge.
; 2-, 3-way valves, w; thermocouple,
499
; radioactivity sensor,
from the NIRS cyclotron (HM18, Sumitomo Heavy Industries, Tokyo) at 15 mA for 20 min in a closed circuit (6-way valve; closed).
was monitored continuously to determine the end point of distillation by using a small Si detector (Oyokoken, Tokyo). The product was then analyzed.
2.4.1. Hydrogen and ethanol methods The irradiated water was transported into a collection vial equipped with a gas collection bag by He gas pressure. The He gas was allowed to bubble through the collected solution for 20 s to remove radioactive gas. The radioactive liquid and gas fractions were measured separately using a curiemeter IGC-3R (Aloka, Tokyo) and radio-ion/radio-gas chromatography systems.
2.4.3. TiCl3 method The irradiated water was introduced into a reaction vessel (maintained at 1008C) containing 1.2 g of NaOH (Fluka) and then 1 ml of 7.5% TiCl3 in hydrochloric acid (Fluka) was added. Distillation and analysis of the product were carried out in a similar manner as above.
2.4.2. Devarda's alloy method The irradiated water was introduced into a reaction vessel containing 5 mg of DeVarda's alloy (Fluka) and 20 mg of NaOH (Fluka), maintained at 1008C, by He gas pressure. Then, the temperature was increased to 3508C. The radioactivity distilled into a collection vial
3. Results and discussion The measured amounts of nitrogen in the reagents used in the present study are summarized in Table 1, where the amount of distilled ammonia is assumed to imply the amount of nitrogen in the reagents. The values in Table 1 do not refer to the total amount of
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Table 1 Measured amount of nitrogen in the reagents (n = 3) Reagents
Nitrogen (nmol)
NaOH (Nakarai) NaOH (Fluka) NaOH (Aldrich) DeVarda's (Wako) DeVarda's (Fluka) DeVarda's (Aldrich) TiCl3 (Wako) TiCl3 (Fluka) TiCl3 (Aldrich)
0.06020.004* 0.02720.012* 0.02720.014* 0.4 20.1* 0.2 20.1* 0.3 20.1* 86 216$ 70 224$ 106 237$
* Values in 1 mg of the reagent. $ Values in 1 ml of the TiCl3/HCl solution.
nitrogen in the reagents since distillation eciency of ammonia and amount of nitrogen not-converted to ammonia were not taken into account. But, they do suggest the amount of nitrogen related strongly to the speci®c activity of [13 N]NH3 since the values were obtained employing the same procedure used for [13 N]NH3 production. The reagents from Fluka were used in the present study since they gave the smallest contamination of nitrogen. A relatively large amount of nitrogen was detected in a TiCl3 solution. The use of 1 ml of TiCl3 solution and 1.2 g of NaOH as in the
present study would increase the amount of ammonia by 70 nmol and 30 nmol, respectively and cause a remarkable decrease in the speci®c activity of [13 N]NH3. On the other hand, with DeVarda's alloy method, 1 nmol and 0.5 nmol of ammonia is generated in [13 N]NH3 production on using 5 mg of DeVarda's alloy and 20 mg of sodium hydroxide. Therefore, DeVarda's alloy method may be preferable to the TiCl3 method for high speci®c activity of [13 N]NH3, with the smallest amount of reagents which are within the limit which does not cause a remarkable decrease of [13 N]NH3 yield. Fig. 2 shows radiochromatograms of O2-saturated water irradiated at 15 mA for 20 min. The radioactive ÿ 18 peaks were identi®ed to be [13 N]NH+ 4 , [ F]F , ÿ 13 [13 N]NOÿ and [ N]NO on comparison with an auth2 3 entic sample solution. Table 2 summarizes the amount of nitrogen ion in the target solution recovered from the target chamber with or without irradiation. Without irradiation, only 0.1 2 0.01 nmol of NH+ 4 was ÿ detected, and ions NOÿ and NO were below the 2 3 detection limit in the water recovered from the target system according to the same procedure with actual [13 N]NH+ production. Obvious increases of nitrate 4 and nitrite ions were observed following irradiation. The tendency was increased with a higher beam current and longer irradiation particularly for NOÿ 3 . This
Fig. 2. Radio-ionchromatograms of the irradiated water. Upper and lower chromatogram in (a) and (b): Upper; radioactivity output, Lower; conductivity output. (a) anion chromatogram. Column; ICS-A35 + ICS-A3G, eluent; 5 mM Na2CO3+1.5 mM NaHCO3, ¯ow rate; 1 ml/min, oven temp.; 408C. (b) cation chromatogram. Column; IonPac CS-14, eluent; 10 mM methansulfonic acid, ¯ow rate; 1.5 ml/min.
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503
501
Table 2 Amount of nitrogen ions (nmol) in the target solution with or without irradiation (n = 3) Ions
Without irradiation
NH+ 4 NOÿ 2 NOÿ 3
With irradiation
0.1020.01 <0.05 <0.08
5 mA, 5 min
15 mA, 25 min
0.1020.03 (1.020.8) 0.3720.01 (4.020.5) 1.0520.09 (94.026.0)
0.102 0.03 (0.720.6) 0.202 0.04 (3.320.7) 3.602 0.56 (93.523.2)
target: ultra-pure water saturated with a pure O2 gas. bracket: % of 13 N-radioactivity.
observation supports our previous result, where a marked increase of non-radioactive nitrogen ions, especially in the N2-saturated water target, was detected in the ¯ow target system on irradiation of water saturated by pure gas (N2, O2, He and H2) (Sasaki et al., 1995). To avoid the increase of nitrogen ions by irradiation, special attention was given to the following: (1) use of ultra-pure water, (2) purge of nitrogen gas from the water as suggested by Sasaki et al., (3) use of a target chamber welded by electron beam in vacuo, and (4) baking of the target chamber by repeated irradiation at high beam current for long periods. Nevertheless, an increase of nitrogen ions was observed as shown in Table 2, although the extent of this increase was not remarkable. The reason for the increase is still not clear. The purity of the material of the target chamber, especially the window, may be a factor. Table 3 shows the speci®c activity and radiochemical yield obtained in the [13 N]NH3 syntheses under conditions of 20 min irradiation at 15 mA. The highest speci®c activity, 62002 2700 GBq/mmol, of [13 N]NH3 was obtained with the hydrogen method (H2; 3 bar), but the yield, 2.82 0.3 GBq, was only about one fourth of that of the highest value (ethanol method), due to loss of radioactivity by [13 N]N2 gas evolution (70.82 12.3%). The speci®c activity and yield were Table 3 Results of
13
lower at 1 bar H2 gas pressure than at 3 bar. Higher yield of [13 N]NH3 may be achieved by the use of water saturated with a higher pressure H2 gas (Berridge and Landmeier, 1993). On the other hand, the ethanol method produced fairly high speci®c activity, 55002 450 GBq/mmol, and the highest radiochemical yield, 12.72 0.1 GBq. With this method, [13 N]NH3 with a radiochemical purity of >99% was obtained without any puri®cation. The above values of speci®c activity are higher than the reported values, 22 GBq/ mmol for [13 N]glutamate (Knapp et al., 1982), 7.4 GBq/mmol at EOB for [13 N]GABA (Lambrecht et al., 1986), 37 GBq/mmol for [13 N]NH3 (Parks and Krohn, 1978), >30 GBq/mmol for [13 N]NH3 (Channing et al., 1994) and 150 GBq/mmol at EOB for total [13 N]anions (Gatley and Shea, 1991). In the present study, 10 mM EtOH solution saturated with pure O2 gas was used as target material to achieve a higher speci®c activity for N-13 (Sasaki et al., 1995). Although a signi®cant decrease of the [13 N]NH3 yield was reported in an O2-saturated 5 mM EtOH solution for 0.83 mA h irradiation (Channing et al., 1994), we have found no decrease of the [13 N]NH3 yield under the present condition. The disagreement may be attributed to the dierences in ethanol concentration, material of the target chamber, beam pro®le on the target, etc., between the two production systems.
NH3 production by well-known methods (n = 3) Yield* (GBq)
Speci®c activity* (GBq/mmol)
Synthesis time (s)
Remarks
A
5.421.1
590 2200
220227
B
2.820.3
620022700
40
C D E
1.320.1 12.72 0.1 0.320.1
43002930 55002450 14.0 22.8
40 40 390228
purity; >99% 13 13 N2 70.8212.3%, 13 NOÿ NOÿ 2 0.822.0%, 3 2.02 0.6% 13 13 N2 78.123.0%, 13 NOÿ NOÿ 2 0.820.3%, 3 4.52 1.1% purity; >99% purity; >99%
A = DeVarda's alloy method, B = hydrogen method (3 bar), C = hydrogen method (1 bar) D = ethanol method (10 mM), E = TiCl3 method. Irradiation conditions: A, B, C, D = 15 mA/20 min, E = 5 mA/5 min. * Yield and speci®c activity of [13 N]NH3 at EOS.
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By contrast, less speci®c activity of [13 N]NH3 was obtained using the DeVarda's alloy and TiCl3 methods, probably due to contamination from the reagents used in the reductive alkaline distillations after irradiation. The lowest speci®c activity was obtained with the TiCl3 method, the yield and speci®c activity of which should be multiplied by a factor 10 to correct for the low beam current and short period of irradiation. The use of a strongly acidic solution of TiCl3, which would absorb ammonia during storage, explains this ®nding. The yield of [13 N]NH3 produced by the DeVarda's alloy and TiCl3 methods was lower than that with the ethanol method. The dierence can be ascribed to the longer process time, incomplete reduction and distillation, and loss of radioactivity in the line due to the complexity of the production system. For clinical use, the [13 N]NH3 solution produced by the above classical methods can be directly applied, whereas a puri®cation process with an ion-exchange column or a distillation process would be required in the in-target reduction methods to remove undesirable radioactive/non-radioactive impurities. Based on these considerations, we believe the ethanol method to be the best choice for production of [13 N]NH3 as a synthetic precursor with high speci®c activity and high radiochemical yield under the studied conditions. Extremely high speci®c activity of aqueous [13 N]NH3 solution was obtained in the present study. Using the proposed technique, attempts to synthesize 13 N-labeled compounds with high speci®c activity employing automated equipment are underway.
Acknowledgements We are grateful to the sta of cyclotron for operating the NIRS cyclotron HM-18. This work was supported by the International Joint Research Program of Japan Science and Technology Corporation.
References Berridge, M. S., Landmeier, B. J., 1993. In-target production of [13 N]ammonia: Target design, products, and operating parameters. Appl. Radiat. Isot. 44, 1433±1441. Channing, M. A., Dunn, B. B., Kiesewetter, D. O., Plascjak, P., Eckelman, W. C., 1994. The quality of [13 N]ammonia produced by using ethanol as a scavenger. J. Label. Comp. Radiopharm. 37, 334±336. Cooper, A. L., Sheu, K. F., Blass, J. P., 1996. Normal glutamate metabolism in Alzheimer's disease ®broblasts de®cient in alpha-ketoglutarate dehydrogenase complex activity. Developmental Neuroscience 18, 499±504. Conlon, K. C., Bading, J. R., Diresta, G. R., Corbally, M. T., Gelbard, A. S., Brennan, M. F., 1989. Validation of transport measurements in skeletal muscle with N-13 amino
acids using a rabbit isolated hindlimb model. Life Sciences 44, 847±859. Gatley, S. J., Shea, C. 1991. Radiochemical and chemical quality-assurance methods for [13N]-ammonia made from small volume H216O target. Appl. Radiat. Isot. 42, 793± 796. Helus, F., Weber, K., Zeisler, S., Maier-Borst, W., 1991. An automatic system for the enzymatic synthesis of 13 N-glutamate. J. Radioanal. Nucl. Chem. Letters 155, 9±13. Ido, T., Iwata, R., 1981. Fully automated synthesis of 13 NH3. J. Labeled Comp. Radiopharm. 18, 244±246. Irie, T., Inoue, O., Suzuki, K., Tominaga, T., 1985. Labeling of 13 N-labeled adenosine and nicotinamide by ammonolysis. Int. J. Appl. Radiat. Isot. 36, 345±347. Knapp, W. H., Helus, F., Ostertag, H., Tillmanns, H., Kuebler, W., 1982. Uptake and turnover of L-[13 N]glutamate in the normal human heart and in patients with coronary artery disease. Eur. J. Nucl. Med. 7, 211±215. Knapp, W. H., Panzer, M., Helus, F., Layer, K., Sinn, H.-J., Ostertag, H., 1988. Eect of methotrexate on perfusion and nitrogen-13 glutamate uptake in the Walker-256 carcinosarcoma. J. Nucl. Med. 29, 208±216. Korsakov, M. V., Krasikova, R. N., Kuznetsova, O. F., Fedorova, O. S., Khorti, A. G., 1992. Reaction of recoil 13 N atoms in aqueous ethanol. Synthesis of [13 N]NH3. Radiokhimiya 34, 70±76. Korsakov, M. V., Krasikova, R. N., Fedorova, O. S., 1995. Reactions of recoil nitrogen-13 atoms in the ethanol±water system. Formation of [13 N]NH3 upon irradiation of water and dilute aqueous solutions of ethanol under a pressure of various gases. Radiokhimiya 37, 369±373. Krizek, H., Lembares, N., Dinwoodie, R., Gloria, I., Lathrop, K. A., Harper, P. V., 1973. Production of radiochemically pure 13 NH3 for biomedical studies using the 16 O( p, a)13 N reaction. J. Nucl. Med. 14, 629±630. Lambrecht, R. H. D., Slegers, G., Mannens, G., Claeys, A., 1986. Enzymatic synthesis of 13 N-labeled r-amino-butyric acid. J. Label. Comp. Radiopharm. 23, 1114±1115. Merck and Co. (1987) The Merck manual of diagnosis and therapy. Merck, Sharp and Dohme Research Laboratories, Rahway, NJ. Mulholland, G. K., Kilbourn, M. R., Moskwa, J. J., 1990. Direct simultaneous production of [15 O]water and [13 N]ammonia or [18 F]¯uoride ion by 26 MeV proton irradiation of a double chamber water target. Appl. Radiat. Isot. 41, 1193±1199. Parks, N. J., Krohn, K. A., 1978. The synthesis of 13 N labeled ammonia, dinitrogen, nitrite, and nitrate using a single cyclotron target system. Int. J. Appl. Radiat. Isot. 29, 754± 756. Sasaki, M., Haradahira, T., Suzuki, K., 1995. Speci®c activities of 13 N-chemical species generated by the 16 O( p, a)13 N reaction using an ultra pure water target saturated with gases. J. Label. Comp. Radiopharm. 37, 761±763. Suzuki, K., Shikano, N., Kubodera, A., 1995. Development of an automated synthesis apparatus for [13 N]-labeled compounds using anhydrous [13 N]ammonia. J. Label. Comp. Radiopharm. 37, 644±646. Suzuki, K., Tamate, K., 1984. Automatic production of 13 NH3 and L-(N-13) glutamate ready for intravenous injection. Int. J. Appl. Radiat. Isot. 35, 771±777.
K. Suzuki, Y. Yoshida / Applied Radiation and Isotopes 50 (1999) 497±503 Tilbury, R. S., Dahl, J. R., 1979. 13 N species formed by proton irradiation of water. Radiat. Res. 79, 22±33. Tominaga, T., Inoue, O., Suzuki, K., Yamasaki, T., Hirobe, M., 1986. Synthesis of 13 N-labeled amines by reduction of 13 N-labeled amides. Appl. Radiat. Isot. 37, 1209±1212. Tominaga, T., Suzuki, K., Inoue, O., Irie, T., Yamasaki, T., Hirobe, M., 1987. [13 N]ammonia in organic solvents; a potent synthetic precursor for 13 N-labeling. Appl. Radiat. Isot. 38, 437±445. Vaalburg, W., Kamphuis, J. A. A., Beerling-Van Der Molen, H. D., Reiers, S., Rijskamp, A., Woldring, M. G. 1975. An improved method for the cyclotron production of 13Nlabeled ammonia. Int. J. Appl. Radiat. Isot. 26, 316±318. Watanabe, Y., Suzuki, K., Tsukada, H. et al, 1991. Synthesis of 13 N-labeled L-tyrosine. Acta Radiol. Suppl. 376, 110± 111.
503
Wieland, B., Bida, G., Padgett, H., Hendry, G., Zippi, E., Kabalka, G., Morelle, J.-L., Verbruggen, R., Ghyoot, M., 1991. In-target production of [13 N]ammonia via proton irradiation of dilute aqueous ethanol and acetic acid mixtures. Appl. Radiat. Isot. 42, 1095±1098. Wu, H. M., Hoh, C. K., Buxton, D. B., Kuhle, W. G., Schelbert, H. R., Choi, Y., Hawkins, R. A., Phelps, M. E., Huang, S. C., 1995. Quanti®cation of myocardial blood ¯ow using dynamic nitrogen-13-ammonia PET studies and factor analysis of dynamic structures. J. Nucl. Med. 36, 2087±2093. Yoshida, K., Mullani, N., Gould, K. L., 1996. Coronary ¯ow and ¯ow reserve by PET simpli®ed for clinical applications using rubidium-82 or nitrogen-13-ammonia. J. Nucl. Med. 37, 1701±1712.