Abstract:
A composition comprising  82  Sr and an adsorbant selected from the group consisting of tin oxide, hydrated tin oxide, polyantimonic acid, titanium oxide, and ferric oxide. 
     A low  82  Sr breakthrough method of generating  82  Rb from a  82  Sr charged adsorbant comprising eluting wherein said adsorbant is selected from the group consisting of tin oxide, polyantimonic acid, titanium oxide, ferric oxide, and hydrated tin oxide.

Description:
This application is a continuation-in-part of application Ser. No. 162,858 filed June 25, 1980 abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     Rubidium-82, a positron emitter with a half-life of 75-sec readily obtainable from the parent Sr-82 (T 1/2  =25 days). Rubidium can be used as a diffusible flow tracer for the myocardium and kidney, and as a nondiffusible tracer for brain blood flow. Serial injections of Rb-82 can be administered every 5 to 10 minutes by eluting (milking) Rb-82 from its 25-day Sr-82 parent. The advantages of Rb-82 are low radiation dose, ability to provide for repeated examinations every 5 minutes without constraints from body background, and a convenient and economical supply of a short-half-life positron emitter. (Yano et al., The Journal of Nuclear Medicine 20:961-966, 1979.) 
     Significant quantities of  82  Sr are available for clinical investigation. The short-lived daughter, 75-second  82  Rb, is a value in biomedicine for circulation and perfusion studies as well as for myocardial imaging as mentioned in U.S. Pat. No. 3,953,567. 
     Loc[h et al. J. Nucl. Med. 21: 171-173, 1980 disclose a tin dioxide (SnO 2 )/HCl Ga-68 generator. 
     Arino et al. Int. J. Appl. Radiat. Isot. 29: 117-120, 1978 disclose a  68  Ge/ 68  Ga radioisotope generator system which uses polyantimonic acid to selectively adsorb Ge and not Ga. The adsorption was speculated to be due to a dehydration reaction forming chemical bonding between Sb and Ge through oxygen. 
     Neirinckx et al. disclose titanium oxide in a generator for ionic gallium-68, see second International Symposium on Radiopharmaceutical Chemistry MRC. Oxford, 1978, p. 109. 
     Kopecky et al. Int. J. Appl. Radiat. Isot. 25: 263-268, 1974 disclose a  68  Ge/ 68  Ga generator for the production of  68  Ga in an ionic form. Aspects of the adsorption of carrier-free  68  Ge and  68  Ga on alumia, Al(OH) 3  and Fe(OH) 3  are discussed. 
     SUMMARY OF THE INVENTION 
     A composition comprising  82  Sr and an adsorbant selected from the group consisting of tin oxide, hydrated tin oxide, polyantimonic acid, and titanium oxide. 
     A low  82  Sr breakthrough method of generating  82  Rb from a  82  Sr charged adsorbant comprising eluting the  82  Rb from said adsorbant with an eluant solution wherein said adsorbant is selected from the group consisting of hydrated, unhydrated and mixtures of the hydrated and unhydrated forms of tin oxide, titanium oxide and ferric oxide; and unhydrated polyantimonic acid. The eluant can be physiological saline or a buffered isotonic solution. The yields of  82  Rb are high. 
     DETAILED DESCRIPTION OF THE INVENTION 
     Hydrated tin oxide includes hydrated stannic oxide, hydrated stannous oxide, and mixtures of hydrated stannic oxide and hydrated stannous oxide. Preferably the hydrated tin oxide is amorphous. 
     Tin oxide includes stannic oxide, stannous oxide and mixtures of stannous oxide and stannic oxide. 
     Most preferably an amorphous mixture comprising tin oxide and a substantial amount (more than 10% by weight) of hydrated stannic oxide is used as the adsorbant. 
     The method and compositions of the present invention are useful in positron imaging and in the subsequent measurement of blood flow through the myocardium, brain and kidneys. 
     The present invention provides improved breakthrough characteristics. It has been discovered that breakthrough of Sr may be lowered by providing an adsorbant which is preferably polyantimonic acid, titanium oxide (hydrated), ferric oxide (hydrated), hydrated tin oxide or tin oxide. 
     The present invention provides a small bolus size of 2-3 ml which is advantageous for lower volume per unit time infusion while maintaining an effective amount of activity to monitor the patient. 
     Preferably the eluant is isotonic saline or isotonic saline buffered at physiological pH. Preferably a buffered eluant is used and the buffer is a phosphate salt or a carbonate salt. Preferably the buffer is a phosphate salt. Most preferably isotonic saline at physiological pH is used. 
     Bacteriostats may be beneficially added to the eluant. Preferred bacteriostats are those which are pharmaceutically acceptable buffers, for example parabens. 
     Infusion speeds of 5-10 ml per minute or higher are useful when using the compositions and method of the present invention. 
       82  Rb yields of 90% of theoretical maximum are obtained using the present invention. These yields may be obtained over a 0.1 minute interval using an eluant flow rate of 30 ml/min. 
     Low  82  Sr breakthroughs of 10 -9  /ml are obtained using the present invention. 
     Beneficially, the present invention provides high yields of  82  Rb with physiological saline as eluant and high radioactive concentration in the eluate (90% elution yield in 5-10 cc). 
     The eluant may be buffered at a pharmaceutically acceptable pH. Preferably the pH is from 6.0 to Ph 10. Most preferably the pH is from pH 7.0 to pH 7.5 The concentration of the buffer in the eluent preferably is from 0.01 mmol to 200 mmol per liter of eluant solution. 
     The saline concentration of the eluant is a pharmaceutically acceptable concentration. Preferably the saline is isotonic (0.9%). 
     A column containing adsorbant is charged with  82  Sr. Preferably the adsorbant is hydrated tin oxide or polyantimonic acid. Most preferably the adsorbant is hydrated tin oxide. The column is then eluted with the eluant. 
     At clinically useful flow rates of about 20 ml per minute,  82  Sr breakthroughs of 10 -9  per ml of eluant are obtained by the present invention. Breakthrough is the ratio of microcuries of  82  Sr in the eluant to the microcuries of  82  Sr on the adsorber. 
     Phosphate salts include alkali phosphates, alkaline earth phosphates, alkali metal hydrogen phosphates, alkaline earth hydrogen phosphates as well as hydrates of phosphate salts. Also phosphate salts include all phosphorous oxides which form phosphates upon addition to water. 
     A preferred phosphate salt is Na 2  HPO 4  which may be added to the eluant as Na 2  HPO 4 .7H 2  O. In the saline eluant it forms Na +   and PO 4   -3  ⃡HPO 4   -2  ⃡H 2  PO 4 .sup.⊖. Upon addition of NaOH some of the H 2  PO 4 .sup.⊖  would be used up in the formation of HPO 4   -2 . The balanced equation being: 
     
         NaH.sub.2 PO.sub.4 +NaOH⃡Na.sub.2 HPO.sub.4 +H.sub.2 O. 
    
     When acid is added, for example HCl, some H 2  PO 4 .sup.⊖ is formed. The balanced equation is: 
     
         Na.sub.2 HPO.sub.4 +HCl⃡NaH.sub.2 PO.sub.4 +NaCl. 
    
     Carbonate salts include water soluble carbonate salts such as alkali metal carbonates and alkali metal hydrogen carbonates for example NaHCO 3 . In water NaHCO 3  forms Na +   and CO 3   -2  ⃡H CO 3 .sup.⊖ ⃡H 2  CO 3 . Upon addition of NaOH; HCO 3   -1  and H 2  CO 3  are used up and CO 3   -2  and HCO 3   -1  respectively are formed. Upon addition of HCl; CO 3   -2  and HCO 3   -   are used up and HCO 3   -   and H 2  CO 3  respectively are formed. 
    
    
     The procedure used in examples 1-4 is as follows: 
     50 mg amounts of one of Ti(OH) 4 , polyantimonic acid. SnO 2  (hydrated) or ferric oxide are shaken with 5 ml of liquid phase. The liquid phase is either isotonic saline (0.9% NaCl) or saline and phosphate salt solution. The phosphate concentrations are 0.25% and 0.025%. 0.02 ml of Sr-85 or Rb-83 is added. After one hour of equilibration 1 ml fractions are pipetted. The activity in each fraction is measured and the K D  calculated. 
     The SnO 2  (hydrated) used in Example 3 is sold by Applied Research Rue Hercoliers Brussels, Belgium as oxide d&#39;etain hydrate, (which is French for hydrated tin oxide); OXTAIN (Trademark). This material is a chromatographic amorphous mixture comprising tin oxide and a substantial amount of hydrated stannic oxide. Upon heating, this material looses most of its Sr-Rb separation ability. Thus, there is a loss of activity with the loss of hydration of tin oxide. 
     
         ______________________________________Ex-am-  Ad-                        K.sub.D                                  K.sub.Dple  sorbents             pH    Sr-82  Rb-82______________________________________1    Ti(OH).sub.4         saline (0.9%)   8   40,000  52         saline + 0.025% PO.sub.4.sup.-3                         7.8 57,000  54         saline + 0.25% PO.sub.4.sup.-3                         8   71,000  562    poly-    saline (0.9%)   2.7 47,500 &lt;3antimonic         saline 0.025% PO.sub.4.sup.-3                         2.7 114,000                                    &lt;3acid     saline + 0x.25% PO.sub.4.sup.-3                         4.6 64,000 &lt;33    SnO.sub.2         saline (0.9%)   7.6 60,000 &lt;3(hy-     saline + 0.025% PO.sub.4.sup.-3                         7.6 41,000 &lt;3drated)  saline + 0.25% PO.sub.4.sup.-3                         7.6 42,000 &lt;34    Fe.sub.2 O.sub.3         saline (0.9%)   3.6   &lt;3   &lt;3(hy-     saline + 0.025% PO.sub.4.sup.-3                         4.1    7   &lt;3drated)  saline + 0.25% PO.sub.4.sup.-3                         6.5  1.182 &lt;3______________________________________ 
    
     In Examples 1-4 the difference in K D  values for  82  Sr and  82  Rb shows the amount of separation. The high K D  values for  82  Sr and the low K D  values for  82  Rb show that  82  Sr is strongly adsorbed while  82  Rb is only slightly adsorbed. Thus, while a Sr loaded column of the adsorbants in Examples 1-4 is eluted with Sr remains adsorbed strongly with very minute breakthrough into the eluate. The daughter  82  Rb is only slightly adsorbed and passes out with the eluate in yields of about 90%. 
     The bolus volume is the amount of eluant needed to elute the available  82  Rb. 
     EXAMPLE 5 
     Into a column 2 inches long and one fourth inch in diameter is placed 1.5 cc of SnO 2  particles having diameters of from 0.05 to 0.1 mm. Pre-equilibrium is done by washing the SnO 2  (hydrated) with saline three times. 2 ml of Sr-82 in saline solution having a pH of about 11 is loaded onto the SnO 2  (hydrated) particles by gravity in about one minute. The column is eluted at 12 ml per minute. The multi scaler mode on a multi channel analyzer was used to determine the elution profile. The bolus volume is about 3.4 ml. 
     The column is allowed to equilibrate and then counted for 777 KeV(Rb-82) with a Ge(Li) detector. 
     Table 1 shows the eluant composition volumes and the breakthrough fraction of  82  Sr for each volume eluted. 
     Table 2 shows a Summary of Characteristics of  82  Rb Generator System using inorganic adsorbers. At the bottom of the table are shown the characteristics of the SnO 2  (hydrated) adsorbent of the present invention. 
     
                       TABLE 1______________________________________BREAKTHROUGH OF .sup.82 Sr IN A.sup.82 Rb GENERATOR HAVING A SnO.sub.2(HYDRATED) ADSORBENT                            Fraction of SrEluant    Volume (CC)                pH Eluate   loaded/cc______________________________________NaCl pH9   0-150     ˜1    --&#34;         150-160    1.5         7 × 10.sup.-6&#34;         160-170    2           5 × 10.sup.-6&#34;         170-200    2           7 × 10.sup.-6Na.sub.2 HPO.sub.40.25%     200-205    6.5         2 × 10.sup.-6&#34;         210-250    7           1.5 × 10.sup.-7Na.sub.2 HPO.sub.40.025%    250-295    7           9 × 10.sup.-8pH9       295-348    7           7 × 10.sup.-8&#34;         345-600    7           5 × 10.sup.-8&#34;         600-650    7           10.sup.-8&#34;         650-700    7           2 × 10.sup.-8&#34;         700-750    7           2 × 10.sup.-8&#34;         750-800    7           5 × 10.sup.-9&#34;         800-850    7           ≦5 × 10.sup.- 9&#34;         850-900    7           ≦10.sup.-8&#34;         900-950    7           ≦1.5 × 10.sup.-8&#34;          950-1000  7           ≦10.sup.-8&#34;         1000-1050  7           ≦2.5 × 10.sup.-8&#34;         1050-1100  7           ≦10.sup.-8&#34;         1100-1150  7           ≦2 × 10.sup.-8&#34;         1150-1200  7           ≦2.5 × 10.sup.-8&#34;         1200-1250  7           ≦5 × 10.sup.-9&#34;         1250-1300  7           ≦2.5 × 10.sup.-8&#34;         1300-1350  7           ≦3 × 10.sup.-8&#34;         1350-1400  7           ≦5 × 10.sup.-9&#34;         1400-1450  7           ≦1.5 × 10.sup.-8&#34;         1450-1800  7           ≦5 × 10.sup.-9&#34;         1500-1550  7           ≦10.sup.-8&#34;         1550-1600  7           ≦1.5 × 10.sup.-8&#34;         1600-2100  7.4         ≦10.sup.-8&#34;         2100-3100  7.4         ≦5 × 10.sup.-10&#34;         3100-3925&#34;         3925-4600  7.4         1 × 10.sup.-9&#34;         4600-5000  7.4         1 × 10.sup.-9______________________________________ In Table I above a &#34;≦&#34; represents less than or equal to 
    
     
                                           TABLE 2__________________________________________________________________________SUMMARY OF CHARACTERISTICS OF .sup.82 Rb GENERATOR SYSTEMSUSING INORGANIC ADSORBERS   Column       Elution  Rb-82                              Sr-82 Break-                                         No.   Size         Speed                     Eluate                         Yield                              through    ElutionsAdsorbent   (ml) Eluant Used                (ml/sec)                     pH  %    (ml)       Tested__________________________________________________________________________Al.sub.2 O.sub.3   1    NaCl 2% 1.2  8-9 70/10 ml                              4 × 10.sup.-6                                         250        NaCl 0.9%                1.2  8-9 25/10 ml                              5 × 10.sup.-6                                         250Al.sub.2 O.sub.3   2.25 NaCl 2% 0.5  8-9 76/20 ml                              5 × 10.sup.-6 - 5 ×                              10.sup.-8  300Al.sub.2 O.sub.3   2.75 NaCl 0.9%                5    7.5 35/20 ml                              --         600   2.75 NaCl 0.9%                0.1  7.5 --   1 × 10.sup.-7                                         600ZrO.sub.2   2.75 NaCl 0.9%                5    7.5 56/20 ml                              --         600   2.75 NaCl 0.9%                0.1  7.5 --   2 × 10.sup.-7                                         600SnO.sub.2 (hydrated)   1.5  PO.sub.4.sup.-3 buffered                0.2  7.4 95/4 ml                              ≦ 5 × 10.sup. -9                                         1,000(of the      isotonicpresent      saline (pH9)invention)__________________________________________________________________________