the present invention provides an 82 sr / 82 rb generator column for use in positron emission tomography cardiac perfusion imaging . in accordance with the invention , the generator column is filled with an ion exchange material that tightly binds 82 sr but not 82 rb . the ion exchange material is compacted to a density that permits fluid solutions to be pumped through the generator column at a rate of at least 5 ml / min at a fluid pressure of 1 . 5 pounds per square inch ( 10 kpa ). after the generator column is packed with the ion exchange material , it is conditioned with a source of excess sodium cations and loaded with a solution of 82 sr . the generator column in accordance with the invention enables low pressure injections using a peristaltic pump and facilitates precision flow control of patient elutions . advantageously , the generator column in accordance with the invention can also be reloaded with 82 sr a plurality of times . this has distinct advantages . first , residue 82 sr remaining in the column from a previous load is not wasted . second , the expense of building and conditioning the generator column is distributed over a plurality of 82 sr loads , so the overall cost of using , 82 rb for cardiac perfusion imaging is reduced . fig1 illustrates the packing of an 82 rb generator column 10 using a method in accordance with the invention . as is known in the art , the generator column 10 is constructed from stainless steel hardware components that are commercially available . in the embodiment shown in fig1 , a pair of swagelok ® reducing adaptors with nuts and ferrules 12 , 14 are connected to opposite ends of a stainless tubing 16 that is packed with an ion exchange material 18 . in one embodiment of the invention , the ion exchange material 18 is an α - hydrous tin dioxide ( sno 2 . xh 2 o , where x equals 1 - 2 ) wetted with a nh 4 oh / nh 4 cl buffer ( ph 10 ). a 25 micron filter 24 closes a bottom of the cylinder 16 at an outlet end thereof . likewise , a 25 micron filter 22 closes an inlet end of the cylinder 16 after the cylinder 16 is packed with the ion exchange material 18 . a feature of the invention is that , unlike prior art generator columns in which the ion exchange material is tightly packed so that high pressure elution is required , the ion exchange material 18 is packed only to a density that permits fluid solutions to be pumped through the generator column at a rate of at least : 5 ml / min at a fluid pressure of 1 . 5 pounds per square , inch ( 10 kpa ). as shown in fig1 , a simple and practical way of accomplishing , the required packing of the ion exchange material 18 is to repeatedly strike a side of the generator column 10 with an instrument 26 , such as a laboratory wrench , with a force that exerts about 0 . 1 joule . experience has shown that between 50 and 100 strikes are required to achieve the required density of the ion exchange material 18 . after packing of the generator column 10 is complete , a funnel 20 that was used to introduce the ion exchange material 18 into the cylinder 16 is removed and the ion exchange material is leveled with the top of the cylinder 16 . the ion exchange material packed into the generator column 10 has a density of not more than 3 g / cm 3 in the packed state . the filter 22 is then placed on top of cylinder 16 and the swagelok adapter , nut and ferrule 12 is secured to the top of the cylinder in a manner well known in the art . as will be understood by those skilled in the art , the generator column 10 in accordance with the invention is constructed under sterile conditions using sterile components and may be pressure tested for leaks after assembly . fig2 is a cross - sectional view of the generator column 10 suspended in a shielding body 40 . the shielding body 40 is made from a dense shielding material 42 , such as lead , tungsten or depleted uranium optionally encased in a stainless steel shell 44 . the shielding body 42 includes a shielding lid 50 having apertures through which extend an inlet line 34 and outlet line 36 . the inlet line 34 is connected to an inlet end 30 of the generator column 10 . the outlet line 36 is connected to an outlet end 32 of the generator column 10 . the inlet and outlet lines are connected to external tubing lines 60 , 62 using luer fittings 56 and 58 . the shielding lid 50 is likewise constructed of a shielding material 52 such as lead , tungsten or depleted uranium encased in a stainless steel shell 54 . after the generator column 10 is packed with ion exchange material 18 , as explained above with reference to fig1 , the generator column 10 must be loaded with 82 sr before patient elutions can begin . as schematically illustrated in fig2 , in one embodiment a syringe pump 80 is used to deliver 82 sr from a supply 70 through an inlet tube 60 to the generator column 10 . the 82 sr is bound by the ion exchange material 18 in the generator column 10 . waste fluid is evacuated through the outlet tube 36 and outlet line 62 to a shielded waste container 90 , in a manner known in the art . fig3 is a schematic diagram of the generator column 10 configured for daily use as an 82 rb source for cardiac perfusion imaging . a source of sterile saline solution 100 is connected to a saline supply tube 104 . the sterile saline solution 100 is pumped through the saline supply tube 104 by a pump 102 . in one embodiment of the invention , the pump 102 is a peristaltic pump . in accordance with an alternate embodiment , the pump 102 is the syringe pump 80 shown in fig2 . as understood by those skilled in the art , the pump 102 is controlled by a control algorithm that regulates a flow rate and volume of the sterile saline solution 100 pumped through the generator column 10 via the inlet tube 104 to provide an 82 rb eluate via an outlet tube 106 connected to a controlled valve 108 . the valve 108 directs the eluate through a delivery line 112 for a calibration elution or a patient elution 110 , or to a shielded waste container 90 . as is further understood by those skilled in the art , control of the system shown in fig3 is complex and not all of the fluid paths and control mechanisms are depicted because elution control is not a subject of this invention . fig4 is a flowchart illustrating principle steps in constructing the generator column 10 in accordance with the invention . the process begins by preparing the ion exchange material and packing the generator column as explained above with reference to fig1 ( step 200 ). the generator column is then conditioned by saturating the ion exchange material 18 with sodium cations . in one embodiment , this is accomplished by passing 120 ml of 2m nacl through the column at a flow rate of 0 . 5 ml / minute followed by waiting for a period of 12 hours . 500 ml of sterile saline solution is then passed through the column at a flow rate of 10 ml / minute . a nondestructive ph test is performed ( step 202 ) by testing a ph of the initial sterile saline solution passed through the column . this nondestructive ph test prolongs the life of the generator column 10 . if it is determined ( step 204 ) that the ph of the generator column 10 is not alkaline , the generator column 10 is defective and it is disposed of ( step 224 ). if the saline solution is determined in step 204 to be alkaline , the generator column is loaded with 82 sr ( step 206 ) in a manner well known in the art using the equipment briefly described above with reference to fig3 . after the 82 sr is loaded into the generator column 10 , the generator column 10 is flushed with 1 . 0 l of sterile saline solution to clear traces of tin : dioxide and any radionuclide impurities . the generator column is then eluted with sterile saline solution and the eluate is tested for trace metals ; sterility ; radionuclide purity ; pyrogens ; and ph ( step 208 ). if all of those tests are passed ( step 210 ) the generator column 10 is ready for use ( step 212 ). if any one of the tests fails , 82 sr is optionally recovered from the generator column 10 ( step 222 ) and the generator column 10 is disposed of ( step 224 ). during generator use , daily testing is performed for the purpose of patient safety and quality control , as will be described in detail with reference to fig5 . as long as all daily tests are passed , the generator column can continue to be used for patient elutions . as understood by those skilled in the art , one of the daily tests is a measure of 82 rb yield . if it is determined in step 214 that one of the daily tests failed , it is further determined whether a reload of the generator column 10 is permitted ( step 216 ). reloading is permitted if the daily test failed due insufficient 82 rb yield only . if the daily test failed for some other reason the generators column 10 cannot be further used , and the 82 sr is optionally recovered ( step 222 ) before the generator column is disposed of ( step 224 ), as described above . if an 82 sr reload is permitted , it is determined in step 218 whether the number of 82 sr reloads of the generator column 10 has exceeded a predetermined reload limit . a generator column in accordance with the invention can , be loaded with 82 sr at least three times before any significant 82 sr breakthrough occurs . if it determined in step 218 that the reload limit has been reached , certain jurisdictions require that the generator column be flushed and the eluate tested for : trace metals ; sterility ; radionuclide purity ; pyrogens ; and ph . if it is determined in step 218 that the reload limit , has not been reached , the process branches back to step 206 and the generator column is reloaded with 82 sr and steps 208 - 218 are repeated . fig5 is a flowchart illustrating principle steps involved in the daily use of the generator column 10 in accordance with the invention . prior to each day &# 39 ; s use of the generator column 10 , the generator column 10 is flushed with 50 ml of sterile saline solution ( step 300 ) in order , to remove any strontium breakthrough from the generator column 10 into the waste vessel 90 . the operator then waits for a predetermined period of time ( step 302 ) before performing a calibration elution ( step 304 ). as is well understood by those skilled in the art , under stable conditions the generator column maintains a 82 sr / 82 rb equilibrium which is achieved after about 10 minutes . consequently , the predetermined wait before a calibration elution is performed is at least 10 minutes . after the required wait , the generator column is eluted with about 15 ml of sterile saline solution at a constant flow rate of about 15 ml / minute . the calibration eluate is tested ( step 306 ) for 82 rb yield and 82 sr breakthrough . in step 308 it is determined whether the yield is above a predetermined radioactivity limit . as is understood by those skilled in the art , the half life of 82 rb is very short ( i . e . 76 seconds ). consequently , in one embodiment the 82 rb yield is measured using a positron counter during the elution , in a manner well known in , the art . in step 310 , it is determined whether the 82 sr , 85 sr breakthrough is less than a predetermined breakthrough limit . as is also understood by those skilled in the art , all jurisdictions define a threshold for permissible levels of 82 sr , 85 sr breakthrough . as is further understood by those skilled in the art , the strontium breakthrough is readily determined by testing the radioactivity of the elution after about 26 minutes has elapsed , at which time the amount of residual 82 rb is insignificant and does not distort the test results . before daily use begins , a cumulative volume of all fluids flushed and eluted through the generator column 10 is computed . since the generator column 10 in accordance with the invention is repeatedly reloaded with 82 sr , each generator column is identified by a unique identifier , in one embodiment a serial number . if the user of a generator column 10 does not have the facility to reload the generator column 10 , the user must return the generator column 10 to the manufacturer , along with a cumulative total of fluid flushed and eluted through the column during that use . likewise , when a reloaded column is supplied to a user , a cumulative volume of fluid used to flush and elute the column during all prior reload ( s ) and use ( s ) is provided to the user . control software used to control a volume of fluid used during generator column 10 flushes and elutions accepts the cumulative volume and stores it . the control software then recomputes the cumulative volume after each subsequent flush or elution of the generator column 10 . that computed cumulative volume is compared ( step 312 ) to a predefined volume limit . in accordance with one embodiment of the invention , empirical data has shown that 10 to 30 litres of sterile saline solution 100 can be pumped through the generator column 10 before significant 82 sr breakthrough is experienced , so the volume limit may be set between 10 and 30 litres . if each of the tests 308 - 312 is successfully passed , patient elutions ( step 314 ) may be performed in a manner well known in the art . after each elution , it is necessary to wait a predetermined period of time , about 5 to 10 minutes , ( step 316 ) to permit 82 rb to regenerate . after each elution , the cumulative volume is recomputed by adding to the cumulative volume a volume of fluid pumped through the generator column 10 during the patient elution . then it , is determined whether the control system date has , changed , i . e . a new day has begun ( step 318 ). if not , the cumulative volume is compared to the predetermined volume limit . if the volume limit has been exceeded , the generator column is disposed of ( step 324 ). if it is determined in step 318 that the control system date has changed , the generator column 10 must be flushed and re - tested per steps 300 - 312 , as described above . if those tests determine that the 82 rb yield is less than a predetermined limit ( step 308 ) then it is determined in step 320 whether the reload limit has been exceeded and if not the generator column 10 is returned for reload and pre - use testing ( step 322 ). otherwise , the generator column is disposed of ( step 324 ). it should be noted that if any of tests 308 - 312 fail , the generator column 10 may be returned to the manufacturer who determines whether the generator column 10 can be reloaded ( step 320 ) and disposes of the generator column 10 ( step 324 ) if it cannot be reloaded . the generator column 10 in accordance with the invention reduces the expense of cardiac perfusion imaging while ensuring compatibility with 3d pet imaging systems by enabling low pressure , low flow rate elutions that can be precisely flow controlled . research has conclusively established that the generator column 10 in accordance with the invention remains sterile and pyrogen - free for a period of at least six months when used in accordance with the procedures and limits described above . although the invention has been explained with reference to 3d pet imaging systems , it should be understood that the generator column 10 is equally compatible with 2d pet imaging systems and provides the same advantages of low cost , precise flow control , low pressure and low flow elution and a long service life . the embodiment ( s ) of the invention described above is ( are ) intended to be exemplary only . the scope of the invention is therefore intended to be limited solely by the scope of the appended claims .
an 82 sr / 82 rb generator column is made using a fluid impervious cylindrical container having a cover for closing the container in a fluid tight seal , and further having an inlet for connection of a conduit for delivering a fluid into the container and an outlet for connection of a conduit for conducting the fluid from the container . an ion exchange material fills the container , the ion exchange material being compacted within the container to a density that permits the ion exchange material to be eluted at a rate of at least 5 ml / min at a fluid pressure of 1 . 5 pounds per square inch . the generator column can be repeatedly recharged with 82 sr . the generator column is compatible with either three - dimensional or two - dimensional positron emission tomography systems .