82Sr/82Rb generator

82Rb Infusion System

  1. The generator is placed into an infusion system for patient administration.  The essential components to this system are noted above
    1. Saline (upper left) enters the system with the assistance of a pressure injector that is controlled by the technologist
    2. Saline is sent through the radioactive core and then out to the patient
    3. Several filters are used to reduce the possibility of injecting particulate matter
    4. Some specifics regarding the elution and its delivery - First follow the flow of saline(blue = saline, red = tracer, and green = discard)!
      1. The amount of mL flow is regulated by a pressure injector
      2. Saline is sent to the 82Sr/82Rb core where 82Rb is extracted at a specific flow rate (should not exceed 50 mL/minute)
      3. Radioactive saline is monitored and measured within the delivery system
      4. A 3-way valve (also referred to as a divergence or solenoid valve) diverts activity either to the patient or the waste reservoir
      5. Calibration of this system is completed daily during its first elution which is collected and measured, but not injected into the patient.  In addition, breakthrough of 82Sr and 85Sr are analyzed (the procedure is described below)
      6. After the first elution (any elution) it takes 10 minutes for the generator to build up its maximum 82Rb dose. 
      7. Other comments
        1. 82Sr - has a T1/2 of 25.5 days and 82Rb T1/2 is 75 seconds
        2. 82Rb is a K analog and becomes incorporated into the sodium-potassium pump which relates to cardiac physiology
        3. Review the Package insert
    5. Dose criteria
      1. Adult single dose = 40 mCi (30 - 60mCi)
      2. Target organ is the kidneys
      3. Maximum dose: single 60 mCi, total 120 mCi for rest and stress
      4. Maximum flow rate is 50 mL/min
      5. Volume per dose not to exceed 100mL (single), or 200 mL total
    6. Calculate of 82Sr breakthrough
      1. Relate this procedure to 99Mo breakthrough.
      2. Prior to any patient use, in the AM, elute 50 mL and discard it
      3. After 10 minutes send another 50 mL/minute of saline through the system and collect it in a glass elution vial (do not use plastic)
      4. Why is there a 10 minute waiting time?
      5. Measuring 82Rb
        1. Measure 82Rb in its own window setting noting the time between measuring the activity and the time that the elution was started.  You must then decay back to time zero (when the elution was started)
        2. Alternate window setting can be done by measure the activity in the 60Co window and dividing this value by 0.548 (however, you must still decay back to zero time)
        3. If you do not want to decay back to time zero
          1. Measure the dose exactly 2.5 minutes after the elution was started
          2. Take that measurement and multiple the value by 4.  This will give you the original amount of 82Rb activity
      6. Once 82Rb is measured let the vial decay to background.  At 1 hour post elution you will be able to measure the Sr activity and calculate breakthrough (This is a multiple step process)
      7. First you must calculate the Sr ratio (R) via the formula

        1. 85Sr/82Sr is what remains in the vial of the one hour decay
        2. The ratio of 85Sr/82Sr is defined by R in the formula above
          1. The problem with this generator is that 85Sr build up over time, interfering with the 82Sr reading.  Hence, the need to determine the R value becomes critical
          2. You must first look up the 85Sr/82Sr ratio ( Ratio Chart) found in the package insert. The ratio changes over time, specifically increasing after the generator's calibration date. Note: 85Sr is " building up" over time
          3. The second part of the R value calculation requires you to look up Sr ratio found on the calibration label of the generator
          4. Multiplying those two numbers gives you R
        3. Note -F is a correction factor, for 85Sr that is its contribution in activity in the vial. This value is always 0.478
      8. Now that we know all this information let's apply this to the breakthrough problem
        1. First let us hypothetically measure a dose of 82Rb 2.5 minutes post elution. Let us say that the amount measured is 2.59 mCi.  Multiplying by a factor of 4 gives us 45 mCi.  This is the amount of activity present when the elution was initially started
        2. After allowing for 1 hour decay remeasure the vial withe the dose calibrator. Let us say that you get a reading of 0.9 μCi
        3. Now let us determine the R value
          1. Assuming the generator was calibrated 25 days prior, hence the chart's ratio is 1.53
          2. Check the generator's label the value is 0.85
          3. Therefore R = (1.53 x 0.85) = 1.301

            4. Formulas for Breakthrough

          4. Now you are ready to calculate all the values in the denominator of the formula: F = 0.478 x 1.301 + 1
          5. The numerator value is 0.9 μCi for 82/85Sr
          6. Once the numbers are crunched and you end up with total of 82Sr to be 0.55 μCi
          7. Final you are ready calculate the breakthrough where 45 mCi of 82Rb is divided by 0.55μCi of 82Sr
          8. Your answer is !!  1.23 x 10-2 μCi/mCi !!
          9. Breakthrough passes if 82Sr <0.2μCi

      7. Return to the Table of Content

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