TYPES OF IMPURITIES IN THE HOT LAB

The three types of impurities and an example of each are listed in the following chart:

 METHODS USED TO QUANTIFY THESE THREE TYPES OF IMPURITIES:

Mo-99 BREAKTHROUGH TEST

Mo-99 is assayed FIRST on the Mo-99 setting directly in the special lead pig supplied by the manufacturer of your dose calibrator. Tc-99m is THEN assayed on the Tc-99m setting directly in the plastic sleeve. Activity (mCi) of Mo-99 is divided by activity (mCi) of Tc-99m to obtain a ratio. If this ratio is <0.15 mCi Mo-99 per mCi of Tc-99m at time of administration, the generator eluate has passed the Mo-99 Breakthrough Test. As a rule of thumb, if the ratio is <0.038 at time of elution, the material will be suitable for injection for at least 12 hours.

If test is performed in reverse order, failure is extremely likely due to residual charge on ionization chamber that takes a few minutes to dissipate.

SPECIFICATIONS FOR Mo-99 BREAKTHROUGH TEST

•  In NRC States:

            TEST                          FREQUENCY            SPECIFICATIONS

Mo Breakthrough                  First Elution       <0.15 mCi Mo/mCi Tc at t_{administration}

• In many Agreement States:

            TEST                          FREQUENCY            SPECIFICATIONS

Mo Breakthrough                  Every Elution       <0.15 mCi Mo/mCi Tc at t_{administration}

Al³⁺ ION BREAKTHROUGH TEST

According to current NRC regulations, the Al³⁺ Breakthrough test is no longer Mandatory. If performed, the upper limit of Al³⁺ Breakthrough is 10 ppm of Al³⁺; may be expressed as mg/ml. Al³⁺ ion breakthrough is measured colorimetrically. A drop of the eluate is placed on one end of a special test paper; a drop of a standard solution of Al³⁺, concentration 10 ppm, is placed on the other end of the test strip. If the color at the center of the drop of eluate is less red than that of the standard solution, the eluate has passed the Al³⁺ Ion Breakthrough Test. Units may be also be expressed as mg/ml.

SPECIFICATIONS FOR ALUMINUM ION BREAKTHROUGH TEST

• In NRC States:

            TEST                          FREQUENCY                        SPECIFICATIONS

Al ion Breakthrough           Test no longer required       <10 ppm if you choose to

 perform test

• In most Agreement States:

            TEST                          FREQUENCY                        SPECIFICATIONS

Al ion Breakthrough            Test no longer required       <10 ppm if you choose to

 perform test

MOST COMMONLY APPEARING Tc-99m RADIOCHEMICAL IMPURITIES

The chart below identifies the two most commonly observed radiochemical impurities  

Impurity                                                           Chemical Form

Free Tc                                                           pertechnetate, TcO₄^-

Hydrolyzed Reduced Tc                               probably TcO(OH)₂.H₂O, hydrated Tc-oxide

Free Tc localizes in the choroid plexus, salivary glands, thyroid, and gastric mucosa; HR Tc localizes in the liver and spleen. Both are therefore undesirable as they decrease image quality and often increase radiation dose to the patient.