QUALITY CONTROL IN THE HOT LAB

RATIONALE FOR PERFORMING QUALITY CONTROL For certain procedures, IT'S THE LAW.

Non-Diagnostic Study ==> Procedure must be repeated increased radiation dose and patient discomfort.

CRITERION: You must be able to answer "yes" to the question, "Would I inject this into my mother?"

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CLASSIFICATION OF IMPURITIES

Type of impurity.........example......................................effect

Radionuclidic..................Mo-99.......................Increased Radiation Dose; Poor Image Quality

Radiochemical................HR Tc........................Poor Image Quality; Increased Radiation Dose

Chemical........................Al³⁺...........................Poor Image Quality due to labeling problems

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DETECTION OF IMPURITIES

METHOD.......................................................TYPE OF IMPURITY

Dose Calibrator/Multichannel Analyzer...................Radionuclidic

Thin Layer Chromatography...................................Radiochemical

Colorimetric..........................................................Chemical

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REQUIRED QC TESTING OF A Mo/Tc GENERATOR

TEST....................................FREQUENCY ......................................SPECIFICATIONS

Mo Breakthrough....................Every Elution .........................<0.15 µCi Mo/mCi Tc at time of injection

Al³⁺ Ion Breakthrough ...........Every Elution ..........................<10 ppm of Al³⁺; may be expressed as µg/ml

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OPTIONAL QC TESTING OF A Mo/Tc GENERATOR

TEST....................................FREQUENCY......................................SPECIFICATIONS

Hydrolyzed Reduced Tc.........Every Elution .........................< 2% (Reasonable Limit) (presently no legal limit)

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QC TEST PROCEDURES FOR Mo/Tc GENERATOR

1. Mo-99 Breakthrough: Mo-99 is assayed directly in the special lead pig supplied by the manufacturer of your dose calibrator. Tc-99m is then assayed directly in the plastic sleeve in your dose calibrator. Activity (uCi) of Mo-99 is divided by activity (mCi) of Tc-99m to obtain a ratio. If this ratio is <0.15 µCi Mo-99 per mCi of Tc-99m at time of injection, 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.

2. Aluminum Ion Breakthrough: Al³⁺ ion 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 Aluminum Ion Breakthrough Test. Units may be expressed as ug/ml.

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Radiochemical Impurities in Tc-99m Radiopharmaceuticals

• Free Tc (Chemical form is pertechnetate, TcO₄^-)
• Hydrolyzed Reduced Tc (Chemical form probably TcO(OH)₂.H₂O, a hydrated Tc-oxide.
• For Tc-99m MAG3, formation of Tc-99m tartrate is possible
• For Tc-99m HMPAO, there are also stereochemical impurities.

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THIN LAYER CHROMATOGRAPHY SYSTEMS OF Tc-99m COMPOUNDS

For Tc-99m DTPA, MDP, GH, PYP, HDP, MAA, MIAA, SULFUR COLLOID:

SYSTEM ......................................................................IMPURITY MEASURED

Silica Gel/0.9% saline ...........................................................Hydrolyzed Reduced Tc

Paper/acetone or Paper/MEK .........................................Free Tc (Pertechnetate)

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THIN LAYER CHROMATOGRAPHY SYSTEMS: Tc-99m HEPATOBILIARY AGENTS

SYSTEM ...................................................................IMPURITY MEASURED

ITLC-SA/20% saline ..........................................................Free Tc (Pertechnetate)

ITLC-SG/water .....................................................................Hydrolyzed Reduced Tc

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EXCEPTION TO THE RULE

For insoluble Tc-99m Radiopharmaceuticals (e.g., Tc-MAA, Tc-MIAA, Tc-SC), it is only necessary to test for the presence of free Tc. No simple system can effectively separate colloidal HR Tc from an insoluble product, so HR Tc cannot be measured in these products. We therefore ignore its presence.

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Tc-99m RADIOPHARMACEUTICALS: SEPARATION ON STRIP

SYSTEM..........................................................SEPARATION OF RADIOCHEMICAL SPECIES

Silica Gel/saline HR ..........................................................Tc in bottom half; all other species in top half.

Paper/acetone or Paper/MEK......................................Free Tc in top half; all other species in bottom half.

ITLC-SA/20% saline ......................................................HR Tc in bottom half; all other species in bottom half.

ITLC-SG/water ................................................................Free Tc in top half; all other species in bottom half.

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................STRIP DESIGN

......top of strip _____ 6 cm

....solvent front _____ 5 cm

............cut line _____ 3 cm

..............origin _____ 1 cm

bottom of strip _____ 0 cm

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CALCULATIONS

% IMPURITY = (CPM IN HALF OF STRIP / CPM IN WHOLE STRIP ) X 100%

LABELING EFFICIENCY = 100% - % HR Tc - % Free Tc

FULL WIDTH/HALF-MAXIMUM TEST

This test measures the energy resolution capabilities of a NaI detector. It does NOT measure sensitivity, only energy resolution. Following display of the energy spectrum of the isotope, the width of the peak at half the maximum height is determined and then divided by the photopeak energy in keV. The ratio (usually 0.06-0.10, is then ultipled by 100% and the value reported as % full width at half maximum height. Values >10% indicate a crystal is near the end of its useful life.

The figure below indicates a FWHM value of 9.06%, indicating normal crystal energy resulution ability.