Vital Signs For Head Trauma

Quality Control (1)

Purity radionuclidic
(D. Cecchin, F. Bui, University of Padova)

It 's the fraction of the total radioactivity in a source that is present in the form of the radionuclide chosen expressed as a percentage.

When the question arises:

• In the production method of the radionuclide (125I, 123I, present as scrap etc ...)

• the incomplete separation during procedures

• Presence of parents / children (eg: 99Mo with a T1 / 2 of 60 h along with 99mTc with T1 / 2 of 6 h)

Since the 'half-life of radionuclide contaminants can be longer than that of the radionuclide of interest, as in the case of technetium, the proportion of impurities increases over time. This consideration shows that the quality control of radiopharmaceutical to be done immediately before use of the same and not many hours before. As a striking example remember the 201Tl (half-life 73h) that may be contaminated with 202Tl (half-life of 12.2 days).

There are limits tolerated: For example for the product 99mTc generator  99Mo 99mTc where molybdenum is produced by fission are the accepted limits of " 99Mo breakthrough" or the presence of molybdenum eluate should be minimal. To check you can make measurements without and shielding, the vial containing an aliquot of eluate. The shield should be used to mitigate almost all the photons of 140 keV of technetium, but will allow the passage of the photon energy of molybdenum (740 -780 keV).
Correcting the obtained from the radiation shield to measure the attenuation coefficient of the material used for shielding and for the thickness used gives an estimation of molybdenum present in the eluate.


radiochemical purity

It 's the percentage of radioactivity that is present in the form designated

When the question arises:

• Chemical reactions of competition during the marking process

• decomposition by radiolysis of final product

• oxidizing agents and reducing

• Variations in pH and temperature

• Solvents

• Light

be noted that the compounds behave as impure radiochemical different drugs and can have different biodistribution . Often complains about an increase in the background of the image. It follows that in the case of impurities is not useful to inject a dose of radiation. The three species


radionuclides for a drug-related (using tin as a reducing agent) in technetium are

• radiopharmaceutical 99mTc-related (which is the form that I want to get)

• under 99m free form of pertechnetate that has not been reduced by the pool or divalent Sn2 + which was reduced and then oxidized. The consequence is that you can see the bottom of the stomach, thyroid and salivary glands.

• 99mTc IDROSIL or reduced (HR 99mTc), which includes 99mTcO2 (which did not react with the chelating agent) and 99mTc colloid (99mTc-shrunk and consists of Sn2 +-IDROSIL). The consequence of these impurities is that you can see the reticuloendothelial system (liver, spleen, etc ...).

Technetium is in oxidation state 7 + and is not responsive.
Tin technetium than reduces it to +1, +3, +5.



Assessment of radiochemical purity: how?

Analytical methods:

• Thin layer that is the gold standard among the three

• Instant Thin Layer that provides a resolution about how the paper

• Paper cromatography which has the disadvantage of exercise fragile and have a "sensitive child"

Liquid Chromatography (HPLC)

is a method which allows , better than the last, to "quantify". You use a column with a wild series of increasing polarity of solvents used to separate the different radiochemical species.

Advantages:

• is much more precise

Disadvantages:

• is much slower

• Costa More

• We need much larger doses (volumes of solution) and thus more waste of radiopharmaceutical and irradiazionedel staff.

Analytical methods

1. deposit a drop of test solution on a substrate (usually paper chromatography, which is a film made of fiberglass impregnated with silicone gel)  solid phase
2. It plunges this map in a solvent (liquid phase  or mobile) without wetting the source where it was deposited drop
3. The mobile phase brings with it the various species radionuclidichein relationship to the solubility of species in the solvent used and the link between species and solid phase radiochemical

The solvent front: the band is identifiable on the solid phase where I got ls

The Radiochemical solvent front: is a band where the species comes radiochemistry. The Radiochemical front is known and measured for different species and is used to identify them. Typically

:

• The HR-99m remains the origin

• Il99mTc origin remains free

• The migration linked to the solvent front fiinio

At this point divides the map, the is counted (before then the whole piece) and understand that the percentages of steel. In some cases, the related "travels" with the one or the other impurity, and not alone. In these cases, no use of additional strategies (serial counts and equations for Espar).


Common mistakes

• The spot ends in the solvent or solvents

• old maps or exposed to light
• Map not suitable for the species you want to view
• The solvent is made to continue after the solvent front
• grease from fingerprints
• strip
• Solvent Contamination wrong
• contaminated scissors (used a previous strip)

Estimation of activity of the eluate

It is usually measured in terms of activity / weight (Bq/Kg-1) or as " specific activity".

may be used:

the entire container method:

• is estimated that the container with all the eluate (which I know the volume and weight) in the dose calibrator.

method to rate:

• entire container is taken from a syringe with 1 ml and it counts. (Obviously you should then empty the syringe carlcolare and the residual amount in the needle ...)
  

In other words, the eluate to pass the test must have some activity (as declared by tables issued by the manufacturer of the column).



Yield Generator

E 'necessary, in other words, calculate the theoretical yield is expected to have a generator at a certain time and make sure it matches (within a certain range set) to the actual output of the generator.
typically yields vary between 85% and 95% of the theoretical value.
If the production yield falls below the value specified by the manufacturer, the column must be replaced immediately because complications have arisen irreparable affecting the quality of radiopharmaceutical products.
The consequence is a poor quality of marking which results ultimately in a poor investigation.

factors that decrease the yield are:

• Fluctuations "physiological" in the production of the column. (Just repeat the analysis over time)
• "Channels" in the alumina (in this case with due caution we can "shake" a little 'column in an attempt to close
• Auto-radiolysis: the ionization of water produces radicaliperossidi H2O2 and that being strong oxidants attack the pertechnetate and make unmoveable alumina

factors in place that give a low volume are: Air bubbles

• Pipes blocked
• mechanical problems in the alumina