13.07.2015 Views

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

Bush__The_Essential_Physics_for_Medical_Imaging - Biomedical ...

SHOW MORE
SHOW LESS

You also want an ePaper? Increase the reach of your titles

YUMPU automatically turns print PDFs into web optimized ePapers that Google loves.

Method Measures Useful rangePermanentrecordFilm badge Beta; gamma (x and gamma)and x-ray 0.1-15,000 mSv·(beta)0.5-10,000 mSv·TLD Beta; gamma 0.01-10 6 mSv·and x-rayPocketdosimeterBeta; gammaand x-rayGamma andx-rayAnalogo to 0.2 Ro to 0.5 Ro to 5 RDigital0-100 mSvaRoutine personnel monitoring;most common in diagnosticradiology and nuclearmedicineBecoming more common butstill more expensive thanfilm; used <strong>for</strong> phantom andpatient dosimetryAdvantage over TLD includesthe ability to reread thedosimeters and distinguishbetween dynamic and staticexposuresSpecial monitoring (e.g.,cardiac cat h); permits direct(i.e., real-time) reading ofexposure·Multiply mSv by 100 to obtain mrem.bOSL dosimeters are typically retained and can be reread by the manufacturer <strong>for</strong> approximately 1 year.OSL, optically stimulated luminance; TLD, thermoluminescent dosimeter.Pocket dosimeters are utilized when high doses are expected, such as duringcardiac catheterization or manipulation of large quantities of radioactivity. Table23-7 summarizes the characteristics of the various personnel monitoring devicesdiscussed above.Common problems associated with dosimetry include leaving dosimeters in a radiationfield when not worn; radio nuclide contamination of the dosimeter itself; lostand damaged dosimeters; and not wearing the dosimeter when working with radiationsources. If the dosimeter is positioned so that the body is between it and theradiation source, the attenuation will cause a significant underestimation of the trueexposure. Most personnel do not remain in constant geometry with respect to theradiation sources they use. Consequently, the dosimeter measurements are generallyrepresentative of the individual's average exposure. For example, if the film badge isworn properly and the radiation field is multidirectional or the wearer's orientationtoward it is random, then the mean exposure over a period of time will tend to bea good approximation (±1O% to 20%) of the individual's true exposure.23.3 RADIATION DETECTION EQUIPMENT INRADIATION SAFETYA variety of portable radiation detection instruments are used in diagnostic radiologyand nuclear medicine, the characteristics of which are optimized <strong>for</strong> specificapplications. <strong>The</strong> portable GM survey meter and portable ionization chamber sat-

Hooray! Your file is uploaded and ready to be published.

Saved successfully!

Ooh no, something went wrong!