Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies

Mark F. Smith, Margaret E. Daube-Witherspoon, Paul S. Plascjak, Lawrence P. Szajek, Richard E. Carson, James R. Everett, Shielah L. Green, Paul Territo, Robert S. Balaban, Stephen L. Bacharach, William C. Eckelman

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Multi-instrument activity estimation and decay correction techniques were developed for radionuclide mixtures, motivated by the desire for accurate quantitation of Tc-94m positron emission tomography (PET) studies. Tc-94m and byproduct Tc isotopes were produced by proton irradiation of enriched Mo-94 and natural Mo targets. Mixture activities at the end of bombardment were determined with a calibrated high purity germanium detector. The activity fractions of the greatest mixture impurities relative to 100% for Tc-94m averaged 10.0% (Tc-94g) and 3.3% (Tc-93) for enriched targets and 10.1% (Tc-94g), 11.0% (Tc-95), 255.8% (Tc-96m), and 7.2% (Tc-99m) for natural targets. These radioisotopes have different half-lives (e.g., 52.5 min for Tc-94m, 293 min for Tc-94g), positron branching ratios (e.g., 0.72 for Tc-94m, 0.11 for Tc-94g) and gamma ray emissions for themselves and their short-lived, excited Mo daughters. This complicates estimation of injected activity with a dose calibrator, in vivo activity with PET and blood sample activity with a gamma counter. Decay correction using only the Tc-94m half-life overestimates activity and is inadequate. For this reason analytic formulas for activity estimation and decay correction of radionuclide mixtures were developed. Isotope-dependent sensitivity factors for a PET scanner, dose calibrator, and gamma counter were determined using theoretical sensitivity models and fits of experimental decay curves to sums of exponentials with fixed decay rates. For up to 8 h after the end of bombardment with activity from enriched and natural Mo targets, decay-corrected activities were within 3% of the mean for three PET studies of a uniform cylinder, within 3% of the mean for six dose calibrator decay studies, and within 6% of the mean for four gamma counter decay studies. Activity estimation and decay correction for Tc-94m mixtures enable routine use of Tc-94m in quantitative PET, as illustrated by application to a canine Tc-94m sestamibi study.

Original languageEnglish (US)
Pages (from-to)36-45
Number of pages10
JournalMedical Physics
Volume28
Issue number1
DOIs
StatePublished - 2001
Externally publishedYes

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Radioisotopes
Positron-Emission Tomography
Equipment and Supplies
Isotopes
Germanium
Gamma Rays
Half-Life
Protons
Canidae
Theoretical Models
Electrons

Keywords

  • Decay correction
  • PET
  • Positron emission tomography
  • Radioactive mixture
  • Technetium-94m

ASJC Scopus subject areas

  • Biophysics

Cite this

Smith, M. F., Daube-Witherspoon, M. E., Plascjak, P. S., Szajek, L. P., Carson, R. E., Everett, J. R., ... Eckelman, W. C. (2001). Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies. Medical Physics, 28(1), 36-45. https://doi.org/10.1118/1.1333411

Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies. / Smith, Mark F.; Daube-Witherspoon, Margaret E.; Plascjak, Paul S.; Szajek, Lawrence P.; Carson, Richard E.; Everett, James R.; Green, Shielah L.; Territo, Paul; Balaban, Robert S.; Bacharach, Stephen L.; Eckelman, William C.

In: Medical Physics, Vol. 28, No. 1, 2001, p. 36-45.

Research output: Contribution to journalArticle

Smith, MF, Daube-Witherspoon, ME, Plascjak, PS, Szajek, LP, Carson, RE, Everett, JR, Green, SL, Territo, P, Balaban, RS, Bacharach, SL & Eckelman, WC 2001, 'Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies', Medical Physics, vol. 28, no. 1, pp. 36-45. https://doi.org/10.1118/1.1333411
Smith, Mark F. ; Daube-Witherspoon, Margaret E. ; Plascjak, Paul S. ; Szajek, Lawrence P. ; Carson, Richard E. ; Everett, James R. ; Green, Shielah L. ; Territo, Paul ; Balaban, Robert S. ; Bacharach, Stephen L. ; Eckelman, William C. / Device-dependent activity estimation and decay correction of radionuclide mixtures with application to Tc-94m PET studies. In: Medical Physics. 2001 ; Vol. 28, No. 1. pp. 36-45.
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