Abstract:
The main aim of this pilot study was to determine how the energy spectrum of scatter radiation emitted from horses after
injection of the radiopharmaceutical 99mTechnetium-methyl diphosphonate (99mTc-MDP), changed behind lead shielding of varying
thicknesses (0.25 mm, 0.35 mm, and 0.5 mm Pb thickness), and if beam hardening occurred. The effect lead shielding has on the
emitted gamma radiation energy spectrum has not been documented. In particular, the presence of beam hardening effects
behind lead shielding was investigated, to determine whether or not it could discourage the use of lead shields during bone
scintigraphy in horses. Horses were injected intravenously with 99mTc-MDP, and energy spectra emitted from horses without lead
shielding were recorded initially to determine the emitted scatter spectrum. Thereafter, different combinations of lead shields of
the various thicknesses listed above, draped over the horse and on simulated personnel, were recorded. The energy spectra were
obtained at different anatomical locations of five horses on five consecutive days with a pulse height (multichannel) analyser two
and a half hours post-injection. Energy spectra recorded from horses without lead shielding showed polychromatic energy spectra
that encompassed a large portion of predominantly lower scatter energies (averaging around the 88–94 keV peaks). Higher 99mTc-
MDP peaks averaging at 139–143 keV (useful for gamma camera acquisition) were consistently seen in all recordings but made up
a very small part of the emitted spectra. With the application of lead shielding, peaks of 83–86 keV, which coincided with K-edges of
lead, occurred. No significant beam hardening effects behind lead shields of varying thicknesses were observed. Thus, the wearing
of lead shields during bone scintigraphy of horses is encouraged.
