Abstract
Barium-131 is a single photon emission computed tomography (SPECT)-compatible radionuclide for nuclear medicine and a promising diagnostic match for radium-223/-224. Herein, we report on the sufficient production route 133Cs(p,3n)131Ba by using 27.5 MeV proton beams. An average of 190 MBq barium-131 per irradiation was obtained. The SR Resin-based purification process led to barium-131 in high radiochemical purity. An isotopic impurity of 0.01% barium-133 was detectable. For the first time, radiolabeling of the ligand macropa with barium-131 was performed. Radiolabeling methods under mild conditions and reaction controls based on TLC systems were successfully applied. Small animal SPECT/ computed tomography (CT) measurements and biodistribution studies were performed using [131Ba]Ba(NO3)2 as reference and 131Ba-labeled macropa in healthy mice for the first time. Biodistribution studies revealed the expected rapid bone uptake of [131Ba]Ba2+, whereas 131Ba-labeled macropa showed a fast clearance from the blood, thereby showing a significantly (p < 0.001) lower accumulation in the bone. We conclude that barium-131 is a promising SPECT radionuclide and delivers appropriate imaging qualities in small animals. Furthermore, the relative stability of the 131Ba-labeled macropa complex in vivo forms the basis for the development of sufficient new chelators, especially for radium isotopes. Thereby, barium-131 will attain its goal as a diagnostic match to the alpha emitters radium-223 and radium-224.
Highlights
The γ-emitter barium-131 (t 1 = 11.5 d) decays via cesium-131 (t 1 = 9.7 d) to stable xenon-131, each by electron capture [1]
single photon emission computed tomography (SPECT) imaging of a cylindrical syringe source filled with an aqueous solution of [131Ba]Ba(NO3)2 showed that signals at the position of the source were surrounded by noise-derived artifacts accumulating in the periphery of the field of view (FOV) as well as along the central anterior–posterior axis of the FOV (Figure 7C)
Activity measurement in tissue samples confirmed the distribution pattern observed in SPECT images showing that, compared to [131Ba]Ba(NO3)2, significantly (p < 0.001) higher amounts of Pharm13a1Bceau-tlicaablse2le0d20m, 1a3,c2r7o2pa were excreted via the renal pathway (89% initial dose (ID)/organ within 24 h) and via9 of 16 the hepatobiliary pathway (25% ID/organ within 1 h) (Figure 8E)
Summary
SPECT imaging of a cylindrical syringe source filled with an aqueous solution of [131Ba]Ba(NO3) showed that signals at the position of the source were surrounded by noise-derived artifacts accumulating in the periphery of the field of view (FOV) (peripheral artifacts) as well as along the central anterior–posterior axis of the FOV (central artifacts) (Figure 7C) Such artifacts appear because the physical model used in the Tera-Tomo 3D reconstruction algorithm is inconsistent with a rapid and efficient binding of [131Ba]Ba2+ with >99% within 5 min, which led us to the assumption that a rapid in vivo bone uptake will occur. Activity measurement in tissue samples confirmed the distribution pattern observed in SPECT images showing that, compared to [131Ba]Ba(NO3), significantly (p < 0.001) higher amounts of 131Ba-labeled macropa were excreted via the renal pathway (89% ID/organ within 24 h) and via the hepatobiliary pathway (25% ID/organ within 1 h) (Figure 8E). Figure 9Fi.gu(Are) 9P. t(-Ata) rPgte-ttardgiestkd,isPkt,-fPot-iflo, ial,nadndAAl-lh-hoollddeerr ffoorrththeeirirrardaiadtiioanti;o(nB;) (oBp)enopnaetCnsCnlattCarsgCetl atfaterrget after pressingpraenssdinbgeafnodrebecfloorseinclgoswinigthwiPtht fPotiflo;i(l;C(C) )cocommpplleettee ttaarrggeet tafateftre4rh4ohf iorrfaidriraatidoina.tion
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