Tomographic measurement of cerebral blood flow by the 68Ga-labelled-microsphere and continuous-C15O2-inhalation methods

The measurement of cerebral blood flow (CBF) by continuous C¹⁵O₂ inhalation has only been validated previously by indirect experimental protocols. In the present study using baboons, these measurements were compared directly with those obtained by injection of ⁶⁸Ga-labelled serum-albumin microspheres in the left cardiac ventricle. Using a modified labelling technique, no elution of ⁶⁸Ga occurred in vivo. Both methods provided similar regional CBF values, which could be described by a significant linear correlation ( \(CBF_{CO_2 }\) =0.82 CBF_microspheres+5.7; P<0.001). The validity of the labelled-microsphere-injection method was verified. The feasibility of stable in vivo labelling of ⁶⁸Ga to serum-albumin microspheres provides a reference method for organ blood-flow measurements using positron-emission tomography.