PET lung ventilation/perfusion imaging using Gallium-68 aerosol (Galligas) and Gallium-68 labeled macroaggregated albumin (MAA)

Objectives Pulmonary imaging with ventilation/perfusion single photon emission tomography (V/P Scan) is a well-established diagnostic tool in nuclear medicine. Ga-68 aerosol (Galligas) and Ga-68 labeled macroaggregated albumin (MAA) are potential tracer for PET lung ventilation/perfusion imaging and could be in times of the worldwide shortage of Mo-99 an effective widening and upgrading in the diagnosis of clinically suspected pulmonary embolism (PE). In the form of an exploratory study the clinical applicability of Ga-68 labeled tracer for PET lung ventilation/perfusion imaging was investigated.

Methods Five patients with suspicion on pulmonary embolism underwent PET/CT (Philips TF) after inhalation of Galligas and application of 45-116 MBq Ga-68 labeled MAA (injected activity was calculated compared to the activity inhaled). PET scans were acquired in 3-D mode with an acquisition time of 5 min per bed position. The acquisition protocol included a low-dose CT for attenuation correction (AC). Dosimetry measurements and continuative phantom measurements for validation of the quantification were performed.

Results PET lung ventilation/perfusion imaging using Galligas and Ga-68 labeled MAA is clinically feasible. In one case a clinically suspected PE could be detected and verified. Radiation exposure was comparable to the SPECT technique with Technegas® and twice as high as Tc-99m-labeled MAA. Extrapulmonal activity but no free Ga-68 activity could be detected. Phantom measurements revealed effects could be caused by high kinetic energy of positrons and basically by insufficient AC.

Conclusions Although our group of patients was very small the results show Galligas and Ga-68 labeled MAA are in principle adequate surrogates marker for clinical use. However further studies on broad reach of positrons due to high kinetic energy of Ga-68 are urgently needed to investigate the possible effects on PET lung ventilation/perfusion imaging