On the one hand, CZT gamma cameras owing to their high sensitivity allow for a significant reduction in injected activities of 99mTc-MIBI. On the other hand, 82Rubidium has a favourable dosimetry. The on-going prospective RUBIS trial compares the diagnostic performances of myocardial perfusion scintigraphy (MPS) using CZT gamma cameras with 99mTc-MIBI and 82Rubidium-PET-CT for the detection of myocardial ischemia in a population of women and overweighed men (BMI≥25). In this sub-study, we compared the total radiation exposure associated with MPS using 99Tc-MIBI and CZT gamma cameras or 82Rubidium-PET-CT in women and overweighed patients.

Each centre of the study was free to use his own acquisition protocols for MPS with 99mTc-MIBI and CZT gamma cameras. When the stress acquisition was considered as normal, the rest acquisition was not performed. PET acquisitions were performed in a 3D mode during the injection of a recommended activity of 82Rubidium of 10MBq/kg (minimal activity of 740MBq) at rest and at stress. Current intensity modulation was applied to CT acquisitions used for attenuation correction of stress and rest PET images. Effective doses related to the injection of each radiotracer and CT acquisitions were calculated using the recommendations of the ICRP.

Three hundred and nine patients including 142 women and 286 patients with BMI≥25 have been imaged successively with both imaging modalities. Mean total activity injected per patient was 1254±415MBq (13.8MBq/kg) for Tc-MIBI and 1869±408MBq (20.6MBq/kg) for Rubidium. In women, total effective dose was significantly lower with Rubidium-PET-CT in comparison to Tc-MIBI (4.0±1.5 vs. 9.2±3.3mSv; P<0.05). Total effective dose related to Rubidium-PET-CT was significantly higher in patients with BMI≥35 vs. BMI<35 (5.7±1.5 vs. 3.6±1.0mSv; P<0.05) mostly in relation to increased CT radiation exposure (2.9±1.1 vs. 1.3±0.7mSv, 51% vs. 36% of total dose, respectively; P<0.05), but remained lower than the effective dose of 99mTc-MIBI-MPS (BMI≥35: 11.9±3.4mSv; BMI<35: 9.2±3.1mSv).

82Rubidium-PET-CT is associated with significantly lower radiation exposure as compared to 99mTc-MIBI-MPS with CZT cameras in women and in overweighed patients. Total effective dose of 82Rubidium-PET-CT is, however, slightly higher in obese patients owing to increased radiation exposure from CT acquisitions.