Maximum Rubidium-82 activity for accurate myocardial blood flow quantification using digital PET

Objectives: Quantification of myocardial blood flow with PET is increasingly used. However, the performance of commonly used PET systems may be insufficient and could result in deviations between measured and injected activity when dealing with high-count rates from short-lived PET tracers. PET systems with digital photon counting technology using silicon photomultipliers may be more suitable. Our aim was to derive the maximum Rubidium-82 activity that can be used for accurate myocardial quantification using a digital PET system and compare this with conventional analog state-of-the-art systems.

Methods: 1.8 GBq Rubidium-82 was injected into the myocardial wall insert of an anthropomorphic torso phantom, immediately followed by a 10 min scan. Data were acquired on two analog PET systems: the Ingenuity TF (Philips Healthcare) and Discovery 690 (D690, GE Healthcare), and a digital PET system (Philips Healthcare). For each of the reconstructed dynamic images (40x15s), the total activity in a spherical volume-of-interest encapsulating the myocardial insert was measured. The dynamic range, defined as the highest activity for which the measured activity deviated less than 10% from the injected activity, was compared between cameras. The measured maximum activities were also compared.

Results: The dynamic ranges for the analog systems were 302 MBq (Ingenuity TF), 617 MBq (D690), and 690 MBq for digital PET, as shown in Figure 1. Moreover, the maximum measured activity was 474 MBq for the Ingenuity TF, 909 MBq for the D690, and >1279 MBq for digital PET. Although the deviation between the measured and injected activity increased with higher activities, it remained relatively limited for the D690 and digital PET.

Conclusion: Digital PET outperforms the analog systems in both dynamic range and detected maximal Rubidium-82 activity. However, when high tracer activities are used, the dynamic range of digital PET may still be insufficient for accurate myocardial blood flow quantification. Small deviations between measured and injected activity may provide correction possibilities to improve the dynamic range. Research Support: This study is part of a research Exhibit and research support was therefore provided by Philips Healthcare. $$graphic_1A634CE4-C870-42FD-8DC4-339600B506CA$$