Technical considerations
There are no yet published guidelines and studies that provide clear recommendations on the optimal acquisition time for blood pool SPECT images. Current research offers
limited justification for the selected acquisition protocols and often overlooks acceptable noise levels in the reconstructed images. In contrast, scan duration recommendations
for late phase bone imaging are more well-defined. The European Association of Nuclear Medicine EANM) guidelines suggest a planar acquisition time of 4 to 10 minutes for late phase bone imaging. For late phase SPECT imaging, the EANM advises extending the imaging time to 10 to 30 minutes, representing a 2.5 to 3-fold increase compared to planar
scan durations (8). Increasing the recommended planar acquisition times proportionally for
blood pool images would suggest an acquisition duration of 7 to 15 minutes. However, to minimise the effect of osteoblastic activity on tracer distribution, it is important
that the blood pool acquisition is completed within 15 minutes of radiotracer injection. Therefore, an acquisition time of under 12 minutes is recommended to ensure prompt
image capture (1). To reduce patient radiation exposure, it is often recommended to use full
diagnostic CT during late phase imaging and a low-dose protocol or no CT during the blood pool phase. In practice, I would recommend twice a CT in the mid and distal extremities
and a more personalized approach according to age for the trunk and proximal joints. If the latter phase CT is minimised or skipped, images can be fused with late phase diagnostic
CT, though this is challenging with limb imaging due to positioning differences. Ultra-low dose CT protocols (80-100 kV and 20-60 mAs) can reduce doses to below 1 mSv, with dose reduction varying by body region and CT reconstruction methods used (8).