Tc-99m PYP Amyloid Scan Protocol

On this Tc-99m PYP amyloid scan, planar chest images are acquired with ROI circles placed over the heart and lung. According to standard protocol, at what timepoint are these planar images obtained after injection, and why?

1. APlanar images are acquired immediately after injection (0–5 minutes) to capture peak cardiac blood-pool activity before the tracer redistributes into bone and soft tissue
2. BPlanar images for the heart-to-lung ratio are acquired at 1 hour post-injection, allowing adequate blood-pool clearance while capturing tracer uptake in amyloid deposits for quantification
3. CPlanar images are obtained at 48–72 hours post-injection, similar to Ga-67 imaging, because Tc-99m PYP requires an extended delay for amyloid-specific uptake to reach detectable levels
4. DPlanar images are acquired only after SPECT confirms cardiac uptake at 3 hours, since planar imaging alone cannot generate a valid heart-to-lung ratio without prior tomographic confirmation