Partial volume effect in SPECT & PET imaging and impact on radionuclide dosimetry estimates

Area of Science:

• Nuclear Medicine
• Medical Imaging
• Radiopharmaceutical Dosimetry

Background:

• Emission tomographic imaging systems (PET and SPECT) suffer from spatial resolution limitations.
• This leads to underestimation of radioactivity concentration in objects comparable to the system's resolution volume, known as the partial volume effect (PVE).

Purpose of the Study:

• To investigate the impact of PVE on clinical PET and SPECT imaging.
• To assess the implications of PVE on radionuclide dosimetry estimates using current instrumentation.

Main Methods:

• Utilized the IEC Image Quality Phantom to measure uptake underestimation in objects of varying sizes for PET and SPECT.
• Examined single pixel (SUVmax) and region of interest (ROI) mean values.
• Assessed PVE impact on 177Lu SPECT dosimetry in a clinical case using OLINDA software.

Main Results:

• In PET, objects <18 mm minor axis showed underestimation.
• SPECT imaging exhibited greater underestimation, particularly in objects <2-3x resolution volume and ROI means <10 cm diameter.
• Clinical SPECT dosimetry showed >60% underestimate in a 10.2 cc lesion and >99% in a 0.06 cc lesion.

Conclusions:

• PVE remains a significant challenge for in vivo radionuclide uptake estimation, especially in small volumes.
• Accurate absorbed dose calculations for radionuclide therapy are hindered by PVE.
• Development of robust PVE correction methods is crucial for reliable dosimetry.