Abstract
BACKGROUND: (99m)Tc-macroaggregated albumin (MAA) imaging is part of the standard work-up procedure for radioembolization using (90)Y microspheres. In certain scenarios, it may be warranted to visualize the distribution of (99m)Tc in co-presence of (90)Y, for example when validating intra-procedural (99m)Tc-MAA imaging after (90)Y-therapy to enable single-session radioembolization. Another instance involves additional (99m)Tc-MAA administration during the therapeutic procedure itself, e.g. when initial imaging reveals insufficient targeting of a specific liver segment. In these situations, crosstalk from (90)Y can result in reduced (99m)Tc image quality and quantitative accuracy. This study investigates the feasibility and optimal method of (99m)Tc SPECT imaging from combined (99m)Tc+(90)Y data using phantom experiments. RESULTS: An anthropomorphic torso phantom with two liver tumor inserts was filled with (99m)Tc without (single-isotope) and with (90)Y (dual-isotope) in various activities and isotope concentrations. Three collimators (low energy high resolution: LEHR, medium energy: ME, and high energy: HE) and three methods to compensate for (90)Y crosstalk in the (99m)Tc photo peak window (Monte Carlo-based, dual-energy-window and triple-energy-window correction) were evaluated. No substantial dead-time effects were observed in the clinically relevant activity range, up to approximately 12 GBq (99m)Tc+(90)Y (ratio 1:20) with LEHR, 29 GBq with ME and > 30 GBq with HE. Compared to the clinical standard (single-isotope (99m)Tc imaging with LEHR collimator), contrast recovery typically decreased from 70.0 ± 1.3% to 49.0 ± 0.9% (LEHR), 61.2 ± 1.5% (ME) or 62.1 ± 1.4% (HE) due to (90)Y crosstalk. Compensation methods increased contrast recovery, with Monte Carlo-based correction combined with a ME or HE collimator yielding the best recovery at 68.5 ± 1.6% and 68.3 ± 1.5%, respectively. Visual image quality in terms of resolution and scatter contamination was superior when using a ME collimator. Lung shunt fractions were also severely affected by (90)Y crosstalk when using LEHR, but could be effectively mitigated using a ME or HE collimator. CONCLUSION: (99m)Tc imaging in the presence of (90)Y leads to substantial image degradation due to crosstalk effects. Monte Carlo-based crosstalk compensation in combination with a ME or HE collimator was identified as the most accurate, robust and visually optimal reconstruction method for (99m)Tc SPECT from dual-isotope data.