Data-Driven Respiratory SPECT-Gating for Determination of Liver-Lung-Shunt Fraction

Ziel/Aim In hepatic radio-embolization, lungs are at risk of substantial radiation damage. For assessing its probability, each patient undergoes pre-therapeutic imaging with, e.g., Tc-99m-macro-aggregated albumin (MAA) in order to determine the liver-lung-shunt fraction (LLSF).

The aim of this study was to determine the influence of respiratory motion on LLSF determination

Methodik/Methods Thirteen patients underwent Tc-99m-MAA SPECT/CT scans on a Siemens Symbia T2 system. Patients were allowed to breathe freely during SPECT acquisition. SPECT/CT consisted of a single bed-position (~40 cm axial field of view) and was set to include whole liver and as much of the lungs as possible.

Using research software, SPECT projection data was acquired in list-mode format and retrospectively framed into four time bins representing different respiratory states. Gated and ungated SPECT data were reconstructed using ordered-subset conjugate-gradient algorithm (1 subset, 24 iterations). LLSF was calculated as the ratio between pulmonary and hepatic activity and expressed in %. It was computed for gated and ungated data based on manually segmented liver and lung compartments.

Ergebnisse/Results Average segmented liver and lung volumes were 1710 ± 454 mL (ranging 981 - 2474 mL) and 1445 ± 692 mL (355 - 2635 mL), respectively. Average LLSF was 5.0 ± 2.5 % (1.6 - 9.9 %) for gated and 5.2 ± 2.6 % (1.6 - 10.1 %) for ungated data. The span, which is the range from maximum to minimum LLSF of a patient’s gated data, was 3.0 ± 2.5 % (0.5 - 8.3 %), which is equivalent to 59.5 ± 35.2 % (5.0 - 145.0 %) of the respective mean LLSF.

Schlussfolgerungen/Conclusions Respiratory movements lead to a bias potentially leading to under- or overestimation of LLSF. Studies with an increased patient number will be carried out in order to determine its relevance in clinical practice.

Publication History

Article published online:
08 April 2021