Collimator and Energy Window Optimization in Bremsstrahlung SPECT/CT for Imaging Yttrium-90 Microspheres
R Nosrati1, E Olguin2*, M Palmer2, (1) Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, (2) Beth Israel Deaconess Medical Center, Boston, MA
Presentations
MO-E115-IePD-F5-4 (Monday, 7/11/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 5
Purpose: To optimize Y-90 bremsstrahlung-SPECT imaging performance for different collimators and energy windows (EW).
Methods: Spatial resolution was investigated with a point source made from 25mCi of resin microspheres (SIR-Spheres) inside a v-shaped microcentrifuge tube and held within an acrylic block. Planar images were acquired with a Siemens Intevo-BOLD camera with LEHR,MEGP, and HEGP collimators. For each collimator, planar images were acquired in 24 EW, each one 20keV-wide, beginning at 60keV. Resolution was assessed as full-width at half-maximum (FWHM) and full-width at tenth-maximum (FWTM). To evaluate contrast/noise performance, 35mCi of Y-90 microspheres was combined with 1000ml water in a cylindrical container. A polyvinyl-carboxy-polymer (Carbomer-940) was added and then, an organic base (triethanolamine) was added to form a stable/uniform distribution of microspheres. SPECT images were acquired with the same energy windows used for the point-source. Images from different EW were combined and reconstructed offline using iterative reconstruction (OSEM/2-iterations/16-subsets/8mm-Gaussian). Coefficient-of-variation (CoV), average-counts-per-voxel, and penetration-fraction (PF) were calculated for image quality assessment
Results: Spatial resolution decreased with increased EW width for all collimators. The LEHR collimator results in the highest spatial resolution but septal penetration is significant and the FWTM degrades rapidly with energy. The average number of counts was significantly lower with HE collimator whereas it was comparable between LEHR and MEGP collimators. Incorporating the energy bins that span the lead x-rays (~60-100keV) degraded spatial resolution slightly but substantially improves noise performance (reduced CoV). The fraction of photons penetrating the collimator increased almost linearly with energy.
Conclusion: MEGP collimator delivers the best trade-off between spatial resolution and septal penetration. Including lead x-rays significantly improves recorded counts with only a slight degradation of resolution. Noise performance improves with window width but tapers off above 200keV. We conclude that an MEGP collimator and an EW of 60-200keV is near optimal for Y-90 bremsstrahlung imaging.
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