BLUE RIBBON POSTER RADIOPHARMACEUTICALS: Y‑90 Bremsstrahlung SPECT on Nai and CZT Systems Using Energy‑Window-Based Scatter Compensation: Initial Phantom and Clinical Evaluation with Practical Protocol Implications
Abstract
Purpose
Direct imaging of Y‑90 bremsstrahlung with SPECT remains challenging because the continuous photon energy spectrum introduces scatter and septal penetration which reduces contrast and complicates quantitative reconstruction. Optimal energy‑window placement is therefore critical, with prior studies identifying ~80–180 keV often centered around ~90–125 keV, as a practical range for balancing detection efficiency and contrast, while higher‑energy windows support empirical scatter‑estimate techniques. As a result, practical energy‑window (EW) based scatter‑correction (SC) approaches, have gained traction. This study provides an initial comparison of NaI and CZT SPECT/CT systems for Y‑90 bremsstrahlung imaging using matched energy windows and two reconstruction strategies.
Methods
Phantom and clinical data were acquired on a GE NM/CT 670 (NaI, MEGP collimator) and NM/CT 870 (CZT, MEHRS collimator). A 25 mCi Y‑90 vial was imaged with identical primary (108 keV ± 32%) and high‑energy (360 keV ± 28%) windows for 25 minutes. All reconstructions used OSEM with CT‑based attenuation correction (AC) and resolution recovery (RR). Two reconstructions were qualitatively and quantitatively evaluated: AC+RR and AC+RR+SC, where EW‑based SC followed a 0.53× high‑energy‑window scaling. Two radiologists qualitatively reviewed two NaI and two CZT Y‑90 patient studies.
Results
For both detectors, SC reduced background noise and improved sharpness in the phantom images. CZT FWHM improved from 12.29 mm to 8.61 mm; NaI improved from 10.50 mm to 8.04 mm. Post‑SC FWHM values were similar, likely reflecting the low‑scatter phantom geometry. CZT acquired ~4× more counts (8.6M vs 2.0M) and ~3.7×higher count‑rate, indicating potential for >50% shorter acquisitions. Clinical reviews showed improved lesion contrast and reduced halo artifacts with SC, with radiologists preferring AC+RR+SC images.
Conclusion
EW‑based scatter correction meaningfully enhances Y‑90 bremsstrahlung SPECT for both CZT and NaI. CZT’s higher sensitivity offers additional benefits, supporting faster or higher‑quality acquisitions.