title: Quantitative comparison of PET and Bremsstrahlung SPECT for imaging the in vivo yttrium-90 microsphere distribution after liver radioembolization.
abstract: BACKGROUND
  After yttrium-90 ((90)Y) microsphere radioembolization (RE), evaluation of extrahepatic activity and liver dosimetry is typically performed on (90)Y Bremsstrahlung SPECT images. Since these images demonstrate a low quantitative accuracy, (90)Y PET has been suggested as an alternative. The aim of this study is to quantitatively compare SPECT and state-of-the-art PET on the ability to detect small accumulations of (90)Y and on the accuracy of liver dosimetry.
  
  
  RESULTS
  SPECT/CT and PET/CT phantom data were acquired using several acquisition and reconstruction protocols, including resolution recovery and Time-Of-Flight (TOF) PET. Image contrast and noise were compared using a torso-shaped phantom containing six hot spheres of various sizes. The ability to detect extra- and intrahepatic accumulations of activity was tested by quantitative evaluation of the visibility and unique detectability of the phantom hot spheres. Image-based dose estimates of the phantom were compared to the true dose. For clinical illustration, the SPECT and PET-based estimated liver dose distributions of five RE patients were compared. At equal noise level, PET showed higher contrast recovery coefficients than SPECT. The highest contrast recovery coefficients were obtained with TOF PET reconstruction including resolution recovery. All six spheres were consistently visible on SPECT and PET images, but PET was able to uniquely detect smaller spheres than SPECT. TOF PET-based estimates of the dose in the phantom spheres were more accurate than SPECT-based dose estimates, with underestimations ranging from 45% (10-mm sphere) to 11% (37-mm sphere) for PET, and 75% to 58% for SPECT, respectively. The differences between TOF PET and SPECT dose-estimates were supported by the patient data.
  
  
  CONCLUSIONS
  In this study we quantitatively demonstrated that the image quality of state-of-the-art PET is superior over Bremsstrahlung SPECT for the assessment of the (90)Y microsphere distribution after radioembolization.
authors: Department of Radiology and Nuclear Medicine, University Medical Center Utrecht, Utrecht, The Netherlands. m.elschot@umcutrecht.nl
authors: Mattijs
authors: M
authors: Elschot
authors: Bart J
authors: BJ
authors: Vermolen
authors: Marnix G E H
authors: MG
authors: Lam
authors: Bart
authors: B
authors: de Keizer
authors: Maurice A A J
authors: MA
authors: van den Bosch
authors: Hugo W A M
authors: HW
authors: de Jong
mesh_terms: D000328:Adult; D000368:Aged; D001918:Brachytherapy; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008113:Liver Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy / Q000556:secondary; D008297:Male; D008863:Microspheres; D008875:Middle Aged; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D012189:Retrospective Studies; D012680:Sensitivity and Specificity; D014018:Tissue Distribution; D015899:Tomography, Emission-Computed, Single-Photon; D015021:Yttrium Radioisotopes / Q000493:pharmacokinetics
chemical_list: D019275:Radiopharmaceuticals; D015021:Yttrium Radioisotopes