Quantitative and Qualitative Assessment of Yttrium-90 PET/CT Imaging

<div><p>Yttrium-90 is known to have a low positron emission decay of 32 ppm that may allow for personalized dosimetry of liver cancer therapy with ⁹⁰Y labeled microspheres. The aim of this work was to image and quantify ⁹⁰Y so that accurate predictions of the absorbed dose can be made. The measurements were performed within the QUEST study (University of Sydney, and Sirtex Medical, Australia). A NEMA IEC body phantom containing 6 fillable spheres (10–37 mm ∅) was used to measure the ⁹⁰Y distribution with a Biograph mCT PET/CT (Siemens, Erlangen, Germany) with time-of-flight (TOF) acquisition. A sphere to background ratio of 8∶1, with a total ⁹⁰Y activity of 3 GBq was used. Measurements were performed for one week (0, 3, 5 and 7 d). he acquisition protocol consisted of 30 min-2 bed positions and 120 min-single bed position. mages were reconstructed with 3D ordered subset expectation maximization (OSEM) and point spread function (PSF) for iteration numbers of 1–12 with 21 (TOF) and 24 (non-TOF) subsets and CT based attenuation and scatter correction. Convergence of algorithms and activity recovery was assessed based on regions-of-interest (ROI) analysis of the background (100 voxels), spheres (4 voxels) and the central low density insert (25 voxels). For the largest sphere, the recovery coefficient (RC) values for the 30 min –2-bed position, 30 min-single bed and 120 min-single bed were 1.12±0.20, 1.14±0.13, 0.97±0.07 respectively. For the smaller diameter spheres, the PSF algorithm with TOF and single bed acquisition provided a comparatively better activity recovery. Quantification of Y-90 using Biograph mCT PET/CT is possible with a reasonable accuracy, the limitations being the size of the lesion and the activity concentration present. At this stage, based on our study, it seems advantageous to use different protocols depending on the size of the lesion.</p></div

Convergence of the hot spheres (central 4 voxels in each sphere), with the PSF TOF algorithm for the (A) 30 min-2 bed position acquisition and (B) 120 min-one bed position acquisition, reconstruction parameters: 1–12 iterations with 21 (TOF) subsets, 5 mm Gaussian filtering and an image matrix of 400.

<p>Convergence of the hot spheres (central 4 voxels in each sphere), with the PSF TOF algorithm for the (A) 30 min-2 bed position acquisition and (B) 120 min-one bed position acquisition, reconstruction parameters: 1–12 iterations with 21 (TOF) subsets, 5 mm Gaussian filtering and an image matrix of 400.</p

Transverse sections of the phantom reconstructed with 30 min-2 bed position, 30 min and 120 min single bed acquisitions and a matrix size of 400 and Gaussian filtering with FWHM of 5 mm for 21 subsets and 1–3 iterations of PSF TOF algorithms.

<p>Note that the smallest sphere is an empty sphere <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0110401#pone.0110401-Attarwala1" target="_blank">[40]</a>.</p

Counting statistics (kilocounts per second (kcps)) for the 30 min acquisition with 2 bed positions for Day 0, 3, 5 and 7 measurement time points during 1 week and an empty phantom measurement.

<p>Counting statistics (kilocounts per second (kcps)) for the 30 min acquisition with 2 bed positions for Day 0, 3, 5 and 7 measurement time points during 1 week and an empty phantom measurement.</p

Convergence of the background (100 voxels) and lung insert (25 voxels) based on the transverse section through the axial center of the phantom, with the PSF TOF algorithm for the (A) 30 min-2 bed position acquisition and (B) 120 min-one bed position acquisition, reconstruction parameters: 1–12 iterations with 21 (TOF) subsets, 5 mm Gaussian filtering and an image matrix of 400.

<p>Convergence of the background (100 voxels) and lung insert (25 voxels) based on the transverse section through the axial center of the phantom, with the PSF TOF algorithm for the (A) 30 min-2 bed position acquisition and (B) 120 min-one bed position acquisition, reconstruction parameters: 1–12 iterations with 21 (TOF) subsets, 5 mm Gaussian filtering and an image matrix of 400.</p

Recovery coefficients from day 0 acquisition for spheres with diamters (L to R: 13 mm, 17 mm, 22 mm, 28 mm and 37 mm) for OSEM TOF, PSF TOF, OSEM and PSF alogorithms respectively.

<p>Reconstruction parameters: 1 iteration, 24 and 21 (TOF) subsets, image matrix of 400 and Gaussian filtering of 5 mm.</p

Recovery coefficients from day 0 acquisition for PSF TOF to demonstrate the effect of different acquisition times.

<p>Reconstruction parameters: 1 iteration, 21 (TOF) subsets, and image matrix of 400 and Gaussian filtering of 5 mm.</p