Experimental investigation of factors affecting the absolute recovery coefficients in iodine-124 PET lesion imaging

Abstract

The use of recovery coefficients (RCs) in (124)I PET lesion imaging is a simple method to correct the imaged activity concentration (AC) primarily for the partial-volume effect and, to a minor extent, for the prompt gamma coincidence effect. The aim of this phantom study was to experimentally investigate a number of various factors affecting the (124)I RCs. Three RC-based correction approaches were considered. These approaches differ with respect to the volume of interest (VOI) drawn, which determines the imaged AC and the RCs: a single voxel VOI containing the maximum value (maximum RC), a spherical VOI with a diameter of the scanner resolution (resolution RC) and a VOI equaling the physical object volume (isovolume RC). Measurements were performed using mainly a stand-alone PET scanner (EXACT HR(+)) and a latest-generation PET/CT scanner (BIOGRAPH mCT). The RCs were determined using a cylindrical phantom containing spheres or rotational ellipsoids and were derived from images acquired with a reference acquisition protocol. For each type of RC, the influence of the following factors on the RC was assessed: object shape, background activity spill in and iterative image reconstruction parameters. To evaluate the robustness of the RC-based correction approaches, the percentage deviation between RC-corrected and true ACs was determined from images acquired with a clinical acquisition protocol of different AC regimes. The observed results of the shape and spill-in effects were compared with simulation data derived from a convolution-based model. The study demonstrated that the shape effect was negligible and, therefore, was in agreement with theoretical expectations. In contradiction to the simulation results, the observed spill-in effect was unexpectedly small. To avoid variations in the determination of RCs due to reconstruction parameter changes, image reconstruction with a pixel length of about one-third or less of the scanner resolution and an OSEM 1 x 32 algorithm or one with somewhat higher number of effective iterations are recommended. Using the clinical acquisition protocol, the phantom study indicated that the resolution- or isovolume-based recovery-correction approaches appeared to be more appropriate to recover the ACs from patient data; however, the application of the three RC-based correction approaches to small lesions containing low ACs was, in particular, associated with large underestimations. The phantom study had several limitations, which were discussed in detail.

Assessment of Lesion Response in the Initial Radioiodine Treatment of Differentiated Thyroid Cancer Using 124I PET Imaging

“…The PET images were retrospectively reconstructed using parameters optimized for quantitative 124 I imaging (15). The emission images were reconstructed after Fourier rebinning using the iterative attenuation-weighted ordered-subset expectation maximization algorithm with 4 iterations and 16 subsets.…”

Dose–Response Relationship in Differentiated Thyroid Cancer Patients Undergoing Radioiodine Treatment Assessed by Means of 124I PET/CT

“…Several groups have concluded that quantitation of 124 I PET images is feasible (7)(8)(9)(10)(11). Compared with 131 I SPECT, 124 I PET imaging offers a higher image spatial resolution, increased counting rate sensitivity, and higher quantitative capacity, resulting in the application of pretherapeutic 124 I PET/CT-based lesion dosimetry (12)(13)(14)(15)(16)(17).…”

90Y-PET/CT Imaging Quantification for Dosimetry in Peptide Receptor Radionuclide Therapy: Analysis and Corrections of the Impairing Factors

“…Finally, isovolume-RC uses the average of all voxel values equalling physical volume of the targets. 21 According to the PVE correction, different 90 Y-RC curves were defined taking into account different S/N, to evaluate the background spill-in effects.…”