Development of a New Quantification Method Using Partial Volume Effect Correction for Individual Energy Peaks in 111In-pentetreotide SPECT/CT

Abstract

BackgroundSomatostatin receptor scintigraphy (SRS) using 111In-pentetreotide has no established quantification method. The purpose of this study was to develop a new quantitative method to correct the partial volume effect (PVE) for individual energy peaks in 111In-pentetreotide single-photon emission computed tomography (SPECT). MethodsPhantom experiments were performed to construct a new quantitative method. In the phantom experiments, a NEMA IEC body phantom was used. Acquisition was performed using two energy peaks (171 keV and 245 keV) on the SPECT/CT system. In the SPECT images of each energy peak, the region of interest was set at each hot sphere and lung insert, and the recovery coefficient (RC) was calculated to understand the PVE. A new quantitative index, the indium uptake index (IUI), was calculated using the RC to correct the PVE. The quantitative accuracy of the IUI in the hot sphere was confirmed. Case studies were performed to clarify the quantitative accuracy. In a case study, the relationship between the IUI and the Krenning score, which is used as a visual assessment, was evaluated for each lesion. ResultsThe obtained RCs showed that the energy peak at 171 keV was faster in recovering the effect of PVE than that at 245 keV. The IUI in the 17 mm diameter hot sphere was overestimated by 3.1% at 171 keV and underestimated by 0.5% at 245 keV compared to the actual IUI. In case studies, the relationship between IUI and Krenning score was rs = 0.805 (p < 0.005) at sum, rs = 0.77 (p < 0.005) at 171 keV, and rs = 0.84 (p < 0.005) at 245 keV.Conclusion We have developed a new quantification method for 111In-pentetreotide SPECT/CT using RC-based PVE correction for an individual energy peak of 171 keV. The quantitative accuracy of this method was high even for accumulations of less than 20 mm, and it showed a good relationship with the Krenning score; therefore, the clinical usefulness of IUI was demonstrated.

Acquisition Conditions for Lu-177 DOTATATE Imaging

“…Imitation tumors (signals) with diameters of 7, 10, 15, 20, and 30 mm were placed 5 cm equidistant (Figure 2a). BG (liver) was set to 200 kBq/mL with reference to the accumulation ratio of In-111 pentetreotide [9,10], and the imitated tumor was set to five times for the plane phantom. The imaging conditions were a matrix size of 256 × 256 and acquisition time of 5 min.…”

“…However, the detection efficiency of the NaI (Tl) scintillator is large (56.0 keV), and the energy spectrum is different in the performance of the collimators (Figure 1). A low-medium-energy general-purpose (LMEGP)-type [8,9] collimator is used for In-111 pentetreotide in somatostatin receptor scintigraphy (SRS) imaging. The acquisition condition for Lu-177 imaging consists of a combination of a MEGP collimator and one peak (208 keV) or two peaks (113 keV and 208 keV).…”