Performance evaluation of quantitative SPECT/CT using NEMA NU 2 PET methodology

Abstract

Although PET is routinely evaluated using NEMA NU2 as standard in the clinic, standard methodology for evaluating the performance of quantitative SPECT systems has not been established. In this study, the quantitative performance of the Symbia Intevo SPECT/CT was evaluated for two common isotopes (99mTc, 177Lu) and benchmarked against the performance of a PET/CT. A further aim was to demonstrate the utility of adapting NEMA NU2 PET measurements to SPECT. In addition, dead-time and resolution recovery were evaluated to provide more complete system evaluations. Spatial resolution of the SPECT system at 1 cm from the center in the transverse direction was 13.1 mm and 22.4 mm for 99mTc and 177Lu respectively, compared with 4.3 mm (18F) and 5.8 mm (68Ga) for PET. Sensitivity at the center of the FoV was 119 cps MBq−1 and 48 cps MBq−1 (99mTc, 177Lu) for SPECT and 9632 cps MBq−1 and 8216 cps MBq−1 (18F, 68Ga) for PET. Scatter fraction was 0.25 and 0.36 (99mTc, 77Lu) for SPECT and 0.32 and 0.29 (18F, 68Ga) for PET. Contrast recovery coefficient in the largest spheres was 0.79 and 0.65 (99mTc, 177Lu) for SPECT, 1.00 and 0.97 (18F, 68Ga) for PET and the background variability was 2.7%, 6.5% (99mTc, 177Lu), 1.5% and 1.6% (18F, 68Ga), respectively. Partial volume effect was evaluated using the NEMA IQ phantom with six sphere inserts (diameter: 37 mm, 28 mm, 22 mm, 17 mm, 13 mm and 10 mm). Full contrast recovery was reached with the 17 mm for 18F, while SPECT did not reach full recovery for any sphere. Count rate losses were 2% for 99mTc at 1 GBq and 11% for 177Lu at 8.5 GBq which are well below the typical activities for clinical applications. We concluded NEMA NU2 methodology can be easily adapted to SPECT/CT as a routine quality assurance procedure in the clinic.

Variability in lutetium-177 SPECT quantification between different state-of-the-art SPECT/CT systems

“…Although a 42% isocontour method shows good recovery for both PET [36] and SPECT [13], the background-corrected 50% isocontour method was chosen because of its high repeatability for PET in a multicenter settings [37] and to align our results as much as possible with the already existing standards for PET quantification [38]. However, a recently published study by Ryu et al [39] showed that the line profiles over active spheres of reconstructed SPECT images (using 99m Tc and 177 Lu) showed a very different profile than the same spheres measured on PET (using 18 F and 68 Ga). This indicates that a 50% isocontour method might not be the most ideal solution threshold for contouring in SPECT and that a lower threshold might be more appropriate as demonstrated by Collarino et al [13].…”

RetroSPECT: Gallium-67 As A Theranostic Imaging Agent

“…Quantitative SPECT/CT imaging with radiotracers such as gallium-67 and lutetium-177 is available today (42,43). A signi cant limitation on its value in determining lesion dosimetry, however, is the poor spatial resolution in SPECT/CT using a medium energy collimator with values of 20+ mm FWHM in clinical imaging (44). This introduces a signi cant partial volume effect (PVE) whereby the radioconcentration is underestimated by a signi cant amount in regions less than 2.5-3 the spatial resolution, that is, 50-60 mm.…”

The current status of quantitative SPECT/CT in the assessment of transthyretin cardiac amyloidosis

“…It has also been proposed that quantitative SPECT should be subject to the same NEMA NU 2 QC process as PET. 33 If quantitative SPECT is to be used for progress assessment the reproducibility of measurements in individuals with ATTR-CM must be assessed. Larger clinical trials need to be undertaken to determine whether quantitative SPECT measurements can provide prognostic information in ATTR or play a role in assessing disease progression and treatment response.…”