Abstract
Objectives:Harmonisation is the process whereby standardised uptake values from different scanners can be made comparable. This PET/CT pilot study aimed to evaluate the effectiveness of harmonisation of a modern scanner with image reconstruction incorporating resolution recovery (RR) with another vendor older scanner operated in two-dimensional (2D) mode, and for both against a European standard (EARL). The vendor-proprietary software EQ•PET was used, which achieves harmonisation with a Gaussian smoothing. A substudy investigated effect of RR on harmonisation.Methods:Phantom studies on each scanner were performed to optimise the smoothing parameters required to achieve successful harmonisation. 80 patients were retrospectively selected; half were imaged on each scanner. As proof of principle, a cohort of 10 patients was selected from the modern scanner subjects to study the effects of RR on harmonisation.Results:Before harmonisation, the modern scanner without RR adhered to EARL specification. Using the phantom data, filters were derived for optimal harmonisation between scanners and with and without RR as applicable, to the EARL standard. The 80-patient cohort did not reveal any statistically significant differences. In the 10-patient cohort SUVmax for RR > no RR irrespective of harmonisation but differences lacked statistical significance (one-way ANOVA F(3.36) = 0.37, p = 0.78). Bland-Altman analysis showed that harmonisation reduced the SUVmax ratio between RR and no RR to 1.07 (95% CI 0.96–1.18) with no outliers.Conclusions:EQ•PET successfully enabled harmonisation between modern and older scanners and against the EARL standard. Harmonisation reduces SUVmax and dependence on the use of RR in the modern scanner.Advances in knowledge:EQ•PET is feasible to harmonise different PET/CT scanners and reduces the effect of RR on SUVmax.
Highlights
The recent rate of advance of PET/CT equipment technology has led to the everyday use worldwide of many variants of detector and software.[1,2] Some earlier PET/CT scanners (e.g., bismuth germanate (BGO) crystal equipment) allow scanning with or without collimation, that is, in 2D or 3D acquisition modes[3] and these are more prevalent in emerging markets due to healthcare cost factors
All three plots lie within the EARL recommended range, indicating that harmonisation was possible in all cases for all spheres
In the case of scanner A harmonised to scanner B (Figure 3), it is seen that scanner A data can be harmonised to lie within a range based on scanner B data, whose width is proportionately that of the EARL recommendations
Summary
The recent rate of advance of PET/CT equipment technology has led to the everyday use worldwide of many variants of detector and software.[1,2] Some earlier PET/CT scanners (e.g., bismuth germanate (BGO) crystal equipment) allow scanning with or without collimation, that is, in 2D or 3D acquisition modes[3] and these are more prevalent in emerging markets due to healthcare cost factors. Advanced image reconstruction algorithms including resolution recovery (RR) with point spread function modelling or Bayesian reconstruction[4] are in widespread clinical use today. It is frequently necessary to compare standardised uptake values (SUV) of a lesion between two scans, for example in assessing response to therapy using PERCIST.[5] Ideally, standardised protocols would be used to ensure comparability between the SUVs; it is frequently necessary to compare SUVs acquired in 2D and 3D,6 or reconstructed with different algorithms. Harmonisation is the process by which it is assured that SUVs acquired using different scanners or protocols can be compared; if harmonisation is not performed there is a risk of misclassification of lesion response
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