Impact of PET/CT system, reconstruction protocol, data analysis method, and repositioning on PET/CT precision: An experimental evaluation using an oncology and brain phantom

Abstract

PurposeIn longitudinal oncological and brain PET/CT studies, it is important to understand the repeatability of quantitative PET metrics in order to assess change in tracer uptake. The present studies were performed in order to assess precision as function of PET/CT system, reconstruction protocol, analysis method, scan duration (or image noise), and repositioning in the field of view.MethodsMultiple (repeated) scans have been performed using a NEMA image quality (IQ) phantom and a 3D Hoffman brain phantom filled with 18F solutions on two systems. Studies were performed with and without randomly (< 2 cm) repositioning the phantom and all scans (12 replicates for IQ phantom and 10 replicates for Hoffman brain phantom) were performed at equal count statistics. For the NEMA IQ phantom, we studied the recovery coefficients (RC) of the maximum (SUV max), peak (SUV peak), and mean (SUV mean) uptake in each sphere as a function of experimental conditions (noise level, reconstruction settings, and phantom repositioning). For the 3D Hoffman phantom, the mean activity concentration was determined within several volumes of interest and activity recovery and its precision was studied as function of experimental conditions.ResultsThe impact of phantom repositioning on RC precision was mainly seen on the Philips Ingenuity PET/CT, especially in the case of smaller spheres (< 17 mm diameter, P < 0.05). This effect was much smaller for the Siemens Biograph system. When exploring SUV max, SUV peak, or SUV mean of the spheres in the NEMA IQ phantom, it was observed that precision depended on phantom repositioning, reconstruction algorithm, and scan duration, with SUV max being most and SUV peak least sensitive to phantom repositioning. For the brain phantom, regional averaged SUVs were only minimally affected by phantom repositioning (< 2 cm).ConclusionThe precision of quantitative PET metrics depends on the combination of reconstruction protocol, data analysis methods and scan duration (scan statistics). Moreover, precision was also affected by phantom repositioning but its impact depended on the data analysis method in combination with the reconstructed voxel size (tissue fraction effect). This study suggests that for oncological PET studies the use of SUV peak may be preferred over SUV max because SUV peak is less sensitive to patient repositioning/tumor sampling.

What and how should we measure in paediatric oncology FDG-PET/CT? Comparison of commonly used SUV metrics for differentiation between paediatric tumours

“…This similarity is remarkable as the parameters rely on uptake information derived from substantially different volumes (75 mm 3 vs. 1 cm 3 in our study). In general, due to its small size, SUV max is known to be adversely affected by noise and to be sensitive to respiratory motion artifacts that naturally occur during PET acquisition [26,27]. SUV peak on the other hand is less affected by these inherent disadvantages of SUV max and thus preferred by some authors [5]; in contrast, however, SUV peak is more prone to partial volume effects [5].…”

The Influence of Minimal Misalignment on the Repeatability of PET Images Examined by the Repositioning of Point Sources

“…Measurements of the radioactivity of a small region are strongly affected by the partial-volume effect (19). Mansor et al reported that the precision of SUV max was affected by phantom repositioning in a study that used hot spheres of # 15 mm in diameter (20). Furthermore, Adams et al reported that the measured PET count varied and that there was a relationship between the alignment of the hot spot and the pixels (21).…”

Towards guidelines to harmonize textural features in PET: Haralick textural features vary with image noise, but exposure-invariant domains enable comparable PET radiomics

“…From the full range GLCMs, 11 Haralick or so called second-order statistical features were calculated and plotted against exposure (Eqs 12-22). The resulting scatterplots were smoothed by the LOESS method to obtain differentiable curves for every feature (Fig 5).…”

“…However, images-and hence the measured tracer uptake values-typically differ between the various clinical PET/CT systems, even when imaging the very same object [10]. Distinct instrumentation and differences in image reconstruction algorithms impart characteristic imaging properties to PET/CT systems [11]. Resultant differences in imaging properties limit the comparability of datasets acquired on different PET/CT systems or with different acquisition protocols, and hamper the use of quantitative tracer uptake values in clinical routine or in multicenter clinical trials [12].…”