Texture indices are of growing interest for tumor characterization in 18 F-FDG PET. Yet, on the basis of results published in the literature so far, it is unclear which indices should be used, what they represent, and how they relate to conventional indices such as standardized uptake values (SUVs), metabolic volume (MV), and total lesion glycolysis (TLG). We investigated in detail 31 texture indices, 5 firstorder statistics (histogram indices) derived from the gray-level histogram of the tumor region, and their relationship with SUV, MV, and TLG in 3 different tumor types. Methods: Three patient groups corresponding to 3 cancer types at baseline were studied independently: patients with metastatic colorectal cancer (72 lesions), nonsmall cell lung cancer (24 lesions), and breast cancer (54 lesions). Thirty-one texture indices were studied in addition to SUVs, MV, and TLG, and 5 indices extracted from histogram analysis were also investigated. The relationships between indices were studied as well as the robustness of the various texture indices with respect to the parameters involved in the calculation method (sampling schemes and tumor volume of interest). Results: Regardless of the patient group, many indices were highly correlated (Pearson correlation coefficient jrj ≥ 0.80), making it desirable to focus on only a few uncorrelated indices. Three histogram indices were highly correlated with SUVs (jrj ≥ 0.84). Four texture indices were highly correlated with MV, and none was highly correlated with SUVs (jrj ≤ 0.55). The resampling formula used to calculate texture indices had a substantial impact, and resampling using at least 32 discrete values should be used for texture indices calculation. The texture indices change as a function of the segmentation method was higher than that of peak and maximum SUVs but less than mean SUV for 5 texture indices and was larger than that of MV for 14 texture indices and for the 5 histogram indices. All these results were extremely consistent across the 3 tumor types and explained many of the observations reported in the literature so far. Conclusion: None of the histogram indices and only 17 of 31 texture indices were robust with respect to the tumor-segmentation method. An appropriate resampling formula with at least 32 gray levels should be used to avoid introducing a misleading relationship between texture indices and SUV. Some texture indices are highly correlated or strongly correlate with MV whatever the tumor type.Such correlation should be accounted for when interpreting the usefulness of texture indices for tumor characterization, which might call for systematic multivariate analyses.

SUV, metabolic volume-based indices, and CTV after induction chemotherapy give independent prognostic information in stage III NSCLC. However, changes in metabolic TV and TLG under induction treatment provide more accurate prognostic information than SUV alone, and CTD and CTV.

PurposeTo compare the performance of eight metabolic indices for the early assessment of tumour response in patients with metastatic colorectal cancer (mCRC) treated with chemotherapy.MethodsForty patients with advanced mCRC underwent two FDG PET/CT scans, at baseline and on day 14 after chemotherapy initiation. For each lesion, eight metabolic indices were calculated: four standardized uptake values (SUV) without correction for the partial volume effect (PVE), two SUV with correction for PVE, a metabolic volume (MV) and a total lesion glycolysis (TLG). The relative change in each index between the two scans was calculated for each lesion. Lesions were also classified as responding and nonresponding lesions using the Response Evaluation Criteria In Solid Tumours (RECIST) 1.0 measured by contrast-enhanced CT at baseline and 6–8 weeks after starting therapy. Bland-Altman analyses were performed to compare the various indices. Based on the RECIST classification, ROC analyses were used to determine how accurately the indices predicted lesion response to therapy later seen with RECIST.ResultsRECIST showed 27 responding and 74 nonresponding lesions. Bland-Altman analyses showed that the four SUV indices uncorrected for PVE could not be used interchangeably, nor could the two SUV corrected for PVE. The areas under the ROC curves (AUC) were not significantly different between the SUV indices not corrected for PVE. The mean SUV change in a lesion better predicted lesion response without than with PVE correction. The AUC was significantly higher for SUV uncorrected for PVE than for the MV, but change in MV provided some information regarding the lesion response to therapy (AUC >0.5).ConclusionIn these mCRC patients, all SUV uncorrected for PVE accurately predicted the tumour response on day 14 after starting therapy as assessed 4 to 6 weeks later (i.e. 6 to 8 weeks after therapy initiation) using the RECIST criteria. Neither correcting SUV for PVE nor measuring TLG improved the assessment of tumour response compared to SUV uncorrected for PVE. The change in MV was the least accurate index for predicting tumour response.

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Since october 2015, PET/MR has been used extensively for clinical routine in the nuclear medicine department of the Pitié-Salpêtrière Hospital (Paris, France) with a throughput of 11 to 15 patients each day. While many studies have been conducted to investigate dose reduction strategies to patients with hybrid PET/MR devices, no study has focused on staff radiation safety. Knowing that patient positioning within the scanner takes longer in PET/MR than in PET/CT because of the placement of several local MR receive coils, a retrospective study was carried out to measure the radiation doses to nuclear medicine technologists from the patient. The analysis was conducted during one year on 1332 clinical PET/MR studies performed with the Signa PET/MR system (General Electric Healthcare) in our department. The whole-body exposure of the technologist staff was on average for all PET/MR exams10.3 ± 4 nSv per injected MBq of 18 F. When performing brain PET/MR exams only, the whole-body exposure was on average 8.7 ± 2 nSv per injected MBq of 18 F. Brain PET/MR provides lower radiation dose than whole-body examinations for cancer screening due to a lower injected activity (2 vs. 3 MBq kg−1) and shorter patient positioning (5 vs. 15 min). When starting PET/MR in a nuclear medicine department, an important step is to optimise patient positionning within the scanner to minimise radiation dose received by the technical staff from patients.

Purpose: Since 2010, PET/MR has been increasingly used for clinical routine in nuclear medicine departments. One advantage of PET/MR over PET/CT is the lower ionising radiation dose delivered to patients. However, data on the radiation dose delivered to staff operating PET/MR compared to new generation PET/CT is still lacking. Our aim was to compare the radiation dose to nuclear medicine technologists performing routine PET/MR and PET/CT in the same department. Methods: We retrospectively measured during 13 months, the daily radiation dose received by PET technologists by collecting individual dosimetry measurements (from electronic personal dosimeters). Data were analysed taking into account the total number of studies performed of each PET modality (PET/MR with Signa 3T, General Electric Healthcare vs. PET/CT with Biograph mCT flow, Siemens), the type of exploration (brain vs. whole body PET), the 18F activity injected per day and per patient as well as the time spent in contact with patients after tracer injection. Results: Our results show a significantly higher technologist staff whole-body exposure for PET/MR compared to PET/CT of 10.3±3.5 nSv versus 4.7±1.2 nSv per 18F injected MBq, respectively (p<0.05). This difference was related to prolonged contact with injected patients during patient positioning with PET/MR device and MR coils placement, especially in whole-body studies. Conclusions: For an equal injected activity, PET technologist radiation exposure for PET/MR was two-fold that of PET/CT. To minimize radiation dose to staff, efforts should be made to optimize patient positioning, even in departments with extensive PET/CT experience.

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We previously showed that the injected activity could be reduced to 1 MBq/kg without significantly degrading image quality for the exploration of neurocognitive disorders in 18F-FDG-PET/MRI. We now hypothesized that injected activity could be reduced ten-fold. We simulated a 18F-FDG-PET/MRI ultra-low-dose protocol (0.2 MBq/Kg, PETULD) and compared it to our reference protocol (2 MBq/Kg, PETSTD) in 50 patients with cognitive impairment. We tested the reproducibility between PETULD and PETSTD using SUVratios measurements. We also assessed the impact of PETULD for between-group comparisons and for visual analysis performed by three physicians. The intra-operator agreement between visual assessment of PETSTD and PETULD in patients with severe anomalies was substantial to almost perfect (kappa > 0.79). For patients with normal metabolism or moderate hypometabolism however, it was only moderate to substantial (kappa > 0.53). SUV ratios were strongly reproducible (SUVratio difference ± SD = 0.09 ± 0.08). Between-group comparisons yielded very similar results using either PETULD or PETSTD. 18F-FDG activity may be reduced to 0.2 MBq/Kg without compromising quantitative measurements. The visual interpretation was reproducible between ultra-low-dose and standard protocol for patients with severe hypometabolism, but less so for those with moderate hypometabolism. These results suggest that a low-dose protocol (1 MBq/Kg) should be preferred in the context of neurodegenerative disease diagnosis.