Accuracy of thyroid uptake calibration method: a multi-centric study with realistic phantoms.

International audienceAim/Introduction: measurement of the thyroid uptake is of interest in diagnostic and for treatment of benign thyroid disease. The sensitivity obtained from measurement in air or in a standard neck phantom does not take into account the real thyroid anatomy. The goal of this multi-centric study was to assess the accuracy of thyroid uptake measurement using a set of realistic thyroid phantoms of varying size. These measurements were carried-out according to the site-specific local procedure (Local) and according to a standardized protocol (Std). In this preliminary report sensitivities obtained with routine calibration objects were compared with those obtained with the set of phantoms, for both protocols. Material and methods: measurements were carried-out from October 2020 to June 2021 on 20 NaI gamma-cameras and 3 CZT cameras with parallel and pinhole collimators. Radionuclides were Tc-99m and I-123. Five thyroid phantoms between 3 and 30 mL were used. Images were centrally analyzed, a 3DSlicer module has been developed for automatic segmentation and calculation of the sensitivity. The mean sensitivity over five thyroid volumes was compared with the routine calibration factor (Srout) and with the sensitivity in air, obtained with a unique syringue (Sair). The three sensitivities were measured for both protocols. Results: 25 configurations have been analyzed (58% of final set). For pinhole Tc-99m measurements, the mean sensitivities Sair were 101 ±45 counts/MBq/s (Std, n=7) and 148 ±91 counts/MBq/s (Local, n=7). The difference being mainly due to different measurement distances in the protocols.For I-123 measurements with parallel collimators, the mean sensitivities Sair were 73 ±13 counts/MBq/s (Std, n=10) and 72 ±14 counts/MBq/s (Local, n=9). Sair was almost independent of radionuclides and protocol. For pinhole collimator the sensitivity decreased when the thyroid volume increased, whatever the radionuclide and protocol. For the 30 mL phantom, on mean, the sensitivity was 12% lower than . Considering the local protocol and both radionuclides the relative difference between Srout and was greater than 15% in 43% of the cases. The standard protocol did not reduce this difference. For parallel collimators the difference between Srout and was always less than 17%, almost independently of the protocol, radionuclide and parallel collimator model. Conclusion: with parallel collimators, the sensitivity was relatively independent of the thyroid volume and the routine calibration was suitable for thyroid uptake estimation. For pinhole collimators the calibration was strongly influenced by the volume and quantitative measurement were of limited accuracy

Determination of the unmetabolised 18F-FDG fraction by using an extension of simplified kinetic analysis method: clinical evaluation in paragangliomas

International audienceTumours with high (18)F-FDG uptake values on static late PET images do not always exhibit high proliferation indices. These discrepancies might be related to high proportion of unmetabolised (18)F-FDG components in the tissues. We propose a method that enables to calculate different (18)F-FDG kinetic parameters based on a new mathematical approach that integrates a measurement error model. Six patients with diagnosed non-metastatic paragangliomas (PGLs) and six control patients with different types of lesions were investigated in this pilot study using (18)F-FDG PET/CT. In all cases, a whole-body acquisition was followed by four static acquisitions centred over the target lesions, associated with venous blood samplings. We used an extension of the Hunter's method to calculate the net influx rate constant (K H). The exact net influx rate constant and vascular volume fraction (K i and V, respectively) were subsequently obtained by the method of least squares. Next, we calculated the mean percentages of metabolised (PM) and unmetabolised (PUM) (18)F-FDG components, and the times required to reach 80 % of the amount of metabolised (18)F-FDG (T80%). A test-retest evaluation indicated that the repeatability of our approach was accurate; the coefficients of variation were below 2 % regardless of the kinetic parameters considered. We observed that the PGLs were characterised by high dispersions of the maximum standardised uptake value SUVmax (9.7 ± 11, coefficient of variation CV = 114 %), K i (0.0137 ± 0.0119, CV = 87 %), and V (0.292 ± 0.306, CV = 105 %) values. The PGLs were associated with higher PUM (p = 0.02) and T80% (p = 0.02) values and lower k 3 (p = 0.02) values compared to the malignant lesions despite the similar SUVmax values (p = 0.55). The estimations of these new kinetic parameters are more accurate than SUVmax or K i for in vivo metabolic assessment of PGLs at the molecular level

A new methodology to derive 3D kinetic parametric FDG PET images based on a mathematical approach integrating an error model of measurement

International audienceIn FDG-PET, SUV images are hampered by large potential biases. Our aim was to develop an alternative method (ParaPET) to generate 3D kinetic parametric FDG-PET images easy to perform in clinical oncology.NCT 02821936 ; May 2016

A new methodology to derive 3D kinetic parametric FDG PET images based on a mathematical approach integrating an error model of measurement

International audienceIn FDG-PET, SUV images are hampered by large potential biases. Our aim was to develop an alternative method (ParaPET) to generate 3D kinetic parametric FDG-PET images easy to perform in clinical oncology.NCT 02821936 ; May 2016

Value of 123I/99mTc-sestamibi parathyroid scintigraphy with subtraction SPECT/CT in primary hyperparathyroidism for directing minimally invasive parathyroidectomy

International audiencePrimary hyperparathyroidism/(PHPT) is one of the most common endocrinological conditions. Surgery remains the only curative option. We have evaluated the performance of double isotope 123I/99mTc-sestamibi parathyroid scintigraphy/(PS) with subtraction SPECT/CT in PHP for identifying uniglandular disease

Toward a comparison and an optimization of CT protocols using new metrics of dose and image quality part I: prediction of human observers using a model observer for detection and discrimination tasks in low-dose CT images in various scanning conditions

International audienceIn the context of reducing the patient dose coming from CT scanner examinations without penalizing the diagnosis, the assessment of both patient dose and image quality (IQ) with relevant metrics is crucial. The present study represents the first stage in a larger work, aiming to compare and optimize CT protocols using dose and IQ new metrics. We proposed here to evaluate the capacity of the Non-PreWhitening matched filter with an eye (NPWE) model observer to be a robust and accurate estimation of IQ. We focused our work on two types of clinical tasks: a low contrast detection task and a discrimination task. We designed a torso-shaped phantom, including Plastic Water® slabs with cylindrical inserts of different diameters, sections and compositions. We led a human observer study with 13 human observers on images acquired in multiple irradiation and reconstruction scanning conditions (voltage, pitch, slice thickness, noise level of the reconstruction algorithm, energy level in dual-energy mode and dose), to evaluate the behavior of the model observer compared to the human responses faced to changing conditions. The model observer presented the same trends as the human observers with generally better results. We rescaled the NPWE model on the human responses by scanning conditions (kVp, pitch, slice thickness) to obtain the best agreement between both observer types, estimated using the Bland-Altman method. The impact of some scanning parameters was estimated using the correct answer rate given by the rescaled NPWE model, for both tasks and each insert size. In particular, the comparison between the dual-energy mode at 74 keV and the single-energy mode at 120 kVp showed that, if the 120 kVp voltage provided better results for the smallest insert at the lower doses for both tasks, their responses were equivalent in many cases

Health-related quality of life in locally advanced hepatocellular carcinoma treated by either radioembolisation or sorafenib (SARAH trial)

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