Dose Reduction in Brain [18F]FDG PET/MRI: Give It Half a Chance.

PURPOSE: Integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) offers promising tools for evaluating brain disorders, including the minimization of exposure to ionizing radiation. Considering the length of scanning time with PET/MRI systems and their high sensitivity, we assumed that the activity could be reduced by one half compared with recommended activity for brain 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) PET exams without degrading image quality. PROCEDURES: We retrospectively simulated the reduction of injected activity (1 vs. 2 MBq/kg, [18F]FDG) in 100 patients assessed for cognitive impairment with simultaneous PET/MRI imaging. A list-mode acquisition was used to generate a 20-min image set as a reference (PETSTD) and to simulate a low-dose injection with a 10-min image (PETLD). We tested the reproducibility between PETLD and PETSTD with a blinded visual interpretation by two nuclear physicians asked to classify metabolic patterns, and a quantitative analysis conducted with regions-of-interest. Voxelwise comparisons between patients suggestive of Alzheimer's disease (AD) and frontotemporal dementia (FTD) were also conducted. RESULTS: The intra-operator agreement was high between the PETSTD and PETLD visual assessments for both readers (kappa 0.92 and 0.99). SUV ratios were strongly reproducible (intraclass correlation coefficient 0.95). The voxelwise and regional comparisons between AD vs. FTD metabolic profiles yielded very similar results with PETSTD and PETLD. CONCLUSIONS: A reduction of the [18F]FDG dose down to 1 MBq/kg is possible when performing 20-min brain PET/MRI without modifying diagnostic performance and quantitative assessments. The advantage is a significant reduction in the patient effective dose, which is non-negligible in longitudinal follow-up studies and in research protocols involving healthy volunteers.

[Interest and role of brain scintigraphy in the diagnosis of dementia in 2014]. / Intérêt et place de la scintigraphie cérébrale dans le diagnostic de démence en 2014.

Isotopic functional brain imaging is an important tool for the diagnosis and assessment of Alzheimer's disease and related disorders. This paper is a review of currently available radiotracers for PET and SPECT imaging, making a distinction between so-called topographical and pathophysiological markers. The respective indications and limitations of the ligands are presented.

An efficient strategy based on an individualized selection of registration methods. Application to the coregistration of MR and SPECT images in neuro-oncology.

An efficient registration strategy is described that aims to help solve delicate medical imaging registration problems. It consists of running several registration methods for each dataset and selecting the best one for each specific dataset, according to an evaluation criterion. Finally, the quality of the registration results, obtained with the best method, is visually scored by an expert as excellent, correct or poor. The strategy was applied to coregister Technetium-99m Sestamibi SPECT and MRI data in the framework of a follow-up protocol in patients with high grade gliomas receiving antiangiogenic therapy. To adapt the strategy to this clinical context, a robust semi-automatic evaluation criterion based on the physiological uptake of the Sestamibi tracer was defined. A panel of eighteen multimodal registration algorithms issued from BrainVisa, SPM or AIR software environments was systematically applied to the clinical database composed of sixty-two datasets. According to the expert visual validation, this new strategy provides 85% excellent registrations, 12% correct ones and only 3% poor ones. These results compare favorably to the ones obtained by the globally most efficient registration method over the whole database, for which only 61% of excellent registration results have been reported. Thus the registration strategy in its current implementation proves to be suitable for clinical application.

A framework using multimodal imaging for longitudinal monitoring of patients in neuro-oncology. Application to a SPECT/MRI study.

This paper proposes a framework to assess the potential value of 99mTc Sestamibi SPECT in addition to Gadolinium-enhanced MRI for the monitoring of patients with high grade gliomas under antiangiogenic treatment. It includes: 1) multimodal and monomodal high precision registration steps achieved thanks to a registration strategy which selects the best method among several ones for each dataset, 2) tumor segmentation steps dedicated to each modality and 3) a tumor comparison step which consists in the computation of some global (volume, intensity) and local (matching and mismatching) quantitative indices to analyze the tumor using different imaging modalities and at different times during the treatment. Each step is checked via 2D and 3D visualization. This framework was applied to a database of fifteen patients. For all patients, except one, the tumor volumes decrease globally and locally. Furthermore, a high correlation (r=0.77) was observed between MRI and Sestamibi tumor volumes. Finally, local indices show some possible mismatches between MRI Gadolinium uptake and Sestamibi uptake, which need to be further investigated.

A new strategy to improve coregistration of SPECT and MR images in patients with high grade glioma.

This paper proposes a new strategy to optimize the coregistration of Technetium-99m Sestamibi SPECT and MRI data in case of patients with high grade glioma. It consists in a personalized approach which selects, for each data set, the best registration method among several ones. To achieve this selection, a quantitative dedicated evaluation criterion based on the average intensities within specific anatomical structures corresponding to physiological areas of uptake of Sestamibi was defined. The strategy was applied to sixty-two data sets using nine registration methods based on mutual information and chamfer distance registration approaches, with different settings. It was implemented within the Anatomist/Brainvisa environment, using its basic registration functions. The visual evaluation by experts indicated that this strategy provides 60% good quality registrations, and 26% intermediate quality ones. Compared to the single use of the best global registration method, the number of registrations of good quality was multiplied by 1.4 when using the data specific strategy.

Evaluation of PET volume segmentation methods: comparisons with expert manual delineations.

INTRODUCTION: [¹8F]-Fluorodeoxyglucose PET has become an essential technique in oncology. Accurate segmentation is important for treatment planning. With the increasing number of available methods, it will be useful to establish a reliable evaluation tool. METHOD: Five methods for [F]-fluorodeoxyglucose PET image segmentation (MIP-based, Fuzzy C-means, Daisne, Nestle and the 42% threshold-based approach) were evaluated on non-Hodgkin's lymphoma lesions by comparing them with manual delineations performed by a panel of experts. The results were analyzed using different similarity measures. Intraoperator and interoperator variabilities were also studied. RESULTS: The maximum of intensity projection-based method provided results closest to the manual delineations set [binary Jaccard index mean (SD) 0.45 (0.15)]. The fuzzy C-means algorithm yielded slightly less satisfactory results. The application of a 42% threshold-based approach yielded results furthest from the manual delineations [binary Jaccard index mean (SD) 0.38 (0.16)]; the Daisne and the Nestle methods yielded intermediate results. Important intraoperator and interoperator variabilities were demonstrated. CONCLUSION: A simple assessment framework based on comparisons with manual delineations was proposed. The use of a set of manual delineations performed by five different experts as the reference seemed to be suitable to take the intraoperator and the interoperator variabilities into account. The online distribution of the data set generated in this study will make it possible to evaluate any new segmentation method.