La tomographie par émission de positons en cardiologie

Cardiovascular PET imaging is progressively emerging, owing to wider availability of cameras for non-oncology indications, as well as to the development of dedicated imaging agents. This article briefly reviews main indications of cardiovascular PET.     

Les examens cardiaques en tomographie par émission de positons

Cardiac positron emission tomography (PET) is yet considered as a reference imaging technique but remains poorly used in clinical practice. At the present time, the advantages of cardiac PET investigations are far to be evident, when compared with conventional tomoscintigraphy (SPECT), except for perfusion imaging in the obese and for viability assessment in case of very severe cardiac dysfunction. However, this situation might quickly move because of an enhanced availability of PET imaging, dramatic technical progresses and promising new tracers. In particular, the last-generation PET-cameras allow reaching spatial resolutions and detection sensitivities, which are now spectacularly higher than those from conventional SPECT imaging. In addition, the list mode recording allows the subsequent images reconstruction to be synchronized to cardiac cycle but also to respiratory cycle; and the quantifications of myocardial perfusion flow and of coronary flow reserve are now available in clinical routine. Furthermore, new tracers labelled with fluorine-18 are under development, especially for perfusion investigations, and kinetics properties of these new tracers are dramatically enhanced when compared with current perfusion SPECT tracers.     

Tomographie par émission de positons et cancer de la prostate

Positron emission tomography (PET) is a major imaging modality in oncology. Fluorodeoxyglucose (FDG) PET is of limited usefulness in prostate cancer, be it for initial staging or for detection of recurrence. New PET tracers could improve PET performances in prostate cancer staging and when recurrence is suspected. Lipid metabolism tracers, such as choline and fluorine-18-labelled choline analogues, seem to be promising in these indications. The impact of these PET examinations on patient management should be further evaluated, taking into consideration the new therapeutic strategies, in particular salvage local treatment in case of isolated local recurrence.     

Place de la tomographie par émission de positons dans la prise en charge des fièvres d’origine inconnue

FDG-PET has become an established diagnostic tool in oncology. Fluorodeoxyglucose is not a specific tracer for malignant lesions, as uptake depends on accumulation of FDG in cells with an increased glucose metabolism as it is also the case in inflammatory and infectious lesions. Thus, FDG-PET could be valuable in diagnosing patients with fever of unknown origin (FUO). The percentage of FDG-PET scans helpful in the diagnostic process in patients with FUO is estimated in average around 30%. However, more evaluating prospective studies should be awaited before integrating FDG-PET in clinical routine use in order to compare different techniques already validated (biology, radiology, conventional scintigraphic imaging), to evaluate its cost-effectiveness and to determine its place for the managment of FUO.     

Évaluation de méthodes automatiques de segmentation des volumes tumoraux en tomographie par émission de positons par comparaison avec des contours manuels réalisés par un groupe d’experts

Objective

Set up a framework for evaluating automatic segmentation methods of tumour volumes on PET images.

Patient and methods

This study was performed with PET images of 18 patients with non-Hodgkin's lymphoma. One target lesion per patient was pointed out. Each lesion was then three times manually delineated by five experts. Four automatic methods (the application of a threshold of 42% of the maximum SUV, the MIP-based method, the Daisne et al. method and the Nestle et al. method) were evaluated by comparison with the set of manual delineations.

Results

From the manual delineations, we have concluded to a moderate intra-operator variability and to a reduced interoperator reproducibility. From statistical tests performed on various quantitative criteria, there was no significant difference between the MIP-based method, the Daisne et al. method and the Nestle et al. one. The application of a threshold of 42% of the maximum SUV appears to be less efficient.

Conclusion

This work proposes a comparison and an evaluation protocol for segmentation methods. The generated data set will be distributed online for the community to simplify the evaluation of any new method of segmentation.     

Impact de la tomographie par émission de positons au 18fluorodésoxyglucose dans la prise en charge des cancers de primitif inconnu

Aim and methodThis retrospective study, performed on 37 patients, gave us the opportunity to evaluate the impact of ¹⁸F-FDG PET/CT for cancer of unknown primary (CUP). We first wanted to study the precision of the exam to detect the primary, after a negative check-up, for the extension of the disease, and to judge the impact of the results on management and survival of those patients.ResultThe PET/CT led to the detection of the primary for 14 patients out of 37, after a negative check-up composed of five exams on average. For 10 patients, the exam allows the detection of supplementary metastases. The management was changed after the exam in more than one third of the patients, but without any significant impact on the time of survival of these patients, for whom the prognostic is usually dismal.ConclusionThe ¹⁸F-FDG PET/CT appears a valuable tool for detection of primary, changing the management of many of the patients. These results must be completed by a prospective study, in particular to judge the impact of exam's results on the survival.     

Évaluation de la réponse thérapeutique par tomographie par émission de positons (TEP) au fluoro-désoxyglucose (FDG) en oncologie-hématologie

¹⁸Fluoro-deoxyglucose (FDG) positron emission tomography (PET) is an imaging technique which studies the cellular glucidic metabolism. It is particularly indicated in oncology, especially for cancer diagnosis (with a potential prognosis interest) or detection of recurrence. Because of its functional approach to the tissues, its use has logically evolved into the evaluation of cancer treatments, both for the individual care of patients for clinical trials of new therapies. Also, it tends to displace conventional imaging in this indication, whose main limitation is not to assess the viability of residual masses, potentially necrotic or fibrous after treatment. However, the use of FDG-PET requires a rigorous methodology for both the exams achievement but also for the quality of their interpretation, including the choice of the comparison tool. Based on an increasing literature on the subject, were published and updated interpretation criteria for both lymphoma and solid cancers. For lymphoma, standardized assessment criteria were proposed in 2007 during an International Harmonize Project (IHP). For solid cancers, Positron Emission tomography Response Criteria In Solid Tumors (PERCIST) recommendations version 1.0 were recently proposed by an American workshop in 2009 in order to clarify and standardize practices.     

La tomographie par émission de positons au 18FDG dans la caractérisation des masses résiduelles en fin de traitement dans les lymphomes : étude quantitative rétrospective

While the limits of Computed Tomography (CT) in the assessment of post-therapeutic residual masses has been studied extensively, few works have evaluated the interest of the combined use of metabolic and morphological criteria in the management of patients with lymphoma. The purpose of this study is to find out optimal morphological and functional threshold values that are likely to characterize residual masses after the treatment of lymphoma. Nineteen patients referred to the hematological department of a university hospital for the initial treatment of a malignant lymphoma were retrospectively included in the study. Inclusion criteria included the finding of one or more residual masses after the completion of the treatment. At the end of the treatment, all patients underwent a 18-Fluoro-deoxy-glucose Positron Emission Tomography (PET) together with a CT. For each residual mass, the small and large axial diameters and the Standardized Uptake Values of the FDG (SUV max, avg and min) were quantified after the completion of the treatment. All patients underwent clinical examination together with biological and imaging tests five months later to decide the nature of the residual masses (scar or residual disease). Only the SUVmax, the SUVavg and the diameter were useful to predict the follow-up. A SUVmax greater than 4 is in favour of a residual disease with a specificity of 90–100%. A small axial diameter of 11.5 mm has a specificity of 92%. After ROC (Receiver operating characteristic) curves analysis, the combination “SUV– small axial diameter” is more efficient to detect a residual disease than the SUV or the small axial diameter alone, however the difference is not significant. As a consequence, further studies involving a larger population are necessary to confirm the usefulness of the combination of SUV and small axial diameter in the assessment of malignant lymphoma at the end of the treatment.     

Apport de la tomographie par émission de positons au 18F-fluorodéoxyglucose (TEP-FDG) dans la prise en charge du cancer du canal anal

ObjectiveTo evaluate the contribution of FDG-PET in the management of anal carcinoma, with special emphasis on its impact on therapeutic strategy.Materials and methodsFrom March 2005 to August 2008, 48 PET were performed on 43 patients with anal epidermoid carcinoma, in initial staging (IS: 20 exams), therapeutic response assessment (TRA: 11), and recurrence assessment (RA: 17). We compared initial therapeutic strategies defined on conventional assessment results, to final ones chosen after PET.ResultsPET revealed lesions that were undetected by conventional investigation in 23% of cases (IS: 25%; TRA: 18%; RA: 23%) and cleared suspicious lesions in 21% of cases (IS: 10%; TRA: 18%; RA: 35%). It influenced the therapeutic strategy, and sometimes even modified it radically, in 44% of cases (IS: 35%; TRA: 54%; RA: 47%). This therapeutic impact was stronger in settings with diagnostic ambiguity, in which PET allowed to specify the diagnosis and to orientate consequently the therapeutic choice.ConclusionPET is interesting in the management of anal carcinoma, especially in uncertain diagnostic settings, in which the metabolic information brought allows to influence the therapeutic choice in almost half of the cases.     

Évaluation des pratiques professionnelles. Pertinence des indications de la tomographie à émission de positons en cancérologie

IntroductionAs part of the health care quality and safety policy in France, Professional Practice Assessment (PPA) are mandatory in the health services “certification” process. We present our study regarding the pertinence of Positron Emission Tomography (PET) indications in oncology.Materials and methodsA multidisciplinary task group used the Quick Audit method with two rounds of 100 request forms each. The assessment list of criteria comprised four items of decreasing relevance grading the PET scans clinical indications, which were derived from the three French published guidelines (SOR [FNCLCC], “Guide du bon usage des examens d’imagerie médicale” [SFR-SFMN], “Guide pour la rédaction de protocoles pour la TEP au FDG en cancérologie” [SFMN]) and five additional items: clinical information, patient's body weight, previous treatments dates, diabetes, claustrophobia.ResultsThe first round showed that 68% of the requested scans corresponded to the two most relevant groups of indications (SOR Standards and Options). The request forms were correctly filled in regarding the clinical information, but this was not the case for the other items we tested. Several actions were conducted: dedicated PET request form, availability of the SOR on the hospital intranet, boost of the referring physicians awareness during the multidisciplinary oncology meetings (Réunions de Concertation Pluridisciplinaires RCP). The second round showed a better pertinence of the PET scans indications (75% versus 68%); the patient's body weight was more frequently mentioned on the request form.DiscussionThis study is an example of PPA in our discipline. It led to an improvement of the oncologic PET scans clinical indications in our hospital. This work is pursued in everyday discussion with the referring clinicians, especially during the RCP.     

Tomographie à émission de positons et lymphomes

There is an abundant literature dealing with FDG PET imaging in lymphomas and Hodgkin's disease. Several meta-analysis are available, along with international recommendations. In this concise review, we will discuss the major indications of the technique. FDG PET/CT imaging should be performed as part of the initial staging of Hodgkin's disease and potentially curable non-Hodgkin's lymphomas, and possibly for the follicular lymphomas as well. Although the clinical impact at initial diagnosis is fairly limited, the initial metabolic picture will be of great value for assessing the response to treatment. Indeed, FDG PET/CT has become the cornerstone for evaluating the disease status after completion of treatment. Although a negative PET study has a very high predictive value and does not need any further confirmation, a positive PET study cannot be relied upon solely to modify the treatment and a confirmatory biopsy should be performed whenever possible. Furthermore, the predictive value of an interim PET study, performed early on during treatment i.e. after two or three courses of chemotherapy, appears very high, probably higher than when the PET is performed after treatment. However, the available data are not sufficient to support altering the treatment scheme depending on the PET results only. Several large studies are nevertheless under way, which should provide further clarifications in the near future.     

Tomographie par émission de positons au F-fluorodeoxyglucose dans la mise en évidence de la maladie veineuse thromboembolique

Purpose

Association of venous thromboembolism (VTE) and inflammation reported in the literature may allow the use of FDG PET/CT in the detection of thrombotic process. Published studies remain limited and contradictory. The aim was, therefore, to evaluate the performance of FDG PET/CT for the detection of VTE.

Patients and methods

Patients included in a prospective study evaluating FDG PET/CT for the detection of malignancy in patients with idiopathic VTE were analysed (MVTEP, PHRC 2008). PET/CT images were interpreted initially without and then retrospectively with knowledge of VTE locations.

Results

Hundred and fourteen patients were included in MVTEP study from March 13th 2009 to July 1st 2010. Forty-six patients (median age: 74 years [20-87], 27 males, 19 females) were analysed. No abnormal uptake was initially reported in pulmonary vessels. The retrospective analysis of pulmonary embolism locations did not demonstrate any significant difference in FDG uptake between embolic sites and controlateral vessels (P = 0.883). Initial analysis of lower limbs vessels demonstrated sensitivity and specificity of PET/CT for deep venous thrombosis (DVT) diagnosis of 15 and 99%. The metabolic activity of DVT was significantly higher than the activity of controlateral vessels (P < 0.005) but without showing any significant SUV threshold for DVT diagnosis.

Conclusion

In conclusion, there is insufficient evidence to suggest that FDG PET/CT could be accurate in detection of VTE. These results need to be completed in a larger study with shorter delay between VTE and FDG PET/CT.     

Évaluation des paramètres et méthode de contrôle de qualité de la correction d’atténuation en tomographie par émission de positons

ObjectiveThe aim of this study is to evaluate the performance of the Computed Tomography based Attenuation Correction (CTAC) for Positron Emission Tomography (PET) data. Attenuation maps containing linear attenuation coefficients at 511 keV (LAC_511 keV) are calculated by trilinear conversion of Hounsfield Units (HU) obtained from CT slices after matrix size-reduction and gaussian filtering. Our work focusses on this trilinear conversion.Materials and methodsCT slices of an electron density phantom, composed of 17 cylindrical inserts made of different tissue-equivalent materials, were acquired using a Discovery ST4^® PET-CT. Data were processed with a customized version of CT quality control software, giving automatically the experimental conversion function: LAC_511 keV = f(HU). Furthermore, data from patient datasets were assessed using both smoothed CT slices and attenuation maps.ResultsLAC_511 keV extracted from phantom data are in good correlation with the expected theoretical values, except for the standard 10 mm diameter dense bone insert, where the obtained CTAC values are underestimated. Assuming a sample size issue, similar acquisitions were performed with a special 30 mm-diameter dense bone insert, confirming the underestimation as a consequence of the sample size. This effect, caused partly by a too smooth Gaussian filter of the CT images, could be limited by reducing the strength of the filter. Measurements from patients’ data showed the same underestimation of CAL_511 keV for high-density tissues.ConclusionWe assessed an underestimation of the CTAC obtained-values related to the sample size of the insert. A quality control was developed to this effect.