Rappels physiques et outils d’optimisation de la qualité image et de la dose

Many parameters can affect the patient's dose and the CT image quality. It is therefore essential, in order to optimize the patient's dosimetry, to know the influence of these parameters as well as their link with the dose modulation tools.     

Évaluation de la faisabilité de la tomoscintigraphie myocardique précoce au sestamibi synchronisée à l’électrocardiogramme

BackgroundOur aim was to assess the feasibility of early acquisition (10 min) gated single photon emission computed tomography (SPECT) by comparison to conventional imaging at one hour.Methods and resultsOne hundred and four patients referred for exercise test and SPECT were included. Sequential imaging was started 10 min (SPECT 10) and 60 min (SPECT 60) after injection of the radiotracer (Tc-99m sestamibi). Stress myocardial perfusion was visually analyzed from 10 to 60 min stress by two experienced nuclear-cardiologists. Six patients were further excluded, because of high digestive accumulation: one patient at 10 min, three at 10 and 60 min, two at rest. The participants were classified as follows: group G1 (normal SPECT 10 and 60, n = 53), group G2 (abnormal SPECT 10 and/or SPECT 60, n = 45). The left ventricle ejection fraction (EF) and volumes (end-systolic and end-diastolic volumes, ESV, EDV) were calculated with the Cedars-Sinai program.ResultsQuality imaging was the same at SPECT 10 min and SPECT 60 min. Perfusion scores: G1 10 min = 0,4 versus G1 60 min = 0,4 (p = NS); G2 10 min = 10,2 versus G2 60 min = 10,1 (p = NS); EFG1 10 min = 71 ± 11% versus EFG1 60 min = 68 ± 10% (p = 4E-04); EFG2 10 min = 56 ± 15% versus EFG2 60 min = 53 ± 15% (p = 0,002); EDV G1 10 min = 72 ± 20 ml versus EDV G1 60 min = 76 ± 19 (p = 0,002); EDV G2 10 min = 98 ± 46 ml versus EDV G2 60 min = 105 ± 38 (p = 0,08); ESVG1 10 min = 22 ± 12 m versus ESV G1 60 min = 25 ± 12 (p = 9E-04); ESVG2 10 min = 47 ± 35 ml versus ESV G2 60 min = 53 ± 36 (p = 3E-04).ConclusionsThis study suggests that early gated Sestamibi SPECT after stress provides same perfusion analysis than classical late imaging.     

TEP/TDM au 68Ga-PSMA-11 quand la 18F-fluorocholine ne localise pas la récidive biologique du cancer de la prostate : à propos d’un cas et revue de la littérature

A rise in prostate-specific antigen serum level (PSA) is an increasing issue, which occurs in more than one third of the patients who underwent radical prostatectomy. Thus, imaging these patients is of importance in order to localize residual disease and then to propose suitable therapy. The usefulness of ¹⁸F-fluorocholine (FCH) PET/CT in this indication has been demonstrated for several years. Recently, specific ligands of the prostate-specific membrane antigen (PSMA), which is expressed by almost all prostate cancers, were labelled with PET radionuclides. ⁶⁸Ga-PSMA-11 (PSMA-11) PET/CT has been described as superior to FCH and conventional imaging to detect prostate cancer recurrence. We present the case of a patient with history of prostate cancer, treated by surgery, referred for a rise in PSA serum level and without any residual disease targeted neither on FCH, nor on pelvic MRI. The PSMA-11 PET/CT demonstrated a pelvic lymph node, which was suspect of recurrence and allowed to initiate a specific curative therapy, replacing the “palliative” hormonotherapy, which was planned. A short review of the literature on this topic, focusing on the published PSMA-11 performances and main known interpretation pitfalls.     

Utilité de la TEP au 18FDG dans l’épilepsie. Méthodes et indications

Positron emission tomography (PET) using ¹⁸fluorodeoxyglucose (¹⁸FDG) is currently used in presurgical work-up for drug-resistant partial epilepsies in children as in adults, in addition to MRI. Recent cameras with less than 5 mm spatial resolution allow to obtain thin slices (about 2 mm thickness) in 3D planes. ¹⁸FDG is intravenously injected at the mean dose of 3 MBq/kg of body weight in interictal and resting state, in a quiet, dimly lit environment and careful monitoring for head movements and ictal events. In children, sedation may be necessary. Image acquisition starts 30 min after injection and ended 15 to 20 min later. Semiquantitative analysis is visually assessed in clinical practice using colour scales. PET sensibility is improved by superimposition of metabolic imaging on MRI. Statistical analysis with SPM may be useful but comparison with health subjects database is required. In medial temporal lobe epilepsy associated with hippocampal sclerosis, hypometabolism ipsilateral to the epileptogenic focus is found in 70 to 90% of the cases and is predictive of surgical outcome. In other types of temporal and extratemporal epilepsy with negative MRI, focal hypometabolism can be detected, allowing identification of minor gyral abnormalities corresponding to focal cortical dysplasias. In such MRI negative cases, PET findings may improve surgical outcome.     

Évaluation de la TEP au 18F-FDG dans l’exploration de la récidive des carcinomes colorectaux

PurposeThe aim of the study was to evaluate the diagnostic performance, the prognosis factors and the therapeutic impact of 18F-FDG positron emission tomography (FDG-PET) in the detection of recurrent colorectal cancers.MethodsSixty PET/CT with 18F-FDG and CT were performed in 52 patients, at the Paul Papin cancer center between 2003 and 2005, following suspicion of colorectal cancer relapse. The FDG-PET impact on the clinical management was studied by examination of multidisciplinary concertations results. Survival analysis were realized with a mean follow up of 2.2 years.ResultsRecurrence was confirmed for 50 explorations by histologic (n = 32), radiologic (n = 14) or clinical (n = 4) findings. Twenty patients died during the time of the study. On a patient based analysis, FDG-PET sensitivity, specificity and overall accuracy were 90, 90, 90% respectively compared with 74, 50 and 70% for CT. FDG-PET changed the clinical management in 18 cases (30%). A positive FDG-PET signal, more than one hepatic lesion, more than two lymph node lesions detected on FDG-PET and more than two hepatic lesions on CT were characterized as bad prognostic factors for survival. Multivariate analysis showed that the only independent bad prognostic factor was the FDG-PET detection of more than two liver lesions.ConclusionThese results confirmed the important impact of FDG-PET in the clinical management of patients with a suspected recurrence of colorectal cancer.     

Préparation et contrôle de qualité de la solution injectable de gallium-68 édotréotide (DOTATOC (68Ga))

Radiopharmacists of the Nuclear Medicine department of hospital Tenon have prepared and controlled the ⁶⁸Ga-labeled DOTATOC, for 4 years, as part of a clinical research study. The aim of this article is to share our experience, since this activity is not yet developed in France. Radiolabelling of DOTATOC (⁶⁸Ga) requires the settling of a ⁶⁸Ge/⁶⁸Ga generator, which is connected to an automated PC-controlled radiopharmaceutical labelling device (Elusynth ⁶⁸Ga, Iason) and comprises several steps. Performed quality controls (QC) are those commonly used for radiopharmaceuticals including: appearance, pH, radiochemical purity (RCP), radionuclide purity (PRN) and determination of the physical half-life. Bacterial endotoxins and sterility tests are systematically done. We obtained a mean value of radiolabelling yield around 45%. The results of QC are always in accordance with the specifications. The preparation failed in 7% of the 195 DOTATOC (⁶⁸Ga), over the last 4 years. It is important to note that the preparation of DOTATOC (⁶⁸Ga) monopolizes the radiopharmacist during 3 hours. This radiolabelling technique can be easily applied to other peptides, in order to develop other ⁶⁸Ga-labelled PET tracers.     

Imagerie phénotypique et peptides radiomarqués au gallium-68 : au-delà des analogues de la somatostatine

Receptor targeting with radiolabeled peptides has become very important in nuclear oncology in the past few years. The most frequently used peptides in the clinic are analogs of somatostatin. However, other radiolabeled analogs have also been developed and assessed in vitro and in vivo and some of them are already in clinical use. For instance, radiolabeled analogs of alpha-melanocyte-stimulating hormone (alpha-MSH), neurotensin, vasoactive intestinal peptide (VIP), bombesin (BN), substance P (SP), cholecystokinin (CCK), integrins… This review focuses on gallium-68 radiolabeled peptides developed for PET imaging, except for somatostatin analogs, which are discussed in another article.     

Optimisation du protocole d’acquisition de la TEP à la fluorocholine dans la détection des lésions parathyroïdiennes

18F-Fluorocholine (FCH) PET/CT shows very promising potential for detection of hyperfunctioning parathyroid tumors. However, the optimal time to perform imaging after FCH administration has not yet been determined and protocols are highly variable. The aim of this study was to qualitatively and quantitatively compare 5, 10, 15, 20 and 60 min post-injection acquisition times in patients with primary hyperparathyroidism and equivocal traditional imaging. Thirty-one patients were included. Two observers retrospectively analyzed the five protocols. Any focal increase in FCH uptake was localized and graded on a discrete gradation scale between 1 and 5 to assess the likelihood of hyperfunctioning parathyroid tumors. Gold standard was histopathological findings for the 11 operated patients. Regarding quantitative analysis, ratio of SUVmax of parathyroid foci on SUVmean of thyroid background (as signal-to-noise ratio) were compared between protocols. After injection of 2.5 MBq/kg, FCH PET performed 60 min post-injection (2 min) had the best sensitivity and specificity by lesion (92% and 100% respectively and the best signal-to-noise ratio (median of 2). We suggest performing PET scan 60 min after injection, associated with early acquisition so as not to miss a wash-out hyperfunctioning parathyroid tumors.     

Intérêt de l’analyse de la morphologie fine et de la qualité nucléaire des spermatozoïdes dans le cadre des techniques d’AMP

Routine semen examination does not identify minor malformations of the sperm nucleus and chromatin architectural defects, which may be associated with ART outcome and cannot be detected by the embryologist even at 1000x magnification. Recent publications have demonstrated the advantages, compared to routine analysis, of a new method of real-time detailed morphological evaluation of motile spermatozoa: motile sperm organellar morphology examination (MSOME). MSOME is performed with an inverted light microscope equipped with high-power differential interference contrast optics enhanced by digital imaging to achieve a magnification of 10000x. To be considered morphologically normal, a sperm nucleus must have both a normal shape and a normal chromatin content. The aim of the present study was to combine MSOME and sperm DNA fragmentation characteristics to assess reproductive outcome. The study population consisted of the male partners of 52 couples referred for conventional IVF or split cycles (half IVF-half ICSI cycles) and exhibiting normal routine sperm parameters. Spermatozoa were analysed by examining the fine nuclear morphology and DNA integrity using the sperm chromatin dispersion test (SCD test), based on the principle that the deproteinized nuclei of spermatozoa with nonfragmented DNA show extended halos of DNA dispersion that are either absent or only minimally present in sperm nuclei with fragmented DNA. Fertilization rates were significantly lower in the group showing less than 8% of normal spermatozoa according to MSOME criteria, but early embryo development was not affected. Fine sperm morphology correlated with DNA fragmentation rate. These results demonstrate that the assessment of sperm nuclear normality by MSOME analysis and SCD test improves characterization of the semen sample and should be evaluated as a tool for allocating patients to specific assisted reproduction treatments.     

Apport de la TEP/TDM au 18FDG dans la stadification initiale et l’évaluation précoce de la réponse thérapeutique des rhabdomyosarcomes pédiatriques

PurposeThe objective of this study was to retrospectively evaluate the impact of positron emission tomography/computed tomography (PET/CT) using fluorine-18-fluorodeoxyglucose (FDG), in comparison with conventional imaging modalities (CIM), for initial staging and early therapy assessment in paediatric rhabdomyosarcoma.Patients and methodsPrior to treatment, 18 patients (age range, 9 months to 18 years) with histologically proven rhabdomyosarcoma underwent FDG PET/CT in addition to CIM (magnetic resonance imaging of primary site, whole body CT and bone scintigraphy). After three courses of chemotherapy, 12 patients underwent FDG PET/CT in addition to CIM. RECIST criteria and visual analysis of FDG uptake were used for assessment of response. The standard of reference was determined by an interdisciplinary tumor board based on imaging material, histopathology and follow-up data (median = 5 years).ResultsPET/CT sensitivity was superior to CIM's concerning lymph node involvement (100% versus 83%, respectively) and metastases detection (100% versus 50%, respectively). PET/CT results changed therapeutic management in 11% of cases. After three courses of chemotherapy, the rate of complete response was 66% with PET/CT versus 8% with CIM. Five percent of patients relapsed during follow-up (median = 5 years).ConclusionThis study confirms that PET/CT depicts important additional information in initial staging of paediatric rhabdomyosarcomas and suggests a superior prognostic value of PET/CT in early response to chemotherapy assessment.     

Place de la tomographie d’émission de positons (TEP) pour l’évaluation thérapeutique et le suivi du cancer du sein

Positron emission tomography (PET) with fluorodeoxyglucose (FDG) is a nuclear imaging method whose interest in oncology has only grown over the past fifteen years. This article summarizes the results in monitoring and therapeutic evaluation of breast cancer. For the search of locoregional or distant recurrence, the performance of FDG-PET are very interesting. The impact of FDG-PET on the therapeutic management is undeniable. For therapeutic evaluation, this imaging is useful to evaluate the neoadjuvant chemotherapy and hormonotherapy efficacy. FDG-PET is indicated in cases of suspected recurrence (clinical, biological or imaging suspicious). It is the most sensitive exam for the detection of bone or visceral metastases. It allows the re-staging during a relapse proved whether local or remote, and can change the therapeutic management.     

Développement et évaluation d’un algorithme de segmentation automatisée des ventricules gauche et droit sur des images ciné d’IRM

An automated segmentation of the left and right ventricles on cine MRI is presented here. A rectangular region around the object of interest is defined in the original image, a morphological filter is then applied that combines openings and closings on connected sets, providing an image with homogeneous regions, which is finally segmented with an active contour model. The algorithm was tested on two databases with an expert's segmentation on the ventricles. One of the databases was provided by the Multicentric Initiative for a Platform of Evaluation in Cardiac Imaging (IMPEIC) group. Results show a very satisfactory correlation between the area (given in mm²) of expertise (x) and the area of automated segmentation (y) of the left ventricle (y = 1.00x + 8.6, r = 0.99). First results on the right ventricle show more than 83% similarity. The systolic phase proved to be more difficult to segment, which could be taken into consideration by introducing time regularization criteria in the algorithm.     

Réduction des effets de la respiration en imagerie TEP pulmonaire par une acquisition synchronisée à la respiration associée à une TDM en apnée

Respiratory motion causes a spread of lesion uptake over a larger area in Positron Emission Tomography (PET) images for moving structures. When CT images are used for attenuation correction of emission data, this motion may alter the quantization of PET images. We present the clinical results of a respiratory-gated PET processing “CT-based” method, which aims to improve PET-CT coregistration by using an additional breath-hold CT (BH-CT). The CT-based protocol consisted in a 10-min List Mode respiratory-gated PET acquisition, followed by an end-expiration BH-CT acquisition. During these two examinations, the respiratory signal was recorded continuously. Eleven pulmonary lesions were studied. Patients underwent both a standard clinical PET protocol (free breathing) and the CT-based protocol. The respective performances of the CT-based and clinical PET methods were evaluated by comparing the distances between the lesions’ centroids on PET and CT images. SUV_MAX (Standardized Uptake Value) and volume variations were also investigated. The CT-based method showed a significant reduction (p = 0.049) of centroid distances (mean relative change versus standard method: 49%). We also noted a higher SUV_MAX (mean change: 39%). Lesion volumes were significantly lower (p = 0.026) in CT-based PET volumes (mean change: 43%) compared with standard ones. The CT-based method improves PET-CT coregistration of pulmonary lesions. This protocol should lead to more accurate attenuation correction and thus improve SUV measurement.     

Comparaison de différents indices métaboliques et de la méthode SULTAN dans l’évaluation de la réponse thérapeutique par TEP au 18FDG dans le cancer du sein métastatique

Objective18F-FDG PET is a valuable tool in the evaluation of therapeutic response in breast cancer. This retrospective study was designed to compare the performance of six metabolic indices and to define their optimal thresholds, in patients treated with chemotherapy or hormone therapy for metastatic breast cancer. The performances of a parametric analysis by SULTAN method were also evaluated.MethodsTwenty patients, who underwent from 2 to 7 PET during the follow-up were analyzed. For each target, six indices were measured: SUVmax (maximum Standardized Uptake Value), SUVpeak, SAM (Standardized Added Metabolic activity), metabolic volume (MV), SUVmean using an adaptive threshold, and TLG (total lesion glycolysis). The percentage change of each target between each PET was calculated. A method based on parametric imaging (SULTAN) was also applied to each patient. The results were compared to the gold standard, defined by clinical evaluation, biological and morphological imaging RECIST 1.1 criteria. A per-lesion and per-patient analysis were performed and the optimal thresholds for each indices were calculated.ResultsFor the per-lesion analysis, 61 targets and 111 evolutions with 67 responders (R) and 44 non-responders (NR) were studied. Using ROC curve analysis and intercomparison, SUVmax, SUVpeak and SUVmean were significantly better than SAM, TLG and VM (P < 0.05). Using the optimal thresholds of −21%, –21%, –34%, –48% and –23% for SUVmax, SUVpeak, SUVmean, SAM and TLG respectively, these five indices were significantly correlated with the gold standard. SUVmax, SUVpeak and SUVmean showed the best performances of sensitivity (88%, 87% and 78% respectively), specificity (93%, 93% and 98% respectively) and negative predictive value (NPV) (84%, 69% and 74% respectively). For the per-patient analysis, 42 pairs of PET with 22 R and 20 NR were studied. Only SUVmax and SUVpeak were correlated to gold standard with the 30%-PERCIST-threshold and with optimal thresholds with performances of sensitivity of 73% and 77%, specificity of 95% and NPV of 76% and 79%. Parametric analysis with SULTAN showed excellent performances in the per-lesion and per-patient analysis (sensitivity 84% and 82%, specificity 98% and 90%, NPV 80% and 82%, respectively).ConclusionSUVmax and SUVpeak appeared the best indices to evaluate metabolic response in metastatic breast cancer. The SULTAN method was a reliable method to assist interpretation.     

Rôle de la TEP au 18F-FDG dans l’évaluation des volumes cibles chez des patients atteints de CBNPC traités par radiochimiothérapie

Currently ¹⁸F-FDG-PET is the gold standard to evaluate tumor response after chemotherapy in patients with advanced or metastatic non-small cell lung cancer (NSCLC). PET can also determine the volumes to be treated by radiotherapy, in inoperable patients. The aim of our mixed (prospective and retrospective) study concerned 28 patients with NSCLC, was to quantify the variation of the metabolic activity of lesions and their volumes after chemotherapy. We also studied the impact of change of these volumes on the definition of radiotherapy target volumes. Patients with stage II–IV and inoperable NSCLC were included. Two PET scans were performed: before treatment (PET1), then after two to six courses of chemotherapy (PET2). Of the 28 patients included, we observed complete metabolic response in six patients (21%), partial metabolic response in 13 patients (46%), stable disease in seven patients (25%), and progressive metabolic disease in two patients (7%), according to the PERCIST criteria. We observed significant variation (P < 0.001) of metabolic activity (estimated by SULpeak or SUVmax) for primary tumor as well as for overall lesions between the two PET scans. Thus, the target volumes of radiotherapy decreased significantly (P < 0.01) in PET2. Our results confirm that ¹⁸F-FDG-PET is not only a powerful technique for treatment evaluation but also a useful tool for radiotherapy planning after chemotherapy, in the context of personalized treatments.     

Évaluation de la sidération myocardique post-effort immédiat par tomoscintigraphie myocardique au 99mTc-sestamibi couplée à l’ECG

AimRepeated episodes of myocardial stunning may lead to chronic ventricular dysfunction. We attempted to assess the parameters related to post-exercise stunning in patients undergoing gated SPECT.MethodsSix hundred patients undergoing a one-day stress/rest ^99mTc-sestamibi gated SPECT were studied. Stress imaging was acquired within 15 minutes after injection. Summed perfusion scores (SSS, SRS and SDS) were calculated using QPS, and LV function assessed using QGS. Stunning was defined as the association of ischemia (SSS ≥ 4 and SDS > 0) and a minimum of 5% decrease in post-stress EF.ResultsIschemia was found in 225 (37.5%) patients. Among these, 67 (30%) showed myocardial stunning. Patients with stunning had a lower rest ESV (47 ± 24 mL vs 65 ± 52 mL, p < 0.0003) and EDV (108 ± 35 mL vs 122 ± 66 mL, p = 0.03), an increased rest LVEF (58 ± 10% vs 52 ± 13%, p < 0.0001) and a decreased post-stress LVEF (49 ± 10% vs 53 ± 13%, p < 0.02) compared to patients with no stunning. The number of myocardial segments showing reversible perfusion defects was increased in patients with stunning (2.7 ± 2.6 vs 1.7 ± 2.1, p < 0.02). On logistic regression, an extent of ischemia greater than two segments and a rest EF greater than 45% were independent predictors of the occurrence of myocardial stunning in patients with ischemia.ConclusionsIn patients with ischemia, exercise-induced stunning was associated with an increased extent of ischemia but also preserved rest ventricular function.     

Intérêt de la TEP-FDG dans le syndrome d’hyper-IgG4 : à propos d’un cas et revue de la littérature

Hyper-IgG4 syndrome, or IgG4-related systemic disease (IgG4-RSD), is a recently described entity of fibro-inflammatory systemic damage. Multiorgan lesions can occur synchronously or metachronously in a same patient. The common histological features include a lymphoplasmacytic infiltration (especially to IgG4), and fibrosis. Elevated serum level of IgG4 is also often present. The main concerned organs are: pancreas, biliary ducts, mediastinal lymph nodes, peritoneum, lacrimal and salivary glands. We report a case of an unusual location of this disease at the nasophyrnx in a patient of 84 years for which the diagnosis was made through immunolabelling with IgG4 in lesions biopsied, and we illustrate the potential role of PET-FDG in this systemic disease.     

Hyperfixations costales bifocales découvertes à la TEP au fluorure (18F) de sodium lors de la stadification d’un cancer de la prostate

A prostate biopsy screening (PSA = 2 ng/mL) evidenced a prostate adenocarcinoma featuring a Gleason score of 8 (4 + 4) in a 62-year-old patient incurring an increased familial risk of prostate cancer. In order to stage the prostate adenocarcinoma, 2 PET scans were ordered. A PET/CT examination with FNa disclosed two hot spots on distinct ribs matching with heterogeneous sclerotic areas on low dose CT. A PET/CT examination with FDG disclosed a hypermetabolic focus of prostate left lobe and a weak intensity hypermetabolic focus of left ilio-obturator node but no bone metabolic abnormality. Staging was categorized distant (bone) metastatic disease upon FNa PET/CT findings. The patient benefited from pelvic external beam radiation therapy and hormone therapy. One year later, a PET/CT examination with FCH while patient was still on hormone therapy depicted a photopaenic area of prostate left lobe and a questionable hypermetabolic focus of right lobe but no bone metabolic abnormality. Retrospectively, bone lesions visible on PET with FNa were already conspicuous on plain X-rays and a CT examination performed a decade before. A new advice in a center specialized in bone and joint imaging suggested a benign condition for these protracted rib lesions even if the exact benign condition was elusive (fibrous dysplasia, aneurysmal bone cyst…). Two years later, the patient is symptom-free and his PSA level is 0.03 ng/mL.