Max Lonneux

Tri-dimensional automatic segmentation of PET volumes based on measured source-to-background ratios: influence of reconstruction algorithms.

A method for automatic volume segmentation of functional imaging based on a relationship between source-to-background ratio and the iso-activity level to be used is described. Such method, which has been established with radioactive spheres in a phantom, is independent of the a priori knowledge of the lesion of interest and is valid for small (>2 ml) and/or poorly contrasted (S/B>1.5) lesions. Accuracy varies slightly with the image reconstruction algorithm used.

MRI-Based Attenuation Correction for PET/MRI Using Ultrashort Echo Time Sequences

One of the challenges in PET/MRI is the derivation of an attenuation map to correct the PET image for attenuation. Different methods have been suggested for deriving the attenuation map from an MR image. Because the low signal intensity of cortical bone on images acquired with conventional MRI sequences makes it difficult to detect this tissue type, these methods rely on some sort of anatomic precondition to predict the attenuation map, raising the question of whether these methods will be usable in the clinic when patients may exhibit anatomic abnormalities. Methods: We propose the use of the transverse relaxation rate, derived from images acquired with an ultrashort echo time sequence to classify the voxels into 1 of 3 tissue classes (bone, soft tissue, or air), without making any assumptions on patient anatomy. Each voxel is assigned a linear attenuation coefficient corresponding to its tissue class. A reference CT scan is used to determine the voxel-by-voxel accuracy of the proposed method. The overall accuracy of the MRI-based attenuation correction is evaluated using a method that takes into account the nonlocal effects of attenuation correction. Results: As a proof of concept, the head of a pig was used as a phantom for imaging. The new method yielded a correct tissue classification in 90% of the voxels. Five human brain PET/CT and MRI datasets were also processed, yielding slightly worse voxel-by-voxel performance, compared to a CT-derived attenuation map. The PET datasets were reconstructed using the segmented MRI attenuation map derived with the new method, and the resulting images were compared with segmented CT-based attenuation correction. An average error of around 5% was found in the brain. Conclusion: The feasibility of using the transverse relaxation rate map derived from ultrashort echo time MR images for the estimation of the attenuation map was shown on phantom and clinical brain data. The results indicate that the new method, compared with CT-based attenuation correction, yields clinically acceptable errors. The proposed method does not make any assumptions about patient anatomy and could therefore also be used in cases in which anatomic abnormalities are present.

Positron Emission Tomography With [18F]Fluorodeoxyglucose Improves Staging and Patient Management in Patients With Head and Neck Squamous Cell Carcinoma: A Multicenter Prospective Study

PURPOSE To address the impact of positron emission tomography with [(18)F]fluorodeoxyglucose (PET-FDG) on the initial staging and management of patients with head and neck squamous cell carcinoma (HNSCC). PATIENTS AND METHODS This multicenter, prospective study included 233 patients with newly diagnosed and untreated HNSCC. TNM stage and therapeutic decision were first determined based on the conventional work-up (including physical examination, computed tomography [CT]/magnetic resonance imaging of the head and neck region, and thoracic CT) and sealed in envelope 1. Whole-body PET-FDG was then performed, and subsequent TNM stage and therapeutic decision were written in envelope 2. Changes in TNM stages and in patient management as a result of PET-FDG imaging were recorded. Clinical outcome and histopathology were used as gold standards to validate the TNM stage. Conventional and PET stages were compared using the McNemar test. Results Conventional and PET stage were discordant in 100 (43%) of 233 patients. PET proved to be accurate in 47 patients and inaccurate in 13 patients. TNM status was left unconfirmed in 40 patients because no therapeutic change was expected from the stage difference. Conventional + PET TNM classification (envelope 2) was significantly more accurate than conventional classification (envelope 1; P < .0001, McNemar test). PET-FDG altered the therapeutic plan in 32 (13.7%) of 233 patients. CONCLUSION Adding whole-body PET-FDG to the pretherapeutic conventional staging of HNSCC improved the TNM classification of the disease and altered the management of 13.7% of patients. These findings support the implementation of PET-FDG in the routine imaging work-up of HNSCC.

Positron Emission Tomography With Fluorodeoxyglucose for Suspected Head and Neck Tumor Recurrence in the Symptomatic Patient

Objective To analyze the impact of positron emission tomography with fluorodeoxyglucose (FDG‐PET) in the treatment of patients suspected of having head and neck cancer recurrence.

Role of PET in the Initial Staging of Cutaneous Malignant Melanoma: Systematic Review

PURPOSE To calculate summary estimates of the diagnostic performance of fluorine 18 fluorodeoxyglucose (FDG) positron emission tomographic (PET) imaging in the initial staging of cutaneous malignant melanoma (CMM), following the new American Joint Committee on Cancer (AJCC) staging classification on per-patient and per-lesion bases. MATERIALS AND METHODS MEDLINE, EMBASE, Web of Science, and Cochrane Database of Systematic Reviews databases, and reference lists of reviews and included papers were searched, without any language restrictions, for relevant articles published before March 2007. Two reviewers independently assessed study eligibility and methodologic quality by using the quality assessment of diagnostic accuracy studies checklist. A pooled random effect was estimated and a fixed coefficient regression model was used to explore the existing heterogeneity. RESULTS Twenty-eight studies involving 2905 patients met the inclusion criteria. The pooled estimates of FDG PET for the detection of metastasis in the initial staging of CMM were sensitivity, 83% (95% confidence interval [CI]: 81%, 84%); specificity, 85% (95% CI: 83%, 87%); positive likelihood ratio (LR), 4.56 (95% CI: 3.12, 6.64); negative LR, 0.27 (95% CI: 0.18, 0.40); and diagnostic odds ratio, 19.8 (95% CI: 10.8, 36.4). Results from eight studies suggested that FDG PET was associated with 33% disease management changes (range, 15%-64%). CONCLUSION There is good preliminary evidence that FDG PET is useful for the initial staging of patients with CMM, especially as adjunctive role in AJCC stages III and IV, to help detect deep soft-tissue, lymph node, and visceral metastases. FDG PET-computed tomographic imaging seemed to be more precise than PET alone, as suggested by four eligible studies. Further evaluation by using a well-designed prospective study, with clinical outcome-focused measures and cost effectiveness analysis, is needed to clarify the appropriate role of FDG PET in CMM staging. SUPPLEMENTAL MATERIAL http://radiology.rsnajnls.org/cgi/content/full/249/3/836/DC1.

Prognostic value of FDG uptake in early stage non-small cell lung cancer

BACKGROUND Non-small cell lung cancer (NSCLC) has a poor prognosis even for early stages of the disease (stage I and II). We studied the prognostic value of PET FDG in patients with completely resected stage I and II NSCLC. METHODS Retrospective study of 96 patients with NSCLC whose staging included 18F-FDG PET (fluoro deoxy glucose positron emission tomography). Histopathological stage was either stage I (75) or stage II (n=21). FDG uptake was measured as maximal standardized uptake value for body weight (SUVmax). Mean follow-up was 45+/-30 months (1-142 months). Overall and cancer-free survival rates were recorded. RESULTS SUVmax were higher for stage II than for stage I (10.5+/-4.5 vs 8.5+/-5, p=0.04). Mean tumor volumes were equivalent for both stages (33 cm3, p=0.18), excluding a partial volume effect. The median SUVmax in the whole study population was 7.8. The median survival was significantly longer in patients with a lower (SUVmax<or=7.8) FDG uptake (127 months vs 69 months, p=0.001). For stage I tumors (n=75), high FDG uptake was significantly associated with reduced median survival: 127 months if SUVmax<or=7.8 and 69 months if SUVmax>7.8 (p=0.001). For stage II tumors (n=21), no statistical difference was observed: 72 months vs 40 months for SUVmax<or=7.8 and for SUVmax>7.8, respectively (p=0.11), although there was a clear trend towards reduced survival for highly metabolic tumors. Disease-free survival was also significantly better for lower metabolic tumors: 96.1 months vs 87.7 months (p=0.01). CONCLUSION High FDG uptake is associated with reduced overall survival and disease-free survival of patients with completely resected stage I-II NSCLC. Whether patients with highly metabolic tumors should undergo a closer postoperative surveillance or adjuvant chemotherapy has to be addressed in a properly designed prospective trial.

PET-FDG scan enhances but does not replace preoperative surgical staging in non-small cell lung carcinoma.

OBJECTIVE To assess the effectiveness of positron emission tomography with radiolabeled [18F]-2-fluoro-deoxy-D-glucose (PET-FDG) imaging in mediastinal lymph node (LN) staging for non-small cell lung carcinoma (NSCLC) and to compare it to conventional clinical and surgical staging. METHODS From June 1998 to February 2000, we enrolled 64 potentially resectable NSCLC patients in a prospective study of PET-FDG imaging of the mediastinum to assess LN involvement. Results of this technique were compared to conventional clinical and surgical staging. Diagnostic efficacy was determined by calculating sensitivity, specificity, overall accuracy, and positive and negative predictive values for each method. RESULTS PET-FDG imaging correctly identified nodal stage (N0-N1 vs. N2) in 50 out of 61 patients (82%), overstaging occurred in eight patients (13%), and understaging in three patients (4.9%). The sensitivity, specificity, accuracy, and positive and negative predictive values for PET-FDG scan imaging were 67, 85, 82, 43, and 93.6%, respectively. Conventional staging correctly identified nodal stage (N0-N1 vs. N2) in 51 out of 62 patients (82%), overstaging occurred in five patients (8.1%), and understaging in six patients (9.7%). The sensitivity, specificity, accuracy, and positive and negative predictive values for conventional staging were 33, 90.6, 82, 37, and 89%, respectively. With regard to N2 disease, conventional staging showed a poor sensitivity (33%). Indeed, six out of 64 patients were understaged for mediastinal LN involvement. Even though the improvement was not statistically significant (McNemar P=0.08), the combined use of PET-FDG scan and computerized tomography (CT) scan allowed a two-fold increase in the sensitivity of our clinical preoperative staging. Moreover, relying on the PET-scan high negative predictive value might have contributed to a three-fold decrease in the number of required surgical staging procedures. CONCLUSIONS Our study shows that the PET-FDG imaging strength lies in its very high negative predictive value and increased sensitivity. In this study, the overall accuracy of PET-FDG scan (82%) was lower than previously reported. Combined with chest CT-scan preoperatively, it may alleviate the need for surgical staging when PET-FDG studies of the mediastinum are negative. However, with a positive PET-FDG scan result, further diagnostic procedures should be pursued in order to avoid overstaging and allow better surgical patient selection.

Preoperative Assessment of Pancreatic Tumors Using Magnetic Resonance Imaging, Endoscopic Ultrasonography, Positron Emission Tomography and Laparoscopy

Background: The appropriate preoperative evaluation of a pancreatic tumor remains a matter of debate. Methods: We retrospectively evaluated an institutional strategy including magnetic resonance imaging (MRI), endoscopic ultrasonography (EUS), positron emission tomography (PET) and laparoscopy (LAP) for detection and staging of pancreatic tumors suspected to be malignant. Results: In a consecutive series of 59 patients screened by MRI, PET, EUS and LAP between July 1998 and November 2002, 48 patients were found to bear pancreatic adenocarcinoma and surgery was performed in 27 of them. For tumor detection, the sensitivity of EUS was superior to MRI and PET (98 vs. 87.5 and 87.5%, respectively, p = 0.13). MRI best assessed loco-regional staging, i.e. arterial involvement. For the detection of distant metastases, the sensitivity of all preoperative examinations taken separately was low. When laparotomy was performed with a curative intent according to all four examinations, occult metastasis or carcinomatosis was discovered in 7/27 patients and the overall predictive value of resectability was thus 74%. Five-year and median survival were significantly better in resected vs. non-resected patients (39% and 26 months vs. 0% and 8 months, p = 0.0006). Conclusions: MRI can be recommended has the first examination in patients bearing pancreatic tumors, complemented by EUS if the findings of MRI are non-conclusive. For detection of distant metastasis, only the combination of all preoperative examination was proved to be more accurate than a single technique.

FDG-PET improves the staging and selection of patients with recurrent colorectal cancer

Abstract Whole-body fluorine-18 fluorodeoxyglucose positron emission tomography (FDG-PET) has proved effective in the diagnosis and staging of recurrent colorectal cancer. In this study, we analysed how PET affects the management of patients with recurrent colorectal cancer by permitting more accurate selection of candidates for curative resection. The data of 79 patients with known or suspected recurrent colorectal cancer were analysed. Conventional imaging modalities (CIM) and PET results were compared with regard to their accuracy in determining the extent and the resectability of tumour recurrence. Recurrence was demonstrated in 68 of the 79 patients. The data indicate that PET was superior to CIM for detection of recurrence at all sites except the liver. Based on the CIM+PET staging, surgery with curative intent was proposed in 39 patients and was indeed achieved in 31 of them (80%). PET was more accurate than CIM alone in predicting the resectability or non-resectability of the recurrence (82% vs 68%, P=0.02). It is concluded that whole-body FDG-PET is highly sensitive for both the diagnosis and the staging of patients with recurrent colorectal cancer. Its use in conjunction with conventional imaging procedures results in a more accurate selection of patients for surgical treatment with curative intent.

Fast iterative image reconstruction of 3D PET data

For count-limited PET imaging protocols, two different approaches to reducing statistical noise are volume, or 3D, imaging to increase sensitivity, and statistical reconstruction methods to reduce noise propagation. These two approaches have largely been developed independently, likely due to the perception of the large computational demands of iterative 3D reconstruction methods. The authors present results of combining the sensitivity of 3D PET imaging with the noise reduction and reconstruction speed of 2D iterative image reconstruction methods. This combination is made possible by using the recently-developed Fourier rebinning technique (FORE), which accurately and noiselessly rebins 3D PET data into a 2D data set. The resulting 2D sinograms are then reconstructed independently by the ordered-subset EM (OSEM) iterative reconstruction method, although any other 2D reconstruction algorithm could be used. The authors demonstrate significant improvements in image quality for whole-body 3D PET scans by using the FORE+OSEM approach compared with the standard 3D Reprojection (3DRP) algorithm. In addition, the FORE+OSEM approach involves only 2D reconstruction and it therefore requires considerably less reconstruction time than the 3DRP algorithm, or any fully 3D statistical reconstruction algorithm.