RESUMO
While point spread function (PSF)-based positron emission tomography (PET) reconstruction effectively improves the spatial resolution and image quality of PET, it may damage its quantitative properties by producing edge artifacts, or Gibbs artifacts, which appear to cause overestimation of regional radioactivity concentration. In this report, we investigated how edge artifacts produce negative effects on the quantitative properties of PET. Experiments with a National Electrical Manufacturers Association (NEMA) phantom, containing radioactive spheres of a variety of sizes and background filled with cold air or water, or radioactive solutions, showed that profiles modified by edge artifacts were reproducible regardless of background µ values, and the effects of edge artifacts increased with increasing sphere-to-background radioactivity concentration ratio (S/B ratio). Profiles were also affected by edge artifacts in complex fashion in response to variable combinations of sphere sizes and S/B ratios; and central single-peak overestimation up to 50% was occasionally noted in relatively small spheres with high S/B ratios. Effects of edge artifacts were obscured in spheres with low S/B ratios. In patient images with a variety of focal lesions, areas of higher radioactivity accumulation were generally more enhanced by edge artifacts, but the effects were variable depending on the size of and accumulation in the lesion. PET images generated using PSF-based reconstruction are therefore not appropriate for the evaluation of SUV.
Assuntos
Imagens de Fantasmas , Tomografia por Emissão de Pósitrons/métodos , Humanos , Tomografia Computadorizada por Raios X/métodosRESUMO
We showed scanner dependence of brain (18)F-FDG and (11)C-PiB images by using phantom examination with nine kinds of positron emission tomography (PET) scanners. We used two types of phantoms, cylindrical phantom with 15 cm inside diameter and three-dimensional (3D) brain phantom, and we set the body phantom on the bed to examine the effect of scatter and random coefficients from outside of the axial field of view (AFOV). Radioactivity and distance of the two phantoms were determined by a pilot study to obtain a condition similar to the clinical study. Axial uniformity was evaluated by circular region of interest (ROI) of 12 cm diameter, set in the center of the reconstruction image of the cylindrical phantom. As a result, the standardized uptake value (SUV) was lower than the true value in some scanners, and there was a scanner in which the axial uniformity was deteriorated by high radioactivity outside the AFOV. In the cylindrical phantom, the axial uniformity of the scanner was improved using the new dead-time correction method; however, it was not improved in the 3D brain phantom. Quality-controlled PET scanners are important to maintain constant levels for multicenter studies.
Assuntos
Encéfalo/diagnóstico por imagem , Imagens de Fantasmas , Tomografia por Emissão de Pósitrons/instrumentação , Doença de Alzheimer/diagnóstico por imagem , Compostos de Anilina , Fluordesoxiglucose F18 , Humanos , Controle de Qualidade , Compostos Radiofarmacêuticos , TiazóisRESUMO
UNLABELLED: This study was designed to compare tumor (18)F-FDG uptake between a single 20-s acquisition of deep-inspiration breath-hold PET/CT and free-breathing PET/CT for lung cancer. METHODS: Before the clinical study, a phantom study was performed to determine the optimum breath-hold time for the PET scan. We studied 47 patients with lung cancer who underwent free-breathing PET/CT with the standard clinical protocol, followed by deep-inspiration breath-hold PET/CT of the thorax. In breath-hold PET/CT, the patients were asked to hold their breath in deep inspiration for 10 s during the CT scan and for 20 s during the PET scan. Maximum tumor (18)F-FDG standardized uptake value (SUVmax) was measured in free-breathing PET and breath-hold PET, and the percentage difference between these 2 values was calculated. RESULTS: Breath-hold PET showed a significant increase in SUVmax, as compared with free-breathing PET (8.26 +/- 4.59 vs. 11.25 +/- 7.24, P < 0.0001). The mean difference in SUVmax was 39.5% +/- 43.4%, and the range was 2.9%-248.3%. The difference in SUVmax was significant when compared between tumors in the upper lung (n = 22) and tumors in the lower lung (n = 25) (24.4% +/- 17.7% vs. 52.9% +/- 54.3%, P = 0.0077). The mean tumor size of the group with a high SUVmax difference (n = 13) was significantly smaller than that of the group with a low SUVmax difference (n = 34) (2.45 +/- 0.87 cm vs. 3.21 +/- 1.22 cm, P = 0.043), using a cutoff of 39.5%. CONCLUSION: The single 20-s acquisition of breath-hold PET/CT enabled more precise measurement of SUVmax, especially in the lower lung field and for small tumors, which may be affected by respiratory motion. This technique is feasible in the clinical setting and requires only a minor increase in examination time.
Assuntos
Inalação , Neoplasias Pulmonares/diagnóstico , Neoplasias Pulmonares/fisiopatologia , Tomografia por Emissão de Pósitrons/métodos , Tomografia Computadorizada por Raios X/métodos , Idoso , Idoso de 80 Anos ou mais , Estudos de Viabilidade , Feminino , Fluordesoxiglucose F18/metabolismo , Humanos , Neoplasias Pulmonares/metabolismo , Masculino , Pessoa de Meia-Idade , Imagens de Fantasmas , Fatores de TempoRESUMO
OBJECTIVE: This study was designed to assess whether tumor uptake of (18)F-FDG (FDG) expressed as the standardized uptake value (SUV) can be used to predict survival in patients with head and neck cancer. Furthermore, a prognostic maximum SUV was determined with univariate and bivariate analyses. CONCLUSION: Low SUVs (= 7.0) predicted significantly higher rates of 2-year local control (p = 0.0067) and disease-free survival (p = 0.0051) as compared with high SUVs (> 7.0). In the Cox proportional hazards model, tumor SUV was a significant and independent predictor of local control (p = 0.022) and disease-free survival (p = 0.019). In addition, in the group of high SUV, high T stage was more associated with poorer outcome than low T stage (p = 0.0502). Therefore, patients with higher tumor FDG uptake should be considered for a more aggressive treatment approach.