Browsing by Author "Parafita, Rui"
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- Evaluation of SPECT imaging: a multi-center and multi-vendor phantom studyPublication . Gonçalves, Maria Inês Rebelo; Parafita, Rui; Costa, Mauro; Geão, Ana; Pereira, Edgar; Vieira, Lina OliveiraBackground: Single-photon emission computed tomography (SPECT) is a nuclear medicine (NM) imaging method sensitive to the evaluation and quantification of physiological processes in patients. However, there are different factors that affect qualitatively and quantitatively the SPECT images and, consequently, the reliability of the data. There is a degree of variability underlying the intrinsic performance of systems from the same or different manufacturers. In addition, the different configurations of the gamma cameras (GC) and the acquisition and reconstruction protocols used may lead to heterogeneity of results. This study compared SPECT images acquired in three GC from three NM centers, using the Jaszczak and NEMA IEC Body phantoms, filled with a homogeneous solution of technetium-99m. Acquisitions were performed in each GC, following the protocols used in the clinical practice of the respective NM center, and the images were analyzed and compared in terms of spatial resolution, sensitivity, noise, contrast, and contrast recovery (CR). Subsequently, the processing and reconstruction parameters were harmonized to assess their impact on the standardization of results. Results: With the clinical protocols, the images acquired with the three GC showed small differences in spatial resolution, noise, and contrast, with the greatest difference being observed in the quantitative accuracy, since the CR has achieved variabilities of 0.17 and 0.28, for different activity concentrations. This intersystem variability was reduced to 0.09 and 0.08 after reconstruction algorithm standardization. However, this change increased the differences in the contrast percentage. Conclusion: GC from different manufacturers showed the greatest heterogeneity of results, however, by eliminating possible sources of variation it is possible to reduce the differences between systems. It was demonstrated the need to include different parameters for the evaluation and comparison of SPECT images so that procedures can be established between the different NM centers to ensure a trade-off between the various parameters assessed here, as the improvement of some usually leads to the deterioration of others.
- Imobilização da região da cabeça por prototipagem rápida para fins de diagnóstico e terapêuticaPublication . Craveiro, D. S.; Loja, M. A.; Vieira, Lina; Sousa, Eva; Costa, Durval C.; Parafita, Rui; Rodrigues, J. A.Objetivo do estudo: Modelar e testar, por procedimentos de prototipagem rápida, máscaras de imobilização da cabeça através da imagem médica. Conclusões: Dispositivos de imobilização construídos por prototipagem rápida têm características favoráveis para aplicação em imobilização em diagnóstico e terapia. Para dispositivos de imobilização da cabeça as diferenças encontradas na análise estática realizada foram mínimas.
- Imobilização da região da cabeça por prototipagem rápida para fins de diagnóstico e terapêuticaPublication . Craveiro, D. S.; Loja, Amélia; Vieira, Lina; Sousa, Eva; C. Costa, Durval; Parafita, Rui; Rodrigues, José AlbertoObjetivo do estudo: Modelar e testar, por procedimentos de prototipagem rápida, máscaras de imobilização da cabeça através da imagem médica. Conclusões: Dispositivos de imobilização construídos por prototipagem rápida têm características favoráveis para aplicação em imobilização em diagnóstico e terapia. Para dispositivos de imobilização da cabeça as diferenças encontradas na análise estática realizada foram mínimas
- Minimisation of acquisition time in a TOF PET/CT scanner without compromising image qualityPublication . Oliveira, Joana; Parafita, Rui; Branco, SusanaSignificant improvements have been made in Positron Emission Tomography (PET) to enhance the image quality, namely, the development of time-of-flight (TOF) technology. This technique is useful to localize the emission point of the beta plus-emitter (β+) radiopharmaceutical inside the body, allowing better lesion contrast and leading to a short scan time. The main goal of this study is to investigate the shortest acquisition time without compromising the image quality in both a NEMA body phantom and patients, using a TOF PET/Computed Tomography (PET/CT) scanner and the radionuclide Gallium-68 (68Ga). Image quality parameters and quantification in terms of standardized uptake value (SUV) were acquired. A time between 45 and 60 s per bed position is proposed for future clinical practices.
- Minimisation of acquisition time in a TOF PET/CT scanner without compromising image qualityPublication . Oliveira, Joana; Parafita, Rui; Branco, SusanaIntroduction - Significant improvements have been made in Positron Emission Tomography/Computed Tomography (PET/CT) to enhance the image quality, namely, the development of time-of-flight (TOF) technology. This technique is useful to localize the emission point of the beta plus-emitter (β+) radiopharmaceutical inside the body, allowing better lesion contrast, especially for large patients, improving structural details and leading to a short scan time. The main goal of this study is to verify the shortest acquisition time per bed position, in a TOF PET scanner, without compromising the image quality, in both phantom and clinical imaging. Methods - For that purpose, images of a torso NEMA phantom were acquired with different acquisition times per bed position (30, 45, 60, 80 and 120 s) in a TOF PET/CT scanner (GEMINI TF 16, Philips), using Gallium-68 (68Ga) citrate. Clinical images were also acquired of an aleatory patient (male, 64 y) with 68Ga-prostate specific membrane antigen (68Ga-PSMA). Image quality parameters, such as signal-to-noise ratio (SNR), noise, contrast, contrast-to-noise ratio (CNR), contrast recovery coefficient (CRC) and quantification in terms of standardized uptake value (SUV) were acquired. Results - The increased contrast and CRC in larger spheres and with longer acquisition times produces an increase on the noise, leading to a decrease in SNR and CNR. In phantom imaging, SUVmax varied between 1.1 and 1.6 for background (normal uptake) and between 2.1 and 8.0 for spheres (abnormal uptake). A strong correlation was found for both SUVmax and SUVmean between the different acquisition times (R>0.7). Inpatient imaging, spleen showed higher SNR, contrast, noise, and CNR than liver. Median SUVmax was 7.1 for liver, 9.8 for spleen and 1.8 for bone. Conclusions - A time between 45 and 60 s per bed position is proposed for future clinical practices, allowing schedule more scans per day, contributing to an optimization of protocols without compromising the image quality.
- Níveis de referência de diagnóstico em mamografiaPublication . Martins, Bruno; Machado, Nuno; Parafita, Rui; Carvoeiras, Pedro; Azevedo, João; Trindade, Hugo; Pinto, Ildefonso; Teixeira, NunoNíveis de exposição em exames de mamografia: 1) os NRD permitem a orientação em relação às doses a utilizar num exame radiológico específico para um doente padrão; 2) não representam um limite de dose; 3) são normalmente definidos pelo valor que engloba 75% das doses mais baixas da população alvo, para um determinado exame; 4) permitem uma triagem dos resultados observados, com o fim de evitar exposições injustificadamente altas ou baixas; 5) promover a utilização de uma pequena gama de valores que representem uma boa prática para uma imagem médica específica.
- Using 3D anthropometric data for the modelling of customised head immobilisation masksPublication . Loja, Amélia; Sousa, E.; Vieira, Lina Oliveira; Craveiro, D.S.; Parafita, Rui; C. Costa, Durval; Costa, DMSHead immobilization thermoplastic masks for radiotherapy purposes involve a distressful modelling procedure for the patient. To assess the possibility of using different acquisition and reconstruction methods to obtain a 3Dskin surface model of PIXY-phantom-head and to present a proposal of an alternative head immobilisation mask prototype. Phantom head geometry acquisitions using: computed tomography (reconstructed with ImageJ and Osirix); and 3DLaserScanner (reconstructed with SolidWorks). From these reconstructed surface models a set of landmarks was measured and subsequently compared with physical measurements obtained with a Rosscraft-Calliper. For statistical evaluation, relative deviations graphics and Friedman-test for non-parametrical paired samples were used, with a significance level of 5%. For a first assessment of the proposed mask performance, a radiotransparent material was considered, the strength and stiffness evaluation being performed using the finite element method. There are small differences between all the acquisitions and reconstructions methods and the physical measurements, statistically significant differences (X2F(6)) = 6.863, p=0.334) were not found. The proposed mask performed well from the strength and stiffness perspectives, leading to the desired immobilisation aim. The immobilisation mask design proposal may be an effective alternative to the present completely hand-made situation, which presents a high-degree of discomfort and stress to the patients.