Lesion detection performance in an anthropomorphic chest phantom: comparative analysis of low-dose CT data on two hybrid imaging systems

Introduction: multimodality environment; requirement for greater understanding of the imaging technologies used, the limitations of these technologies, and how to best interpret the results; dose optimization; introduction of new techniques; current practice and best practice; incidental findings, in low-dose CT images obtained as part of the hybrid imaging process, are an increasing phenomenon with advancing CT technology; resultant ethical and medico-legal dilemmas; understanding limitations of these procedures important when reporting images and recommending follow-up; free-response observer performance study was used to evaluate lesion detection in low-dose CT images obtained during attenuation correction acquisitions for myocardial perfusion imaging, on two hybrid imaging systems.

Lesion detection performance: comparative analysis of low-dose CT data of the chest on two hybrid imaging systems

Incidental findings on low-dose CT images obtained during hybrid imaging are an increasing phenomenon as CT technology advances. Understanding the diagnostic value of incidental findings along with the technical limitations is important when reporting image results and recommending follow-up, which may result in an additional radiation dose from further diagnostic imaging and an increase in patient anxiety. This study assessed lesions incidentally detected on CT images acquired for attenuation correction on two SPECT/CT systems. Methods: An anthropomorphic chest phantom containing simulated lesions of varying size and density was imaged on an Infinia Hawkeye 4 and a Symbia T6 using the low-dose CT settings applied for attenuation correction acquisitions in myocardial perfusion imaging. Twenty-two interpreters assessed 46 images from each SPECT/CT system (15 normal images and 31 abnormal images; 41 lesions). Data were evaluated using a jackknife alternative free-response receiver-operating-characteristic analysis (JAFROC). Results: JAFROC analysis showed a significant difference (P < 0.0001) in lesion detection, with the figures of merit being 0.599 (95% confidence interval, 0.568, 0.631) and 0.810 (95% confidence interval, 0.781, 0.839) for the Infinia Hawkeye 4 and Symbia T6, respectively. Lesion detection on the Infinia Hawkeye 4 was generally limited to larger, higher-density lesions. The Symbia T6 allowed improved detection rates for midsized lesions and some lower-density lesions. However, interpreters struggled to detect small (5 mm) lesions on both image sets, irrespective of density. Conclusion: Lesion detection is more reliable on low-dose CT images from the Symbia T6 than from the Infinia Hawkeye 4. This phantom-based study gives an indication of potential lesion detection in the clinical context as shown by two commonly used SPECT/CT systems, which may assist the clinician in determining whether further diagnostic imaging is justified.

Otimiza����o da imagem em tomografia computorizada no exame de t��rax

Mestrado em Radia����es Aplicadas ��s Tecnologias da Sa��de. ��rea de especializa����o: Imagem Digital.

PET/CT com 18-fluor-fluorodeoxiglucose no seguimento do melanoma maligno cut��neo

Introdu����o ��� O melanoma maligno cut��neo (MMC) �� considerado uma das mais letais neoplasias e no seu seguimento recorre-se, para al��m dos exames cl��nicos e da an��lise de marcadores tumorais, a diversos m��todos imagiol��gicos, como �� o exame Tomografia por Emiss��o de Positr��es/Tomografia Computorizada (PET/CT, do acr��nimo ingl��s Positron Emission Tomography/Computed Tomography) com 18fluor-fluorodeoxiglucose (18F-FDG). O presente estudo tem como objetivo avaliar a utilidade da PET/CT relativamente �� an��lise da extens��o e �� suspeita de recidiva do MMC, comparando os achados imagiol��gicos com os descritos em estudos CT. Metodologia ��� Estudo retrospetivo de 62 estudos PET/CT realizados em 50 pacientes diagnosticados com MMC. Excluiu-se um estudo cujo resultado era duvidoso (n��dulo pulmonar). As informa����es relativas aos resultados dos estudos anatomopatol��gicos e dos exames imagiol��gicos foram obtidas atrav��s da hist��ria cl��nica e dos relat��rios m��dicos dos estudos CT e PET/CT. Foi criada uma base de dados com os dados recolhidos atrav��s do software Excel e foi efetuada uma an��lise estat��stica descritiva. Resultados ��� Dos estudos PET/CT analisados, 31 foram considerados verdadeiros positivos (VP), 28 verdadeiros negativos (VN), um falso positivo (FP) e um falso negativo (FN). A sensibilidade, especificidade, o valor preditivo positivo (VPP), o valor preditivo negativo (VPN) e a exatid��o da PET/CT para o estadiamento e avalia����o de suspeita de recidiva no MMC s��o, respetivamente, 96,9%, 96,6%, 96,9%, 96,6% e 96,7%. Dos resultados da CT considerados na an��lise estat��stica, 14 corresponderam a VP, 12 a VN, tr��s a FP e cinco a FN. A sensibilidade, especificidade, o VPP e o VPN e a exatid��o da CT para o estadiamento e avalia����o de suspeita de recidiva no MMC s��o, respetivamente, 73,7%, 80,0%, 82,4%, 70,6% e 76,5%. Comparativamente aos resultados CT, a PET/CT permitiu uma mudan��a na atitude terap��utica em 23% dos estudos. Conclus��o ��� A PET/CT �� um exame ��til na avalia����o do MMC, caracterizando-se por uma maior acuidade diagn��stica no estadiamento e na avalia����o de suspeita de recidiva do MMC comparativamente �� CT isoladamente.

Otimiza����o do co-registo metabolismo-morfologia em estudos de PET/CT com 18F-DG de n��dulos pulmonares: compara����o de dois protocolos - 4D vs CT lento

Mestrado em Medicina Nuclear - ��rea de especializa����o: Tomografia por Emiss��o de Positr��es.

Modelo de data mining para dete����o de embolias pulmonares

Trabalho de Projeto para obten����o do grau de Mestre em Engenharia Inform��tica e de Computadores

A comparison of Sinogram Affirmed Iterative Reconstruction and filtered back projection on image quality and dose reduction in paediatric head CT: a phantom study

Background: Computed tomography (CT) is one of the most used modalities for diagnostics in paediatric populations, which is a concern as it also delivers a high patient dose. Research has focused on developing computer algorithms that provide better image quality at lower dose. The iterative reconstruction algorithm Sinogram-Affirmed Iterative Reconstruction (SAFIRE) was introduced as a new technique that reduces noise to increase image quality. Purpose: The aim of this study is to compare SAFIRE with the current gold standard, Filtered Back Projection (FBP), and assess whether SAFIRE alone permits a reduction in dose while maintaining image quality in paediatric head CT. Methods: Images were collected using a paediatric head phantom using a SIEMENS SOMATOM PERSPECTIVE 128 modulated acquisition. 54 images were reconstructed using FBP and 5 different strengths of SAFIRE. Objective measures of image quality were determined by measuring SNR and CNR. Visual measures of image quality were determined by 17 observers with different radiographic experiences. Images were randomized and displayed using 2AFC; observers scored the images answering 5 questions using a Likert scale. Results: At different dose levels, SAFIRE significantly increased SNR (up to 54%) in the acquired images compared to FBP at 80kVp (5.2-8.4), 110kVp (8.2-12.3), 130kVp (8.8-13.1). Visual image quality was higher with increasing SAFIRE strength. The highest image quality was scored with SAFIRE level 3 and higher. Conclusion: The SAFIRE algorithm is suitable for image noise reduction in paediatric head CT. Our data demonstrates that SAFIRE enhances SNR while reducing noise with a possible reduction of dose of 68%.