Influence of reconstruction parameters during filtered backprojection and ordered-subset expectation maximization in the measurement of the left-ventricular volumes and function during gated SPECT

A crucial method for investigating patients with coronary artery disease (CAD) is the calculation of the left ventricular ejection fraction (LVEF). It is, consequently, imperative to precisely estimate the value of LVEF--a process that can be done with myocardial perfusion scintigraphy. Therefore, the present study aimed to establish and compare the estimation performance of the quantitative parameters of the reconstruction methods filtered backprojection (FBP) and ordered-subset expectation maximization (OSEM). Methods: A beating-heart phantom with known values of end-diastolic volume, end-systolic volume, and LVEF was used. Quantitative gated SPECT/quantitative perfusion SPECT software was used to obtain these quantitative parameters in a semiautomatic mode. The Butterworth filter was used in FBP, with the cutoff frequencies between 0.2 and 0.8 cycles per pixel combined with the orders of 5, 10, 15, and 20. Sixty-three reconstructions were performed using 2, 4, 6, 8, 10, 12, and 16 OSEM subsets, combined with several iterations: 2, 4, 6, 8, 10, 12, 16, 32, and 64. Results: With FBP, the values of end-diastolic, end-systolic, and the stroke volumes rise as the cutoff frequency increases, whereas the value of LVEF diminishes. This same pattern is verified with the OSEM reconstruction. However, with OSEM there is a more precise estimation of the quantitative parameters, especially with the combinations 2 iterations �� 10 subsets and 2 iterations �� 12 subsets. Conclusion: The OSEM reconstruction presents better estimations of the quantitative parameters than does FBP. This study recommends the use of 2 iterations with 10 or 12 subsets for OSEM and a cutoff frequency of 0.5 cycles per pixel with the orders 5, 10, or 15 for FBP as the best estimations for the left ventricular volumes and ejection fraction quantification in myocardial perfusion scintigraphy.

Image quality of myocardial perfusion-gated studies: effect of ingestion of different fat content in the reduction of extra-myocardial abdominal signal

Myocardial perfusion-gated-SPECT (MP-gated-SPECT) imaging often shows radiotracer uptake in abdominal organs. This accumulation interferes frequently with qualitative and quantitative assessment of the infero-septal region of myocardium. The objective of this study is to evaluate the effect of ingestion of different fat content on the reduction of extra-myocardial uptake and to improve MP-gated-SPECT image quality. In this study, 150 patients (65 ^ 18 years) who were referred for MP-gated-SPECT underwent a 1-day-protocol including imaging after stress (physical or pharmacological) and resting conditions. All patients gave written informed consent. Patients were subdivided into five groups: GI, GII, GIII, GIV and GV. In the first four groups, patients ate two chocolate bars with different fat content. Patients in GV ��� control group (CG) ��� had just water. Uptake indices (UI) of myocardium (M)/liver(L) and M/stomach���proximal bowel(S) revealed lower UI of M/S at rest in all groups. Both stress and rest studies using different food intake indicate that patients who ate chocolate with different fat content showed better UI of M/L than the CG. The UI of M/L and M/S of groups obtained under physical stress are clearly superior to that of groups obtained under pharmacological stress. These differences are only significant in patients who ate high-fat chocolate or drank water. The analysis of all stress studies together (GI, GII, GIII and GIV) in comparison with CG shows higher mean ranks of UI of M/L for those who ate high-fat chocolate. After pharmacological stress, the mean ranks of UI of M/L were higher for patients who ate high- and low-fat chocolate. In conclusion, eating food with fat content after radiotracer injection increases, respectively, the UI of M/L after stress and rest in MP-gated-SPECT studies. It is, therefore, recommended that patients eat a chocolate bar after radiotracer injection and before image acquisition.

Study of the influence of count���s number in myocardium in the determination of reproducible functional parameters in Gated-SPECT studies simulated with GATE

Myocardial Perfusion Gated Single Photon Emission Tomography (Gated-SPET) imaging is used for the combined evaluation of myocardial perfusion and left ventricular (LV) function. But standard protocols of the Gated-SPECT studies require long acquisition times for each study. It is therefore important to reduce as much as possible the total duration of image acquisition. However, it is known that this reduction leads to decrease on counts statistics per projection and raises doubts about the validity of the functional parameters determined by Gated-SPECT. Considering that, it���s difficult to carry out this analysis in real patients. For ethical, logistical and economical matters, simulated studies could be required for this analysis. Objective: Evaluate the influence of the total number of counts acquired from myocardium, in the calculation of myocardial functional parameters (LVEF ��� left ventricular ejection fraction, EDV ��� end-diastolic volume, ESV ��� end-sistolic volume) using routine software procedures.

Impact of the background Region of Interest in the relative renal function

Renal scintigraphy with 99mTc-dimercaptosuccinic acid (99mTc-DMSA) is performed with the aim of detect cortical abnormalities related to urinary tract infection and accurately quantify relative renal function (RRF). For this quantitative assessment Nuclear Medicine Technologist should draw regions of interest (ROI) around each kidney (KROI) and peri-renal background (BKG) ROI although controversy still exists about BKG-ROI. The aim of this work was to evaluate the effect of the normalization procedure, number and location of BKG-ROI on the RRF in 99mTc-DMSA scintigraphy.

Analysis of the interference of endogenous circadian rhythms on 3'- deoxy- 3'- [18F]Fluorothymidine physiological uptake at the human bone marrow

The main purpose of the present study is to determine if the circadian rhythms present in the human bone marrow are likely to influence 3���- deoxy- 3���-[18F] Fluorothymidine (18F-FLT) uptake in the same organ. The 18F-FLT is a Thymidine analogous proliferation agent. The relatively high physiological uptake of this tracer in the bone marrow diminishes the Tumor/Background (T/B) ratio, decreasing the detection accuracy of PET/CT and possibly affecting SUV quantifications.

A comparison of two attenuation correction methods in 111In-Pentetriotide abdominal SPECT

Tomographic image can be degraded, partially by patient based attenuation. The aim of this paper is to quantitatively verify the effects of attenuation correction methods Chang and CT in 111In studies through the analysis of profiles from abdominal SPECT, correspondent to a uniform radionuclide uptake organ, the left kidney.

Dosimetria numa popula����o de profissionais expostos a radia����es ionizantes

Mestrado em Radia����es Aplicadas ��s Tecnologias da Sa��de - ��rea de especializa����o: Prote����o Contra as Radia����es.

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.

Compostos de dextrano-manose marcados com o 67Ga para a dete����o do g��nglio sentinela

Mestrado em Medicina Nuclear - ��rea de especializa����o: Radiofarm��cia.

Molecular imaging agents for detection of ��-amyloid plaques in Alzheimer���s disease

The formation of amyloid structures is a neuropathological feature that characterizes several neurodegenerative disorders, such as Alzheimer��s and Parkinson��s disease. Up to now, the definitive diagnosis of these diseases can only be accomplished by immunostaining of post mortem brain tissues with dyes such Thioflavin T and congo red. Aiming at early in vivo diagnosis of Alzheimer��s disease (AD), several amyloid-avid radioprobes have been developed for b-amyloid imaging by positron emission tomography (PET) and single-photon emission computed tomography (SPECT). The aim of this paper is to present a perspective of the available amyloid imaging agents, special those that have been selected for clinical trials and are at the different stages of the US Food and Drugs Administration (FDA) approval.

Influ��ncia de diferentes par��metros na diminui����o da atividade extra-mioc��rdica nos estudos Gated-SPECT

Introdu����o ��� A cintigrafia de perfus��o do mioc��rdio (CPM) �� um dos exames complementares de diagn��stico mais indicados na patologia cardiovascular. A atividade extramioc��rdica �� um problema recorrente na aquisi����o e avalia����o da imagem. Par��metros como o radiof��rmaco (RF) administrado, o tipo de esfor��o, a ingest��o de alimentos, o posicionamento e o processamento de imagem influenciam a atividade extramioc��rdica na CPM. O objetivo deste estudo �� identificar o protocolo da CPM a n��vel nacional e avaliar a percentagem de repeti����es das aquisi����es provocadas por este problema. Metodologia ��� Para a realiza����o deste estudo, a popula����o selecionada foram os Servi��os de Medicina Nuclear (SMN) em Portugal Continental. Foram analisados 15 question��rios, respondidos pelos T��cnicos Coordenadores dos v��rios SMN. Foi realizada a associa����o do comportamento das vari��veis, atrav��s da estat��stica descritiva e do Coeficiente de Correla����o de Spearman. Resultados ��� A percentagem de repeti����es �� menor com o uso da 99mTecn��cio(Tc)-Tetrofosmina, aquisi����o de imagens tardias, ingest��o de diversos alimentos (��gua, leite, sumo, p��o com manteiga) e com a corre����o de atenua����o. Conclus��o ��� Os resultados obtidos demonstram que a maioria das solu����es aplicadas nos SMN resultam numa diminui����o das repeti����es.

Avalia����o do desempenho de um sistema h��brido de tomografia por emiss��o de positr��es e tomografia computorizada

Mestrado em Medicina Nuclear.

Monte Carlo simulation of the basic features of the GE Millennium MG single photon emission computed tomography gamma camera

Objective - To describe and validate the simulation of the basic features of GE Millennium MG gamma camera using the GATE Monte Carlo platform. Material and methods - Crystal size and thickness, parallel-hole collimation and a realistic energy acquisition window were simulated in the GATE platform. GATE results were compared to experimental data in the following imaging conditions: a point source of 99mTc at different positions during static imaging and tomographic acquisitions using two different energy windows. The accuracy between the events expected and detected by simulation was obtained with the Mann���Whitney���Wilcoxon test. Comparisons were made regarding the measurement of sensitivity and spatial resolution, static and tomographic. Simulated and experimental spatial resolutions for tomographic data were compared with the Kruskal���Wallis test to assess simulation accuracy for this parameter. Results - There was good agreement between simulated and experimental data. The number of decays expected when compared with the number of decays registered, showed small deviation (���0.007%). The sensitivity comparisons between static acquisitions for different distances from source to collimator (1, 5, 10, 20, 30cm) with energy windows of 126���154 keV and 130���158 keV showed differences of 4.4%, 5.5%, 4.2%, 5.5%, 4.5% and 5.4%, 6.3%, 6.3%, 5.8%, 5.3%, respectively. For the tomographic acquisitions, the mean differences were 7.5% and 9.8% for the energy window 126���154 keV and 130���158 keV. Comparison of simulated and experimental spatial resolutions for tomographic data showed no statistically significant differences with 95% confidence interval. Conclusions - Adequate simulation of the system basic features using GATE Monte Carlo simulation platform was achieved and validated.

Variabilidade introduzida pelo operador no processamento dos estudos Gated-SPECT do mioc��rdio

Introdu����o ��� Os estudos Gated ��� Single Photon Emission Computed Tomography (SPECT) s��o uma das t��cnicas de imagiologia card��aca que mais evoluiu nas ��ltimas d��cadas. Para a an��lise das imagens obtidas, a utiliza����o de softwares de quantifica����o leva a um aumento da reprodutibilidade e exatid��o das interpreta����es. O objetivo deste estudo consiste em avaliar, em estudos Gated-SPECT, a variabilidade intra e interoperador de par��metros quantitativos de fun����o e perfus��o do mioc��rdio, obtidos com os softwares Quantitative Gated SPECT (QGS) e Quantitative Perfusion SPECT (QPS). Material e m��todos ��� Recorreu-se a uma amostra n��o probabil��stica por conveni��ncia de 52 pacientes, que realizaram estudos Gated-SPECT do mioc��rdio por raz��es cl��nicas e que integravam a base de dados da esta����o de processamento da Xeleris da ESTeSL. Os cinquenta e dois estudos foram divididos em dois grupos distintos: Grupo I (GI) de 17 pacientes com imagens com perfus��o do mioc��rdio normal; Grupo II (GII) de 35 pacientes que apresentavam defeito de perfus��o nas imagens Gated-SPECT. Todos os estudos foram processados 5 vezes por 4 operadores independentes (com experi��ncia de 3 anos em Servi��os de Medicina Nuclear com casu��stica m��dia de 15 exames/semana de estudos Gated-SPECT). Para a avalia����o da variabilidade intra e interoperador foi utilizado o teste estat��stico de Friedman, considerando ��=0,01. Resultados e discuss��o ��� Para todos os par��metros avaliados, os respectivos valores de p n��o traduziram diferen��as estatisticamente significativas (p>��). Assim, n��o foi verificada variabilidade intra ou interoperador significativa no processamento dos estudos Gated-SPECT do mioc��rdio. Conclus��o ��� Os softwares QGS e QPS s��o reprodut��veis na quantifica����o dos par��metros de fun����o e perfus��o avaliados, n��o existindo variabilidade introduzida pelo operador.

Rela����o entre fun����o ventricular esquerda e os ��ndices de capta����o mioc��rdio/pulm��o em estudos Gated-SPECT

Introdu����o ��� A tomografia de emiss��o de fot��o simples sincronizada com o sinal eletrocardiogr��fico (Gated-SPECT) �� essencial para a avalia����o conjunta da perfus��o e da fun����o ventricular esquerda (VE) do mioc��rdio. Objetivo ��� Investigar a rela����o entre a fun����o VE e o ��ndice de capta����o (IC) mioc��rdio/pulm��o direito (M/PD) e M/P esquerdo (M/PE) nos estudos Gated-SPECT com 99mTc-Tetrofosmina. Metodologia ��� Amostra de 32 pacientes que realizaram estudos Gated-SPECT por indica����o cl��nica, sendo subdividida em dois grupos: Grupo I (GI) ��� pacientes com a informa����o cl��nica de enfarte agudo do mioc��rdio (EAM); Grupo II (GII) ��� pacientes com a informa����o cl��nica de isquemia. Por cada paciente adquiriram-se imagens est��ticas tor��cico-abdominais e dois estudos Gated-SPECT do mioc��rdio (protocolo de um dia esfor��o/repouso). Nas imagens est��ticas definiram-se regi��es de interesse (Regions of interest ��� ROI) para calcular os IC. Nos estudos Gated-SPECT utilizou-se o software Quantitative Gated SPECT/Quantitative Perfusion SPECT para calcular a Fra����o de Eje����o do Ventr��culo Esquerdo (FEVE). Efetuou-se an��lise estat��stica descritiva para caracteriza����o da amostra. Aplicou-se o teste de Spearman para avaliar a correla����o entre a FEVE e os IC por grupo de pacientes. O Teste de Willcoxon foi usado para comparar FEVE em repouso e em esfor��o. Resultados ��� Nos estudos Gated-SPECT em esfor��o n��o se verificou correla����o estatisticamente significativa entre a FEVE e os IC, para GI e GII; em repouso existe correla����o positiva estatisticamente significativa entre a FEVE e os IC, para GI; para GII n��o se verificou correla����o. Na compara����o dos valores de FEVE em esfor��o e repouso nos dois grupos constatou-se a exist��ncia de diferen��as estatisticamente significativas, sendo a FEVE em Esfor��o<FEVE em repouso. Conclus��o ��� IC associado ao valor da FEVE pode indicar disfun����o VE, contudo, n��o �� poss��vel aplicar de forma vi��vel esta dedu����o para a amostra total que realizou Gated���SPECT (GI e GII).