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AIMS: To assess the evolution of silent myocardial ischaemia prevalence and of cardiovascular disease risk factor management over 10 years in people with Type 2 diabetes. METHODS: This repeated cross-sectional study prospectively included 770 people with Type 2 diabetes who presented at our centre in the period 1999-2009. All had at least one additional cardiovascular disease risk factor, no history of coronary disease and were screened for silent myocardial ischaemia using myocardial perfusion imaging. The prevalence of silent myocardial ischaemia, clinical and biological variables and treatments were collected and compared among participants screened in three periods: 1999 to 2002; 2003 to 2005; and 2006 to 2009. We also identified predictive factors for silent myocardial ischaemia. RESULTS: Participants had a mean ± sd age of 62.3 ± 9.3 years, 57.4% were men and the mean time from diagnosis of diabetes was 13.4 ± 9.3 years. Overall, silent myocardial ischaemia screening was positive in 13.9% of participants. This prevalence decreased sharply over the 10-year study period (22.6% in 1999-2002, 13.7% in 2003-2005 and 5.9% in 2006-2009; P<0.0001). In parallel, diastolic and systolic blood pressure, HbA1c and LDL cholesterol significantly decreased and glitazone and statin use increased (all P<0.001). Male gender, peripheral artery disease, diastolic blood pressure >80 mmHg and LDL cholesterol >2.6 mmol/l were independently associated with silent myocardial ischaemia. Further adjustment showed the screening period had a significant effect, which erased the effects of diastolic blood pressure and LDL cholesterol. CONCLUSIONS: The prevalence of silent myocardial ischaemia decreased sharply over time, and control of the main cardiovascular disease risk factors improved. Although the causality link cannot be established, the present study supports current recommendations advocating glycaemic control and intensive management of cardiovascular factors instead of systematic screening.
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Doenças Assintomáticas/epidemiologia , Doenças Cardiovasculares/epidemiologia , Diabetes Mellitus Tipo 2/epidemiologia , Isquemia Miocárdica/epidemiologia , Idoso , Doenças Cardiovasculares/etiologia , Estudos Transversais , Diabetes Mellitus Tipo 2/complicações , Angiopatias Diabéticas/epidemiologia , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Prevalência , Fatores de RiscoRESUMO
UNLABELLED: Low bone mass is a consequence of anorexia nervosa (AN). This study assessed the effects of energy deficiency on various bone and hormonal parameters. The interrelationships between energy deficiency and bone remodelling, glucose homeostasis and adipokines underscore the importance of preventing energy deficiency to limit demineralisation and hormonal alterations in AN patients. INTRODUCTION: Low areal bone mineral density (aBMD) is a well-known consequence of AN. However, the impact of reduced energy expenditure on bone metabolism is unknown. This study assessed the effects of energy deficiency on bone remodelling and its potential interactions with glucose homeostasis and adipose tissue-derived hormones in AN, a clinical model for reduced energy expenditure. METHODS: Fifty women with AN and 50 age-matched controls (mean age 18.1 ± 2.7 and 18.0 ± 2.1 years, respectively) were enrolled. aBMD was determined with DXA. Resting energy expenditure (REEm), a marker of energy status, was indirectly assessed by calorimetry. Bone turnover markers, undercarboxylated osteocalcin (ucOC), parameters of glucose homeostasis, adipokines and growth factors were concomitantly evaluated. RESULTS: AN patients presented low aBMD at all bone sites. REEm, bone formation markers, ucOC, glucose, insulin, HOMA-IR, leptin and IGF-1 were significantly reduced, whereas the bone resorption marker, leptin receptor (sOB-R) and adiponectin were elevated in AN compared with CON. In AN patients, REEm was positively correlated with weight, BMI, whole body (WB) fat mass, WB fat-free soft tissue, markers of bone formation, glucose, insulin, HOMA-IR, leptin and IGF-1 and negatively correlated with the bone resorption marker and sOB-R. Biological parameters, aBMD excepted, appeared more affected by the weight variation in the last 6 months than by the disease duration. CONCLUSIONS: The strong interrelationships between REEm and bone remodelling, glucose homeostasis and adipokines underscore the importance of preventing energy deficiency to limit short- and long-term bone demineralisation and hormonal alterations in AN patients.
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Adipocinas/sangue , Anorexia Nervosa/fisiopatologia , Glicemia/metabolismo , Remodelação Óssea/fisiologia , Metabolismo Energético/fisiologia , Adolescente , Anorexia Nervosa/sangue , Anorexia Nervosa/complicações , Antropometria/métodos , Biomarcadores/sangue , Peso Corporal/fisiologia , Densidade Óssea/fisiologia , Doenças Ósseas Metabólicas/sangue , Doenças Ósseas Metabólicas/etiologia , Doenças Ósseas Metabólicas/fisiopatologia , Estudos de Casos e Controles , Feminino , Homeostase/fisiologia , Humanos , Peptídeos e Proteínas de Sinalização Intercelular/sangue , Menstruação/fisiologia , Fatores de Tempo , Adulto JovemRESUMO
Recent experimental data suggest that circulating serotonin interacts with bone metabolism, although this is less clear in humans. This study investigated whether serum serotonin interferes with bone metabolism in young women with anorexia nervosa (AN), a clinical model of energy deprivation. Serum serotonin, markers of bone turnover [osteocalcin (OC), procollagen type I N-terminal propeptide (PINP), type I-C telopeptide breakdown products (CTX)], leptin, soluble leptin receptor (sOB-R), and insulin-like growth factor-1 (IGF-1) and its binding protein (IGFBP-3) were assessed. Whole body, spine, hip, and radius areal bone mineral density BMD (aBMD) were assessed by dual-energy X-ray absorptiometry in 21 patients with AN and 19 age-matched controls. Serum serotonin, leptin, IGF-1, IGFBP-3, OC, PINP, and aBMD at all sites, radius excepted, were significantly reduced in AN whereas CTX and sOB-R were increased compared with controls. Serum serotonin levels were positively correlated with weight, body mass index, whole body fat mass, leptin, and IGF-1, and negatively with CTX for the entire population. Low serum serotonin levels are observed in patients with AN. Although no direct link between low serum serotonin levels and bone mass was identified in these patients, the negative relationship between serotonin and markers of bone resorption found in all population nevertheless suggests the implication of serotonin in bone metabolism. Impact of low serum serotonin on bone in AN warrants further studies.
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Anorexia Nervosa/sangue , Reabsorção Óssea/sangue , Serotonina/sangue , Adolescente , Anorexia Nervosa/complicações , Anorexia Nervosa/fisiopatologia , Antropometria , Densidade Óssea , Reabsorção Óssea/complicações , Reabsorção Óssea/fisiopatologia , Estudos de Casos e Controles , Feminino , Hormônios , HumanosRESUMO
UNLABELLED: Peripubertal artistic gymnasts display elevated areal bone mineral density at various bone sites, despite delayed menarche and a high frequency of menstrual disorders, factors that may compromise bone health. The concomitant improvement in femoral bone geometry and strength suggested that this type of physical activity might have favourable clinical impact. INTRODUCTION: The purpose of this study is to evaluate the effect of artistic gymnastics (GYM) on areal bone mineral density (aBMD), femoral bone geometry and bone markers and its relationship with the osteoprotegerin (OPG)/rank-ligand (RANKL) system in peripubertal girls. METHODS: Forty-six girls (age 10-17.2 years) were recruited for this study: 23 elite athletes in the GYM group (training 12-30 h/week, age at start of training 5.3 years) and 23 age-matched (± 6 months; leisure physical activity ≤ 3 h/week) controls (CON). The aBMD at whole body, total proximal femur, lumbar spine, mid-radius and skull was determined using dual-X-ray absorptiometry. Hip structural analysis (HSA software) was applied at the femur to evaluate cross-sectional area (CSA, cm(2)), cross-sectional moment of inertia (CSMI, cm(4)), and the section modulus (Z, cm(3)) and buckling ratio at neck, intertrochanteric region and shaft. Markers of bone turnover and OPG/RANKL levels were also analysed. RESULTS: GYM had higher (5.5-16.4%) non-adjusted aBMD and adjusted aBMD for age, fat-free soft tissue and fat mass at all bone sites, skull excepted and the difference increased with age. In the three femoral regions adjusted for body weight and height, CSA (12.5-18%), CSMI (14-18%), Z (15.5-18.6%) and mean cortical thickness (13.6-21%) were higher in GYM than CON, while the buckling ratio (21-27.1%) was lower. Bone markers decreased with age in both groups and GYM presented higher values than CON only in the postmenarchal period. A similar increase in RANKL with age without OPG variation was observed for both groups. CONCLUSION: GYM is associated not only with an increase in aBMD but also an improvement in bone geometry associated with an increase in bone remodelling. These adaptations seem to be independent of the OPG/RANKL system.
Assuntos
Densidade Óssea/fisiologia , Fêmur/anatomia & histologia , Ginástica/fisiologia , Osteoprotegerina/metabolismo , Ligante RANK/metabolismo , Absorciometria de Fóton , Adolescente , Remodelação Óssea/fisiologia , Criança , Estudos Transversais , Feminino , Fêmur/diagnóstico por imagem , Humanos , Vértebras Lombares/diagnóstico por imagem , Osteoprotegerina/sangue , Ligante RANK/sangue , Rádio (Anatomia)/diagnóstico por imagemRESUMO
BACKGROUND: The additional benefit of 18FDG-Positron Emission Tomography-Computed Tomography (FDG PET-CT) compared with conventional imaging is still a controversial issue in MCC. OBJECTIVES: This study was designed to evaluate the ability of FDG PET-CT to detect secondary lesions clinically inconspicuous and not shown by conventional imaging. METHODS: Clinical records of 15 MCC patients were retrospectively reviewed to investigate the specific interest of FDG PET-CT compared with X-computed tomography (CT). The main endpoint was the ability of FDG PET-CT to detect secondary lesions and the possible resulting changes in disease staging and management compared with pre-FDG PET-CT data including clinical examination, sentinel lymph node biopsy (SLNB), and diagnostic CT. RESULTS: FDG PET-CT was relevant with a single false negative result and led to significant changes in disease staging and management in 46% of patients compared with clinical examination alone. However, additional secondary lesions not detected by CT were evidenced during follow-up in a single patient with an already known metastatic disease, data which did not result in any change in staging and treatment. Sensitivity, specificity, positive predictive value and negative predictive value were respectively 0.66, 1, 1 and 0.8 for SLNB, 0.89, 1, 1 and 0.93 for CT and 0.89, 1, 1 and 0.93 for FDG PET-CT. No additional neoplasm was detected by FDG PET-CT. CONCLUSION: Although FDG PET-CT is of questionable value in MCC management when used in parallel with CT, it may be considered as a valuable option as a single whole-body survey procedure.
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Carcinoma de Célula de Merkel/patologia , Carcinoma de Célula de Merkel/terapia , Fluordesoxiglucose F18 , Imagem Multimodal , Tomografia por Emissão de Pósitrons , Tomografia Computadorizada por Raios X , Adulto , Idoso , Idoso de 80 Anos ou mais , Carcinoma de Célula de Merkel/diagnóstico , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Retrospectivos , Biópsia de Linfonodo SentinelaRESUMO
AIM: Investigated the relationship between leptin levels or bone remodelling and physical fitness level in healthy elderly participants. METHODS: Twenty women and 18 men (mean age 72.7 years, range 59-90) performed a maximal incremental exercise test to evaluate their maximal oxygen uptake (VOmax). Basal blood concentrations of bone biochemical markers (BM) and leptin were analysed. RESULTS: Women presented higher values of leptin than men (+34.7%, P=0.024), but no difference related to gender was observed for the other biological parameters. Leptin levels were positively correlated with Body Mass Index (BMI) in both genders. Whether adjusted or not for BMI, leptin was negatively correlated with VOmax only in men (r=-0.55, P=0.02 and r=-0.57, P=0.01, respectively). No relationship between VOmax or leptin and BM was observed, except for leptin and osteocalcin in men (r=-0.66, P=0.015). CONCLUSION: Our data suggest that neither physical fitness nor leptin level seems to have a noticeable effect in the regulation of bone cell activity in healthy elderly participants. In this specific population, physical fitness plays a crucial role on leptin secretion, independently of BMI variation, and this action appears to be sex-dependent.
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Remodelação Óssea/fisiologia , Osso e Ossos/metabolismo , Leptina/sangue , Aptidão Física/fisiologia , Idoso , Idoso de 80 Anos ou mais , Índice de Massa Corporal , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Osteocalcina/sangue , Consumo de Oxigênio/fisiologia , Fatores SexuaisRESUMO
In this paper, a new generic regularized reconstruction framework based on confidence interval constraints for tomographic reconstruction is presented. As opposed to usual state-of-the-art regularization methods that try to minimize a cost function expressed as the sum of a data-fitting term and a regularization term weighted by a scalar parameter, the proposed algorithm is a two-step process. The first step concentrates on finding a set of images that rely on the direct estimation of confidence intervals for each reconstructed value. Then, the second step uses confidence intervals as a constraint to choose the most appropriate candidate according to a regularization criterion. Two different constraints are proposed in this paper. The first one has the main advantage of strictly ensuring that the regularized solution will respect the interval-valued data-fitting constraint, thus preventing over-smoothing of the solution while offering interesting properties in terms of spatial and statistical bias/variance trade-off. Another regularization proposition based on the design of a smoother constraint also with appealing properties is proposed as an alternative. The competitiveness of the proposed framework is illustrated in comparison to other regularization schemes using analytical and GATE-based simulation and real PET acquisition.
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Processamento de Imagem Assistida por Computador/métodos , Processamento de Imagem Assistida por Computador/estatística & dados numéricos , Tomografia por Emissão de Pósitrons/métodos , Tomografia por Emissão de Pósitrons/normas , Algoritmos , Doença de Alzheimer/diagnóstico por imagem , Encéfalo/diagnóstico por imagem , Intervalos de Confiança , Humanos , Imagens de FantasmasRESUMO
PURPOSE: The purpose of this study was to assess liver function deterioration, as assessed using the model for end-stage liver disease (MELD) score variations, following transarterial chemo-embolization (TACE) versus selective internal radiation therapy (SIRT) in patients with unresectable unilobar hepatocellular carcinomas (HCC). PATIENTS AND METHODS: We retrospectively evaluated all patients who underwent a single conventional TACE or SIRT procedure in our department from May 2013 to May 2018 for unilobar unresectable HCC. A total of 86 patients (76 men, 20 women; mean age, 65.5 years) were included. There were 63 patients in the TACE group [56 men, 7 women; mean age, 65.1±9.6 (SD) years] and 23 patients in the SIRT group [20 men, 3 women; mean age, 70±9.2 (SD) years]. Delta MELD, defined as post treatment minus pre-treatment MELD score, was considered for liver function deterioration and compared between patients who underwent single lobar treatment of SIRT versus TACE. RESULTS: Patients in SIRT group had significant higher tumor burden, alpha-fetoprotein serum level, and rates of macroscopic vessel invasion. Mean pre-treatment MELD scores did not differ between TACE [mean, 8.41±1.71 (SD); range: 7.24-9.24] and SIRT groups [mean, 8.36±1.74 (SD); range: 7.07-9.21] (P=0.896) as well as Child-Pugh class and albumin-bilirubin (ALBI) grade distribution. However, following treatment, mean DeltaMELD was greater in TACE group (mean, 0.83±1.83 [SD]; range: -0.30--1.31) than in SIRT group (mean, -0.13±1.06 [SD]; range: -0.49-0.32) (P=0.021). At multivariate analysis, SIRT treatment was independently associated with a lower DeltaMELD score than TACE (R=-0.955 [-1.68; -0.406]; P=0.017;). CONCLUSION: Whereas performed in patients with higher tumor burden, SIRT resulted in lower degrees of liver function worsening as assessed using MELD score variations.
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Carcinoma Hepatocelular/terapia , Embolização Terapêutica/métodos , Neoplasias Hepáticas/terapia , Idoso , Carcinoma Hepatocelular/patologia , Carcinoma Hepatocelular/radioterapia , Quimioembolização Terapêutica/métodos , Doença Hepática Terminal , Feminino , Humanos , Testes de Função Hepática , Neoplasias Hepáticas/patologia , Neoplasias Hepáticas/radioterapia , Masculino , Análise Multivariada , Invasividade Neoplásica , Estudos Retrospectivos , Índice de Gravidade de Doença , Carga Tumoral , alfa-Fetoproteínas/análiseRESUMO
This study investigated how the choice of fixed planes for the representation of the projection data of a cylindrical positron emission tomography (PET) scanner simplifies the frequency interpolation required by the 3D Fourier slice theorem (3D-FST). A new gridding algorithm based on a two-plane geometry and requiring only 1D interpolations in the Fourier domain was compared with the direct implementation of the 3D-FST. We show that the use of two orthogonal planes leads to signal to noise ratios similar to those achieved with the 3D-FST algorithm from projection data acquired with up to two times more count rates, while the resolution remains similar.
Assuntos
Algoritmos , Encéfalo/diagnóstico por imagem , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Tomografia por Emissão de Pósitrons/métodos , Análise de Fourier , Humanos , Imagens de Fantasmas , Tomografia por Emissão de Pósitrons/instrumentação , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
This paper describes how the stability of the inverse problem underlying emission tomography can be measured and controlled in clinical settings. We show how the Lanczos approximation provides a way to regularize a certain class of iterative reconstruction algorithms through a given level of noise or resolution in the slices and for a given acquisition protocol. Moreover, we show how the same Lanczos approximation can be used to decide when the iterative reconstruction algorithm actually converges for a given machine precision. These ideas are illustrated by means of reconstructions of simulated and actual emission datasets.
Assuntos
Análise de Fourier , Processamento de Imagem Assistida por Computador/métodos , Tomografia Computadorizada de Emissão/normas , Algoritmos , França , HumanosRESUMO
OBJECTIVE: To evaluate the effect of strenuous exercise on bone metabolism and related hormones in elderly subjects. METHODS: Twenty one active elderly subjects (11 men and 10 women; mean age 73.3 years) showing a mean theoretical Vo2max of 151.4% participated. Concentrations of plasma ionised calcium (iCa), serum intact parathyroid hormone (iPTH), 25-hydroxyvitamin D (25(OH)D), and 1.25-dihydroxy-vitamin D3 (1.25(OH)2D3), as well as the bone biochemical markers type I collagen C-telopeptide for bone resorption and osteocalcin and bone alkaline phosphatase for bone formation, were analysed before and after a maximal incremental exercise test. RESULTS: At basal level, iPTH was positively correlated with age (r = 0.56, p < 0.01) and negatively correlated with 25(OH)D (r = -0.50; p < 0.01) and 1.25(OH)2D3 (r = -0.47; p < 0.05). Moreover, 25(OH)D and 1.25(OH)2D3 levels were negatively correlated with age (r = -0.50, p < 0.01 and r = -0.53, p < 0.01, respectively). After exercise, iCa and 25(OH)D decreased (p < 0.001 and p = 0.01, respectively) while iPTH increased (p < 0.001). The levels of 1.25(OH)2D3, bone biochemical markers, haematocrit, and haemoglobin were unchanged. The variations in iCa and 25(OH)D were not related to age and/or sex. The iPTH variation was directly related to basal iPTH levels (p < 0.01) and indirectly related to age. CONCLUSIONS: In active elderly subjects, strenuous exercise disturbed calcium homeostasis and bone related hormones without immediate measurable effect on bone turnover. Although an increase in iPTH could have an anabolic action on bone tissue, our findings from our short term study did not allow us to conclude that such action occurred.
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Osso e Ossos/metabolismo , Hormônios/sangue , Caminhada/fisiologia , Idoso , Idoso de 80 Anos ou mais , Biomarcadores/sangue , Índice de Massa Corporal , Reabsorção Óssea/metabolismo , Cálcio/sangue , Ensaio de Imunoadsorção Enzimática/métodos , Feminino , Homeostase/fisiologia , Humanos , Hidroxicolecalciferóis/sangue , Masculino , Pessoa de Meia-Idade , Osteocalcina/análise , Osteogênese/fisiologia , Consumo de Oxigênio/fisiologia , Hormônio Paratireóideo/sangueRESUMO
UNLABELLED: The current major limitation to development of electrocardiographically (ECG) gated blood-pool SPECT (GBPS) for measurement of the left ventricular (LV) ejection fraction (LVEF) and volumes is the lack of availability of clinically validated automatic processing software. Recently, 2 processing software methods for quantification of the LV function have been described. Their LVEFs have been validated separately, but no validation of the LV volume measurement has been reported. METHODS: We compared 3 processing methods for evaluation of the LVEF (n = 29) and volumes (n = 58) in 29 patients: automatic geometric method (GBPS(G)), semiautomatic activity method (GBPS(M)), and 35% maximal activity manual method (GBPS(35%)). The LVEF provided by the ECG gated equilibrium planar left anterior oblique view (planar(LAO)) and the LV volumes provided by LV digital angiography (Rx) were used as gold standards. RESULTS: Whereas the GBPS(G) and GBPS(M) methods present similar low percentage variabilities, the GBPS(35%) method provided the lowest percentage variabilities for the LVEF and volume measurements (P < 0.04 and P < 0.02, respectively). The LVEF and volume provided by the 3 methods were highly correlated with the gold standard methods (r > 0.98 and r > 0.83, respectively). The LVEFs provided by the GBPS(35%) and GBPS(M) methods are similar and higher than those of the GBPS(G) method and planar(LAO) method, respectively (P < 0.0001). For the LVEF, there is no correlation between the average and paired absolute difference for the 3 GBPS methods against the planar(LAO) method, and the limits of agreement are relatively large. LV volumes are lower when calculated with the GBPS(M), GBPS(G), and Rx methods (P < 0.0001). However, the GBPS(35%) and Rx methods provide LV volumes that are similar. There is no linear correlation between the average and the paired absolute difference of volumes calculated with the GBPS(G) and GBPS(35%) methods against Rx LV volumes. However, a moderate linear correlation was found with the GBPS(M) method (r = 0.6; P = 0.0001). The 95% limits of agreement between the Rx LV volumes and the 3 GBPS methods are relatively large. CONCLUSION: GBPS is a simple, highly reproducible, and accurate technique for the LVEF and volume measurement. The reported findings should be considered when comparing results of different methods (GBPS vs. planar(LAO) LVEF; GBPS vs. Rx volume) and results of different GBPS processing methods.
Assuntos
Eletrocardiografia , Imagem do Acúmulo Cardíaco de Comporta , Processamento de Imagem Assistida por Computador/métodos , Volume Sistólico , Tomografia Computadorizada de Emissão de Fóton Único , Função Ventricular Esquerda , Humanos , Masculino , Pessoa de Meia-Idade , Angiografia Cintilográfica , Processamento de Sinais Assistido por Computador , Software , Tomografia Computadorizada de Emissão de Fóton Único/métodosRESUMO
Theoretical and experimental studies have been conducted to explore the possibilities of triple photon energy absorptiometry in the measurement of bone mineral content. The purpose of this technique is to correct the measured bone mineral density for fat and soft tissues. However, theoretical considerations lead us to doubt the precision and accuracy of such measurements. In a first approximation the absorption coefficient can be split into Compton and photoelectric energy-independent factors. A consequence of such a model is the impossibility of finding more than two independent mass attenuation coefficients for different energies. The existence of an energy-dependent third factor may justify the use of triple photon energy absorptiometry but experimental tests and numerical simulations have shown that its value is too low for triple photon energy absorptiometry to be considered as an adequate method for the measurement of bone mineral content.
Assuntos
Absorciometria de Fóton/métodos , Densidade Óssea , Humanos , Matemática , Modelos TeóricosRESUMO
A dual-energy x-ray tomodensimeter adapted for the determination of bone mineral density (BMD) of the lumbar vertebrae has been directly developed from a typical dual-energy x-ray absorptiometer. This apparatus consists of two fundamental parts: a dual energy x-ray tube, and a multidetector made by an array of 24 NaI(T1) crystals. It provides both tomographic and non-tomographic (anteroposterior, lateral etc) measurement. The detection area is limited to 132 mm. In this condition, the choice of the best reconstruction algorithm in order to give a direct BDM is considered. Preliminary studies based on numerical simulated projections and hydroxyapatite phantoms demonstrated the superiority of algebraic reconstruction algorithms, such as conjugated gradient, in order to resolve the problems of (i) the impossibility of defining an internal calibration, and (ii) the potential for reconstruction errors due to the presence of bone structures located out of the detection area. The accuracy of BMD measurement is within 2%, with in vitro precision approximately 1%, and linearity characterized by a standard error of estimation (SEE) of 2 mg cm-3 in the range of lumbar BMD (less than 400 mg cm-3). Experimental data derived from two volunteers are presented.
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Algoritmos , Densidade Óssea , Processamento de Imagem Assistida por Computador , Vértebras Lombares , Tomografia Computadorizada por Raios X/instrumentação , Desenho de Equipamento , Humanos , Modelos EstruturaisRESUMO
Thanks to an experimental study based on simulated and physical phantoms, the propagation of the stochastic noise in slices reconstructed using the conjugate gradient algorithm has been analysed versus iterations. After a first increase corresponding to the reconstruction of the signal, the noise stabilises before increasing linearly with iterations. The level of the plateau as well as the slope of the subsequent linear increase depends on the noise in the projection data.
Assuntos
Algoritmos , Processamento de Imagem Assistida por Computador , Tomografia Computadorizada de Emissão de Fóton Único , Simulação por Computador , Humanos , Imagens de Fantasmas , Distribuição de Poisson , Processos EstocásticosRESUMO
Multimodal images registration can be very helpful for diagnostic applications. However, even if a lot of registration algorithms exist, only a few really work in clinical routines. We developed a method based on surface matching and compared two minimization algorithms: Powell's and Downhill Simplex. We studied the influence of some factors (chamfer map computation, number and order of parameters to determine, minimization criteria) on the final accuracy of the algorithm. Using this comparison, we improved some processing steps to allow a clinical use, and selected the simplex algorithm which presented the best results.
Assuntos
Algoritmos , Encéfalo/diagnóstico por imagem , Encéfalo/anatomia & histologia , Humanos , Imageamento por Ressonância Magnética/métodos , Controle de Qualidade , Reprodutibilidade dos Testes , Tomografia Computadorizada de Emissão/métodos , Tomografia Computadorizada de Emissão de Fóton Único/métodosRESUMO
OBJECTIVE: We propose a statistical stopping criterion for iterative reconstruction in emission tomography based on a heuristic statistical description of the reconstruction process. METHODS: The method was assessed for MLEM reconstruction. Based on Monte-Carlo numerical simulations and using a perfectly modeled system matrix, our method was compared with classical iterative reconstruction followed by low-pass filtering in terms of Euclidian distance to the exact object, noise, and resolution. The stopping criterion was then evaluated with realistic PET data of a Hoffman brain phantom produced using the GATE platform for different count levels. RESULTS: The numerical experiments showed that compared with the classical method, our technique yielded significant improvement of the noise-resolution tradeoff for a wide range of counting statistics compatible with routine clinical settings. When working with realistic data, the stopping rule allowed a qualitatively and quantitatively efficient determination of the optimal image. CONCLUSIONS: Our method appears to give a reliable estimation of the optimal stopping point for iterative reconstruction. It should thus be of practical interest as it produces images with similar or better quality than classical post-filtered iterative reconstruction with a mastered computation time.
Assuntos
Processamento de Imagem Assistida por Computador/métodos , Tomografia por Emissão de Pósitrons/métodos , Estatística como Assunto/métodos , Encéfalo/diagnóstico por imagem , Método de Monte Carlo , Imagens de Fantasmas , Razão Sinal-RuídoRESUMO
Our aim is to describe an original method for estimating the statistical properties of regions of interest (ROIs) in emission tomography. Drawn upon the works of Louis on the approximate inverse, we propose a dual formulation of the ROI estimation problem to derive the ROI activity and variance directly from the measured data without any image reconstruction. The method requires the definition of an ROI characteristic function that can be extracted from a co-registered morphological image. This characteristic function can be smoothed to optimize the resolution-variance tradeoff. An iterative procedure is detailed for the solution of the dual problem in the least-squares sense (least-squares dual (LSD) characterization), and a linear extrapolation scheme is described to compensate for sampling partial volume effect and reduce the estimation bias (LSD-ex). LSD and LSD-ex are compared with classical ROI estimation using pixel summation after image reconstruction and with Huesman's method. For this comparison, we used Monte Carlo simulations (GATE simulation tool) of 2D PET data of a Hoffman brain phantom containing three small uniform high-contrast ROIs and a large non-uniform low-contrast ROI. Our results show that the performances of LSD characterization are at least as good as those of the classical methods in terms of root mean square (RMS) error. For the three small tumor regions, LSD-ex allows a reduction in the estimation bias by up to 14%, resulting in a reduction in the RMS error of up to 8.5%, compared with the optimal classical estimation. For the large non-specific region, LSD using appropriate smoothing could intuitively and efficiently handle the resolution-variance tradeoff.
Assuntos
Processamento de Imagem Assistida por Computador/métodos , Tomografia por Emissão de Pósitrons/métodos , Encéfalo/diagnóstico por imagem , Análise dos Mínimos Quadrados , Método de Monte Carlo , Imagens de FantasmasRESUMO
Ageing is associated with a gradual bone loss and physical activity has been suggested as practical strategy for a non-pharmacological prevention of osteoporosis. However, until now, the specific mechanism by which physical activity affects bone tissue is not thoroughly understood. The aim of this study was to evaluate the effect of strenuous exercise on bone metabolism as a function of age and fitness level. Eighteen physically highly active elderly participants (mean age 71.7+/-7.3 years, HAcEl group), 18 moderately active elderly participants (mean age 71.9+/-8.6 years, ModEl group) and 9 young physically active participants (mean age 25.8+/-2.3 years, AcYo) participated in this study. Concentrations of plasma ionised calcium (iCa), serum parathyroid hormone (iPTH), 25-hydroxy-vitamin D [25(OH)D], and 1,25-dihydroxy-vitamin D3 [1,25(OH)(2)D3] as well as the bone biochemical markers type-I collagen C-telopeptide (CTX) for bone resorption and osteocalcin (OC) and bone alkaline phosphatase (B-ALP) for bone formation, were analyzed before and after a maximal incremental exercise test. In all groups, iCa decreased significantly (p<0.05 for ModEl and AcYo and p<0.001 for HAcEl) while iPTH increased significantly (p<0.01 for ModEl and HAcEl and p<0.001 for AcYo) after exercise. The levels of 1,25(OH)(2)D3, OC and CTX remained unchanged, while 25(OH)D decreased only in HAcEl group while B-ALP increased in ModEl group. In conclusion, strenuous exercise disturbed calcium homeostasis, mainly the iCa/iPTH equilibrium independently of gender, age or fitness level of the participants while no immediate effect on bone turnover was observed.
Assuntos
Envelhecimento/fisiologia , Remodelação Óssea , Cálcio/sangue , Exercício Físico/fisiologia , Aptidão Física , Adulto , Idoso , Idoso de 80 Anos ou mais , Teste de Esforço , Feminino , Humanos , Masculino , Hormônio Paratireóideo/sangue , Caminhada/fisiologia , Adulto JovemRESUMO
AIMS: To assess the association between abnormal stress myocardial perfusion imaging (MPI) and cardiac events (CE) in asymptomatic patients with diabetes and with > or = 1 additional risk factor. Predictors of abnormal stress MPI were also evaluated. METHODS: Four hundred and forty-seven consecutive patients who underwent stress MPI were prospectively followed for 2.1 [0.5-4.1] years for the subsequent occurrence of hard CE (myocardial infarction and sudden or coronary death) and soft CE (unstable angina and ischaemic heart failure requiring hospitalization). Re-vascularization procedures performed as a result of the screening protocol were not included in the analysis. RESULTS: Follow-up was successful in 419 of 447 patients (94%), of whom 71 had abnormal MPI at baseline. Medical therapy was intensified in all subjects and especially in those with abnormal MPI. Twenty-three patients with abnormal MPI underwent a re-vascularization procedure. CEs occurred in 14 patients, including six of 71 patients (8.5%) with abnormal MPI and eight of 348 patients (2.3%) with normal MPI (P < 0.005). Only two patients developed a hard CE and 12 a soft CE. In multivariate analysis, abnormal MPI was the strongest predictor for CEs [odds ratio (OR) (95% CI) = 5.6 (1.7-18.5)]. Low-density lipoprotein cholesterol > or = 3.35 mmol/l [OR (95% CI) = 7.3; 1.5-34.7] and age > median [OR (95% CI) = 6.0 (1.2-28.6)] were additional independent predictors for CE. The independent predictors for abnormal MPI were male gender, plasma triglycerides > or = 1.70 mmol/l, creatinine clearance < 60 ml/min and HbA1c > 8%, with male gender the strongest [OR (95% CI) = 4.0 (1.8-8.8)]. CONCLUSIONS: Asymptomatic patients with diabetes in this study had a very low hard cardiac event rate over an intermediate period. This could be explained by the effects of intervention or by the low event rate in the background population. Randomized studies of cardiac heart disease screening are required in asymptomatic subjects with diabetes to determine the effectiveness of this intervention.