RESUMO
Since the publication of the European Association of Nuclear Medicine (EANM) procedural guidelines for radionuclide myocardial perfusion imaging (MPI) in 2005, many small and some larger steps of progress have been made, improving MPI procedures. In this paper, the major changes from the updated 2015 procedural guidelines are highlighted, focusing on the important changes related to new instrumentation with improved image information and the possibility to reduce radiation exposure, which is further discussed in relation to the recent developments of new International Commission on Radiological Protection (ICRP) models. Introduction of the selective coronary vasodilator regadenoson and the use of coronary CT-contrast agents for hybrid imaging with SPECT/CT angiography are other important areas for nuclear cardiology that were not included in the previous guidelines. A large number of minor changes have been described in more detail in the fully revised version available at the EANM home page: http://eanm.org/publications/guidelines/2015_07_EANM_FINAL_myocardial_perfusion_guideline.pdf .
Assuntos
Imagem de Perfusão do Miocárdio/métodos , Guias de Prática Clínica como Assunto , Sociedades Médicas , Tomografia Computadorizada por Raios X/métodos , Adulto , Meios de Contraste , Doença da Artéria Coronariana/diagnóstico por imagem , Doença da Artéria Coronariana/fisiopatologia , Relação Dose-Resposta a Droga , Exercício Físico , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Pessoa de Meia-Idade , Imagem Multimodal , Imagem de Perfusão do Miocárdio/efeitos adversos , Imagem de Perfusão do Miocárdio/instrumentação , Purinas/efeitos adversos , Purinas/farmacologia , Pirazóis/efeitos adversos , Pirazóis/farmacologia , Exposição à Radiação , Segurança , Software , Tomografia Computadorizada por Raios X/efeitos adversos , Tomografia Computadorizada por Raios X/instrumentação , Vasodilatadores/efeitos adversos , Vasodilatadores/farmacologiaRESUMO
BACKGROUND: Low bone mineral density (BMD) has been reported in 30.4% of adult patients with atopic dermatitis (AD). OBJECTIVE: The aim of this study was to determine the prevalence of low BMD in children with moderate to severe AD and to investigate the relation between BMD and corticosteroid and cyclosporine therapy. METHODS: Lumbar spine BMD was measured by dual-energy X-ray absorptiometry in 60 children (age 5-16 years) with moderate to severe AD. BMD (in g/cm(2)) was expressed in Z-scores, the number of SD above or below the mean value of an age- and sex-matched reference population. In children, low BMD was defined as a Z-score less than -2. Information on lifestyle parameters and bone fractures were collected by use of a standardized questionnaire. The cumulative dose of corticosteroids and cyclosporine therapy was calculated for the previous 5-year period. RESULTS: Three patients (5%) had low BMD; one patient (1.7%) had osteoporosis. The observed prevalence of low BMD in this study (6.7%; 95% confidence interval 1.8%-16.2%) does not differ from the expected prevalence of low BMD in the general population (P = .06). Overall, use of topical corticosteroids in the previous 5 years was not associated with a decrease in BMD (Z-score). When children received additional systemic treatment (oral corticosteroids and/or cyclosporine) in the previous 5 years, BMD decreased, although the decrease was not statistically significant. Correction for lifestyle parameters did not change these associations. LIMITATIONS: The number of patients studied was limited. The cumulative dose of corticosteroids and cyclosporine therapy was only registered for the previous 5 years, and relatively low amounts of topical corticosteroids were used. The definition of low BMD differs between adults (Z-score < -1) and children (Z-score < -2). Because there is no Dutch BMD reference population for children, normative BMD references were obtained from a different population (US children). CONCLUSIONS: Low BMD did not occur more frequently in this population of children with moderate to severe AD compared with the general population. Use of topical corticosteroids in the previous 5 years was not associated with a decrease in BMD.
Assuntos
Densidade Óssea/efeitos dos fármacos , Dermatite Atópica/tratamento farmacológico , Dermatite Atópica/epidemiologia , Imunossupressores/efeitos adversos , Osteoporose/induzido quimicamente , Osteoporose/epidemiologia , Absorciometria de Fóton , Adolescente , Corticosteroides/administração & dosagem , Corticosteroides/efeitos adversos , Criança , Pré-Escolar , Ciclosporina/administração & dosagem , Ciclosporina/efeitos adversos , Feminino , Fraturas Ósseas/epidemiologia , Humanos , Imunossupressores/administração & dosagem , Vértebras Lombares/diagnóstico por imagem , Masculino , Osteoporose/diagnóstico por imagem , Prevalência , Fatores de Risco , Índice de Gravidade de Doença , Tacrolimo/administração & dosagem , Tacrolimo/efeitos adversos , Tacrolimo/análogos & derivadosRESUMO
The InSPira HD system, a novel brain-dedicated SPECT scanner, allows for imaging with a high spatial resolution. Here, we tested whether this scanner can be used to image the dopamine transporter adequately. Therefore, striatal phantom and patient data acquired on the InSPira were compared head-to-head with the well-validated brain-dedicated NeuroFocus system. A striatal phantom filled with [123I] and 14 subjects (after [123I]FP-CIT injection) were scanned on both systems. [123I]FP-CIT SPECT scans were visually assessed. Striatal binding ratios were calculated automatically using the software package BRASS. Striatal phantom and patient data showed strong correlations with respect to striatal ratios (R = 0.99 and R = 0.92; p < 0.05 and p < 0.01, respectively). Slightly higher ratios were found for the NeuroFocus patient data, probably due to differences in system performance. Visual assessment of [123I]FP-CIT scans showed agreement between systems in 13 of the 14 cases. We conclude that [123I]FP-CIT SPECT imaging can be performed adequately on the new InSPira system.
RESUMO
OBJECTIVE: Brown adipose tissue (BAT) activity in humans is stimulated by cold and by a limited number of pharmacological agents, including ß3-adrenergic agonists and bile acids. Although thyrotropin-releasing hormone (TRH) is known to activate BAT in several mammals, this has not been reported in humans. DESIGN: A randomized, placebo-controlled, double-blind, cross-over trial. METHODS: We investigated the effects of intravenous bolus administration of 400 µg TRH or 2 mL saline on BAT activity in healthy, lean men. BAT activity was measured as standardized 18F-fluorodeoxyglucose (18F-FDG) uptake and glucose metabolic rate (MRglu) using dynamic PET/CT imaging. The first six individuals were studied at room temperature, while subsequently nine were exposed to mild cold (17°C ± 1°C) for 60 min before imaging. During the dynamic scan, blood was withdrawn for measurement of thyroid hormone and catecholamine concentrations. This trial is registered with The Netherlands National Trial Register (number NTR5512). RESULTS: Sixteen participants were recruited. Six men studied at room temperature showed no visible BAT activity during either session. After exposure to mild cold, four of nine men (44.4%) showed clear increase of 18F-FDG uptake after TRH administration compared to placebo. Maximal standardized 18F-FDG uptake showed a trend toward increase after TRH compared to placebo (P = 0.066). MRglu showed a significant increase after TRH administration (P = 0.014). The increase in 18F-FDG uptake was not paralleled by changes in plasma thyroid hormone or catecholamine concentrations. CONCLUSION: Systemic TRH administration can increase the activity of cold-stimulated BAT in adult men. These findings may assist developing pharmacological strategies for modulating BAT activity in the management of obesity.
Assuntos
Tecido Adiposo Marrom/efeitos dos fármacos , Hormônios/farmacologia , Termogênese/efeitos dos fármacos , Hormônio Liberador de Tireotropina/farmacologia , Tecido Adiposo Marrom/diagnóstico por imagem , Administração Intravenosa , Adulto , Temperatura Baixa , Estudos Cross-Over , Método Duplo-Cego , Fluordesoxiglucose F18 , Voluntários Saudáveis , Humanos , Masculino , Tomografia por Emissão de Pósitrons combinada à Tomografia Computadorizada , Compostos RadiofarmacêuticosRESUMO
UNLABELLED: (201)Tl-Chloride ((201)Tl) is a myocardial perfusion SPECT agent with excellent biochemical properties commonly used for assessing tissue viability. However, cardiac (201)Tl SPECT images are severely degraded by photons scattered in the thorax. Accurate correction for this scatter is complicated by the nonuniform density and varied sizes of thoraxes, by the additional attenuation and scatter caused by female patients' breasts, and by the energy spectrum of (201)Tl. Monte Carlo simulation is a general and accurate method well suited to modeling this scatter. METHODS: Statistical reconstruction that includes Monte Carlo modeling of scatter was compared with statistical reconstruction algorithms not corrected for scatter. In the ADS method, corrections for attenuation, detector response, and scatter (Monte Carlo-based) were implemented simultaneously via the dual-matrix ordered-subset expectation maximization algorithm with a Monte Carlo simulator as part of the forward projector. The ADS method was compared with the A method (ordered-subset expectation maximization with attenuation correction) and with the AD method (a method like the A method but with detector response modeling added). A dual-head SPECT system equipped with two (153)Gd scanning line sources was used for simultaneously acquiring transmission and emission data. Four clinically realistic phantom configurations (a large thorax and a small thorax, each with and without breasts) with a cardiac insert containing 2 cold defects were used to evaluate the proposed reconstruction algorithms. We compared the performance of the different algorithms in terms of noise properties, contrast-to-noise ratios, the contrast separability of perfusion defects, uniformity, and robustness to anatomic variations. RESULTS: The ADS method provided images with clearly better visual defect contrast than did the other methods. The contrasts achieved with the ADS method were 10%-24% higher than those achieved with the AD method and 11%-37% higher than those achieved with the A method. For a typical contrast level, the ADS method exhibited noise levels around 27% lower than the AD method and 34% lower than the A method. Compared with the other 2 algorithms, the ADS reconstructions were less sensitive to anatomic variations and had better image uniformity in the homogeneously perfused myocardium. Finally, we found that the improvements that can be achieved with Monte Carlo-based scatter correction are stronger for (201)Tl than for (99m)Tc imaging. CONCLUSION: Our results indicate that Monte Carlo-based scatter correction is suitable for (201)Tl cardiac imaging and that such correction simultaneously improves several image-quality metrics.
Assuntos
Processamento de Imagem Assistida por Computador/métodos , Imageamento Tridimensional/métodos , Miocárdio/patologia , Espalhamento de Radiação , Radioisótopos de Tálio/farmacocinética , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Algoritmos , Humanos , Modelos Estatísticos , Método de Monte Carlo , Perfusão , Imagens de Fantasmas , Reprodutibilidade dos TestesRESUMO
UNLABELLED: Cardiac SPECT images are degraded by photons scattered in the thorax. Accurate correction for scatter is complicated by the nonuniform density and varied sizes of thoraxes and by the additional attenuation and scatter caused by female patients' breasts. Monte Carlo simulation is a general and accurate method for detailed modeling of scatter. Hence, for 99mTc we compared statistical reconstruction based on Monte Carlo modeling of scatter with statistical reconstruction that incorporates the more commonly used triple-energy-window scatter correction. Both of these scatter correction methods were used in conjunction with attenuation correction and resolution recovery. METHODS: Simultaneous attenuation, detector response, and Monte Carlo-based scatter correction were implemented via the dual-matrix ordered-subset expectation maximization algorithm with a Monte Carlo simulator as part of the forward projector (ADS-MC). ADS-MC was compared to (i) ordered-subset expectation maximization with attenuation correction and with detector response modeling (AD); (ii) like (i) but with scatter correction added using the triple-energy-window method (ADS-TEW). A dual-detector SPECT system equipped with 2 153Gd scanning line sources was used for acquiring 99mTc emission data and attenuation maps. Four clinically realistic phantom configurations (a large thorax and a small thorax, each with and without breasts) with a cardiac insert containing 2 cold defects were used to evaluate the proposed reconstruction algorithms. In these phantom configurations, we compared the performance of the algorithms in terms of noise properties, contrast-to-noise ratios, contrast separability of cold defects, and robustness to anatomic variation. RESULTS: Noise was found to be approximately 14% lower in the ADS-MC images than in the ADS-TEW and AD images. Typically, the contrast obtained with the ADS-MC algorithm was 10%-20% higher than that obtained with the other 2 methods. Furthermore, compared with the other 2 algorithms, the ADS-MC method was less sensitive to anatomic variations. CONCLUSION: Our results indicate that the imaging performance of 99mTc SPECT can be improved more by Monte Carlo-based scatter correction than by window-based scatter correction.
Assuntos
Coração/diagnóstico por imagem , Tecnécio , Simulação por Computador , Humanos , Imageamento Tridimensional , Método de Monte Carlo , Perfusão , Imagens de Fantasmas , Fótons , Espalhamento de Radiação , Tórax/diagnóstico por imagem , Tomografia Computadorizada de Emissão de Fóton ÚnicoRESUMO
Ho-166 is a combined beta-gamma emitter of which the betas can be used therapeutically. From the 81 keV gammas of Ho-166, SPECT images can be obtained, which give opportunities to guide Ho-166 therapy. Accurate reconstruction of Ho-166 images is currently hampered by photopeak-scatter in the patient, down-scatter in the detector, collimator and patient caused by the 1.4 MeV photons and by bremsstrahlung. We developed and validated a method for quantitative SPECT of Ho-166 that involves correction for both types of scatter plus non-uniform attenuation correction using attenuation maps. Photopeak-scatter (S) is compensated for by a rapid 3D Monte Carlo (MC) method that is incorporated in ordered subset (OS) reconstruction of the emission data, together with simultaneous correction for attenuation (A) and detector response (D); this method is referred to as OS-ADS. Additionally, for correction of down-scatter, we use a 14 keV wide energy window centred at 118 keV (OS-ADSS). Due to a limited number of available energy windows, the same 118 keV energy window was used for down-scatter correction of the simultaneously acquired Gd-153 transmission data. Validations were performed using physical phantom experiments carried out on a dual-head SPECT system; Gd-153 transmission line sources were used for acquiring attenuation maps. For quantitative comparison of OS-ADS and OS-ADSS, bottles filled with Ho-166 were placed in both a cylindrical phantom and an anthropomorphic thorax phantom. Both OS-ADS and OS-ADSS were compared with an ordered subset reconstruction without any scatter correction (OS-AD). Underestimations of about 20% in the attenuation map were reduced to a few per cent after down-scatter correction. The average deviation from the true activity contained in the bottles was +72% with OS-AD. Using OS-ADS, this average overestimation was reduced to +28% and with OS-ADSS the deviation was further reduced to 16%. With OS-AD and OS-ADS, these numbers were more sensitive to the choice of volumes of interest than with OS-ADSS. For the reconstructed activity distributions, erroneous background activity found with OS-AD was reduced by a factor of approximately 2 by applying OS-ADS and reduced by a factor of approximately 4 by applying OS-ADSS. The combined attenuation, photopeak-scatter and down-scatter correction framework proposed here greatly enhanced the quantitative accuracy of Ho-166 imaging, which is of the uppermost importance for image-guided therapies. It is expected that the method, with adapted window settings, also can be applied to other isotopes with high energy peaks that contaminate the photopeak data, such as I-131 or In-111.
Assuntos
Hólmio/farmacologia , Radioisótopos/farmacologia , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Humanos , Processamento de Imagem Assistida por Computador , Modelos Estatísticos , Método de Monte Carlo , Imagens de Fantasmas , Compostos Radiofarmacêuticos/química , Espalhamento de RadiaçãoRESUMO
AIM: The 123I-metaiodobenzylguanidine (123I-MIBG) late heart-to-mediastinum ratio (H/M) is a well-established prognostic parameter in patients with chronic heart failure (CHF). However, 123I presents imaging problems owing to high-energy photon emission leading to penetration of collimator septa and subsequent reduction in image quality. Most likely this affects the H/M ratio and may subsequently lead to incorrect patient risk classification. In this prospective study we assessed the intrapatient variation in late H/M ratio between low-energy high-resolution (LEHR) and medium-energy (ME) collimators in patients with CHF. MATERIALS AND METHODS: Fifty-three patients with CHF (87% male, age 63±8.3 years, left ventricular ejection fraction 29±7.8) referred for 123I-MIBG scintigraphy were enrolled in the study. In each patient, after the administration of 185 MBq I-MIBG, early (15 min after injection) and late (4 h after injection) planar anterior thoracic images were acquired with both LEHR and ME collimators. Early and late H/M ratios were calculated on the basis of the mean count densities from the manually drawn regions of interest (ROIs) over the left ventricle and a predefined fixed ROI placed in the upper mediastinum. Additional ROIs were drawn over the liver and lungs. Liver/lung to myocardium and liver/lung to mediastinal ratios were calculated to estimate the effect of collimator septa penetration from liver and lung activity on the myocardial and mediastinal ROIs. RESULTS: The mean LEHR collimator-derived parameters were lower compared with those from the ME collimator (late H/M 1.41±0.18 vs. 1.80±0.41, P<0.001). Moreover, Bland-Altman analysis showed that with increasing late H/M ratios the difference between the ratios from the two collimator types increased (R2=0.73, P=0.001). Multivariate regression analysis showed that almost 90% of the variation in the difference between ME and LEHR late H/M ratios could be explained by scatter from the liver in both the mediastinal and myocardial ROIs (R2=0.90, P=0.001). Independent predictors for the difference in the late H/M between ME and LEHR were the liver-to-heart ratio and the liver-to-mediastinum ratio assessed by ME (standardized coefficient of -1.69 and 1.16, respectively) and LEHR (standardized coefficient of 1.24 and -0.90, respectively) (P<0.001 for all). CONCLUSION: Intrapatient comparison in H/M between the ME and LEHR collimators in patients with CHF showed that with increasing H/M the difference between the ratios increased in favour of the ME collimator. These differences could be explained by septal penetration of high-energy photons from both the liver and the lung in the mediastinum and myocardium, being lowest when using the ME collimator. These results strengthen the importance of the recommendation to use ME collimators in semiquantitative 123I-MIBG studies.
Assuntos
3-Iodobenzilguanidina , Coração/diagnóstico por imagem , Fígado/diagnóstico por imagem , Pulmão/diagnóstico por imagem , Mediastino/diagnóstico por imagem , Imagem de Perfusão do Miocárdio/instrumentação , Fótons , 3-Iodobenzilguanidina/farmacocinética , Doença Crônica , Feminino , Insuficiência Cardíaca/diagnóstico por imagem , Insuficiência Cardíaca/metabolismo , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Pessoa de Meia-Idade , Análise MultivariadaRESUMO
PURPOSE: To investigate the potential of magnetic resonance imaging (MRI) for accurate assessment of the three-dimensional (166)Ho activity distribution to estimate radiation-absorbed dose distributions in (166)Ho-loaded poly (L-lactic acid) microsphere ((166)Ho-PLLA-MS) liver radioembolization. METHODS AND MATERIALS: MRI, computed tomography (CT), and single photon emission CT (SPECT) experiments were conducted on an anthropomorphic gel phantom with tumor-simulating gel samples and on an excised human tumor-bearing liver, both containing known amounts of (166)Ho-PLLA-MS. Three-dimensional radiation-absorbed dose distributions were estimated at the voxel level by convolving the (166)Ho activity distribution, derived from quantitative MRI data, with a (166)Ho dose point-kernel generated by MCNP (Monte Carlo N-Particle transport code) and from Medical Internal Radiation Dose Pamphlet 17. MRI-based radiation-absorbed dose distributions were qualitatively compared with CT and autoradiography images and quantitatively compared with SPECT-based dose distributions. Both MRI- and SPECT-based activity estimations were validated against dose calibrator measurements. RESULTS: Evaluation on an anthropomorphic phantom showed that MRI enables accurate assessment of local (166)Ho-PLLA-MS mass and activity distributions, as supported by a regression coefficient of 1.05 and a correlation coefficient of 0.99, relating local MRI-based mass and activity calculations to reference values obtained with a dose calibrator. Estimated MRI-based radiation-absorbed dose distributions of (166)Ho-PLLA-MS in an ex vivo human liver visually showed high correspondence to SPECT-based radiation-absorbed dose distributions. Quantitative analysis revealed that the differences in local and total amounts of (166)Ho-PLLA-MS estimated by MRI, SPECT, and the dose calibrator were within 10%. Excellent agreement was observed between MRI- and SPECT-based dose-volume histograms. CONCLUSIONS: Quantitative MRI was demonstrated to provide accurate three-dimensional (166)Ho-PLLA-MS activity distributions, enabling localized intrahepatic radiation-absorbed dose estimation by convolution with a (166)Ho dose point-kernel for liver radioembolization treatment optimization and evaluation.
Assuntos
Embolização Terapêutica/métodos , Hólmio/farmacocinética , Ácido Láctico/farmacocinética , Neoplasias Hepáticas/metabolismo , Imageamento por Ressonância Magnética/métodos , Microesferas , Polímeros/farmacocinética , Radioisótopos/farmacocinética , Algoritmos , Autorradiografia/métodos , Humanos , Fígado/diagnóstico por imagem , Fígado/metabolismo , Neoplasias Hepáticas/diagnóstico por imagem , Método de Monte Carlo , Imagens de Fantasmas , Poliésteres , Dosagem Radioterapêutica , Distribuição Tecidual , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Tomografia Computadorizada por Raios XRESUMO
INTRODUCTION: Ex vivo storage phosphor imaging rat studies reported increased brain dopamine D2/3 receptor (DRD2/3) availability following treatment with varenicline, a nicotinergic drug. However, ex vivo studies can only be performed using cross-sectional designs. Small-animal imaging offers the opportunity to perform serial assessments. We evaluated whether high-resolution pinhole single photon emission computed tomography (SPECT) imaging in rats was able to reproduce previous ex vivo findings. METHODS: Rats were imaged for baseline striatal DRD2/3 availability using ultra-high-resolution pinhole SPECT (U-SPECT-II) and [123I]IBZM as a radiotracer, and randomized to varenicline (n=7; 2 mg/kg) or saline (n=7). Following 2 weeks of treatment, a second scan was acquired. RESULTS: Significantly increased striatal DRD2/3 availability was found following varenicline treatment compared to saline (timeâtreatment effect): posttreatment difference in binding potential between groups corrected for initial baseline differences was 2.039 (P=.022), indicating a large effect size (d=1.48). CONCLUSIONS: Ultra-high-resolution pinhole SPECT can be used to assess varenicline-induced changes in DRD2/3 availability in small laboratory animals over time. Future small-animal studies should include imaging techniques to enable repeated within-subjects measurements and reduce the amount of animals.
Assuntos
Benzamidas , Benzazepinas/farmacologia , Neostriado/diagnóstico por imagem , Neostriado/metabolismo , Pirrolidinas , Quinoxalinas/farmacologia , Receptores de Dopamina D2/metabolismo , Receptores de Dopamina D3/metabolismo , Tomografia Computadorizada de Emissão de Fóton Único , Animais , Masculino , Neostriado/efeitos dos fármacos , Agonistas Nicotínicos/farmacologia , Ligação Proteica/efeitos dos fármacos , Ratos , Ratos Wistar , VareniclinaRESUMO
PURPOSE: Thallous (201Tl) chloride is a single-photon emission computed tomography (SPECT) tracer mainly used for assessing perfusion and viability of myocardial tissue. 201Tl emits X-rays around 72 keV and gammas at 167 keV, and has a half-life of 73 h. Regulations allow an intrinsic contamination up to 3-5%, which is mainly caused by 200Tl (368 keV; 26 h) and by 202Tl (439 keV; 12.2 days). Contra-intuitive to the low-level percentages in which these contaminants are present, their impact may be significant because of much higher gamma camera sensitivity for these high-energy photon emissions. Therefore, we investigate the effects of the contaminants in terms of detected fractions of photons in projections and contrast degradation in reconstructed images. METHODS: Acquisitions of a digital thorax phantom filled with thallous (201Tl) chloride were simulated with a validated Monte Carlo tool, thereby, modelling 1% of contamination by 200Tl and 202Tl each. In addition, measurements of a thorax phantom on a dual-headed gamma camera were performed. The product used was contaminated by 0.17% of 200Tl and 0.24% of 202Tl at activity reference time (ART). This ART is specified by the manufacturer, thereby, accounting for the difference in half-lives of 201Tl and its contaminants. These measurements were repeated at different dates associated with various contamination levels. RESULTS: Simulations showed that, with 1% of 200Tl and 202Tl, the total contamination in the 72 keV window can rise up to one out of three detected photons. For the 167 keV window, the contamination is even more pronounced: more than four out of five detections in this photopeak window originate from contaminants. Measurements indicate that cold lesion contrast in myocardial perfusion SPECT imaging is at maximum close to ART. In addition to a higher noise level, relative contrast decreases 15% 2 days early to ART, which is explained by an increase in 200Tl contamination. After ART, contrast decreased by 16% when the 202Tl contamination increased to the maximal allowed limit. CONCLUSIONS: Contra-intuitive to the low-level percentages in which they are typically present, penetration and downscatter of high-energy photons from 200Tl and 202Tl significantly contribute to thallous (201Tl) chloride images, thereby, reducing contrast and adding noise. These findings may prompt for improved production methods, for updated policies with regard to timing of usage, and they also render the usefulness of adding the high photopeak window (167 keV) questionable. A window-based correction method for this contamination is advisable.
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Artefatos , Contaminação de Medicamentos , Aumento da Imagem/métodos , Interpretação de Imagem Assistida por Computador/métodos , Tálio , Tomografia Computadorizada de Emissão de Fóton Único/métodos , Imagens de Fantasmas , Compostos Radiofarmacêuticos , Reprodutibilidade dos Testes , Sensibilidade e Especificidade , Tomografia Computadorizada de Emissão de Fóton Único/instrumentaçãoRESUMO
Noninvasive imaging techniques like magnetic resonance imaging (MRI), computed tomography (CT) and single photon emission computed tomography (SPECT) play an increasingly important role in the diagnostic workup and treatment of cancerous disease. In this context, a distinct trend can be observed towards the development of contrast agents and radiopharmaceuticals that open up perspectives on a multimodality imaging approach, involving all three aforementioned techniques. To promote insight into the potentialities of such an approach, we prepared an overview of the strengths and limitations of the various imaging techniques, in particular with regard to their capability to quantify the spatial distribution of a multimodal diagnostic agent. To accomplish this task, we used a two-step approach. In the first step, we examined the situation for a particular therapeutic anti-cancer agent with multimodal imaging opportunities, viz. holmium-loaded microspheres (HoMS). Physical phantom experiments were performed to enable a comparative evaluation of the three modalities assuming the use of standard equipment, standard clinical scan protocols, and signal-known-exactly conditions. These phantom data were then analyzed so as to obtain first order estimates of the sensitivity and detection limits of MRI, CT and SPECT for HoMS. In the second step, the results for HoMS were taken as a starting point for a discussion of the factors affecting the sensitivity and detection limits of MRI, CT and SPECT for multimodal agents in general. In this, emphasis was put on the factors that must be taken into account when extrapolating the findings for HoMS to other diagnostic tasks, other contrast agents, other experimental conditions, and other scan protocols.