RESUMO
Recent studies have demonstrated the potential of dynamic contrast-enhanced magnetic resonance imaging (MRI) describing pulmonary perfusion. However, breathing motion, susceptibility artifacts, and a low signal-to-noise ratio (SNR) make automatic pixel-by-pixel analysis difficult. In the present work, we propose a novel method to compensate for breathing motion. In order to test the feasibility of this method, we enrolled 53 patients with pulmonary embolism (N = 24), chronic obstructive pulmonary disease (COPD) (N = 14), and acute pneumonia (N = 15). A crucial part of the method, an automatic diaphragm detection algorithm, was evaluated in all 53 patients by two independent observers. The accuracy of the method to detect the diaphragm showed a success rate of 92%. Furthermore, a Bayesian noise reduction technique was implemented and tested. This technique significantly reduced the noise level without removing important clinical information. In conclusion, the combination of a motion correction method and a Bayesian noise reduction method offered a rapid, semiautomatic pixel-by-pixel analysis of the lungs with great potential for research and clinical use.
Assuntos
Diafragma/fisiologia , Pneumopatias/fisiopatologia , Imageamento por Ressonância Magnética/métodos , Algoritmos , Teorema de Bayes , Meios de Contraste/administração & dosagem , Feminino , Gadolínio DTPA/administração & dosagem , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Pessoa de Meia-Idade , MovimentoRESUMO
To assess the relationship between baseline left ventricle function, functional reserve and resting myocardial perfusion in patients with acute myocardial infarction (AMI). After AMI the presence of dysfunctioning but viable myocardium plays a determinant role in clinical outcome. Regional ventricular function was evaluated by echocardiography both in resting conditions and during dobutamine infusion (10 microg/kg/min). Perfusion was assessed by magnetic resonance imaging in a single slice approach where the first pass of an intravenously injected bolus of gadolinium-based contrast agent was followed through six regions of interest within the myocardium. In each patient a region with normal function was used as reference and the cross-correlation coefficient (CCC), which described the myocardial perfusion relatively to the reference region (CCC = 1 means equivalent perfusion), was obtained for the other five myocardial regions. Twenty-two patients were enrolled into the study. Sixty-one segments had normal function and normal perfusion (CCC = 0.92+/-0.23). The perfusion deficit was more marked in the 29 regions with resting akinesia-dyskinesia than in the 20 hypokinetic regions (CCC = 0.71+/-0.45 vs. 0.84+/-0.23; p < 0.05). Out of the 29 regions with resting akinesia-dyskinesia the 13 segments which showed functional improvement following dobutamine had a higher resting perfusion than the 16 segments which were unresponsive to dobutamine (CCC = 0.83+/-0.32 vs. 0.61+/-0.52, p < 0.05). Similarly, out of the 20 regions with resting hypokinesia the 11 segments having functional reserve showed an higher resting perfusion than the segments which did not (0.96+/-0.21 vs. 0.69+/-0.19; p < 0.05). Early after AMI, the perfusion deficit reflects the severity of the mechanical dysfunction. In regions with baseline dyssynergy resting perfusion is, in general, higher when contractile reserve can be elicited by stress-echo.
Assuntos
Infarto do Miocárdio/fisiopatologia , Infarto do Miocárdio/cirurgia , Reperfusão Miocárdica , Função Ventricular Esquerda/fisiologia , Agonistas Adrenérgicos beta , Adulto , Idoso , Meios de Contraste , Angiografia Coronária , Dobutamina , Ecocardiografia , Feminino , Gadolínio DTPA , Humanos , Itália/epidemiologia , Imagem Cinética por Ressonância Magnética , Masculino , Pessoa de Meia-Idade , Contração Miocárdica/fisiologia , Infarto do Miocárdio/diagnóstico , Noruega/epidemiologia , Variações Dependentes do Observador , Estatística como Assunto , Fatores de Tempo , Resultado do TratamentoRESUMO
UNLABELLED: The relatively low specificity of dynamic contrast-enhanced T1-weighted magnetic resonance imaging (MR) imaging of breast cancer has lead several groups to investigate different approaches to data acquisition, one of them being the use of rapid T2*-weighted imaging. Analyses of such data are difficult due to susceptibility artifacts and breathing motion. MATERIALS AND METHODS: One-hundred-twenty-seven patients with breast tumors underwent MR examination with rapid, single-slice T2*-weighted imaging of the tumor. Different methods for classifying the image data set using leave-one-out cross validation were tested. Furthermore, a semi-automatic region of interest (ROI) definition tool was presented and compared with manual ROI definitions from a previous study. Finally, pixel-by-pixel analysis was done and compared with ROI analysis. The analyses were done with and without noise reduction. RESULTS: The minimum enhancement parameter was the most robust and accurate of the parameters tested. The semi-automatic ROI definition method was fast and produced similar results as the manually defined ROIs. Noise reduction improved both sensitivity and specificity, but the improvement was not statistically significant. The pixel-based analysis methods used in the present study did not improve classification results. CONCLUSIONS: Analysis of T2*-weighted breast images can be done in a rapid and robust manner by using semi-automatic ROI definition tools in combination with noise reduction. Minimum enhancement gives an indication of malignancy in T2*-weighted imaging.
Assuntos
Adenocarcinoma/classificação , Adenocarcinoma/diagnóstico , Neoplasias da Mama/classificação , Neoplasias da Mama/diagnóstico , Imageamento por Ressonância Magnética/métodos , Mamografia/métodos , Intensificação de Imagem Radiográfica/métodos , Interpretação de Imagem Radiográfica Assistida por Computador/métodos , Adenocarcinoma Mucinoso/diagnóstico , Adulto , Idoso , Carcinoma in Situ/diagnóstico , Carcinoma Ductal de Mama/diagnóstico , Carcinoma Lobular/diagnóstico , Meios de Contraste/administração & dosagem , Meios de Contraste/farmacocinética , Estudos de Viabilidade , Feminino , Gadolínio DTPA , Humanos , Pessoa de Meia-Idade , Sensibilidade e Especificidade , Processos EstocásticosRESUMO
The present paper reports our own experience with MR perfusion imaging and gives an overview of contrast-enhanced pulmonary MR perfusion imaging, MR angiography, and ventilation MR imaging using hyperpolarized gases or oxygen as contrast agent. These methods are discussed within the context of their possible role in the diagnosis of pulmonary diseases, particularly embolism and emphysema.
Assuntos
Meios de Contraste , Aumento da Imagem/métodos , Pneumopatias/diagnóstico , Imageamento por Ressonância Magnética/métodos , Enfisema/diagnóstico , Gadolínio DTPA , Humanos , Pulmão/patologia , Pneumopatias Obstrutivas/diagnóstico , Angiografia por Ressonância Magnética/métodos , Pneumonia/diagnóstico , Embolia Pulmonar/diagnósticoRESUMO
The relaxivities r1 and r2 of magnetic resonance contrast agents and the T1 relaxation time values of tissues are strongly field dependent. We present quantitative data and simulations of different gadolinium-based extracellular fluid contrast agents and the modulation of their contrast enhancement by the magnetic field to be able to answer the following questions: How are the dose and field dependences of their contrast enhancement? Is there an interrelationship between dose and field dependence? Should one increase or decrease doses at specific fields? Nuclear magnetic relaxation dispersion data were acquired for the following contrast agents: gadopentetate dimeglumine, gadoterate meglumine, gadodiamide injection, and gadoteridol injection, as well as for several normal and pathological human tissue samples. The magnetic field range stretched from 0.0002 to 4.7 T, including the entire clinical imaging range. The data acquired were then fitted with the appropriate theoretical models. The combination of the diamagnetic relaxation rates (R1 = 1/T1 and R2 = 1/T2) of tissues with the respective paramagnetic contributions of the contrast agents allowed the prediction of image contrast at any magnetic field. The results revealed a nearly identical field and dose-dependent increase of contrast enhancement induced by these contrast agents within a certain dose range. The target tissue concentration (TTC) was an important though nonlinear factor for enhancement. The currently recommended dose of 0.1 mmol/kg body weight seems to be a compromise close to the lower limits of diagnostically sufficient contrast enhancement for clinical imaging at all field strengths. At low field contrast enhancement might be insufficient. Adjustment of dose or concentration, or a new class of contrast agents with optimized relaxivity, would be a valuable contribution to a better diagnostic yield of contrast enhancement at all fields.
Assuntos
Meios de Contraste/administração & dosagem , Gadolínio , Imageamento por Ressonância Magnética , Encéfalo/anatomia & histologia , Encéfalo/patologia , Gadolínio/administração & dosagem , Humanos , Espectroscopia de Ressonância MagnéticaRESUMO
A simple two-compartment model was used to study the effects of water exchange on the signal produced by an inversion recovery prepared rapid gradient-echo sequence during the first passage of a low dose of an intravascular contrast agent. Water exchange at intermediate rates of exchange (1-10 Hz) between the vascular and extravascular spaces caused the form of the signal changes during the first pass to be dependent on both the fractional sizes of the vascular and extravascular compartments and on the exchange rate. Unless the effects of exchange are minimized by using a very short inversion time, parameters such as the peak height and area under the curve will be affected by regional and/or pathological variations in the exchange rate and the size of the vascular fraction. The mean transit time (MTT) is, however, less affected by water exchange. Experimental first-pass data produced by intravascular low-dose injections of iron oxide particles were studied in five pigs at 0.5 T. The MTT as derived from the first-pass curves, without deconvolution with the arterial input function, was well correlated with the myocardial blood flow (MBF) as measured using radioactive microspheres (r = 0.70, n = 52, P < 0.01). Other first-pass parameters such as the peak height or area under the curve exhibited either a poorer, or no, correlation with the MBF. The data suggest that the MTT of the first pass of an intravascular contrast agent may be a robust, quantitative method for assessing myocardial blood flow in patients.
Assuntos
Água Corporal/metabolismo , Meios de Contraste/farmacocinética , Vasos Coronários/fisiopatologia , Imageamento por Ressonância Magnética/métodos , Animais , Transporte Biológico/fisiologia , Velocidade do Fluxo Sanguíneo , Injeções Intra-Arteriais , Modelos Biológicos , Reperfusão Miocárdica , Fluxo Sanguíneo Regional , Sensibilidade e Especificidade , Suínos , Fatores de TempoRESUMO
Image-guided localized proton MR spectroscopy (MRS) of normal breasts and breast tumors (ductal and undifferentiated carcinomas) was performed using a dedicated double breast coil. In vivo 1H MR spectra from 10 normal volunteers showed signals from water and lipids only, even in breasts with small contribution of fatty breast tissue. In the spectra from 6 of the 12 examined patients, an intense signal assigned to choline compounds was detected. The signal was also detected at lower levels in the remaining patients. This study shows that in vivo 1H MRI/MRS examinations of breast tumors can be performed within an examination time of 45 to 60 minutes. Signals from breast tumor metabolites may be detected using in vivo 1H MRS.
Assuntos
Neoplasias da Mama/diagnóstico , Mama/anatomia & histologia , Carcinoma Ductal de Mama/diagnóstico , Colina/análise , Espectroscopia de Ressonância Magnética/métodos , Adulto , Idoso , Idoso de 80 Anos ou mais , Mama/química , Neoplasias da Mama/química , Carcinoma Ductal de Mama/química , Feminino , Humanos , Imageamento por Ressonância Magnética , Espectroscopia de Ressonância Magnética/instrumentação , Pessoa de Meia-Idade , PrótonsRESUMO
Myocardial perfusion was assessed in nine pigs using ultrafast gradient-echo MRI (.5 T, 15-mT/m gradients) at different levels of myocardial blood flow (range, .005-1.84 ml/min/g), generated either by adenosine infusion or by a mechanical occluder, and measured independently using radiolabeled microspheres. Sixty-four consecutive, ECG-triggered, diastolic, short axis images of the left ventricle were obtained during intravenous bolus injections (n = 30) of .05 mmol/kg of gadopentetate dimeglumine. Relative changes in peak intensity, time to peak intensity, washin slope, correlation coefficient, and cross-correlation coefficient were computed from the time-intensity curves obtained from four regions of interest, namely septal, anterior, lateral, and inferior walls. The values from the inferior wall acted as reference for evaluating relative changes in the other three regions. The cross-correlation coefficient (P < .001, rho = .60) and the peak intensity (P < .001, r = .72) showed the best correlation with myocardial blood flow. The washin slope showed a weak positive trend (P < .05), but the low value of r (r = .28) indicated that the use of this parameter to predict flow was invalid; the correlation coefficient and time to peak intensity were not correlated (P = ns). In conclusion, this study shows that it is possible to evaluate relative myocardial perfusion after the first pass of a an intravenously injected bolus of gadopentetate dimeglumine, using dynamic MRI on a conventional medium field MRI system. The cross-correlation coefficient and the peak intensity resulted in more efficient parameters to evaluate relative inhomogeneity of regional myocardial perfusion.
Assuntos
Circulação Coronária/fisiologia , Imageamento por Ressonância Magnética , Adenosina/farmacologia , Animais , Meios de Contraste , Interpretação Estatística de Dados , Gadolínio DTPA , Fluxo Sanguíneo Regional , SuínosRESUMO
Some fundamentals of image processing, its applications to MR imaging, and inherent problems are discussed. Processing of contrast-enhanced dynamic imaging studies is introduced and some clinical examples explain the applications in research and clinical routine.
Assuntos
Meios de Contraste , Processamento de Imagem Assistida por Computador/métodos , Imageamento por Ressonância Magnética/métodos , Artefatos , Feminino , Humanos , Masculino , Fatores de TempoRESUMO
The evaluation of myocardial perfusion is of clinical relevance in ischemic heart disease. New noninvasive and nonionizing imaging techniques for the evaluation of myocardial perfusion are progressing. The present status and the future development of echo-contrast and dynamic-contrast MR imaging are discussed for myocardial perfusion studies.
Assuntos
Circulação Coronária , Ecocardiografia/métodos , Coração/anatomia & histologia , Imageamento por Ressonância Magnética/métodos , Meios de Contraste , HumanosRESUMO
PURPOSE: A computer system for the manual, semi-automatic, and automatic analysis of dynamic MR images was to be developed on UNIX and personal computer platforms. The system was to offer an integrated and standardized way of performing both image processing and analysis that was independent of the MR unit used. MATERIAL AND METHODS: The system consists of modules that are easily adaptable to special needs. Data from MR units or other diagnostic imaging equipment in techniques such as CT, ultrasonography, or nuclear medicine can be processed through the ACR-NEMA/DICOM standard file formats. A full set of functions is available, among them cine-loop visual analysis, and generation of time-intensity curves. Parameters such as cross-correlation coefficients, area under the curve, peak/maximum intensity, wash-in and wash-out slopes, time to peak, and relative signal intensity/contrast enhancement can be calculated. Other parameters can be extracted by fitting functions like the gamma-variate function. Region-of-interest data and parametric values can easily be exported. RESULTS AND CONCLUSION: The system has been successfully tested in animal and patient examinations.
Assuntos
Processamento de Imagem Assistida por Computador/instrumentação , Imageamento por Ressonância Magnética/instrumentação , Software , Algoritmos , Bases de Dados Factuais , Desenho de EquipamentoAssuntos
Imageamento por Ressonância Magnética , Tomografia Computadorizada por Raios X , Meios de Contraste/normas , Controle de Custos , Análise Custo-Benefício , Humanos , Imageamento por Ressonância Magnética/economia , Imageamento por Ressonância Magnética/tendências , Tomografia Computadorizada por Raios X/economia , Tomografia Computadorizada por Raios X/tendênciasRESUMO
RATIONALE AND OBJECTIVES: In this phase III study, we evaluated the efficacy and safety of a negative contrast medium, ferristene (oral magnetic particles), among 277 patients undergoing magnetic resonance (MR) imaging of the abdomen. METHODS: Enhanced (800 ml ferristene) MR images were compared with unenhanced MR images in an intraindividual-patient control design. Adverse events were recorded. The examinations were performed on 1.5-T MR systems (T1- and T2-weighted sequences). RESULTS: Ferristene increased the diagnostic information in 50.9% of the patients, particularly in those with abdominal masses, lymphoma, or pancreatic disease. Distribution of ferristene in the stomach, duodenum, jejunum, and ileum was complete or sufficient in 70.5-85% of the studies. In 64% of the patients, we were confident in the MR findings after the use of ferristene, and ferristene disclosed additional findings in 22% of the patients. The incidence of adverse events was 9.0%, but only 3.6% of all patients experienced ferristene-related adverse events (e.g., nausea, vomiting). Most events were mild or moderate in intensity. CONCLUSION: Ferristene was well tolerated, and for 50% of the patients it added useful diagnostic information.
Assuntos
Meios de Contraste/administração & dosagem , Doenças do Sistema Digestório/patologia , Sistema Digestório/anatomia & histologia , Compostos Férricos/administração & dosagem , Imageamento por Ressonância Magnética/métodos , Administração Oral , Adolescente , Adulto , Idoso , Feminino , Humanos , Masculino , Pessoa de Meia-IdadeRESUMO
Dynamic magnetic resonance (MR) imaging with contrast agents is a very promising technique for studying tissue perfusion in vivo. A temporal series of magnetic resonance images of the same slice are acquired following the injection of a contrast agent into the blood stream. The image intensity depends on the local concentration of the contrast agent, so that tissue perfusion can be studied by the image series. A new method of analyzing such series is described here. Nonparametric linear regression is used for modeling the image intensity along the series on a pixel by pixel basis. After modeling, some relevant quantities describing the time series are obtained and displayed as images. Due to its flexibility, this approach is preferred to parametric modeling when pathology is present since this can induce a wide spread of patterns for the pixel image intensity along time. Results of the application of the method to series of dynamic magnetic resonance images from ischaemic rat brains after the injection of the susceptibility agent Sprodiamide Inj. (Dy-DTPA-BMA) are shown and compared to results from a related known method.
RESUMO
The paper gives a review of the chemical structure, pharmacology and clinical use of currently available contrast media for CT and MRT examinations.
Assuntos
Meios de Contraste , Imageamento por Ressonância Magnética , Tomografia Computadorizada por Raios X , Encefalopatias/diagnóstico , Encefalopatias/diagnóstico por imagem , Neoplasias Encefálicas/diagnóstico , Neoplasias Encefálicas/diagnóstico por imagem , Cardiopatias/diagnóstico , Cardiopatias/diagnóstico por imagem , HumanosRESUMO
Fifty-two patients underwent MR imaging and conventional radiography of the neck within 4 days after a hyperextension-flexion injury. The patients also had follow-up investigations during the first 2 years. The images did not reveal any serious lesions in any of them. Based on the main MR and radiographical findings the patients were divided into 4 groups; no findings, posture abnormalities, spondylosis and disc pathology (from MR images) or reduced intervertebral space (from the radiographs). The outcomes of the different groups were compared with reference to neck stiffness, neck pain and headache during a 2-year follow-up period. The patient groups did not correspond completely when diagnosed from MR imaging and radiography. However, patients with pre-existing spondylosis had more symptoms when examined by both modalities. Based on the radiographs, the group with posture abnormalities had significant fewer symptoms than the other groups.
Assuntos
Acidentes de Trânsito , Vértebras Cervicais/diagnóstico por imagem , Vértebras Cervicais/patologia , Imageamento por Ressonância Magnética , Traumatismos em Chicotada/diagnóstico , Adolescente , Adulto , Idoso , Análise de Variância , Vértebras Cervicais/lesões , Feminino , Seguimentos , Humanos , Imageamento por Ressonância Magnética/instrumentação , Imageamento por Ressonância Magnética/métodos , Imageamento por Ressonância Magnética/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Radiografia , Estatísticas não ParamétricasRESUMO
The effects of regional myocardial ischemia and reperfusion on magnetization transfer (MT) contrast were investigated in an ex vivo perfused piglet heart model. The extent of the ischemic area was defined with perfusion magnetic resonance (MR) studies performed with use of extracellular contrast agents. Relative MT contrast was calculated for a total of 106 regions of interest in nine hearts. In the areas defined as being severely ischemic in the perfusion studies, a small but significant increase in the MT contrast of 18% +/- 9 (standard deviation) (n = 35) was found as early as 10 minutes after the start of ischemia. This contrast difference was reduced to 11% +/- 10 after 2 hours of total occlusion. The contrast between normal and ischemic tissue can be explained in part by the effect of inflowing blood, which leads to changes in both equilibrium magnetization and the apparent T1 of the perfused tissue. However, theoretical estimation suggests that these flow-related changes would produce a maximal relative change in MT contrast of approximately 4%. The most likely explanation for the rest of the observed changes is alteration in the distribution of cellular water related to the so-called intracellular edema that is known to be associated with the acute phase of myocardial ischemia.
Assuntos
Gadolínio DTPA , Imageamento por Ressonância Magnética/métodos , Isquemia Miocárdica/diagnóstico , Algoritmos , Animais , Meios de Contraste , Circulação Coronária , Disprósio , Gadolínio , Septos Cardíacos/patologia , Ventrículos do Coração/patologia , Aumento da Imagem/métodos , Processamento de Imagem Assistida por Computador , Modelos Teóricos , Isquemia Miocárdica/patologia , Reperfusão Miocárdica , Miocárdio/patologia , Compostos Organometálicos , Ácido Pentético/análogos & derivados , Projetos Piloto , SuínosRESUMO
Magnetic resonance imaging (MRI) was used in 10 female patients with chronic lymphedema of the leg. Soft tissue changes in lymphedema is best visualized by T2-weighted sequences. Three patients had a characteristic honeycomb pattern of the subcutanous tissue, whereas the other patients had either diffuse edema or a reticular pattern. The muscular compartments were normal, while the dermis was significantly thickened in 9 out of 10 patients. In conclusion, characteristic changes were observed in MR images of patients with chronic lymphedema of the leg. Further investigations are necessary to evaluate the role of MRI as an aid in the choice of therapy.
Assuntos
Linfedema/patologia , Estudos de Avaliação como Assunto , Feminino , Humanos , Perna (Membro)/patologia , Sistema Linfático/patologia , Imageamento por Ressonância Magnética , Pessoa de Meia-IdadeRESUMO
Increases in signal intensity enhancement were measured in defined regions of interest (ROIs) to allow distinction between malignant and benign tumors with dynamic gadolinium-enhanced magnetic resonance (MR) mammography. Twenty patients with palpable breast lesions (15 malignant, five benign) underwent MR mammography. The dynamic gradient-echo sequence was performed with intravenous bolus injection of gadopentetate dimeglumine and consisted of 25 images with a time resolution of 30 seconds. Contrast enhancement was calculated by comparing user-defined ROIs on pre- and postcontrast images. An increase in signal intensity of 70% or more on the 1-minute postcontrast image was used as the criterion of malignancy. MR mammographic results correlated with histopathologic findings in all patients when the defined ROI was in the most enhancing part of the tumor. For the ROI in areas of submaximal enhancement or when the ROI surrounded the whole lesion, only five and nine tumors, respectively, fulfilled the malignancy criterion. All malignant tumors showed large variations in signal intensity enhancement that depended on the position of the ROI in the tumor. Dynamic, gadolinium-enhanced MR mammography allows distinction of benign from malignant breast tumors when the selected ROI is in the most enhancing part of the lesion.
Assuntos
Neoplasias da Mama/diagnóstico , Mama/patologia , Carcinoma Ductal de Mama/diagnóstico , Meios de Contraste , Fibroadenoma/diagnóstico , Imageamento por Ressonância Magnética/métodos , Meglumina , Compostos Organometálicos , Ácido Pentético/análogos & derivados , Combinação de Medicamentos , Feminino , Gadolínio , Gadolínio DTPA , Humanos , Pessoa de Meia-IdadeRESUMO
PURPOSE: To evaluate use of magnetic resonance (MR) imaging with saline solution as contrast agent in diagnosis of perianal fistulous disease. MATERIALS AND METHODS: Spin-echo intermediate-, T2-, and T1-weighted images were obtained before and after instillation of saline solution into anal fistulas in 12 of 16 consecutive patients. In four patients without secretory fistulas, images were obtained without contrast enhancement. RESULTS: Fistulous tracts were found in 13 patients, fluid cavities in 13, secondary fibrotic tracts in two, and normal perirectal tissue in one. The extent of fistulas and fluid collections was better delineated or more conspicuous on contrast-enhanced images in eight and 10 examinations, respectively, in part due to expansion of collapsed portions of the fistulous system. T2-weighted images were sufficient for diagnosis. CONCLUSION: MR imaging with saline solution as contrast agent may improve visualization of fistulas and their relationship to normal anatomic structures in patients with complex fistulous systems with relatively sparse secretion.