RESUMO
Magnetization transfer (MT) provides post-gadolinium contrast improvement through decreasing the tissue signal. Our study had two aims: to analyse the effect of MT qualitatively and quantitatively in 13 patients, and to analyse in vitro the competition between two relaxation phenomena, dipole-dipole which is characteristic of MT and proton - electron which is characteristic of gadolinium. Contrast between lesion and white matter improved from 20.6 % before MT to 65.1 % after MT, enabling new lesions to be detected in two patients. The improvement was due mainly to the proton - electron effect of gadolinium rather than the dipole relaxation of MT. These results are in agreement with those in the literature. The existence of spontaneous high-signal induced by MT in the absence of gadolinium indicates that it is preferable to perform an MT sequence before and after administration of gadolinium.
Assuntos
Astrocitoma/diagnóstico , Neoplasias Encefálicas/diagnóstico , Encéfalo/patologia , Meios de Contraste , Compostos Heterocíclicos , Aumento da Imagem , Imageamento por Ressonância Magnética/métodos , Esclerose Múltipla/diagnóstico , Compostos Organometálicos , Adolescente , Adulto , Idoso , Idoso de 80 Anos ou mais , Criança , Pré-Escolar , Feminino , Gadolínio , Humanos , Magnetismo , Masculino , Pessoa de Meia-IdadeRESUMO
OBJECTIVE: Angiotensin-converting enzyme inhibitors may decrease glomerular filtration rate when a significant renal artery stenosis is present. The purpose of this preliminary study is to evaluate the feasibility of captopril-sensitized, dynamic MR imaging of the kidney in a series of patients with a high suspicion of renovascular hypertension and to compare the results with those of captopril scintigraphy. SUBJECTS AND METHODS: Fifteen hypertensive patients with renal artery stenosis shown by angiography were studied with sequential gadolinium-enhanced MR imaging after oral administration of 50 mg of captopril, an inhibitor of angiotensin-converting enzyme. Symmetry of onset and evolution of tubular phases between the two kidneys were analyzed, and medullary signal intensity time curves were drawn for each kidney. When asymmetry between kidneys was noted, the same dynamic study was repeated 24 hr later, without captopril sensitization. All patients also underwent renal scintigraphy after administration of captopril to compare captopril-induced changes in both techniques. Three-dimensional time-of-flight MR angiography was also performed on all patients. RESULTS: MR imaging with normal and symmetric tubular phases showed that 11 patients had no impairment of glomerular filtration after administration of captopril. MR imaging showed that four had impairment of glomerular filtration: studies without captopril were symmetric (n = 2) or slightly asymmetric (n = 2), but administration of captopril induced severe functional impairment on the side of stenosis--that is, a delayed tubular phase with late corticomedullary decrease of signal intensity in the first two patients and absence of tubular phase in the other two. The results of scintigraphy were concordant in all but one case, in which the segmental distribution of filtration impairment, shown by MR imaging, was not shown by scintigraphy. The renal artery stenosis was shown by MR angiography in 10 of 15 patients (67%). CONCLUSION: Captopril-sensitized dynamic MR imaging of the kidney is feasible in patients with renovascular hypertension. However, captopril-induced changes are not present in all patients proven to have the disease. Scintigraphy provides similar results but may ignore segmental functional involvement.
Assuntos
Inibidores da Enzima Conversora de Angiotensina , Captopril , Hipertensão Renovascular/diagnóstico , Imageamento por Ressonância Magnética , Inibidores da Enzima Conversora de Angiotensina/farmacologia , Captopril/farmacologia , Meios de Contraste , Estudos de Viabilidade , Feminino , Gadolínio , Taxa de Filtração Glomerular/efeitos dos fármacos , Humanos , Hipertensão Renovascular/diagnóstico por imagem , Hipertensão Renovascular/fisiopatologia , Rim/diagnóstico por imagem , Angiografia por Ressonância Magnética , Masculino , Meglumina , Pessoa de Meia-Idade , Compostos Organometálicos , Radiografia , Cintilografia , Obstrução da Artéria Renal/diagnóstico , Obstrução da Artéria Renal/diagnóstico por imagem , Tecnécio Tc 99m MertiatidaRESUMO
In stenosis of a renal artery, angiotensin-converting enzyme inhibitor (ACEI) can induce a decrease in ipsilateral glomerular filtration. Dynamic MR imaging with gadolinium chelate enhancement was tested to detect this glomerular filtration reduction in experimental renovascular hypertension in the rat. Thirteen rats, with surgically induced left renal artery stenosis, developed hypertension and were studied before and after intravenous injection of ACEI with sequential Gd-DOTA-enhanced MR imaging. The time to onset of the tubular phase, the time of the maximal drop of signal, and the medullary signal-time curves of both kidneys were compared. Before ACEI, tubular phases were symmetric in 11 rats and slightly asymmetric in 2. Twelve rats showed ACEI-induced changes (positive test): absence of tubular phase on the left side (n = 8) or delay (n = 4) with significant differences (P < .01). Tubular phases remained symmetric in one (negative test). Dynamic MR imaging can identify ACEI-induced Gd-DOTA tubular transit asymmetry, indicative of functionally significant renal artery stenoses, in rats.
Assuntos
Inibidores da Enzima Conversora de Angiotensina/efeitos adversos , Compostos Heterocíclicos , Hipertensão Renovascular/fisiopatologia , Túbulos Renais/efeitos dos fármacos , Compostos Organometálicos , Animais , Meios de Contraste , Taxa de Filtração Glomerular/efeitos dos fármacos , Hipertensão Renovascular/diagnóstico , Túbulos Renais/fisiopatologia , Imageamento por Ressonância Magnética , Masculino , Ratos , Ratos WistarRESUMO
1. Functional magnetic resonance imaging (fMRI) at 1.5 T was used to investigate the lateralization of prefrontal cortex activity during internal mental calculation in 16 human volunteers (8 right-handed and 8 left-handed). Subjects were asked to perform two different tasks: 1) a serial subtraction of prime numbers and 2) a control task in which they mentally recited numbers. 2. Signal modifications were regularly observed in the prefrontal cortex (Brodmann's area 46) during the serial subtraction of prime numbers, whereas the number listing task poorly activated the same areas. 3. In right-handed subjects, activation was clearly lateralized in the left dorsolateral prefrontal cortex, whereas a frequent bilateral activation was found in left-handed subjects. 4. We conclude that prefrontal activation during mental calculation is lateralized in a manner similar to that reported during linguistic tasks, i.e., a clear lateralization in right- but not in left-handed subjects.
Assuntos
Nível de Alerta/fisiologia , Atenção/fisiologia , Lateralidade Funcional/fisiologia , Imageamento por Ressonância Magnética , Processos Mentais/fisiologia , Córtex Pré-Frontal/fisiologia , Adulto , Feminino , Humanos , Masculino , Matemática , Córtex Pré-Frontal/anatomia & histologia , Valores de ReferênciaRESUMO
Effects of magnetization transfer were evaluated in vitro on circulating blood. Various velocities were tested from 0 to 72 cm/second. Decrease signal intensity caused by magnetization transfer effects was inversely proportional to inflow velocity. It reached 10% at very low velocities and disappeared at velocities higher than 30 cm/second.
Assuntos
Velocidade do Fluxo Sanguíneo/fisiologia , Angiografia por Ressonância Magnética/instrumentação , Modelos Cardiovasculares , Processamento de Sinais Assistido por Computador/instrumentação , Adulto , Encéfalo/irrigação sanguínea , Feminino , Humanos , Masculino , Valores de ReferênciaRESUMO
RATIONALE AND OBJECTIVES: Renal perfusion can be evaluated with first-pass study of superparamagnetic iron oxide particles (SPIO). We applied this technique to a unilateral renal hypoperfusion model in rabbits. METHODS: Turbo fast low-angle shot sequences (acquisition time = 440 msec), after bolus injection of SPIO (100-140 mumol/kg iron), were performed in two control groups (n = 5 in each) and one group (n = 5) with a left renal blood flow reduction caused by a surgical interrenal aortic ligature (140 mumol/kg iron). Qualitative and quantitative analysis using relative blood volume (rRBV), relative blood flow (rRBF), and mean transit time (MTT) were performed. RESULTS: Signal changes were symmetric in control groups without significant differences between the kidneys. The experimental group showed a significantly delayed and less pronounced maximal reduction of signal related to a significantly decreased rRBF and increased rRBV and MTT in the left kidney (p < .05). CONCLUSION: This study shows the effectiveness of a dynamic magnetic resonance study using SPIO to detect unilateral kidney perfusion reduction.
Assuntos
Meios de Contraste/administração & dosagem , Ferro , Rim/irrigação sanguínea , Imageamento por Ressonância Magnética/métodos , Óxidos , Obstrução da Artéria Renal/fisiopatologia , Animais , Velocidade do Fluxo Sanguíneo , Modelos Animais de Doenças , Estudos de Avaliação como Assunto , Nefropatias/diagnóstico , Coelhos , Estatísticas não ParamétricasRESUMO
Major clinical challenges are involved in applications of MR-angiography for the study of renal arteries, mostly for the diagnosis of renovascular hypertension. This technique now competes with color Doppler flow sonography and spiral CT. MR angiography of the renal arteries can be performed with 2D or 3D, flight-time or phase contrast sequences. Main and co-dominant arteries are usual by visualized on all sequences, but small accessory arteries are often missed. The diagnosis of stenosis is based on the presence of an area of signal extinction. The degree of extinction depends on the degree of turbulence, the type of technique, the length of TE and spatial resolution parameters, which is why scoring of stenoses is difficult and frequently overestimated. The diagnostic performance for stenosis is between 50 and 100% for sensitivity and between 80 and 97% for specificity. Detection of distal stenoses is poor because of respiratory artifacts. Multiphase acquisitions make it possible to measure the renal blood flow on each renal artery, adding hemodynamic criteria to this diagnosis.
Assuntos
Hipertensão Renovascular/diagnóstico , Angiografia por Ressonância Magnética/métodos , Obstrução da Artéria Renal/diagnóstico , Artéria Renal/diagnóstico por imagem , Humanos , Radiografia , Artéria Renal/anormalidadesRESUMO
Enhanced-MR imaging in combination with ultrasmall superparamagnetic iron oxide (USPIO) was used in the glycerol-induced model of acute renal failure (ARF) in the rabbit to detect renal perfusion abnormalities. A control group (n = 5) and an ARF group (n = 5) were studied after intramuscular injection of glycerol (10 ml/kg) with T2-weighted spin-echo sequence at 1.5 T and a 27 mumol/kg IV dose of iron. The signal intensity (SI) was quantified in the cortex, the outer medulla (OM), and the inner medulla (IM). In control rabbits, the maximum SI decrease after USPIO injection was in the OM (76% +/- 3.6), as this is the region of maximal vascular density, then in the IM (73.4% +/- 2.9). In the glycerol group, SI loss in the OM (61% +/- 12.6) and the IM (45.2% +/- 16.24) was significant less than in the control group (p < .05). Pathology results showed fibrinous thrombus in the efferent arterioles and congestive aspect of the vasa recta in the medulla. We argue that a reduced medullary concentration of USPIO in the renal failure group is indicative of medullary hypoperfusion.
Assuntos
Injúria Renal Aguda/diagnóstico , Meios de Contraste , Ferro , Rim/patologia , Imageamento por Ressonância Magnética/métodos , Óxidos , Injúria Renal Aguda/induzido quimicamente , Animais , Dextranos , Feminino , Óxido Ferroso-Férrico , Glicerol , Isquemia/diagnóstico , Rim/irrigação sanguínea , Medula Renal/irrigação sanguínea , Medula Renal/patologia , Nanopartículas de Magnetita , Tamanho da Partícula , CoelhosRESUMO
RATIONALE AND OBJECTIVES: The steady-state intrarenal distribution of ultrasmall superparamagnetic iron oxide (USPIO) particles in the cortex, the outer medulla (OM), and the inner medulla (IM) was investigated using magnetic resonance imaging in the normal rabbit kidney and in situations that modify the corticopapillary osmotic gradient. METHODS: Experiments were performed on rabbit kidneys with T2-weighed spin-echo sequence and T2-weighted gradient-recalled-echo sequence. The intravenous dose was 27 mumole/kg of iron in all rabbits. Three groups were studied: normally hydrated rabbits (n = 5), after water restriction (n = 5) to increase the osmotic gradient, and after furosemide injection (n = 5) to decrease the osmotic gradient. The signal intensity (SI) was quantified by region of interest placed on the cortex, the OM and the IM. RESULTS: In normally hydrated rabbits, a maximal decrease of the SI after USPIO was noted in the medulla, without significant difference between the OM and the IM on spin-echo sequences. The decrease of the SI was maximal in the IM on gradient-recalled echo sequences. In dehydrated animals, the maximum SI loss was in the OM. The furosemide-induced transient enhancement of the IM lasted a few minutes. CONCLUSIONS: The observed SI changes due to the distribution of the USPIO between OM and IM were not based on modifications of the osmotic gradient. The authors suggest that these SI changes were mostly dependent on the vascular density.
Assuntos
Meios de Contraste , Furosemida/farmacologia , Ferro , Rim/anatomia & histologia , Imageamento por Ressonância Magnética/métodos , Óxidos , Animais , Dextranos , Feminino , Óxido Ferroso-Férrico , Rim/metabolismo , Nanopartículas de Magnetita , Osmose , Coelhos , Privação de Água/fisiologiaRESUMO
To improve 3D-time of flight (3D-TOF) magnetic resonance angiography, we used magnetisation transfer (MT) to increase the contrast between flowing blood and stationary tissues. With a 1.5 KHz off-resonance radio-frequency MT applied for 16 ms at a maximum power within specific absorption rate (SAR) limits, a 37% decrease in the signal of white matter was obtained, whereas the signal from flowing blood decreased by only 8%. An improvement in maximum intensity projection (MIP) image quality was obtained all MT-3DTOF studies on seven volunteers using progressively more powerful MT pulses. Routine clinical use of MT-3DTOF appears promising and can be achieved at any strength field.
Assuntos
Encéfalo/irrigação sanguínea , Aumento da Imagem/métodos , Imageamento por Ressonância Magnética/métodos , Adulto , Velocidade do Fluxo Sanguíneo/fisiologia , Humanos , Processamento de Imagem Assistida por Computador , Masculino , Modelos Anatômicos , Valores de ReferênciaRESUMO
First-pass intrarenal hemodynamics were studied with superparamagnetic iron oxide particles and a T2-weighted TurboFLASH (fast low-angle shot) magnetic resonance (MR) imaging sequence. Four groups of five rabbits each were imaged after bolus injection of 40, 100, 140, and 200 mumol/kg iron, respectively. Images were acquired every 1.2 seconds, with an acquisition time of 700 msec. The signal intensity was measured in the cortex, outer medulla, inner medulla, and globally. In preliminary pathologic applications, two rabbits were imaged after ligation of the lumbar ureter and two after embolization of the renal artery. The reproducibility of the normal dynamics was evaluated with a cross-correlation test. On the images, the intravascular progression of the iron particles could be visualized within the cortex and the two compartments of the medulla in all cases. The maximal reduction in signal intensity in the cortex and medulla increased with the dose. The relationship between signal intensity decrease and dose was not linear, and the reproducibility of the signal intensity versus time plots was acceptable only at the 140 and 200 mumol/kg doses. The decrease in signal intensity was reduced and delayed in the embolized and hydronephrotic kidneys.