RESUMO
OBJECTIVE: Better prediction of tissue prognosis in acute stroke might improve treatment decisions. We hypothesized that there are metabolic ischemic disturbances measurable noninvasively by proton magnetic resonance spectroscopy ((1)H MRS) that occur earlier than any structural changes visible on diffusion-tensor imaging (DTI), which may therefore serve for territorial identification of tissue at risk. METHODS: We performed multivoxel (1)H MRS plus DTI within a maximum of 26 hours, and DTI at 3-7 days, after ischemic stroke. We compared choline, lactate, N-acetylaspartate, and creatine concentrations in normal-appearing voxels that became infarcted (infarct expansion) with normal-appearing voxels around the infarct that remained "healthy" (nonexpansion) on follow-up DTI. Each infarct expansion voxel was additionally classified as either complete infarct expansion (infarcted tissue on follow-up DTI covered > or =50% of the voxel) or partial infarct expansion (<50% of voxel). RESULTS: In 31 patients (NIH Stroke Scale score 0-28), there were 108 infarct nonexpansion voxels and 113 infarct expansion voxels (of which 80 were complete expansion and 33 partial expansion voxels). Brain choline concentration increased for each change in expansion category from nonexpansion, via partial expansion to complete expansion (2,423, 3,843, 4,158 IU; p < 0.05). Changes in lactate, N-acetylaspartate, and creatine concentrations in expansion category were insignificant although for lactate there was a tendency to such association. CONCLUSIONS: Choline concentration measurable with (1)H MRS was elevated in peri-ischemic normal-appearing brain that became infarcted by 3-7 days. The degree of elevation was associated with the amount of infarct expansion. (1)H MRS might identify DTI-normal-appearing tissue at risk of conversion to infarction in early stroke.
Assuntos
Isquemia Encefálica/diagnóstico , Encéfalo/metabolismo , Infarto Cerebral/diagnóstico , Colina/metabolismo , Espectroscopia de Ressonância Magnética/métodos , Idoso , Idoso de 80 Anos ou mais , Isquemia Encefálica/metabolismo , Mapeamento Encefálico , Infarto Cerebral/metabolismo , Creatina/metabolismo , Imagem de Tensor de Difusão , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Ácido Láctico/metabolismo , Masculino , Pessoa de Meia-Idade , Valor Preditivo dos Testes , PrognósticoRESUMO
BACKGROUND AND PURPOSE: The mechanisms by which the glucocorticoid dexamethasone produces its therapeutic action in patients with intracranial tumors still remain unclear. The purpose of this study was to investigate whether dexamethasone affects cerebral perfusion and water molecule diffusion by using quantitative dynamic susceptibility contrast perfusion MR imaging (DSC-MR imaging) and diffusion tensor MR imaging (DT-MR imaging). METHODS: Ten consecutive patients with glioblastoma multiforme underwent DSC-MR imaging and DT-MR imaging before and 48-72 hours after dexamethasone treatment (16 mg/day). Cerebral blood flow (CBF), cerebral blood volume (CBV), mean transit time (MTT), and water mean diffusivity (
Assuntos
Barreira Hematoencefálica/efeitos dos fármacos , Neoplasias Encefálicas/irrigação sanguínea , Encéfalo/irrigação sanguínea , Dexametasona/uso terapêutico , Imagem de Difusão por Ressonância Magnética/métodos , Glioblastoma/irrigação sanguínea , Aumento da Imagem/métodos , Processamento de Imagem Assistida por Computador/métodos , Adulto , Idoso , Velocidade do Fluxo Sanguíneo/efeitos dos fármacos , Volume Sanguíneo/efeitos dos fármacos , Edema Encefálico/diagnóstico , Edema Encefálico/tratamento farmacológico , Neoplasias Encefálicas/tratamento farmacológico , Meios de Contraste , Feminino , Gadolínio DTPA , Glioblastoma/tratamento farmacológico , Humanos , Masculino , Pessoa de Meia-Idade , Estudos Prospectivos , Fluxo Sanguíneo Regional/efeitos dos fármacos , Sensibilidade e EspecificidadeRESUMO
BACKGROUND AND PURPOSE: An acute mismatch on diffusion-weighted MRI (DWI) and perfusion-weighted MRI (PWI) may represent the "tissue-at-risk." It is unclear which "semiquantitative" perfusion parameter most closely identifies final infarct volume. METHODS: Acute stroke patients underwent DWI and PWI (dynamic-susceptibility contrast imaging) on admission (baseline), and T2-weighted imaging (T2WI) at 1 or 3 months after stroke. "Semiquantitative" mean transit time (MTTsq=first moment of concentration/time curve), cerebral blood volume (CBVsq=area under concentration/time curve), and cerebral blood flow (CBFsq=CBVsq/MTTsq) were calculated. DWI and PWI lesions were measured at baseline and final infarct volume on T2WI acquired > or =1 month after stroke. Baseline DWI, CBFsq, and MTTsq lesion volumes were compared with final T2WI lesion volume. RESULTS: Among 46 patients, baseline DWI and CBFsq lesions were not significantly different from final T2WI lesion volume, but baseline MTTsq lesions were significantly larger. The correlation with final T2WI lesion volume was strongest for DWI (Spearman rank correlation coefficient rho=0.68), intermediate for CBFsq (rho=0.55), and weakest for MTTsq (rho=0.49) baseline lesion volumes. Neither DWI/CBFsq nor DWI/MTTsq mismatch predicted lesion growth; lesion growth was equally common in those with and without mismatch. CONCLUSIONS: Of the 2 PWI parameters, CBFsq lesions most closely identifies, and MTTsq overestimates, final T2WI lesion volume. "DWI/PWI mismatch" does not identify lesion growth. Patients without "DWI/PWI mismatch" are equally likely to have lesion growth as those with mismatch and should not be excluded from acute stroke treatment.
Assuntos
Imagem de Difusão por Ressonância Magnética/métodos , Isquemia/patologia , Imageamento por Ressonância Magnética/métodos , Acidente Vascular Cerebral/patologia , Adulto , Idoso , Idoso de 80 Anos ou mais , Circulação Cerebrovascular , Difusão , Feminino , Humanos , Processamento de Imagem Assistida por Computador , Isquemia/diagnóstico , Masculino , Pessoa de Meia-Idade , Modelos Estatísticos , Perfusão , Estudos Prospectivos , Acidente Vascular Cerebral/diagnóstico , Fatores de TempoRESUMO
OBJECTIVES: Our purpose was to investigate whether differences exist in the values and temporal evolution of mean diffusivity (
Assuntos
Isquemia Encefálica/patologia , Encéfalo/patologia , Acidente Vascular Cerebral/patologia , Idoso , Idoso de 80 Anos ou mais , Anisotropia , Isquemia Encefálica/complicações , Imagem de Difusão por Ressonância Magnética , Feminino , Seguimentos , Humanos , Masculino , Pessoa de Meia-Idade , Acidente Vascular Cerebral/complicações , Fatores de TempoRESUMO
One of the main causes of failure of expanded polytetrafluoroethylene (PTFE) bypass grafts used in the lower limbs is the development of myointimal hyperplasia (MIH). Clinical studies show that higher patency rates can be obtained with the use of an autologous vein cuff (the Miller cuff) interposed between the graft and artery. The reasons for the improved performance are still unclear, but preliminary studies suggest that the change in local haemodynamics due to the cuff geometry may be the significant factor rather than the presence of autologous material. If this is the case, then PTFE grafts can be produced with an integral cuff, i.e. a precuffed graft, with similar haemodynamic patterns to that of the Miller cuff. In this paper, two different types of precuffed graft are presented and their flow patterns are compared with those recorded in the Miller cuff and the conventional end-to-side anastomosis. The haemodynamic studies were carried out using optically clear silicone rubber models under simulated in vivo pulsatile flow conditions. Flow structures similar to those observed in the Miller cuff were seen in the precuffed grafts.