Hideto Toyoshima

Cerebral Blood Volume in Acute Brain Infarction A Combined Study With Dynamic Susceptibility Contrast MRI and 99mTc-HMPAO-SPECT

BACKGROUND AND PURPOSE The aim of this study was to correlate the abnormality in cerebral blood volume (CBV) measured by dynamic susceptibility contrast-enhanced MRI with that in cerebral blood flow (CBF) estimated by single-photon emission CT with [99mTc]hexamethylpropylenamine-oxime in patients with acute ischemic stroke. METHODS Nine patients with unilateral occlusion of either the middle cerebral artery or the internal carotid artery (4 men and 5 women; mean+/-SD age, 74.4+/-11.6 years) were studied within 6 hours after stroke onset. The relative CBV (relCBV) and CBF (relCBF) in the lesions were defined relative to the contralateral mirror regions. RESULTS In the brain regions with mild (relCBF >/=0.60), moderate (0.40</=relCBF<0.60), and severe (relCBF <0.40) hypoperfusion, the mean relCBV values were 1.29+/-0.31, 0.94+/-0.49, and 0.30+/-0.22, respectively. The relCBV was significantly elevated in the brain areas with mild hypoperfusion (P<0.001) and significantly reduced in the brain areas with severe hypoperfusion (P<0.001). The relCBF was significantly better than the relCBV in predicting the evolution of infarction (P<0.02). The probability of evolving infarction for the hypervolemic (relCBV >1.0) regions was significantly lower than that for hypovolemic (relCBV <1.0) regions in the relCBF range between 0.40 and 0.50 (P<0.02). CONCLUSIONS In acute ischemic stroke within 6 hours of onset the CBV can be either increased, normal, or decreased, depending on the severity of hypoperfusion. The increased CBV has a protective effect on evolving infarction. Although the CBF is a better predictor of tissue outcome, the CBV measurement may help detect potentially salvageable brain tissue in the penumbra with compromised blood flow.

Subcortical Hypoperfusion Associated With Asymptomatic White Matter Lesions on Magnetic Resonance Imaging

BACKGROUND AND PURPOSE We examined whether hemodynamic and metabolic abnormalities in the cerebral white matter, basal ganglia, and thalamus are associated with asymptomatic white matter lesions (WML) depicted on MR images. METHODS A positron emission tomographic study with H2(15)O, C15O, and 15O2 was performed in eight normal control subjects without any WML (mean +/- 1 SD age, 68.5 +/- 10.2 years) and in 15 asymptomatic subjects with WML (71.3 +/- 8.5 years) to measure regional cerebral blood flow (CBF), cerebral blood volume, oxygen extraction fraction (OEF), and oxygen metabolic rate. RESULTS In the cerebral white matter in the asymptomatic subjects with WML, significantly lower CBF (20.3 +/- 3.9 mL/100 mL per minute; P < .05) and significantly higher OEF (0.43 +/- 0.08; P < .05) were found compared with those for control subjects (23.5 +/- 2.6 mL/100 mL per minute and 0.37 +/- 0.06, respectively). The severity of WML was not related to the magnitude of hypoperfusion. In the basal ganglia, significantly lower CBF (44.9 +/- 6.9 mL/100 mL per minute; P < .01) and significantly higher OEF (0.54 +/- 0.08; P < .01) were found in the WML group than in control subjects (70.1 +/- 12.0 mL/100 mL/min and 0.39 +/- 0.03, respectively). In the thalamus, there was no significant difference in CBF and OEF between the control and WML groups. CONCLUSIONS Hypoperfusion of the cerebral white matter and basal ganglia in asymptomatic WML subjects may be induced by the arteriosclerosis of long penetrating medullary arteries and lenticulostriate arteries but may not be directly related to the production of WML. The role of hypoperfusion in the production of WML and acceleration of its development remains to be elucidated.

Cerebral vascular mean transit time in healthy humans : a comparative study with PET and dynamic susceptibility contrast-enhanced MRI

Cerebral vascular mean transit time (MTT), defined as the ratio of cerebral blood volume to cerebral blood flow (CBV/CBF), is a valuable indicator of the cerebral circulation. Positron emission tomography (PET) and dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI) are useful for the quantitative determination of MTT in the clinical setting. The aim of this study was to establish a normal value set of MTT as determined by PET and by DSC-MRI and to identify differences between these methods. Seven healthy volunteers were studied with 15O-PET (H215O and C15O) and gradient-echo echo-planar DSC-MRI at 1.5 T. In the DSC-MRI study with bolus injection of contrast agent, deconvolution analysis was performed. Comparison of gray-to-white matter ratios showed fairly good agreement between PET and DSC-MRI for all parameters (relative CBV, relative CBF, and relative MTT), confirming the validity of relative measurements with DSC-MRI. However, quantitative MTT measured by DSC-MRI was significantly shorter than that measured by PET in cerebral cortical regions (2.8 to 3.0 secs for DSC-MRI versus 3.9 to 4.3 secs for PET) and the centrum semiovale (3.5secs for DSC-MRI versus 4.8secs for PET). These discrepancies may be because of the differences in the intrinsic sensitivity of each imaging modality to vascular components; whereas PET measurement of CBV is equally sensitive to all vascular components, measurement with DSC-MRI originates from the microvasculature in the vicinity of the brain parenchyma. This underlying difference may influence interpretation of MTT determined by PET or by DSC-MRI for patients with cerebrovascular disease.

Detection of Deoxygenation-Related Signal Change in Acute Ischemic Stroke Patients by T2*-Weighted Magnetic Resonance Imaging

Background and Purpose— Acute decreases in the MR T2*-weighted signal have been reported in experimental models of middle cerebral artery occlusion. This has been attributed to blood deoxygenation in association with an increased brain oxygen extraction fraction. The aim of this study was to detect this signal by susceptibility-weighted MR imaging in acute ischemic stroke patients. Methods— Dynamic susceptibility contrast-enhanced MR (DSC-MR) imaging was performed within 4 hours of stroke onset in 6 patients with unilateral cerebral artery occlusion (middle cerebral artery, n=5; internal carotid artery, n=1). Cerebral blood volume was estimated on a pixel-by-pixel basis. DSC-MR images taken before arrival of the contrast medium were examined visually to identify hypointense areas. Bilateral regions of interest were set in the middle cerebral artery territory for comparison of the mean signal intensity. A semilogarithmic plot of signal intensity versus cerebral blood volume for every pixel in the region of interest was also analyzed. Results— The side on which the hypointense area was seen was significantly correlated with the side of arterial occlusion. The mean signal intensity was significantly smaller on the affected side than on the contralateral side. The semilogarithmic plot of signal intensity versus cerebral blood volume indicated greater deoxyhemoglobin concentrations for the ipsilateral than for the contralateral region of interest. Conclusions— DSC-MR images allow detection of hypointensity in the affected cerebral hemisphere in acute ischemic stroke patients. Such hypointensity may indicate increased oxygen extraction fraction (misery perfusion) and may provide information valuable to patient care.

Metabolic penumbra of acute brain infarction: A correlation with infarct growth

Volume expansion associated with brain infarction occurs in perfusion–diffusion mismatch of magnetic resonance imaging. We aimed at elucidating the metabolic impairment of this phenomenon with 15O positron emission tomography and perfusion and diffusion magnetic resonance imaging. Eleven patients with acute unilateral embolic occlusion of the internal carotid or middle cerebral artery were studied within 6 hours of onset. Regional cerebral blood flow and cerebral metabolic rate of oxygen (CMRO2) were compared with those in the contralateral cerebral hemisphere. The relative apparent diffusion coefficient of water was estimated as a marker of cytotoxic edema. Relative cerebral blood flow and relative CMRO2 in an evolving infarct (normal diffusion initially, but abnormal on day 3) were significantly (p < 0.05) less than those in the periinfarct area (normal diffusion initially and on day 3). The relative apparent diffusion coefficient between the evolving infarct and periinfarct showed no significant difference. These findings indicated that the initial 3‐day volume expansion of an embolic brain infarction was associated with disturbed CMRD2 but not with cytotoxic edema as early as 6 hours after onset. The “metabolic penumbra” defined as normal water diffusion with depressed CMRO2 is a target to reduce the volume expansion of brain infarction. Ann Neurol 2005;57:495–504

Tracer delay correction of cerebral blood flow with dynamic susceptibility contrast-enhanced MRI.

Cerebral blood flow (CBF) and vascular mean transit time (MTT) can be determined by dynamic susceptibility contrast-enhanced magnetic resonance imaging and deconvolution with an arterial input function. However, deconvolution by a singular value decomposition (SVD) method is sensitive to the tracer delay that often occurs in patients with cerebrovascular disease. We investigated the effect of tracer delay on CBF determined by SVD deconvolution. Simulation study showed that underestimation of CBF due to tracer delay was larger for shorter MTTs. We developed a delay correction method that determines tracer delay by means of least-squares fitting pixel-by-pixel. The corrected CBF was determined by SVD deconvolution after time-shifting of the measured concentration curve. The simulations showed that the corrected CBF was insensitive to tracer delay irrespective of the vascular model, although CBF fluctuation increased slightly. We applied the delay correction to the CBF and MTT images acquired for nine patients with hyperacute stroke and unilateral occlusion of the middle cerebral artery. We found in some patients that the delay correction modulated the contrast of CBF and MTT images. For hyperacute stroke patients, tracer delay correction is essential to obtain reliable perfusion image when SVD deconvolution is used.

18F-FDG accumulation in atherosclerosis: use of CT and MR co-registration of thoracic and carotid arteries

PurposeThe purpose of this study was to depict 18F-fluoro-2-deoxy-D-glucose (FDG) accumulation in atherosclerotic lesions of the thoracic and carotid arteries on CT and MR images by means of automatic co-registration software.MethodsFifteen hospitalised men suffering cerebral infarction or severe carotid stenosis requiring surgical treatment participated in this study. Automatic co-registration of neck MR images and FDG-PET images and of contrast-enhanced CT images and FDG-PET images was achieved with co-registration software. We calculated the count ratio, which was standardised to the blood pool count of the superior vena cava, for three arteries that branch from the aorta, i.e. the brachial artery, the left common carotid artery and the subclavian artery (n=15), for atherosclerotic plaques in the thoracic aorta (n=10) and for internal carotid arteries with and without plaque (n=13).ResultsFDG accumulated to a significantly higher level in the brachial artery, left common carotid artery and left subclavian artery at their sites of origin than in the superior vena cava (p=0.000, p=0.000 and p=0.002, respectively). Chest CT showed no atherosclerotic plaque at these sites. Furthermore, the average count ratio of thoracic aortic atherosclerotic plaques was not higher than that of the superior vena cava. The maximum count ratio of carotid atherosclerotic plaques was significantly higher than that of the superior vena cava but was not significantly different from that of the carotid artery without plaque.ConclusionThe results of our study suggest that not all atherosclerotic plaques show high FDG accumulation. FDG-PET studies of plaques with the use of fused images can potentially provide detailed information about atherosclerosis.

Whole-brain perfusion measurement using 320-detector row computed tomography in patients with cerebrovascular steno-occlusive disease: comparison with 15O-positron emission tomography.

Objective: The 320-detector row computed tomography (CT) can provide whole-brain CT perfusion (CTP) maps with continuous angiographic images by performing a single dynamic scan. We investigated the reliability of CTP cerebral blood flow (CTP-CBF) with 320-detector row CT by comparing findings with 15O-positron emission tomography (PET-CBF). Methods: Whole-brain CTP and PET were performed in 10 patients with chronic unilateral steno-occlusive disease. We compared absolute and relative CBF values of bilateral middle cerebral artery territories between CTP and PET. Results: Although mean CTP-CBF values were approximately 30% lower than mean PET-CBF values, the mean ischemic-to-nonischemic CBF ratios of CTP and PET were almost identical (P = 0.804). Regression analysis showed a significant correlation between CTP-CBF and PET-CBF values for each patient (r = 0.52-0.85, P < 0.001). Conclusions: Whole-brain CTP using 320-detector row CT is useful for evaluating the degree of ischemia for the entire brain with chronic cerebrovascular disease.

Influence of arterial partial pressure of carbon dioxide on cerebral MRA in normal volunteers.

Objective Signal intensity of MR angiography (MRA) is influenced by the physiological factors of flowing blood in the vessels. We examined whether MRA can detect a cerebral hemodynamic change induced by reducing or elevating the arterial partial pressure of carbon dioxide (Paco2). Materials and Methods Cerebral MRA was performed in six normal volunteers, each having three measurements during hyperventilation, normal breathing, and 7% CO2 inhalation. The MRA data were obtained by a 0.5 T whole-body scanner and a time-of-flight technique of three-dimensional GE imaging. In addition to the visual inspection, the signal intensity and the lengths of the middle cerebral artery (MCA) and posterior cerebral artery (PCA) were estimated in relation to Paco2. Results The MRA appearances of major cerebral arteries were remarkably different depending on the breathing conditions. There was significant difference in the mean signal intensity (p < 0.01) and the mean length (p < 0.01) of the MCA and PCA between the hyperventilation and normal breathing trials. Conclusion The MRA signal was sensitive to the changes in Paco2 level of flowing blood. This phenomenon may result from changes in the velocity of blood flow in major cerebral arteries.

Automated method to compute Evans index for diagnosis of idiopathic normal pressure hydrocephalus on brain CT images

The early diagnosis of idiopathic normal pressure hydrocephalus (iNPH) considered as a treatable dementia is important. The iNPH causes enlargement of lateral ventricles (LVs). The degree of the enlargement of the LVs on CT or MR images is evaluated by using a diagnostic imaging criterion, Evans index. Evans index is defined as the ratio of the maximal width of frontal horns (FH) of the LVs to the maximal width of the inner skull (IS). Evans index is the most commonly used parameter for the evaluation of ventricular enlargement. However, manual measurement of Evans index is a time-consuming process. In this study, we present an automated method to compute Evans index on brain CT images. The algorithm of the method consisted of five major steps: standardization of CT data to an atlas, extraction of FH and IS regions, the search for the outmost points of bilateral FH regions, determination of the maximal widths of both the FH and the IS, and calculation of Evans index. The standardization to the atlas was performed by using linear affine transformation and non-linear wrapping techniques. The FH regions were segmented by using a three dimensional region growing technique. This scheme was applied to CT scans from 44 subjects, including 13 iNPH patients. The average difference in Evans index between the proposed method and manual measurement was 0.01 (1.6%), and the correlation coefficient of these data for the Evans index was 0.98. Therefore, this computerized method may have the potential to accurately compute Evans index for the diagnosis of iNPH on CT images.