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Yoshinobu Iwasaki - One of the best experts on this subject based on the ideXlab platform.
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combination of a Mean Transit Time measurement with an acetazolamide test increases predictive power to identify elevated oxygen extraction fraction in occlusive carotid artery diseases
The Journal of Nuclear Medicine, 2008Co-Authors: Masaaki Hokari, Naoki Nakayama, Satoshi Kuroda, Tohru Shiga, Nagara Tamaki, Yoshinobu IwasakiAbstract:UNLABELLED: Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide have been used as predictors for subsequent ischemic stroke in patients with occlusive carotid artery diseases, called type 3 ischemia. However, recent studies have shown that reduced cerebrovascular reactivity to acetazolamide does not always represent elevated oxygen extraction fraction (OEF). The aim of this study was to establish the methodology to improve the validity of an acetazolamide test identifying elevated OEF. METHODS: This study included 65 patients who developed transient ischemic attack or minor completed stroke attributable to occlusive carotid artery diseases. Hemodynamic and metabolic parameters in the bilateral middle cerebral artery territories were determined in all patients by (15)O-gas PET. RESULTS: Type 3 ischemia alone had 100% sensitivity and 83.2% specificity for identifying elevated OEF, but its positive predictive value and accuracy were low, 47.2% and 0.85, respectively. However, type 3 ischemia and delayed Mean Transit Time combined had an 83.3% positive predictive value and 0.96 accuracy. CONCLUSION: The results strongly suggest that type 3 ischemia and delayed Mean Transit Time together may be powerful predictors in identifying elevated OEF with high sensitivity and specificity, predictive values, and accuracy. SPECT may be able to define the patients with elevated OEF more easily and at lower costs than PET, although further study would be necessary to compare the results by using SPECT.
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combination of a Mean Transit Time measurement with an acetazolamide test increases predictive power to identify elevated oxygen extraction fraction in occlusive carotid artery diseases
The Journal of Nuclear Medicine, 2008Co-Authors: Masaaki Hokari, Naoki Nakayama, Satoshi Kuroda, Tohru Shiga, Nagara Tamaki, Yoshinobu IwasakiAbstract:UNLABELLED: Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide have been used as predictors for subsequent ischemic stroke in patients with occlusive carotid artery diseases, called type 3 ischemia. However, recent studies have shown that reduced cerebrovascular reactivity to acetazolamide does not always represent elevated oxygen extraction fraction (OEF). The aim of this study was to establish the methodology to improve the validity of an acetazolamide test identifying elevated OEF. METHODS: This study included 65 patients who developed transient ischemic attack or minor completed stroke attributable to occlusive carotid artery diseases. Hemodynamic and metabolic parameters in the bilateral middle cerebral artery territories were determined in all patients by (15)O-gas PET. RESULTS: Type 3 ischemia alone had 100% sensitivity and 83.2% specificity for identifying elevated OEF, but its positive predictive value and accuracy were low, 47.2% and 0.85, respectively. However, type 3 ischemia and delayed Mean Transit Time combined had an 83.3% positive predictive value and 0.96 accuracy. CONCLUSION: The results strongly suggest that type 3 ischemia and delayed Mean Transit Time together may be powerful predictors in identifying elevated OEF with high sensitivity and specificity, predictive values, and accuracy. SPECT may be able to define the patients with elevated OEF more easily and at lower costs than PET, although further study would be necessary to compare the results by using SPECT.
Shuichi Miura - One of the best experts on this subject based on the ideXlab platform.
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cerebral vascular Mean Transit Time in healthy humans a comparative study with pet and dynamic susceptibility contrast enhanced mri
Journal of Cerebral Blood Flow and Metabolism, 2007Co-Authors: Masanobu Ibaraki, Hiroshi Ito, Iwao Kanno, Kazuhiro Takahashi, Eku Shimosegawa, Hideto Toyoshima, Keiichi Ishigame, Shuichi MiuraAbstract: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 (15)O-PET (H(2)(15)O and C(15)O) 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 (3.5 secs for DSC-MRI versus 4.8 secs 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.
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regional distribution of human cerebral vascular Mean Transit Time measured by positron emission tomography
NeuroImage, 2003Co-Authors: Hiroshi Ito, Iwao Kanno, Kazuhiro Takahashi, Masanobu Ibaraki, Shuichi MiuraAbstract:Cerebral vascular Mean Transit Time (MTT) characterizes the cerebral circulation. MTT has been measured in humans by carotid angiography, x-ray computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET). However, regional distribution of MTT has not been investigated in detail. Thus, we investigated regional distribution of normal human MTT. Regional cerebral blood flow (CBF) and cerebral blood volume (CBV) were measured by PET with H215O and 11CO, respectively, in each of 10 normal subjects. MTT was calculated as MTT = CBV/CBF. MTT for cerebral cortical regions was 3.2 to 4.4 s. These values were in accord with MTT measured by carotid angiography, CT, and MRI. Considered regionally, MTT was longest in the temporooccipital cortex, and shorter in the cerebellum, thalamus, and putamen, than in all other regions. These regional differences in MTT that are inversely proportional to cerebral perfusion pressure might relate to regional differences in cerebral vascular tone. Simulation studies showed that errors in CBF and thus MTT caused by regional differences in regional tracer appearance Time, distribution volume, and gray–white matter mixing were negligible.
Tingyim Lee - One of the best experts on this subject based on the ideXlab platform.
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gw24 e2929 evaluation of functional significance of coronary artery stenosis with baseline myocardial Mean Transit Time
Heart, 2013Co-Authors: Gerald Wisenberg, Tingyim Lee, Ali IslamAbstract:Objectives Mean Transit Time (MTT) is inversely related to perfusion pressure. We herein investigated the relationship between baseline myocardial MTT measured by dynamic contrast-enhanced (DCE) CT imaging and the degree and hemodynamic significance of coronary stenosis in patients with coronary artery disease (CAD). Methods Thirteen CAD patients underwent invasive coronary angiography and CT myocardial perfusion (MP) imaging within 2 weeks. Degree of stenosis in each coronary artery and its branches was qualitatively classified from angiogram as non-significantly stenosed (NS, normal, mildly irregular or = 70% narrowed). For the CT MP study, 8x5 mm of the heart was scanned for 30 s using a GE Healthcare Discovery VCT scanner with 140 kV, 50 mA and 0.4 s gantry period after a bolus injection of contrast (Omnipaque 300, 0.7 mgI/mL) at 4 mL/s. The study was repeated at 3 min after a 4-min infusion of dipyridamole (Persantine, 0.56 mg/kg). DCE cardiac images from each scan were corrected for beam hardening using an image-based correction algorithm before analysed using a model-based deconvolution algorithm (CT Perfusion, GE Healthcare) to generate functional maps of MP and MTT. In each map, myocardium in horizontal long-axis was divided into six segments and assigned to a supply coronary artery according to the AHA schema. Myocardial perfusion reserve (MPR) in each segment was calculated as the ratio of MP at stress to that at rest. Baseline MTT and MPR in segments perfused by NS and SS coronary arteries were averaged over all slices and compared using paired t-tests. Results Mean baseline MTT in NS myocardial segment was 5.20 ± 0.61 s and was significantly lower than that in SS segment (5.56 ± 0.69 s, p Conclusions Flow pressure across SS lesions in coronary arteries was much reduced leading to decrease in the downstream perfusion pressure hence prolonged baseline myocardial MTT and attenuated MPR compared to those in remote NS segments. A single DCE CT protocol acquired at rest without stressing the heart with pharmacologic stimuli is sufficient for assessing the functionally significance of coronary artery stenosis.
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ct perfusion derived Mean Transit Time predicts early mortality and delayed vasospasm after experimental subarachnoid hemorrhage
American Journal of Neuroradiology, 2008Co-Authors: A M Laslo, James D Eastwood, P Pakkiri, F Chen, Tingyim LeeAbstract:BACKGROUND AND PURPOSE: There are limited indicators available to predict cerebral vasospasm in patients with subarachnoid hemorrhage (SAH). The purpose of this study was to determine if CT perfusion–derived hemodynamic parameters are predictors of vasospasm severity and outcome after experimental SAH. MATERIALS AND METHODS: SAH was induced in 25 New Zealand white rabbits. Cerebral blood flow (CBF), cerebral blood volume (CBV), and Mean Transit Time (MTT) were measured with CT perfusion before SAH, within 1 hour after SAH, and on days 2, 4, 7, 9, and 16 after SAH. Basilar artery diameter, measured with CT angiography and neurologic scoring, was also obtained on the same days. Differences between animals with moderate-severe delayed vasospasm (≥24% basilar artery narrowing) and mild delayed vasospasm (<24% basilar artery narrowing) were investigated with repeated measures analysis of variance. Multiple linear regression analysis was used to investigate the relationship between CT perfusion parameters (CBF, CBV, MTT), basilar artery diameter, and neurologic score. RESULTS: MTT increase <1 hour after SAH independently predicted mortality within 48 hours of SAH ( P < .05). MTT and neurologic deficits were significantly greater with moderate-severe than with mild vasospasm ( P < .05). MTT on day 2, but not CBF or CBV, was a significant predictor of subsequent moderate-severe delayed vasospasm ( P < .05). CONCLUSION: In the rabbit model of experimental SAH, the CT-derived hemodynamic parameter MTT on day 0 predicted early mortality, and MTT on day 2 predicted development of moderate-severe delayed vasospasm. MTT was also significantly correlated with arterial diameter and neurologic score.
Masaaki Hokari - One of the best experts on this subject based on the ideXlab platform.
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combination of a Mean Transit Time measurement with an acetazolamide test increases predictive power to identify elevated oxygen extraction fraction in occlusive carotid artery diseases
The Journal of Nuclear Medicine, 2008Co-Authors: Masaaki Hokari, Naoki Nakayama, Satoshi Kuroda, Tohru Shiga, Nagara Tamaki, Yoshinobu IwasakiAbstract:UNLABELLED: Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide have been used as predictors for subsequent ischemic stroke in patients with occlusive carotid artery diseases, called type 3 ischemia. However, recent studies have shown that reduced cerebrovascular reactivity to acetazolamide does not always represent elevated oxygen extraction fraction (OEF). The aim of this study was to establish the methodology to improve the validity of an acetazolamide test identifying elevated OEF. METHODS: This study included 65 patients who developed transient ischemic attack or minor completed stroke attributable to occlusive carotid artery diseases. Hemodynamic and metabolic parameters in the bilateral middle cerebral artery territories were determined in all patients by (15)O-gas PET. RESULTS: Type 3 ischemia alone had 100% sensitivity and 83.2% specificity for identifying elevated OEF, but its positive predictive value and accuracy were low, 47.2% and 0.85, respectively. However, type 3 ischemia and delayed Mean Transit Time combined had an 83.3% positive predictive value and 0.96 accuracy. CONCLUSION: The results strongly suggest that type 3 ischemia and delayed Mean Transit Time together may be powerful predictors in identifying elevated OEF with high sensitivity and specificity, predictive values, and accuracy. SPECT may be able to define the patients with elevated OEF more easily and at lower costs than PET, although further study would be necessary to compare the results by using SPECT.
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combination of a Mean Transit Time measurement with an acetazolamide test increases predictive power to identify elevated oxygen extraction fraction in occlusive carotid artery diseases
The Journal of Nuclear Medicine, 2008Co-Authors: Masaaki Hokari, Naoki Nakayama, Satoshi Kuroda, Tohru Shiga, Nagara Tamaki, Yoshinobu IwasakiAbstract:UNLABELLED: Reduced cerebral blood flow and cerebrovascular reactivity to acetazolamide have been used as predictors for subsequent ischemic stroke in patients with occlusive carotid artery diseases, called type 3 ischemia. However, recent studies have shown that reduced cerebrovascular reactivity to acetazolamide does not always represent elevated oxygen extraction fraction (OEF). The aim of this study was to establish the methodology to improve the validity of an acetazolamide test identifying elevated OEF. METHODS: This study included 65 patients who developed transient ischemic attack or minor completed stroke attributable to occlusive carotid artery diseases. Hemodynamic and metabolic parameters in the bilateral middle cerebral artery territories were determined in all patients by (15)O-gas PET. RESULTS: Type 3 ischemia alone had 100% sensitivity and 83.2% specificity for identifying elevated OEF, but its positive predictive value and accuracy were low, 47.2% and 0.85, respectively. However, type 3 ischemia and delayed Mean Transit Time combined had an 83.3% positive predictive value and 0.96 accuracy. CONCLUSION: The results strongly suggest that type 3 ischemia and delayed Mean Transit Time together may be powerful predictors in identifying elevated OEF with high sensitivity and specificity, predictive values, and accuracy. SPECT may be able to define the patients with elevated OEF more easily and at lower costs than PET, although further study would be necessary to compare the results by using SPECT.
A Benzer - One of the best experts on this subject based on the ideXlab platform.
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influence of equianaesthetic concentrations of nitrous oxide and isoflurane on regional cerebral blood flow regional cerebral blood volume and regional Mean Transit Time in human volunteers
BJA: British Journal of Anaesthesia, 2001Co-Authors: Ingo H Lorenz, Christian Kolbitsch, Christoph Hormann, T J Luger, Michael Schocke, S Felber, Fritz Zschiegner, M Hinteregger, Christian Kremser, A BenzerAbstract:Nitrous oxide and isoflurane have cerebral vasodilatory effects. The use of isoflurane in neuroanaesthesia is widely accepted, whereas the use of nitrous oxide in neuroanaesthesia is still the subject of debate. In the present study, contrast-enhanced magnetic resonance (MR) perfusion measurement was used to compare the effects of 0.4 MAC nitrous oxide (n=9) and 0.4 MAC isoflurane (n=9) on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV) and regional Mean Transit Time (rMTT) in spontaneously breathing human volunteers. Nitrous oxide increased rCBF and rCBV in supratentorial regions more than did isoflurane. Isoflurane, by contrast, increased rCBF and rCBV in basal ganglia more than did nitrous oxide. An increased rMTT was caused by a relatively greater increase in rCBV than in rCBF supratentorially by isoflurane and infratentorially by nitrous oxide. In conclusion, nitrous oxide increases rCBF and rCBV predominantly in supratentorial grey matter, whereas isoflurane increases rCBF and rCBV predominantly in infratentorial grey matter.
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the impact of increased Mean airway pressure on contrast enhanced mri measurement of regional cerebral blood flow rcbf regional cerebral blood volume rcbv regional Mean Transit Time rmtt and regional cerebrovascular resistance rcvr in human volunteer
Human Brain Mapping, 2000Co-Authors: Christian Kolbitsch, Ingo H Lorenz, Christoph Hormann, Michael Schocke, S Felber, Fritz Zschiegner, Christian Kremser, A BenzerAbstract:Contrast-enhanced magnetic resonance imaging (MRI) measurement of cerebral perfusion is a diagnostic procedure increasingly gaining access to clinical practice not only in spontaneously breathing patients but also in mechanically ventilated patients. Effects of increased Mean airway pressure on cerebral perfusion are entirely possible. Therefore, the present study used continuous positive airway pressure (CPAP) (12 cm H2O) to study the effects of increased Mean airway pressure on cerebral perfusion in volunteers. CPAP significantly reduced regional cerebral blood flow (rCBF) and regional cerebral blood volume (rCBV) but increased regional Mean Transit Time (rMTT) and regional cerebrovascular resistance (rCVR). Active vasoconstriction (e.g., arterial) and/or passive compression of capillary and/or venous vessel areas are the most likely underlying mechanisms. The number of interhemispheric differences in rCBF, rCBV, rMTT, and rCVR found at baseline rose when Mean airway pressure was increased. These results, although obtained in volunteers, should be taken into consideration for the interpretation of contrast-enhanced MRI perfusion measurements in mechanically ventilated patients with an increased positive airway pressure.
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low dose remifentanil increases regional cerebral blood flow and regional cerebral blood volume but decreases regional Mean Transit Time and regional cerebrovascular resistance in volunteers
BJA: British Journal of Anaesthesia, 2000Co-Authors: Ingo H Lorenz, Christian Kolbitsch, Christoph Hormann, Michael Schocke, S Felber, Fritz Zschiegner, M Hinteregger, Christian Kremser, A BenzerAbstract:We have used contrast media-enhanced perfusion magnetic resonance imaging MRI to measure regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional Mean Transit Time (rMTT) and regional cerebrovascular resistance (rCVR) in volunteers at baseline and during infusion of remifentanil (0.1 μg kg−1 min−1). Remifentanil increased rCBF and rCBV in white and grey matter (striatal, thalamic, occipital, parietal, frontal) regions, with a parallel decrease in rMTT in those regions with the exception of occipital grey matter. rCVR was decreased in all regions studied. The relative increase in rCBF was greater than that in rCBV. Cerebral haemodynamics were increased significantly in areas less rich in μ-opioid receptors with a tendency towards more pronounced increases in rCBF and rCBV in pain-processing areas. Furthermore, interhemispheric differences in rCBF, rCBV and rMTT found prior to drug administration were almost eliminated during infusion of remifentanil. We conclude that, apart from direct and indirect cerebrovascular effects of remifentanil, these findings are consistent with cerebral excitement and/or disinhibition.
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a subanesthetic concentration of sevoflurane increases regional cerebral blood flow and regional cerebral blood volume and decreases regional Mean Transit Time and regional cerebrovascular resistance in volunteers
Anesthesia & Analgesia, 2000Co-Authors: Christian Kolbitsch, Ingo H Lorenz, Christoph Hormann, Michael Schocke, S Felber, Fritz Zschiegner, Christian Kremser, Alexander Lockinger, Karl P Pfeiffer, A BenzerAbstract:Inhaled anesthetics exert metabolically mediated effects on cerebral blood vessels both directly and indirectly. We investigated the effects of a 0.4 minimum alveolar subanesthetic concentration of sevoflurane on regional cerebral blood flow (rCBF), regional cerebral blood volume (rCBV), regional cerebrovascular resistance (rCVR), and regional Mean Transit Time (rMTT) in volunteers by Means of contrast-enhanced magnetic resonance imaging perfusion measurement. Sevoflurane increased rCBF by 16% to 55% (control, 55. 03 +/- 0.33 to 148.83 +/- 1.9 mL. 100 g(-1). min(-1); sevoflurane, 71.75 +/- 0.36 to 193.26 +/- 2.14 mL. 100 g(-1). min(-1)) and rCBV by 7% to 39% (control, 4.66 +/- 0.03 to 10.04 +/- 0.12 mL/100 g; sevoflurane, 5.04 +/- 0.03 to 13.6 +/- 0.15 mL/100 g); however, sevoflurane decreased rMTT by 7% to 18% (control, 3.75 +/- 0.04 to 5. 39 +/- 0.04 s; sevoflurane, 3.4 +/- 0.03 to 4.44 +/- 0.03 s) and rCVR by 22% to 36% (control, 0.74 +/- 0.01 to 1.9 +/- 0.2 mm Hg/[mL. 100 g(-1). min(-1)]; sevoflurane, 0.54 +/- 0.01 to 1.41 +/- 0.01 mm Hg/[mL. 100 g(-1). min(-1)]). Interhemispheric differences in rCBF, rCBV, and rCVR were markedly reduced after the administration of sevoflurane. These findings are consistent with the known direct vasodilating effect of sevoflurane. The decrease in rMTT further shows that rCBF increases more than does rCBV. Furthermore, we can show that the observed increase in rCBF during inhalation of sevoflurane is not explained by vasodilation alone.