Relationship between the housing coldness/warmth evaluation by CASBEE Housing Health Checklist and psychological distress based on TMM Community-Based Cohort Study: a cross-sectional analysis

OBJECTIVES

Previous studies have reported the relationship between housing environment and health, although due to cost and effort, it was difficult to conduct housing condition surveys on a large scale. The CASBEE Housing Health Checklist (the Checklist) made it possible to easily evaluate the housing condition from the resident's perspective. This study examined the relationship between housing coldness/warmth evaluation using the Checklist and psychological distress in a large-scale general Japanese population.

STUDY DESIGN

A cross-sectional study.

METHODS

We analysed data from 29,380 people aged ≥20 years who lived in Miyagi Prefecture, Japan. As an assessment of housing coldness/warmth, we used the Checklist. We classified participants' total scores on the Checklist related to coldness/warmth into quartiles. The Kessler 6 scale was used as an indicator of psychological distress. Multivariable logistic regression models were used to estimate the adjusted odds ratio (OR) and 95% confidence intervals (CIs). Adjusted OR and P-values for linear trends were calculated using the quartiles of the Checklists' score.

RESULTS

Among participants in Q1 (i.e., poorer subjective house condition), the percentage of people with psychological distress was high. Compared to the highest quartile, Q1 showed poorer evaluation of housing coldness/warmth, and higher OR for psychological distress. The OR (95% CI) of psychological distress for Q3, Q2, and Q1 compared with Q4 were 1.93 (1.74-2.14), 2.82 (2.55-3.12), and 5.78 (5.25-6.35), respectively.

CONCLUSIONS

Housing coldness/warmth evaluation was significantly related to psychological distress. This finding suggests that maintaining a comfortable thermal environment at home could be important for residents' mental health.

Clinical Value of Pet with 18F-Fluorodeoxyglucose and L-Methyl-11C-Methionine for Diagnosis of Recurrent Brain Tumor and Radiation Injury

We studied 15 patients clinically suspected to have recurrent brain tumor or radiation injury, using positron emission tomography (PET) with 18F-fluorodeoxyglucose (18FDG) and L-methyl-11C-methionine (11C-Met). PET with 11C-Met (Met-PET) clearly delineated the extent of recurrent brain tumor as focal areas of increased accumulation of 11C-Met, and was useful for early detection of recurrent brain tumor. PET with 18FDG (FDG-PET) showed focal 18FDG-hypermetabolism in one patient with malignant transformation of low grade glioma, and demonstrated its usefulness for evaluation of malignant transformation. 18FDG-hypometabolism was observed in all patients with radiation injury, but was also found in one patient with recurrent malignant brain tumor. 11C-Met uptake in 3 patients with radiation injury was similar to that of the normal cortical tissue. FDG-PET can be used to initially exclude recurrent brain tumor which is seen as 18FDG-hypermetabolism. The combined use of Met-PET in addition to FDG-PET can improve the accuracy of differentiation of recurrent brain tumor with 18FDG-hypometabolism from radiation injury.

Bridging macroscopic and microscopic methods for the measurements of cerebral blood flow: Toward finding the determinants in maintaining the CBF homeostasis

Methods exist to evaluate the cerebral blood flow (CBF) at both the macroscopic and microscopic spatial scales. These methods provide complementary information for understanding the mechanism in maintaining an adequate blood supply in response to neural demand. The macroscopic CBF assesses perfusion flow, which is usually measured using radioactive tracers, such as diffusible, nondiffusible, or microsphere. Each of them determines CBF based on indicator dilution principle or particle fraction principle under the assumption that CBF is steady state during the measurement. Macroscopic CBF therefore represents averaged CBF over a certain space and time domains. On the other hand, the microscopic CBF assesses bulk flow, usually measures using real-time microscopy. The method assesses hemodynamics of microvessels, ie, vascular dimensions and flow velocities of fluorescently labeled or nonlabeled RBC and plasma markers. The microscopic CBF continuously fluctuates in time and space. Smoothing out this heterogeneity may lead to underestimation in the macroscopic CBF. To link the two measurements, it is needed to introduce a common parameter which is measurable for the both methods, such as mean transit time. Additionally, applying the defined physiological and/or pharmacological perturbation may provide a good exercise to determine how the specific perturbations interfere the quantitative relationships between the macroscopic and microscopic CBF. Finally, bridging these two-scale methods potentially gives a further indication how the absolute CBF is regulated with respect to a specific type of the cerebrovascular tones or capillary flow velocities in the brain.

Repeated longitudinal in vivo imaging of neuro-glio-vascular unit at the peripheral boundary of ischemia in mouse cerebral cortex

Understanding the cellular events evoked at the peripheral boundary of cerebral ischemia is critical for therapeutic outcome against the insult of cerebral ischemia. The present study reports a repeated longitudinal imaging for cellular-scale changes of neuro-glia-vascular unit at the boundary of cerebral ischemia in mouse cerebral cortex in vivo. Two-photon microscopy was used to trace the longitudinal changes of cortical microvasculature and astroglia following permanent middle cerebral artery occlusion (MCAO). We found that sulforhodamine 101 (SR101), a previously-known marker of astroglia, provide a bright signal in the vessels soon after the intraperitoneal injection, and that intensity was sufficient to detect the microvasculature up to a depth of 0.8 mm. After 5-8 h from the injection of SR101, cortical astroglia was also imaged up to a depth of 0.4 mm. After 1 day from MCAO, some microvessels showed a closure of the lumen space in the occluded MCA territory, leading to a restructuring of microvascular networks up to 7 days after MCAO. At the regions of the distorted microvasculature, an increase in the number of cells labeled with SR101 was detected, which was found as due to labeled neurons. Immunohistochemical results further showed that ischemia provokes neuronal uptake of SR101, which delineate a boundary between dying and surviving cells at the peripheral zone of ischemia in vivo. Finally, reproducibility of the MCAO model was evaluated with magnetic resonance imaging (MRI) in a different animal group, which showed the consistent infarct volume at the MCA territory over the subjects.

Relationship between baseline cerebral blood flow and vascular responses to changes in PaCO2 measured by positron emission tomography in humans: implication of inter-individual variations of cerebral vascular tone

AIM

Inter-individual variations in normal human cerebral blood flow (CBF) at rest condition have been reported. Inter-individual variation of cerebral vascular tone is considered to contribute to this, and several determinants of cerebral vascular tone have been proposed. In the present study, the relationship between CBF and cerebral vascular tone to inter-individual variation at rest condition was investigated using positron emission tomography (PET).

METHODS

CBF was measured using PET with H(2) (15)O in each of 20 healthy subjects (20-28 years) under three conditions: at rest (baseline), during hypercapnia and during hypocapnia. The vascular response to change in P(a)CO(2) was calculated as the percentage changes in CBF per absolute change in P(a)CO(2) in response to hypercapnia and hypocapnia.

RESULTS

A significant negative correlation between baseline CBF and the vascular response to hypocapnia was observed in the thalamus, temporal cortex, parietal cortex, occipital cortex and cerebral cortex (P < 0.05). A trend towards negative correlation between baseline CBF and the vascular response to hypocapnia was observed in the cerebellum and putamen (P < 0.1). A significant negative correlation between baseline CBF and the vascular response to hypercapnia was observed in the occipital cortex (P < 0.05). No significant correlation was observed between baseline CBF and haemoglobin concentration, and P(a)CO(2).

CONCLUSION

These findings support the assumption that cerebral vascular tone might incline towards vasoconstriction and vasodilatation when baseline CBF is low and high between individuals respectively. Although several determinants of cerebral vascular tone have been proposed, the mechanism of such inter-individual differences in cerebral vascular tone is unknown.

Heart and brain circulation and CO2 in healthy men

AIM

To compare blood flow response to arterial carbon dioxide tension change in the heart and brain of normal elderly men.

METHODS

Thirteen healthy elderly male volunteers were studied. Hypercapnea was induced by carbon dioxide inhalation and hypocapnea was induced by hyperventilation. Myocardial blood flow [mL min(-1) x (100 g of perfusable tissue)(-1)] and cerebral blood flow [mL min(-1) x (100 g of perfusable tissue)(-1)] were measured simultaneously at rest, under carbon dioxide gas inhalation and hyperventilation using the combination of two positron emission tomography scanners.

RESULTS

Arterial carbon dioxide tension increased significantly during carbon dioxide inhalation (43.1 +/- 2.7 mmHg, P < 0.05) and decreased significantly during hyperventilation (29.2 +/- 3.4 mmHg, P < 0.01) from baseline (40.2 +/- 2.4 mmHg). Myocardial blood flow increased significantly during hypercapnea (88.7 +/- 22.4, P < 0.01) from baseline (78.2 +/- 12.6), as did the cerebral blood flow (baseline: 39.8 +/- 5.3 vs. hypercapnea: 48.4 +/- 10.4, P < 0.05). During hypocapnea cerebral blood flow decreased significantly (27.0 +/- 6.3, P < 0.01) from baseline as did the myocardial blood flow (55.1 +/- 14.6, P < 0.01). However, normalized myocardial blood flow by cardiac workload [100 mL mmHg(-1) x (heart beat)(-1) x (gram of perfusable tissue)(-1)] was not changed from baseline (93.4 +/- 16.6) during hypercapnea (90.5 +/- 14.3) but decreased significantly from baseline during hypocapnea (64.5 +/- 18.3, P < 0.01).

CONCLUSION

In normal elderly men, hypocapnea produces similar vasoconstriction both in the heart and brain. Mild hypercapnea increased cerebral blood flow but did not have an additional effect to dilate coronary arteries beyond the expected range in response to an increase in cardiac workload.

Cyclooxygenase-pathway participates in the regulation of regional cerebral blood flow in response to neuronal activation under normo- and hypercapnia

The present study was designed to investigate whether cyclooxygenase products are involved in the regulation of the regional cerebral blood flow, evoked by somatosensory activation (evoked rCBF) under normo- and hypercapnia. Indomethacin (IMC) was used as cyclooxygenase inhibitor. It was applied intravenously (i.v., 10 mg/kg/h) in two experimental protocols-before hypercapnia (i) and after hypercapnia (ii). Somatosensory activation was induced by electrical hind paw stimulation (5 Hz frequency, 5 s duration, 1.5 mA). The evoked rCBF-response was measured in alpha -chloralose anesthetized rats using laser-Doppler flowmetry. IMC abolished completely the effect of hypercapnia on the baseline level of CBF. The drug reduced significantly evoked rCBF-response also. The inhibitory effect of IMC on evoked rCBF-response is better expressed under normocapnia (approximately 70%) than that under hypercapnia (approximately 40%). After IMC application, the normalized evoked rCBF curves peaked earlier as compared to that before its application (P<0.05), although the rise time of 0.5 s was nearly constant regardless of stimulus frequency. In conclusion, the results suggest a participation of IMC-sensitive and cyclooxygenase-dependent mechanisms in the regulation of evoked rCBF, induced by somatosensory stimulation.

Changes in red blood cell behavior during cerebral blood flow increase in the rat somatosensory cortex: a study of laser-Doppler flowmetry

The purpose of this study was to investigate red blood cell (RBC) behavior during an increase in local cerebral blood flow (LCBF). We measured changes in RBC behavior by using laser-Doppler flowmetry (LDF) in alpha-chloralose-anesthetized rats. An increase in LCBF was carried out by approximately 2.5 and 4.0% CO(2) inhalation and activation of the somatosensory cortex. The activation of the cortex was induced by electrical stimulation of the hind paw with 1.5-mA pulses (0.1 ms) applied at frequencies of 0.2, 1, 5, and 10 Hz for a 5 s duration. The increases in LCBF and RBC velocity during both CO(2) inhalations were larger than that in RBC concentration (p < 0.05). LCBF and RBC velocity during 4.0% CO(2) inhalation were larger than those during 2.5% CO(2) inhalation (p < 0.05), though there was no significant difference in RBC concentration between the two conditions, suggesting a limitation of capillary volume. During somatosensory stimulation, the evoked LCBF increased with increasing stimulus frequency up to 5 Hz and decreased at 10 Hz. The responses of RBC concentration at 0.2 and 10 Hz were greater than those of RBC velocity (p < 0.05), but no significant differences in response magnitude were found at 1 and 5 Hz between RBC concentration and RBC velocity. These results suggest that the increase in LCBF during neuronal activity is different from that of controlling the LCBF as induced by CO(2), and that the regulation of RBC concentration and RBC velocity is controlled by independent mechanisms.

Quantitative and temporal relationship between local cerebral blood flow and neuronal activation induced by somatosensory stimulation in rats

In many studies on functional neuroimaging, change in local cerebral blood flow induced by sensory stimulation (evoked LCBF) is used as a marker for change in cortical neuronal activity, although a full description of the relationship between the evoked LCBF and neuronal activity has not been given. The purpose of this study was to estimate the close relationship between the evoked LCBF and neuronal activity. We measured the field potential using an electrode inserted into the cortex and the evoked LCBF using Laser-Doppler flowmetry in alpha-chloralose-anesthetized rats during somatosensory stimulation. Activation of the cortex was carried out by electrical stimulation of the hind paw with 1.5 mA pulses (0.1 ms) applied at the frequencies of 0.2,1,5 and 10 Hz for a 5 s duration, and at the frequencies of 1 and 5 Hz for 2,5 and 15 s durations. The response magnitude of the evoked LCBF reached the maximum at 5 Hz. During the 5 s stimulation, the pattern of change in the response magnitude of evoked LCBF to various frequencies reflected the integrated amplitude of field potentials. During the 15 s stimulation, the evoked LCBF at 5 Hz exhibited an initial peak followed by a plateau phase, although there was no initial peak at 1 Hz. These changes in evoked LCBF during the 15 s stimulation reflected change in field potentials, but they were delayed during the temporal change in field potentials. These results suggest that the response of evoked LCBF reflects the integrated neuronal activity during the stimulation period, and it is modulated by a temporal slow function.

Bayesian technique for investigating linearity in event-related BOLD fMRI

Event-related BOLD fMRI data is modeled as a linear time-invariant system. Together with Bayesian inference techniques, a statistical test is developed for rigorously detecting linearity/nonlinearity in the BOLD response system. The test is applied to data collected from eight subjects using an event-related paradigm with a switching checkerboard as the visual stimulus. Analyzed as a group, the results clearly find the response to be nonlinear. When each subject is analyzed individually, however, the results are predominantly nonlinear, but there is some evidence to suggest that there may be a crossover from a linear to a nonlinear regime and vice versa. This could be important when estimating physiological parameters for individuals. Additionally, estimates of the hemodynamic response function and corresponding response were obtained, but there was no consistent appearance of a poststimulus undershoot in the event-related BOLD response.

Hemodynamics of local cerebral blood flow induced by somatosensory stimulation under normoxia and hyperoxia in rats

We observed changes in the local cerebral blood flow (LCBF), red blood cell (RBC) concentration and RBC velocity in alpha-chloralose anesthetized rats using laser-Doppler flowmetry during activation of the somatosensory cortex following electrical stimulation of the hind paw under hyperoxia (PaO(2)=513.5+/-48.4 mmHg; mean+/-S.D.) and normoxia (PaO(2)=106.4+/-8.4 mmHg). Electrical stimuli of 5 and 10 Hz (pulse width 0.1 ms) with an intensity of 1.5 mA were applied for 5 s (n=13 at 5 Hz, n=9 at 10 Hz). Baseline levels of LCBF and RBC concentration under hyperoxia were, respectively, 5.6+/-3.3 and 8.8+/-3.0% lower than those under normoxia (P<0.05), and that of RBC velocity under hyperoxia was slightly higher than that under normoxia (NS), suggesting mild vasoconstriction at rest under hyperoxia. At 5 Hz stimulation, after normalization to each baseline level, normalized response magnitudes of LCBF, RBC concentration and RBC velocity under hyperoxia were, respectively, 68.2+/-48.0, 71.1+/-65.5 and 66.0+/-56.3% greater than those under normoxia (P<0.05). At 10-Hz stimulation, normalized response magnitudes of LCBF and RBC concentration under hyperoxia were, respectively, 44.6+/-32.0 and 55.9+/-43.5% greater than those under normoxia (P<0.05), although a significant difference in the normalized response magnitude of RBC velocity was not detected between both conditions. The evoked LCBF under hyperoxia increased earlier, by approximately 0.15 s, than that under normoxia regardless of the stimulus frequency (P<0.05). These results suggest the involvement of oxygen interaction on the regulation of LCBF during neuronal activation.

Changes in human regional cerebral blood flow and cerebral blood volume during visual stimulation measured by positron emission tomography

The hemodynamic mechanism of increase in cerebral blood flow (CBF) during neural activation has not been elucidated in humans. In the current study, changes in both regional CBF and cerebral blood volume (CBV) during visual stimulation in humans were investigated. Cerebral blood flow and CBV were measured by positron emission tomography using H(2)(15)O and (11)CO, respectively, at rest and during 2-Hz and 8-Hz photic flicker stimulation in each of 10 subjects. Changes in CBF in the primary visual cortex were 16% +/- 16% and 68% +/- 20% for the visual stimulation of 2 Hz and 8 Hz, respectively. The changes in CBV were 10% +/- 13% and 21% +/- 5% for 2-Hz and 8-Hz stimulation, respectively. Significant differences between changes in CBF and CBV were observed for visual stimulation of 8 Hz. The relation between CBF and CBV values during rest and visual stimulation was CBV = 0.88CBF(0.30). This indicates that when the increase in CBF during neural activation is great, that increase is caused primarily by the increase in vascular blood velocity rather than by the increase in CBV. This observation is consistent with reported findings obtained during hypercapnia.

Frequency dependence of local cerebral blood flow induced by somatosensory hind paw stimulation in rat under normo- and hypercapnia

We measured the field potential and the changes in local cerebral blood flow (LCBF) response during somatosensory activation (evoked LCBF) in alpha-chloralose--anesthetized rats by laser-Doppler flowmetry under normocapnia (PaCO(2)=34.3+/-3.8 mmHg) and hypercapnia (PaCO(2)=70.1+/-9.8 mmHg). Somatosensory activation was induced by electrical stimulation (0.2, 1, and 5 Hz with 1.5 mA for 5 s) of the hind paw. The neuronal activity of the somatosensory area of the hind paw was linear to the stimulus frequency, and there was no significant difference in the neuronal activity between hypercapnia and normocapnia. The baseline level of LCBF under hypercapnia was about 72.2% higher than that under normocapnia (p<0.01). The absolute response magnitude under hypercapnia was greater than that under normocapnia (p<0.05). The evoked LCBF under both conditions showed a frequency-dependent increase in the 0.2 to 5 Hz range, and the difference in the absolute response magnitude at the same stimulus frequency between normocapnia and hypercapnia became large with increasing stimulus frequency (p<0.05). On the other hand, after normalization to each baseline level there was no significant difference in the response magnitude of the normalized evoked LCBF between normocapnia and hypercapnia, indicating that the normalized evoked LCBF reflects neuronal activity even when the baseline LCBF was changed by the PaCO(2) level. The peak time and termination time of LCBF response curves with respect to the graded neuronal activity at 1 and 5 Hz stimulation increased significantly under hypercapnia, compared with those under normocapnia (p<0.05), although the rise time of 0.5 s was nearly constant. In conclusion, the results suggest a synergistic effect of the combined application of graded neuronal stimuli and hypercapnia on the LCBF response.

Arterial fraction of cerebral blood volume in humans measured by positron emission tomography

In quantitative functional neuroimaging with positron emission tomography (PET) and magnetic resonance imaging (MRI), cerebral blood volume (CBV) and its three components, arterial, capillary, and venous blood volumes are important factors. The arterial fraction for systemic circulation of the whole body has been reported to be 20-30%, but there is no report of this fraction in the brain. In the present study, we estimated the arterial fraction of CBV with PET in the living human brain. C(15)O and dynamic H2(15)O PET studies were performed in each of seven healthy subjects to determine the CBV and arterial blood volume (Va), respectively. A two-compartment model (influx: K1, efflux: k2) that takes Va into account was applied to describe the regional time-activity curve of dynamic H2(15)O PET. K1, k2 and Va were calculated by a non-linear least squares fitting procedure. The Va and CBV values were 0.011 +/- 0.004 ml/ml and 0.031 +/- 0.003 ml/ml (mean +/- SD), respectively, for cerebral cortices. The arterial fraction of CBV was 37%. Considering the limited first-pass extraction fraction of H2(15)O, the true arterial fraction of CBV is estimated to be about 30%. The estimated arterial fraction of CBV was quite similar to that of the systemic circulation, whereas it was greater than that (16%) widely used for the measurement of cerebral metabolic rate of oxygen (CMRO2) using PET. The venous plus capillary fraction of CBV was 63-70% which is a important factor for the measurement of CMRO2 with MRI.

Hyperoxia modified activation-induced blood oxygenation level-dependent response of human visual cortex (V1): an event-related functional magnetic resonance imaging study

To investigate the effect that hyperoxia has on the blood oxygenation level-dependent (BOLD) response to visual stimulation of human V1, an event-related functional magnetic resonance imaging technique was applied. The event-related paradigm consisted of 2 s of stimulation by a checkerboard reversing at a frequency of 8 Hz, followed by 18 s of control scans. The peak height and peak time of the BOLD response curves were compared under normoxic and hyperoxic conditions. It was found that the peak height was larger and the peak time shorter for hyperoxia than for normoxia. These results suggest that hyperoxia modified the activation-induced hemodynamic response of human V1.

Temporal characteristics of event-related BOLD response and visual-evoked potentials from checkerboard stimulation of human V1: a comparison between different control features

This work is concerned with the temporal characteristics of event-related blood oxygenation level-dependent (ER-BOLD) and visual-evoked potential (VEP) signals produced by checkerboard stimulation of human V1. The study investigated whether different control features produce different amplitude VEPs, and if so, whether this corresponds to different ER-BOLD responses. The results showed that there was a difference in the amplitude of the P1-N1 components of the VEPs, and also in the magnitude and extent of the ER-BOLD responses. These results suggest the possibility that the P1-N1 components may be related to the difference in the magnitude and extent of the ER-BOLD response. Magn Reson Med 45:212-216, 2001.

Cerebral circulation and metabolism in the acute stage of subarachnoid hemorrhage

OBJECT

The mechanism of reduction of cerebral circulation and metabolism in patients in the acute stage of aneurysmal subarachnoid hemorrhage (SAH) has not yet been fully clarified. The goal of this study was to elucidate this mechanism further.

METHODS

The authors estimated cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2), O2 extraction fraction (OEF), and cerebral blood volume (CBV) preoperatively in eight patients with aneurysmal SAH (one man and seven women, mean age 63.5 years) within 40 hours of onset by using positron emission tomography (PET). The patients' CBF, CMRO2, and CBF/CBV were significantly lower than those in normal control volunteers. However, OEF and CBV did not differ significantly from those in control volunteers. The significant decrease in CBF/CBV, which indicates reduced cerebral perfusion pressure, was believed to be caused by impaired cerebral circulation due to elevated intracranial pressure (ICP) after rupture of the aneurysm. In two of the eight patients, uncoupling between CBF and CMRO2 was shown, strongly suggesting the presence of cerebral ischemia.

CONCLUSIONS

The initial reduction in CBF due to elevated ICP, followed by reduction in CMRO, at the time of aneurysm rupture may play a role in the disturbance of CBF and cerebral metabolism in the acute stage of aneurysmal SAH.

Evoked local cerebral blood flow induced by somatosensory stimulation is proportional to the baseline flow

The purpose of this study was to determine the relationship between the increase in local cerebral blood flow during neuronal activation (evoked LCBF) and the baseline flow level. We measured the hemodynamics in alpha-chloralose-anesthetized rats using laser-Doppler flowmetry during somatosensory stimulation under the hypocapnic, normocapnic and hypercapnic conditions. The baseline levels of LCBF and red blood cell (RBC) velocity under hypocapnia (PaCO(2)=26.4+/-1.1 mmHg) were, respectively, 10 and 11% lower than those under normocapnia (PaCO(2)=34.2+/-1.4 mmHg) (P<0.01). The evoked response magnitude of LCBF and RBC velocity under hypocapnia were, respectively, 22 and 18% lower than those under normocapnia. There was no significant difference in the baseline level and evoked response magnitude of RBC concentration. On the other hand, the baseline levels of LCBF, RBC velocity and RBC concentration under hypercapnia (PaCO(2)=73.4+/-13.3 mmHg) were, respectively, 47, 24 and 14% higher than those under normocapnia (PaCO(2)=34.7+/-2.5 mmHg) (P<0.01). The evoked response magnitude of LCBF, RBC velocity and RBC concentration under hypercapnia were, respectively, 96, 82 and 62% greater than those under normocapnia. After normalization with respect to each baseline level, there was no significant difference in normalized evoked response magnitude of LCBF, RBC velocity and RBC concentration, either between hypocapnic and normocapnic conditions or between hypercapnic and normocapnic conditions, indicating that evoked LCBF is proportional to the baseline flow. These results suggest that the amount of evoked LCBF is not determined by the demand for metabolic substrates.

Regional differences in cerebral vascular response to PaCO2 changes in humans measured by positron emission tomography

Hypercapnia and hypocapnia produce cerebral vasodilation and vasoconstriction, respectively. However, regional differences in the vascular response to changes in Paco2 in the human brain are not pronounced. In the current study, these regional differences were evaluated. In each of the 11 healthy subjects, cerebral blood flow (CBF) was measured using 15O-water and positron emission tomography at rest and during hypercapnia and hypocapnia. All CBF images were globally normalized for CBF and transformed into the standard brain anatomy. t values between rest and hypercapnia or hypocapnia conditions were calculated on a pixel-by-pixel basis. In the pons, cerebellum, thalamus, and putamen, significant relative hyperperfusion during hypercapnia was observed, indicating a large capacity for vasodilatation. In the pons and putamen, a significant relative hypoperfusion during hypocapnia, that is, a large capacity for vasoconstriction, was also observed, indicating marked vascular responsiveness. In the temporal, temporo-occipital, and occipital cortices, significant relative hypoperfusion during hypercapnia and significant relative hypoperfusion during hypocapnia were observed, indicating that cerebral vascular tone at rest might incline toward vasodilatation. Such regional heterogeneity of the cerebral vascular response should be considered in the assessment of cerebral perfusion reserve by hypercapnia and in the correction of CBF measurements for variations in subjects' resting Paco2.

A sealed cranial window system for simultaneous recording of blood flow, and electrical and optical signals in the rat barrel cortex

We have developed a new sealed cranial window technique which allows the manipulation of simultaneously and independently multiple sensor probes, such as a glass microelectrode and a laser-Doppler probe. possible. Furthermore, normal intracranial pressure (4 mmHg) can be maintained throughout the craniectomy and the experiment. Using this technique, we have measured the neuronal activity and local cerebral blood flow together with the intrinsic optical properties in the rat barrel cortex during mechanical stimulation of the whiskers. The onset of the field response recorded by an extracellular electrode in the principal barrel columns occurred about 8 ms from the beginning of stimulation. These responses were well correlated with the whisker displacements (3 Hz, 2 s). The local cerebral blood flow, measured by laser-Doppler flowmetry, started to increase about 0.5 s after the first field response, peaked at about 1.7 s, and then gradually waned. A similar time-course of changes in the local blood volume was observed by simultaneous intrinsic optical imaging at the hemoglobin-isosbestic wavelength (570 nm). These results suggest that our technique would be useful for assessing the mechanism underlying neurovascular coupling under physiological conditions in vivo.

Hyperoxia-enhanced activation-induced hemodynamic response in human VI: an fMRI study

The effect hyperoxia had on the hemodynamic response to visual stimulation (black and white checkerboard alternating at a frequency of 8 Hz) of human VI was investigated using a blood oxygenation level-dependent (BOLD) contrast with an fMRI technique. Data were acquired with a 5 on/5 off block paradigm using single-shot gradient-echo echo-planar imaging. Using a two-tailed paired t-test (p < 0.05, n = 13) it was found that the mean percentage signal change and the mean number of activated pixels was significantly increased for hyperoxia (5.7 +/- 0.9, 187 +/- 73, mean +/- SD) relative to those for normoxia (5.4 +/- 0.9, 168 +/- 58). We believe that these results indicate that hyperoxia enhances the activation-induced hemodynamic response in human VI.

Modulation of evoked cerebral blood flow under excessive blood supply and hyperoxic conditions

We measured the field potential and local cerebral blood flow (LCBF) using laser-Doppler flowmetry in alpha-chloralose anesthetized rats during activation of the somatosensory cortex by electrical stimulation of the hind paw under independent administration of additional carbon dioxide and oxygen. The aim of this study was to test the hypothesis that the increase in LCBF during activation of the cortex (evoked LCBF) is not directed toward supplying oxygen for oxidative metabolism. Under the hypercapnic condition (PaCO(2) = 74. 9 +/- 14.3 mmHg), the baseline LCBF was about 46.5% higher than that under the normocapnic condition (PaCO(2) = 35.7 +/- 2.1 mmHg) (p < 0. 001), but after normalization for each baseline (divided by the prestimulus level), there was no significant difference in the peak value and the rise time of normalized evoked LCBF. On the other hand, the baseline level of LCBF under the hyperoxic condition (PaO(2) = 479.4 +/- 77.2 mmHg) was about 5.0% lower than that under the normoxic condition (PaO(2) = 105.5 +/- 7.8 mmHg) (p < 0.01), suggesting mild vasoconstriction under the condition of hyperoxia at rest. The peak value of normalized evoked LCBF under the hyperoxic condition was about 6.5% higher than that under the normoxic condition (p < 0.05). In addition, the rise time of evoked LCBF was earlier under the hyperoxic condition (0.37 +/- 0.16 s) than that under the normoxic condition (0.52 +/- 0.12 s) (p < 0.01). The field potential measured during stimulation under hypercapnic and hyperoxic conditions was not significantly different when compared with that under normal gas conditions. These results support our hypothesis and suggest that the excess oxygen is involved in the mechanism underlying the regulation of LCBF.

Application of Bayesian inference to fMRI data analysis

The methods of Bayesian statistics are applied to the analysis of fMRI data. Three specific models are examined. The first is the familiar linear model with white Gaussian noise. In this section, the Jeffreys' Rule for noninformative prior distributions is stated and it is shown how the posterior distribution may be used to infer activation in individual pixels. Next, linear time-invariant (LTI) systems are introduced as an example of statistical models with nonlinear parameters. It is shown that the Bayesian approach can lead to quite complex bimodal distributions of the parameters when the specific case of a delta function response with a spatially varying delay is analyzed. Finally, a linear model with auto-regressive noise is discussed as an alternative to that with uncorrelated white Gaussian noise. The analysis isolates those pixels that have significant temporal correlation under the model. It is shown that the number of pixels that have a significantly large auto-regression parameter is dependent on the terms used to account for confounding effects.

Hemodynamics evoked by microelectrical direct stimulation in rat somatosensory cortex

The aim of this study was to estimate the timing (latency) of the increase in red blood cell (RBC) velocity and RBC concentration, and the magnitude of response in local cerebral blood flow (LCBF) for neuronal activation. We measured LCBF change during activation of the somatosensory cortex by direct microelectrical stimulation. Electrical stimuli of 5, 10 and 50 Hz of 1 ms pulse with 10-15 microA, were given for 5 s. LCBF, RBC velocity and RBC concentration were monitored by laser-Doppler flowmetry (LDF) in alpha-chloralose anesthetized rats (n = 7). LCBF, RBC velocity and RBC concentration increased nearly proportionally to stimulus frequency, i.e. neuronal activity. LCBF rose approximately 0.5 s after the onset of stimulation, and there was no significant time lag of the latencies among LCBF, RBC velocity and RBC concentration at the same stimulus frequency. We interpret these results to mean that the onset of LCBF increase on cortical activation is reflected by a rapid change in arteriole (resistance vessel) dilation and capillary volume. The data also elucidate the linear relationship between LCBF increase and cortical activity.

CBF change evoked by somatosensory activation measured by laser-Doppler flowmetry: independent evaluation of RBC velocity and RBC concentration

The purpose of this study was to examine the timing and magnitude of cerebral blood flow (CBF) responses to neuronal activation. We measured the changes in local CBF (LCBF), red blood cell (RBC) velocity and RBC concentration by laser-Doppler flowmetry (LDF) as well as field potential recordings during activation of the somatosensory cortex of the rat in response to electrical stimulation of the hind paw. Electrical stimuli, 0.1 ms pulses of 1-1.5 mA for 5 s, were applied at 0.2, 0.5, 5, 10 and 50 Hz under alpha-chloralose anesthesia. LCBF showed the maximum increase at 5 Hz, and rose approximately 0.5 s after the onset of stimulation regardless of the frequency. The maximum frequency of the field potentials was also obtained at 5 Hz. During activation of the somatosensory cortex, the onset of rise in RBC concentration did not precede that of RBC velocity, and the peak RBC concentration was noted earlier than that of both LCBF and RBC velocity, suggesting that both arteriolar diameter and active changes in the capillary contributed to the LCBF response.

11C-methionine uptake to the pancreas and its secretion: a positron emission tomography study in humans

The aim of this study was to investigate the uptake of [11C-methyl]-L-methionine (11C-methionine) in the human pancreas by analyzing dynamic positron emission tomography (PET) images and the duodenal aspirate. A double-lumen tube was inserted in the duodenum and dynamic PET was performed in seven healthy volunteers for 110 min after intravenous (i.v.) injection of 11C-methionine during the continuous i.v. administration of secretin (125 ng/kg/h) and cerulein (30 ng/kg/h). For the calculation of the radioactivity in the pancreas, the regions of interest were set on the PET images. Radioactivity was measured in 10-min fractions of duodenal juice. After i.v. injection, 11C-methionine accumulated in the pancreas within a few minutes, and the radioactivity plateaued during the study. The radiolabeled proteins in the duodenal juice increased linearly 30 min after 11C-methionine injection, but the relative rates of radioactivity in the protein precipitate to the total count in the duodenal juice were 44-48%. From these findings, it was concluded that 11C-methionine accumulation in the pancreas is very rapid after the i.v. administration, and only a part of methionine uptake to the pancreas is incorporated into secretory proteins. The pancreatic 11C-methionine uptake detected by PET may represent a new aspect of exocrine pancreatic function that has not been expressed by the conventional intubation method.

Synthesis and autoradiographic localization of muscarinic cholinergic antagonist (+)N-[11C]methyl-3-piperidyl benzilate as a potent radioligand for positron emission tomography

(+)N-[11C]methyl-3-piperidyl benzilate, a relatively low affinity muscarinic cholinergic receptor antagonist was synthesized by N-[11C]methylation of (+)3-piperidyl benzilate using [11C]methyl iodide. The product was isolated by HPLC, and obtained with radiochemical yield of 60-70% from [11C]methyl iodide, and a specific activity of 500-1000 Ci mmol-1 (18.5-37 GBq mumol-1) at EOS and radiochemical purity of > 98%. In vitro autoradiographic studies showed selective binding for this radiotracer in the different regions of the rat brain: high in corpus striatum, hippocampus and cerebral cortex, and low in cerebellum, consistent with muscarinic cholinergic receptor distributions. This radiotracer thus had potential as radioligand for positron emission tomography.

Activation detection in functional MRI using subspace modeling and maximum likelihood estimation

A statistical method for detecting activated pixels in functional MRI (fMIRI) data is presented. In this method, the fMRI time series measured at each pixel is modeled as the sum of a response signal which arises due to the experimentally controlled activation-baseline pattern, a nuisance component representing effects of no interest, and Gaussian white noise. For periodic activation-baseline patterns, the response signal is modeled by a truncated Fourier series with a known fundamental frequency but unknown Fourier coefficients. The nuisance subspace is assumed to be unknown. A maximum likelihood estimate is derived for the component of the nuisance subspace which is orthogonal to the response signal subspace. An estimate for the order of the nuisance subspace is obtained from an information theoretic criterion. A statistical test is derived and shown to be the uniformly most powerful (UMP) test invariant to a group of transformations which are natural to the hypothesis testing problem. The maximal invariant statistic used in this test has an F distribution. The theoretical F distribution under the null hypothesis strongly concurred with the experimental frequency distribution obtained by performing null experiments in which the subjects did not perform any activation task. Application of the theory to motor activation and visual stimulation fMRI studies is presented.

Anatomic validation of spatial normalization methods for PET

Spatial normalization methods, which are indispensable for intersubject analysis in current PET studies, have been improved in many aspects. These methods have not necessarily been evaluated as anatomic normalization methods because PET images are functional images. However, in view of the close relation between brain function and morphology, it is very intriguing how precisely normalized brains coincide with each other. In this report, the anatomic precision of spatial normalization is validated with three different methods.

METHODS

Four PET centers in Japan participated in this study. In each center, six normal subjects were recruited for both H2(15)O-PET and high-resolution MRI studies. Variations in the location of the anterior commissure (AC) and size and contours of the brain and the courses of major sulci were measured in spatially normalized MR images for each method. Spatial normalization was performed as follows. (a) Linear: The AC-posterior commissure and midsagittal plane were identified on MRI and the size of the brain was adjusted to the Talairach space in each axis using linear parameters. (b) Human brain atlas (HBA): Atlas structures were manually adjusted to MRI to determine linear and nonlinear transformation parameters and then MRI was transformed with the inverse of these parameters. (c) Statistical parametric mapping (SPM) 95: PET images were transformed into the template PET image with linear and nonlinear parameters in a least-squares manner. Then, coregistered MR images were transformed with the same parameters used for the PET transformation.

RESULTS

The AC was well registered in all methods. The size of the brain normalized with SPM95 varied to a greater extent than with other approaches. Larger variance in contours was observed with the linear method. Only SPM95 showed significant superiority to the linear method when the courses of major sulci were compared.

CONCLUSION

The results of this study indicate that SPM95 is as effective a spatial normalization as HBA, although it does not use anatomic images. Large variance in structures other than the AC and size of the brain in the linear method suggests the necessity of nonlinear transformations for effective spatial normalization. Operator dependency of HBA also must be considered.

Verb generation in Japanese--A multicenter PET activation study

Cerebral blood flow (CBF) during silent verb generation was measured at four Japanese PET centers. To minimize the variance of the measurement, speakers of a single language (Japanese) served as subjects and experimental conditions at the four PET centers were controlled as much as possible. Two types of activation patterns were observed: activations in the left dorsolateral prefrontal cortices and the medial frontal cortex (at the two centers with a 2D PET scanner) and additional activation in the left posterior temporal cortex (at the two centers with a 3D scanner). This suggests either a difference in the sensitivity of the two types of PET scanners (viz., a 3D scanner is generally more sensitive than a 2D scanner) and/or subject bias due to the small number of subjects at the individual centers. The pooled activation pattern was fundamentally similar to activation patterns obtained in the previous studies for verb generation in English and other European languages, suggesting that regions for verb generation are independent of particular languages. Regions relevant to verb generation are discussed.

Statistical methods for detecting activated regions in functional MRI of the brain

Two statistical tests for detecting activated pixels in functional MRI (fMRI) data are presented. The first test (t-test) is the optimal solution to the problem of detecting a known activation signal in Gaussian white noise. The results of this test are shown to be equivalent to the cross-correlation method that is widely used for activation detection in fMRI. The second test (F test) is the optimal solution when the measured data are modeled to consist of an unknown activation signal that lies in a known lower dimensional subspace of the measurement space with added Gaussian white noise. A model for the signal subspace based on a truncated trigonometric Fourier series is proposed for periodic activation-baseline imaging paradigms. The advantage of the second method is that it does not assume any information about the shape or delay of the activation signal, except that it is periodic with the same period as the activation-baseline pattern. The two models are applied to experimental echo-planar fMRI data sets and the results are compared.

Influence of ANOVA design and anatomical standardization on statistical mapping for PET activation

We have created images of z value, error, and variation components for a PET activation study using various ANOVA designs and anatomical standardization methods. Data were acquired in four PET centers. In each center, CBF was measured on six normal male subjects under resting and covert verb generation, three times for each. The images were anatomically standardized with LINEAR transformation, SPM (Ver. 95), HBA (Karolinska/Tohoku), or MICHIGAN (Minoshima). ANOVA was performed pixel by pixel to compute t (and z) for the task main effect (Verb vs Rest) in four different designs: (i) two way (subject and task) (2W), (ii) two-way with interaction (2WI), (iii) subject considered a random factor (2WI-MX), and (iv) three-way (subject, task, and replication) (3W). A large area extending from the Broca to the left premotor cortex was activated. The localization of the highest peak depended both on the anatomical standardization and on the ANOVA design, the variation ranging 3-4 cm. Smoothing reduced the variation while erasing possible subfoci. The z images of 2W, 2WI, and 3W looked alike, whereas 2WI-MX presented lower peak z values. SPM tended to present higher z values than the other methods. The error was high in the gray and low in the white matter. The root mean square for the subject effect was high on the border of gray matter especially in LINEAR and HBA, revealing intersubject mismatch in the gray matter distribution. The root mean square for the subject-by-task interaction effect revealed individual variation in activation.

Noninvasive quantitation of cerebral blood flow using oxygen-15-water and a dual-PET system

Measurement of the arterial input function is essential for quantitative assessment of physiological function in vivo using PET. However, frequent arterial blood sampling is invasive and labor intensive. Recently, a PET system has been developed that consists of two independent PET tomographs for simultaneously scanning the brain and heart, which should avoid the need for arterial blood sampling. The aim of this study was to validate noninvasive quantitation with this system for 15O-labeled compounds.

METHODS

Twelve healthy volunteers underwent a series of PET studies after C15O inhalation and intravenous H2(15)O administration using a Headtome-V-Dual tomograph (Shimadzu Corp., Kyoto, Japan). The C15O study provided gated blood-pool images of the heart simultaneously with quantitative static blood-volume images of both the brain and heart. Weighted-integrated H2(15)O sinograms were acquired for estimating rate constant (K1) and distribution-volume (Vd) images in the brain, in addition to single-frame sinograms for estimating autoradiographic cerebral blood flow images. Noninvasive arterial input functions were determined from the heart scanner (left ventricular chamber) according to a previously developed model and compared directly to invasive input functions measured with an on-line beta probe in six subjects.

RESULTS

The noninvasive input functions derived from this PET system were in good agreement with those obtained by continuous arterial blood sampling in all six subjects. There was good agreement between quantitative values obtained noninvasively and those using the invasive input function: average autoradiographic regional cerebral blood flow was 0.412 +/- 0.058 and 0.426 +/- 0.062 ml/min/g, K1 of H2(15)O was 0.416 +/- 0.073 and 0.420 +/- 0.067 ml/min/ml and Vd of H2(15)O was 0.800 +/- 0.080 and 0.830 +/- 0.070 ml/ml for the noninvasive and invasive input functions, respectively. In addition to the brain functional parameters, the system also simultaneously provided cardiac function such as regional myocardial blood flow (0.84 +/- 0.19 ml/min/g), left ventricular volume (132 +/- 22 mm at end diastole and 45 +/- 14 ml at end systole) and ejection fraction (66% +/- 5%).

CONCLUSION

This PET system allows noninvasive quantitation in both the brain and heart simultaneously without arterial cannulation, and may prove useful in clinical research.

Parapharyngeal meningioma extending from the intracranial space evaluated by FDG PET

We report a rare case of parapharyngeal meningioma extending from the intracranial space evaluated by PET with [18F]-2-fluorodeoxyglucose (FDG). Although the parapharyngeal meningioma had a high rate of glucose metabolism, it was proved to be pathohistologically benign. The high rate of glucose metabolism of the tumor reflected tumor aggressiveness well because the tumor grew in a relatively short time.

Vascular imprints of neuronal activity: relationships between the dynamics of cortical blood flow, oxygenation, and volume changes following sensory stimulation

Modern functional neuroimaging methods, such as positron-emission tomography (PET), optical imaging of intrinsic signals, and functional MRI (fMRI) utilize activity-dependent hemodynamic changes to obtain indirect maps of the evoked electrical activity in the brain. Whereas PET and flow-sensitive MRI map cerebral blood flow (CBF) changes, optical imaging and blood oxygenation level-dependent MRI map areas with changes in the concentration of deoxygenated hemoglobin (HbR). However, the relationship between CBF and HbR during functional activation has never been tested experimentally. Therefore, we investigated this relationship by using imaging spectroscopy and laser-Doppler flowmetry techniques, simultaneously, in the visual cortex of anesthetized cats during sensory stimulation. We found that the earliest microcirculatory change was indeed an increase in HbR, whereas the CBF increase lagged by more than a second after the increase in HbR. The increased HbR was accompanied by a simultaneous increase in total hemoglobin concentration (Hbt), presumably reflecting an early blood volume increase. We found that the CBF changes lagged after Hbt changes by 1 to 2 sec throughout the response. These results support the notion of active neurovascular regulation of blood volume in the capillary bed and the existence of a delayed, passive process of capillary filling.

Automatic detection of the mid-sagittal plane in 3-D brain images

This article presents a detailed description of an algorithm for the automatic detection of the mid-sagittal plane in three-dimensional (3-D) brain images. The algorithm seeks the plane with respect to which the image exhibits maximum symmetry. For a given plane, symmetry is measured by the cross-correlation between the image sections lying on either side. The search for the plane of maximum symmetry is performed by using a multiresolution approach which substantially decreases computational time. The choice of the starting plane was found to be an important issue in optimization. A method for selecting the initial plane is presented. The algorithm has been tested on brain images from various imaging modalities in both humans and animals. Results were evaluated by visual inspection by neuroradiologists and were judged to be consistently correct.

Regional correlations between the EEG and oxygen metabolism in dementia of Alzheimer's type

To determine the relationship between EEG slowing and cerebral hypometabolism in dementia, 10 patients with dementia of Alzheimer's type (DAT) were evaluated with quantitative topographic EEG and positron emission tomography (PET). Power in each 1-Hz frequency band from 2-20 Hz, power ratio index, and normalised PET data from corresponding cortical sites were compared to data obtained from 20 normal volunteers. PET revealed significant parieto-temporal hypometabolism, and topographic EEG mapping and power spectrum analysis revealed a slowing of the background EEG that was most pronounced in the parietal-temporal areas. Correlation analysis between EEG power spectrum data and CMRO2 revealed significant negative correlations for frequencies below 8 Hz and significant positive correlations above 8 Hz in the parieto-temporal regions, which have previously been identified as the areas most severely affected by pathological changes associated with DAT. Correlation coefficients plotted as functions of frequency illustrated the relationships between EEG changes and reduced CMRO2, supporting previous views that EEG slowing in DAT may be related to hypometabolism in cortical regions most affected by the disease.