Naohiko Oku

Nuclear neuroimaging in acute and subacute ischemic stroke

Neuroimaging in ischemic stroke continues to be one of the most developing fields in nuclear medicine. Many studies have established the efficacy of blood flow and metabolism measurements in acute ischemic stroke. Although the release of recombinant tissue plasminogen activator in clinical practice has minimized the use of SPECT or PET in the first few hours of ischemic stroke onset, implementing these techniques into a set of initial examinations is still beneficial to exclude risky patients for reperfusion therapy beyond several hours after onset. Rescuing of viable tissue suffering ischemic penumbra is an important target of early therapeutic strategy. Ischemic penumbra can be visualized by means of perfusion imaging, central type benzodiazepine receptor imaging, and hypoxy imaging. In the later phase of subacute ischemic stroke, inflammation and apoptosis can be visualized by means of peripheral-type benzodiazepine receptor imaging and annexin V imaging, respectively. Imaging of the penumbra and cellular responses will help evaluate the effects of drugs and interventions for ischemic stroke, suggesting its potential as a marker of the efficacy of future therapeutic regimens.

Chronic Middle Cerebral Artery Occlusion: A Hemodynamic and Metabolic Study with Positron-Emission Tomography

BACKGROUND AND PURPOSE: Chronic middle cerebral artery (MCA) occlusion is more common than generally thought. It is important to assess the cerebral hemodynamic status in patients with this chronic condition. We investigated the cerebral hemodynamic and metabolic disturbances in these patients in relation to the development of the collateral vasculature. MATERIALS AND METHODS: We studied 13 patients with chronic unilateral MCA occlusion who had a minor or no stroke by using positron-emission tomography (PET). PET was performed by the oxygen 15 (15O) gas steady-state inhalation method. The intracranial arteries were evaluated by digital subtraction angiography. We divided the patients into 2 subgroups according to whether they had a normal or increased oxygen extraction fraction (OEF) in the occluded MCA territory and compared the 2 groups. RESULTS: Of the 13 patients, 9 were classified into the normal OEF and 4 were classified into the increased OEF group. In the increased OEF group, the mean OEF values were also increased in the territories of the ipsilateral anterior cerebral artery, ipsilateral posterior cerebral artery, and contralateral MCA. The patients in the increased OEF group had more than 1 steno-occlusive lesion in the major intracranial arteries (P = .008). Three of the 4 patients in the increased OEF group also had vascular lesions in the collateral pathways to the MCA territory. CONCLUSION: Most patients with chronic MCA occlusion did not show severe hemodynamic impairment. Those with increased OEF tended to have other areas of severe hemodynamic impairment and other vascular lesions, especially in the collateral pathways.

Functional brain areas associated with manipulation of a prehensile tool: A PET study

Using PET, brain areas representing the use of a well‐learned tool (chopsticks) were investigated in 10 normal common users. The experimental task was to hold the tool in their right hand and use it to pick up and transport a small pin from a table. Data for the same task performed using only the fingers were also obtained as a control. The results showed an extensive overlap in activated areas with and without the use of the tool. The tool‐use prehension, compared to the finger prehension, was associated with higher activities in the caudal‐ventral premotor, dorsal premotor, superior parietal, posterior intraparietal, middle temporal gyrus, and primary sensory, occipital cortices, and the cerebellum. These are thus considered to be the human cortical and subcortical substrates representing the use of the tool studied. The activity of the posterior intraparietal area was negatively correlated with the number of drops of the pin, whereas occipital activity was positively correlated with the same error parameter. The caudal‐ventral premotor and posterior intraparietal areas are together known to be involved in tool use‐related modulation in peripersonal space. The correlation results suggest that this modulation depends on the level of performance. The coactivated left middle temporal gyrus further suggests that familiarity with a tool as well as the knowledge about its usage plays a role in peripersonal space modulation. Superior parietal activation, along with occipital activation, indicates the involvement of visual‐spatial attention in the tool use, possibly reflecting the effect of interaction between the prehension (task) and the tool. Hum Brain Mapp 2009.

Statistical Parametric Analysis of Cerebral Blood Flow in Vascular Dementia with Small-Vessel Disease Using 99mTc-HMPAO SPECT

Background: Subcortical ischemic vascular dementia (SVD) caused by small-artery disease is a major cause of dementia. It still remains unclear, however, whether SVD may present with localized regional cerebral blood flow (rCBF) changes. We aimed to clarify the local rCBF changes associated with dementia in patients with early-stage SVD. Methods: The subjects consisted of 15 patients with early-stage SVD [Mini Mental State Examination (MMSE) score: 20 ± 3.5] without apparent brain atrophy (SVD group), 11 patients without dementia with white matter lesions (non-dementia-WML group) and 16 age-matched controls. All the subjects were right-handed and underwent brain perfusion single photon emission computed tomography (SPECT), magnetic resonance imaging and cognitive function testing. Statistical analysis of the differences in the SPECT rCBF was performed by SPM2. The degree of severity of the WMLs was evaluated based on the Scheltens rating scale. Results: The results of SPM analysis revealed that the rCBF in the SVD group was significantly decreased in the pulvinar nuclei of the thalamus of both sides as compared with that in the controls, and in the left pulvinar nucleus as compared with that in the non-dementia-WML group. On the other hand, SPM analysis revealed no significant reduction in rCBF in the non-dementia-WML group as compared with that in the controls. The WMLs in the left parietal region were severer in the SVD group than in the non-dementia-WML group. Conclusions: In patients with early-stage SVD without apparent brain atrophy, significant rCBF reduction in the bilateral pulvinar nuclei as compared with that in normal controls, and in the left pulvinar nucleus as compared with that in patients without dementia with WMLs was found.

Cerebral hemodynamics and oxygen metabolism in patients with moyamoya syndrome associated with atherosclerotic steno-occlusive arterial lesions.

Background: Patients with major cerebral artery steno-occlusion and the formation of the moyamoya-like vessels associated with some other disorders have been distinguished from moyamoya disease and classified as moyamoya syndrome. The hemodynamic and metabolic backgrounds of the moyamoya syndrome associated with atherosclerosis have not yet been investigated. We aimed to elucidate the hemodynamic and metabolic characteristics associated with the development of basal moyamoya-like vessels in moyamoya syndrome with atherosclerosis. Methods: Twenty-one patients with chronic unilateral atherosclerotic steno-occlusive lesions of the internal carotid artery or middle cerebral artery (MCA) were enrolled in the study. Based on the angiographic findings, the patients were classified into 2 groups: the moyamoya syndrome group (n = 7) and the non-moyamoya-syndrome group (n = 14). We conducted angiographic evaluations of the extent of the development of basal moyamoya-like vessels in the moyamoya syndrome group. The cerebral blood flow, cerebral metabolic rate of oxygen, oxygen extraction fraction (OEF) and cerebral blood volume were measured using PET in the ipsilateral MCA area in the patients and in normal controls (n = 6). Results: The OEF in the ipsilateral MCA area, except in the basal ganglia, was significantly higher in the moyamoya syndrome group than in the non-moyamoya-syndrome group (p < 0.001). The extent of the development of basal moyamoya-like vessels was closely correlated with the elevation of the OEF (r > 0.999, p < 0.001). Conclusion: The basal moyamoya-like vessels are evidence of misery perfusion in patients with unilateral chronic atherosclerotic steno-occlusive lesions of major cerebral artery trunks.

Blood Pressure Lowering with Valsartan Is Associated with Maintenance of Cerebral Blood Flow and Cerebral Perfusion Reserve in Hypertensive Patients with Cerebral Small Vessel Disease

BACKGROUNDnThe purpose of this study was to determine the effect of systemic blood pressure-lowering treatment with an angiotensin II receptor blocker, valsartan, on cerebral hemodynamics in patients with hypertension and evidence of cerebral small vessel disease.nnnMETHODSnWe used positron emission tomography and acetazolamide challenge tests to measure cerebral blood flow (CBF) and cerebrovascular reserve (CVR) in 8 patients with hypertension (mean age 70.8 years) with lacunar infarcts and white matter lesions before and after valsartan therapy.nnnRESULTSnSystemic blood pressure was significantly decreased from baseline after treatment with valsartan. The baseline global CBFs before and after treatment were 38.2 +/- 5.6 mL/min/100 g and 39.9 +/- 9.0 mL/min/100 g, respectively. The CVRs before and after treatment were 52.2 +/- 18.4% and 39.7 +/- 18.9%, respectively. Differences in these parameters were not significant. Both regional CBF and CVR in the corona radiata with moderate or severe white matter lesions were also preserved after valsartan therapy compared with those before treatment.nnnCONCLUSIONSnCerebral hemodynamics were preserved after blood pressure lowering with valsartan therapy. Valsartan could be a feasible antihypertensive regimen in terms of cerebral circulation in patients with cerebral small vessel disease.

Hemodynamic Influences of Azelnidipine, a Novel Calcium Channel Blocker, on Cerebral Circulation in Hypertensive Patients with Ischemic White Matter Lesions

Calcium channel blockers have been widely used for the treatment of hypertension because several clinical trials have demonstrated their strong action on lowering blood pressure and their role in preventing cardiovascular events such as stroke and coronary heart disease. However, there have been few reports on the effects on cerebral hemodynamics when blood pressure is lowered with this class of drug. In this study, we used positron emission tomography and acetazolamide challenge tests to measure cerebral blood flow and cerebrovascular reserve before and after administration of a novel calcium channel blocker, azelnidipine, in nine hypertensive patients (mean age, 66.1 years) with ischemic white matter lesions. Systemic blood pressure was significantly decreased from baseline (153.8±15.5/92.1±8.5 mmHg) after treatment with azelnidipine (138.4±16.3/81.8±6.2 mmHg). The baseline global cerebral blood flow values before and after treatment were 40.1±7.2 mL/min/100 g and 39.2±8.2 mL/min/100 g, respectively. The cerebrovascular reserve values before and after treatment were 58.6±21.7% and 56.3±21.3%, respectively. Differences in these parameters were not significant. A regional analysis showed no statistical differences in regional cerebral blood flow or cerebral perfusion reserve throughout the brain before and after treatment. No associations between the decreased blood pressure and the changes in cerebral blood flow or cerebrovascular reserve were found in the whole brain or in the deep white matter with ischemic lesions. In conclusion, we found that the cerebral blood flow and cerebral vascular reserve were preserved after blood pressure lowering with azelnidipine administration in hypertensive patients with ischemic white matter lesions. Azelnidipine, a novel calcium channel blocker, could be a feasible antihypertensive regimen in terms of cerebral circulation in patients with ischemic white matter lesions.

18F-Fluorodeoxyglucose uptake and clinicopathological features of recurrent or metastatic endometrial stromal sarcoma

Maximum standardized uptake value on 18F‐fluorodeoxyglucose positron emission tomography was evaluated as a predictive surrogate marker in developing treatment strategies for recurrent or metastatic endometrial stromal sarcoma.

Auditory and tactile processing in a postmeningitic deaf–blind patient with a cochlear implant

The authors examined the neural function of a postmeningitic deaf–blind patient who regained his hearing with a multichannel cochlear implant. Auditory stimuli activated the temporal cortices of both sides in a manner similar to that of controls, reflecting the successful recruitment of the auditory cortex after implantation. The patient’s occipital lobes were deactivated during the tactile language task, the results of which were completely different from those before cochlear implantation.

Clinical impact of “true whole-body” 18 F-FDG PET/CT: lesion frequency and added benefit in distal lower extremities

ObjectivesThe purpose of this study was to evaluate the lesion frequency and incremental added benefit with “true whole-body” 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) of distal lower extremities. We compared this field of view with the typical whole-body view, from head to upper thighs, in numerous patients with known or suspected malignancy.MethodsTrue whole-body 18F-FDG PET/CT, from the top of the head to the bottom of the feet, was performed on 4574 consecutively registered patients with known or suspected malignancy. Using a variable sampling method, the PET images of head and torso were acquired for 90xa0s per bed position, and the images of lower extremities were acquired for 30xa0s per position, thus requiring between 22 and 24xa0min of emission scanning per patient. A log was maintained to record cases of abnormal findings in distal lower extremities outside the typical whole-body field of view. Suspected malignant lesions in distal lower extremities were verified by correlation with pathological findings and clinical follow-up.ResultsAbnormal findings in distal lower extremities were found in 647 (14.1xa0%; 95xa0% CI 13.1–15.2xa0%) of 4574 examinations. Increased FDG uptake was found in 559 examinations (12.2xa0%; 95xa0% CI 11.3–13.2xa0%). Lesions appeared malignant or equivocal in 67 examinations (1.5xa0%; 95xa0% CI 1.1–1.8xa0%) on the PET images. In 42 (0.9xa0%; 95xa0% CI 0.6–1.2xa0%) of 4574 examinations, these lesions were pathologically or clinically proven to be malignant. Detection of these malignancies resulted in changing clinical management in 21 (50xa0%) of 42 examinations. Definitive benign lesions were found in 492 examinations (10.7xa0%; 95xa0% CI 9.9–11.7xa0%) on the PET images. Abnormal findings were noted in 90 examinations (2.0xa0%; 95xa0% CI 1.6–2.4xa0%) consisting of 88 benign and 2 malignancies on the CT images alone.ConclusionTrue whole-body 18F-FDG PET/CT was not of high yield and appears to offer little additional benefit, as to detection of additional metastases and involvement, but it may affect clinical management in patients with known or suspected malignancy.