SPECT has the potential to provide parametric functional images, in a "quantitative" manner, for several radiotracers in vivo, as has been widely done with PET. Due to the ready availability of SPECT, in addition to the well-established delivery/transportation of various radio-ligands, SPECT has an advantage for large-scale clinical evaluation. It has, however, been considered that the accuracy and inter-institutional reproducibility of SPECT are not well verified, which is largely attributed to a lack of general consensus of reconstruction procedures (attenuation/scatter correction). We have recently developed a novel method to reconstruct SPECT images from existing projection data including appropriate corrections for scatter and attenuation in the object. We have demonstrated that this program is capable of providing accurate radio-distribution in the brain and thorax regions, and also rest-Diamox CBF using split-dose ^<123>I amphetamine (IMP). Various phantom experiments also supported the validity of inter-institutional reproducibility. These data suggested that QSPECT could be a useful tool for quantitative mapping in clinical research, allowing for large scale clinical evaluations even when using SPECT cameras from different manufacturers.

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Single photon emission computed tomography (SPECT) can provide information to help decide on the indication of surgical revascularization for hemodynamic cerebral ischemia. A recent Japanese EC-IC Bypass Trial (JET Study) showed that the EC-IC Bypass was beneficial for stroke prevention in patients with Stage II hemodynamic cerebral ischemia determined by quantified resting and acetazolamide-activated CBF-SPECT. Stage II hemodynamic cerebral ischemia may also be a surrogate marker of stroke recurrence. However, stratification of hemodynamic cerebral ischemia using quantified CBF-SPECT is not standardized enough at present. The dual table ARG (DTARG) method provided same-day quantification of both resting and acetazolamide-activated CBF using a split dose of ^<123>I-IMP and common arterial input function. In this method, both resting and acetazolamide-activated CBF-SPECT could be quantified pixel-by-pixel using the table look-up method with high measurement accuracy. On the other hand, segmental extraction estimation (SEE) analysis of CBF-SPECT displayed resting CBF, acetazolamide-activated CBF, cerebrovascular reserve [(acetazolamide-activated CBF-Resting CBF)/Resting CBF×100%] and severity of hemodynamic cerebral ischemia (Stage 0-II) pixel by pixel on the platform of 3-dimensional stereotactic surface projections (3D-SSP) of the standardized brain. In this analysis, severity of the hemodynamic cerebral ischemia could be estimated stereotactically based on identical vascular territories with high judgment accuracy. Stratification of hemodynamic cerebral ischemia using quantified CBF-SPECT should be standardized with high accuracy using the DTARG method and SEE analysis for universalizing the effectiveness of EC-IC Bypass surgery and organizing a future clinical trial.

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In patients with atherothrombotic internal carotid artery (ICA) or middle cerebral artery (MCA) occlusive disease, the chronic reduction in cerebral perfusion pressure (chronic hemodynamic compromise) increases the risk for cerebral ischemic damage. We have shown that severe hemodynamic compromise, demonstrated as an increased oxygen extraction fraction (misery perfusion) with positron enmission tomography (PET), is a risk factor for subsequent ischemic stroke. Because a recent Japanease EC/IC bypass trial for patients with severe hemodynamic compromise demonstrated a benefit of bypass surgery for preventing ischemic stroke, detection of the patients with severe hemodynamic compromise is crucial for improving the prognosis of patients with atherothrombotic ICA or MCA occlusive disease. Hemodynamic cerebral ischemia due to ICA or MCA occlusive disease may not only cause cerebral infarction but also minor tissue damage in the cerebral cortex that is not detectable as an infarction on CT or MRI. Recently, imaging of the central type benzodiazepine receptors, which are expressed by most cortical neurons, has made it possible to visualize the neuronal alterations induced by ischemia in vivo in humans. Using PET, we have shown that selective neuronal damage demonstrated as a decrease in central benzodiazepine receptors in the normal-appearing cerebral cortex is associated with increased oxygen extraction fraction (misery perfusion). Misery perfusion is important for the development of selective neuronal damage as well as infarction in atherothrombotic ICA or MCA occlusive disease, and vascular reconstruction surgery may also lead to the prevention of selective neuronal damage. Benzodiazepine receptor imaging may become a useful tool for evaluating the success of future therapeutic interventions for protecting neurons from ischemic damage. Understanding the pathophysiology of hemodynamic cerebral ischemia is essential for the management of patients with atherothrombotic ICA or MCA occlusive disease.

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In the neurosurgery field, morphometric images such as CT, MRI and angiography were employed for diagnostic imaging, since individual specific information such as cerebral form and the clinical profile were used for planning the treatment. Today, however, standardized surgical-treatment and its application must derive from evidence based medicine and this has led to the establishment of standardized diagnostic imaging for the evaluation of the clinical condition. An analyzing technique of brain SPECT, which is one of the methods used for measuring cerebral blood flow quantitatively, has been developed for use as an objective guideline with a standard brain map. We introduce a brain coordinate analyzer which evaluates the brain circulation in the standard brain space, as has been requested in the neurosurgery field.

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Neurocritical care focuses on the critical care management of patients with catastrophic neurologic diseases including vascular and traumatic brain damage. Methods commonly used for monitoring the brain in neurocritical care include computed tomographic (CT) scan and magnetic resonance (MR) imaging. Positron emission tomography (PET) is a powerful, noninvasive tool used to study the biochemistry and physiology of the working brain. Positron emitting isotopes are administered via an inhalational or intravenous route, and for imaging of the brain, oxygen (^<15>O) is employed to measure CBF, CBV CMRO_2 and OEF, while fluorodeoxyglucose (^<18>F-FDG) is used to measure cerebral glucose metabolism. PET has been used to evaluate the stage of hemodynamic deficiency in occlusive cerebrovascular disease and the malignancy of the brain tumors. We used PET aggressively to map the pathophysiology in acute vascular and traumatic brain damage. Important findings from our experiences and previous reports are as follows. (1) Acute ischemic stroke studies have shown that a considerable part of the final infarct has already lost cellular integrity and is not accessible to therapy even in the early phase. However, PET detected viable but hypoperfused tissue that is characterized by an elevated OEF and accessibility to acute therapy. (2) A zone of reversible hypoperfusion has been demonstrated around acute intracerebral hemorrhage (ICH). PET studies have shown that CMRO_2 is reduced to a greater degree than CBF in the periclot region in acute ICH, resulting in reduced OEF. Thus, the hypoperfused area observed around acute ICH is not cerebral ischemia. (3) PET studies have shown that global values of CBF CMRO_2 and CBF/CBV ratio are reduced in acute aneurysmal subarachnoid hemorrhage (SAH). Among patients who developed delayed neurological deficits due to vasospasm after SAH, a wide range of CBF disturbance has been observed. (4) Acute-phase ^<18>F-FDG PET studies have revealed that some areas of the brain show a relative increase in glucose utilization in traumatic brain injury (TBI). In addition to the areas showing increased glucose uptake, the human PET studies have also shown decreased glucose utilization in pericontusional and remote areas. Measurements of CBF and CMRO_2 with PET have demonstrated wide regional variations in CBF with consistent decreased CMRO_2 in early TBI patients. In conclusion, recent developments in PET technology provide the neurointensivist with functional information, at the cellular level, that may help guide management in patients with neurocritical care. To understand the absolute values derived from PET, we must consider the effects of anesthetics on cerebral blood flow and metabolism.

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We previously reported that transcranial color-coded real time sonography (TCCS) is useful for detecting hyperperfusion syndrome. However, a limiting factor in the use of TCCS as a screening tool can be an insufficient temporal bone window. Our newly developed window-making TCCS method that creates a temporal burr hole opening has resolved this limitation. This window-making TCCS method is applicable for evaluation of hyperperfusion after carotid endarterectomy (CEA) on those selected patients who have insufficient temporal bone windows.

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We report a case of cavernous sinus dural arteriovenous fistulas (CS-dAVFs) presenting with intracranial hemorrhage a few days after eye symptoms appeared. An 82-year-old woman visited our hospital for left exophthalmos and chemosis. MRI showed CS-dAVFs with retrograde leptomeningeal venous drainage (RLVD). We therefore planned early treatment, however, before surgery, her consciousness deteriorated gradually with right hemiparesis and aphasia. Her CT scan revealed intracerebral hemorrhage involving the left putamen and venous infarction extending to the inferior part of the left frontal lobe and temporal lobe, and the insular cortex. Cerebral angiography showed CS-dAVFs with RLVD not only in the superficial middle cerebral vein but also in the deep middle cerebral vein. Transvenous embolization was performed using mechanically detachable coils. After embolization, the patient's dAVFs with RLVD disappeared and her symptoms improved within a few months. We think that advanced age is one of the risk factors for CS-dAVFs hemorrhages. Therefore, elderly patients with CS-dAVFs with RLVD should be treated as soon as possible. Moreover, Volume subtracted 3D-CT angiography is very effective for understanding the underling mechanism of the hemorrhage.

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