Diagnostic and Prognostic Value of 11C-Methionine PET for Nonenhancing Gliomas.

BACKGROUND AND PURPOSE: Noninvasive radiologic evaluation of glioma can facilitate correct diagnosis and detection of malignant transformation. Although positron-emission tomography is considered valuable in the care of patients with gliomas, (18)F-fluorodeoxyglucose and (11)C-methionine have reportedly shown ambiguous results in terms of grading and prognostication. The present study compared the diagnostic and prognostic capabilities of diffusion tensor imaging, FDG, and (11)C-methionine PET in nonenhancing gliomas. MATERIALS AND METHODS: Thirty-five consecutive newly diagnosed, histologically confirmed nonenhancing gliomas that underwent both FDG and (11)C-methionine PET were retrospectively investigated (23 grade II and 12 grade III gliomas). Apparent diffusion coefficient, fractional anisotropy, and tumor-to-normal tissue ratios of both FDG and (11)C-methionine PET were compared between grade II and III gliomas. Prognostic values of these parameters were also tested by using progression-free survival. RESULTS: Grade III gliomas showed significantly higher average tumor-to-normal tissue and maximum tumor2-to-normal tissue than grade II gliomas in (11)C-methionine (P = .013, P = .0017, respectively), but not in FDG-PET imaging. There was no significant difference in average ADC, minimum ADC, average fractional anisotropy, and maximum fractional anisotropy. (11)C-methionine PET maximum tumor-to-normal tissue ratio of 2.0 was most suitable for detecting grade III gliomas among nonenhancing gliomas (sensitivity, 83.3%; specificity, 73.9%). Among patients not receiving any adjuvant therapy, median progression-free survival was 64.2 ± 7.2 months in patients with maximum tumor-to-normal tissue ratio of <2.0 for (11)C-methionine PET and 18.6 ± 6.9 months in patients with maximum tumor-to-normal tissue ratio of >2.0 (P = .0044). CONCLUSIONS: (11)C-methionine PET holds promise for World Health Organization grading and could offer a prognostic imaging biomarker for nonenhancing gliomas.

MR imaging-based correction for partial volume effect improves detectability of intractable epileptogenic foci on iodine 123 iomazenil brain SPECT images: an extended study with a larger sample size.

BACKGROUND AND PURPOSE: It has been suggested, on the basis of a previous pilot study conducted in a small number of patients, that MR imaging-based PVE correction in I-123 iomazenil brain SPECT improves the detectability of cortical epileptogenic foci. In the present study, we performed an investigation by using a larger sample size to establish the effectiveness of the PVE correction and to conduct a detailed evaluation based on the histologic classification of lesions. MATERIALS AND METHODS: Seventy-five patients (male/female, 37/38; age, 28 ± 12 years) with intractable epilepsy who had undergone surgical treatment were enrolled in this study. I-123 iomazenil SPECT and MR imaging examinations were performed before the operation in all patients. I-123 iomazenil SPECT images with and without MR imaging-based PVE correction were assessed visually and by semiquantitative analysis based on the AI(%) of the SPECT count in the resected lesions. RESULTS: The sensitivity, specificity, and accuracy of foci detection by visual assessment were significantly higher after PVE correction compared with the values obtained before the correction. The results of the semiquantitative analysis revealed that the asymmetry of the SPECT counts was significantly increased after the PVE correction in the surgically resected lesions in cases of mesial temporal sclerosis, tumor, and malformations of cortical development. CONCLUSIONS: The effectiveness of MR imaging-based PVE correction in I-123 iomazenil brain SPECT in improving the detection of cortical epileptogenic foci with abnormal histologic findings was established by our investigation conducted on a large sample size.

Distribution of cortical benzodiazepine receptor binding in right-handed healthy humans: a voxel-based statistical analysis of iodine 123 iomazenil SPECT with partial volume correction.

BACKGROUND AND PURPOSE: CBR imaging is highly susceptible to a PVE produced by morphologic changes in the brain related to aging and brain laterality. We assessed the influence of PVE produced by regional age-related changes in gray matter volume on I-123 iomazenil SPECT and elucidated the age-related changes in human CBR binding by using PVE-corrected SPECT images. MATERIALS AND METHODS: Nineteen right-handed healthy volunteers (range, 25-82 years; mean, 55 ± 21 years) underwent MR imaging and quantitative I-123 iomazenil SPECT imaging. The influence of age-related changes in rGMC on SPECT images before PVE correction was assessed. PVE correction of the SPECT images was performed by using an MR imaging-based method. Voxel-based linear regression analyses of the PVE-corrected SPECT images were performed by using SPM5. RESULTS: The age-related reductions in rGMC and BP without PVE correction revealed a significant direct proportional correlation. Voxel-based statistical analysis with PVE correction showed no significant age-related changes in BP. CONCLUSIONS: PVE correction was indispensable for the analysis of I-123 iomazenil SPECT images. PVE-corrected quantitative I-123 iomazenil SPECT images revealed no age-related changes in CBR binding in right-handed healthy humans.

Development of a pixelated GSO gamma camera system with tungsten parallel hole collimator for single photon imaging.

PURPOSE: In small animal imaging using a single photon emitting radionuclide, a high resolution gamma camera is required. Recently, position sensitive photomultiplier tubes (PSPMTs) with high quantum efficiency have been developed. By combining these with nonhygroscopic scintillators with a relatively low light output, a high resolution gamma camera can become useful for low energy gamma photons. Therefore, the authors developed a gamma camera by combining a pixelated Ce-doped Gd(2)SiO(5) (GSO) block with a high quantum efficiency PSPMT. METHODS: GSO was selected for the scintillator, because it is not hygroscopic and does not contain any natural radioactivity. An array of 1.9 mm × 1.9 mm × 7 mm individual GSO crystal elements was constructed. These GSOs were combined with a 0.1-mm thick reflector to form a 22 × 22 matrix and optically coupled to a high quantum efficiency PSPMT (H8500C-100 MOD8). The GSO gamma camera was encased in a tungsten gamma-ray shield with tungsten pixelated parallel hole collimator, and the basic performance was measured for Co-57 gamma photons (122 keV). RESULTS: In a two-dimensional position histogram, all pixels were clearly resolved. The energy resolution was ∼15% FWHM. With the 20-mm thick tungsten pixelated collimator, the spatial resolution was 4.4-mm FWHM 40 mm from the collimator surface, and the sensitivity was ∼0.05%. Phantom and small animal images were successfully obtained with our developed gamma camera. CONCLUSIONS: These results confirmed that the developed pixelated GSO gamma camera has potential as an effective instrument for low energy gamma photon imaging.

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 ((15)O) 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.

Positron-emission tomography of brain regions activated by recognition of familiar music.

BACKGROUND AND PURPOSE: We can easily recognize familiar music by listening to only one or 2 of its opening bars, but the brain regions that participate in this cognitive processing remain undetermined. We used positron-emission tomography (PET) to study changes in regional cerebral blood flow (rCBF) that occur during listening to familiar music. METHODS: We used a PET subtraction technique to elucidate the brain regions associated with the recognition of familiar melodies such as well-known nursery tunes. Nonmusicians performed 2 kinds of musical tasks: judging the familiarity of musical pieces (familiarity task) and detecting deliberately altered notes in the pieces (alteration-detecting task). RESULTS: During the familiarity task, bilateral anterior portions of bilateral temporal lobes, superior temporal regions, and parahippocampal gyri were activated. The alteration-detecting task bilaterally activated regions in the precunei, superior/inferior parietal lobules, and lateral surface of frontal lobes, which seemed to show a correlation with the analysis of music. CONCLUSION: We hypothesize that during the familiarity task, activated brain regions participate in retrieval from long-term memory and verbal and emotional processing of familiar melodies. Our results reinforced the hypothesis reported in the literature as a result of group and case studies, that temporal lobe regions participate in the recognition of familiar melodies.

Effect of CT acquisition parameters in the detection of subtle hypoattenuation in acute cerebral infarction: a phantom study.

BACKGROUND AND PURPOSE: We evaluated the effects of varying tube voltage, current per rotation, and section thickness on detectability of 2- and 4-Hounsfield unit (HU) differences on brain CT between normal and ischemic gray matter within 6 hours of ischemia onset, by using a low-contrast phantom. METHODS: The phantom with an attenuation of 36 HU corresponding to normal gray matter contained 2 sets of spheres (34 HU and 32 HU) corresponding to the early CT signs of ischemic brain and complete infarction, respectively. The reproducibility of the CT numbers and the contrast-to-noise ratio (CNR), defined as the CT number difference between the background (36 HU) and the spheres (34 HU or 32 HU) divided by the SD of the background CT number were measured. Five radiologists rated the phantom images for detection of the low-contrast spheres by visual inspection. RESULTS: The CT numbers were reproducible within 1 HU with a tube current of > or =150 mAs at 120 kVp. The CNRs for the 34- and 32-HU spheres were positively correlated with the tube voltage, tube current per rotation, and the section thickness. A CNR of 1.0 was obtained for the 34-HU sphere when scanning was conducted with a section thickness of 10 mm at 120 kVp and 700 mAs, or 135kVp and 450 mAs, respectively. A significant improvement of the accuracy of detection was found with increasing tube current, tube voltage per rotation, and section thickness. CONCLUSION: Our study indicated that the 2-HU hypoattenuation corresponding to the early CT sign of acute ischemic stroke can be detected by using appropriate parameter settings.

Chordoma with postoperative subcutaneous implantation and meningeal dissemination: MRI.

Chordomas are histologically benign tumours which are locally invasive. We present an unusual case of recurrent chordoma with subcutaneous implantation and widespread meningeal dissemination after surgery. Contrast-enhanced MRI was useful for determining the extent of the tumour.

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.

[11C]methionine positron emission tomography for the evaluation of pancreatic exocrine function in chronic pancreatitis.

Positron emission tomography (PET) can be used for the quantitative analysis of amino acid metabolism. The aim of this study was to investigate whether pancreatic exocrine function can be evaluated by [11C]methionine PET in chronic pancreatitis (CP) patients. Dynamic PET scan of the pancreas and liver was performed in eight healthy subjects and seven patients with CP after intravenous (i.v.) injection of [11C]methionine. Simultaneously, duodenal juice was collected with the background of continuous i.v. administration of secretin (125 ng/kg/h). The radioactivity ratio of the pancreas to that of the liver (PLR) was calculated by regions of interest (ROI) analysis. Amylase output and bicarbonate concentration were measured in the duodenal aspirates. The PLR of CP patients was significantly lower than that of healthy subjects at all time points after methionine injection. The PLRs at 4.5 minutes (PLR4.5) after methionine injection were positively correlated with the amylase output, mean bicarbonate concentration, and volume of duodenal aspirates (R = 0.74, 0.69, 0.46). It is concluded that [11C]methionine PET would be a noninvasive method for the evaluation of exocrine pancreatic function, which may represent total amino acids uptake of viable acinar cells in the pancreas.

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.

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.

Cerebral blood volume in acute brain infarction: A combined study with dynamic susceptibility contrast MRI and 99mTc-HMPAO-SPECT.

BACKGROUND AND PURPOSE: The aim of this study was to correlate the abnormality in cerebral blood volume (CBV) measured by dynamic susceptibility contrast-enhanced MRI with that in cerebral blood flow (CBF) estimated by single-photon emission CT with [99mTc]hexamethylpropylenamine-oxime in patients with acute ischemic stroke. METHODS: Nine patients with unilateral occlusion of either the middle cerebral artery or the internal carotid artery (4 men and 5 women; mean+/-SD age, 74.4+/-11.6 years) were studied within 6 hours after stroke onset. The relative CBV (relCBV) and CBF (relCBF) in the lesions were defined relative to the contralateral mirror regions. RESULTS: In the brain regions with mild (relCBF >/=0.60), moderate (0.401.0) regions was significantly lower than that for hypovolemic (relCBV <1.0) regions in the relCBF range between 0.40 and 0.50 (P<0.02). CONCLUSIONS: In acute ischemic stroke within 6 hours of onset the CBV can be either increased, normal, or decreased, depending on the severity of hypoperfusion. The increased CBV has a protective effect on evolving infarction. Although the CBF is a better predictor of tissue outcome, the CBV measurement may help detect potentially salvageable brain tissue in the penumbra with compromised blood flow.

Imaging neurochemistry of cerebrovascular disease with PET and SPECT.

Pathophysiology of cerebrovascular disease has been studied by measuring cerebral blood flow and energy metabolism using single photon emission computed tomography (SPECT) and positron emission tomography (PET). These parameters are measures for brain tissue consisting of heterogeneous components such as neurons, glial cells, and blood vessels. It is still difficult to evaluate brain damages specifically involving either neurons or other components. Several trials were recently conducted to visualize neuron-specific injury in cerebrovascular disease by means of 11C flumazenil for PET and 123I-iomazenil for SPECT. These tracers selectively bind to central benzodiazepine receptor which is purely neuronal. A reduced accumulation of these ligands was found in the area surrounding the complete infarction and in the cortex remote from putaminal hemorrhage, indicating the existence of neuron specific injury not visualized by CT and MR. Neurological deficits were well correlated with the loss of cortical accumulation of these ligands. These preliminary studies indicated a potential of neurochemical imaging in cerebrovascular disease. Vulnerability to ischemia which may differ among brain tissue components, among subpopulations of neurons, and among pre-synaptic and post-synaptic functions can be more precisely examined. Neurochemical imaging can be also applied to reveal releases and re-organization of each neurotransmitter-acceptor system after stroke.

Subcortical hypoperfusion associated with asymptomatic white matter lesions on magnetic resonance imaging.

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

Regional cerebral blood flow measurement with iodine-123-IMP autoradiography: normal values, reproducibility and sensitivity to hypoperfusion.

UNLABELLED: We recently proposed a simplified technique for measuring regional cerebral blood flow (rCBF) using the [123I]N-isopropyl-p-iodoamphetamine (IMP) autoradiographic (ARG) method with SPECT (the IMP-ARG method). We examined normal values of rCBF and the reproducibility and sensitivity to hypoperfusion in stroke patients using this method. METHODS: By using a standard arterial input, a single static scan, a fixed distribution volume (Vd) and one-point arterial blood sampling, we measured rCBF in 39 normal volunteers (19 men and 20 women; mean ages 61 +/- 11 yr for the men and 60 +/- 12 yr for the women). Eighteen neurologically stable patients with prior stroke (mean age = 65 +/- 11 yr) were studied twice at a mean interval of 97 days. In 16 patients (7 men and 9 women, mean age = 63 +/- 5 yr) with subarachnoid hemorrhage, rCBF was measured 1-2 wk after onset. Cerebral vasospasm was evaluated by repeated angiography. The mean rCBF in the vasospastic area was compared with that in a nonvasospastic area. RESULTS: The mean rCBFs of the cerebral cortex and centrum semiovale in the volunteers were 33.0 +/- 5.1 ml/100 g/min and 25.0 +/- 4.5 ml/100 g/min, respectively. There was no age-dependent change in rCBF, but the women showed significantly higher cortical rCBF than the men (p < 0.05). In the stroke patients, the whole-brain CBF values showed high reproducibility, with high correlations between those obtained at the first and second studies (y = -3.5 + 1.03x; r = 0.90; p < 0.001). In the subarachnoid hemorrhage patients, the vasospastic area showed significantly lower rCBF than the normal cortical rCBF (p < 0.01) and the nonvasospastic area (p < 0.01). Brain regions with rCBF levels below 20 ml/100 g/min showed infarction on the follow-up CT scan. CONCLUSION: The IMP-ARG method is reproducible, sensitive to hypoperfusion and feasible for the quantitative evaluation of rCBF in routine clinical practice.

MRI of acute cerebral infarction: a comparison of FLAIR and T2-weighted fast spin-echo imaging.

Fluid-attenuated inversion-recovery (FLAIR) sequences have been reported to provide high sensitivity to a wide range of central nervous system diseases. To our knowledge, however, FLAIR sequences have not been used to study patients with acute cerebral infarcts. We evaluated the usefulness of FLAIR sequences in this context. FLAIR sequences were acquired on a 0.5 T superconducting unit within 8 h of the onset in 19 patients (aged 26-80 years) with a total of 23 ischaemic lesions. The images were reviewed retrospectively by three neuroradiologists, and the FLAIR images were compared with T2-weighted fast spin-echo images. All but one of the ischaemic lesions involving grey matter was clearly demonstrated on FLAIR images as increased signal intensity in cortical or central grey matter. FLAIR images were particularly useful for detecting the hyperacute cortical infarcts within 3 h of onset, which were not readily detected on the spin-echo images. In 9 of 11 patients with complete proximal occlusion, the distal portion of the cerebral artery was visible as an area of high signal intensity on FLAIR images.

Technetium-99m-ECD brain SPECT in misery perfusion.

UNLABELLED: Discordant findings of 99mTc-methyl cysteinate dimer (99mTc-ECD) brain distribution have been reported when brain tissue is supplied by excess blood flow. We evaluated changes in 99mTc-ECD brain activity in the opposing pathological state, in which cerebral blood flow (CBF) is more profoundly impaired than metabolism, and analyzed the relationship of 99mTc-ECD activity with CBF and metabolism to investigate the dominant regulating factor on 99mTc-ECD distribution. METHODS: Twelve patients with unilateral intracranial steno-occlusive diseases were evaluated using dynamic and static 99mTc-ECD SPECT. Relative 99mTc-ECD activities and the retention ratio of the affected and unaffected cortices were compared with CBF and oxygen metabolism obtained by PET. Change in the relationships until 1 hr after tracer injection were also analyzed. RESULTS: Relative 99mTc-ECD activity was significantly correlated with CBF, and the highest correlation was obtained for the first minute of imaging (r = 0.674, p < 0.0010. Fifteen minutes after injection, the correlation coefficient with CBF decreased, whereas higher correlation was observed with the parameter of oxygen metabolism (r = 0.758-0.815, p < 0.001). Changes in the retention ratio were dependent on changes in oxygen metabolism, and the retention ratio for the high oxygen extraction fraction (OEF) area was the same as that for the normal OEF area. CONCLUSION: In addition to CBF, brain distribution on 99mTc-ECD SPECT images is affected by brain metabolism, especially on delayed images after injection. The degree of discrepancy between CBF and metabolism should be considered when interpreting images of the misery perfusion state.

Subacute and chronic subarachnoid hemorrhage: diagnosis with fluid-attenuated inversion-recovery MR imaging.

PURPOSE: To evaluate fluid-attenuated inversion-recovery (FLAIR) magnetic resonance (MR) imaging in the detection of subacute and chronic subarachnoid hemorrhage. MATERIALS AND METHODS: The authors performed 19 FLAIR MR imaging examinations at 0.5 T in 14 adult patients with subarachnoid hemorrhage 3-45 days after the ictus and 22 FLAIR examinations in 22 adult control subjects. The detection of subacute and chronic subarachnoid hemorrhage on FLAIR images was compared with the detection on conventional spin-echo MR and computed tomographic (CT) images. RESULTS: In the detection of subacute subarachnoid hemorrhage, FLAIR (100% detection) was significantly superior to T1-weighted imaging (36% detection, P < .01), T2-weighted imaging (0% detection, P < .02), and CT (45% detection, P < .02 [Fisher exact test]). Although FLAIR imaging (63% detection) was superior in chronic subarachnoid hemorrhage detection, there were no statistically significant differences between modalities. FLAIR imaging demonstrated all subarachnoid hemorrhage areas as high-signal-intensity areas within 18 days and up to a maximum of 45 days after the ictus. In a blind comparison, no FLAIR images acquired in control subjects were confused with those acquired in patients. CONCLUSION: FLAIR diagnostic images are superior to conventional MR or CT images in patients with subacute subarachnoid hemorrhage.