Unusual widening of Virchow-Robin spaces: MR appearance

MR in two patients with unusual widening of the Virchow-Robin spaces showed multiple cystic foci up to 2 cm in diameter along the perforating medullary arteries in the cerebral white matter, mainly in one cerebral hemisphere. These areas were of the same signal intensity as cerebrospinal fluid on all pulse sequences. In one patient, the cystic foci in the white matter were biopsied and histologically confirmed to be large Virchow-Robin spaces.

Photic stimulation study of changing the arterial partial pressure level of carbon dioxide

To investigate the effect of the level of baseline cerebral blood flow (CBF) on local CBF augmentation by activation, we have used positron emission tomography to measure regional CBF (rCBF) in 12 normal volunteers with and without photic stimulation during hypocapnia, normocapnia, and hypercapnia. The increase in rCBF in the primary visual cortex by photic stimulation was 10.8 +/- 3.1, 18.6 +/- 9.3, and 19.5 +/- 6.1 ml 100 ml-1 min-1 in hypo-, normo-, and hypercapnia, respectively. The increase was significantly smaller in hypocapnia than in normocapnia (p < 0.005). The fractional CBF increase caused by the photic stimulation was the same in all breathing conditions. This result indicates that the magnitude of the CBF increase induced by neuronal activity correlates proportionally with the level of baseline CBF.

Positron emission tomographic assessment of cerebral hemocirculation and glucose metabolism in malignant glioma following treatment with intracarotid recombinant human tumor necrosis factor-alpha

Cerebral hemocirculation and glucose metabolism in a malignant astrocytoma were repeatedly quantified before and after intracarotid injection of recombinant human tumor necrosis factor-alpha (rH-TNF) using positron emission tomography (PET). The patient received an intracarotid injection of a 3 x 10(4) U/m2 dose of rH-TNF three times over a two week period. PET was performed prior to and 24 hr after the first injection, and two weeks after the third injection. Prior to the first rH-TNF treatment, two lesions demonstrating high perfusion and hypermetabolism of glucose were noted in the right frontal and temporal regions. The frontal hypermetabolic lesion showed decreases in hemocirculation and metabolism 24 hr after the first injection and then increases beyond the pre-treatment level two weeks after the third treatment, whereas the temporal lesion remained unchanged during the follow-up period. No appreciable changes were noted in the adjacent cortex where rH-TNF was perfused, with the exception of a transient decrease in regional blood volume. Magnetic resonance images of the tumor showed no changes as a result of treatment with intracarotid rH-TNF. Intracarotid rH-TNF preferentially affects tumor tissue as opposed to normal cortex.

Clinical application of 18F-FUdR in glioma patients--PET study of nucleic acid metabolism

Positron emission tomography was used to investigate the metabolism of nucleic acids by 18F-fluoro-2'-deoxyuridine (18F-FUdR) in 22 patients with gliomas. Sixteen cases of high grade glioma clearly demonstrated a region of high activity with a differential absorption rate (DAR) of 0.64 +/- 0.34. Six cases of low grade glioma failed to reveal a positive image of the tumor and the DAR in tumor was 0.21 +/- 0.042 (p < 0.01). This PET-18F-FUdR study succeeded in differentiating high and low grade gliomas from the view point of nucleic acid metabolism.

Quantitative mapping of regional cerebral blood flow using iodine-123-IMP and SPECT

A method was developed to calculate functional images of regional cerebral blood flow (rCBF) from a single scan using SPECT following intravenous 123I-N-isopropyl-p-iodoamphetamine (IMP) infusion.

METHODS

A two-compartment model that includes two parameters of rCBF and regional distribution volume of IMP (Vd) was employed to correct for clearance of IMP from the brain. Using a given input function and a fixed Vd value (30 ml/ml according to an analysis on dynamic SPECT data), a unique value of rCBF was calculated for each pixel of the SPECT image according to the table-look-up procedure. This technique was applied to 15 human subjects, and the calculated rCBF values were compared with those measured by PET.

RESULTS

A set of simulation studies demonstrated an optimal SPECT midscan time at 30 to 40 min postinjection of IMP, providing the minimal error sensitivity to the individual difference of the input function (rCBF values with an accuracy of +/- 10%). Another set of simulation suggested validity of fixing the Vd values, i.e., errors in calculated rCBF values were around +/- 7% for a change of Vd of +/- 10%. The measured rCBF values obtained from 15 human subjects were independent on the SPECT scan time. The calculated rCBF values also agreed well with those obtained by the nonlinear least-squares fitting analysis that were obtained from the dynamic SPECT scan and the frequent arterial blood sampling and measurement of lipophilic fraction for each sample (0.54 + 0.88x, r = 0.86), suggesting the validity of the simplified procedures in this method.

CONCLUSION

These observations suggested the validity of this method as a clinical tool for quantitative measurement of rCBF.

[Longitudinal analysis of glucose metabolism in recurrent meningioma]

We repeatedly measured kinetic rate constants and glucose metabolic rate (kinetic rCMRG1) using dynamic positron emission tomography (PET) and autoradiographic rCMRG1 in a patient with recurrent meningioma. A 50-year-old woman who presented with a left visual disturbance was admitted to our hospital. MR images revealed a mass lesion occupying the left middle fossa. The patient underwent Simpson grade IV surgery. The histological diagnosis was meningothelial meningioma. One year later the tumor had grown back to almost the same size as before treatment and was removed again by Simpson grade IV procedure. Postoperatively, the patient underwent radiation therapy (54 Gy). Two years after the second operation, the tumor was found to have invaded the left orbit and was resected by Simpson grade IV procedure. After additional radiation therapy, the patient was discharged. The rate constants were analyzed preoperatively and whenever the tumor recurred according to the three compartment 18F-fluorodeoxyglucose (FDG) model. Preoperative PET indicated tumor k1 and k2 values higher than in the contralateral gray matter, suggesting high permeability due to absence of the blood-tumor barrier and an abundant blood supply. The tumor k3 value, an indicator of hexokinase activity, was as high as in the contralateral gray matter. When the tumor recurred, the tumor k1, k2 and k3 values remained consistently high, indicating high proliferative activity. In contrast, the contralateral gray matter k1, k2 and k3 values decreased to some extent, suggesting effects of surgery or radiotherapy. Tumor rCMRG1 values, both autoradiographic and kinetic, were enhanced markedly.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of dopamine metabolism in brain of patients with dementia by means of 18F-fluorodopa and PET

By means of positron emission tomography (PET) and 18F-fluorodopa (FDOPA), a study was initiated to analyze the cerebral dopamine (DA) metabolism of 32 subjects including those with AD/SDAT and vascular dementia (VD, multi-infarct type). A semiautomated irregular ROI drawing routine to identify the striatum was developed that interactively defined the PET threshold pixels referring to the count histograms and location of the corresponding pixels. A comparative study by five examiners showed significant improvement in the area size definition and count linearity particularly for low contrast objects. The graphical plot was employed to calculate the FDOPA influx rate (Ki) for the ROI data with cerebellar radioactivity as an input function. The striatal Ki value was found to be relatively stable and did not show signs of a significant age-related change. The vascular patients had smaller Ki to the striatum than the aged control. Although the mean Ki of AD/SDAT was almost compatible with that of age-matched normals, their Ki was more scattered with higher and lower Ki cases. The multiple regression analysis revealed that the Ki could be predicted by age and the mini-mental state (MMS) performance (r2 = 0.590, p < 0.01 for AD/SDAT, r2 = 0.401, and p < 0.05 for VD). MMS was found to be a more dominant factor than age. We conclude that dopamine metabolism became disturbed as dementia became progressively severe.

[Circulation time determined by carotid angiography in patients with chronic internal carotid artery occlusion: comparison with cerebral blood flow and oxygen metabolism measured by PET]

The degree of collateral circulation in patients with unilaterally chronic internal carotid artery occlusion was estimated by mean transit time of contrast material in rapid sequence carotid angiography (Angiographic MTT), and compared with cerebral blood flow and oxygen metabolism measured by PET. In normal density region on X-ray CT, a significant negative correlation was observed between Angiographic MTT and cerebral blood flow (CBF). This indicates that cerebral blood flow can be estimated by Angiographic MTT. It has been reported that the ratio of cerebral blood volume (CBV) to CBF (CBV/CBF), i.e., mean transit time determined by PET well agreed with OEF, and is good indicator for brain circulation reserve. In this study, no significant correlation was observed between Angiographic MTT and CBV/CBF. However, a significant positive correlation was observed between Angiographic MTT and oxygen extraction fraction (OEF), and no significant correlation was observed between Angiographic MTT and oxygen consumption rate (CMRO2). These indicates that Angiographic MTT may be indicator for brain circulation reserve.

Accumulation of L-[2-(F-18)]fluorophenylalanine in peri-infarct area in a patient with acute cerebral infarction

We studied the brain uptake of amino acid in a patient with acute cerebral infarction with L-[2-(F-18)]fluorophenylalanine and positron emission tomography. The increased accumulation of the ligand was specifically found in the peri-infarct area where oxygen metabolism was still maintained but decreased later in the 72-day follow-up period. The kinetic analysis revealed that increased accumulation was not due to increased transport from the blood to the brain but delayed washout from the brain to the blood. Although the mechanism is still unknown, abnormally high accumulation of L-[F-18]fluorophenylalanine may predict delayed neuronal changes after ischemic insults of the brain.

Cerebral infarction within six hours of onset: prediction of completed infarction with technetium-99m-HMPAO SPECT

Technetium-99m-HMPAO can be used to evaluate abnormal brain perfusion in the hyperacute stage of stroke.

METHODS

We investigated cerebral blood flow using 99mTc-HMPAO SPECT in 31 patients within 6 hr after the onset of cerebral infarction and analyzed the relationship between abnormal perfusion and morphological changes on follow-up CT scans. Patients were classified into an infarct group and a noninfarct group, and the lesions on SPECT images were divided into infarct and peri-infarct regions.

RESULTS

Among a total of 30 infarct regions, three lesions studied at 1.5, 2.5 and 5 hr after the ictus showed local hyperperfusion suggestive of early postischemic hyperemia, while the other 27 lesions demonstrated local hypoperfusion. All of the peri-infarct regions showed moderate hypoperfusion. The noninfarct group consisted of five patients, four of whom showed no perfusion abnormalities. The lesion-to-contralateral radioactivity ratios for the infarct and peri-infarct regions were respectively 0.48 +/- 0.14 and 0.75 +/- 0.10 in the patients with hypoperfusion, while the right-to-left ratio in the noninfarct group was 0.97 +/- 0.10.

CONCLUSION

This SPECT study of cerebral blood flow demonstrates that local hyperperfusion occurs in some infarcts even within 6 hr of onset and that infarcted and morphological viable brain can be distinguished by a lesion-to-contralateral radioactivity ratio of 0.6 within this time range.

Perfusion and metabolism in predicting the survival of patients with cerebral gliomas

BACKGROUND

Noninvasive measurements of cerebral circulation and metabolism may be useful for diagnosis in patients with brain tumors. The authors tested the prognostic significance of circulatory and metabolic values or ratios determined by positron emission tomography (PET) in patients with gliomas.

METHODS

The subjects were 23 patients, who underwent a complete PET study of cerebral circulation and metabolism with long-term follow-up of at least 57 months. Regional cerebral blood flow (rCBF), blood volume (rCBV), oxygen extraction fraction, and the metabolic rates of oxygen (rCMRO2) and glucose (rCMRGl) were measured before treatment. Data regarding tumors, the contralateral gray matter and white matter, and the ratio between tumor and gray matter or between tumor and white matter were compared with survival time from the time of the PET study. Prognostic factors were tested using Cox's regression analysis.

RESULTS

Among clinical parameters, histologic grade and performance status were important variables regulating survival. When survival times of patients with values or ratios equal to or higher than the median were compared to those of patients with values or ratios lower than the median, significant determinant PET measurements were tumor rCMRGl and the ratios of tumor:gray rCMRGl and tumor:white rCMRGl. Median survival time in the patients with an rCMRGl value of 4.4 mg/100ml/minute (median value) or more indicated 9 months, which was significantly shorter than greater than 113 months in the patients with a value lower than the median (P = 0.003 by the generalized Wilcoxon test). Patients with a higher value of gray rCBF, rCBV, or rCMRO2 had significantly longer survival times than those with a lower value.

CONCLUSIONS

Cerebral circulation and metabolism as determined by PET can be of ancillary significance in predicting the prognosis of patients with gliomas.

Evolution of crossed cerebellar diaschisis in middle cerebral artery infarction

To elucidate the evolution of crossed cerebellar diaschisis, cerebral oxygen metabolism was measured repeatedly by positron emission tomography (PET) in 35 consecutive patients with unilateral cerebral infarction within the territory of middle cerebral artery. The crossed cerebellar diaschisis was defined as significant when the laterality ratio of cerebral oxygen metabolism between the left and right cerebellar hemispheres exceeded the control range (mean +/- 2 standard deviations) as derived from 27 age-matched normal volunteers. Significant crossed cerebellar diaschisis was observed in 31 patients (89%) on the initial PET studies. Of these 31 patients, 23 with infarcts involving the frontal sensorimotor cortex persistently had crossed cerebellar diaschisis up to 5 years after onset, whereas the diaschisis disappeared in 8 patients with smaller infarcts mainly in the frontal or parietal lobe without recovery of oxygen metabolism in the infarcted areas. These present results suggest that crossed cerebellar diaschisis can exist persistently even in the late stage in those having a lesion involving the cortical pontine-cerebellar pathways.

Comparison of carbon dioxide responsiveness of cerebellar blood flow between affected and unaffected sides with crossed cerebellar diaschisis

BACKGROUND AND PURPOSE

Concerning vasoreactivity of cerebellar blood flow (CeBF) in patients affected with crossed cerebellar diaschisis (CCD), several controversies have been reported. One is reduced asymmetry of CeBF after acetazolamide administration in 99mTc hexamethylpropyleneamine oxime single-photon emission-computed tomography, and the other is persistent asymmetry with alternation in PaCO2 using the 133Xe clearance method. The purpose of this study is to examine whether CeBF vasoreactivity in the side affected with CCD is the same as that in the unaffected side.

METHODS

We analyzed CeBF during hypocapnia, normocapnia, and hypercapnia performed in 27 patients with cerebrovascular disease (age range, 38 to 73 years; mean age, 62.0 +/- 8.5 years) affected by CCD. CeBF was measured using H2(15)O and positron emission tomography.

RESULTS

The CeBF ratio of CCD-affected side to CCD-unaffected side was consistent during the perturbation of PaCO2. This ratio was 0.82 +/- 0.08 for PaCO2 elevation and 0.83 +/- 0.07 for PaCO2 lowering. Both were not significantly different from unity.

CONCLUSIONS

The percent change of CeBF per millimeter of mercury PaCO2 change was uniform across affected and unaffected sides with CCD. These findings are consistent with our recent findings observed in activated cerebral tissue during photic stimulation.

[Some consideration about cerebellar ataxia and crossed cerebellar diaschisis in Dejerine-Roussy syndrome]

We report a 68-year-old right-handed male who exhibited Dejerine-Roussy syndrome including a persistent cerebellar ataxia following the left thalamic hemorrhage with special reference to the evolution of crossed cerebellar diaschisis (CCD) measured with positron emission tomography (PET). The initial PET studies performed 50 days after onset revealed a mild reduction of blood flow and glucose metabolism in the right cerebellar hemisphere in addition to the severe reduction in the left thalamus. Even in the chronic stage when the motor weakness almost disappeared, he persistently showed a cerebellar ataxia in his right extremities. The cerebellar blood flow and metabolism became normalized without laterality in the follow-up PET studies which were performed 29 months after onset, although the left thalamus and left cerebral cortices were still severely involved. The cerebellar ataxia with preserved cerebellar blood flow and metabolism following the thalamic hemorrhage was possibly associated with damage to the efferent fibers from the cerebellum, whereas the CCD observed in the early stage probably was caused by a transient involvement of the cortico-ponto-cerebellar tract at the level of the internal capsule.

Influence of arterial partial pressure of carbon dioxide on cerebral MRA in normal volunteers

OBJECTIVE

Signal intensity of MR angiography (MRA) is influenced by the physiological factors of flowing blood in the vessels. We examined whether MRA can detect a cerebral hemodynamic change induced by reducing or elevating the arterial partial pressure of carbon dioxide (PaCO2).

MATERIALS AND METHODS

Cerebral MRA was performed in six normal volunteers, each having three measurements during hyperventilation, normal breathing, and 7% CO2 inhalation. The MRA data were obtained by a 0.5 T wholebody scanner and a time-of-flight technique of three-dimensional GE imaging. In addition to the visual inspection, the signal intensity and the lengths of the middle cerebral artery (MCA) and posterior cerebral artery (PCA) were estimated in relation to PaCO2.

RESULTS

The MRA appearances of major cerebral arteries were remarkably different depending on the breathing conditions. There was significant difference in the mean signal intensity (p < 0.01) and the mean length (p < 0.01) of the MCA and PCA between the hyperventilation and normal breathing trials.

CONCLUSION

The MRA signal was sensitive to the changes in PaCO2 level of flowing blood. This phenomenon may result from changes in the velocity of blood flow in major cerebral arteries.

Methionine PET for follow-up of radiation therapy of primary lymphoma of the brain

Positron emission tomography (PET) with carbon-11 methionine, computed tomography (CT), and magnetic resonance (MR) imaging were performed in 10 patients with histologically verified central nervous system (CNS) lymphoma before and after radiation therapy to compare the radiologic findings and to evaluate the usefulness of PET in monitoring tumor response to radiation therapy. Methionine PET clearly depicted CNS lymphoma before radiation therapy as an increased accumulation of C-11 methionine. The extent of increased accumulation of the radiotracer in tumor tissue markedly decreased after radiation therapy. The area of increased uptake was larger than the enhancing lesions on CT or MR images in most cases. One patient was confirmed to have tumor recurrence at the region of residual increased accumulation on methionine PET images. Methionine PET is useful for the delineation of CNS lymphoma and for monitoring the therapeutic effect of irradiation.

Effects of fasudil hydrochloride on cerebral blood flow in patients with chronic cerebral infarction

To evaluate the effect of the novel intracellular calcium antagonist fasudil hydrochloride, cerebral blood flow (CBF) was measured quantitatively with positron emission tomography following the intravenous administration of fasudil in five patients with chronic cerebral infarction. The hemispheric mean CBF increased significantly on both hemispheres 30, 60, and 90 min after the administration of fasudil when the CBF values were corrected according to PaCO2 level, although there was no significant change in raw CBF data. A significant increase of CBF was seen in the cerebellar hemisphere and thalamus at 30 min and in the occipital cortex at 90 min. There was no significant fall in the systemic blood pressure after the administration of fasudil.

Changes of regional cerebral blood flow during listening to an unfamiliar spoken language

The regional cerebral blood flow (rCBF) was measured with positron emission tomography in eight normal volunteers with the purpose of measuring rCBF changes related to the comprehension of an unfamiliar spoken languages. When attempting to comprehend the meaning of words, the left hemisphere showed dominant increases in rCBF, however, when subjects attempted to evaluate the emotional tone of the same spoken passage, relatively large increases in rCBF more found in the right hemisphere. The results indicate that there may be several different auditory representations of language which involve both left and right hemispheres, both of which may contribute to the overall comprehension of spoken language.

[The effect of neuroleptics on human brain estimated by SPECT and PET]

In order to estimate the effect of neuroleptics on human central nervous system, a number of trials are now performed by means of SPECT and PET. Of these, the changes in glucose and oxygen metabolism and blood flow are good indicators of drug effects. The receptor occupancy during neuroleptics medication may provide the information on the most effective dose to be administered without side effect. By measuring both of the neural transmission and its effects on metabolism, brain function can be further clearly understood.

High accumulation of 2-deoxy-2-fluorine-18-fluoro-D-galactose by well-differentiated hepatomas of mice and rats

The potential application of 2-deoxy-2-[18F]fluoro-D-galactose for the detection and evaluation of hepatomas with PET was examined in mouse and rat liver tumor models. Biodistribution studies showed that uptake of this marker was high in well-differentiated, spontaneous hepatoma of C3H mice at almost 92% of the normal liver level. The uptake by well-differentiated Morris rat hepatoma (5123D) was relatively high and second to that of the C3H hepatoma. On the other hand, uptake values for poorly differentiated mouse hepatoma (MH129P), rat hepatomas (AH109A, AH272), mouse melanoma (B-16) and mammary carcinoma (FM3A) were very low and only 14%-18% of that in the normal liver. The results suggest that while well-differentiated hepatomas maintain a high galactose metabolic activity, poorly differentiated hepatomas or other tumors lose this to a large extent. Consequently, this radiopharmaceutical can be used with PET for biochemical characterization of hepatomas and the differential diagnosis between hepatomas and other cancers.

Embolic cerebral infarction: MR findings in the first 3 hours after onset

OBJECTIVE

MR imaging has a high sensitivity for detecting ischemic brain parenchyma. The aim of this study was to evaluate the changes in the signal intensity of infarcted brain parenchyma on MR images obtained within the first 3 hr after the onset of signs and symptoms in patients with embolic cerebral infarction.

MATERIALS AND METHODS

We studied MR images of 16 patients who had a diagnosis of embolic cerebral infarction (highly probable according to criteria of the National Institute of Neurological and Communicative Disorders and Stroke). T1-weighted, T2-weighted, and proton density-weighted MR images were obtained within 3 hr after the onset of symptoms. Two neuroradiologists who had no knowledge of the diagnoses reviewed the MR images of these 16 patients and 20 control subjects in random order and evaluated signal-intensity changes in the gray and white matter.

RESULTS

On proton density-weighted images, the central and cortical gray matter showed increased signal intensity in 63-69% and 88-94% of the patients, respectively. No abnormalities of the brain parenchyma were apparent on T1-weighted and T2-weighted images obtained within 3 hr after the onset of symptoms. The adjacent white matter appeared hyperintense on long TR images in only a few cases.

CONCLUSION

An increased signal intensity in the gray matter on proton density-weighted images was the most characteristic parenchymal change seen on MR images of the brain obtained within 3 hr after embolic cerebral infarction.