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Biomedical subjects

R H Ackerman

Publications and source records attributed to R H Ackerman.

At least 19 recordsLinked to original sources
PubMed1990

Dipole-tracing of abnormal slow brain potentials after cerebral stroke--EEG, PET, MRI correlations.

A patient with major neurological deficits 5 years after a left cerebral infarction underwent correlative EEG, MRI and PET studies of cerebral blood flow and oxygen metabolism. The EEG showed abnormal slow electroencephalographic activity in the frontopolar region. The intracranial location of the slow electrical activity was estimated, as an equivalent current dipole, by using a newly developed dipole tracing (DT) method. The DT analysis showed that the dipole equivalent of the slow wave is approximately located at the frontal part of the left cingulate gyrus, away from the margins of the infarction and enlarged left lateral ventricle demonstrated by MRI, and in a region with intact oxygen consumption rate. The genesis of the slow wave is discussed.

Adult↗
PubMed1989

Evaluation of the 11CO2 positron emission tomographic method for measuring brain pH. II. Quantitative pH mapping in patients with ischemic cerebrovascular diseases.

A practical method has been developed that, using 11CO2 and positron emission tomography (PET), computes and maps (a) "effective pH" (pHt), a weighted average of intra- and extracellular pH, and (b) "clearance" (K1), product of blood flow and 11CO2 extraction. This method, together with measurements of cerebral blood flow (CBF) and oxygen extraction fraction (OEF), was applied to 12 patients with cerebral ischemia or stroke. The regional K1 was positively correlated with CBF (n = +0.78). The k1/CBF ratio, representing the extraction fraction ratio of 11CO2 to H2 15O, was negatively correlated with CBF (r = -0.54), suggesting that 11CO2 extraction decreases as flow increases. In five acute stroke patients within 2 days of onset, the injured cortex had lower CBF (20.6 ml/min/100 g), higher OEF (78.1%), and lower pHt (6.96) than the contralateral cortex (CBF = 41.4 ml/min/100 g, OEF = 53.3%, pHt = 7.00), suggesting intracellular acidosis with intact cell membranes. In three stroke patients 5-8 days after onset, the injured cortex had higher CBF (60.9 ml/min/100 g), lower OEF (32.0%), and higher pHt (7.12) than the contralateral cortex (CBF = 45.3 ml/min/100 g, OEF = 58.0%, pHt = 7.06), which suggested an increase in extracellular volume compartment reflecting loss of cell membrane integrity. This method provides information on the regional tissue acid-base status and cell membrane integrity, which may be prognostic of tissue viability.

Adult↗
PubMed1988

The 15O steady-state method: correction for variation in arterial concentration.

One of the factors limiting the accuracy of the 15O steady-state method for the measurement of regional cerebral blood flow and oxygen metabolism is the requirement that a constant arterial blood concentration be maintained over long periods. A new method has been developed to correct for the variation of the arterial concentration in the C15O2 and 15O2 steady-state inhalation technique. The time course of the arterial activity is obtained by multiple sampling over the study period. The same 15O model as is used in the steady-state method is employed but is solved without assuming equilibrium. Look-up tables are generated to relate flow and oxygen extraction fraction to tissue activity, and from them the regional parameters are estimated. Theory and simulation studies suggest that substantial improvement in accuracy can be obtained with no increase in statistical error. The validity of the method was checked experimentally by making repeated measurements in the same subject after perturbing the gas delivery. The conventional steady-state method showed significantly larger deviations in repeat measurement than did the new method. Thus, it is concluded that the proposed method is superior.

Adult↗
PubMed1988

Measurement of end-capillary PO2 with positron emission tomography.

The analysis of positron emission tomography measurements of oxygen metabolism has been extended to provide a quantitative estimate of end-capillary PO2. The principle of this extension rests on the idea that the oxygen extraction fraction can be used to calculate the end-capillary oxygen saturation of the blood. The relation between oxygen saturation and PO2 is obtained through the oxygen dissociation curve. Our studies show that in addition to the local oxygen extraction fraction, arterial PO2 and pH values are needed in the calculation, whereas fairly large variations in factors such as PCO2, hematocrit, hemoglobin, and plasma protein levels have little or no effect. Rough estimates of end-capillary PO2 can be made using standard O2 dissociation nomograms. Blood gas and acid-base properties of blood have been known for decades, making it possible to account accurately for individual differences that may be encountered when studying patients. Measurements in nine normal subjects yielded a mean end-capillary PO2 value of 31.2 mm Hg. The ability to make a quantitative visualization of altered patterns of end-capillary PO2 provides an additional dimension to the investigation of stroke disease and tumor metabolism.

Blood Gas Analysis↗
PubMed1987

Evaluation of the 11CO2 positron emission tomographic method for measuring brain pH. I. pH changes measured in states of altered PCO2.

The 11CO2 method for measuring local brain pH with positron emission tomography (PET) has been experimentally evaluated, testing the adequacy of the kinetic model and the ability of the method to measure changes in brain pH. Plasma and tissue time/activity curves measured during and following continuous inhalation of 11CO2 were fit with a kinetic model that includes effects of tissue pH, blood flow, and fixation of CO2 into compounds other than dissolved gas and bicarbonate ions. For each of ten dogs, brain pH was measured with PET at two values of PaCO2 (range 21-67 mm Hg). The kinetic model fit the data well during both inhalation and washout of the label, with residual root mean square (RMS) deviations of the model from the measurements consistent with the statistical quality of the PET data. Brain pH calculated from the PET data shows a linear variation with log(PaCO2). These results were in good agreement with previously reported measurements of brain pH, both in absolute value and in variation with PCO2. The interpretation of these pH values in normal and pathological states is discussed.

Administration, Intranasal↗
PubMed1986

N-[11C-Methyl]chlorphentermine and N,N-[11C-dimethyl]chlorphentermine as brain blood-flow agents for positron emission tomography.

N-[11C-methyl]chlorphentermine ([11C]NMCP) and N,N-[11C-dimethyl]chlorphentermine ([11C]NDMCP) were prepared from chlorphentermine and 11CH3I in DMF and evaluated in rats as brain blood-flow agents for positron emission tomography (PET). Tissue distribution of [11C]NMCP showed that brain uptake was 2.70 +/- 0.40% of injected dose per organ at 5 min with no change in radioactivity concentration up to 30 min after i.v. injection. Approximately 80% of the initial brain uptake remained at 60 min. On the other hand, initial brain uptake of [11C] NDMCP (3.66 +/- 0.31 and 3.63 +/- 0.88% injected dose per organ at 5 and 15 min, respectively) was greater than that of [11C]NMCP. The brain activity however, rapidly decreased to 2.38 +/- 0.17 and 1.82 +/- 0.32% at 30 and 60 min, respectively. Because of its longer retention in the brain compared with [11C]NDMCP, [11C]NMCP would be a potential brain blood-flow agent for quantitative PET studies.

Animals↗
PubMed1985

Analysis of some errors in the measurement of oxygen extraction and oxygen consumption by the equilibrium inhalation method.

Some sources of error in the equilibrium inhalation method for the measurement of oxygen extraction fraction and CMRO2 by positron emission computed tomography scanning have been evaluated by computer simulation. Emphasis has been placed on errors that have not been thoroughly studied in past work. These include effects of random statistical errors, systematic errors in arterial blood radioactivity concentrations, and errors due to perturbations of the equilibrium state, to tissue inhomogeneity, and to subject motion.

Blood Volume↗
PubMed1979

Symptomatic middle cerebral artery stenosis.

The clinical course of 16 consecutive patients with stenosis of the middle cerebral artery angiographically diagnosed between 1970 and 1977 was reviewed. All were managed nonsurgically with medical treatment including anticoagulation. Prior to therapy, transient ischemic attacks had occurred in 15 and cerebral infarction in 11. Initially, none exhibited more than a minor neurological deficit. Follow-up from one month to six years showed a benign course in 14 patients: 13 experienced no subsequent transient attacks or new stroke; 1 had repeated transient attacks for two years but not in the following four years. Two of the 16 developed a severe stroke early in the course, before medical therapy was started. No distinctive clinical or radiographic features were identified that permitted prediction of the outcome. This small series supports the need for a randomized study of bypass efficacy in these patients.

Aged↗
PubMed1979

Mechanisms of acute carotid stroke.

In a three-year study, the clinical course and results of intracranial angiography were compared in patients having an acute stroke in the carotid artery territory combined with angiographic abnormalities indicating severe extracranial carotid stenosis or occlusion. Two major mechanisms of stroke were delineated. In one group, the angiographic intracranial abnormalities strongly suggested the presence of embolism in the cerebral vessels supplied by the stenotic or occluded carotid artery; many of these patients had no obvious transient ischemic attacks prior to their stroke and experienced a moderate to severe clinical deficit. In the other group, evidence of embolism was absent; many showed a widespread delay in cerebral arterial perfusion, experienced a greater frequency of transient ischemic attacks before their stroke, and had a milder stroke than did those with embolism.

Carotid Artery Diseases↗
PubMed1977

Computed tomography of cerebral infarction: hemorrhagic, contrast enhancement, and time of appearance.

Large confluent petechial hemorrhages and/or hemorrhage within infarct may be seen on CT scan. Small petechial hemorrhages are not resolved by current equipment and techniques. Elevation of absorption values of an infarct following contrast media primarily occurs in the first month after onset, and may be occasionally confused with a tumor. Sequential CT changes in infarcts correlate well with established pathologic changes. Cerebral infarction may be seen on CT scan in some cases as early as 24--48 hr after its onset.

Cerebral Hemorrhage↗
PubMed1976

Some limitations of computed tomography in the diagnosis of neurological diseases.

Some of the limitations of CT in the diagnosis of neurologic disease are reported. Problem areas include small lesions; lesions obscured by adjoining structures; small vascular structures and detail of large vessels; cases in which the diagnosis is made but information is incomplete for treatment; cases of incorrect diagnosis; non-nenoplastic lesions mistaken for neoplasms; some subdural hematomas; occasional false negative findings; and misinterpretation due to technical errors. Knowledge and use of the clinical presentation, the performance of other complementary diagnostic procedures, repeat CT scans tailored to the region of interest, and repeat serial scans may assist in reaching the proper diagnosis and diminishing potential error.

Computers↗
PubMed1976

CSF enhancement for computerized tomography.

Metrizamide cisternography, combined with hypocycloidal tomography, has been performed in 12 patients with possible posterior fossa or parasellar mass lesions with finely detailed images of the basal cisterns resulting. Computed tomography was performed in nine of these patients and produced exceptional images of the cisternal anatomy. The technique of cerebrospinal fluid enhancement may be efficacious in identifying small basal masses not shown with conventional computed tomography, and thus may form an important complement to enhancement by intravenous injection of contrast medium.

Brain Neoplasms↗