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R E Carson

Publications and source records attributed to R E Carson.

84 records · Page 5Linked to original sources
PubMed1984

Tomographic mapping of human cerebral metabolism: subcortical responses to auditory and visual stimulation.

We measured cerebral glucose metabolism with positron computed tomography during audio-visual stimulation in 42 studies of 21 subjects. Metabolic activations and stimulus-induced asymmetries were examined in subcortical structures (thalamus, caudate, lenticular nuclei). Bilateral activations of the thalamus occurred with verbal stimuli. The head of the left caudate was activated when subjects used visual imagery as a strategy to identify sequences of tones. These two types of stimuli produced dominant (left) hemisphere cortical activations in this same group of subjects. Clinical evidence has implicated the participation of subcortical (thalamus and basal ganglia) structures in the processing of language and auditory information. The present results demonstrate this functional role directly in normal subjects.

Acoustic Stimulation↗
PubMed1983

Quantitative measurement of local cerebral blood flow in humans by positron computed tomography and 15O-water.

A noninvasive method that employs 15O-water and positron-computed tomography (PCT) was used to measure quantitative local cerebral blood flow (lCBF) in man. 15O-Water (about 30-50 mCi) was introduced through a single-breath inhalation of 15O-carbon dioxide or through an intravenous bolus injection of 15O-water. A sequence of five 2-min PCT scans was initiated at the time of tracer administration. A series of 15-20 blood samples (1 ml each) was withdrawn from the radial artery of the subject over a period of 10 min. Oxygen-15 radioactivities in the blood samples were immediately counted in a well counter to give an input function, which together with the projection data collected by PCT were processed to provide images of 1CBF and local water distribution volume. The method was found to be convenient to use and gave good-quality images of 1CBF. Quantitative values of 1CBF in images were 59 +/- 11 and 20 +/- 4 ml/min/100 g for gray and white matter, respectively, with a gray-to-white matter ratio of 2.93 and a global flow value of 42 +/- 8 ml/min/100 g. Distribution volume of water was 0.85 +/- 0.03, 0.76 +/- 0.03, and 0.81 +/- 0.02 ml/g respectively, for gray matter, white matter, and whole brain.

Adult↗
PubMed1983

Cerebral glucose metabolism as a function of age in man: influence of the rate constants in the fluorodeoxyglucose method.

Measurement of the local cerebral metabolic rate of glucose (LCMRGlc) with the fluorodeoxyglucose (FDG) method requires the utilization of appropriate values for the rate constants of the transport and phosphorylation processes. We measured these rate constants as a function of age to determine whether a decline in LCMRGlc as a function of age, in prior studies with the FDG method, actually represents changes in the rate constants. We found that measurements of LCMRGlc are not significantly affected by changes in rate constants as a function of aging, and that LCMRGlc did not change significantly with age.

Adolescent↗
PubMed1982

Tomographic mapping of human cerebral metabolism: sensory deprivation.

Local cerebral glucose metabolism was measured in 22 right-handed, normal volunteers using 18F-fluorodeoxy-glucose and positron computed tomography. Three states consisting of selective or combined auditory or visual deprivation were examined. Results demonstrated a progressive decline in overall glucose metabolism with reduced sensory inputs. The relative metabolism of the frontal cortex compared to that of the parietal and occipital cortex progressively increased from the eyes-closed to the both-closed states. Left-right symmetry was found throughout the distribution of structures within the region of brain samples for both the selective auditory and visual deprivation test conditions, but a relative decrease in right-sided metabolism occurred in the combined audiovisual deprivation state. The most significant metabolic asymmetries occurred in the perisylvian, inferior prefrontal, and lateral occipital cortex. The relative metabolic rates of the medial occipital cortex, measured as a percentage of the hemispheric mean, doubled bilaterally with eye opening. The results demonstrate the difficulties inherent in defining a stable and reproducible "resting" state for the human brain.

Adult↗
PubMed1982

Measurement of local blood flow and distribution volume with short-lived isotopes: a general input technique.

A new technique for measuring local blood flow and distribution volume is proposed. The technique uses short-lived isotopes but is different from the equilibrium method in that no constant input is necessary, and no assumption about distribution volume is needed. The theoretical basis of the technique is developed, and the results of a computer-simulation study are presented to show the potential of the technique. The technique is expected to be easier to perform and to give more accurate flow values than the equilibrium method.

Blood Volume Determination↗
PubMed1982

Tomographic mapping of human cerebral metabolism: auditory stimulation.

Cerebral metabolic responses to verbal and nonverbal auditory stimuli were examined, using 18F-fluorodeoxyglucose and positron CT. Twenty right-handed subjects were studied in both control and stimulated states. Monaural verbal stimuli produced diffuse metabolic changes in the left hemisphere and bilateral activation of the transverse and posterior temporal lobes. Monaural nonverbal stimulation with chords demonstrated bilateral parietotemporal activations and diffuse right greater than left frontotemporal asymmetries. Tone sequence pairs presented monaurally produced asymmetries that differed by the subject's analysis strategy. Nonanalytical, musically naive subjects had right greater than left frontotemporal asymmetries, whereas analytic or musically sophisticated subjects had an absence of right greater than left relative hypermetabolism and demonstrated left greater than right temporal asymmetries. Binaural presentation of a factual story and music produced diffuse bilateral activations of the temporal and frontal cortex. Known anatomic asymmetries of the perisylvian cortex were revealed by high-resolution tomography. These results demonstrate that metabolic responses to auditory stimuli are determined by the content of the stimulus and the analysis strategy of the subject rather than the side of stimulation. The results also demonstrate the capacity of functional imaging techniques to study the physiologic cerebral mechanisms underlying auditory processing.

Acoustic Stimulation↗
PubMed1982

An investigation of a double-tracer technique for positron computerized tomography.

We describe a double-tracer technique for positron computed tomography (PCT) that utilizes the differences in physical decay rates to distinguish between two positron emitters. The technique is applied to PCT studies on phantoms (a) to separate two tracers with different half-lives, and (b) to measure simultaneously the attenuation coefficients and the tracer concentrations in a phantom. Results from these experiments are encouraging, but they also reveal a major limitation of the technique, namely, noise enhancement that is related to the relative half-lives of the two tracers and the time duration of the PCT scans, as well as to the relative concentrations of the two tracers. If these parameters are carefully selected, the double-tracer technique will have high potential for examining simultaneously two different biological processes with PCT and for measuring tracer concentrations and attenuation correction factors at the same time.

Copper↗
PubMed1981

A boundary method for attenuation correction in positron computed tomography.

A new method for attenuation correction in positron computed tomography (PCT) has been developed, and it can improve the quality of PCT images. The method requires a short transmission scan by the PCT system. Then boundaries between tissues with significantly different attenuation coefficients are determined from the transmission image by edge-finding techniques. Attenuation correction factors(ACF) are then calculated using these boundaries and the average attenuation coefficients within the enclosed regions. The method has been tested on computer-simulated data, on scans of phantoms, and on patient studies, and has been found effective in reducing the random noise in transmission measurements and in providing more accurate ACFs than the method using geometric attenuation correction. As a result, transmission scan times can be shortened, inconvenience to patients is reduced, and PCT images are improved.

Brain↗
PubMedDate not supplied

Activation of cerebral blood flow during a visuoperceptual task in patients with Alzheimer-type dementia.

Changes in regional cerebral blood flow (rCBF) associated with a face-matching task were examined using positron emission tomography (PET) and H2(15)O in 7 patients with mild-moderate dementia of the Alzheimer type (DAT) and in 8 healthy age-matched controls. rCBF was normalized to whole brain flow and pixel-by-pixel difference images were computed by contrasting flow during a control task to flow during face matching. Both patients and controls showed bilateral rCBF increases in occipitotemporal extrastriate cortex during face matching. The magnitude of these increases was not significantly different between the groups. In addition, the patients showed greater rCBF activation in regions of occipital and frontal cortex. These results show that early in the course of DAT, patients utilize extrastriate cortex to perform a visuoperceptual task, as do control subjects but also show rCBF increases in additional cortical areas. Activation of these additional areas of cortex in the patients may reflect an increased attentional load during face matching due to their reduced cognitive capacity.

Aged↗
PubMedDate not supplied

A maximum likelihood method for region-of-interest evaluation in emission tomography.

A maximum likelihood (ML) estimation method, called the ML-ROI algorithm, is presented for the calculation of region-of-interest (ROI) values from emission tomography scans. The EM algorithm is used to directly estimate ROI values from tomographic projection data given the location, size, and shape of all ROIs. The algorithm requires for the specification of a detailed model of the physical factors contributing to projection measurements including resolution and attenuation. The ML-ROI algorithm also provides an estimate of the variability of the ROI estimator (covariance matrix). The algorithm was tested with simulation and phantom data and compared with ROI estimation strategies using filtered backprojection (FBP) images. The ML-ROI estimates were unbiased, i.e., the partial volume effect was eliminated. Except for regions smaller than the detector resolution, the variability of the ML estimates was comparable to or less than the biased FBP estimators. Computation time for the ML-ROI algorithm was between 5 and 10 s/iteration. An evaluation of the sensitivity of the algorithm to misdefinition of the location and size of the ROIs was also performed.

Humans↗