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Biomedical subjects

A M Paans

Publications and source records attributed to A M Paans.

At least 19 recordsLinked to original sources
PubMed2000

Language localization in cases of left temporal lobe arachnoid cyst: evidence against interhemispheric reorganization.

We investigated whether left-hemisphere arachnoid cysts lead to reorganization of the language function using PET. A group analysis demonstrated that patients showed no more right-hemisphere activation than a matched control group. Several patients had clear language localizations in the left hemisphere during language comprehension; none of the patients showed right-hemisphere activation. We conclude that left-hemisphere tissue must suffer considerable compromise before reorganization of language into the right hemisphere becomes necessary. Language activations within the left hemisphere are clearly displaced. This is consistent with mere physical displacement in some patients rather than reorganization within the left hemisphere; in others intrahemispheric reorganization cannot be excluded.

Adult↗
PubMed2000

Visual feedback about time estimation is related to a right hemisphere activation measured by PET.

In previous EEG experiments we have presented a time estimation task to our subjects, who had to press a button with either the left or right index finger 3 s after an auditory warning stimulus (WS). Two seconds later a visual Knowledge of Results (KR) stimulus was presented on a screen in front, informing them about whether the movement had been made in the correct time window (a vertical line), whether it was too early (a minus sign) or too late (a plus sign). The potential distribution underlying the anticipatory attention for the KR stimulus suggested a right hemisphere network in which the prefrontal cortex, the insula Reili and the parietal cortex were involved. In the present positron emission tomography (PET) activation study we aimed to further localize the exact positions of these regions, using the same paradigm. Two conditions were compared in which the WS had to be followed by a button press with the left index finger. In experimental condition A, subjects received true information about their performance, while in condition B false information was given, utilizing the same stimuli, but randomly, thus without any relation to the actual performance. In both conditions identical stimuli were presented and identical movements were made. Therefore we applied statistical parameter mapping (SPM) for comparison of condition A with B in order to identify regional increases in perfusion related to the anticipation and use of the KR. We found in line with our predictions a right hemisphere activation of (1) BA45, (2) the junction of the posterior insula with the temporal transverse gyrus and (3) the posterior part of the parietal cortex. This activation pattern was accompanied by a better performance due to KR. A second, though not predicted, effect was the increase in correct responses during the last two sessions compared to the first two sessions, independent of KR. This learning effect was accompanied by an activation of BA46 and the supplementary motor area (SMA), again in the right hemisphere. Summarizing, two different prefrontal areas in the right hemisphere were activated: a more ventral area, related to the use of external stimuli providing feedback about a past performance, in order to produce movements in time, and another mid-dorsal one, related to temporal programming on the basis of internal cues.

Acoustic Stimulation↗
PubMed2000

Positron emission tomography in drug development and drug evaluation.

Positron Emission Tomography (PET) is an imaging modality which can determine biochemical and physiological processes in vivo in a quantitative way by using radiopharmaceuticals labeled with positron emitting radionuclides as (11)C, (13)N, (15)O and (18)F and by measuring the annihilation radiation using a coincidence technique. This includes also measurement of the pharmacokinetics of labeled drugs and the assessment of the effects of drugs on metabolism. Because only very low amounts of the radiolabeled drug have to be administered, far below toxicity levels, human studies can be carried out even before the drug is entered in Phase I. Such studies can provide cost-effective predictive toxicology data and information on the metabolism and mode of action of drugs. PET is also very useful to study the metabolic consequences of gene expression or gene defects. In the last decade many genetically engineered small animal models have been developed. The study of these animals with high resolution small animal PET cameras provides new opportunities in drug development. Especially valuable is the contribution of PET to bridge the gap between molecular biology, understanding of pathology and to the design of a new generation of drugs.

Drug Evaluation↗
PubMed1999

Brain activation related to the change between bimanual motor programs.

By using positron emission tomography, we aimed to identify cerebral foci of neuronal activation associated with the initiation of a specific motor program. To that end, a state of repeatedly alternating in- and antiphase of bimanual flexion and extension movements was compared with similar movement responses except phase changing. This comparison provided the opportunity to eliminate confounding effects of attention and simple movements. Change between the two bimanual motor programs was related with activation at the posterior border of the left angular gyrus, the right precuneus, and the right premotor and right medial prefrontal cortex. In a subsequent experiment, with attention and random movements as additional variables, activation at the posterior border of the left angular gyrus was found at the same significance level. This posterior parietal activation may indicate an equivalence with the coding of intention in monkey posterior parietal cortex. Lesion of the left posterior parietal cortex in human gives rise to left-right disorientation and ideomotor apraxia. Our results may support the view that these symptoms reflect the inability to transpose a motor plan to the representation of a personal body scheme. Activation of the right premotor and right medial prefrontal cortex was related both to the change between motor programs and to the condition with strictly regular movement in which no additional responses were made to randomly presented signals. This is consistent with the concept that motor preparation is associated with both the selection of internally instructed movements and the suppression of irrelevant environmental stimuli.

Adult↗
PubMed1999

The distribution of cerebral activity related to visuomotor coordination indicating perceptual and executional specialization.

The distribution of increased regional cerebral blood flow (rCBF) related to visuomotor coordination was studied by means of positron emission tomography (PET) in normal subjects. An experimental condition, in which a vertically presented zigzag figure had to be copied in a horizontal orientation, was compared with a control condition in which the same horizontal drawing was made, guided by a horizontally presented example. Cognitive components dealing with the mismatch in visual orientation resulted in activation of (i) right dorsal premotor cortex, (ii) right posterior parietal cortex, (iii) visual cortex (area V1) and (iv) left fusiform gyrus. In a second experiment, conditions were compared in which the same horizontal zigzag figure was copied in either a vertical or a horizontal orientation. Now, the motor components of the transformation of orientation appeared to be associated only with left premotor cortex activation. The differential distribution of activations is regarded to reflect the selective effort to cope with either the visual or the motor component of spatial incongruity, and indicates specialization for perceptual and executive components in visuomotor control. We propose that the perceptual component of visuomotor transformation in our experiment relates to a realignment of the coordinates of a percept to an internally defined coordinate system. The executive component relates to guidance of movement within an internal representation of space. In a preceding behavioural experiment, a majority of patients with Parkinson's disease (PD) failed on the task in which they had to make a horizontal copy of a vertically presented picture. This finding may suggest a deficit in the maintenance of an internal spatial representation to guide movement.

Adolescent↗
PubMed1999

Sentence comprehension and word repetition: a positron emission tomography investigation.

Using positron emission tomography, visual presentation of sentences was shown to cause increased regional cerebral blood flow relative to word lists in the left lateral anterior superior and middle temporal gyri, attributable to cognitive processes that occur during sentence comprehension in addition to those carried out during word comprehension. Additional comparisons showed that repeating words (in a different context, when subjects did not attempt to learn the initial lists) led to significant patterns of both increased blood flow (left putamen and right caudate) and decreased blood flow (left posterior temporal lobe). Increases are argued to reflect retrieval of memory traces, whereas decreases reflect diminished necessity for processing of input. A decrease in the left inferior parietal lobe was attributable to other factors.

Adult↗
PubMed1998

Localizing components of a complex task: sentence processing and working memory.

Three areas of the left hemisphere play different roles in sentence comprehension. An area of posterior middle and superior temporal gyrus shows activation correlated with the structural complexity of a sentence, suggesting that this area supports processing of sentence structure. The lateral anterior temporal gyrus is more activated bilaterally by all sentence conditions than by word lists; thus the function of the area probably does not directly support processing of structure but rather processing of words specific to a sentence context. Left inferior frontal cortex also shows activation related to sentence complexity but is also more activated in word list processing than in simple sentences; this region may thus support a form of verbal working memory which maintains sentence structural information as well as lexical items.

Adult↗
PubMed1998

11C-tyrosine position emission tomography and 1H magnetic resonance spectroscopy of the response of brain gliomas to radiotherapy.

We monitored 10 patients with unresected (9) or partially resected (1) supratentorial gliomas with 11C-tyrosine position emission tomography (TYR-PET) before and after radiotherapy. TYR-PET tumour volumes were measured using a threshold technique. In seven patients the tumour volume decreased after radiotherapy, although all gliomas persisted on TYR-PET images. In eight patients the tumour protein synthesis rate (PSR) was calculated using a dynamic study protocol in combination with a PATLAK analysis. There were no changes in PSR after radiotherapy, but the PSR was calculated on the remaining tumour volume using the same threshold technique as before therapy, i.e. the decrease in tumour volume was not taken into account. In eight patients the PET data were compared with magnetic resonance spectroscopic imaging (1H-MRSI) performed simultaneously. Although there was no statistically significant correlation between TYR-PET volume changes and 1H-MRSI choline level we observed a simultaneous decrease in volume and choline in four patients.

Adult↗
PubMed1998

Skeletal muscle perfusion measured by positron emission tomography during exercise.

The applicability of H215O-positron emission tomographic (PET) imaging for the assessment of skeletal muscle perfusion during exercise was investigated in five healthy subjects performing intermittent isometric contractions on a calf ergometer. The workload of the left calf muscles was kept constant in all exercises, while that of the right calf muscles was varied. During exercise H215O distribution in the calf muscles was measured by PET. Radioactivity measured in the left calf muscles was used as a reference for the radioactivity measured in the right calf muscles. In all studies, muscles were delineated by uptake of radioactivity. Four subjects demonstrated high radioactivity in the gastrocnemius medialis muscle, in one subject high radioactivity was distributed over the triceps surae muscles. The observed muscles demonstrated also local foci of radioactivity indicating regionally enhanced tissue perfusion. The right-left ratio of radioactivity in the active muscles increased as a function of the load. We conclude that inter- and intramuscle perfusion differences can be measured during exercise by H215O-PET imaging.

Adult↗
PubMed1998

Glucose consumption by various tissues in pregnant rats: effects of a 6-day euglycaemic hyperinsulinaemic clamp.

In the course of pregnancy maternal tissues become increasingly more insensitive to insulin. As 6 days of euglycaemic hyperinsulinaemic clamping, from day 8 until 14 of gestation, ameliorates total glucose consumption, we analysed the contribution of individual tissues in this phenomenon. We measured not only glucose consumption, but also concentrations of the glucose transporter protein GLUT4 in selected tissues. On day 15 of pregnancy in saline-infused (pregnant control) rats, 18F-fluoro-2-deoxy-D-glucose (FDG) consumption, as measured by positron emission tomography, as well as GLUT4 content were diminished in heart (P < 0.05), and in brown (P < 0.05) and white adipose tissues (P < 0.05) when compared with non-pregnant controls. During clamping, on day 13 of the experiments, both in pregnant and non-pregnant rats FDG consumption was increased in liver (P < 0.05), skeletal muscle (P < 0.05), brown (P < 0.05) and white adipose tissues (P < 0.05) when compared with saline-infused controls. In both the reproductive conditions, only in white adipose tissue was this increased FDG consumption associated with increased GLUT4 levels (P < 0.05); GLUT4 content of m. gastrocnemius, m. soleus, heart and brown adipose tissue was unaffected by clamping. In non-pregnant rats, 24 h after clamping ceased, FDG consumption was diminished in heart compared with control non-pregnant rats (P < 0.05). In pregnant rats, however, 24 h after clamping (i.e. day 15 of pregnancy) both FDG consumption (P < 0.05) and GLUT4 content (P < 0.05) were still increased in white adipose tissue only, when compared with saline-infused pregnant rats on the same day of gestation. It is suggested that hyperinsulinaemic euglycaemic clamping ameliorates insulin action halfway pregnancy, in particular by stimulation of glucose consumption and GLUT4 protein content in white adipose tissue.

Adaptation, Physiological↗
PubMed1997

Detection of local recurrence of soft-tissue sarcoma with positron emission tomography using [18F]fluorodeoxyglucose.

BACKGROUND: It is often difficult to detect a local recurrence of soft-tissue sarcomas due to disturbance of the normal anatomy by previous surgery and radiotherapy. The aim of this study was to assess the value of positron emission tomography (PET) with [18F]fluoro-2-deoxy-D-glucose (FDG) for detecting local recurrences. METHODS: In the period 1992-1995, 17 patients with proven or suspected local recurrence of soft-tissue sarcoma were examined using FDG-PET. Fifteen of these patients were ultimately proven to have a recurrence. RESULTS: Recurrence was visualized in 14 patients (93%). Small tumors (maximum diameter 0.5 cm) were as easily visible as large lesions (maximum diameter 20 cm). In one patient the PET scan was positive, but the recurrence could not be proven histologically. Recurrence was proven 1 year later. A recurrent low-grade liposarcoma was not visualized. The two patients with benign lesions had a negative PET scan. The mean glucose metabolic rate was calculated to be 13.2 mumol/100 g/min (range 1.9-28.4). A correlation was found between the histological malignancy grade and the metabolic rate (p < 0.05; Kruskal-Wallis). CONCLUSION: PET with FDG is a useful addition to the diagnostic armamentarium for detecting local recurrence of soft-tissue sarcomas and provides an indication of the malignancy grade of the recurrent lesion.

Adult↗
PubMed1997

Cobalt-55 positron emission tomography in ischemic stroke.

After acute cerebral stroke, the (peri-) infarct tissue is characterized by calcium (Ca)-mediated neuronal damage and inflammatory processes. Monitoring Ca-mediated damage using the isotope cobalt-55 (Co) as a Ca-tracer may enable PET-imaging of this tissue. Since the fate of (peri-) infarct tissue determines clinical outcome, Co-PET may have prognostic value in stroke. Six stroke patients were examined with Co-PET, MRI and a middle cerebral artery (mca) stroke scale (Orgogozo). In every patient, specific Co-accumulation in the appropriate brain region was seen, irrespective of the integrity of the blood-brain barrier. This pilot study suggests Co-PET as a diagnostic tool in stroke, which may provide additional information on the clinical outcome. Validation of method in larger patient series is necessary.

Aged↗
PubMed1997

Regional cerebral blood flow changes related to affective speech presentation in persistent vegetative state.

A story told by his mother was presented on tape to a trauma patient in persistent vegetative state (PVS). During auditory presentation, measurements of regional cerebral blood flow (rCBF) were performed by means of positron emission tomography (PET). Changes in rCBF related to this stimulus condition, as compared to presenting non-word sound, were evaluated by means of statistical parametric mapping (SPM). This analysis indicated activation of rostral anterior cingulate, right middle temporal and right premotor cortices, which may reflect appropriate cortical involvement in processing emotional attributes of sound or speech.

Adolescent↗
PubMed1997

Positron emission tomography in primary brain tumours using cobalt-55.

Primary brain tumours are usually assessed by computed tomography (CT) and magnetic resonance imaging (MRI), sometimes in conjunction with positron emission tomography (PET). We used cobalt-55 (55Co) as a calcium (Ca) tracer to visualize decaying tumour tissue, based on the fact that Ca-influx is essential in both cell death and leukocyte activation. Net 55Co uptake may be the result of cell decay, leukocyte infiltration, (re)perfusion and the pharmacological profile of 55Co. Three patients with primary malignant brain tumours (first presentation) were studied with CT, MRI and Co-PET after the intravenous administration of 0.5 mCi 55Co. Histopathological diagnosis was obtained by biopsy or resection. Co-PET demonstrated each of the brain tumours and showed good topographical agreement with CT and MRI. Co-PET provided additional detail as to the site and size of the necrotic core and the perinecrotic rim of decaying tumour. The 55Co uptake indices varied between 2.6 and 5.3. 55Co demonstrated uptake in decaying tissue, irrespective of the integrity of the blood-brain barrier. Neither necrotic nor viable tumour tissue showed affinity for 55Co. Since 55Co is readily applicable to both PET and single photon emission tomography (SPET), differences in the uptake mechanism and functional significance of the 55Co tracer are discussed in relation to 201Tl SPET. We present a (limited) pilot series of three patients to forward the claim of this new functional technique in nuclear neurology.

Aged↗
PubMed1997

Relative changes in regional cerebral blood flow during spinal cord stimulation in patients with refractory angina pectoris.

Spinal cord stimulation applied at thoracic level 1 (T1) has a neurally mediated anti-anginal effect based on anti-ischaemic action in the myocardium. Positron emission tomography was used to study which higher brain centres are influenced by spinal cord stimulation. Nine patients with a spinal cord stimulator for angina pectoris were studied using H(2)(15)O as a flow tracer. Relative changes in regional cerebral blood flow related to stimulation compared with non-stimulation were assessed and analysed using the method of statistical parametric mapping. Increased regional cerebral blood flow was observed in the left ventrolateral periaqueductal grey, the medial prefrontal cortex [Brodmann area (BA) 9/10], the dorsomedial thalamus bilaterally, the left medial temporal gyrus (BA 21), the left pulvinar of the thalamus, bilaterally in the posterior caudate nucleus, and the posterior cingulate cortex (BA 30). Relative decreases in rCBF were noticed bilaterally in the insular cortex (BA 20/21 and BA 38), the right inferior temporal gyrus (BA 19/37), the right inferior frontal gyrus (BA 45), the left inferior parietal lobulus (BA 40), the medial temporal gyrus (BA 39) and the right anterior cingulate cortex (BA 24). It is concluded that spinal cord stimulation used as an additional treatment for angina applied at T1 modulates regional cerebral blood flow in brain areas known to be associated with nociception and in areas associated with cardiovascular control.

Aged↗
PubMed1997

Characterization of pulmonary and myocardial beta-adrenoceptors with S-1'-[fluorine-18]fluorocarazolol.

UNLABELLED: S-1'-[18F]fluorocarazolol was administered to healthy volunteers to assess its potential for noninvasive measurement of regional pulmonary and myocardial beta-adrenoceptor densities. METHODS: High-specific activity fluorocarazolol was intravenously injected on two separate occasions within a 1-wk interval. The initial injection was without pretreatment, but before the second injection, the volunteers either inhaled salbutamol (2 x 200 micrograms aerosol) or they ingested pindolol (3 x 5 mg during a 12-hr interval). Twenty-eight PET time frames of 31 planes were acquired over a period of 60 min after each injection. Blood samples were drawn and analyzed for the presence of fluorocarazolol and radioactive metabolites. RESULTS: Uptake of fluorocarazolol in the target tissues was hardly affected by salbutamol but was strongly depressed by pindolol. Pulmonary and myocardial tissue-to-plasma concentration ratios of fluorocarazolol reached plateau values of 11.6 +/- 0.6 (lungs) and 18.1 +/- 1.0 (heart) at 45-50 min postinjection. These values were reduced to 2.0 +/- 0.4 and 2.0 +/- 0.6 after treatment with pindolol. CONCLUSION: These data indicate that: 1. Pulmonary and myocardial uptake of radioactivity after intravenous administration of S-1'-[18F]fluorocarazolol represents radioligand binding to beta-adrenoceptors. 2. Pulmonary binding occurs mainly in alveoli rather than in airway smooth muscle under these conditions. 3. Binding kinetics do not preclude quantification of receptors with compartment models.

Adrenergic beta-Agonists↗
PubMed1997

Standardized uptake value and quantification of metabolism for breast cancer imaging with FDG and L-[1-11C]tyrosine PET.

UNLABELLED: The aims of the study were to compare the value of L-[1-11C]tyrosine (TYR) and [IBF]fluoro-2-deoxy-D-glucose (FDG) as tumor tracers in patients with breast cancer, to investigate the correlation between quantitative values and standardized uptake values (SUVs) and to estimate the value of SUVs for the evaluation of therapy. METHODS: Eleven patients with one or more malignant breast lesions and two patients with one or more benign breast tumors were studied with TYR and FDG. Doses of 300 MBq of TYR and 230 MBq of FDG were given intravenously. All PET sessions were performed using a Siemens ECAT 951/31 camera. Of 10 malignant tumors and the 3 benign lesions, glucose consumption and protein synthesis rate were quantified. All lesions were studied using SUVs based on body weight, body surface area and lean body mass, with and without correction for plasma glucose or tyrosine levels. RESULTS: All malignant tumors were visualized with both FDG and TYR, but the visual contrast was better with FDG. Increased uptake of the tracers was seen in patients with fibrocystic tissue and complicated the visual assessment and the outlining of tumor tissue. Uptake in fibrocystic disease was more prominent with FDG than with TYR. No difference in tumor/nontumor ratio between the two tracers could be established. FDG showed a false-positive result in one benign lesion. No major differences between the SUVs as defined above were found, although the best correlation between glucose consumption and the SUV was observed when the SUV was based on body surface area and corrected for plasma glucose level (r = 0.85-0.87). The SUV based on lean body mass was found to correlate best with protein synthesis rate (r = 0.83-0.94). CONCLUSION: In this group of patients, TYR appears to be a better tracer than FDG for breast cancer imaging, because of lower uptake in fibrocystic disease. SUVs correlate well with quantitative values, but future studies must determine whether treatment evaluation is also reliable with SUVs.

Blood Glucose↗