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Biomedical subjects

J Pavía

Publications and source records attributed to J Pavía.

At least 37 records · Page 2Linked to original sources
PubMed1998

Predictive value of 99Tcm-sestamibi gated SPET for long-term myocardial perfusion and functional recovery after an acute myocardial infarction.

We assessed the predictive value of 99Tcm-sestamibi gated single photon emission tomography (SPET) for changes in perfusion and functional outcome after an acute myocardial infarction and compared the findings on functional recovery with echocardiography using low-dose dobutamine. Gated 99Tcm-sestamibi SPET and radionuclide angiocardiography were performed in 17 patients 4-10 days after an acute myocardial infarction. Six months later, both isotopic studies and rest-dobutamine echocardiography were performed to assess outcome. Perfusion improved in six of seven severely hypoperfused segments (positive predictive value = 85.7%) that showed wall thickening but not in any of 28 segments (negative predictive value = 100%) without wall thickening. The mean ejection fraction improved from 47.7 to 52.3% (P = 0.018). Furthermore, there was a greater improvement in ejection fraction in the group of patients in whom wall thickening predicted a recovery in perfusion (9.0 vs 3.7%, P = 0.01). A comparison of the assessment of functional recovery between gated SPET and dobutamine echocardiography showed good agreement (81.4%). We conclude that the presence of wall thickening in severely hypoperfused segments on 99Tcm-sestamibi gated SPET is predictive of changes in perfusion and functional recovery after acute myocardial infarction, thus identifying the presence of viable myocardium. In contrast, segments showing hypoperfusion and dysfunction after an acute myocardial infarction probably contain scar tissue only.

Adult↗
PubMed1998

Alzheimer's disease: relationship between muscarinic cholinergic receptors, beta-amyloid and tau proteins.

Senile dementia is one of the most important health problems in developed countries. The main disease causing dementia is Alzheimer's disease that is characterized by the progressive deterioration of the cholinergic system, beta-amyloid production and deposition, and neurofibrillary tangle formation. Most of the reviewed data, along with data from experiments performed in our laboratory, suggest that there are no changes in the number of muscarinic receptors between Alzheimer and control brains, although the receptors expressed in Alzheimer's disease brains can be anomalous in their function. The muscarinic receptor-G-protein interaction also seems to be impaired in Alzheimer's disease compared with control brains, as well as the G-protein system, with an important decrease in the function of the Gq/11, the most important G-protein stimulating phosphoinositide hydrolysis in human brain; in addition, the second messenger system is also impaired, with a decrease in the synthesis of phosphoinositides and in the number of IP3 receptors. Muscarinic cholinergic receptors are also linked to beta-amyloid production, stimulation of the M1 subtype with agonists results in the processing of the beta-amyloid precursor protein to non-amyloidogenic products and administration of a fraction of the beta-amyloid (beta-amyloid 25-35) to rats, results in a decrease in the number of muscarinic receptors in brain. M1 agonists also decrease the phosphorylation of tau proteins, playing again a modulatory role in the pathogenesis of Alzheimer's disease. The existence of a link between beta-amyloid and tau proteins also has been reported; treatment of hippocampal neurones with beta-amyloid, or the 25-35 residue fragment, resulted in an increase in tau protein phosphorylation. The particular contribution of muscarinic receptors, beta-amyloid and tau proteins in the pathogenesis of Alzheimer's disease remains still unclear. Probably Alzheimer's disease could be due to a progressive degeneration in the relationship between the three components covered in this review.

Alzheimer Disease↗
PubMed1998

Single photon emission computed tomography (SPECT) in a patient with bilateral temporal seizures: correlation between ictal EEG and postictal/ictal SPECT.

We report a patient with bilateral independent temporal lobe seizures in whom two [99mTc]HMPAO single photon emission computed tomograph (SPECT) scans were performed during two different seizures. In the first periictal SPECT, [99mTc]HMPAO was injected in the interval between two closely spaced seizures (one localized in the left temporal lobe and the other in the right temporal lobe). SPECT images showed hypoperfusion in the left lateral temporal lobe, hyperperfusion of the left mesial temporal region, and pronounced hyperperfusion in the right anterior temporal lobe. These results suggest both a postictal left temporal SPECT pattern and an ictal right temporal pattern. In the second periictal SPECT, [99mTc]HMPAO was injected immediately after a right temporal lobe seizure and showed right lateral temporal lobe hypoperfusion and right mesial hyperperfusion, suggesting a postictal right temporal SPECT pattern. Interpretation of the periictal SPECT should take into account EEG changes at the time or in the minutes immediately after injection of [99mTc]HMPAO.

Adult↗
PubMed1998

[Cerebral SPECT in partial epilepsy].

UNLABELLED: Effective surgical treatment of patients with medically intractable complex partial seizures depends on accurate preoperative localization of the seizure focus. 99mTc-HMPAO brain SPECT could assist us in localizing the epileptic foci showing focal hypoperfusion on interictal SPECT and hyperperfusion on ictal SPECT. METHODS: Video-EEG monitoring, MRI, as well as interictal and peri-ictal brain SPECT were performed on 37 patients with refractory epilepsy. Ictal brain SPECT was performed on 14 patients and in the remaining 23 patients a postictal SPECT was obtained. Video-EEG was used as the gold standard procedure for localizing the seizure focus and was compared to the interictal and peri-ictal brain SPECT results. Twenty-four patients suffered from temporal lobe epilepsy and 13 had extratemporal seizures. RESULTS: Interictal brain SPECT correctly localized the seizure focus in 43% of the patients (58.3% of the patients with temporal lobe seizures and 15.4% of the patients with extratemporal seizures). Ictal SPECT correctly identified the seizure focus in the 93% of cases (100% of the patients with temporal lobe seizures and 75% of the patients with extratemporal seizures). Finally, 52% of the patients were correctly identified with postictal SPECT (71.4% of the patients with temporal lobe seizures and 22.2% of the patients with extratemporal seizures). CONCLUSION: Our findings suggest that interictal brain SPECT could assist in the localization of temporal lobe seizures. Tracer injection during seizure or immediately after it (peri-ictal SPECT) is the method of choice for SPECT imaging aimed at the non-invasive localization of seizure focus.

Adolescent↗
PubMed1997

Pharmacological characterization and distribution of muscarinic receptors in human placental syncytiotrophoblast brush-border and basal plasma membranes.

Based on the existence of choline acetyltransferase and acetylcholine in human placenta, we have investigated the presence of muscarinic acetylcholine receptors in brush-border and basal plasma membranes from human term placenta. Radioligand binding assay, using [3H]N-methyl-scopolamine as tracer, showed the existence of acetylcholine muscarinic receptors in brush-border (Kd 0.28 +/- 0.04 nM; Bmax 9.4 +/- 1.6 fmol/mg protein) and basal plasma membranes (Kd 0.24 +/- 0.05 nM; Bmax 34.3 +/- 6.3 fmol/mg protein). In order to perform a pharmacological characterization of these receptors, competition binding experiments were carried out using the muscarinic receptor antagonists pirenzepine, (11(2-diethyl-amino)methyl)-1-piperidinylacetyl-5-11-dihydro-6H-py rido(14) benzodiazepine (AF-DX 116), himbacine, 4-diphenylacetoxy-N-methylpiperidine methiodide (4-DAMP), dicyclomine and hexahydro-sila-difenidol (HHSD). The results obtained showed that the muscarinic receptors in brush-border and basal plasma membranes belong to different subtypes. In brush-border membranes, the receptor found match in terms of affinity for the antagonists with the muscarinic M1 receptor subtype (Ki pirenzepine, 13.6 +/- 8.2 nM; Ki AF-DX 116, 1680 +/- 271 nM; Ki himbacine, 212 +/- 6.5 nM; Ki 4-DAMP. 1.5 +/- 0.4 nM; Ki dicyclomine, 5.1 +/- 0.8 nM; Ki HHSD, 34.3 +/- 7.3 nM), whereas the receptor in basal plasma membrane seems to be of the muscarinic M2 receptor subtype (Ki pirenzepine, 202 +/- 48 nM; Ki AF-DX 116, 124 +/- 60 nM; Ki himbacine, 20.6 +/- 4.8 nM; Ki 4-DAMP, 4.5 +/- 1.2 nM; Ki dicyclomine, 54.6 +/- 22 nM; Ki HHSD, 89.2 +/- 15.8 nM). The results obtained show the existence of muscarinic acetylcholine receptors in brush-border and basal plasma membranes from human term placenta with a different distribution pattern in terms of number of receptors and distribution of different subtypes. The functional significance of these findings is as yet unknown, but these receptors probably mediate different functions as they belong to different subtypes and are coupled to different second messengers.

Binding, Competitive↗
PubMed1996

The influence of a relaxation parameter on SPECT iterative reconstruction algorithms.

Algebraic reconstruction techniques (ARTs) have been intensively studied in image reconstruction. However, reconstructed images often exhibit a characteristic noise when applied to emission tomography. In this work, we study the influence of the ART relaxation parameter and identify values of that parameter which yield smooth images and good convergence. The study includes both simulated and real single photon emission computed tomographic (SPECT) data. In the simulated studies, scattering, attenuation, noise and detector response were included. Relaxation factors ranging between 0.01 and 0.35 were considered. Total counts in projections were between 2.5 x 10(5) and 10(6) in one slice. The goodness of the reconstructions was assessed by using the correlation coefficient between the pattern and the actual reconstruction (CC), the background coefficient of variation (CV), the contrast (CON) and the signal-to-noise ratio (SNR). The results show that values for the relaxation factor and number of interations close to 0.1 and 8, respectively, yield reconstructed images in which CC, CV, CON and SNR have well balanced values and CC, CV and SNR are very close to the extremal. An increase in either the number of iterations or in the relaxation factor results in a rise of CON but the other three FOMs deteriorate. The results from the real phantom, which are in agreement with those of the simulated studies, validate the simulation method and demonstrate the influence of the relaxation parameter.

Algorithms↗
PubMed1996

Baseline, visual deprivation and visual stimulation 99TCm-HMPAO-related changes in visual cortex can be detected with a single-head SPET system.

To determine the sensitivity of 99TCm-hexamethylpropylene amine oxime (99TCm-HMPAO) and a single-head SPET (single photon emission tomography) system in the detection of perfusion changes in the visual cortex due to different visual conditions, six normal healthy volunteers were studied under conditions of visual deprivation (blindfolded), visual stimulation (stroboscopic light) and baseline (dim light and eyes open). Visual cortex/whole-brain activity ratios, and the percentage of activity change between the different visual conditions were calculated after three-dimensional realignment of the images. The activity in the visual cortex was higher during visual stimulation than during the visual deprivation (P = 0.002, 17.6 +/- 8.6% increase) and baseline conditions (P = 0.009, 8.8 +/- 5.6% increase). Furthermore, the activity in the visual cortex was lower during the visual deprivation than in the baseline condition (P = 0.001, 8.1 +/- 2.9% decrease). 99TCm-HMPAO SPET, even with a single-head system, is capable of detecting changes in rCBF in the striate cortex, not only between conditions of visual stimulation and deprivation, but also between these two conditions and the baseline state.

Adult↗
PubMed1995

Tc-99m galactosyl-neoglycoalbumin hepatic scintigraphy in fulminant hepatic failure.

Tc-99m galactosyl-neoglycoalbumin (NGA) is a new liver imaging agent that specifically binds to a hepatocyte specific membrane receptor, the hepatic binding protein. Scintigraphy with Tc-99m NGA is a noninvasive method that provides functional images of the liver. This report deals with one case of fulminant hepatic failure in which hepatic scintigraphy with Tc-99m NGA predicted hepatic recovery before clinical and biochemical parameters, being a prognostic index in this patient.

Adult↗
PubMed1994

Procedure for red blood cell labelling with 99mTc-HMPAO. Methodology and quality control.

We present here results on the labelling of red blood cells with 99mTc-HMPAO as an alternative method to the usual in vitro technique. Anticoagulant agents, the labelling medium with plasma, and the lapse of time between 99mTc-HMPAO preparation and labelling are the main factors which affect the efficiency of the procedure. A 93.9 +/- 2.3% labelling yield was obtained with freshly prepared 99mTc-HMPAO. In vitro (tracer elution of 4.3 +/- 1.2% at 60 mins) and in vivo (percentage of plasma activity at 60 mins, 7.8 +/- 2.8%) stability of the label, as well as image quality, qualify 99mTc-HMPAO labelled red blood cells as a suitable agent for clinical use.

Erythrocytes↗
PubMed1994

Prefrontal and temporal blood flow in schizophrenia: resting and activation technetium-99m-HMPAO SPECT patterns in young neuroleptic-naive patients with acute disease.

UNLABELLED: This study assesses prefrontal and temporal regional cerebral blood flow (rCBF) changes in young, neuroleptic-naive schizophrenic patients with acute disease. METHODS: A selected population of 10 young, never-treated schizophrenic women with acute disease was studied by two hexamethylpropyleneamine oxime (HMPAO) brain SPECT sessions, performed 48 hr apart, both at rest and during a prefrontal activation task using the Wisconsin Card Sort Test (WCST). All patients met Diagnostic and Statistical Manual of Mental Disorders, 3rd edition-revised criteria for schizophrenia or schizophreniform disorder, were neuroleptic-naive and had acute symptoms. RESULTS: Under resting conditions, the schizophrenic group had significantly higher rCBF in the prefrontal regions, mainly in the left side and including the anterior cingulate, than did the controls. In addition, schizophrenic patients showed significant interhemispheric differences in prefrontal and posterior temporal index values at rest (left hyperfrontality and left hypotemporality). During WCST activation, the control group showed significant increases in prefrontal blood flow, whereas the schizophrenic group did not. CONCLUSION: These results support a physiologic dysfunction of the prefrontal cortex in schizophrenia that is present at the onset of the illness prior to neuroleptic treatment. Furthermore, both left hyperfrontality and left hypotemporality may indicate a brain lateralization defect in schizophrenia.

Acute Disease↗
PubMed1991

Comparative study of the kinetics of the renal tracers 99Tcm-MAG3 and 131I-hippuran.

Serial measurements of plasma activity, plasma protein binding and urine excretion were obtained in order to study 99Tcm-MAG3 (MAG) and 131I-Hippuran (OIH) kinetics after simultaneous injection of both tracers in 21 patients with various renal diseases. Results were compared on the basis of a compartmental model, calculating the rate constants as well as the clearance and volume of distribution. Protein binding was calculated in 10 patients (mean: MAG = 54.7%, OIH = 33.8%). The dependence of time, tracer and patient factors was shown by ANOVA. Time was independent, with tracer and patient factors and their interaction being significant. The mean value of the renal excretion constant was equal for the two tracers (k12 = 0.052 min-1). The clearance values were found to be highly correlated (r = 0.982) with a ratio of 0.57 between them. The volumes of distribution in litres were 4.1 (MAG) and 7.0 (OIH). One-hour urine excretion was nearly the same for both tracers (MAG: 64%, OIH: 63% of the injected dose).

Blood Proteins↗
PubMed1991

Evaluation of thallium myocardial-perfusion imaging by means of washout parametric images: a simulation study.

A method for the evaluation of myocardial perfusion with 201Tl scintigraphic images is presented. The method is based on making a pixel-by-pixel comparison of the stress and the redistribution images aligned by using bidimensional correlation techniques between the nonpathologic regions of the myocardium. The comparison is made by means of parametric images of the washout, which are evaluated by calculating separately the mean values in the normal and the abnormal regions. The study is carried out on controlled models that contain myocardium, an artifact, and noise. The results show the suitability of the method and confirm the validity of its application to individualized studies of clinical interest.

Computer Simulation↗
PubMed1989

Thallium-201 myocardial planar scintigrams. Alignment of stress and rest images by correlation.

The utility of the correlation for alignment of myocardial perfusion imaging with 201TI was studied. The tests were made by numerical simulation of a heart model with an artefact and a theoretical background superimposed in normal and pathological situations. The methods used were bidimensional and unidimensional correlation techniques and were applied either with or without previous background subtraction. Our results show the suitability of this alignment technique, useful in finding the displacement between images with an average error inferior to one pixel in different situations of myocardial damage.

Computer Simulation↗
PubMed1989

Methods of background subtraction in myocardial perfusion imaging with thallium-201: a comparative study in the presence of an artefact.

For thallium imaging quantitation, a simulation study has been made using different methods of interpolation for background subtraction and studying their behaviour in the presence of an artefact. Two artefacts were used, one simulating hepatic or splenic uptake and the other diaphragmatic activity. The interpolative methods used were three classic techniques using standard masks. Their algorithms were modified so that they could also be used with arbitrarily shaped masks enclosing myocardium, and a comparison between the original and modified methods was made. Our results show an improvement when using the modified algorithms adapted to the arbitrarily outlined mask.

Computer Simulation↗
PubMed1989

Indium-111-labeled platelets in monitoring human pancreatic transplants.

We have performed 59 111In-labeled platelet scintigraphies in 12 patients with pancreas transplant, and we have compared retrospectively the 111In platelet uptake with the graft immunological situation. A diffuse uptake in the graft was seen in five of six patients with pancreatic rejection. The scans became positive before changes in biochemical tests were detected. No 111In platelet uptake was seen in five of seven normally functioning grafts. Two cases of venous thrombosis and two perigraft hematomas appeared like a focal 111In platelet accumulation. Indium-111-labeled platelet scintigraphy can be a useful method for monitoring pancreas transplants. It may be helpful in the early detection of pancreatic allograft rejection and in the differential diagnosis between this and other complications such as thrombosis or hematomas.

Adult↗
PubMed1988

Optimal filtering values in renogram deconvolution.

The evaluation of the isotopic renogram by means of the renal retention function (RRF) is a technique that supplies valuable information about renal function. It is not unusual to perform a smoothing of the data because of the sensitivity of the deconvolution algorithms with respect to noise. The purpose of this work is to confirm the existence of an optimal smoothing which minimises the error between the calculated RRF and the theoretical value for two filters (linear and non-linear). In order to test the effectiveness of these optimal smoothing values, some parameters of the calculated RRF were considered using this optimal smoothing. The comparison of these parameters with the theoretical ones revealed a better result in the case of the linear filter than in the non-linear case. The study was carried out simulating the input and output curves which would be obtained when using hippuran and DTPA as tracers.

Humans↗