Biomedical subjects

D Pareto

Publications and source records attributed to D Pareto.

4 recordsLinked to original sources

PubMed2004

Study of the point spread function (PSF) for 123I SPECT imaging using Monte Carlo simulation.

The iterative reconstruction algorithms employed in brain single-photon emission computed tomography (SPECT) allow some quantitative parameters of the image to be improved. These algorithms require accurate modelling of the so-called point spread function (PSF). Nowadays, most in vivo neurotransmitter SPECT studies employ pharmaceuticals radiolabelled with 123I. In addition to an intense line at 159 keV, the decay scheme of this radioisotope includes some higher energy gammas which may have a non-negligible contribution to the PSF. The aim of this work is to study this contribution for two low-energy high-resolution collimator configurations, namely, the parallel and the fan beam. The transport of radiation through the material system is simulated with the Monte Carlo code PENELOPE. We have developed a main program that deals with the intricacies associated with tracking photon trajectories through the geometry of the collimator and detection systems. The simulated PSFs are partly validated with a set of experimental measurements that use the 511 keV annihilation photons emitted by a 18F source. Sensitivity and spatial resolution have been studied, showing that a significant fraction of the detection events in the energy window centred at 159 keV (up to approximately 49% for the parallel collimator) are originated by higher energy gamma rays, which contribute to the spatial profile of the PSF mostly outside the 'geometrical' region dominated by the low-energy photons. Therefore, these high-energy counts are to be considered as noise, a fact that should be taken into account when modelling PSFs for reconstruction algorithms. We also show that the fan beam collimator gives higher signal-to-noise ratios than the parallel collimator for all the source positions analysed.

Fluorine Radioisotopes↗

PubMed2004

Can the Wada test evaluate mesial temporal function? A SPECT study.

OBJECTIVE: To assess the value of SPECT during intracarotid amobarbital procedure (IAP) to discriminate which patients performed the test with the hippocampus inactivated and correlate it with the risk of amnesia after anterior temporal lobectomy (ATL). METHODS: The authors studied 40 consecutive patients undergoing ATL for refractory epilepsy. SPECT was performed after IV injection of 99mTc-HMPAO during the IAP (IAP-SPECT). Interictal SPECT and IAP-SPECT were realigned to obtain the perfusion change percentage (PCP), allowing a quantitative measurement. Wechsler Memory Scale Revised (WMS-R) before and during the first year of follow-up was used to assess memory impairment after surgery. RESULTS: A decrease between 10 and 12% of the mean PCP values was observed in the frontal, parietal, and lateral temporal lobes of the injected side and in the contralateral cerebellum. However, no significant PCP changes were observed in the occipital or mesial temporal lobes. Thirty-eight passed the memory evaluation of the IAP and in 6 of those 38 patients a decline in memory was demonstrated 1 year after ATL. However, high preoperative neuropsychological score (in two patients) and IAP asymmetry scores (in other three patients) predicted postoperative memory risk in five of these six patients. Fourteen of the 38 patients (40%) had hypoperfusion of the hippocampus during the IAP-SPECT (i.e., the hippocampus was inactivated) and only 1 of these 14 patients (2.5%) developed memory impairment after temporal lobectomy. On the other hand, 5 of the 24 patients (13%) who had a functional hippocampus on IAP-SPECT developed memory impairment. CONCLUSIONS: The results suggest that the combination of SPECT, intracarotid amobarbital procedure, and neuropsychological testing predicted risk for all patients who had postoperative memory decline, indicating that risk prediction should be based on multiple factors. IAP-SPECT results demonstrated that the hippocampus is not inactivated in over 60% of patients and that the lack of accuracy of the IAP alone in predicting the risk of amnesia is probably related to an insufficient inactivation of the ipsilateral hippocampus during the test.

Adolescent↗

PubMed2004

In vivo occupancy of female rat brain estrogen receptors by 17beta-estradiol and tamoxifen.

Estrogens or antiestrogens are currently used by millions of women, but the interaction of these hormonal agents with brain estrogen receptors (ER) in vivo has not been characterized to date. Our goal was to assess, in vivo, the extent and regional distribution of brain ER occupancy in rats chronically exposed to 17beta-estradiol (E(2)) or tamoxifen (TAM). For that purpose, female ovariectomized Sprague-Dawley rats were implanted with subcutaneous pellets containing either placebo (OVX), E(2), or TAM for 3 weeks. ER occupancy in grossly dissected regions was quantified with 16alpha-[(18)F]fluoroestradiol ([(18)F]FES). Both E(2) and TAM produced significant decreases in radioligand uptake in the brain although the effect of E(2) was larger and more widespread than the effect of TAM. Detailed regional analysis of the interaction was then undertaken using a radioiodinated ligand, 11beta-methoxy-16alpha-[(125)I]iodo-estradiol ([(125)I]MIE(2)), and quantitative ex vivo autoradiography. E(2) treatment resulted in near-complete (86.6 +/- 17.5%) inhibition of radioligand accumulation throughout the brain, while ER occupancy in the TAM group showed a marked regional distribution such that percentage inhibition ranged from 40.5 +/- 15.6 in the ventrolateral part of the ventromedial hypothalamic nucleus to 84.6 +/- 4.5 in the cortical amygdala. These results show that exposure to pharmacologically relevant levels of TAM produces a variable, region-specific pattern of brain ER occupancy, which may be influenced by the regional proportion of ER receptor subtypes. These findings may partially explain the highly variable and region-specific effects observed in neurochemical, metabolic, and functional studies of the effects of TAM in the brain of experimental animals as well as human subjects.

Animals↗

PubMed2001

Characterisation of fan-beam collimators.

Fan-beam collimators offer a good balance between resolution and noise. The collimator response may be included in iterative reconstruction algorithms in order to improve single-photon emission tomography (SPET) resolution. To this end, accurate determination of the focal region and characterisation of the collimator response as a function of the source co-ordinates must be performed. In this paper, a method to characterise fanbeam collimators is evaluated. First, we calculated the real focal region and the accuracy of the collimator convergence. Then, we confirmed the hypothesis that Gaussian distributions adequately fit the collimator responses, although no individualised treatment was performed for the tails of detector response which are associated with scattering and septal penetration. Finally, analytical functions were used to model the resolution and sensitivity. The parameter values in these functions were obtained from experimental measures by non-linear regression fitting. Our findings show differences of 1.43% between nominal and real focal length and standard deviations of 2.5 mm in the x-direction and 7.1 mm in the y-direction for the focal convergence. The correlation coefficients between experimental and predicted values were 0.994 for resolution and 0.991 for sensitivity. As a consequence, the proposed method can be used to characterise the collimator response.

Algorithms↗