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L Mascaro

Publications and source records attributed to L Mascaro.

14 recordsLinked to original sources
PubMed2004

Multicenter trial for the set-up of a MRI quality assurance programme.

Many international protocols related to RMI-QC program are focused on acquisition methods and analysis of several image quality parameters but rarely normality ranges or measurement frequencies are presented. To address this problem we investigated the variability of many magnetic resonance imaging (MRI) systems with the set-up of multicenter trial. The trial was set up to investigate short-and mid-term variability of two fundamental nongeometric image quality parameters: signal-to-noise (SNR) and integral percent uniformity (U%). Ten centers (12 devices) participated to data collection consisting of a three-step-protocol. First, 10 consecutive images of a phantom were collected with a spin echo sequence. As second step the series collection was repeated 24 h later. Finally a single image acquisition was performed twice a week for 5 weeks. The analysis of results allowed us to define a "physiological" variability of +/-3% of the reference level for both parameters and to conclude that a weekly measurement is adequate to detect relevant variations of device performance.

Analysis of Variance↗
PubMed1999

T2 relaxation of the parotid gland of patients affected by pleomorphic adenoma.

The T2 behavior of parotid gland tissue was investigated in 11 patients affected by pleomorphic adenoma. A protocol that was previously set up to define acquisition and post-processing procedures, reaching an accuracy of 2.5% in phantoms and an in vivo long term reproducibility of 0.9-8.5%, was used for the evaluations. The measurements were carried out on a whole body, superconducting imager, using a neck coil as a receiver. Some reference gel samples were imaged together with the patient and used to correct T2 results. The sequence protocol was a multispin-echo, 16 echoes. Signals were fitted with mono and biexponential decay models and an automatic choice of the best model was performed using the two chisquared comparison. Two T2 maps (T2 monoexponential or short T2 component, and long T2 component) and chisquared maps were then produced. Pathologic and normal tissues showed a dominant monoexponential decay with a good level of biexponentiality (16%-27% of total fitted pixels) due to partial volume effects from the liquid content. Concerning the biexponentiality, no significant differences were found between the fitted pixel fraction of normal and pathologic tissue, because the T2 long component of the lesion was related both to the edema and saliva content, but probably the increase in the first compensated the decrease in the second. Chisquared maps showed that most of the lesions presented a monoexponential core surrounded by a biexponential border probably due to a solid component similar to normal tissue with partial volume effects from saliva content. Ninety-five percent confidence intervals for normal tissue were 69.40-87.80 ms (monoexponential relaxation), 38.19-44.67 ms and 285.84-691.28 ms (short and long components of biexponential relaxation). For pathologic tissue they resulted 172.17-275.83 ms, 53.86-89.98 ms and 442.10-814.58 ms. The monoexponential component, mostly present in the core of the lesion, was the parameter that better characterized pathologic tissue. A comparison was performed between normal tissue of patients and normal tissue of volunteers, whose statistics was collected in a previous study with the same evaluation protocol. Results showed no significant differences in the biexponential fitted fractions and the comparison of relaxation times. We conclude that, for tissue characterization, a multiexponential analysis should be carried out in order to improve accuracy and to obtain more reliable results. Moreover, other than relaxation calculations, a topographical analysis of relaxation distribution, using for instance the chisquared maps, might in the future give us more useful information on tissue structure.

Adenoma, Pleomorphic↗
PubMed1999

Multicentre magnetic resonance texture analysis trial using reticulated foam test objects.

Texture analysis in magnetic resonance imaging has the ability to provide useful diagnostic information with respect to the discrimination of disease states of a single tissue or the separation of different tissues. However, for widespread use it is necessary to determine how texture measurements carried out in one center relate to those carried out in another. To this end, a multicentre trial has been performed where reticulated foam test objects have been scanned in six European centers according to a fixed protocol. It has been concluded that texture measurements are not transportable between centers. Principal component models calculated from the texture parameters collected in one center do not fit the data collected in another. Further trials are to investigate whether the reticulated foam test objects may be used to normalize tissue texture data collected in different centers.

Europe↗
PubMed1999

[Definition criteria for a magnetic resonance quality assurance program: multicenter study].

PURPOSE: We report the preliminary results of a multicenter trial aimed at defining methods, reference values and frequency of measurements for an MR quality assurance program. In particular, we stress the definition of two attention levels (investigation and intervention) for image uniformity and signal-to-noise ratio (SNR) by means of short- and long-term measurements. MATERIAL AND METHODS: The short-term protocol consisted of 10 successive spin-echo (SE, 2 echoes) acquisitions and was repeated after 24 hours. Measurements were made with the same test phantom which was circulated among all the participating centers. Image uniformity and SNR were evaluated using the software available on each MR unit. The long-term protocol, consisting of a single SE acquisition with the same parameters used for the short-term one, was performed once a month for 12 months. A mid term protocol was also performed twice a week for 5 weeks, and the analysis of the results is still in progress. RESULTS AND DISCUSSION: The short-term protocol results allowed absolute comparison of system performance. Uniformity and SNR were significantly different among centers (p < 0.05), also in the statistical comparison of two MR units of the same model (Siemens Magnetom SP63-1.5 T). Overall, three 1.5 T systems provided similar SNR values, while the results obtained for the 1 T system were markedly lower (51% of the maximum). This result can be explained by the dependence of the analytical expression of SNR on the magnetic field. The other 1.5 T system performed more poorly than the others operating at the same magnetic field. This difference can be explained by the specific characteristics of the coil and by technological aging. Because of the small sample size (5 units), the maximum variation coefficients (3% for the first echo and 3.5% for the second one) were assumed as a reference value for the both parameters (SNR and uniformity). These values were used for the long-term analysis: at every measurement the evaluated parameter was statistically compared with the result of the previous month. We propose to set an investigation level at p = 0.05: when the newly measured parameter differs from the previous value (p < 0.05), we should investigate if this is due to a normal long-term variation or to a system fault. The intervention level is then defined as the 95% prediction interval of the evaluated parameter regression vs time. Measurements that do not fall within the prediction interval are not used for future statistics. CONCLUSIONS: Some preliminary results concerning SNR and uniformity were obtained in the investigation performed on 5 MR systems to define methods and references for a Quality Assurance program. We introduced an "investigation level" and an "intervention level" related to short-term and long-term variability. The investigation levels could be a useful reference value to predict the short-term variability of an MR system with similar characteristics, thus avoiding a long and onerous series of measurements. Concerning the optimization of measurement frequencies, the preliminary analysis of these results showed that a daily measurement frequency is excessive in stable equipment conditions, while monthly measurements showed that the investigation level was often exceeded. However, frequency optimization will be investigated after the analysis of the mid-term measurements, which is still in progress.

Magnetic Resonance Imaging↗
PubMed1995

Characterization of parotid gland tissue: a description of an MRI protocol set-up and results of in-vivo applications.

A reliable protocol for proton T2 mapping of the parotid region was set up for future characterization of parotid gland disease. A Carr-Purcell-Meiboom-Gill sequence, phase compensated, available on our 1.5 T imager, was selected and acquisition parameters were chosen on the basis of tests performed on phantoms (agarose-doped gels with T2 in the physiological range). Some experiments were carried out to evaluate the accuracy of T2 calculations for selective and nonselective refocussing pulses, for image uniformity corrections, and for different situations of slice shift and repetition times. The chosen protocol was then applied to in vivo evaluations to check the long-term precision by means of repeated measurements performed on the same subject over a 2-month period. Two or more reference gels were positioned both in the phantom and volunteer at the edge of the field-of-view (FOV). Image postprocessing consisted of an automatic procedure, written by the authors in Fortran 77, that selected the best fit for each pixel between mono- and biexponential decay models, and prepared four parametric images (T2 and Rho slow and fast contribution, Rho being a function of proton density and of T1) that may be used for future elaborations. The phantom experiment results showed an accuracy of 2.5% if a linear correction was performed using the reference gels at the edge of the FOV. No significant differences in accuracy were found between selective and nonselective refocussing pulse, and a homogeneity correction was not demonstrated necessary. The measurements performed on four volunteers showed that the best decaying model for healthy parotid tissue was monoexponential. Evaluated T2 resulted 80.18 +/- 6.11 ms (72.96 +/- 4.97 ms for uncorrected results). Long-term reproducibility of the group of measurements from one volunteer, summarizing all the measurement errors, ranged from 0.9 to 8.5%. The two-way ANOVA that was carried out considering the two classes of volunteers and of parotid positions (right or left) showed that differences found between the two parotids were not significant, while T2 differences among individuals are significant if a probability level higher than 1.1% is accepted. As in this case, the main source of error can be attributed to the biological variations among individuals. Future statistics collected on patients for the T2 evaluations of the pathologic tissue will clarify whether the T2 relaxation is a sufficient parameter for T2 discrimination of healthy and pathologic tissue.

Humans↗
PubMed1993

85Sr contaminant as a reliable tracer of 89Sr for monitoring urinary radioactivity in patients treated with 89Sr for bone metastases.

Measurement of radioactivity levels in the urine of patients undergoing strontium-89 therapy can be used to evaluate the efficacy of therapy or for patient's management (radiation protection rules and waste disposal). The complex beta counting procedures require extensive sample manipulation during preparation of the liquid scintillation cocktail. The high activity levels that may be found permit one to measure 89Sr activity sample by counting the low yield gamma emission (909 keV) of the radionuclide. However, the contamination of 85Sr due to the reaction for producing 89Sr, if measured with sufficient precision, could be used to evaluate 89Sr activity in urine samples. In other words, the contaminant 85Sr can be used as a tracer of 89Sr. This method was tested in four patients and the accuracy was found to be sufficient to obtain the individual time-activity curves of the urinary excretion.

Bone Neoplasms↗
PubMed1992

[Results of the quality control of magnetic resonance images].

The results are reported of an image quality control performed by the Medical Physics Dept. of Spedali Civili, Brescia, Italy, after the implementation of an MR unit (Siemens-Magnetom 1.5 T) in the Radiology Department. Image quality parameters were evaluated, with the methods suggested in literature, for test objects images acquired in the conventional projections (axial, sagittal, and coronal) using RF body and head coils. Our aim was to evaluate system evolution during optimization of the equipment and to identify, when possible, eventual situations of stability and the time needed to achieve them. The results obtained for the uniformity and the signal-to-noise ratio parameters are evaluated as time curves with the analysis of linear regressions of parameters evolution over time. The measurements were made over a 14-month period, on a fortnight basis. The long-term variations are emphasized. The uniformity parameter exhibits no significant changes over time, while signal-to-noise ratio tends to increase, mostly due to noise decrease. Noise was observed to stabilize in the last months. A second analysis, with a statistical test on the difference of two subsequent measurements, was carried out to confirm this trend. Stability periods could be identified for all parameters. As for noise, in particular, a stability interval from May to October 1990 confirmed the regression results. A normality range was defined in this period as a reference for subsequent measurements.

Magnetic Resonance Imaging↗
PubMed1990

Measurements of radiocesium transfer to milk and calculation of resulting dose in Brescia, Italy, following the Chernobyl accident.

Results are presented of several measurements on components of the cows' milk chain performed at our Medical Physics Service after the Chernobyl accident. Values were obtained for Cs isotope transfer coefficients, namely, for cows' diet-milk and diet-feces transfers. Other measured parameters were the effective half-life of Cs in milk and the 134Cs:137Cs ratio. In addition, an evaluation of Cs contribution to the absorbed dose to population from milk is performed.

Accidents↗
PubMed1990

[Simulation of an instrumental head for 6 MeV electron beam therapy].

Simulation of a therapy head for 6 MeV electron beams. We present the results of a simulation, performed using a Monte Carlo method, of depth dose curves in water for electron beams of initial kinetic energy of 6.4 MeV, generated by a radiotherapy microtron MM22 Scanditronix. The Fortran code in EGS4: comparison is made between simulated curves, obtained using various approximation criteria, and the experimental one.

Electrons↗
PubMed1977

Stereochemistry of the dTDP-glucose oxidoreductase reaction.

The stereochemical course of the dTDP-glucose oxidoreductase (EC 4.2.1.46) reaction was studied using enzyme partially purified from Escherichia coli and dTDP-(6R)- and (6S)-[4-2H, 6-3H]glucose as substrate. The latter was prepared enzymatically by reduction of (3R)- and (3S)-3-P-[3-3H]glycerate to the 1-deuterated 3-P-glyceraldehyde with (4S)-[4-2H]NADH, followed first by conversion to glucose-1-P with the glycolytic enzymes, and then by transformation into the dTDP derivative. The stereospecifically labeled dTDP-glucose samples were mixed with nonlabeled carrier material and converted to dTDP-4-keto-6-deoxyglucose, which contained a chiral methyl group as shown by chirality analysis of the acetic acid resulting from Kuhn-Roth oxidation of the sugar nucleotide. These results confirm that the hydrogen transfer from C4 to C6 is intramolecular and show that the migrating hydrogen replaces the 6-hydroxyl group with inversion of configuration. Assuming that the hydrogen transfer, since it is intramolecular, must be suprafacial, it follows that the elimination of water from C5 and C6 is formally syn, whereas the reduction of the resulting delta5,6-double bond formally involves an anti addition of H+ and H-.

Deuterium↗
PubMedDate not supplied

Enzymatic-ultraviolet determination of glucose and fructose in wine: collaborative study.

This collaborative study on the determination of glucose and fructose in wine was performed by 18 laboratories on 4 matched pairs of commercial wine. The method uses the enzymes hexokinase, glucose-6-phosphate dehydrogenase, and phosphoglucose isomerase and the coenzyme nicotinamide-adenine dinucleotide phosphate. Both glucose and fructose can be determined in the same sample without separation. The method is simple but care is necessary to ensure precise transfer of small volumes. Repeatability and reproducibility standard deviations for glucose ranged from 2.6 to 14.6 mg/L and 4.7 to 16.5 mg/L, respectively. Repeatability and reproducibility values for fructose ranged from 2.4 to 16.1 mg/L and 6.0 to 21.3 mg/L, respectively. The method has been adopted official first action.

Fructose↗
PubMedDate not supplied

Enzymatic-ultraviolet determination of L-citric acid in wine: collaborative study.

A collaborative study was carried out on an enzymatic method for the determination of L-citric acid in wine, using the enzymes citrate lyase, malate dehydrogenase, and lactate dehydrogenase and the coenzyme nicotinamide-adenine dinucleotide phosphate. The study was performed by 18 laboratories using 4 blind duplicates of commercial wine. The method is simple and shows good precision. Coefficients of variation (CV) for reproducibility ranged from 1.8 to 3.4%; CVs for repeatability ranged from 0.76 to 2.62%. Analysts are cautioned to check the linear absorbance response of their spectrophotometers when performing this assay and also to take care in pipetting the relatively small volumes used in this procedure. The method has been adopted official first action.

Citrates↗