Μέτρηση καταναλωτικών προτιμήσεων για τα προϊόντα ιδιωτικής ετικέτας των Σούπερ Μάρκετ σε σχέση με τα επώνυμα προϊόντα ανά προϊοντική κατηγορία

Περίληψη: Στόχος της εργασίας είναι η μέτρηση των προτιμήσεων των καταναλωτών σχετικά με τα προϊόντα ιδιωτικής ετικέτας στα σουπερμάρκετ και ιδιαίτερα η σύγκριση τους με τα επώνυμα προϊόντα. H προσέγγιση θα γίνει για κάθε προϊοντική κατηγορία ξεχωριστά. Θα χρησιμοποιηθούν πρωτογενή δεδομένα τα οποία θα συλλεχθούν με χρήση ερωτηματολογίων τόσο σε σουπερμάρκετ όσο και μέσω του διαδικτύου. Για τη σχεδίαση του ερωτηματολογίου και την ανάλυση των δεδομένων που θα συλλεχθούν θα γίνει χρήση της μεθόδου CONJOINT ANALYSIS

Quantitative accuracy of177Lu SPECT imaging for molecular radiotherapy

The purpose of this study is to investigate the optimal reference geometry for gamma camera calibration. Yet another question of interest was to assess the influence of the number of 3D Ordered Subsets Expectation Maximization (3D-OSEM) updates on activity quantification for SPECT imaging with177Lu. The accuracy of177Lu activity quantification was assessed both in small and in large objects. Two different reference geometries, namely a cylindrical homogeneous phantom and a Jaszczak 16 ml sphere surrounded by cold water, were used to determine the gamma camera calibration factor of a commercial SPECT/CT system. Moreover, the noise level and the concentration recovery coefficient were evaluated as a function of the number of 3D-OSEM updates by using the SPECT/CT images of the reference geometry phantoms and those of a cold Jaszczak phantom with three hot spheres (16ml, 8ml and 4ml), respectively. The optimal choice of the number of 3D-OSEM updates was based on a compromise between the noise level achievable in the reconstructed SPECT images and the concentration recovery coefficients. The quantitative accuracy achievable was finally validated on a test phantom, where a spherical insert composed of two concentric spheres was used to simulate a lesion in a warm background. Our data confirm and extend previous observations. Using the calibration factor obtained with the cylindrical homogeneous phantom and the Jaszczak 16 ml sphere, the recovered activity in the test phantom was underestimated by -16.4% and -24.8%, respectively. Our work has led us to conclude that gamma camera calibration performed with large homogeneous phantom outperforms calibration executed with the Jaszczak 16ml sphere. Furthermore, the results obtained support the assumption that approximately 50 OSEM updates represent a good trade-off to reach convergence in small volumes, meanwhile minimizing the noise level

Validation anthropomorphic phantom.

<p>A) Coronal, B) sagittal and C) transaxial CT views of the validation anthropomorphic phantom. D) transaxial view of fused SPECT/CT images.</p

Results of the noise values for the Hp reference geometry.

<p>Results of the noise values for the Hp reference geometry.</p

Concentration recovery coefficient for the the Js geometry.

<p><i>cRCs</i> data versus <i>COV</i> and <i>EI</i> for the 16ml, 8ml and 4ml sphere considered in the Rp phantom and relative to A) 5 subsets, B) 10 subsets and C) 15 subsets. The continuous vertical lines refer to the 17% noise threshold.</p

<i>cRC</i> values for the Rp phantom.

<p>The data in the table corresponds to the points in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0182888#pone.0182888.g005" target="_blank">Fig 5</a> relative to the 16 ml sphere.</p

CT images of the phantoms used for SPECT calibration and activity recovery evaluation.

<p>From left to right: coronal (first column), sagittal (second column) and transaxial (third column) CT views of A) Hp, B) Js and C) Rp phantom. The insets shown in the third column refer to the different volumes of interest (blue color) used for SPECT calibration (right inferior corner of A) and B)), noise (left superior corner of A), together with the location of VOI_w) and activity recovery (right inferior corner of C)).</p

Concentration recovery coefficient for the Hp geometry.

<p><i>cRCs</i> data versus <i>COV</i> and <i>EI</i> for the 16 ml, 8 ml and 4 ml spheres considered in the Rp phantom and using A) 5 subsets, B) 10 subsets and C) 15 subsets. The continuous vertical lines refer to the 17% noise threshold.</p

Relationship between <i>COV</i> and <i>EI</i>.

<p><i>COV</i> as a function of <i>EI</i> and the subsets considered for A) Hp and B) Js geometry. The insets show the <i>COV</i> values as a function of the number of iterations.</p

Results of the noise values for the Js reference geometry.

<p>Results of the noise values for the Js reference geometry.</p