Comparison Of Point Spread Functions Research Articles

Comparison of PSF and Non PSF BLOB based reconstructed image in Time-of-Flight PET/CT

Hybrid PET/CT imaging with the use of 18F FDG is a widely used imaging technique with major indications in oncology for staging, re-staging and monitoring response to therapy. There is a major issue of partial volume effect in PET images which affects image quality as well as quantitative accuracy in small lesions. Multiple attempts have been made to resolve these issues. The aim of our study was to look into impact of Point‐spread-function (PSF) on reconstructed attenuation corrected (AC) images of PET/CT and to find out best combination of the number of PSF iterations with regularization level while applying PSF.

Impact of Point-Spread Function Reconstruction on 68Ga-DOTATATE PET/CT Quantitative Imaging Parameters.

OBJECTIVE. The objective of our study was to investigate the impact of point-spread function (PSF) reconstruction and lesion size on 68Ga-tetraazacyclododecanetetraacetic acid-DPhe1-Tyr3-octreotate (DOTATATE) PET/CT quantitative parameters. MATERIALS AND METHODS. A total of 38 patients with 42 68Ga-DOTATATE PET/CT studies and 125 lesions were included. Scans were reconstructed with and without PSF modulation. For each lesion, the maximum standardized uptake value (SUVmax) and peak standardized uptake value (SUVpeak), metabolic tumor volume (MTV), total lesion somatostatin avidity, and tumor somatostatin receptor expression heterogeneity using the AUC method were measured. Intraclass correlation coefficient (ICC) and Bland-Altman analyses were used to compare PSF and non-PSF values. A subgroup analysis was performed to determine the impact of lesion size. RESULTS. Of the 125 lesions, 51 were in the liver, 31 in lymph nodes, 17 in bone, eight in pancreas, four in lung, and 14 in other sites. The ICCs between PSF and non-PSF values were excellent for SUVmax, SUVpeak, MTV, and total lesion somatostatin avidity (ICC = 0.97-0.99), and the ICC was good for tumor somatostatin receptor expression heterogeneity (ICC = 0.81). Comparison of PSF with non-PSF values showed a bias (mean percentage change ± SD) of 27.5% ± 14.7% for SUVmax, 15.5% ± 9.5% for SUVpeak, -18.6% ± 37.6% for MTV, 0.8% ± 28.1% for total lesion somatostatin avidity, and -7.1% ± 11.0% for tumor somatostatin receptor expression heterogeneity. Comparison of PSF with non-PSF values for lesions less than 2 cm (n = 75) showed corresponding biases greater than those for lesions 2 cm or larger (n = 50). CONCLUSION. PSF reconstruction effected higher values for SUVmax and SUVpeak, produced decreased values for tumor somatostatin receptor expression heterogeneity, and had a variable effect on MTV and total lesion somatostatin avidity depending on lesion size.

Impact of point spread function reconstruction on quantitative 18F-FDG-PET/CT imaging parameters and inter-reader reproducibility in solid tumors.

This study aims to determine the impact of point-spread function (PSF) reconstruction on quantitative PET/computed tomography (CT) indices and the inter-reader reproducibility of these measurements. The study was approved by the Institutional Review Board under a waiver of informed consent. A total of 42 oncology patients with 85 lesions (all ≥ 2 cm) were included. The PET/CT images were reconstructed with PSF (OSEM+TOF, 2i, 21s, all-pass filter) and without PSF (OSEM+TOF, 2i, 21s, 5 mm Gaussian). For each lesion, the maximum, mean, and peak standardized uptake values (SUV), total lesion glycolysis (TLG), and metabolic tumor volume (MTV) were measured by two readers (R1 and R2) using a semiautomatic gradient segmentation method. Intraclass correlation coefficient (ICC) and Bland-Altman analyses were performed. There was excellent correlation between non-PSF and PSF reconstruction PET/CT values (ICC ≥ 0.96 for all parameters, P < 0.0001). Comparison of PSF with non-PSF images showed a mean bias (percentage change) of +11.97% (R1) and +11.94% (R2) for SUV max, +7.63% (R1) and +7.82% (R2) for SUV mean, +7.45% (R1) and +7.37% (R2) for SUV peak, -0.82% (R1) and -0.1% (R2) for TLG, and -6.68% (R1) and -5.65% (R2) for MTV. PSF reconstruction resulted in a decrease in MTV in 77.6% (R1) and 83.5% (R2) of lesions. Percentage changes in PSF versus non-PSF indices were not related to the site of the lesions (P > 0.05). Close agreement was observed between two readers (ICC ranged between 0.9 and 1.0, P < 0.0001). The PSF reconstruction increased the SUV max, SUV mean, and SUV peak, as expected, whereas it tended to produce lower values for MTV and had variable effect on TLG. This can be attributed to the ability of PSF reconstruction to better discern tumor uptake from activity spill-out.

Comparison of Point Spread Function in p- and n-Channel CCDs

This paper presents a brief review of charge-redistrbution effects in charge-couple devices observed in both flat-field and spot data. Experiments are described that allow such phenomenon to be measured simply in the parallel transfer direction using only equipment capable of providing flat-field illuminations. A more detailed investigation into signal-dependant PSF shape distortions are descibed for both p- and n-channel CCDs of identical design. A number of methods to minimise the effect are presented that include different image electrode configurations and bias levels during integration and novel pixel architectures.

A circle-detection algorithm simulating wave propagation

Based on the analogy of the Hough transform and Huygens's principle, we present a circle-detection algorithm that numerically solves a two-dimensional wave equation using neighbor-based operations only, that is, Laplacian, frame addition, and multiplication of constants with frame contents, all basic functions of standard image processors. Because it does not use edge extraction, the algorithm detects circles even from low-contrast and blurred images. A comparison of point spread functions shows the algorithm to be equivalent to the weighted Hough transform but requiring much less computation. We applied the algorithm to disk-surface inspection of low-contrast and blurred microscopic images.

Experimentally measured scatter fractions and energy spectra as a test of Monte Carlo simulations

A method for the validation of Monte Carlo photon transport calculations is presented, with particular emphasis on the scatter component of such calculations. The method is based on a quantitative comparison of calculated and experimental scatter fractions. In addition, the method includes a qualitative comparison of point spread functions and energy spectra. An application of the method is demonstrated by comparing the results of an existing Monte Carlo code with experimental results obtained with a gamma camera viewing a point source of 99Tcm (140 keV gamma rays) centred within a water-filled cylinder. The results of the comparisons show good agreement between experiment and calculation. These results allow the code to be used with increased confidence in a variety of situations, and they define more precisely the region of applicability of the code. In addition, the determination of scatter fractions and energy spectra is useful for other applications. For example, scatter fractions can be a useful parameter for evaluating possible techniques for scatter compensation.