Daisuke Kidera

Improvement in PET/CT image quality in overweight patients with PSF and TOF

ObjectiveThe aim of this study was to evaluate the effect of the point spread function (PSF) and time of flight (TOF) on PET/CT images of overweight patients in relation to the iteration number and the acquisition time.MethodsThis study consisted of a phantom study and a clinical study. The NEMA IEC body phantom and a 40xa0cm diameter large phantom (LG phantom) simulating an overweight patient were used in this study. Both phantoms were filled with 18F solution with a sphere to background ratio of 4:1. The PET data were reconstructed with the baseline ordered-subsets expectation maximization (OSEM) algorithm, with the OSEMxa0+xa0PSF model, with the OSEMxa0+xa0TOF model and with the OSEMxa0+xa0PSFxa0+xa0TOF model. The clinical study was a retrospective analysis of 66 patients who underwent 18F-FDG PET/CT. The image quality was evaluated using the background variability (coefficient of variance, CVphantom and CVliver) and the contrast (CONTHOT and SNR).ResultsIn phantom study, the CVphantom of the LG phantom was higher than that of the NEMA phantom. The PSF decreased the CVphantom of the LG phantom to the NEMA phantom level. The TOF information accelerated the CVphantom plateau earlier. The best relationship between the CVphantom and the CONTHOT was observed for the OSEMxa0+xa0PSFxa0+xa0TOF. In clinical study, the combination of PSF and TOF decreased the CVliver for overweight patients to that for normal weight patients while it increased the SNR similarly between two patient groups.ConclusionThe combination of the PSF and TOF correction improved the image quality of the LG phantom and overweight patients.

The edge artifact in the point-spread function-based PET reconstruction at different sphere-to-background ratios of radioactivity

ObjectiveThe aim of this study was to quantitatively evaluate the edge artifacts in PET images reconstructed using the point-spread function (PSF) algorithm at different sphere-to-background ratios of radioactivity (SBRs).MethodsWe used a NEMA IEC body phantom consisting of six spheres with 37, 28, 22, 17, 13 and 10xa0mm in inner diameter. The background was filled with 18F solution with a radioactivity concentration of 2.65xa0kBq/mL. We prepared three sets of phantoms with SBRs of 16, 8, 4 and 2. The PET data were acquired for 20xa0min using a Biograph mCT scanner. The images were reconstructed with the baseline ordered subsets expectation maximization (OSEM) algorithm, and with the OSEMxa0+xa0PSF correction model (PSF). For the image reconstruction, the number of iterations ranged from one to 10. The phantom PET image analyses were performed by a visual assessment of the PET images and profiles, a contrast recovery coefficient (CRC), which is the ratio of SBR in the images to the true SBR, and the percent change in the maximum count between the OSEM and PSF images (Δ % counts).ResultsIn the PSF images, the spheres with a diameter of 17xa0mm or larger were surrounded by a dense edge in comparison with the OSEM images. In the spheres with a diameter of 22xa0mm or smaller, an overshoot appeared in the center of the spheres as a sharp peak in the PSF images in low SBR. These edge artifacts were clearly observed in relation to the increase of the SBR. The overestimation of the CRC was observed in 13xa0mm spheres in the PSF images. In the spheres with a diameter of 17xa0mm or smaller, the Δ % counts increased with an increasing SBR. The Δ % counts increased to 91xa0% in the 10-mm sphere at the SBR of 16.ConclusionsThe edge artifacts in the PET images reconstructed using the PSF algorithm increased with an increasing SBR. In the small spheres, the edge artifact was observed as a sharp peak at the center of spheres and could result in overestimation.

Accuracy of amplitude-based respiratory gating for PET/CT in irregular respirations

ObjectiveWe evaluated the accuracy of amplitude gating PET (AG-PET) compared with phase gating PET (PG-PET) in relation to respiratory motion patterns based on a phantom analysis.MethodWe used a NEMA IEC body phantom filled with an 18F solution with a 4:1 sphere-to-background radioactivity ratio (12.6 and 2.97xa0kBq/mL). PET/CT scans were acquired in a motionless and moving state on a Biograph mCT. The respiratory movements were simulated by four different waveform patterns consisting of ideal breathing, breathing with a pause period, breathing with a variable amplitude and breathing with a changing baseline. AG-PET selects the narrow bandwidth containing 20xa0% of the respiratory cycle. PG-PET was reconstructed with five gates. The image quality was physically assessed using the percent contrast (QH,10mm), background variability (N10mm) recovery coefficient (RC), and sphere volumes.ResultIn regular motion patterns with ideal breathing and breathing with a pause period, the QH,10mm, RC and sphere volumes were not different between AG-PET and PG-PET. In the variable amplitude pattern, the QH,10mm of AG-PET was higher than that of PG-PET (35.8 vs 28.2xa0%), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.4 vs 8.6xa0mL). In the changing baseline pattern, the QH,10mm of AG-PET was higher than that of PG-PET (42.4 vs 16.7xa0%), the RC of AG-PET was higher than that of PG-PET and sphere volume of AG-PET was smaller than that of PG-PET (6.2 vs 9.8xa0mL). The N10mm did not differ between AG-PET and PG-PET, irrespective of the motion pattern.ConclusionAmplitude gating PET is considered to be more accurate than phase gating PET for examining unstable respiratory motion patterns, such as those involving a variable amplitude or changing baseline.

The influence of respiratory motion on the cumulative SUV-volume histogram and fractal analyses of intratumoral heterogeneity in PET/CT imaging

Objective The purpose of this study was to investigate the influence of respiratory motion on the evaluation of the intratumoral heterogeneity of FDG uptake using cumulative SUV-volume histogram (CSH) and fractal analyses.MethodsWe used an NEMA IEC body phantom with a homogeneous hot sphere phantom (HO) and two heterogeneous hot sphere phantoms (HE1 and HE2). The background radioactivity of 18F in the NEMA phantom was 5.3xa0kBq/mL. The ratio of radioactivity was 4:2:1 for the HO and the outer rims of the HE1 and HE2 phantoms, the inner cores of the HE1 and HE2 phantoms, and background, respectively. Respiratory motion was simulated using a motion table with an amplitude of 2xa0cm. PET/CT data were acquired using Biograph mCT in motionless and moving conditions. The PET images were analyzed by both CSH and fractal analyses. The area under the CSH (AUC-CSH) and the fractal dimension (FD) was used as quantitative metrics.ResultsIn motionless conditions, the AUC-CSHs of the HO (0.80), HE1 (0.75) and HE2 (0.65) phantoms were different. They did not differ in moving conditions (HO, 0.63; HE1, 0.65; HE2, 0.60). The FD of the HO phantom (0.77) was smaller than the FDs of the HE1 (1.71) and HE2 (1.98) phantoms in motionless conditions; however, the FDs of the HO (1.99) and HE1 (2.19) phantoms were not different from each other and were smaller than that of the HE2 (3.73) phantom in moving conditions.ConclusionRespiratory motion affected the results of the CSH and fractal analyses for the evaluation of the heterogeneity of the PET/CT images. The influence of respiratory motion was considered to vary depending on the object size.

standardization of dual time point (18F) 2-Deoxy-2-fluoro-D-glucose-positron emission tomography performed with different positron emission tomography scanners using partial volume correction

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