Analysis of Image Gently Abdominal CT Protocol With the Use of Body Phantom Adapted to the Japanese Size

Optimization of pediatric FDG-PET/CT examinations based on physical indicators using the SiPM-PET/CT system

OBJECTIVE

This study aimed to investigate the appropriate Silicon photomultiplier -PET/CT acquisition and image reconstruction conditions for each age group.

METHODS

The original phantom was developed to reflect the thickness and width of the torso in each age group (neonates, 1-year-olds, 5-year-olds, 10-year-olds, 15-year-olds, and adults). The ratio of hot spheres to background radioactivity was 4:1, and the radioactivity concentration was adjusted according to the Japanese consensus guidelines for appropriate implementation of pediatric nuclear medicine examinations. We evaluated the root mean square error (RMSE) as an assessment/function of the standardized uptake value of each hot sphere, the background variability (N10 mm), the % contrast of the hot sphere (QH, 10 mm/N10 mm), and the noise equivalent counts to determine the optimal reconstruction parameters and the appropriate acquisition time.

RESULTS

The minimum RMSE was obtained by setting the half-width of the Gaussian filter to 0-2 mm for iteration 1 or 2 and to 2-4 mm for iteration 3 or more. The acquisition times that satisfied the image quality equivalent to 120 s acquisitions in the adult phantoms were 30 s in the neonatal and 1-year-old phantoms, 60 s in the 5- and 10-year-old phantoms, and 75 s in the 15-year-old phantoms.

CONCLUSION

This study demonstrated that good PET images could be obtained with short acquisition times when the examination is performed under appropriate reconstruction conditions.

DEVELOPMENT OF A SPECIALISED TAPE MEASURE TO ESTIMATE THE SIZE-SPECIFIC DOSE ESTIMATE

The risk in computed tomography (CT) examinations is radiation exposure. We aimed to develop a specialised tape measure for determining the size-specific dose estimate (SSDE) for patients undergoing CT scans. The scanning parameters used were those of the abdominal protocol in our institute. With this method, the SSDE220 and standard deviations obtained from CT images for the liver, pelvic and lung areas, corresponded closely to the SSDEtape and standard deviations obtained using the tape measure. We thus devised a new idea that allows the estimation of the SSDE220 using a specialised tape measure before the CT examination, allowing for an informed explanation of the radiation dose to the patient. Although the tape measure developed in this study is specific to one particular CT instrument, the method could be adapted to a wide range of radiography applications.

DEVELOPMENT OF RADIATION DOSE CALCULATION SOFTWARE USING THE SIZE-SPECIFIC DOSE ESTIMATE

We aimed to develop a software for facilitating absorbed dose per pixel (pixel dose) calculation using a size-specific dose estimate (SSDE). We calculated the pixel dose at nine equal points inserted into the radiophotoluminescence glass dosemeter (RPLD) and compared the pixel dose with the measured doses using RPLD. With this method, the relative errors of average pixel dose was -0.1% for adults and 2.86, 3.36 and 1.17% for those aged 10, 5 and 1 years without tube current modulation, respectively. In contrast, the relative error of SSDE was 17.37% for adults and 20.38, 20.73 and 19.20% for those aged 10, 5 and 1 years, respectively. In other words, the pixel dose was almost equal to the measured doses. Therefore, our software can be useful for determining arbitrary point.