SUV_max of Normal Tissues in Pediatric and Adult Patients on FDG PET/MR

Objectives To measure SUV_max of various normal tissues in pediatric and adult patients and compare them to each other.

Methods A total of 22 (9 pediatric [<18 y/o] and 13 adult) patients with a pre-therapy FDG PET/MR scan (Biograph mMR) were included in this retrospective study. SUV_max in aortic arch, liver (periphery and central), subcutaneous fat (right and left flanks and chest walls) and lungs (right and left) was calculated by placing a 3-D ROI. Data were analyzed by 2-tailed Student’s t-test and Pearson’s correlation coefficient (R).

Results The average age was 14.3 + 2.7 years in pediatric and 54.6 + 10.7 years in adult patients. The average uptake time was 71 + 4.8 minutes in the pediatric and 67 + 3.8 minutes in the adult group (P=0.055). The SUV_max of various tissues are given in the attached table. There was a statistically significant difference in SUV_max between the pediatric and adult group in the aorta, liver and lungs (P<0.005 for all). Age and SUVmax correlated well across all these tissues (R > +0.6; P<0.01). There was no statistically significant difference in SUV_max of the subcutaneous fat between the pediatric and adult group, and this correlated only minimally with age (R < +0.3 across both tissues). There was no statistically significant difference in SUV_max measured in various locations (e.g. central and periphery of the liver) of the same tissue.

Conclusions The SUV_max of various normal tissues is lower than the corresponding known values on PET/CT, which goes along with the described generally lower SUV on PET/MR comparted to PET/CT. However, SUV_max is reproducible in various location of the same tissue, which indicates the robustness of the measurements. Finally, there is an age-dependent increase in SUV_max on PET/MR in aorta, liver and lungs from pediatric to adult patients. These preliminary data will help to establish normal tissue reference standards on FDG PET/MR but need to be confirmed in larger studies.