Comparison of Standardized Uptake Values in Normal Structures Between PET/CT and PET/MRI in a Tertiary Pediatric Hospital: A Prospective Study

Objective: The purpose of this study was to compare standardized uptake values (SUVs) of normal tissues using MR attenuation-corrected versus CT attenuation-corrected (18)F-FDG PET in a pediatric population.

Subjects and methods: Thirty-five patients (21 boys; mean age, 13.3 years) referred for 47 PET/CT scans were recruited to undergo PET/MRI. MR attenuation correction was performed using an automated three-segment model. ROIs were drawn over nine normal structures to estimate SUV(min), SUV(mean), and SUV(max). Pearson rank correlation coefficients were calculated to compare SUVs obtained from MR and CT attenuation correction. In nine patients who underwent multiple PET/MRI studies, coefficients of variance and intraclass correlation coefficients were calculated to evaluate intrapatient SUV(max) variation.

Results: Mean (± SD) time to imaging after FDG injection was 108 ± 17 minutes for PET/CT and 61 ± 6 minutes for PET/MRI. PET/MRI SUVs in all tissues were lower than those for PET/CT (mean difference, -28.9% ± 31.1%; p < 0.05). Very high or high correlation between PET/MRI and PET/CT SUV(max) was found in brain (r = 0.72), myocardium (r = 0.95), and bone marrow (r = 0.85) (p < 0.001). Moderate correlation was found in liver (r = 0.54), fat (r = 0.41), mean blood pool (r = 0.40), and psoas muscle (r = 0.38) (p < 0.01). Weak correlation was found in lung (r = 0.12) and iliacus muscle (r = 0.12). Compared with PET/CT, PET/MRI systematically undermeasured SUV. In nine patients who underwent multiple PET/MRI examinations, moderate or strong agreement was found in the SUV(max) of six of nine tissues, similar to the corresponding PET/CT examinations.

Conclusion: Our study showed overall high correlation for SUV measurements obtained from MR attenuation correction compared with CT attenuation correction, although PET/MRI underestimated SUV compared with PET/CT. SUVs measured from PET/MRI indicated good intrapatient reliability.