Influence of Amplitude-related Perfusion Parameters in the Parotid Glands by Non-fat-saturated Dynamic Contrast-enhanced Magnetic Resonance Imaging

Purpose: To investigate the discrepancy of perfusion parameters of the parotid gland acquired by fat-saturated (FS) versus non-fat-saturated (NFS) dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Materials and Methods: Approved by a local institutional review board with written informed consent obtained, this study consisted of three parts. First, a retrospective study analyzed DCE-MRI data previously acquired using NFS (18 patients) or FS scans (18 patients). Second, a phantom study simulated the signal enhancements in the presence of Gd contrast agent at 6 different concentrations and 3 different fat contents. Finally, a prospective study recruited 9 healthy volunteers to investigate the influence of fat suppression on perfusion quantification on the same subjects. T tests and linear regression analysis were used for statistical analysis with Bonferroni correction applied for multiple comparisons. Results: Patients undergoing NFS DCE-MR scan showed significantly lower parameter A (5.08±2.95 a.u.), peak enhancement (PE) (34.44±12.48%), and slope (1.08±0.60%/s) as compared to 8.90±4.03 a.u., 74.55±13.79%, and 1.79±0.85%/s, respectively, in those with FS scan (all P<0.0167). Phantom study showed that the relative signal enhancement was proportional to the dose of gadolinium contrast agent and was higher in FS scan than in NFS scan. Volunteer study showed significantly lower parameter A (6.75±2.38 a.u.), PE (42.12±14.87%), and slope (1.43±0.54%/s) in NFS scan as compared to 17.63±8.56 a.u., 104.22±25.15%, and 3.68±1.67%/s, respectively, in those with FS scan (all P<0.005). These perfusion parameter differences were remedied by using skeletal muscles and pure water as reference on in vivo and phantom studies, respectively. Conclusion: DCE-MRI perfusion characterization is affected by the use of FS on fat-containing tissues such as parotid glands. The use of fat saturation is important to reduce the influence of parotid fat content on perfusion quantification. The selection of a relatively fat-free tissue as baseline is a simple and effective method to reduce bias from fat content in DCE MRI of the parotid glands.