Dynamic contrast enhanced-MRI in head and neck cancer patients: Variability of the precontrast longitudinal relaxation time (T10)

Purpose: Calculation of the precontrast longitudinal relaxation times (T-10) is an integral part of the Tofts-based pharmacokinetic (PK) analysis of dynamic contrast enhanced-magnetic resonance images. The purpose of this study was to investigate the interpatient and over time variability of T-10 in head and neck primary tumors and involved nodes and to determine the median T-10 for primary and nodes (T-10(p,n)). The authors also looked at the implication of using voxel-based T-10 values versus region of interest (ROI)-based T-10 on the calculated values for vascular permeability (K-trans) and extracellular volume fraction (v(e)). Methods: Twenty head and neck cancer patients receiving concurrent chemoradiation and molecularly targeted agents on a prospective trial comprised the study population. Voxel-based T-10's were generated using a gradient echo sequence on a 1.5 T MR scanner using the variable flip angle method with two flip angles [J. A. Brookes et al., Measurement of spin-lattice relaxation times with FLASH for dynamic MRI of the breast, Br. J. Radiol. 69, 206-214 (1996)]. The voxel-based T-10, K-trans, and v(e) were calculated using iCAD's (R) (Nashua, NH) software. The mean T-10's in muscle and fat ROIs were calculated (T-10(m,f)). To assess reliability of ROI drawing, T-10(p,n) values from ROIs delineated by 2 users (A and B) were calculated as the average of the T-10's for 14 patients. For a subset of three patients, the T-10 variability from baseline to end of treatment was also investigated. The K-trans and v(e) from primary and node ROIs were calculated using voxel-based T-10 values and T-10(p,n) and differences reported. Results: The calculated T-10 values for fat and muscle are within the range of values reported in literature for 1.5 T, i.e., T-10(m) = 0.958 s and T-10(f) = 0.303 s. The average over 14 patients of the T-10's based on drawings by users A and B were T-10(pA) = 0.804 s, T-10(nA) = 0.760 s, T-10(pB) = 0.849 s, and T-10(nB) = 0.810 s. The absolute percentage difference between K-trans and v(e) calculated with voxel-based T-10 versus T-10(p,n) ranged from 6% to 81% and from 2% to 24%, respectively. Conclusions: There is a certain amount of variability in the median T-10 values between patients, but the differences are not significant. There were also no statistically significant differences between the T-10 values for primary and nodes at baseline and the subsequent time points (p = 0.94 Friedman test). Voxel-based T-10 calculations are essential when quantitative Tofts-based PK analysis in heterogeneous tumors is needed. In the absence of T-10 mapping capability, when a relative, qualitative analysis is deemed sufficient, a value of T-10(p,n) = 0.800 s can be used as an estimate for T-10 for both the primary tumor and the affected nodes in head and neck cancers at all the time points considered. (C) 2010 American Association of Physicists in Medicine. [DOI: 10.1118/1.3427487]