While test objects (phantoms) in MRI are crucial for sequence development, protocol validation and quality control, studies on the preparation of phantoms has been scarce, particularly at fields exceeding 3 Tesla. Here we present a framework for the preparation of phantoms with well-defined T 1 and T 2 times at 3 and 7 Tesla.
MethodsPhantoms with varying concentrations of agarose and Gd-DTPA were prepared and measured at 3 and 7 Tesla using T 1 and T 2 mapping techniques. An empirical, polynomial model was constructed that best represents the data at both field strengths, enabling the preparation of new phantoms with specified combinations of both T 1 and T 2 . Instructions for three different tissue types (brain grey matter, brain white matter, and renal cortex) are presented and validated.
ResultsT 1 times in the samples ranged from 698ms to 2820ms and from 695ms to 2906ms, whereas T 2 times ranged from 39ms to 227ms and from 34ms to 235ms for 3 and 7 Tesla scans, respectively. Models for both relaxation times used six parameters to represent the data with an adjusted R² of 0.998 and 0.997 for T 1 and T 2 , respectively.
ConclusionBased on the equations derived from the current study, it is now possible to obtain accurate weight specifications for a test object with desired T 1 and T 2 relaxation times. This will spare researchers the laborious task of trail-and-error approaches in test object preparation attempts.