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Phantom standards with temperature- and field-independent relaxation rates for magnetic resonance imaging
1Nycomed Amersham Imaging, Wayne, PA 19087-8630, USA. keke@americas.nycomed.com
Rationale And Objectives:
For use as magnetic resonance imaging reference standards, the optimal set of phantoms should cover a wide range of T1 values, with each phantom having a T1 that is stable over time and is independent of temperature and magnetic field strength. To date, no set of phantoms fulfilling these four requirements has been prepared. In the current work, the construction of such optimal phantom standards is attempted.
Methods:
Two linear gadolinium DTPA polymers are used: the first with relaxivities that are independent of temperature and magnetic field strength, and the second with relaxivities that are independent of magnetic field strength, but have an opposite temperature dependence from that of the 1/T1 of the diamagnetic matrix (agarose gel or water). Depending on the desired T1, either one or a combination of the two agents is used.
Results:
Phantom standards were constructed with 1/T1 values that are independent of temperature (20-35 degrees C) and magnetic field strength (0.47-1.2 T) over a wide range of 1/T1 values (> or = 0.95 s-1). Phantom standards prepared in water were found to be stable with respect to 1/T1 for at least 18 months.
Conclusions:
Stable phantoms standards have been constructed covering a wide range of T1 values, where the T1 of any particular phantom is independent of temperature and magnetic field strength for magnetic resonance imaging conditions.