Magnetic resonance study of virgin and explanted silicone breast prostheses. Can proton relaxation times be used to monitor their biostability?

The development of sensitive and non invasive magnetic resonance (MR) techniques for monitoring the fate of silicones in breast prostheses in vivo requires detailed knowledge of the MR properties of these silicones. To characterize changes in the proton dynamics, relaxation time measurements (T1 and T2) were obtained on virgin and explanted breast prostheses using both spectroscopic and imaging techniques in a magnetic field of 1.5 Tesla. Averaged transverse relaxation times (T2) were observed to depend neither on the measurement technique employed (virgin silicone, T2 = 160 +/- 5 msec with imaging and 154 +/- 9 msec spectroscopically) nor on the effect of being implanted in the body for various periods of time ranging from 4 months to 17 years (explanted silicone, T2 = 164 +/- 16 msec with imaging and 159 +/- 25 msec spectroscopically). Average longitudinal relaxation times (T1) were also found to be similar for virgin and explanted prostheses (virgin silicone T1 = 899 +/- 32 msec, explanted silicone T1 = 879 +/- 75 msec, measured with imaging), but appeared to depend on the measurement technique employed (virgin silicone T1 = 764 +/- 17 msec, explanted silicone T1 = 765 +/- 23 msec, measured spectroscopically). Although the measured relaxation times did not reveal any differences between virgin and explanted prostheses, marginal differences were detected between the relaxation times of explanted prostheses from different manufacturers. More reference data on standard silicone products may be required before changes in implanted silicone can be assessed using proton magnetic relaxation times.