1 3 Magn Reson Mater Phy DOI 10.1007/s10334-015-0501-8 RESEARCH ARTICLE Surface coil with reduced specific absorption rate for rat MRI at 7 T Sergio E. Solis-Najera 1 · Rodrigo Martin 1,2 · Fabian Vazquez 1 · Alfredo O. Rodriguez 2 Received: 27 April 2015 / Revised: 6 September 2015 / Accepted: 15 September 2015 © ESMRMB 2015 Keywords Specific absorption rate · Slotted surface coil · Animal model Introduction The use of rodent models to study human disease has resulted in a surge of interest in developing animal mag- netic resonance imaging (MRI) at higher fields [1–7]. For this reason, it is important to investigate how to improve image quality, which, in turn, will necessarily lead us to new methods to improve the signal-to-noise ratio (SNR). One way to meet this goal is through radio frequency (RF) coil technology. Doty et al. [8] and Haase et al. [9] have reviewed the basic physics, technology, and applications of RF coils for small-animal MRI, and more recently, other phase-array coil designs have been introduced [10–12]. Cryogenic MRI probes have been used to increase the sen- sitivity of coils for rat imaging (reviewed by Darrase and Ginefri [13]). Because the MR coil has a strong influence on SNR, specially tailored coils are critical for imaging the rat brain. The coil geometry plays an important role in the MRI experiment to improve the SNR and to reduce the possible damage to the tissue as measured by the specific absorption rate (SAR) numerical computations [14]. Bottomley and Roemer [15] have studied theoretical SAR produced by a circular coil and a figure-eight-shaped coil. The measure- ment of SAR inside a living object is impractical and nearly impossible at present, making it necessary to numerically estimate the electromagnetic field quantities. For decades, SAR has been calculated to design and evaluate different general RF coil geometries for MRI using anatomical mod- els of the human subject. Abstract Objective A scaled-down slotted surface radio frequency (RF) coil was built, and the specific absorbance rate (SAR) in 100 mg of tissue (SAR 100 mg ) produced in a rat brain phantom was computed at 7 T. Materials and methods A slotted coil 2-cm in diameter with six circular slots was developed. Its theoretical and experimental performance was computed and compared using the signal-to-noise ratio (SNR) expression and phan- tom images obtained with a spin echo sequence. Electro- magnetic simulations were performed using the finite inte- gral method with saline sphere and rat brain phantoms. SAR 100 mg was computed for the circular coil, by varying its radius, and was also computed for the slotted coil. Results The slotted coil quality factor gave a twofold increment over the circular coil, and noise was reduced by 17 %. The experimental SNR of the slotted coil produced a 30 % improvement for points near the coil plane. The theo- retical and experimental results showed substantial agree- ment. Axial map histograms and profiles showed greater SAR 100 mg values for the circular coil than for the slotted coil. Conclusions The slotted surface coil offers improved per- formance and low SAR 100 mg for rat brain imaging at 7 T. This approach may be used with new RF coils to investi- gate SAR in humans. * Alfredo O. Rodriguez arog@xanum.uam.mx 1 Department of Physics, Faculty of Sciences, Universidad Nacional Autonoma de Mexico, 04510 Mexico, D.F., Mexico 2 Department of Electrical Engineering, Universidad Autonoma Metropolitana Iztapalapa, 09340 Mexico, D.F., Mexico