A detunable elliptic transmission line resonator for body imaging at 3 Tesla

Abstract

AbstractIn this work, we demonstrate and characterize a large‐volume radiofrequency (RF) coil insert used to perform human torso magnetic resonance imaging at 3 T. The coil is a transmission line resonator of elliptic cross‐section that can be actively detuned for operation with localized receive‐only surface coils. The coil fits within the 55 cm inner bore liner of a 3 T whole body imager and accommodates small‐ to medium‐sized torsos. Sixteen flat transmission line elements are used; each is 32 cm in length and composed of multiple microstrip capacitors spaced equally inside the elliptic shield (52 cm and 40 cm major and minor axes, respectively). A four‐port electrical drive was used to improve B1 homogeneity and power efficiency. The power required for a 90° 2 ms single side‐lobe sinc pulse for the chest loaded coil was less than 2 kW. Active detuning for operation with receive‐only surface coils was achieved by placement of a low‐voltage PIN diode network on each individual transmission line element. A quadrature pair of 10 × 15 cm2 rectangular surface coils with active detuning traps was used for high spatial resolution cardiac and spine imaging. Since the coil is completely portable, any anatomical region of interest may be centered within the active volume. The head loaded coil required less power and enabled the use of standard 180° pulses well within specific absorption rate limits. Occipital lobe images using a receive‐only quadrature 8 cm loop surface coil pair are also presented. As the number of high‐field whole body systems increases, an RF coil insert optimized for the torso provides an economical and efficient strategy for extending the capabilities of these systems beyond neuroimaging. © 2002 Wiley Periodicals, Inc. Concepts in Magnetic Resonance (Magn Reson Engineering) 15: 92–100, 2002.