Rapid development of application-specific flexible MRI receive coils

Abstract

Over the last 30 years, there have been dramatic changes in phased array coil technology leading to increasing channel density and parallel imaging functionality. Current receiver array coils are rigid and often mismatched to patient's size. Recently there has been a move towards flexible coil technology, which is more conformal to the human anatomy. Despite the advances of so-called flexible surface coil arrays, these coils are still relatively rigid and limited in terms of design conformability, compromising signal-to-noise (SNR) for flexibility, and are not designed for optimum parallel imaging performance. The purpose of this study is to report on the development and characterization of a 15-channel flexible foot and ankle coil, rapidly designed and constructed using highly decoupled RF coil elements. Coil performance was evaluated by performing SNR ratio and g-factor measurements. In vivo testing was performed in a healthy volunteer using both the 15-channel coil and a commercially available 8-channel foot coil. The highly decoupled elements used in this design allow for extremely rapid development and prototyping of application-specific coils for different patient sizes (adult vs child) with minimal additional design consideration in terms of coil overlap and geometry. Image quality was comparable to a commercially available RF coil.

Characterization of a Low-Profile, Flexible, and Acoustically Transparent Receive-Only MRI Coil Array for High Sensitivity MR-Guided Focused Ultrasound

“…The coil is designed to be placed conformally, and in a close-fitting fashion, around the circumference of the patient's head (Figure 1). The RF elements consist of a thin malleable conductor construction [36,39,[42][43][44][45][46] comprising two parallel conductor wires encapsulated and separated by a dielectric material, the two parallel conductor wires maintained separate by the dielectric material along the entire length of the loop portion between terminating ends thereof (INCA, integrated distributed capacitors -thickness = 0.6 mm) with a polytetrafluoroethylene (PTFE) jacket (outer diameter ~1 mm) (GE Healthcare, Waukesha, WI, USA). The RF element is created from a flexible link resonator structure with the length of each resonator being no greater than 1/10th of the wavelength of the resonant RF field [47].…”

The Core of Medical Imaging: State of the Art and Perspectives on the Detectors

“…Parallel transmitter array coil was proposed for cardiac MRI [73], and an improvement of image quality and speed was obtained thanks to the increase in the number of transceiver coils in cardiac imaging at 7 T [74]. The use of flexible form-fitting phased-array coils assembled to be conformed to the anatomy of various sizes or shapes can significantly reduce the spatial distance between the coil and the human body portion, thus achieving the maximization of the image SNR [75]. Moreover, the use of a modular structure permits minimizing coupling between neighboring coil elements when the array is bent differently [76].…”

External waveguide magnetic resonance imaging for lower limbs at 3 T

“…Illustrations of LF MR imagers for lower extremity applications (a) and (b), and a whole‐body MR imager (c), commonly used in clinical practice. Schematics of RF coil arrays with multiple elements used to acquire images of lower limbs with whole‐body MR imagers: (d), 12 (e), 13 (f), 14 (g), 15 and (h) two standard birdcage coils for lower limbs 17 …”

“…[7][8][9][10] Another cause of patient motion is prolonged examination, which demands efficient imaging acquisition protocols involving optimal pulse sequences and acquisition times. 3,10,11 Additionally, special interest must be paid to adequate RF coils [12][13][14][15][16][17][18][19][20][21][22][23] ; ideally, an MR imager specially built for this purpose has been recommended. [24][25][26][27][28] The results of the still-improving imaging performances, new functionalities, and more affordable prices represent a pronounced trend toward equipping hospitals and clinics with MRI scanners.…”

“…20,[31][32][33][34][35][36][37][38][39] F I G U R E 1 Illustrations of LF MR imagers for lower extremity applications (a) and (b), and a whole-body MR imager (c), commonly used in clinical practice. Schematics of RF coil arrays with multiple elements used to acquire images of lower limbs with whole-body MR imagers: (d), 12 (e), 13 (f), 14 (g), 15 and (h) two standard birdcage coils for lower limbs 17 The traveling-wave (tw) MRI approach provides an alternative to coil arrays with a larger number of coil elements. 40 This method is based on the use of a waveguide and a transmitter antenna, in order to acquire images with larger fields of view, such as at 7 T, 41 9.4 T, 42 and 10.5 T. 43 The viability of twMRI at ultrahigh fields (UHFs) using small-bore systems has also been demonstrated.…”