Receive Coil Array Research Articles

2D SENSE for faster 3D MRI.

Sensitivity encoding in two spatial dimensions (2D SENSE) with a receiver coil array is discussed as a means of improving the encoding efficiency of three-dimensional (3D) Fourier MRI. It is shown that in Fourier imaging with two phase encoding directions, 2D SENSE has key advantages over one-dimensional parallel imaging approaches. By exploiting two dimensions for hybrid encoding, the conditioning of the reconstruction problem can be considerably improved, resulting in superior signal-to-noise behavior. As a consequence, 2D SENSE permits greater scan time reduction, which particularly benefits the inherently time-consuming 3D techniques.Along with the principles of 2D SENSE imaging, the properties of the technique are discussed and investigated by means of simulations. Special attention is given to the role of the coil configuration, yielding practical setups with four and six coils. The in vivo feasibility of the two-dimensional approach is demonstrated for 3D head imaging, permitting four-fold scan time reduction.

Cardiac real-time imaging using SENSE. SENSitivity Encoding scheme.

Sensitivity encoding is used to improve the performance of real-time MRI. The encoding efficiency of single-shot and segmented echo-planar imaging is tripled by means of a 6-element receiver coil array. The feasibility of this approach is verified for double oblique cardiac real-time imaging of human subjects at rest as well as under physiological stress. Sample images are presented with scan times per image down to 13 msec at a spatial resolution of 4.1 mm, and 27 msec at a resolution of 2.6 mm. Moreover, multiple slice real-time imaging is demonstrated at a rate of 38 double-frames per second.

Sensitivity profiles from an array of coils for encoding and reconstruction in parallel (SPACE RIP).

A new parallel imaging technique was implemented which can result in reduced image acquisition times in MRI. MR data is acquired in parallel using an array of receiver coils and then reconstructed simultaneously with multiple processors. The method requires the initial estimation of the 2D sensitivity profile of each coil used in the receiver array. These sensitivity profiles are then used to partially encode the images of interest. A fraction of the total number of k-space lines is consequently acquired and used in a parallel reconstruction scheme, allowing for a substantial reduction in scanning and display times. This technique is in the family of parallel acquisition schemes such as simultaneous acquisition of spatial harmonics (SMASH) and sensitivity encoding (SENSE). It extends the use of the SMASH method to allow the placement of the receiver coil array around the object of interest, enabling imaging of any plane within the volume of interest. In addition, this technique permits the arbitrary choice of the set of k-space lines used in the reconstruction and lends itself to parallel reconstruction, hence allowing for real-time rendering. Simulated results with a 16-fold increase in temporal resolution are shown, as are experimental results with a 4-fold increase in temporal resolution. Magn Reson Med 44:301-308, 2000.

Contrast-enhanced 3D MRA using SENSE

Sensitivity encoding (SENSE) was used to improve the performance of three-dimensional contrast-enhanced magnetic resonance angiography (3D CE-MRA). Utilizing an array of receiver coils for sensitivity encoding, the encoding efficiency of gradient-echo imaging was increased by factors of up to three. The feasibility of the approach was demonstrated for imaging of the abdominal vasculature. On the one hand, using a SENSE reduction factor of two, the spatial resolution of a breath-hold scan of 17 seconds was improved to 1.0 x 2.0 x 2.0 mm(3). On the other hand, using threefold reduction, time-resolved 3D CE-MRA was performed with a true temporal resolution of 4 seconds, at a spatial resolution of 1.6 x 2.1 x 4.0 mm(3). CE-MRA with SENSE was performed in healthy volunteers and patients and compared with a standard protocol. Throughout, diagnostic quality images were obtained, showing the ability of sensitivity encoding to enhance spatial and/or temporal resolution considerably in clinical angiographic examinations.

SENSE: Sensitivity encoding for fast MRI

New theoretical and practical concepts are presented for considerably enhancing the performance of magnetic resonance imaging (MRI) by means of arrays of multiple receiver coils. Sensitivity encoding (SENSE) is based on the fact that receiver sensitivity generally has an encoding effect complementary to Fourier preparation by linear field gradients. Thus, by using multiple receiver coils in parallel scan time in Fourier imaging can be considerably reduced. The problem of image reconstruction from sensitivity encoded data is formulated in a general fashion and solved for arbitrary coil configurations and k-space sampling patterns. Special attention is given to the currently most practical case, namely, sampling a common Cartesian grid with reduced density. For this case the feasibility of the proposed methods was verified both in vitro and in vivo. Scan time was reduced to one-half using a two-coil array in brain imaging. With an array of five coils double-oblique heart images were obtained in one-third of conventional scan time. Magn Reson Med 42:952–962, 1999. © 1999 Wiley-Liss, Inc.

SENSE: Sensitivity encoding for fast MRI

New theoretical and practical concepts are presented for considerably enhancing the performance of magnetic resonance imaging (MRI) by means of arrays of multiple receiver coils. Sensitivity encoding (SENSE) is based on the fact that receiver sensitivity generally has an encoding effect complementary to Fourier preparation by linear field gradients. Thus, by using multiple receiver coils in parallel scan time in Fourier imaging can be considerably reduced. The problem of image reconstruction from sensitivity encoded data is formulated in a general fashion and solved for arbitrary coil configurations and k-space sampling patterns. Special attention is given to the currently most practical case, namely, sampling a common Cartesian grid with reduced density. For this case the feasibility of the proposed methods was verified both in vitro and in vivo. Scan time was reduced to one-half using a two-coil array in brain imaging. With an array of five coils double-oblique heart images were obtained in one-third of conventional scan time. Magn Reson Med 42:952-962, 1999.

Bilateral imaging using separate interleaved 3D volumes and dynamically switched multiple receive coil arrays.

Multiple receive coil arrays are often designed for unilateral imaging of anatomy having bilateral symmetry. A technique is described for extending the utility of such arrays to simultaneously image both bilaterally symmetric anatomical features. A separate, complete multiple receive coil array is placed at each location. Two separate, noncontiguous 3D volumes are then acquired, one at each location, in an interleaved fashion. High-impedance blocking networks are alternately activated and deactivated to minimize coupling between the arrays. It is demonstrated that there is no degradation in image quality when compared to a unilateral exam. A general method for analyzing the interactions between separate multiple coil arrays is presented.

Calculation of the signal-to-noise ratio for simple surface coils and arrays of coils.

This paper describes a new method to calculate the signal-to-noise ratio (SNR) of MR signals obtained from single receiver coils and arrays of receiver coils. The coils are assumed to be place on the surface of a conducting half-space and the SNR is sample-noise dominated. While in conventional methods line integrals over the electric currents in the coils are chosen to calculate the electric and magnetic fields, this new method uses surface integrals over magnetic dipoles covering the area enclosed by the antenna to derive these fields. Using this method, the SNR for simple circular and square coils was analytically calculated. The calculations show that the theoretical difference in SNR between circular and square antennas is very low. Furthermore, based on the new method, a derivation of the ultimate gain in SNR for arrays of surface coils is presented. The SNR of such an array approaches a limit even if the total number of coils is increased to infinity. This ultimate SNR of a coil array is 35.8% above that of a single circular-shaped, size-optimized and linear polarized coil.

MR flow measurement using RF phase gradients in receiver coil arrays.

Radio frequency (RF) phase gradients in the receiver coil field pattern can encode flow velocity information in magnetic resonance (MR) images in the form of phase variations. These phase variations are not readily observed in MR images because they are relatively small compared to phase variations caused by static magnetic field (B0) inhomogeneities, susceptibility variations, and other sources. However, the phase contributions from these other sources are independent of the receiver coil. Therefore, the RF phase gradient encoded flow information can be recovered by subtracting images obtained simultaneously using arrays of independent receiver coils and a multiple channel receiver. This flow velocity information can be extracted retrospectively from standard imaging sequences, including flow-compensated sequences. No additional time is required for the flow study as the flow measurements are made using sequences chosen for optimal imaging, and the images from each coil are obtained simultaneously. Initial results indicate that sufficient sensitivity is obtained to make flow measurements in the range of velocities commonly found in the carotid arteries and other major vessels. In principle, the method works with only two receiver coils. However, additional elements provide additional phase measurements that can be used to increase accuracy, remove ambiguities in flow direction or velocity calculations, and increase the region over which velocity measurements can be accurately made.

A programmable data acquisition and control system for magnetic resonance imaging: application to mutually coupled surface coil arrays and temperature monitoring

A programmable data acquisition and control system was developed for use in conjunction with magnetic resonance imaging (MRI). The controller consists of two functional blocks: a host system and a remote system. The remote system resides inside the shielded room housing the magnet. The host, an IBM compatible personal computer, is located at the technician's console. Communication between these devices is implemented over a fiber optic RS-232 data link. This configuration allows experiments to be performed remotely by using a series of keyboard typed commands, by programming the host to send a series of commands, or by directly programming the remote system. As an example of its capabilities, the controller was used to tune and match arrays of receiver coils for localized imaging and to record the rectal temperature of a sedated rat during image acquisition.