Interchangeable Patient-Specific Receive-Only Carotid Coils for Simultaneous Imaging with Radio Frequency Head Coils at 3 Tesla
Michael J Beck1, Dennis L Parker1, Bradley D Bolster, Jr.2, Seong-Eun Kim1, J Scott McNally1,3, Gerald S Treiman1,4,5, and J Rock Hadley1

1Utah Center for Advanced Imaging Research, Salt Lake City, UT, United States, 2Siemens Healthcare, Salt Lake City, UT, United States, 3University of Utah Department of Radiology, Salt Lake City, UT, United States, 4University of Utah Department of Surgery, Salt Lake City, UT, United States, 5Veterans Affairs Department of Surgery (VASLCHCS), Salt Lake City, UT, United States


We developed interchangeable carotid coils that can image simultaneously with clinical head coils. Both 7 and 9 channel carotid coils were built to demonstrate the interchangeability concept. SNR results show that the 7 channel coil has ~4x the SNR and the 9 channel coil has ~3x the SNR of the commercial neck coil at the carotids. The carotid coils image simultaneously with a head coil providing greater coil sensitivity at the carotid bifurcation and extending total coverage from the carotid bifurcation to the circle of Willis.


High Resolution Magnetic Resonance Imaging (MRI) of the human carotid bifurcation can be achieved with dedicated carotid coils due to the increase in signal-to-noise ratio (SNR) they provide (1-5); however dedicated carotid coils with a two paddle design have a small field of view (FOV), are hard to position reproducibly and are typically not designed for integration with a clinical head coil. Large FOV neck coils are designed to accommodate the full range of patient neck habitus at the expense of SNR. Clinically, only large FOV neck coils have been integrated with clinical head coils. To maximize SNR, a dedicated carotid coil would fit closely to and conform to the shape of the neck. Because of the great variability in neck habitus between subjects, it is difficult for any one neck coil to match all subjects and give maximum SNR for each subject. In this work we have developed the interchangeable carotid coil concept and demonstrate the concept by developing two interchangeable robust large FOV dedicated carotid coils (small and large circumference formers for medium height necks). These coils can image simultaneously with clinical head coils without the need of extra positioning hardware (Fig 1). This integration provides extended high resolution vessel imaging from the carotid bifurcation to the circle of Willis.


The interchangeable concept was tested by building a 7 channel carotid coil (7Rx coil) (Fig 1a) and a 9 channel carotid coil (9Rx coil) (Fig 1b) that form fits to the neck and works in conjunction with the 3T Head/Neck 20 coil (large FOV coil). The thermoplastic formers were molded to volunteer’s necks who had the desired neck diameter. Then using a ladder array configuration, 7 mm wide copper traces were bonded to the former. Electromagnetic simulations aided in determining the coil element dimensions. The 7Rx coil elements are 6.5-7.5 cm long and vary in width from 2.5-3.0 cm; the 9Rx coil elements vary in width from 2.5–3.5 cm and are 6-12 cm long. Each element was attached to a preamp via a 60 cm cable (the net length of the cable was 40 cm since 20 cm was used for a solenoid balun). That cable length resulted in negligible SNR loss so that the preamp housing could be placed next to the head coil and not on the patient’s torso. Preamps were not placed at the coil to keep the former thin enough to fit under the anterior neck portion of the large FOV coil when scanning large patients. The 7Rx and 9Rx coil formers were interchangeably connected to a single preamp station using low loss connectors (Fig 1c). Each channel was actively and passively decoupled and isolation, between adjacent elements of the array, was achieved with capacitive decoupling in the common leg between elements. Imaging measurements were performed on the MAGNETOM Prisma (Siemens Healthcare, Erlangen, DE). Images were acquired with approval from our institutional review board.


Comparing the 7Rx coil (Fig 2a), the 9Rx coil (Fig 2c), and the large FOV neck coil (Fig2b,d) shows that the 7Rx coil and 9Rx coils demonstrate SNR gains of approximately 4x and 3x over the large FOV coil at the carotids (~1.75 cm and ~ 4 cm below the surface of the skin respectively) for these volunteers (6). Coupling between the Siemens head coil and the 7Rx (Fig 3a) and 9Rx (Fig 3b) coils was negligible. Inverse geometry factor maps for both carotid coils (Fig 4) show that acceleration can be done in both the anterior-posterior and left-right phase encoding direction (7). Fig 5 compares clinical images obtained using the 9Rx coil and the large FOV neck coil. The 9Rx coil has significantly better vessel depiction and the 7Rx coil gives similar results. Fig 5 also demonstrates the large FOV of the carotid coil, eliminating the need to reposition it due to varying carotid bifurcation location. Future work will include determining the minimum number of interchangeable neck formers for sufficient imaging of all neck habitus and the optimal shape and size of these formers. Finally, the carotid coils will improve imaging of the neck for other purposes.


We have presented interchangeable carotid coils that provide significantly higher SNR than the standard 3T product head/neck coil at the location of the carotid bifurcation. The carotid coils image simultaneously with a head coil providing greater coil sensitivity in the carotid bifurcation and extending total coverage from the carotid bifurcation to the circle of Willis without the need for positioning hardware.


We would like to acknowledge Siemens Healthcare for providing the funding for this project.


1. Hadley et al. Relative RF coil performance in carotid imaging. Magn Reson Imaging. 2005;23:629-639.

2. Hayes et al. Surface coil phased arrays for high-resolution imaging of the carotid arteries. J Magn Reson Imaging. 1996;6:109-112.

3. Liffers et al. Geometrical optimization of a phased array coil for high-resolution MR imaging of the carotid arteries. Magn Reson Med. 2003;50:439-443.

4. Balu et al. Improvements in carotid plaque imaging using a new eight-element phased array coil at 3T. J Magn Reson Imaging. 2009;30:1209-1214.

5. Tate et al. Increased vessel depiction of the carotid bifurcation with a specialized 16-channel phased array coil at 3T. Magn Reson Med. 2013;69:1486-1493.

6. Kellman et al. Image reconstruction in SNR units: a general method for SNR measurement. Magn Reson Med. 2005;54:1439-1447.

7. Pruessmann et al. SENSE: sensitivity encoding for fast MRI. Magn Reson Med. 1999;42:952-962.


The Siemens 20 channel head/neck coil with the A) 7 channel carotid coil and B) the 9 channel carotid coil. The neck coil on the Siemens coil limits the size of the carotid coil formers. Also shown are the C) connectors allowing the carotid coils to be interchangeable.

SNR comparison between the A) 7 channel carotid coil and the B) commercial neck coil and the C) 9 channel carotid coil and the D) commercial neck coil. 2D GRE sequence, TE/TR=4.0/500ms, Flip Angle=90 Degrees, Matrix Size=320x320, FOV=300x300 mm, Bandwidth=260 Hertz/pixel.

Correlation plots between the commercial head coil (1-16) and the A) 7 channel carotid coil (17-23) and the B) 9 channel carotid coil (17-25). Maximum correlation between carotid coil elements is less than 0.36. Maximum correlation between carotid coils and the head coil is less than 0.27.

Inverse g-factor maps for 7 channel carotid coil A) anterior-posterior and B) left-right and for the 9 channel carotid coil C) anterior-posterior and D) left-right.

Clinical Images comparing image quality between A) 9 channel carotid coil and the B) commercial neck coil. Image results for the 7 channel carotid coil are similar to the 9 channel carotid coil. 3D T1w SPACE sequence with DATE flow suppression, TE/TR=22/800ms, isotropic voxel dimension=0.73mm and scan time=5minutes.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)