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Development of 1H/13C RF Head Coil for Hyperpolarized 13C Imaging of Human Brain
Junjie Ma1, Ralph S. Hashoian2, Chenhao Sun3, Steve M. Wright3, Alexander Ivanishev4, Robert E. Lenkinski4, Craig R. Malloy1,5, Albert P. Chen6, and Jae Mo Park1,4,7

1Advanced Imaging Research Center, UT Southwestern Medical Center, Dallas, TX, United States, 2Clinical MR Solutions, Brookfield, WI, United States, 3Electrical and Computer Engineering, Texas A&M University, College Station, TX, United States, 4Department of Radiology, UT Southwestern Medical Center, Dallas, TX, United States, 5Internal Medicine, UT Southwestern Medical Center, Dallas, TX, United States, 6GE Healthcare, Toronto, ON, Canada, 7Electrical Engineering, UT Dallas, Richardson, TX, United States

Synopsis

A customized 1H/13C RF head coil that consists of a 1H quadrature transmit (Tx) and receive (Rx) coil and 13C quadrature transmit and array receive (QTAR) coils was developed. The performance of the new head coil was evaluated using phantoms and compared to the existing 13C-only quadrature Tx/Rx (QTR) head coil. Metabolic imaging of human brain was performed using the 1H/13C head coil, following an injection of hyperpolarized [1-13C]pyruvate.

Background

A dedicated 1H/13C head coil is an essential piece of equipment for clinical neuroimaging studies using hyperpolarized 13C imaging. It is important to co-register the 13C images to the conventional 1H mages for appropriate interpretation of the metabolic data. Unfortunately, a 1H/13C head coil with multi-channel capability is not commercially available. Most human brain studies using hyperpolarized 13C pyruvate have been using a modified clamshell/paddle array coils1,2 or 13C-only head coils3. Therefore, a customized 1H/13C RF head coil that consists of a 1H quadrature transmit (Tx) and receive (Rx) coil and 13C quadrature transmit and array receive (QTAR) coils was developed in collaboration with Clinical MR Solutions. In this work, the coil safety was tested first, then the performance of the new head coil was evaluated using phantoms and compared to the existing 13C-only quadrature Tx/Rx (QTR) head coil (diameter=25cm). Finally, metabolic imaging of human brain was performed using the 1H/13C head coil, following an injection of hyperpolarized [1-13C]pyruvate.

Methods

A rigid nested design was applied to the 1H coil and the 13C Tx coil. The anterior 13C Rx array (5-8 channels) are attached to the inner surface of the 13C Tx coil, and the posterior Rx array (1-4 channels) are flexible to maximize the receive sensitivity. The entire anterior portion of the head coil is detachable for head positioning. The 1H channel and the 13C channel were tuned to the resonance frequencies at 3T. The 1H birdcage has a 15.2cm radius with the leg length of 30.5cm, and the 13C birdcage has a radius of 13.4cm with 25.4cm length. The structure of the head coil is shown in Figure 1A. All of the studies using the QTAR coil were conducted at a clinical 3T MR scanner (GE healthcare, 750w Discovery). To verify the safety of the 1H/13C coil, temperature change was measured in a saline phantom using a fiber optic temperature measurement system. Both the temperature changes (up to 0.08oC increase) and the SAR values (1.1W/kg) were within the safety guideline. A gadolinium-doped spherical [13C]bicarbonate phantom (0.4M, diameter=18cm) and non-labeled pure ethylene glycol (CH2OHCH2OH, 35M) cylindrical phantom (diameter=13cm) were used for the coil performance test. For the SNR comparison between the 1H/13C QTAR coil and the 13C QTR coil, a free induction decay chemical shift imaging (FID CSI) sequence was used (flip angle=90°, matrix size=16x16, TR=5s, FOV=24x24cm2). The B1+ profile was calculated using double-angle method with θ1=22.5° and θ2=45°. The coil was tested with a healthy subject (25 y.o. male) using a hyperpolarized 13C protocol that includes both 1H sequences (T2-weighted FSE with dual echo times, T2-weighted FLAIR, SWI, DWI) and 13C sequences (2D spiral CSI4).

Results and Discussion

The 1H SNR of the QTAR head coil was comparable to that of the standard 1H QTR GE head coil. The peak-integrated 13C images of individual channels acquired from the ethylene glycol phantom are shown in the Figure 1A. The SNR of the channel-combined 13C image (sum-of-square) from the QTAR coil was comparable to the SNR from the 13C QTAR coil (Figure 1B). The QTR coil outperformed the QTAR coil in terms of spatial homogeneity. Figure 2A shows multi-slice images of the bicarbonate phantom acquired from the 13C QTAR head coil with flip angle=45° (upper images) and flip angle=22.5° (lower images). The 13C B1+ map calculated by the double-angle method showed a homogeneous spatial profile (Figure 2B). Similarly, 1H B1+ map was also estimated as shown in Figure 2C. Figure 3 shows (A) 1H T2-weighted FSE images (echo time=11.3ms/56.7ms) and (B) hyperpolarized 13C images from an axial brain slice of the healthy subject. It was noted that 13C signal sensitivities from the posterior channels (ch 1-4) were higher compared to those from the anterior channels (ch 5-8, Figure 3C) primarily due to the asymmetrical positions of the 8 13C receiver coils from the brain. As is shown in Figure 3B, the channels 1-4 are typically positioned closer to the brain than the channels 5-8. Reshaping the channel 5-8 to make them more flexible would be beneficial to improve the inhomogeneous signal distribution.

Conclusion

The newly developed 1H-QTR/13C-QTAR head coil showed comparable SNRs in both 13C and 1H with standard 13C QTR and 1H QTR coils, respectively. The coil has two advantages: 1) Due to the multi-channel array receive in 13C, data acquisition can be accelerated through parallel imaging techniques. 2) The dual-frequency coil will allow proper 1H and 13C image co-registration and integration of hyperpolarized 13C sequences to the existing neuro 1H imaging protocols.

Acknowledgements

Clinical Research Team: We appreciate research nurses (Lucy Christie, Jeannie Baxter, Kelley Durner, Carol Parcel), Maida Tai, MR technician (Salvador Pena) and technical support for operating the SPINlab (Jeff Liticker, Crystal Harrison, Thomas Hever, Galen Reed, Richard Martin). We also thank Sergey Cheshkov and Ivan Dimitrov for guiding the coil safety test. Funding: The Mobility Foundation; The Texas Institute of Brain Injury and Repair; National Institutes of Health of the United States (P41 EB015908, S10 OD018468).

References

  1. Park, P. E. Z. Larson, J. W. Gordon, L. Carvajal, H.-Y. Chen, R. Bok, M. Van Criekinge, M. Ferrone, J. B. Slater, D. Xu, J. Kurhanewicz, D. B. Vigneron, S. Chang, and S. J. Nelson, “Development of methods and feasibility of using hyperpolarized carbon-13 imaging data for evaluating brain metabolism in patient studies.,” Magn Reson Med, Jan. 2018.
  2. V. Z. Miloushev, K. L. Granlund, R. Boltyanskiy, S. K. Lyashchenko, L. M. DeAngelis, I. K. Mellinghoff, C. W. Brennan, V. Tabar, T. J. Yang, A. I. Holodny, R. E. Sosa, Y. W. Guo, A. P. Chen, J. Tropp, F. Robb, and K. R. Keshari, “Metabolic Imaging of the Human Brain with Hyperpolarized 13C Pyruvate Demonstrates 13C Lactate Production in Brain Tumor Patients.,” Cancer Res., p. canres.0221.2018, May 2018.
  3. A. Mareyam, L. Carvajal, D. Xu, J. Gordon, I. Park, D. Vigneron, S. Nelson, J. Stockmann, B. Keil, and L. Wald, “31-Channel Brain Array for Hyperpolarized 13C Imaging at 3T.,” Int’l Soc Magn Reson Med. #1225, 2016.
  4. J. M. Park, S. Josan, T. Jang, M. Merchant, Y.-F. Yen, R. E. Hurd, L. Recht, D. M. Spielman, and D. Mayer, “Metabolite kinetics in C6 rat glioma model using magnetic resonance spectroscopic imaging of hyperpolarized [1-(13)C]pyruvate.,” Magn Reson Med, vol. 68, no. 6, pp. 1886–1893, Dec. 2012.

Figures

Figure 1. Coil structure and phantom images. (A) The new 1H/13C QTAR RF head coil is displayed. (B) The same phantom was tested for 13C imaging using a homemade 13C QTR coil for comparison.

Figure 2. B1+ homogeneities of the 1H/13C head coil. (A) Multi-slice 2D 13C images were acquired using two different flip angles (θ1 = 45° and θ2 = 22.5°). (B) Double-angle method was used for the calculation of B1+ mapping of 13C channel from the two data sets. (C) The same method was used for B1+ mapping of 1H channel.

Figure 3. In vivo brain imaging. (A) 1H images were acquired with short (left) and long echo times (right). (B) [1-13C] pyruvate and [1-13C] lactate images were acquired from a healthy volunteer with an injection of hyperpolarized [1-13C]pyruvate. The approximate positions of the 1H QTR coil and the 13C receiver array coils are shown in blue and red, respectively. (C) Hyperpolarized [1-13C]pyruvate images of individual channels.

Proc. Intl. Soc. Mag. Reson. Med. 27 (2019)
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