An asymmetric quadrature birdcage body coil for hyperpolarized (HP) 3 He lung imaging at 1.5T is presented. The coil is designed to rest on top of the patient support and be used as a temporary insert in a clinical system. A two-part construction facilitates patient access and the asymmetric design makes maximal use of available bore space to ensure comfort. Highly homogeneous, circularly polarized RF magnetic fields are produced at 48.5 MHz using a conformal mapping method for the geometrical design, combined with an algebraic method to calculate the individual capacitance values on the birdcage coil's ladder network. Efficiency and isolation from the system's proton body coil are ensured by an integrated RF screen. The design methodology is readily applicable to other field strengths or nuclei. Improvements over existing 3 He coils were found in terms of sensitivity and transmit field homogeneity, an important feature in HP MRI. Magn Reson Med 60: 431-438, 2008.

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription.For more information, please contact eprints@nottingham.ac.uk Thomas's Hospital, Kings College, London; 3 Pulseteq Ltd., Wotton-under-Edge, Gloucestershire. Abstract:The design and operation of a receive-only liquid nitrogen (LN 2 ) cooled coil and cryostat suitable for medical image on 3T whole body MR scanner is presented. The coil size, optimised for murine imaging, was determined by using electromagnetic (EM) simulations. This process is therefore easier and more cost-effective than building a range of coils. A non-magnetic cryostat suitable for small animal imaging was developed having a good vacuum and cryogenic temperature performance. The cooled probe had an active detuning circuit allowing use with the scanner's built-in body coil. External tuning and matching was adopted to allow for changes to the coil due to temperature and loading. The performance of the probe was evaluated by comparison of signalto-noise (SNR) performance with the same radio-frequency (RF) coil operating at room temperature (RT). The performance of the RF coil at RT was also benchmarked against a commercial surface coil with similar dimensions to ensure a fair SNR comparison. The cryogenic coil achieved a 1.6 -2 fold SNR gain for several different medical image applications: For the mouse brain image, a 100 μm resolution was achieved in an imaging time of 3 minutes with an SNR of 25-40, revealing finer anatomical details unseen at lower resolution in the same time. For other heavy loading condition, such as hind legs and liver, the SNR enhancement was slightly reduced to 1.6 fold. The observed SNR was in good agreement with the expected SNR gain correlated to the loaded quality factor of RF coils from EM simulations. With the aid of this enduser friendly and economically attractive cryogenic RF coil, the enhanced SNR available can be used to improve resolution or reduce time of individual scans in a number of biomedical applications.Introduction:

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Background: Accurate assessment of plaque accumulation near the carotid bifurcation is important for the effective prevention and treatment of stroke. However, vessel and plaque delineation using MRI can be limited by low contrast-to-noise ratio (CNR) and long acquisition times. In this work, a novel 10-channel phased-array receive coil design for bilateral imaging of the carotid bifurcation using 3T MRI is proposed. Methods: The novel 10-channel receive coil was compared to a commercial 4-channel receive coil configuration using data acquired from phantoms and healthy volunteers (N = 9). The relative performance of the coils was assessed, by comparing signal-to-noise ratio (SNR), g-factor noise amplification, and the CNR between vessel wall and lumen using black-blood sequences. Patient data were acquired from 12 atherosclerotic carotid artery disease patients. Results: The 10-channel coil consistently provided substantially increased SNR in phantoms (+88 ± 2%) and improved CNR in healthy carotid arteries (+62 ± 11%), or reduced g-factor noise amplification. Patient data showed excellent delineation of atherosclerotic plaque along the length of the carotid bifurcation using the 10-channel coil. Conclusions: The proposed 10-channel coil design allows for improved visualization of the carotid arteries and the carotid bifurcation and increased parallel imaging acceleration factors.