Abstract
PurposeUltra-high field (UHF) MR scanning in the body requires novel coil designs due to B1 field inhomogeneities. In the transverse electromagnetic field (TEM) design, maximum B1 transmit power can only be achieved if each individual transmit element is tuned and matched for different coil loads, which requires a considerable amount of valuable scanner time.MethodsAn integrated system for autotuning a multichannel parallel transmit (pTx) cardiac TEM array was devised, using piezoelectric actuators, power monitoring equipment and control software. The reproducibility and performance of the system were tested and the power responses of the coil elements were profiled. An automated optimization method was devised and evaluated.ResultsThe time required to tune an eight-element pTx cardiac RF array was reduced from a mean of 30 min to less than 10 min with the use of this system.ConclusionPiezoelectric actuators are an attractive means of tuning RF coil arrays to yield more efficient B1 transmission into the subject. An automated mechanism for tuning these elements provides a practical solution for cardiac imaging at UHF, bringing this technology closer to clinical use. Magn Reson Med 73:2390–2397, 2015. © 2014 The Authors. Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine.
Highlights
Cardiovascular MRI (CMR) is an increasingly important tool in the investigation of cardiac disease [1]
ultra-high field (UHF) MR scanners have been shown to provide increases in the achievable signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) [3], which may extend the diagnostic capabilities of CMR
The mean number of steps and the standard deviation (SD) for each direction were calculated, along with the difference in steps in each case when at B0 compared with no field
Summary
Cardiovascular MRI (CMR) is an increasingly important tool in the investigation of cardiac disease [1]. But in contrast with other imaging modalities such as computed tomography and positron emission tomography, CMR avoids exposing the patient to the risk of ionizing radiation which makes it a very attractive technique for both researchers and clinicians. Perhaps the most significant challenge in the application of CMR techniques such as spectroscopy or perfusion imaging is that the signal-to-noise ratio (SNR) is often insufficient at established field strengths [2]. As research in MR progresses, increasing static magnetic field strengths (B0) of MR scanners are becoming available. The use of ultra-high field (UHF) scanners, where B0 is greater than or equal to 7 Tesla (T), brings significant benefits. UHF MR scanners have been shown to provide increases in the achievable SNR and contrast-to-noise ratio (CNR) [3], which may extend the diagnostic capabilities of CMR
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