Resonant Modes of the Birdcage Coil

Leifer, Mark C.

doi:10.1006/jmre.1996.7488

Cited by 89 publications

(70 citation statements)

References 3 publications

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“…It is well known (9) that the symmetry of traditional circular birdcage coils yields an inductance matrix whose circulant symmetry (10) is conveniently exploited by using equal capacitances at each of the ladder network's meshes, resulting in two degenerate modes having the desired current distributions. For a coil lacking such symmetry, however, it may be readily shown that to reduce the resonance eigenvalue problem to one having circulant symmetry, the topology of the ladder network would need to be modified to include capacitive connections between all meshes, rather than only those between adjacent meshes available in the birdcage coil.…”

Section: Capacitance Calculationmentioning

confidence: 99%

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T

Zanche

Chhina

Teh

et al. 2008

Magnetic Resonance in Med

162

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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.

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Section: Capacitance Calculationmentioning

confidence: 99%

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T

Zanche

Chhina

Teh

et al. 2008

Magnetic Resonance in Med

162

View full text Add to dashboard Cite

show abstract

“…In another work by Vullo et al, a noncylindrical birdcage coil design was also demonstrated (6). Recently, treating the coil as a periodic structure, Leifer performed the resonant frequency calculation using discrete Fourier transform of the coupling vectors (7). These previous studies focus on predicting resonant frequencies and corresponding current patterns from known capacitances and calculated inductances.…”

Section: Introductionmentioning

confidence: 96%

BirdcageBuilder: Design of specified‐geometry birdcage coils with desired current pattern and resonant frequency

Chin

Collins

Li³

et al. 2002

Concepts Magn. Reson.

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A simple method for birdcage coil design (high pass, low pass, and band pass) is presented. Rather than iteratively approaching the Larmor resonant frequency with known capacitances and calculated inductances, a more versatile approach to birdcage coil design is developed and validated, in which the necessary capacitances are calculated using a desired current pattern, a calculated inductance, and a predetermined resonant frequency. In order to expedite coil design for experienced and novice coil builders, a computer program (BirdcageBuilder) is also implemented based on this method. Experimental results show that the calculated capacitances and actual capacitances for several existing birdcage coils are in good agreement.

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“…[9], S 11 modulations by cylindrical ferrites (length-to-diameter ratio ϳ3Ϭ4) were recorded in the center of the resonator using a network analyzer. Fourier transformation revealed the double frequency of rotation (␦ / ϳ sin 2 ) and no higherorder harmonics were found (within 5% accuracy).…”

Section: Methodsmentioning

confidence: 99%

Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation

Avdievich¹,

Krymov²,

Hetherington³

2003

Magnetic Resonance in Med

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A modified perturbation method for tuning and testing volume head coils was developed. The common perturbation method, utilizing the change in resonance frequency of a resonator in response to the presence of a small dielectric or magnetic probe, was modified to modulate the frequency shift due to rotation of a probe. This modification enabled the RF magnetic and electric fields as well as the angular distribution of current in the longitudinal elements of the coil to be mapped. The latter serves as a quick test of magnetic field homogeneity by comparing the measured distribution with the sinusoidal function required for the field to be homogenous. High frequency (Ͼ100 MHz) MRI and magnetic resonance spectroscopy (MRS) provide valuable biomedical information due to their intrinsically higher spatial and spectral resolution and signal-to-noise ratio (SNR) (1-3). However, at these higher frequencies the use of standard humansized "bird-cage" (BC) coils (4) becomes difficult due to self-resonance and radiation losses (5). To overcome these limitations transverse electromagnetic (TEM) based head and body coils have been described (3,6 -8). This design decreases radiation losses, improves current distributions (no end ring current), and provides a better loaded quality factor (Q). However, TEM coils require more careful tuning and adjustment than a standard BC coil. Specifically, the splitting between resonance modes in the TEM coil are substantially smaller than that of the BC coil, making the magnetic field B 1 distribution of the TEM coil more susceptible to a sample distortion (7,9 -11). Adjustment of the B 1 field distribution on the bench can be time-consuming, requiring multiple measurements for each alteration of the coil. To aid in the bench optimization of RF coils, we developed a modified perturbation method to provide measurements of the magnetic and electric field distributions along with a rapid visualization of the current flow in each coil element. This method utilizes the change in resonance frequency of the TEM coil in response to the presence of a small dielectric, magnetic, or conductive probe. Previously, this effect has been applied to map fields in microwave cavity resonators operating in the GHz range and to test properties of dielectric and magnetic materials (12)(13)(14). Also, Doty et al. (15) used this method to measure the magnetic field filling factor for MRI coils. THEORYThe resonance frequency shift due to the placement of a small dielectric or conductive body into a cavity resonator based on the perturbation theory (14) is given by:where E 1 , D 1 , H 1 , B 1 are unperturbed fields, E 2 , D 2 , H 2 , B 2 are field changes, V S and V C are small sample and cavity volumes, respectively. Substituting D 2 and B 2 with:and the numerator of Eq.[1] to four times the energy of the entire cavity W t we obtain:where E 1 and H 1 are perturbed electric and magnetic fields, respectively. Assuming fields H 1 , H 1 , and E 1 , E 1 to be homogeneous over the small sample volume V S (in our case V S ...

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Resonant Modes of the Birdcage Coil

Cited by 89 publications

References 3 publications

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T

BirdcageBuilder: Design of specified‐geometry birdcage coils with desired current pattern and resonant frequency

Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation

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Resonant Modes of the Birdcage Coil

Cited by 89 publications

References 3 publications

Asymmetric quadrature split birdcage coil for hyperpolarized 3He lung MRI at 1.5T

Asymmetric quadrature split birdcage coil for hyperpolarized 3He lung MRI at 1.5T

BirdcageBuilder: Design of specified‐geometry birdcage coils with desired current pattern and resonant frequency

Modified perturbation method for transverse electromagnetic (TEM) coil tuning and evaluation

Contact Info

Product

Resources

About

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T

Asymmetric quadrature split birdcage coil for hyperpolarized ³He lung MRI at 1.5T