Automatic probe tuning and matching

Hwang, Feng-Jang; Hoult, D. I.

doi:10.1002/mrm.1910390208

Cited by 28 publications

(33 citation statements)

References 3 publications

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“…It minimizes the coupling needed to attain a matched condition and also renders the matching process independent of tuning in this simple situation (11). This in turn, it may be shown, opens up the possibility of automatic matching (37,39) and tuning. …”

Section: Tuning the Matching Coilmentioning

confidence: 95%

Use of mutually inductive coupling in probe design

Hoult

Tomanek

2002

Concepts Magn. Reson.

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An analysis is presented of mutually inductive coupling in probe design. It is assumed that near field couplings predominate and that lumped constants may therefore be employed. Using three published designs as examples, analytic techniques are presented for assessing B 1 field strength, losses, and signal-to-noise ratio in increasingly complex situations. The perturbing effect of the B 1 field from a matching coil is examined and it is shown that if the coil is too close to the sample there can be an asymmetry introduced in the rotating frame B 1 field. It is then shown that such asymmetries are potentially a general feature of inductively coupled, loaded coils. The importance of suppressing unwanted resonances is highlighted if tuning and matching are to be orthogonal, a potential advantage of mutually inductive matching. Finally, a lumped-constant simulation is briefly described for those situations where an analytic approach becomes too cumbersome.

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Section: Tuning the Matching Coilmentioning

confidence: 95%

Use of mutually inductive coupling in probe design

Hoult

Tomanek

2002

Concepts Magn. Reson.

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“…Flexible coils may contain a range of coil conductors for different volume coverage which are enabled as needed [72,101]. Ideally they include automatic re-tuning of inevitable changes when they are flexed [42,75]. Tissue beyond the volume of operation of the gradient coils forms bright spots.…”

Section: Hardware Requirements: Radio Frequency (Rf) Systemmentioning

confidence: 99%

The Cardiovascular Magnetic Resonance Machine: Hardware and Software Requirements

Gatehouse¹,

Firmin

2000

Herz

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The flexibility of cardiac magnetic resonance imaging (MRI) includes faster imaging for applications such as stress tests, ventricular function, myocardial perfusion and coronary artery imaging. Faster imaging makes greater demands on the hardware and software. Although some cardiac imaging can be performed at 0.5 T, some of the faster techniques demand the higher signal-to-noise ratio of higher main field, and fat suppression in cardiac images is more easily achieved at higher field. Main field inhomogeneity affects rapid imaging and performance in open-access magnets. High gradient performance, low eddy currents and surface receiver coils are essential for fast cardiac imaging and the hardware of these systems including interventional imaging is discussed. The use of ECG signals for prospective and retrospective cardiac synchronization of MRI is examined. Techniques for reducing the major problem of respiratory motion in MRI are surveyed. Flexibility in the computer architecture of the scanner and the electronics generating the pulse sequence and controlling data acquisition is vital in cardiac imaging, for retrospective cardiac gating, respiratory navigator-controlled imaging and "real-time interactive" imaging in a similar manner to ultrasound imaging. Automated measurements from MR images remain under development. The pulse sequences and image display functions a cardiovascular MRI system should support for basic cardiac imaging applications and current clinical research areas are summarized.

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“…To minimize dielectric losses and sample-related frequency change, each Helmholtz ring is tuned with four 20 pF capacitors spaced 90°apart, the pair resonating at the Larmor frequency. The series-tuned, inductive coupling renders tuning and matching independent for small errors in these two quantities (19). The probe holder was made of high-density polyethylene, while the three rings, each of conductor diameter 9.6 mm, were machined from acrylic that was carefully cleaned and then copper-plated to avoid the ferromagnetic impurities commonly found in commercial copper tubing.…”

Section: Design and Constructionmentioning

confidence: 99%