Search PubMed⌕ Search
Home/Archive/PubMed

PubMed · 8812896

A field-gradient coil using concentric return paths.

W W Brey·T H Mareci·J Dougherty
View original source ↗Export metadata ↓

Abstract

An approach to transverse field-gradient coil design is presented which locates all current elements in planes perpendicular to the main magnetic field. The linear volume of the resulting coil structure can be made to extend nearly to both ends of the coil. This design is based on forming a concentric return path in the same plane as the field-producing arcs. The coil structure consists of stacked planar units which give a desired field-gradient configuration. The size of the linear-field region is optimized by varying the current in each plane, by varying the location of a plane relative to the others in the stack, or by varying both current and location. Coils with linear regions having a wide range of length-to-diameter ratios can be designed, as illustrated by two examples. The construction of a prototype coil is presented and its performance in imaging confirms the analysis. This type of design is suited to magnetic resonance of the human head without obstruction from the shoulders.

Explore related subjects

Equipment DesignHeadHumansMagnetic Resonance ImagingMagneticsMathematicsPhantoms, ImagingJournal ArticleResearch Support, U.S. Gov't, P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

W W Brey, T H Mareci, J Dougherty. 1996. A field-gradient coil using concentric return paths.. https://doi.org/10.1006/jmrb.1996.0122

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed1999

Setup reproducibility in radiation therapy for lung cancer: a comparison between T-bar and expanded foam immobilization devices.

PURPOSE: Physiologic and non-physiologic tumor motion complicates the use of tight margins in three-dimensional (3D) conformal radiotherapy. Setup reproducibility is an important non-physiologic cause of tumor motion. The objective of this study is to evaluate and compare patient setup reproducibility using the reusable T-bar and the disposable expanded foam immobilization device (EFID) in radiation therapy for lung cancer. METHODS AND MATERIALS: Two hundred forty-four portal films were taken from 16 prospectively accrued patients treated for lung cancer. Patients were treated with either a pair of anterior and posterior parallel opposing fields (POF), or a combination of POF and a three-field isocentric technique. Each patient was treated in a supine position using either the T-bar setup or EFID. Six patients were treated in both devices over their treatment courses. Field placement analysis was used to evaluate 3D setup reproducibility, by comparing positions of bony landmarks relative to the radiation field edges in digitized simulator and portal images. Anterior-posterior, lateral, and longitudinal displacements, as well as field rotations along coronal and sagittal planes were measured. Statistical analyses of variance were applied to the deviations among portal films of all patients and the subgroup treated with both immobilization methods. RESULTS: For the T-bar immobilization device, standard deviations of the setup reproducibility were 5.1, 3.7, and 5.1 mm in the anterior-posterior, lateral, and longitudinal dimensions, respectively. Rotations in the coronal plane and the sagittal plane were 0.9 degrees and 1.0 degrees, respectively. For the EFID, corresponding standard deviations of set up reproducibility were 3.6 mm, 5.3 mm, 5.4 mm, 0.7 degrees and 1.4 degrees, respectively. There was no statistically significant difference (p = 0.22) in the 3D setup reproducibility between T-bar and EFID. Subgroup analysis for the patients who were treated with both immobilization devices did not reveal a difference either. There was no consistent systematic error from simulator to treatment unit identified for either immobilization device. CONCLUSION: Although the optimal immobilization technique and patient positioning for thoracic radiotherapy have yet to be determined, this study indicates that T-bar is comparable with EFID in its setup reproducibility. In view of the inherent advantages of T-bar, it has become a standard immobilization device at our institution. The observed range of displacements in field positioning with either immobilization device implies that one cm (two standard deviations [SD] of setup error) will be a more appropriate margin to allow for setup variability in radiation therapy for lung cancer.

Equipment Design↗