High-field head radiofrequency volume coils using transverse electromagnetic (TEM) and phased array technologies. 2009

Nikolai I Avdievich, and Hoby P Hetherington
Department of Neurosurgery, Yale University, New Haven, CT, USA. nikolai.avdievich@yale.edu

This article describes technological advances in quadrature transverse electromagnetic (TEM) volume coils and phased arrays reported recently from our laboratory developed for MRI and MRS imaging of the human brain. The first part of this work presents a new method for tuning TEM volume coils based on measurements of the radiofrequency current distribution in the coil elements. This technique facilitates bench adjustment of the coils' homogeneity and is particularly important for tuning double-tuned TEM volume coils. We have also used this method to optimize other TEM configurations such as a quadrature TEM half-volume coil and a split TEM coil. TEM half-volume coils provide greater sensitivity over localized regions than conventional full-volume coils, and the split TEM coil provides greater patient access and ease of use. The second part of this work describes the development of single-tuned and double-tuned transmit TEM volume coils in combination with phased arrays. A variety of different techniques for active detuning of single-tuned and double-tuned TEM volume coils are presented along with the development of phased arrays and transmission line preamplifier decoupling. The final section describes the use of counter rotating current (CRC) surface coils in phased arrays. Because of the intrinsic isolation of CRC coils from transmit volume coils, CRC arrays can be used simultaneously with volume coils for both reception and transmission. Near the center of the human head where both the phased array and the volume coil produce similar sensitivities, simultaneous reception enhances the signal-to-noise ratio. Conversely, simultaneous transmission can be used to boost the transmit field in peripheral brain regions from the volume coil to provide a more homogeneous transmit field.

UI MeSH Term Description Entries
D008279 Magnetic Resonance Imaging Non-invasive method of demonstrating internal anatomy based on the principle that atomic nuclei in a strong magnetic field absorb pulses of radiofrequency energy and emit them as radiowaves which can be reconstructed into computerized images. The concept includes proton spin tomographic techniques. Chemical Shift Imaging,MR Tomography,MRI Scans,MRI, Functional,Magnetic Resonance Image,Magnetic Resonance Imaging, Functional,Magnetization Transfer Contrast Imaging,NMR Imaging,NMR Tomography,Tomography, NMR,Tomography, Proton Spin,fMRI,Functional Magnetic Resonance Imaging,Imaging, Chemical Shift,Proton Spin Tomography,Spin Echo Imaging,Steady-State Free Precession MRI,Tomography, MR,Zeugmatography,Chemical Shift Imagings,Echo Imaging, Spin,Echo Imagings, Spin,Functional MRI,Functional MRIs,Image, Magnetic Resonance,Imaging, Magnetic Resonance,Imaging, NMR,Imaging, Spin Echo,Imagings, Chemical Shift,Imagings, Spin Echo,MRI Scan,MRIs, Functional,Magnetic Resonance Images,Resonance Image, Magnetic,Scan, MRI,Scans, MRI,Shift Imaging, Chemical,Shift Imagings, Chemical,Spin Echo Imagings,Steady State Free Precession MRI
D011846 Radio Waves Electromagnetic waves with frequencies between about 3 kilohertz (very low frequency - VLF) and 300,000 megahertz (extremely high frequency - EHF). They are used in television and radio broadcasting, land and satellite communications systems, radionavigation, radiolocation, and DIATHERMY. The highest frequency radio waves are MICROWAVES. Hertzian Waves,High Frequency Waves,Radiowave,Radiowaves,Short Waves,Very High Frequency Waves,Frequency Wave, High,Frequency Waves, High,High Frequency Wave,Radio Wave,Short Wave,Wave, High Frequency,Wave, Radio,Wave, Short,Waves, Hertzian,Waves, High Frequency,Waves, Radio,Waves, Short
D001921 Brain The part of CENTRAL NERVOUS SYSTEM that is contained within the skull (CRANIUM). Arising from the NEURAL TUBE, the embryonic brain is comprised of three major parts including PROSENCEPHALON (the forebrain); MESENCEPHALON (the midbrain); and RHOMBENCEPHALON (the hindbrain). The developed brain consists of CEREBRUM; CEREBELLUM; and other structures in the BRAIN STEM. Encephalon
D001931 Brain Mapping Imaging techniques used to colocalize sites of brain functions or physiological activity with brain structures. Brain Electrical Activity Mapping,Functional Cerebral Localization,Topographic Brain Mapping,Brain Mapping, Topographic,Functional Cerebral Localizations,Mapping, Brain,Mapping, Topographic Brain
D004560 Electricity The physical effects involving the presence of electric charges at rest and in motion.
D004574 Electromagnetic Fields Fields representing the joint interplay of electric and magnetic forces. Electromagnetic Field,Field, Electromagnetic,Fields, Electromagnetic
D006801 Humans Members of the species Homo sapiens. Homo sapiens,Man (Taxonomy),Human,Man, Modern,Modern Man
D013499 Surface Properties Characteristics or attributes of the outer boundaries of objects, including molecules. Properties, Surface,Property, Surface,Surface Property

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