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Radio-frequency Coil Selection for MR Imaging of the Brain and Skull Base¹

¹ From the Department of Radiology, Division of Neuroradiology, University of Utah, Salt Lake City (K.M.W., J.S.T., J.R.H.); and Department of Radiology, University of Washington, Seattle (C.E.H.). From the 2000 RSNA scientific assembly. Received September 15, 2000; revision requested October 24; revision received January 30, 2001; accepted February 6. Supported by National Institutes of Health grants R01HL48223 and R01HL53596. J.S.T. supported in part by GE Medical Systems. C.E.H. supported in part by Pathway MRI (formerly Ultraimage). Address correspondence to K.M.W., Department of Radiology, Naval Medical Center, 620 John Paul Jones Circle, Portsmouth, VA 23708 (e-mail: kmwelker@pnh10.med.navy.mil).

View larger version (97K): [in a new window]   Figure 1a. Drawings show birdcage coils viewed from the inferior aspect. (a) Standard birdcage coil. Internal view demonstrates circular conducting end elements joined by conducting rungs. Arrowheads point to three of the many trim capacitors. (b) Reduced-volume birdcage coil with reflecting end cap (arrows). The metallic end cap on the superior aspect of the coil replaces the superior circular conducting element found on standard birdcage coils. This end cap increases SNR throughout the imaging volume and improves field homogeneity within the superior aspect of the coil.

View larger version (121K): [in a new window]   Figure 1b. Drawings show birdcage coils viewed from the inferior aspect. (a) Standard birdcage coil. Internal view demonstrates circular conducting end elements joined by conducting rungs. Arrowheads point to three of the many trim capacitors. (b) Reduced-volume birdcage coil with reflecting end cap (arrows). The metallic end cap on the superior aspect of the coil replaces the superior circular conducting element found on standard birdcage coils. This end cap increases SNR throughout the imaging volume and improves field homogeneity within the superior aspect of the coil.

View larger version (97K): [in a new window]   Figure 2a. Drawings of a neurovascular coil, with the top of coil located at the lower right-hand side. (a) Cutaway view shows the modified-saddle-design cephalic receiving elements. (b) Cutaway view shows anterior (A) and posterior (P) cervical receiving elements.

View larger version (99K): [in a new window]   Figure 2b. Drawings of a neurovascular coil, with the top of coil located at the lower right-hand side. (a) Cutaway view shows the modified-saddle-design cephalic receiving elements. (b) Cutaway view shows anterior (A) and posterior (P) cervical receiving elements.

View larger version (89K): [in a new window]   Figure 3. Drawing shows a temporal dual phased-array coil. Cutaway view demonstrates a coupled pair of phased-array receiving elements (arrows). One such pair of receiving elements is placed on each side of the head. The coil is housed in a flexible housing that allows the elements to be applied closely to the cranium.

View larger version (86K): [in a new window]   Figure 4. Drawing shows a dual single-circular-element coil (temporomandibular joint coil). Cutaway view demonstrates the single circular receiving element that is placed on each side of the head. As with other dual coils, the elements can be used in a combined mode or each element can function independently to decrease the imaging time for bilateral interleaved acquisitions.

View larger version (38K): [in a new window]   Figure 5. Schematic shows a generalized coil-selection algorithm. Shapes are related to the three major steps in the constraining process that is applied to the pool of all available coils to generate a final RF coil choice: Rectangles indicate factors in the algorithm related to anatomic coverage constraints. Ovals indicate factors related to imaging protocol constraints. Circles indicate the application of patient tolerance considerations.

View larger version (143K): [in a new window]   Figure 6a. Cranial nerve MR imaging with temporal dual phased-array coils. (a) Transverse fast SE T2-weighted image (4,000/126 [repetition time msec/echo time msec], reformatted) demonstrates both trigeminal nerves crossing the prepontine cistern (black arrowheads) and trifurcating within the Meckel cavity (trigeminal cave) (white arrowheads). Spatial resolution is 0.2 mm3/voxel. (b) Coronal T1-weighted SPGR image (23/4; flip angle, 45°) demonstrates the right oculomotor nerve (arrow) passing beneath the right posterior cerebral artery (arrowheads). Spatial resolution is 0.7 mm3/voxel.

View larger version (151K): [in a new window]   Figure 6b. Cranial nerve MR imaging with temporal dual phased-array coils. (a) Transverse fast SE T2-weighted image (4,000/126 [repetition time msec/echo time msec], reformatted) demonstrates both trigeminal nerves crossing the prepontine cistern (black arrowheads) and trifurcating within the Meckel cavity (trigeminal cave) (white arrowheads). Spatial resolution is 0.2 mm3/voxel. (b) Coronal T1-weighted SPGR image (23/4; flip angle, 45°) demonstrates the right oculomotor nerve (arrow) passing beneath the right posterior cerebral artery (arrowheads). Spatial resolution is 0.7 mm3/voxel.

View larger version (130K): [in a new window]   Figure 7a. Orbital MR imaging with temporal dual phased-array coils. (a) Coronal T1-weighted SE image (550/15) obtained after surgery in a patient with right superior oblique muscle dysfunction. A small osseous defect (white arrow) of the superomedial orbital wall is noted. In addition, scar tissue (arrowheads) is visible adjacent to the right superior oblique muscle. The normal left superior oblique muscle (black arrow) is visible for comparison. Spatial resolution is 0.4 mm3/voxel. (b) Coronal T2-weighted fat-suppressed short-inversion-time inversion recovery image (4,000/38; inversion time, 160 msec) in the same patient demonstrates excellent reception characteristics in the posterior orbit. The optic nerves are clearly defined within the cerebral spinal fluid of the optic nerve sheaths. An osseous defect (arrowhead) is again noted within the right medial orbital wall. Spatial resolution is 1.2 mm3/voxel.

View larger version (168K): [in a new window]   Figure 7b. Orbital MR imaging with temporal dual phased-array coils. (a) Coronal T1-weighted SE image (550/15) obtained after surgery in a patient with right superior oblique muscle dysfunction. A small osseous defect (white arrow) of the superomedial orbital wall is noted. In addition, scar tissue (arrowheads) is visible adjacent to the right superior oblique muscle. The normal left superior oblique muscle (black arrow) is visible for comparison. Spatial resolution is 0.4 mm3/voxel. (b) Coronal T2-weighted fat-suppressed short-inversion-time inversion recovery image (4,000/38; inversion time, 160 msec) in the same patient demonstrates excellent reception characteristics in the posterior orbit. The optic nerves are clearly defined within the cerebral spinal fluid of the optic nerve sheaths. An osseous defect (arrowhead) is again noted within the right medial orbital wall. Spatial resolution is 1.2 mm3/voxel.

View larger version (149K): [in a new window]   Figure 8. MR imaging of prelocalized (with electroencephalography) cerebral heterotopia by using temporal dual phased-array coils. Coronal T1-weighted SPGR image (28/3; flip angle, 45°) obtained with coils placed over the frontal lobes demonstrates a small focus of subependymal nodular gray matter heterotopia (arrowhead) adjacent to the frontal horn of the left lateral ventricle (arrow). Spatial resolution is 0.6 mm3/voxel.

View larger version (170K): [in a new window]   Figure 9a. Cortical MR imaging with the reduced-volume birdcage end-cap coil. (a) Transverse T2-weighted fast SE image (4,000/108) demonstrates normal cerebral cortex with high spatial resolution and excellent contrast between gray and white matter. Spatial resolution is 0.7 mm3/voxel. (b) Transverse T1-weighted SPGR reformatted image (23/4; flip angle, 45°) in another patient demonstrates a small focus of heterotopic gray matter (arrowhead) within the white matter of the right temporal lobe. Spatial resolution is 0.6 mm3/voxel. Arrow = temporal horn of the right lateral ventricle.

View larger version (163K): [in a new window]   Figure 9b. Cortical MR imaging with the reduced-volume birdcage end-cap coil. (a) Transverse T2-weighted fast SE image (4,000/108) demonstrates normal cerebral cortex with high spatial resolution and excellent contrast between gray and white matter. Spatial resolution is 0.7 mm3/voxel. (b) Transverse T1-weighted SPGR reformatted image (23/4; flip angle, 45°) in another patient demonstrates a small focus of heterotopic gray matter (arrowhead) within the white matter of the right temporal lobe. Spatial resolution is 0.6 mm3/voxel. Arrow = temporal horn of the right lateral ventricle.

View larger version (187K): [in a new window]   Figure 10a. MR imaging of mesial temporal sclerosis by using temporal dual phased-array coils. (a) Coronal T1-weighted SPGR volume acquisition (23/4; flip angle, 45°) demonstrates volume loss and architectural distortion of the left hippocampus, consistent with mesial temporal sclerosis. Spatial resolution is 0.6 mm3/voxel. Arrow = alveus of left hippocampus. (b) Coronal T2-weighted fast SE image (4,875/108) in the same patient demonstrates a subtle increase in signal intensity (arrow) and an absence of internal architecture in the diseased left hippocampus. Compare with the well-defined internal architecture of the normal right hippocampus, where the low-signal-intensity perforant pathway (arrowhead) is visible. Spatial resolution is 0.4 mm3/voxel.

View larger version (164K): [in a new window]   Figure 10b. MR imaging of mesial temporal sclerosis by using temporal dual phased-array coils. (a) Coronal T1-weighted SPGR volume acquisition (23/4; flip angle, 45°) demonstrates volume loss and architectural distortion of the left hippocampus, consistent with mesial temporal sclerosis. Spatial resolution is 0.6 mm3/voxel. Arrow = alveus of left hippocampus. (b) Coronal T2-weighted fast SE image (4,875/108) in the same patient demonstrates a subtle increase in signal intensity (arrow) and an absence of internal architecture in the diseased left hippocampus. Compare with the well-defined internal architecture of the normal right hippocampus, where the low-signal-intensity perforant pathway (arrowhead) is visible. Spatial resolution is 0.4 mm3/voxel.

View larger version (157K): [in a new window]   Figure 11a. High-spatial-resolution MR imaging of the internal auditory canal by using dual single-circular-element coils (temporomandibular joint coils). (a) Transverse T2-weighted fast SE 3D Fourier transform image (4,000/126) demonstrates a vestibular schwannoma (arrow) in the left internal auditory canal. Spatial resolution is 0.4 mm3/voxel. (b) Oblique sagittal T2-weighted fast SE 3D Fourier transform image (4,000/110) in another patient demonstrates nerves within the internal auditory canal: superior vestibular (small arrowhead), inferior vestibular (large arrowhead), facial (curved arrow), and cochlear (straight arrow) nerves. Spatial resolution is 0.2 mm3/voxel.

View larger version (79K): [in a new window]   Figure 11b. High-spatial-resolution MR imaging of the internal auditory canal by using dual single-circular-element coils (temporomandibular joint coils). (a) Transverse T2-weighted fast SE 3D Fourier transform image (4,000/126) demonstrates a vestibular schwannoma (arrow) in the left internal auditory canal. Spatial resolution is 0.4 mm3/voxel. (b) Oblique sagittal T2-weighted fast SE 3D Fourier transform image (4,000/110) in another patient demonstrates nerves within the internal auditory canal: superior vestibular (small arrowhead), inferior vestibular (large arrowhead), facial (curved arrow), and cochlear (straight arrow) nerves. Spatial resolution is 0.2 mm3/voxel.

View larger version (159K): [in a new window]   Figure 12a. High-spatial-resolution MR angiography with the reduced-volume birdcage end-cap coil. Spatial resolution is 0.2 mm3 per voxel. (a) Transverse collapsed view from an SPGR 3D time-of-flight MR angiographic image (54/4; flip angle, 25°) of the circle of Willis demonstrates an aneurysm (arrow) of the P2 segment of the right posterior cerebral artery. (b) Sagittal maximum intensity projection image of the right posterior circulation in the same patient shows the aneurysm (arrow) of the P2 segment. Dual superior cerebellar arteries (arrowheads) are also visible.

View larger version (129K): [in a new window]   Figure 12b. High-spatial-resolution MR angiography with the reduced-volume birdcage end-cap coil. Spatial resolution is 0.2 mm3 per voxel. (a) Transverse collapsed view from an SPGR 3D time-of-flight MR angiographic image (54/4; flip angle, 25°) of the circle of Willis demonstrates an aneurysm (arrow) of the P2 segment of the right posterior cerebral artery. (b) Sagittal maximum intensity projection image of the right posterior circulation in the same patient shows the aneurysm (arrow) of the P2 segment. Dual superior cerebellar arteries (arrowheads) are also visible.