Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges

doi:10.1148/rg.275065204

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Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges¹

Mara M. Barth, MD, Martin P. Smith, MD, Ivan Pedrosa, MD, Robert E. Lenkinski, PhD, and Neil M. Rofsky, MD

¹ From the Department of Radiology, Beth Israel Deaconess Medical Center, 330 Brookline Ave, Boston, MA 02215. Presented as an education exhibit at the 2005 RSNA Annual Meeting. Received December 18, 2006; revision requested January 31, 2007; revision received March 14 and accepted March 23. N.M.R. has received research support from GE Healthcare and has served on the advisory board for Schering (Berlex) and as a consultant with CAD Sciences and EPIX Pharmaceuticals; all remaining authors have no financial relationships to disclose.

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Figure 1. Diagram shows the basis of increased signal at 3.0 T: a proportional increase in the number of protons aligned in the direction of the main magnetic field. The number of protons that contribute to the MR signal remains a fraction of the total number within the imaged object.

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Figure 2a. Comparison of prostate images acquired with an endorectal coil at 1.5 T (a, c) and 1 year later at 3.0 T (b, d) in a patient with benign prostatic hyperplasia shows improved resolution at 3.0 T, with sharper delineation of the margins of the central gland (arrowheads) and of nodules. The SNR remains robust despite a 44% reduction in voxel size at 3.0 T. Axial unenhanced images (a, b) were obtained with a fast SE sequence (a: TR msec/ echo time [TE] msec, 7000/161; section thickness, 3 mm; FOV, 16; matrix, 320 x 192; number of signals acquired [NSA], six; b: 3900/160; section thickness, 2.2 mm; FOV, 14; matrix, 320 x 192; NSA, four). Axial contrast-enhanced images (c, d) were obtained with a spoiled gradient-echo sequence (c: 9/4; section thickness, 3.2 mm; FOV, 16; matrix, 256 x 160; NSA, two; d: 7/2; section thickness, 3 mm; FOV, 14; matrix, 256 x 192; NSA, two).

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Figure 2b. Comparison of prostate images acquired with an endorectal coil at 1.5 T (a, c) and 1 year later at 3.0 T (b, d) in a patient with benign prostatic hyperplasia shows improved resolution at 3.0 T, with sharper delineation of the margins of the central gland (arrowheads) and of nodules. The SNR remains robust despite a 44% reduction in voxel size at 3.0 T. Axial unenhanced images (a, b) were obtained with a fast SE sequence (a: TR msec/ echo time [TE] msec, 7000/161; section thickness, 3 mm; FOV, 16; matrix, 320 x 192; number of signals acquired [NSA], six; b: 3900/160; section thickness, 2.2 mm; FOV, 14; matrix, 320 x 192; NSA, four). Axial contrast-enhanced images (c, d) were obtained with a spoiled gradient-echo sequence (c: 9/4; section thickness, 3.2 mm; FOV, 16; matrix, 256 x 160; NSA, two; d: 7/2; section thickness, 3 mm; FOV, 14; matrix, 256 x 192; NSA, two).

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Figure 2c. Comparison of prostate images acquired with an endorectal coil at 1.5 T (a, c) and 1 year later at 3.0 T (b, d) in a patient with benign prostatic hyperplasia shows improved resolution at 3.0 T, with sharper delineation of the margins of the central gland (arrowheads) and of nodules. The SNR remains robust despite a 44% reduction in voxel size at 3.0 T. Axial unenhanced images (a, b) were obtained with a fast SE sequence (a: TR msec/ echo time [TE] msec, 7000/161; section thickness, 3 mm; FOV, 16; matrix, 320 x 192; number of signals acquired [NSA], six; b: 3900/160; section thickness, 2.2 mm; FOV, 14; matrix, 320 x 192; NSA, four). Axial contrast-enhanced images (c, d) were obtained with a spoiled gradient-echo sequence (c: 9/4; section thickness, 3.2 mm; FOV, 16; matrix, 256 x 160; NSA, two; d: 7/2; section thickness, 3 mm; FOV, 14; matrix, 256 x 192; NSA, two).

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Figure 2d. Comparison of prostate images acquired with an endorectal coil at 1.5 T (a, c) and 1 year later at 3.0 T (b, d) in a patient with benign prostatic hyperplasia shows improved resolution at 3.0 T, with sharper delineation of the margins of the central gland (arrowheads) and of nodules. The SNR remains robust despite a 44% reduction in voxel size at 3.0 T. Axial unenhanced images (a, b) were obtained with a fast SE sequence (a: TR msec/ echo time [TE] msec, 7000/161; section thickness, 3 mm; FOV, 16; matrix, 320 x 192; number of signals acquired [NSA], six; b: 3900/160; section thickness, 2.2 mm; FOV, 14; matrix, 320 x 192; NSA, four). Axial contrast-enhanced images (c, d) were obtained with a spoiled gradient-echo sequence (c: 9/4; section thickness, 3.2 mm; FOV, 16; matrix, 256 x 160; NSA, two; d: 7/2; section thickness, 3 mm; FOV, 14; matrix, 256 x 192; NSA, two).

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Figure 3a. Comparison of axial (a, c) and coronal (b, d) reformatted images obtained at 1.5 T (a, b) and subsequently at 3.0 T (c, d) shows the clearer depiction of a right adrenal mass (arrow in a and c, arrowhead in b and d) at 3.0 T. Because of the higher SNR at 3.0 T, the voxel size could be reduced, allowing increased spatial resolution, while the SNR was maintained. In b, the lesion appears to be extra-adrenal and to have displaced the entire adrenal gland laterally. In d, it is clear that the mass arises from the medial limb of the adrenal gland and splays the limbs of the gland. The lesion was resected and was found at pathologic analysis to be an adrenal pheochromocytoma. Parameters at 1.5-T imaging were as follows: 4.0/1.9; matrix, 256 x 192; FOV, 31 cm; reformatted section thicknesses, 4 mm (a) and 2 mm (b). Parameters at 3.0-T imaging were as follows: 5.4/2.5; matrix, 320 x 224; FOV, 35 cm; reformatted section thicknesses, 3 mm (c) and 1.5 mm (d).

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Figure 3b. Comparison of axial (a, c) and coronal (b, d) reformatted images obtained at 1.5 T (a, b) and subsequently at 3.0 T (c, d) shows the clearer depiction of a right adrenal mass (arrow in a and c, arrowhead in b and d) at 3.0 T. Because of the higher SNR at 3.0 T, the voxel size could be reduced, allowing increased spatial resolution, while the SNR was maintained. In b, the lesion appears to be extra-adrenal and to have displaced the entire adrenal gland laterally. In d, it is clear that the mass arises from the medial limb of the adrenal gland and splays the limbs of the gland. The lesion was resected and was found at pathologic analysis to be an adrenal pheochromocytoma. Parameters at 1.5-T imaging were as follows: 4.0/1.9; matrix, 256 x 192; FOV, 31 cm; reformatted section thicknesses, 4 mm (a) and 2 mm (b). Parameters at 3.0-T imaging were as follows: 5.4/2.5; matrix, 320 x 224; FOV, 35 cm; reformatted section thicknesses, 3 mm (c) and 1.5 mm (d).

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Figure 3c. Comparison of axial (a, c) and coronal (b, d) reformatted images obtained at 1.5 T (a, b) and subsequently at 3.0 T (c, d) shows the clearer depiction of a right adrenal mass (arrow in a and c, arrowhead in b and d) at 3.0 T. Because of the higher SNR at 3.0 T, the voxel size could be reduced, allowing increased spatial resolution, while the SNR was maintained. In b, the lesion appears to be extra-adrenal and to have displaced the entire adrenal gland laterally. In d, it is clear that the mass arises from the medial limb of the adrenal gland and splays the limbs of the gland. The lesion was resected and was found at pathologic analysis to be an adrenal pheochromocytoma. Parameters at 1.5-T imaging were as follows: 4.0/1.9; matrix, 256 x 192; FOV, 31 cm; reformatted section thicknesses, 4 mm (a) and 2 mm (b). Parameters at 3.0-T imaging were as follows: 5.4/2.5; matrix, 320 x 224; FOV, 35 cm; reformatted section thicknesses, 3 mm (c) and 1.5 mm (d).

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Figure 3d. Comparison of axial (a, c) and coronal (b, d) reformatted images obtained at 1.5 T (a, b) and subsequently at 3.0 T (c, d) shows the clearer depiction of a right adrenal mass (arrow in a and c, arrowhead in b and d) at 3.0 T. Because of the higher SNR at 3.0 T, the voxel size could be reduced, allowing increased spatial resolution, while the SNR was maintained. In b, the lesion appears to be extra-adrenal and to have displaced the entire adrenal gland laterally. In d, it is clear that the mass arises from the medial limb of the adrenal gland and splays the limbs of the gland. The lesion was resected and was found at pathologic analysis to be an adrenal pheochromocytoma. Parameters at 1.5-T imaging were as follows: 4.0/1.9; matrix, 256 x 192; FOV, 31 cm; reformatted section thicknesses, 4 mm (a) and 2 mm (b). Parameters at 3.0-T imaging were as follows: 5.4/2.5; matrix, 320 x 224; FOV, 35 cm; reformatted section thicknesses, 3 mm (c) and 1.5 mm (d).

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Figure 4a. Comparison of liver-spleen contrast on T1-weighted images obtained at 1.5 T (a) and at 3.0 T (b) shows decreased contrast in b because of increased T1 at the higher field strength. The decrease in contrast might have been mitigated by altering the pulse sequence used at 3.0-T imaging. Parameters at 1.5-T imaging were as follows: 180/2.34; section thickness, 7 mm; matrix, 256 x 123; flip angle, 70°. Parameters at 3.0-T imaging were the same, except for the matrix, which was 320 x 192.

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Figure 4b. Comparison of liver-spleen contrast on T1-weighted images obtained at 1.5 T (a) and at 3.0 T (b) shows decreased contrast in b because of increased T1 at the higher field strength. The decrease in contrast might have been mitigated by altering the pulse sequence used at 3.0-T imaging. Parameters at 1.5-T imaging were as follows: 180/2.34; section thickness, 7 mm; matrix, 256 x 123; flip angle, 70°. Parameters at 3.0-T imaging were the same, except for the matrix, which was 320 x 192.

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Figure 5a. Comparison of contrast-enhanced three-dimensional T1-weighted fat-saturated images obtained at 1.5 T (a) and 3.0 T (b) in a patient with focal nodular hyperplasia demonstrates an improved contrast-to-noise ratio at 3.0 T. Although the intrinsic image contrast is decreased at 3.0 T, the T1 shortening effect of gadolinium relative to adjacent tissues is more pronounced; therefore, the liver lesion (arrow) stands out more markedly from the adjacent parenchyma, and the outlines of the portal vein (arrowhead) are more readily apparent at 3.0 T than at 1.5 T. Parameters at 1.5-T imaging were as follows: 4.3/1.98; section thickness, 4.4 mm; matrix, 256 x 154. Parameters at 3.0-T imaging were as follows: 3.9/1.06; section thickness, 3.6 mm; matrix, 320 x 224.

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Figure 5b. Comparison of contrast-enhanced three-dimensional T1-weighted fat-saturated images obtained at 1.5 T (a) and 3.0 T (b) in a patient with focal nodular hyperplasia demonstrates an improved contrast-to-noise ratio at 3.0 T. Although the intrinsic image contrast is decreased at 3.0 T, the T1 shortening effect of gadolinium relative to adjacent tissues is more pronounced; therefore, the liver lesion (arrow) stands out more markedly from the adjacent parenchyma, and the outlines of the portal vein (arrowhead) are more readily apparent at 3.0 T than at 1.5 T. Parameters at 1.5-T imaging were as follows: 4.3/1.98; section thickness, 4.4 mm; matrix, 256 x 154. Parameters at 3.0-T imaging were as follows: 3.9/1.06; section thickness, 3.6 mm; matrix, 320 x 224.

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Figure 6a. Breath-hold MR spectroscopy at 3.0 T. (a) Single-shot fast SE image shows a voxel ( ${square}$ ) selected for spectroscopic analysis within a renal cell carcinoma metastasis in the right adrenal gland. (b) Spectrum from the selected voxel shows clear separation of the metabolite peaks, which are easily distinguishable from background noise. Note the marked trimethylamine (TMA) or choline peak at 3.2 ppm, a feature associated with malignancy. The increased SNR and increased spectral dispersion at 3.0 T allow clearer identification and separation of metabolites. In addition, the increased SNR may enable a reduction in acquisition time, allowing spectroscopy to be performed in a single breath hold and thus eliminating respiratory motion.

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Figure 6b. Breath-hold MR spectroscopy at 3.0 T. (a) Single-shot fast SE image shows a voxel ( ${square}$ ) selected for spectroscopic analysis within a renal cell carcinoma metastasis in the right adrenal gland. (b) Spectrum from the selected voxel shows clear separation of the metabolite peaks, which are easily distinguishable from background noise. Note the marked trimethylamine (TMA) or choline peak at 3.2 ppm, a feature associated with malignancy. The increased SNR and increased spectral dispersion at 3.0 T allow clearer identification and separation of metabolites. In addition, the increased SNR may enable a reduction in acquisition time, allowing spectroscopy to be performed in a single breath hold and thus eliminating respiratory motion.

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Figure 7a. RF magnetic field inhomogeneity. Comparison of coronal single-shot fast SE images acquired at 1.5 T (a) and 24 hours later at 3.0 T (b) shows improved contrast of a tumor thrombus (arrow) in the left renal vein and an overall increase in the SNR with less graininess at 3.0 T. However, a standing wave artifact at 3.0 T (* in b) obscures the liver, particularly the dome, which has more-uniform signal intensity at 1.5 T (* in a). Parameters at 1.5-T imaging were as follows: 911/76; section thickness, 5 mm; matrix, 256 x 205; per-pixel bandwidth, 488 Hz. Parameters at 3.0-T imaging were as follows: 1168/59; section thickness, 4.6 mm; matrix, 256 x 192; per-pixel bandwidth, 651 Hz.

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Figure 7b. RF magnetic field inhomogeneity. Comparison of coronal single-shot fast SE images acquired at 1.5 T (a) and 24 hours later at 3.0 T (b) shows improved contrast of a tumor thrombus (arrow) in the left renal vein and an overall increase in the SNR with less graininess at 3.0 T. However, a standing wave artifact at 3.0 T (* in b) obscures the liver, particularly the dome, which has more-uniform signal intensity at 1.5 T (* in a). Parameters at 1.5-T imaging were as follows: 911/76; section thickness, 5 mm; matrix, 256 x 205; per-pixel bandwidth, 488 Hz. Parameters at 3.0-T imaging were as follows: 1168/59; section thickness, 4.6 mm; matrix, 256 x 192; per-pixel bandwidth, 651 Hz.

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Figure 8a. Signal loss due to ascites at 3.0 T. Comparison of coronal images obtained with a single-shot fast SE sequence at 1.5 T (a) and 3.0 T (b) shows dramatic standing wave and conductivity effects at the higher field strength because of ascitic fluid, which produced a nonuniform lower RF field centrally, seen in b. The programmed excitation and refocusing pulse angles were effectively reduced, yielding signal reduction or loss. In this case, the patient was first examined at 3.0 T and then was transferred to a 1.5-T system to obtain images of higher diagnostic quality. Parameters at 1.5-T imaging were as follows: 1157/58; section thickness, 4 mm; matrix, 256 x 256. Parameters at 3.0-T imaging were as follows: 925/58; section thickness, 4.6 mm; matrix, 256 x 256.

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Figure 8b. Signal loss due to ascites at 3.0 T. Comparison of coronal images obtained with a single-shot fast SE sequence at 1.5 T (a) and 3.0 T (b) shows dramatic standing wave and conductivity effects at the higher field strength because of ascitic fluid, which produced a nonuniform lower RF field centrally, seen in b. The programmed excitation and refocusing pulse angles were effectively reduced, yielding signal reduction or loss. In this case, the patient was first examined at 3.0 T and then was transferred to a 1.5-T system to obtain images of higher diagnostic quality. Parameters at 1.5-T imaging were as follows: 1157/58; section thickness, 4 mm; matrix, 256 x 256. Parameters at 3.0-T imaging were as follows: 925/58; section thickness, 4.6 mm; matrix, 256 x 256.

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Figure 9a. Effect of coil design on SNR. Comparison of images obtained with a body coil (a, c) and with a phased-array coil (b, d) at 1.5 T (1204/60.1; matrix, 256 x 192) (a, b) and at 3.0 T (25,224/65.0; matrix, 256 x 192) (c, d) shows that a small surface coil has an inherent SNR advantage over a body coil at both field strengths. Image quality with use of the body coil at 3.0 T (c) approaches that with the phased-array coil at 1.5 T (b), but the best image quality is demonstrated with the phased-array coil at 3.0 T (d).

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Figure 9b. Effect of coil design on SNR. Comparison of images obtained with a body coil (a, c) and with a phased-array coil (b, d) at 1.5 T (1204/60.1; matrix, 256 x 192) (a, b) and at 3.0 T (25,224/65.0; matrix, 256 x 192) (c, d) shows that a small surface coil has an inherent SNR advantage over a body coil at both field strengths. Image quality with use of the body coil at 3.0 T (c) approaches that with the phased-array coil at 1.5 T (b), but the best image quality is demonstrated with the phased-array coil at 3.0 T (d).

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Figure 9c. Effect of coil design on SNR. Comparison of images obtained with a body coil (a, c) and with a phased-array coil (b, d) at 1.5 T (1204/60.1; matrix, 256 x 192) (a, b) and at 3.0 T (25,224/65.0; matrix, 256 x 192) (c, d) shows that a small surface coil has an inherent SNR advantage over a body coil at both field strengths. Image quality with use of the body coil at 3.0 T (c) approaches that with the phased-array coil at 1.5 T (b), but the best image quality is demonstrated with the phased-array coil at 3.0 T (d).

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Figure 9d. Effect of coil design on SNR. Comparison of images obtained with a body coil (a, c) and with a phased-array coil (b, d) at 1.5 T (1204/60.1; matrix, 256 x 192) (a, b) and at 3.0 T (25,224/65.0; matrix, 256 x 192) (c, d) shows that a small surface coil has an inherent SNR advantage over a body coil at both field strengths. Image quality with use of the body coil at 3.0 T (c) approaches that with the phased-array coil at 1.5 T (b), but the best image quality is demonstrated with the phased-array coil at 3.0 T (d).

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Figure 10a. Diagrams show the use of a parallel imaging technique with a single-shot fast SE sequence to decrease acquisition time and motion-related artifacts by summing multiple echoes (TE) within a single TR interval. (a) Single-shot fast SE sequence without the use of parallel imaging. (b–d) Use of a parallel imaging technique with the sequence diagrammed in a: Intermittent phase encoding steps (lower dashed arrows in b) and received echoes (upper dashed arrows in b) are excluded to decrease the echo train duration and, thus, the image acquisition time, producing the result shown in c. The missing data are then virtually recreated by using the known sensitivity profiles of the individual elements in the multiple-element receiver coil. The reduction in the SNR that occurs with a decrease in the number of phase encoding steps may be mitigated by decreasing the bandwidth. Although a decrease in the bandwidth in turn results in an increase in the echo spacing and, thus, the echo train duration (d), the trade-off yields images with less motion-related artifact and a lesser penalty on the SNR than those acquired without the use of parallel imaging.

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Figure 10b. Diagrams show the use of a parallel imaging technique with a single-shot fast SE sequence to decrease acquisition time and motion-related artifacts by summing multiple echoes (TE) within a single TR interval. (a) Single-shot fast SE sequence without the use of parallel imaging. (b–d) Use of a parallel imaging technique with the sequence diagrammed in a: Intermittent phase encoding steps (lower dashed arrows in b) and received echoes (upper dashed arrows in b) are excluded to decrease the echo train duration and, thus, the image acquisition time, producing the result shown in c. The missing data are then virtually recreated by using the known sensitivity profiles of the individual elements in the multiple-element receiver coil. The reduction in the SNR that occurs with a decrease in the number of phase encoding steps may be mitigated by decreasing the bandwidth. Although a decrease in the bandwidth in turn results in an increase in the echo spacing and, thus, the echo train duration (d), the trade-off yields images with less motion-related artifact and a lesser penalty on the SNR than those acquired without the use of parallel imaging.

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Figure 10c. Diagrams show the use of a parallel imaging technique with a single-shot fast SE sequence to decrease acquisition time and motion-related artifacts by summing multiple echoes (TE) within a single TR interval. (a) Single-shot fast SE sequence without the use of parallel imaging. (b–d) Use of a parallel imaging technique with the sequence diagrammed in a: Intermittent phase encoding steps (lower dashed arrows in b) and received echoes (upper dashed arrows in b) are excluded to decrease the echo train duration and, thus, the image acquisition time, producing the result shown in c. The missing data are then virtually recreated by using the known sensitivity profiles of the individual elements in the multiple-element receiver coil. The reduction in the SNR that occurs with a decrease in the number of phase encoding steps may be mitigated by decreasing the bandwidth. Although a decrease in the bandwidth in turn results in an increase in the echo spacing and, thus, the echo train duration (d), the trade-off yields images with less motion-related artifact and a lesser penalty on the SNR than those acquired without the use of parallel imaging.

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Figure 10d. Diagrams show the use of a parallel imaging technique with a single-shot fast SE sequence to decrease acquisition time and motion-related artifacts by summing multiple echoes (TE) within a single TR interval. (a) Single-shot fast SE sequence without the use of parallel imaging. (b–d) Use of a parallel imaging technique with the sequence diagrammed in a: Intermittent phase encoding steps (lower dashed arrows in b) and received echoes (upper dashed arrows in b) are excluded to decrease the echo train duration and, thus, the image acquisition time, producing the result shown in c. The missing data are then virtually recreated by using the known sensitivity profiles of the individual elements in the multiple-element receiver coil. The reduction in the SNR that occurs with a decrease in the number of phase encoding steps may be mitigated by decreasing the bandwidth. Although a decrease in the bandwidth in turn results in an increase in the echo spacing and, thus, the echo train duration (d), the trade-off yields images with less motion-related artifact and a lesser penalty on the SNR than those acquired without the use of parallel imaging.

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Figure 11a. Chemical shift artifact of the first kind. Comparison of axial in-phase gradient-echo images acquired at 1.5 T (a) and at 3.0 T (b) with the same FOV, base resolution, and receiver bandwidth shows a significantly more apparent artifact at 3.0 T. The artifact appears as a low-signal-intensity band (black arrowheads) toward the higher part of the frequency-encoding gradient field and a high-signal-intensity band (white arrowheads) toward the lower part of the frequency-encoding gradient field. The difference in resonance frequency is directly proportional to the main magnetic field strength. Parameters at 1.5-T imaging were as follows: 180/4.2; bandwidth, 15 kHz; section thickness, 7 mm; matrix, 256 x 160. Parameters at 3.0-T imaging were the same except for the TE, which was 2.1 msec.

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Figure 11b. Chemical shift artifact of the first kind. Comparison of axial in-phase gradient-echo images acquired at 1.5 T (a) and at 3.0 T (b) with the same FOV, base resolution, and receiver bandwidth shows a significantly more apparent artifact at 3.0 T. The artifact appears as a low-signal-intensity band (black arrowheads) toward the higher part of the frequency-encoding gradient field and a high-signal-intensity band (white arrowheads) toward the lower part of the frequency-encoding gradient field. The difference in resonance frequency is directly proportional to the main magnetic field strength. Parameters at 1.5-T imaging were as follows: 180/4.2; bandwidth, 15 kHz; section thickness, 7 mm; matrix, 256 x 160. Parameters at 3.0-T imaging were the same except for the TE, which was 2.1 msec.

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Figure 12a. Increasing the bandwidth to lessen chemical shift artifact of the first kind. Comparison of axial in-phase gradient-echo images acquired at 3.0 T (180/2.1; section thickness, 7 mm; matrix, 256 x 160) with bandwidths of 15 kHz (a) and 32 kHz (b) demonstrates a less apparent artifact in b, with a decrease in the width of the low-signal-intensity bands (black arrowheads) and high-signal-intensity bands (white arrowheads) at the kidney margins as well as the low-signal-intensity band at the liver margin (black arrow).

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Figure 12b. Increasing the bandwidth to lessen chemical shift artifact of the first kind. Comparison of axial in-phase gradient-echo images acquired at 3.0 T (180/2.1; section thickness, 7 mm; matrix, 256 x 160) with bandwidths of 15 kHz (a) and 32 kHz (b) demonstrates a less apparent artifact in b, with a decrease in the width of the low-signal-intensity bands (black arrowheads) and high-signal-intensity bands (white arrowheads) at the kidney margins as well as the low-signal-intensity band at the liver margin (black arrow).

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Figure 13a. Avoiding chemical shift artifact of the first kind while maintaining a constant bandwidth. Axial in-phase gradient-echo images acquired at 3.0 T (180/ 2.1; section thickness, 7 mm; matrix, 256 x 160; bandwidth, 15 kHz) show chemical shift artifacts at the margins of the kidneys (arrowheads) and liver (arrow). The artifacts are in the usual positions and are most obvious in a, an image acquired with the frequency-encoding gradient applied along the transverse axis. In b, an image obtained by applying the frequency-encoding gradient in the anteroposterior direction, the position of the artifacts has shifted and allows evaluation of the regions that were obscured in a. In c, an image obtained with a fat saturation technique and with the same orientation of the frequency-encoding gradient as in a, the artifacts are much less obtrusive.

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Figure 13b. Avoiding chemical shift artifact of the first kind while maintaining a constant bandwidth. Axial in-phase gradient-echo images acquired at 3.0 T (180/ 2.1; section thickness, 7 mm; matrix, 256 x 160; bandwidth, 15 kHz) show chemical shift artifacts at the margins of the kidneys (arrowheads) and liver (arrow). The artifacts are in the usual positions and are most obvious in a, an image acquired with the frequency-encoding gradient applied along the transverse axis. In b, an image obtained by applying the frequency-encoding gradient in the anteroposterior direction, the position of the artifacts has shifted and allows evaluation of the regions that were obscured in a. In c, an image obtained with a fat saturation technique and with the same orientation of the frequency-encoding gradient as in a, the artifacts are much less obtrusive.

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Figure 13c. Avoiding chemical shift artifact of the first kind while maintaining a constant bandwidth. Axial in-phase gradient-echo images acquired at 3.0 T (180/ 2.1; section thickness, 7 mm; matrix, 256 x 160; bandwidth, 15 kHz) show chemical shift artifacts at the margins of the kidneys (arrowheads) and liver (arrow). The artifacts are in the usual positions and are most obvious in a, an image acquired with the frequency-encoding gradient applied along the transverse axis. In b, an image obtained by applying the frequency-encoding gradient in the anteroposterior direction, the position of the artifacts has shifted and allows evaluation of the regions that were obscured in a. In c, an image obtained with a fat saturation technique and with the same orientation of the frequency-encoding gradient as in a, the artifacts are much less obtrusive.

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Figure 14a. Chemical shift artifact of the second kind. Comparison of in-phase (a, c) and out-of-phase (b, d) gradient-echo images acquired at 1.5 T (a, b) and at 3.0 T (c, d) demonstrates an increased chemical shift artifact in c and d, a change associated with the use of longer TEs at 3.0 T. To avoid an unacceptable reduction in image quality at very short TEs (such as 2.2 msec and 1.1 msec, which would have been exactly half the TEs used at in-phase and out-of-phase 1.5-T imaging), TEs of 2.3 msec and 5.8 msec were used for in-phase and out-of-phase 3.0-T imaging, respectively. In d, note the increased susceptibility artifacts (arrowheads), which represent siderotic nodules in the liver and Gamna-Gandy bodies in the spleen. These features are more prominent in d than in a or b because of the increased field strength and more visible than in c because of the increased TE.

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Figure 14b. Chemical shift artifact of the second kind. Comparison of in-phase (a, c) and out-of-phase (b, d) gradient-echo images acquired at 1.5 T (a, b) and at 3.0 T (c, d) demonstrates an increased chemical shift artifact in c and d, a change associated with the use of longer TEs at 3.0 T. To avoid an unacceptable reduction in image quality at very short TEs (such as 2.2 msec and 1.1 msec, which would have been exactly half the TEs used at in-phase and out-of-phase 1.5-T imaging), TEs of 2.3 msec and 5.8 msec were used for in-phase and out-of-phase 3.0-T imaging, respectively. In d, note the increased susceptibility artifacts (arrowheads), which represent siderotic nodules in the liver and Gamna-Gandy bodies in the spleen. These features are more prominent in d than in a or b because of the increased field strength and more visible than in c because of the increased TE.

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Figure 14c. Chemical shift artifact of the second kind. Comparison of in-phase (a, c) and out-of-phase (b, d) gradient-echo images acquired at 1.5 T (a, b) and at 3.0 T (c, d) demonstrates an increased chemical shift artifact in c and d, a change associated with the use of longer TEs at 3.0 T. To avoid an unacceptable reduction in image quality at very short TEs (such as 2.2 msec and 1.1 msec, which would have been exactly half the TEs used at in-phase and out-of-phase 1.5-T imaging), TEs of 2.3 msec and 5.8 msec were used for in-phase and out-of-phase 3.0-T imaging, respectively. In d, note the increased susceptibility artifacts (arrowheads), which represent siderotic nodules in the liver and Gamna-Gandy bodies in the spleen. These features are more prominent in d than in a or b because of the increased field strength and more visible than in c because of the increased TE.

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Figure 14d. Chemical shift artifact of the second kind. Comparison of in-phase (a, c) and out-of-phase (b, d) gradient-echo images acquired at 1.5 T (a, b) and at 3.0 T (c, d) demonstrates an increased chemical shift artifact in c and d, a change associated with the use of longer TEs at 3.0 T. To avoid an unacceptable reduction in image quality at very short TEs (such as 2.2 msec and 1.1 msec, which would have been exactly half the TEs used at in-phase and out-of-phase 1.5-T imaging), TEs of 2.3 msec and 5.8 msec were used for in-phase and out-of-phase 3.0-T imaging, respectively. In d, note the increased susceptibility artifacts (arrowheads), which represent siderotic nodules in the liver and Gamna-Gandy bodies in the spleen. These features are more prominent in d than in a or b because of the increased field strength and more visible than in c because of the increased TE.

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Figure 15a. Susceptibility effects. Comparison of axial prostate images obtained with gradient-echo sequences at 1.5 T (9.3/4.2; section thickness, 3.4 mm; matrix, 256 x 256) (a) and, in another patient, at 3.0 T (7.1/2.1; section thickness, 2.6 mm; matrix, 256 x 256) (b) demonstrates improved visibility of brachytherapy seeds (arrowheads) at 3.0 T. Despite the shorter TE used for in-phase imaging at 3.0 T, the T2* is shorter at the higher field strength, with resultant increased sensitivity to susceptibility effects.

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Figure 15b. Susceptibility effects. Comparison of axial prostate images obtained with gradient-echo sequences at 1.5 T (9.3/4.2; section thickness, 3.4 mm; matrix, 256 x 256) (a) and, in another patient, at 3.0 T (7.1/2.1; section thickness, 2.6 mm; matrix, 256 x 256) (b) demonstrates improved visibility of brachytherapy seeds (arrowheads) at 3.0 T. Despite the shorter TE used for in-phase imaging at 3.0 T, the T2* is shorter at the higher field strength, with resultant increased sensitivity to susceptibility effects.

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Figure 16a. Susceptibility artifact. Axial in-phase gradient-echo images obtained immediately after bilateral uterine artery embolization at 1.5 T (155/2.28; section thickness, 5 mm; matrix, 256 x 160; flip angle, 80°) (a) and 6 months later at 3.0 T (160/2.5; section thickness, 6 mm; matrix, 256 x 160; flip angle, 80°) (b) show bilateral susceptibility artifacts (arrowheads) due to the embolization coils. On comparison, the artifacts are less apparent in a than in b, despite the similar TE values. Axial image obtained at 3.0 T with a fast SE sequence (5520/101.2; section thickness, 4 mm; matrix, 338 x 384; flip angle, 90°) (c) shows decreased artifacts (arrowheads), an improvement due to the application of multiple refocusing pulses, which mitigated the effect of T2* dephasing.

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Figure 16b. Susceptibility artifact. Axial in-phase gradient-echo images obtained immediately after bilateral uterine artery embolization at 1.5 T (155/2.28; section thickness, 5 mm; matrix, 256 x 160; flip angle, 80°) (a) and 6 months later at 3.0 T (160/2.5; section thickness, 6 mm; matrix, 256 x 160; flip angle, 80°) (b) show bilateral susceptibility artifacts (arrowheads) due to the embolization coils. On comparison, the artifacts are less apparent in a than in b, despite the similar TE values. Axial image obtained at 3.0 T with a fast SE sequence (5520/101.2; section thickness, 4 mm; matrix, 338 x 384; flip angle, 90°) (c) shows decreased artifacts (arrowheads), an improvement due to the application of multiple refocusing pulses, which mitigated the effect of T2* dephasing.

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Figure 16c. Susceptibility artifact. Axial in-phase gradient-echo images obtained immediately after bilateral uterine artery embolization at 1.5 T (155/2.28; section thickness, 5 mm; matrix, 256 x 160; flip angle, 80°) (a) and 6 months later at 3.0 T (160/2.5; section thickness, 6 mm; matrix, 256 x 160; flip angle, 80°) (b) show bilateral susceptibility artifacts (arrowheads) due to the embolization coils. On comparison, the artifacts are less apparent in a than in b, despite the similar TE values. Axial image obtained at 3.0 T with a fast SE sequence (5520/101.2; section thickness, 4 mm; matrix, 338 x 384; flip angle, 90°) (c) shows decreased artifacts (arrowheads), an improvement due to the application of multiple refocusing pulses, which mitigated the effect of T2* dephasing.

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Figure 17. Photograph shows a stretcher that was pulled into a 3.0-T magnet by the static magnetic field surrounding an MR imaging system. This accident might have had catastrophic consequences if a patient had been undergoing MR imaging at the time. The presence of a higher-field-strength magnet requires placement of the 5-G line at a greater distance from the magnet than is needed for a 1.5-T magnet.

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Figure 18a. Phosphorus imaging at 3.0 T. Comparison of axial MR images obtained at 3.0-T proton (hydrogen) imaging (a, b) and phosphorus imaging (c, d) in a normal foot (a, c) and a diabetic foot (b, d) shows improved depiction of peripheral vascular disease and increased capability for measuring the phosphorus concentration in tissue with phosphorus imaging. At 1.5 T, phosphorus protons do not produce sufficient signal to allow phosphorus imaging and quantification within practical acquisition times. At 3.0 T, the higher SNR allows both imaging and measurement of phosphorus for a more accurate assessment of the severity of diabetic lower-extremity peripheral vascular disease and the response to medical and surgical therapies. (Images courtesy of Robert Greenman, PhD, Beth Israel Deaconess Medical Center.)

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Figure 18b. Phosphorus imaging at 3.0 T. Comparison of axial MR images obtained at 3.0-T proton (hydrogen) imaging (a, b) and phosphorus imaging (c, d) in a normal foot (a, c) and a diabetic foot (b, d) shows improved depiction of peripheral vascular disease and increased capability for measuring the phosphorus concentration in tissue with phosphorus imaging. At 1.5 T, phosphorus protons do not produce sufficient signal to allow phosphorus imaging and quantification within practical acquisition times. At 3.0 T, the higher SNR allows both imaging and measurement of phosphorus for a more accurate assessment of the severity of diabetic lower-extremity peripheral vascular disease and the response to medical and surgical therapies. (Images courtesy of Robert Greenman, PhD, Beth Israel Deaconess Medical Center.)

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Figure 18c. Phosphorus imaging at 3.0 T. Comparison of axial MR images obtained at 3.0-T proton (hydrogen) imaging (a, b) and phosphorus imaging (c, d) in a normal foot (a, c) and a diabetic foot (b, d) shows improved depiction of peripheral vascular disease and increased capability for measuring the phosphorus concentration in tissue with phosphorus imaging. At 1.5 T, phosphorus protons do not produce sufficient signal to allow phosphorus imaging and quantification within practical acquisition times. At 3.0 T, the higher SNR allows both imaging and measurement of phosphorus for a more accurate assessment of the severity of diabetic lower-extremity peripheral vascular disease and the response to medical and surgical therapies. (Images courtesy of Robert Greenman, PhD, Beth Israel Deaconess Medical Center.)

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Figure 18d. Phosphorus imaging at 3.0 T. Comparison of axial MR images obtained at 3.0-T proton (hydrogen) imaging (a, b) and phosphorus imaging (c, d) in a normal foot (a, c) and a diabetic foot (b, d) shows improved depiction of peripheral vascular disease and increased capability for measuring the phosphorus concentration in tissue with phosphorus imaging. At 1.5 T, phosphorus protons do not produce sufficient signal to allow phosphorus imaging and quantification within practical acquisition times. At 3.0 T, the higher SNR allows both imaging and measurement of phosphorus for a more accurate assessment of the severity of diabetic lower-extremity peripheral vascular disease and the response to medical and surgical therapies. (Images courtesy of Robert Greenman, PhD, Beth Israel Deaconess Medical Center.)

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Figure 19a. Three-dimensional sodium imaging at 3.0 T. Comparison of coronal projections obtained at 25 minutes (a) and at 12 minutes (b) of acquisition time with a diagram of the human kidney (c) shows the general distribution of sodium within the right kidney. Although a and b were acquired by using the same custom-built quadrature surface coil and the same gradient-echo sequence (30/1.8; FOV, 38 x 38 x 24 cm; matrix, 128 x 128 x 16), the improved SNR due to a longer acquisition time produces a more accurate depiction in a (and in d, a topographic rendering of image data from a) of the higher sodium gradient in the renal medulla compared with that in the cortex. (Adapted and reprinted, with permission, from reference (38).

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Figure 19b. Three-dimensional sodium imaging at 3.0 T. Comparison of coronal projections obtained at 25 minutes (a) and at 12 minutes (b) of acquisition time with a diagram of the human kidney (c) shows the general distribution of sodium within the right kidney. Although a and b were acquired by using the same custom-built quadrature surface coil and the same gradient-echo sequence (30/1.8; FOV, 38 x 38 x 24 cm; matrix, 128 x 128 x 16), the improved SNR due to a longer acquisition time produces a more accurate depiction in a (and in d, a topographic rendering of image data from a) of the higher sodium gradient in the renal medulla compared with that in the cortex. (Adapted and reprinted, with permission, from (38).

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Figure 19c. Three-dimensional sodium imaging at 3.0 T. Comparison of coronal projections obtained at 25 minutes (a) and at 12 minutes (b) of acquisition time with a diagram of the human kidney (c) shows the general distribution of sodium within the right kidney. Although a and b were acquired by using the same custom-built quadrature surface coil and the same gradient-echo sequence (30/1.8; FOV, 38 x 38 x 24 cm; matrix, 128 x 128 x 16), the improved SNR due to a longer acquisition time produces a more accurate depiction in a (and in d, a topographic rendering of image data from a) of the higher sodium gradient in the renal medulla compared with that in the cortex. (Adapted and reprinted, with permission, from (38).

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Figure 19d. Three-dimensional sodium imaging at 3.0 T. Comparison of coronal projections obtained at 25 minutes (a) and at 12 minutes (b) of acquisition time with a diagram of the human kidney (c) shows the general distribution of sodium within the right kidney. Although a and b were acquired by using the same custom-built quadrature surface coil and the same gradient-echo sequence (30/1.8; FOV, 38 x 38 x 24 cm; matrix, 128 x 128 x 16), the improved SNR due to a longer acquisition time produces a more accurate depiction in a (and in d, a topographic rendering of image data from a) of the higher sodium gradient in the renal medulla compared with that in the cortex. (Adapted and reprinted, with permission, from (38).

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Figure 20. Schema of arterial spin labeling shows the application of a spatially selective saturation band upstream from a lesion to invert the proton spins as they flow toward the lesion. The inverted spins within the lesion are measured to evaluate the tumor blood flow and determine the response to therapy.

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Figure 21. Comparison of pretherapeutic (top) and posttherapeutic (bottom) MR images obtained with arterial spin labeling shows decreased blood flow to a large renal cell carcinoma metastasis in the left hemi-thorax 1 month after the initiation of therapy.

Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges1

Body MR Imaging at 3.0 T: Understanding the Opportunities and Challenges¹