DOI: 10.1148/rg.255045202
Parallel MR Imaging: A User’s Guide1
James F. Glockner, MD, PhD,
Houchun H. Hu, BME,
David W. Stanley, BS,
Lisa Angelos, PhD and
Kevin King, PhD
1 From the Department of Radiology, Mayo Clinic, 200 First St SW, Rochester, MN 55905 (J.F.G., H.H.H.); and GE Medical Systems, Milwaukee, Wis (D.W.S., L.A., K.K.). Recipient of a Certificate of Merit award for an education exhibit at the 2003 RSNA Annual Meeting. Received November 10, 2004; revision requested January 4, 2005; revision received and accepted March 30. J.F.G. and H.H.H. have no financial relationships to disclose.
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Figure 1. Example of the SENSE technique. Reference image of a phantom (a), obtained with the body receiver coil. Sum-of-squares image (b) from two individual coil elements. Spins at spatial locations closer to the coil elements (arrowheads) exhibit higher signal levels than those that are farther away (arrow). A corresponding reference k-space containing 20 phase-encoding views is shown at left. FT = Fourier transform. Low-resolution full-FOV calibration images (c and d) for each coil, which were obtained to calculate the complex sensitivity profiles of each coil element. Sensitivities (s1 and s2) of each coil element are illustrated at two arbitrary points. Reduced-FOV SENSE images (e and f) from each coil element contain extensive wraparound artifacts along the superior-to-inferior phase-encoding axis. a1 and a2 represent the signal intensities of the aliased images that correspond to the arbitrary points chosen in c and d. Diagram of the unaliased image (g) with desired pixel intensities p1 and p2. These intensities can be calculated because the sensitivities of the individual coil elements and the pixel intensities of the aliased images are known. Unaliased image without (h) and with (i) intensity correction, which represents the SENSE-reconstructed image.
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Figure 2. Axial contrast-enhanced 2D spoiled gradient-echo (SPGR) image obtained with SENSE (acceleration factor = 2, applied in the anteroposterior phase-encoding direction) shows extensive artifact in the center of the image due to uncorrected aliasing. This artifact could be reduced by increasing the FOV in the anteroposterior direction.
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Figure 3a. (a) Standard axial 2D steady-state free precession image of the liver. (b) SENSE image (acceleration factor = 2, applied in the anteroposterior phase-encoding direction) obtained with the same FOV as in a. Noise and reconstruction artifacts in the middle of the FOV limit the diagnostic quality of the image. (c) SENSE image (acceleration factor = 2) obtained with an increased phase FOV in the anteroposterior direction shows that the artifacts have been eliminated. Note that the phase ghosting artifact due to aortic pulsation in the standard image has been significantly reduced in the SENSE images.
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Figure 3b. (a) Standard axial 2D steady-state free precession image of the liver. (b) SENSE image (acceleration factor = 2, applied in the anteroposterior phase-encoding direction) obtained with the same FOV as in a. Noise and reconstruction artifacts in the middle of the FOV limit the diagnostic quality of the image. (c) SENSE image (acceleration factor = 2) obtained with an increased phase FOV in the anteroposterior direction shows that the artifacts have been eliminated. Note that the phase ghosting artifact due to aortic pulsation in the standard image has been significantly reduced in the SENSE images.
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Figure 3c. (a) Standard axial 2D steady-state free precession image of the liver. (b) SENSE image (acceleration factor = 2, applied in the anteroposterior phase-encoding direction) obtained with the same FOV as in a. Noise and reconstruction artifacts in the middle of the FOV limit the diagnostic quality of the image. (c) SENSE image (acceleration factor = 2) obtained with an increased phase FOV in the anteroposterior direction shows that the artifacts have been eliminated. Note that the phase ghosting artifact due to aortic pulsation in the standard image has been significantly reduced in the SENSE images.
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Figure 4a. Partial volume maximum intensity projection images from 3D contrast-enhanced renal MR angiography. The images were obtained in the right (a, c) and left (b, d) lateral oblique projections without (a, b) and with (c, d) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). Note the improved visualization of segmental renal arteries in the SENSE images. The patient was short of breath and had difficulty suspending respiration for the standard acquisition time. Parallel imaging was used to reduce the acquisition time from 19 seconds to 10 seconds.
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Figure 4b. Partial volume maximum intensity projection images from 3D contrast-enhanced renal MR angiography. The images were obtained in the right (a, c) and left (b, d) lateral oblique projections without (a, b) and with (c, d) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). Note the improved visualization of segmental renal arteries in the SENSE images. The patient was short of breath and had difficulty suspending respiration for the standard acquisition time. Parallel imaging was used to reduce the acquisition time from 19 seconds to 10 seconds.
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Figure 4c. Partial volume maximum intensity projection images from 3D contrast-enhanced renal MR angiography. The images were obtained in the right (a, c) and left (b, d) lateral oblique projections without (a, b) and with (c, d) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). Note the improved visualization of segmental renal arteries in the SENSE images. The patient was short of breath and had difficulty suspending respiration for the standard acquisition time. Parallel imaging was used to reduce the acquisition time from 19 seconds to 10 seconds.
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Figure 4d. Partial volume maximum intensity projection images from 3D contrast-enhanced renal MR angiography. The images were obtained in the right (a, c) and left (b, d) lateral oblique projections without (a, b) and with (c, d) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). Note the improved visualization of segmental renal arteries in the SENSE images. The patient was short of breath and had difficulty suspending respiration for the standard acquisition time. Parallel imaging was used to reduce the acquisition time from 19 seconds to 10 seconds.
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Figure 5a. Partial volume maximum intensity projection images from renal MR angiography of a patient with fibromuscular dysplasia, obtained without (a) and with (b) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). In the standard image, early filling of the left renal vein limits visualization of the left renal artery. Venous contamination is eliminated in the SENSE image, which was obtained with the acquisition time reduced by half. Collecting system activity in the SENSE image is due to excretion of contrast material from the first non-SENSE acquisition.
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Figure 5b. Partial volume maximum intensity projection images from renal MR angiography of a patient with fibromuscular dysplasia, obtained without (a) and with (b) SENSE (acceleration factor = 2, applied in the in-plane right-left phase-encoding direction). In the standard image, early filling of the left renal vein limits visualization of the left renal artery. Venous contamination is eliminated in the SENSE image, which was obtained with the acquisition time reduced by half. Collecting system activity in the SENSE image is due to excretion of contrast material from the first non-SENSE acquisition.
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Figure 6a. Time-resolved pulmonary MR angiography performed with SENSE (acceleration factor = 2.4) in a patient suspected to have a pulmonary embolus. A 5-mL dose of contrast material was injected at 4 mL/sec, and images were acquired from five phases with a temporal resolution of 2.4 seconds. Maximum intensity projection images from successive frames show minimal contrast material in the right ventricle and outflow tract (a), optimal demonstration of the pulmonary arteries (b), mixed signal from the pulmonary arteries and veins (c), optimal demonstration of the pulmonary veins (d), and the aorta (e).
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Figure 6b. Time-resolved pulmonary MR angiography performed with SENSE (acceleration factor = 2.4) in a patient suspected to have a pulmonary embolus. A 5-mL dose of contrast material was injected at 4 mL/sec, and images were acquired from five phases with a temporal resolution of 2.4 seconds. Maximum intensity projection images from successive frames show minimal contrast material in the right ventricle and outflow tract (a), optimal demonstration of the pulmonary arteries (b), mixed signal from the pulmonary arteries and veins (c), optimal demonstration of the pulmonary veins (d), and the aorta (e).
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Figure 6c. Time-resolved pulmonary MR angiography performed with SENSE (acceleration factor = 2.4) in a patient suspected to have a pulmonary embolus. A 5-mL dose of contrast material was injected at 4 mL/sec, and images were acquired from five phases with a temporal resolution of 2.4 seconds. Maximum intensity projection images from successive frames show minimal contrast material in the right ventricle and outflow tract (a), optimal demonstration of the pulmonary arteries (b), mixed signal from the pulmonary arteries and veins (c), optimal demonstration of the pulmonary veins (d), and the aorta (e).
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Figure 6d. Time-resolved pulmonary MR angiography performed with SENSE (acceleration factor = 2.4) in a patient suspected to have a pulmonary embolus. A 5-mL dose of contrast material was injected at 4 mL/sec, and images were acquired from five phases with a temporal resolution of 2.4 seconds. Maximum intensity projection images from successive frames show minimal contrast material in the right ventricle and outflow tract (a), optimal demonstration of the pulmonary arteries (b), mixed signal from the pulmonary arteries and veins (c), optimal demonstration of the pulmonary veins (d), and the aorta (e).
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Figure 6e. Time-resolved pulmonary MR angiography performed with SENSE (acceleration factor = 2.4) in a patient suspected to have a pulmonary embolus. A 5-mL dose of contrast material was injected at 4 mL/sec, and images were acquired from five phases with a temporal resolution of 2.4 seconds. Maximum intensity projection images from successive frames show minimal contrast material in the right ventricle and outflow tract (a), optimal demonstration of the pulmonary arteries (b), mixed signal from the pulmonary arteries and veins (c), optimal demonstration of the pulmonary veins (d), and the aorta (e).
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Figure 7. Image from 3D contrast-enhanced MR angiography of the abdominal aorta performed with SENSE (acceleration factor = 2, applied in the in-plane right-left direction) to improve spatial resolution. Forty 1.6-mm-thick sections were obtained in 21 seconds with an in-plane matrix of 320 x 256 and a 32-cm FOV, yielding a high spatial resolution of 1.0 x 1.25 x 1.6 mm.
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Figure 8. Coronal 2D fat-saturated steady-state free precession image of a patient with a metastatic pheo-chromocytoma, obtained with SENSE (acceleration factor = 2, applied in the in-plane right-left direction), shows metastases compressing the intrahepatic inferior vena cava. Twenty 2-mm-thick sections with a 224 x 256 matrix were obtained in a breath hold of 15 seconds.
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Figure 9a. Contrast-enhanced fat-saturated SPGR imaging performed with SENSE (acceleration factor = 2) in a patient with a renal cell carcinoma invading the right renal vein and inferior vena cava. (a) Coronal early venous phase 3D image. Sixty 3-mm-thick sections with a 256 x 224 matrix were obtained in 18 seconds. (b) Axial 2D image. SENSE was used to improve the spatial resolution (320 x 256 matrix) with only minimally increased acquisition time.
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Figure 9b. Contrast-enhanced fat-saturated SPGR imaging performed with SENSE (acceleration factor = 2) in a patient with a renal cell carcinoma invading the right renal vein and inferior vena cava. (a) Coronal early venous phase 3D image. Sixty 3-mm-thick sections with a 256 x 224 matrix were obtained in 18 seconds. (b) Axial 2D image. SENSE was used to improve the spatial resolution (320 x 256 matrix) with only minimally increased acquisition time.
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Figure 10a. Axial arterial phase (a, b) and portal venous phase (c, d) fat-saturated 3D SPGR images of a patient with a metastatic neuroendocrine tumor. The images were obtained with SENSE (acceleration factor = 2, applied in the anteroposterior phase-encoding direction), with a and c acquired slightly superior to b and d. SENSE was used to achieve both excellent temporal and excellent spatial resolution. In this case, achieving optimal timing and adequate coverage in the arterial phase was crucial because many of the early enhancing hepatic and osseous metastases could not be visualized on images from subsequent phases.
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Figure 10b. Axial arterial phase (a, b) and portal venous phase (c, d) fat-saturated 3D SPGR images of a patient with a metastatic neuroendocrine tumor. The images were obtained with SENSE (acceleration factor = 2, applied in the anteroposterior phase-encoding direction), with a and c acquired slightly superior to b and d. SENSE was used to achieve both excellent temporal and excellent spatial resolution. In this case, achieving optimal timing and adequate coverage in the arterial phase was crucial because many of the early enhancing hepatic and osseous metastases could not be visualized on images from subsequent phases.
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Figure 10c. Axial arterial phase (a, b) and portal venous phase (c, d) fat-saturated 3D SPGR images of a patient with a metastatic neuroendocrine tumor. The images were obtained with SENSE (acceleration factor = 2, applied in the anteroposterior phase-encoding direction), with a and c acquired slightly superior to b and d. SENSE was used to achieve both excellent temporal and excellent spatial resolution. In this case, achieving optimal timing and adequate coverage in the arterial phase was crucial because many of the early enhancing hepatic and osseous metastases could not be visualized on images from subsequent phases.
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Figure 10d. Axial arterial phase (a, b) and portal venous phase (c, d) fat-saturated 3D SPGR images of a patient with a metastatic neuroendocrine tumor. The images were obtained with SENSE (acceleration factor = 2, applied in the anteroposterior phase-encoding direction), with a and c acquired slightly superior to b and d. SENSE was used to achieve both excellent temporal and excellent spatial resolution. In this case, achieving optimal timing and adequate coverage in the arterial phase was crucial because many of the early enhancing hepatic and osseous metastases could not be visualized on images from subsequent phases.
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Figure 11. Axial contrast-enhanced fat-saturated 3D SPGR image of a patient with renal insufficiency who was suspected to have a pulmonary embolus. SENSE (acceleration factor = 2.2, applied in the anteroposterior in-plane phase-encoding direction) was used to reduce the acquisition time to 10 seconds because the patient was moderately short of breath. Note the large embolus in the left lower lobe segmental artery (arrow).
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Figure 12a. Coronal single-shot fast SE image obtained without (a) and with (b) SENSE (acceleration factor = 2). Although the SENSE image has slightly diminished SNR, it also has slightly less blurring.
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Figure 12b. Coronal single-shot fast SE image obtained without (a) and with (b) SENSE (acceleration factor = 2). Although the SENSE image has slightly diminished SNR, it also has slightly less blurring.
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Figure 13. Maximum intensity projection image from 3D fast-recovery fast SE MR cholangiopancreatography. SENSE (acceleration factor = 2) was used to reduce the acquisition time sufficiently so that an adequate volume could be obtained within a comfortable breath hold.
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Figure 14a. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 14b. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 14c. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 14d. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 14e. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 14f. Short-axis cardiac steady-state free precession cine images (in end diastole) obtained from apex to base by using SENSE (acceleration factor = 2). Three sections were acquired per breath hold, allowing the total acquisition time to be considerably shortened.
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Figure 15a. Axial double (a) and triple (b) inversion-recovery images of a patient with lung cancer and mediastinal metastases. SENSE (acceleration factor = 2) was used to reduce the acquisition time from 15 seconds to 8 seconds.
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Figure 15b. Axial double (a) and triple (b) inversion-recovery images of a patient with lung cancer and mediastinal metastases. SENSE (acceleration factor = 2) was used to reduce the acquisition time from 15 seconds to 8 seconds.
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Figure 16. Subvolume maximum intensity projection image of the right coronary artery from nonenhanced fat-saturated steady-state free precession MR angiography performed with SENSE (acceleration factor = 2). Both spatial resolution and spatial coverage were slightly increased over those achieved with the standard acquisition.
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Figure 17. Sagittal image of a patient with residual breast carcinoma after an excisional biopsy, obtained with a dynamic contrast-enhanced 3D fat-saturated SPGR sequence. Use of SENSE (acceleration factor = 2) allowed coverage of both breasts with adequate spatial resolution and adequate temporal resolution.
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Figure 18. Coronal contrast-enhanced fat-saturated 2D SPGR image of a patient with Crohn disease shows mild thickening and enhancement of the terminal ileum. SENSE (acceleration factor = 2) was used to reduce the acquisition time and thereby decrease motion artifact caused by peristalsis.
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Copyright © 2005 by the Radiological Society of North America.
