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Holdsworth SJ, Yeom KW, Antonucci MU, Andre JB, Rosenberg J, Aksoy M, Straka M, Fischbein NJ, Bammer R, Moseley ME, Zaharchuk G, Skare S. Diffusion-weighted imaging with dual-echo echo-planar imaging for better sensitivity to acute stroke. AJNR Am J Neuroradiol 2014; 35:1293-302. [PMID: 24763417 DOI: 10.3174/ajnr.a3921] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
BACKGROUND AND PURPOSE Parallel imaging facilitates the acquisition of echo-planar images with a reduced TE, enabling the incorporation of an additional image at a later TE. Here we investigated the use of a parallel imaging-enhanced dual-echo EPI sequence to improve lesion conspicuity in diffusion-weighted imaging. MATERIALS AND METHODS Parallel imaging-enhanced dual-echo DWI data were acquired in 50 consecutive patients suspected of stroke at 1.5T. The dual-echo acquisition included 2 EPI for 1 diffusion-preparation period (echo 1 [TE = 48 ms] and echo 2 [TE = 105 ms]). Three neuroradiologists independently reviewed the 2 echoes by using the routine DWI of our institution as a reference. Images were graded on lesion conspicuity, diagnostic confidence, and image quality. The apparent diffusion coefficient map from echo 1 was used to validate the presence of acute infarction. Relaxivity maps calculated from the 2 echoes were evaluated for potential complementary information. RESULTS Echo 1 and 2 DWIs were rated as better than the reference DWI. While echo 1 had better image quality overall, echo 2 was unanimously favored over both echo 1 and the reference DWI for its high sensitivity in detecting acute infarcts. CONCLUSIONS Parallel imaging-enhanced dual-echo diffusion-weighted EPI is a useful method for evaluating lesions with reduced diffusivity. The long TE of echo 2 produced DWIs that exhibited superior lesion conspicuity compared with images acquired at a shorter TE. Echo 1 provided higher SNR ADC maps for specificity to acute infarction. The relaxivity maps may serve to complement information regarding blood products and mineralization.
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Affiliation(s)
- S J Holdsworth
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - K W Yeom
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - M U Antonucci
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - J B Andre
- Department of Radiology (J.B.A.), University of Washington, Seattle, Washington
| | - J Rosenberg
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - M Aksoy
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - M Straka
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - N J Fischbein
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - R Bammer
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - M E Moseley
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - G Zaharchuk
- From the Department of Radiology (S.J.H., K.W.Y., M.U.A., J.R., M.A., M.S., N.J.F., R.B., M.E.M., G.Z.), Stanford University, Stanford, California
| | - S Skare
- Clinical Neuroscience (S.S.), Karolinska Institute, Stockholm, Sweden
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Choli M, Jakob PM, Loeffler RB, Hillenbrand CM. Mixed-bandwidth acquisitions: signal-to-noise ratio and signal-to-noise efficiency. J Magn Reson Imaging 2010; 32:997-1002. [PMID: 20882633 DOI: 10.1002/jmri.22327] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022] Open
Abstract
PURPOSE To evaluate signal-to-noise ratio (SNR) and SNR efficiency in mixed-bandwidth acquisition (MBA). SNR efficiency describes the achievable SNR per unit time and is a basic aspect in clinical applications to optimize work flow. MATERIALS AND METHODS Corresponding simulations were performed and predictions of the theory verified in phantom experiments and volunteers. Specifically, SNR and SNR efficiencies were compared for an MBA fast low-angle shot (MBA-FLASH) sequence and traditional single-bandwidth acquisitions. RESULTS MBAs result in an SNR penalty compared to single-bandwidth acquisitions for a given sampling time. Furthermore, the nonuniform distribution of noise characteristics in k-space introduced by MBA sequences caused potential changes in noise texture of the image. CONCLUSION Overall, the MBA-FLASH imaging experiments in phantoms and healthy volunteers support the feasibility of using dual or multiple bandwidth acquisitions, which may be important in alternative imaging schemes that combine multiple acquisition techniques.
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Affiliation(s)
- Morwan Choli
- Research Center for Magnetic Resonance Bavaria e.V. (MRB), Wuerzburg, Germany.
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Mekle R, Wu EX, Meckel S, Wetzel SG, Scheffler K. Combo acquisitions: balancing scan time reduction and image quality. Magn Reson Med 2006; 55:1093-105. [PMID: 16598731 DOI: 10.1002/mrm.20882] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
Abstract
Recently a new technique for the combined acquisition of multicontrast images, termed "combo acquisition," was introduced. In combo acquisitions, the three concepts of 1) variable acquisition parameters, 2) k-space data sharing, and 3) multicontrast imaging are systematically integrated to reduce MRI scan time and improve data utilization in a clinical setting. In this study, two-contrast and three-contrast spin-echo (SE) and turbo spin-echo (TSE) combo acquisition protocols that were designed and optimized in simulation experiments were implemented on a 1.5 T clinical scanner. Phantom and human brain data from volunteers and patients were acquired. Scan time reductions of 25-52% were achieved compared to standard acquisitions, largely confirming the simulation results. We evaluated the resulting images by quantitatively analyzing the preservation of contrast and the signal-to-noise ratio (SNR). In addition, data sets for 10 clinical cases obtained with TSE combo and corresponding standard acquisitions were graded by two experienced neuroradiologists in terms of the level of artifacts and image quality for comparison. Only minor image degradation with the combo scans was observed, indicating an inherent trade-off between scan time reduction and image quality. The specific aspects of combo acquisitions with respect to motion, flow, and k-space data weighting are discussed.
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Affiliation(s)
- Ralf Mekle
- MR-Physics, Department of Medical Radiology, University of Basel/University Hospital, Basel, Switzerland.
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Mekle R, Laine AF, Wu EX. Combined MR data acquisition of multicontrast images using variable acquisition parameters and K-space data sharing. IEEE TRANSACTIONS ON MEDICAL IMAGING 2003; 22:806-823. [PMID: 12906235 DOI: 10.1109/tmi.2003.815054] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/24/2023]
Abstract
A new technique to reduce clinical magnetic resonance imaging (MRI) scan time by varying acquisition parameters and sharing k-space data between images, is proposed. To improve data utilization, acquisition of multiple images of different contrast is combined into a single scan, with variable acquisition parameters including repetition time (TR), echo time (TE), and echo train length (ETL). This approach is thus referred to as a "combo acquisition." As a proof of concept, simulations of MRI experiments using spin echo (SE) and fast SE (FSE) sequences were performed based on Bloch equations. Predicted scan time reductions of 25%-50% were achieved for 2-contrast and 3-contrast combo acquisitions. Artifacts caused by nonuniform k-space data weighting were suppressed through semi-empirical optimization of parameter variation schemes and the phase encoding order. Optimization was assessed by minimizing three quantitative criteria: energy of the "residue point spread function (PSF)," energy of "residue profiles" across sharp tissue boundaries, and energy of "residue images." In addition, results were further evaluated by quantitatively analyzing the preservation of contrast, the PSF, and the signal-to-noise ratio. Finally, conspicuity of lesions was investigated for combo acquisitions in comparison with standard scans. Implications and challenges for the practical use of combo acquisitions are discussed.
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Affiliation(s)
- Ralf Mekle
- Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA.
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Melhem ER, Patel RT, Whitehead RE, Bhatia RG, Rockwell DT, Jara H. MR imaging of hemorrhagic brain lesions: a comparison of dual-echo gradient- and spin-echo and fast spin-echo techniques. AJR Am J Roentgenol 1998; 171:797-802. [PMID: 9725319 DOI: 10.2214/ajr.171.3.9725319] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE Our objective was to assess the usefulness of the dual-echo gradient- and spin-echo (GRASE) technique in revealing acute hemorrhagic brain lesions and compare GRASE and fast spin-echo techniques for revealing acute hemorrhagic lesions and image artifacts. MATERIALS AND METHODS Thirty-two consecutive patients with acute intracranial hemorrhage underwent dual-echo GRASE (TEeff1/TEeff2, 35/85) and fast spin-echo (25/110) imaging. The techniques were matched for TR (3032 msec), spatial resolution, and acquisition time. Two neuroradiologists reviewed the images independently, documenting the number, size (<1, >1, or 1 cm in diameter), location, and signal characteristics (hypointense versus hyperintense compared with brain) of detectable lesions. These observers also compared matched T2- and proton density-weighted GRASE and fast spin-echo images for paramagnetic lesion conspicuity, diamagnetic susceptibility artifacts, chemical shift artifacts along the phase- and frequency-encoding directions, and artifactual CSF hyperintensity in the thin curvilinear cortical sulci and the Virchow-Robin spaces on only the proton density-weighted images. RESULTS The average number and conspicuity of dark (paramagnetic) lesions were significantly greater on GRASE than on fast spin-echo images (p < .05 and p < .001, respectively). We found no significant difference in the average number of bright lesions revealed by either technique (p > .1). Chemical shift artifacts along the phase-encoding directions were more prominent on GRASE than on fast spin-echo imaging. Chemical shift artifacts along the frequency-encoding directions and artifactual CSF hyperintensity were more prominent on fast spin-echo than on GRASE imaging. No visually apparent difference was found in the degree of diamagnetic susceptibility artifacts seen with the two techniques. CONCLUSION Dual-echo GRASE imaging can be helpful in the examination of patients with suspected acute brain hemorrhage.
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Affiliation(s)
- E R Melhem
- Department of Radiology, Boston University School of Medicine, Boston Medical Center, MA 02118, USA
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7
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Hittmair K, Umek W, Schindler EG, Ba-Ssalamah A, Pretterklieber ML, Herold CJ. Fast flair imaging of the brain using the fast spin-echo and gradient spin-echo technique. Magn Reson Imaging 1997; 15:405-14. [PMID: 9223041 DOI: 10.1016/s0730-725x(96)00381-5] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
The purpose of this study was to compare the gradient spin-echo (GRASE) to the fast spin-echo (FSE) implementation of fast fluid-attenuated inversion recovery (FLAIR) sequences for brain imaging. Thirty patients with high signal intensity lesions on T2-weighted images were examined on a 1.5 T MR system. Scan time-minimized thin-section FLAIR-FSE and FLAIR-GRASE sequences were obtained and compared side by side. Image assessment criteria were lesion conspicuity, contrast between different types of normal tissue, image quality, and artifacts. In addition, contrast ratios and contrast-to-noise ratios were determined. Compared to FSF, the GRASE technique allowed a 17% reduction in scan time but conspicuity of small lesions in particular was significantly lower on FLAIR-GRASE images because of higher image noise and increased artifacts. Gray-white differentiation was slightly worse on FLAIR-GRASE. Physiological ferritin deposition appeared slightly darker on FLAIR-GRASE images and susceptibility artifacts were stronger. Fatty tissue was less bright with FLAIR-GRASE. With current standard hardware equipment, the GRASE technique is not an adequate alternative to FSE for the implementation of fast FLAIR sequences in routine clinical MR brain imaging.
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Affiliation(s)
- K Hittmair
- Department of Neuroradiology, University of Vienna, Austria
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Keller PJ, Karis JP, Fram EK, Heiserman JE, Drayer BP. An alternative to GRASE: toward spin-echo-like contrast with independent reconstruction of gradient-echo images. Magn Reson Med 1996; 36:804-8. [PMID: 8916034 DOI: 10.1002/mrm.1910360523] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Multiple gradient echoes are generated for each RF echo of a Carr-Purcell-Meiboom-Gill (CPMG) train. Independently, phase-encoded fast spin-echo images are obtained from the different gradient echoes. Presently, three images are formed from three gradient-echoes from each of four RF echoes. The two peripheral gradient echo images are encoded for a late effective TE, then summed after reconstruction: this image has decreased fat intensity and increased susceptibility contrast compared with fast spin echo. The central gradient echoes yielded another image of intermediate contrast useful for neuroimaging. Raw data from the variously timed gradient echoes are not combined as they are in GRASE.
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Affiliation(s)
- P J Keller
- Department of MRI Research, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ 85013-4496, USA
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Fellner F, Schmitt R, Trenkler J, Fellner C, Böhm-Jurkovic H. Turbo gradient-spin-echo (GRASE): first clinical experiences with a fast T2-weighted sequence in MRI of the brain. Eur J Radiol 1995; 19:171-6. [PMID: 7601166 DOI: 10.1016/0720-048x(94)00598-7] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The aim of this study was to obtain first clinical experiences with Turbo gradient-spin-echo (TGSE). This fast MRI technique is based on the GRASE sequence which combines the gradient-echo and the spin-echo technique. In 60 patients suffering from different brain pathologies, a T2-weighted TGSE sequence was compared to a conventional spin-echo sequence. Anatomical and pathological structures were evaluated visually by three independent observers; signal and contrast behavior was assessed in regions of interest. TGSE showed reduced signal-to-noise-ratios of anatomical structures except for cerebrospinal fluid. The contrast of tumors, infarctions, and hematomas was similar in both sequence types. Small microangiopathic and inflammatory lesions as well as basal ganglia degeneration presented with diminished contrast in TGSE. The TGSE sequence can already now be used to acquire T2-weighted images in additional orientations requiring extremely short measurement time. However, further improvements of image quality are necessary for routine use of TGSE.
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Affiliation(s)
- F Fellner
- Department of Radiodiagnostics, Klinikum Ingolstadt, Germany
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