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Eisen CK, Liebig P, Herrler J, Ritter D, Lévy S, Uder M, Nagel AM, Grodzki D. Fast online spectral-spatial pulse design for subject-specific fat saturation in cervical spine and foot imaging at 1.5 T. MAGMA (NEW YORK, N.Y.) 2024; 37:257-272. [PMID: 38366129 PMCID: PMC10995033 DOI: 10.1007/s10334-024-01149-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/04/2023] [Revised: 01/12/2024] [Accepted: 01/12/2024] [Indexed: 02/18/2024]
Abstract
OBJECTIVE To compensate subject-specific field inhomogeneities and enhance fat pre-saturation with a fast online individual spectral-spatial (SPSP) single-channel pulse design. METHODS The RF shape is calculated online using subject-specific field maps and a predefined excitation k-space trajectory. Calculation acceleration options are explored to increase clinical viability. Four optimization configurations are compared to a standard Gaussian spectral selective pre-saturation pulse and to a Dixon acquisition using phantom and volunteer (N = 5) data at 1.5 T with a turbo spin echo (TSE) sequence. Measurements and simulations are conducted across various body parts and image orientations. RESULTS Phantom measurements demonstrate up to a 3.5-fold reduction in residual fat signal compared to Gaussian fat saturation. In vivo evaluations show improvements up to sixfold for dorsal subcutaneous fat in sagittal cervical spine acquisitions. The versatility of the tailored trajectory is confirmed through sagittal foot/ankle, coronal, and transversal cervical spine experiments. Additional measurements indicate that excitation field (B1) information can be disregarded at 1.5 T. Acceleration methods reduce computation time to a few seconds. DISCUSSION An individual pulse design that primarily compensates for main field (B0) inhomogeneities in fat pre-saturation is successfully implemented within an online "push-button" workflow. Both fat saturation homogeneity and the level of suppression are improved.
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Affiliation(s)
- Christian Karl Eisen
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany.
| | - Patrick Liebig
- Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany
| | - Jürgen Herrler
- Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany
| | - Dieter Ritter
- Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany
| | - Simon Lévy
- MR Research Collaborations, Siemens Healthcare Pty Ltd, Melbourne, Australia
| | - Michael Uder
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
| | - Armin Michael Nagel
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
- Division of Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany
| | - David Grodzki
- Institute of Radiology, University Hospital Erlangen, Friedrich-Alexander-Universität Erlangen-Nürnberg (FAU), Erlangen, Germany
- Magnetic Resonance, Siemens Healthcare GmbH, Erlangen, Germany
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Feuerriegel GC, Sutter R. Managing hardware-related metal artifacts in MRI: current and evolving techniques. Skeletal Radiol 2024:10.1007/s00256-024-04624-4. [PMID: 38381196 DOI: 10.1007/s00256-024-04624-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/15/2023] [Revised: 02/11/2024] [Accepted: 02/12/2024] [Indexed: 02/22/2024]
Abstract
Magnetic resonance imaging (MRI) around metal implants has been challenging due to magnetic susceptibility differences between metal implants and adjacent tissues, resulting in image signal loss, geometric distortion, and loss of fat suppression. These artifacts can compromise the diagnostic accuracy and the evaluation of surrounding anatomical structures. As the prevalence of total joint replacements continues to increase in our aging society, there is a need for proper radiological assessment of tissues around metal implants to aid clinical decision-making in the management of post-operative complaints and complications. Various techniques for reducing metal artifacts in musculoskeletal imaging have been explored in recent years. One approach focuses on improving hardware components. High-density multi-channel radiofrequency (RF) coils, parallel imaging techniques, and gradient warping correction enable signal enhancement, image acquisition acceleration, and geometric distortion minimization. In addition, the use of susceptibility-matched implants and low-field MRI helps to reduce magnetic susceptibility differences. The second approach focuses on metal artifact reduction sequences such as view-angle tilting (VAT) and slice-encoding for metal artifact correction (SEMAC). Iterative reconstruction algorithms, deep learning approaches, and post-processing techniques are used to estimate and correct artifact-related errors in reconstructed images. This article reviews recent developments in clinically applicable metal artifact reduction techniques as well as advances in MR hardware. The review provides a better understanding of the basic principles and techniques, as well as an awareness of their limitations, allowing for a more reasoned application of these methods in clinical settings.
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Affiliation(s)
- Georg C Feuerriegel
- Department of Radiology, Balgrist University Hospital, Faculty of Medicine, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland.
| | - Reto Sutter
- Department of Radiology, Balgrist University Hospital, Faculty of Medicine, University of Zurich, Forchstrasse 340, 8008, Zurich, Switzerland
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Sacher SE, Koff MF, Tan ET, Burge A, Potter HG. The role of advanced metal artifact reduction MRI in the diagnosis of periprosthetic joint infection. Skeletal Radiol 2023:10.1007/s00256-023-04483-5. [PMID: 37875571 PMCID: PMC11039568 DOI: 10.1007/s00256-023-04483-5] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/03/2023] [Revised: 10/09/2023] [Accepted: 10/10/2023] [Indexed: 10/26/2023]
Abstract
Identification and diagnosis of periprosthetic joint infection (PJI) are challenging, requiring a multi-disciplinary approach involving clinical evaluation, laboratory tests, and imaging studies. MRI is advantageous to alternative imaging techniques due to superior soft tissue contrast and absence of ionizing radiation. However, the presence of metallic implants can cause signal loss and artifacts. Metal artifact suppression (MARS) MRI techniques have been developed that mitigate metal artifacts and improve periprosthetic soft tissue visualization. This paper provides a review of the various MARS MRI techniques, their clinical applicability and accuracy in PJI diagnosis and evaluation, and current challenges and future perspectives.
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Affiliation(s)
- Sara E Sacher
- Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th St, New York, NY, 10021, USA.
| | - Matthew F Koff
- Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th St, New York, NY, 10021, USA
| | - Ek T Tan
- Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th St, New York, NY, 10021, USA
| | - Alissa Burge
- Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th St, New York, NY, 10021, USA
| | - Hollis G Potter
- Department of Radiology and Imaging, Hospital for Special Surgery, 535 East 70th St, New York, NY, 10021, USA.
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Azhar S, Chong LR. Clinician's guide to the basic principles of MRI. Postgrad Med J 2023; 99:894-903. [PMID: 37130816 DOI: 10.1136/pmj-2022-141998] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2022] [Accepted: 09/06/2022] [Indexed: 11/04/2022]
Abstract
MRI is an important and widely used imaging modality for clinical diagnosis. This article provides a concise discussion of the basic principles of MRI physics for non-radiology clinicians, with a general explanation of the fundamentals of signal generation and image contrast mechanisms. Common pulse sequences, tissue suppression techniques and use of gadolinium contrast with relevant clinical applications are presented. Knowledge of these concepts would provide an appreciation of how MR images are acquired and interpreted to facilitate interdisciplinary understanding between radiologists and referring clinicians.
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Affiliation(s)
- Syifa Azhar
- Department of Radiology, SingHealth Group, Singapore
| | - Le Roy Chong
- Department of Radiology, Changi General Hospital, Singapore
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5
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Stewart HL, Easley JT, Selberg KT, Puttlitz CM, Nakamura LK, Johnson JW, Kawcak CE. Experimental models of bone marrow lesions in ovine femoral condyles. Vet Surg 2023; 52:284-298. [PMID: 36523261 PMCID: PMC10108275 DOI: 10.1111/vsu.13919] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2022] [Revised: 09/27/2022] [Accepted: 10/31/2022] [Indexed: 12/23/2022]
Abstract
OBJECTIVE To develop an in vivo experimental model for bone marrow lesions (BMLs) in ovine femorotibial joints. STUDY DESIGN Randomized, prospective experimental study. ANIMALS Eighteen healthy, skeletally-mature Dorper cross ewes. METHODS One medial femoral condyle was penetrated with a 1.1 mm pin, and the contralateral medial femoral condyle was treated with transcutaneous extracorporeal shockwave (ESW) at 0.39 ± 0.04 mJ/mm2 . Clinical examination, magnetic resonance imaging (MRI), computed tomography (CT), and histopathological analyses were used to detect and characterize the development and progression of BMLs in the medial femoral condyle at 4, 8, and 12 weeks post-surgery. RESULTS Pin penetration induced a BML detected on MRI within 2 weeks and lasted at least 12 weeks. BMLs were not observed in ESW-treated condyles. Histologically, BMLs were characterized by hemorrhage and inflammatory cellular infiltrate, and progressed to more dense fibrous tissue over time. Pathological changes were not observed in the articular cartilage overlying the region of BMLs. CONCLUSIONS Direct, focal trauma to all layers of the osteochondral unit was sufficient to create an experimentally-induced BML which persisted for at least 90 days. The protocol used for ESW in this study did not induce BMLs. CLINICAL SIGNIFICANCE Experimental induction of BMLs is possible and mimicked naturally occurring disease states. Volumetric imaging is a sensitive method for characterization of the dynamic nature of these lesions.
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Affiliation(s)
- Holly L Stewart
- Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA
| | - Jeremiah T Easley
- Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA
| | - Kurt T Selberg
- Environmental & Radiological Health Sciences Department, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA
| | - Christian M Puttlitz
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado, USA
| | - Lucas K Nakamura
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado, USA
| | - Jimmy W Johnson
- Department of Mechanical Engineering, Colorado State University, Fort Collins, Colorado, USA
| | - Christopher E Kawcak
- Department of Clinical Sciences, College of Veterinary Medicine and Biomedical Sciences, Colorado State University, Fort Collins, Colorado, USA
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Germann C, Nanz D, Sutter R. Magnetic Resonance Imaging Around Metal at 1.5 Tesla: Techniques From Basic to Advanced and Clinical Impact. Invest Radiol 2021; 56:734-748. [PMID: 34074944 DOI: 10.1097/rli.0000000000000798] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
ABSTRACT During the last decade, metal artifact reduction in magnetic resonance imaging (MRI) has been an area of intensive research and substantial improvement. The demand for an excellent diagnostic MRI scan quality of tissues around metal implants is closely linked to the steadily increasing number of joint arthroplasty (especially knee and hip arthroplasties) and spinal stabilization procedures. Its unmatched soft tissue contrast and cross-sectional nature make MRI a valuable tool in early detection of frequently encountered postoperative complications, such as periprosthetic infection, material wear-induced synovitis, osteolysis, or damage of the soft tissues. However, metal-induced artifacts remain a constant challenge. Successful artifact reduction plays an important role in the diagnostic workup of patients with painful/dysfunctional arthroplasties and helps to improve patient outcome. The artifact severity depends both on the implant and the acquisition technique. The implant's material, in particular its magnetic susceptibility and electrical conductivity, its size, geometry, and orientation in the MRI magnet are critical. On the acquisition side, the magnetic field strength, the employed imaging pulse sequence, and several acquisition parameters can be optimized. As a rule of thumb, the choice of a 1.5-T over a 3.0-T magnet, a fast spin-echo sequence over a spin-echo or gradient-echo sequence, a high receive bandwidth, a small voxel size, and short tau inversion recovery-based fat suppression can mitigate the impact of metal artifacts on diagnostic image quality. However, successful imaging of large orthopedic implants (eg, arthroplasties) often requires further optimized artifact reduction methods, such as slice encoding for metal artifact correction or multiacquisition variable-resonance image combination. With these tools, MRI at 1.5 T is now widely considered the modality of choice for the clinical evaluation of patients with metal implants.
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Hopp AC, Fahrenholtz SJ, Bashford JV, Long JR, Panda A, Katz DS, Flug JA. The Magnet Is Sometimes "Off"-Practical Strategies for Optimizing Challenging Musculoskeletal MR Imaging. Curr Probl Diagn Radiol 2021; 51:392-402. [PMID: 33836928 DOI: 10.1067/j.cpradiol.2021.03.007] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/02/2020] [Revised: 02/05/2021] [Accepted: 03/04/2021] [Indexed: 11/22/2022]
Abstract
To describe practical solutions to the unique technical challenges of musculoskeletal magnetic resonance imaging, including off-isocenter imaging, artifacts from motion and metal prostheses, small field-of-view imaging, and non-conventional scan angles and slice positioning. Unique challenges of musculoskeletal magnetic resonance imaging require a collaborative approach involving radiologists, physicists, and technologists utilizing optimized magnetic resonance protocols, specialized coils, and unique patient positioning, in order to reliably diagnose critical musculoskeletal MR image findings.
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Affiliation(s)
- Alix C Hopp
- Mayo Clinic Arizona, Department of Radiology, Phoenix, AZ.
| | | | | | | | - Anshuman Panda
- Mayo Clinic Arizona, Department of Radiology, Phoenix, AZ
| | - Douglas S Katz
- NYU Langone Hospital-Long Island, Department of Radiology, Mineola, NY
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Bachrata B, Strasser B, Bogner W, Schmid AI, Korinek R, Krššák M, Trattnig S, Robinson SD. Simultaneous Multiple Resonance Frequency imaging (SMURF): Fat-water imaging using multi-band principles. Magn Reson Med 2021; 85:1379-1396. [PMID: 32981114 PMCID: PMC7756227 DOI: 10.1002/mrm.28519] [Citation(s) in RCA: 7] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2019] [Revised: 07/31/2020] [Accepted: 08/24/2020] [Indexed: 12/15/2022]
Abstract
PURPOSE To develop a fat-water imaging method that allows reliable separation of the two tissues, uses established robust reconstruction methods, and requires only one single-echo acquisition. THEORY AND METHODS The proposed method uses spectrally selective dual-band excitation in combination with CAIPIRINHA to generate separate images of fat and water simultaneously. Spatially selective excitation without cross-contamination is made possible by the use of spatial-spectral pulses. Fat and water images can either be visualized separately, or the fat images can be corrected for chemical shift displacement and, in gradient echo imaging, for chemical shift-related phase discrepancy, and recombined with water images, generating fat-water images free of chemical shift effects. Gradient echo and turbo spin echo sequences were developed based on this Simultaneous Multiple Resonance Frequency imaging (SMURF) approach and their performance was assessed at 3Tesla in imaging of the knee, breasts, and abdomen. RESULTS The proposed method generated well-separated fat and water images with minimal unaliasing artefacts or cross-excitation, evidenced by the near absence of water signal attributed to the fat image and vice versa. The separation achieved was similar to or better than that using separate acquisitions with water- and fat-saturation or Dixon methods. The recombined fat-water images provided similar image contrast to conventional images, but the chemical shift effects were eliminated. CONCLUSION Simultaneous Multiple Resonance Frequency imaging is a robust fat-water imaging technique that offers a solution to imaging of body regions with significant amounts of fat.
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Affiliation(s)
- Beata Bachrata
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria,Christian Doppler Laboratory for Clinical Molecular MR ImagingViennaAustria
| | - Bernhard Strasser
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria,Athinoula A. Martinos Center for Biomedical Imaging, Department of RadiologyMassachusetts General Hospital, Harvard Medical SchoolBostonMAUSA
| | - Wolfgang Bogner
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria
| | - Albrecht Ingo Schmid
- High Field MR Centre, Center for Medical Physics and Biomedical EngineeringMedical University of ViennaViennaAustria
| | - Radim Korinek
- Institute of Scientific Instruments of the CASBrnoCzech Republic
| | - Martin Krššák
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria,Christian Doppler Laboratory for Clinical Molecular MR ImagingViennaAustria,Department of Internal Medicine III, Division of Endocrinology and MetabolismMedical University of ViennaViennaAustria
| | - Siegfried Trattnig
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria,Christian Doppler Laboratory for Clinical Molecular MR ImagingViennaAustria
| | - Simon Daniel Robinson
- High Field MR Centre, Department of Biomedical Imaging and Image‐Guided TherapyMedical University of ViennaViennaAustria,Centre of Advanced ImagingUniversity of QueenslandBrisbaneQLDAustralia,Department of NeurologyMedical University of GrazGrazAustria
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Xu F, Li W, Liu D, Zhu D, Schär M, Myers K, Qin Q. A novel spectrally selective fat saturation pulse design with robustness to B 0 and B 1 inhomogeneities: A demonstration on 3D T 1-weighted breast MRI at 3 T. Magn Reson Imaging 2020; 75:156-161. [PMID: 33130057 DOI: 10.1016/j.mri.2020.10.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2020] [Revised: 10/25/2020] [Accepted: 10/26/2020] [Indexed: 12/01/2022]
Abstract
PURPOSE Spectrally selective fat saturation (FatSat) sequence is commonly used to suppress signal from adipose tissue. Conventional SINC-shaped pulses are sensitive to B0 off-resonance and B1+ offset. Uniform fat saturation with large spatial coverage is especially challenging for the body and breast MRI. The aim of this study is to develop spectrally selective FatSat pulses that offer more immunity to B0/B1+ field inhomogeneities than SINC pulses and evaluate them in bilateral breast imaging at 3 T. MATERIALS AND METHODS Optimized composite pulses (OCP) were designed based on the optimal control theory with robustness to a targeted B0/ B1+ conditions. OCP pulses also allows flexible flip angles to meet different requirements. Comparisons with the vendor-provided SINC pulses were conducted by numerical simulation and in vivo scans using a 3D T1-weighted (T1w) gradient-echo (GRE) sequence with coverage of the whole-breast. RESULTS Simulation revealed that OCP pulses yielded almost half of the transition band and much less sensitivity to B1+ inhomogeneity compared to SINC pulses with B0 off-resonance within ±200 Hz and B1+ scale error within ±0.3 (P < 0.001). Across five normal subjects, OCP FatSat pulses produced 25-41% lower residual fat signals (P < 0.05) with 27-36% less spatial variation (P < 0.05) than SINC. CONCLUSION In contrast to conventional SINC-shaped pulses, the newly designed OCP FatSat pulses mitigated challenges of wide range of B0/ B1+ field inhomogeneities and achieved more uniform fat suppression in bilateral breast T1w imaging at 3 T.
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Affiliation(s)
- Feng Xu
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA.
| | - Wenbo Li
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Dapeng Liu
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
| | - Dan Zhu
- Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, USA
| | - Michael Schär
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Kelly Myers
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA
| | - Qin Qin
- The Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins University School of Medicine, Baltimore, MD, USA; F.M. Kirby Research Center for Functional Brain Imaging, Kennedy Krieger Institute, Baltimore, MD, USA
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Dalto VF, Assad RL, Lorenzato MM, Crema MD, Louzada-Junior P, Nogueira-Barbosa MH. Comparison between STIR and T2-weighted SPAIR sequences in the evaluation of inflammatory sacroiliitis: diagnostic performance and signal-to-noise ratio. Radiol Bras 2020; 53:223-228. [PMID: 32904772 PMCID: PMC7458563 DOI: 10.1590/0100-3984.2019.0077] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Objective To compare two different fat-saturated magnetic resonance imaging (MRI) techniques-STIR and T2 SPAIR-in terms of image quality, as well as in terms of their diagnostic performance in detecting sacroiliac joints (SIJ) active inflammation. Materials and Methods We included 69 consecutive patients with suspected spondyloarthritis undergoing MRI between 2012 and 2014. The signal-to-noise ratio (SNR) was calculated with the method recommended by the American College of Radiology. Two readers evaluated SIJ MRI following ASAS criteria to assess diagnostic performance regarding the detection of active SIJ inflammation. T1 SPIR Gd+ sequence was used as the reference standard. Results The mean SNR was 72.8 for the T1 SPIR Gd+ sequence, compared with 14.1 and 37.6 for the STIR and T2 SPAIR sequences, respectively. The sensitivity and specificity of STIR and SPAIR T2 sequences did not show any statistically significant differences, for the diagnosis of sacroiliitis with active inflammation. Conclusion Our results corroborate those in the recent literature suggesting that STIR sequences are not superior to T2 SPAIR sequences for SIJ evaluation in patients with suspected spondyloarthritis. On 1.5-T MRI, T2-weighted SPAIR sequences provide better SNRs than do STIR sequences, which reinforces that T2 SPAIR sequences may be an advantageous option for the evaluation of sacroiliitis.
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Affiliation(s)
- Vitor Faeda Dalto
- Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FMRP-USP), Ribeirão Preto, SP, Brazil
| | - Rodrigo Luppino Assad
- Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FMRP-USP), Ribeirão Preto, SP, Brazil
| | | | - Michel Daoud Crema
- Institut National du Sport, de l'Expertise et de la Performance (INSEP), Paris, France
| | - Paulo Louzada-Junior
- Faculdade de Medicina de Ribeirão Preto da Universidade de São Paulo (FMRP-USP), Ribeirão Preto, SP, Brazil
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Huang J, Chen L, Chan KWY, Cai C, Cai S, Chen Z. Super-resolved water/fat image reconstruction based on single-shot spatiotemporally encoded MRI. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 314:106736. [PMID: 32361511 DOI: 10.1016/j.jmr.2020.106736] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/26/2019] [Revised: 04/11/2020] [Accepted: 04/18/2020] [Indexed: 06/11/2023]
Abstract
Single-shot spatiotemporally encoded (SPEN) MRI has been validated to possess considerable performance in both spatial and temporal resolution. Water/fat separation is essential for MRI applications in which only water signal is needed. In this article, a super-resolved water/fat image reconstruction method (dubbed SWAF) combined prior knowledge was developed based on single-shot SPEN MRI. The point spread function of spatiotemporal encoding under multiple chemical shifts situation was derived and used for constructing an equation for SWAF image reconstruction. By processing the prior chemical shift information with filtering operation, an initial spin density profile of water/fat and a weighting matrix for water/fat residual artifacts suppression were obtained to guide the reconstruction process. A l1 norm minimization problem with regularization was exploited to reconstruct separated water/fat images with high spatial resolution and less residual/aliasing artifacts. Numeric simulation and experiments on water-oil phantom and rat abdomen/neck imaging demonstrated the effectiveness and robustness of this new method. The SWAF method proposed herein would promote the application of SPEN MRI in the cases where water/fat separation is required.
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Affiliation(s)
- Jianpan Huang
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China; Department of Biomedical Engineering, City University of Hong Kong, Hong Kong, China
| | - Lin Chen
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China
| | - Kannie W Y Chan
- Department of Biomedical Engineering, City University of Hong Kong, Hong Kong, China
| | - Congbo Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China.
| | - Shuhui Cai
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China.
| | - Zhong Chen
- Department of Electronic Science, Fujian Provincial Key Laboratory of Plasma and Magnetic Resonance, Xiamen University, Xiamen, China
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Clinical experience with two-point mDixon turbo spin echo as an alternative to conventional turbo spin echo for magnetic resonance imaging of the pediatric knee. Pediatr Radiol 2019; 49:791-800. [PMID: 30725178 DOI: 10.1007/s00247-019-04349-w] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/01/2018] [Revised: 12/11/2018] [Accepted: 01/16/2019] [Indexed: 10/27/2022]
Abstract
BACKGROUND Two-point modified Dixon (mDixon) turbo spin-echo (TSE) sequence provides an efficient, robust method of fat suppression. In one mDixon acquisition, four image types can be generated: water-only, fat-only, in-phase and opposed-phase images. OBJECTIVE To determine whether PD mDixon TSE water-only and, by proxy, PD in-phase images generated by one acquisition can replace two conventional PD TSE sequences with and without fat suppression in routine clinical MR examination of the knee. MATERIALS AND METHODS This is a retrospective study of 50 consecutive pediatric knee MR examinations. PD mDixon TSE water-only and PD fat-saturated TSE sequences (acquired in the sagittal plane with identical spatial resolution) were reviewed independently by two pediatric radiologists for homogeneity of fat suppression and detection of intra-articular pathology. Thirteen of the 50 patients underwent arthroscopy, and we used the arthroscopic results as a reference standard for the proton-density fat-saturated and proton-density mDixon results. We used the Kruskal-Wallis rank test to assess difference in fat suppression between the proton-density mDixon and proton-density fat-saturated techniques. We used kappa statistics to compare the agreement of detection of intra-articular pathology between readers and techniques. We also calculated sensitivity, specificity and accuracy between arthroscopy and MR interpretations. RESULTS Proton-density mDixon water-only imaging showed significant improvement with the fat suppression compared with proton-density fat-saturated sequence (P=0.02). Each observer demonstrated near-perfect agreement between both techniques for detecting meniscal and ligamentous pathology and fair to substantial agreement for bone contusions, and chondral and osteochondral lesions. CONCLUSION Two-point mDixon water-only imaging can replace conventional proton-density fat-saturated sequence. When same-plane proton-density fat-saturated and non-fat-saturated sequences are required, proton-density water-only and proton-density in-phase image types acquired in the same acquisition shorten the overall examination time while maintaining excellent intra-articular lesion conspicuity.
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Colotti R, Omoumi P, van Heeswijk RB, Bastiaansen JAM. Simultaneous fat-free isotropic 3D anatomical imaging and T 2 mapping of knee cartilage with lipid-insensitive binomial off-resonant RF excitation (LIBRE) pulses. J Magn Reson Imaging 2018; 49:1275-1284. [PMID: 30318667 DOI: 10.1002/jmri.26322] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2018] [Revised: 08/13/2018] [Accepted: 08/13/2018] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND Improved knee cartilage morphological delineation and T2 mapping precision necessitates isotropic 3D high-resolution and efficient fat suppression. PURPOSE To develop and assess an isotropic 3D lipid-insensitive T2 mapping technique of the knee for improved cartilage delineation and precise measurement of T2 relaxation times. STUDY TYPE Prospective. PHANTOM/SUBJECTS Phantoms (n = 6) used in this study were designed to mimic the T1 and T2 relaxation times of cartilage and fat. The study cohort comprised healthy volunteers (n = 7) for morphometry and T2 relaxation time measurements. FIELD STRENGTH/SEQUENCE A high-resolution isotropic 3D T2 mapping technique that uses sequential T2 -prepared segmented gradient-recalled echo (Iso3DGRE) images and lipid-insensitive binomial off-resonant radiofrequency (RF) excitation (LIBRE) at 3T. ASSESSMENT Numerical simulations and phantom experiments were performed to optimize the LIBRE pulse. Phantom studies were carried out to test the accuracy of the technique against reference standard spin-echo (SE) T2 mapping. Subsequently, T2 maps with and without LIBRE pulses were acquired in knees of healthy volunteers and the T2 relaxation time values in different cartilage compartments were compared. STATISTICAL TESTS A two-tailed paired Student's t-test was used to compare the average T2 values and the relative standard deviations (inverse measurement of the precision) obtained with and without LIBRE pulses. RESULTS A LIBRE pulse of 1 msec suppressed fat with an RF excitation frequency offset of 1560 Hz and optimal RF excitation angle of 35°. These results were corroborated by phantom and knee experiments. Robust and homogeneous fat suppression was obtained (a fat signal-to-noise ratio (SNR) decrease of 86.4 ± 2.4%). In phantoms, T2 values were found in good agreement when comparing LIBRE-Iso3DGRE with SE (slope 0.93 ± 0.04, intercept 0.11 ± 1.6 msec, R2 >0.99). In vivo, LIBRE excitation resulted in more precise T2 estimation (23.7 ± 7.4%) than normal excitation (30.5 ± 9.9%, P < 0.0001). DATA CONCLUSION Homogeneous LIBRE fat signal suppression was achieved with a total RF pulse duration of 1 msec, allowing for the removal of chemical shift artifacts and resulting in improved cartilage delineation and precise T2 values. LEVEL OF EVIDENCE 2 Technical Efficacy: Stage 1 J. Magn. Reson. Imaging 2019;49:1275-1284.
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Affiliation(s)
- Roberto Colotti
- Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
| | - Patrick Omoumi
- Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
| | - Ruud B van Heeswijk
- Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland.,Centre for Biomedical Imaging (CIBM), Lausanne, Switzerland
| | - Jessica A M Bastiaansen
- Department of Radiology, University Hospital (CHUV) and University of Lausanne (UNIL), Lausanne, Switzerland
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Edmonson HA, Carlson ML, Patton AC, Watson RE. MR Imaging and Cochlear Implants with Retained Internal Magnets: Reducing Artifacts near Highly Inhomogeneous Magnetic Fields. Radiographics 2018; 38:94-106. [PMID: 29320320 DOI: 10.1148/rg.2018170135] [Citation(s) in RCA: 39] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The number of patients receiving cochlear implants and auditory brainstem implants for severe to profound sensorineural hearing loss has rapidly increased. These implants consist of an internal component implanted between the skull and the temporal scalp and an external removable speech processor unit. A small magnet within the internal component is commonly used to hold the external speech processor unit in place. Several cochlear implant models have recently received U.S. Food and Drug Administration and European Economic Area regulatory approval to allow magnetic resonance (MR) imaging examinations to be performed under certain specified conditions. The small internal magnet presents a challenge for imaging of the head and neck near the implant, creating a nonlinear magnetic field inhomogeneity and significant MR imaging artifacts. Fat-saturation failures and susceptibility artifacts severely degrade image quality. Typical artifacts at diffusion-weighted imaging and accelerated imaging are exacerbated. Each examination may require impromptu adjustments to allow visualization of the tissue or contrast of interest. Patients may also be quite uncomfortable during the examination, as a result of either imposed magnetic forces or a tight head wrap that is often applied to minimize internal magnet movement. Translational forces and torque sometimes displace the implanted magnet even when a head wrap is used. Diseases such as neurofibromatosis type 2 that are associated with bilateral vestibular schwannomas and hearing loss often require lifelong tumor surveillance with MR imaging. A collaborative team of radiologists, technologists, and/or medical physicists or MR imaging scientists, armed with strategies to mitigate artifacts near implanted magnets, can customize the examination for better visualization of tissue and consistent comparison examinations over time. ©RSNA, 2018.
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Affiliation(s)
- Heidi A Edmonson
- From the Departments of Radiology (H.A.E., A.C.P., R.E.W.) and Otorhinolaryngology (M.L.C.), Mayo Clinic, 200 First St SW, Rochester, MN 55905
| | - Matthew L Carlson
- From the Departments of Radiology (H.A.E., A.C.P., R.E.W.) and Otorhinolaryngology (M.L.C.), Mayo Clinic, 200 First St SW, Rochester, MN 55905
| | - Alice C Patton
- From the Departments of Radiology (H.A.E., A.C.P., R.E.W.) and Otorhinolaryngology (M.L.C.), Mayo Clinic, 200 First St SW, Rochester, MN 55905
| | - Robert E Watson
- From the Departments of Radiology (H.A.E., A.C.P., R.E.W.) and Otorhinolaryngology (M.L.C.), Mayo Clinic, 200 First St SW, Rochester, MN 55905
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Sarkar SN, Hackney DB, Greenman RL, Vachha BA, Johnson EA, Nagle S, Moonis G. A subjective and objective comparison of tissue contrast and imaging artifacts present in routine spin echoes and in iterative decomposition of asymmetric spin echoes for soft tissue neck MRI. Eur J Radiol 2018; 102:202-207. [PMID: 29685536 DOI: 10.1016/j.ejrad.2018.03.016] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2017] [Revised: 03/08/2018] [Accepted: 03/13/2018] [Indexed: 11/19/2022]
Abstract
OBJECTIVE FSE sequences play key roles in neck MRI despite the susceptibility issues in neck region. Iterative decomposition of asymmetric echoes (IDEAL, GE) is a promising method that separates fat and water images resulting in high SNR and improved fat suppression. We tested how neck tissue contrasts, image artifacts and fat separation as opposed to fat suppression in terms of image quality compare between routine and IDEAL FSE. METHODS IDEAL based and routine T1 and T2-weighted FSE sequences were applied for neck MRI at 1.5T and 3T. Overall image quality including fat suppression, tissue contrast, image artifacts and lesion conspicuity were subjectively assessed for 20 patients clinically indicated for neck MRI. Quantitative tissue contrast estimates from parotid area were compared between IDEAL and routine FSE for 7 patients. Four patients with oncocytoma were also reviewed to assess benefits of separately reconstructed fat specific image sets. RESULTS Subjective tissue contrast and overall image quality including image sharpness, fat suppression and image artifacts were superior for IDEAL sequences. For oncocytoma fat specific IDEAL images provided additional information. Objective CNR estimates from a central slice were equivalent for IDEAL and routine FSE at both field strengths. CONCLUSIONS We demonstrated that high SNR inherent in IDEAL FSE consistently translates into high tissue contrast with image quality advantages in neck anatomy where large susceptibility variation and physiological motions reduce image quality for conventional FSE T1 and T2. However, the objective contrast estimates for parotid gland at isocenter were statistically equivalent for IDEAL and conventional FSE perhaps because at or near isocenter routine FSE works well. Additionally, fat specific IDEAL image sets add to diagnostic specificity for fat deficient lesions.
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Affiliation(s)
- Subhendra N Sarkar
- Department of Radiologic Technology & Medical Imaging, New York City College of Technology, The City University of New York, New York, NY, United States.
| | - David B Hackney
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States
| | - Robert L Greenman
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States
| | - Behroze A Vachha
- Department of Radiology, Memorial Sloan Kettering Cancer Center, Weil Medical College of Cornell University, New York, NY, United States
| | - Emelia A Johnson
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States
| | - Sue Nagle
- Department of Radiology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, United States
| | - Gul Moonis
- Department of Radiology, New York-Presbyterian Hospital, Columbia University Medical Center, New York, NY, United States
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Stirnberg R, Huijbers W, Brenner D, Poser BA, Breteler M, Stöcker T. Rapid whole-brain resting-state fMRI at 3 T: Efficiency-optimized three-dimensional EPI versus repetition time-matched simultaneous-multi-slice EPI. Neuroimage 2017; 163:81-92. [PMID: 28923276 DOI: 10.1016/j.neuroimage.2017.08.031] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/11/2017] [Revised: 06/28/2017] [Accepted: 08/09/2017] [Indexed: 01/18/2023] Open
Abstract
State-of-the-art simultaneous-multi-slice (SMS-)EPI and 3D-EPI share several properties that benefit functional MRI acquisition. Both sequences employ equivalent parallel imaging undersampling with controlled aliasing to achieve high temporal sampling rates. As a volumetric imaging sequence, 3D-EPI offers additional means of acceleration complementary to 2D-CAIPIRINHA sampling, such as fast water excitation and elliptical sampling. We performed an application-oriented comparison between a tailored, six-fold CAIPIRINHA-accelerated 3D-EPI protocol at 530 ms temporal and 2.4 mm isotropic spatial resolution and an SMS-EPI protocol with identical spatial and temporal resolution for whole-brain resting-state fMRI at 3 T. The latter required eight-fold slice acceleration to compensate for the lack of elliptical sampling and fast water excitation. Both sequences used vendor-supplied on-line image reconstruction. We acquired test/retest resting-state fMRI scans in ten volunteers, with simultaneous acquisition of cardiac and respiration data, subsequently used for optional physiological noise removal (nuisance regression). We found that the 3D-EPI protocol has significantly increased temporal signal-to-noise ratio throughout the brain as compared to the SMS-EPI protocol, especially when employing motion and nuisance regression. Both sequence types reliably identified known functional networks with stronger functional connectivity values for the 3D-EPI protocol. We conclude that the more time-efficient 3D-EPI primarily benefits from reduced parallel imaging noise due to a higher, actual k-space sampling density compared to SMS-EPI. The resultant BOLD sensitivity increase makes 3D-EPI a valuable alternative to SMS-EPI for whole-brain fMRI at 3 T, with voxel sizes well below 3 mm isotropic and sampling rates high enough to separate dominant cardiac signals from BOLD signals in the frequency domain.
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Affiliation(s)
| | - Willem Huijbers
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany; Jheronimus Academy of Data Science, Cognitive Science and Artificial Intelligence, Tilburg University, The Netherlands
| | - Daniel Brenner
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Benedikt A Poser
- Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands
| | - Monique Breteler
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany
| | - Tony Stöcker
- German Center for Neurodegenerative Diseases (DZNE), Bonn, Germany; Department of Physics and Astronomy, University of Bonn, Bonn, Germany
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17
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Double inversion recovery imaging of the brain: deriving the most relevant sequence through real images. Radiol Phys Technol 2017; 10:364-375. [PMID: 28393298 DOI: 10.1007/s12194-017-0396-3] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Revised: 04/03/2017] [Accepted: 04/04/2017] [Indexed: 01/31/2023]
Abstract
We propose a practical method for setting the optimal inversion times (TI) for double inversion recovery (DIR) sequences. Our method used the measurement of signal intensity (SI) from real images to set the optimal TI for white-matter (WM) and gray-matter (GM)-attenuated inversion recovery (WAIR and GAIR, respectively) images. 3D-DIR images of healthy volunteers were obtained on 1.5- and 3.0-T magnetic resonance (MR) scanners and the SIs of GM, WM, and cerebrospinal fluid (CSF) were evaluated on real images. We found TI2s at which the SI of WM or GM was null. Then, we found TI1+2 (=TI1 + TI2) at which the SI of CSF was null. We defined the two TIs as optimal TIs. We assessed the utility of these TIs with additional volunteers and patients, and similar images were obtained with the determined TIs. Optimal TIs for DIR images could be efficiently determined using this method.
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18
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MRI assessment of bone marrow oedema in the sacroiliac joints of patients with spondyloarthritis: is the SPAIR T2w technique comparable to STIR? Eur Radiol 2017; 27:3669-3676. [DOI: 10.1007/s00330-017-4746-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2016] [Revised: 01/06/2017] [Accepted: 01/13/2017] [Indexed: 01/19/2023]
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Korinek R, Bartusek K, Starcuk Z. Fast triple-spin-echo Dixon (FTSED) sequence for water and fat imaging. Magn Reson Imaging 2016; 37:164-170. [PMID: 27890779 DOI: 10.1016/j.mri.2016.11.015] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2016] [Revised: 11/18/2016] [Accepted: 11/20/2016] [Indexed: 01/01/2023]
Abstract
A number of 'Dixon' techniques based on fast spin echo (FSE) sequence have been proposed and successfully used in many branches of medicine. Some require only one scan, but most of them need multiple scans and long scan times. This article describes a new fast triple-spin-echo Dixon (FTSED) technique suitable for ultra-high field MRI, in which three specific time shifts are introduced in the echo train; thus, three images with defined water-fat phase-differences (0, π, 2π) are encoded in the phase of the acquired images without extreme restrictions upon the echo duration. The water and fat images are then calculated by iterative least-squares estimation method. The sequence was successfully implemented at a 9.4T ultra-high field MRI system and tested on a phantom and a rat.
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Affiliation(s)
- Radim Korinek
- Institute of Scientific Instruments of the CAS, v. v. i., Czech Republic.
| | - Karel Bartusek
- Institute of Scientific Instruments of the CAS, v. v. i., Czech Republic
| | - Zenon Starcuk
- Institute of Scientific Instruments of the CAS, v. v. i., Czech Republic
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Fahmy AS, Ibrahim ESH, Osman NF. Spectrally-Presaturated Modulation (SPM): An efficient fat suppression technique for STEAM-based cardiac imaging sequences. Magn Reson Imaging 2016; 37:209-215. [PMID: 27826082 DOI: 10.1016/j.mri.2016.11.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2016] [Accepted: 11/03/2016] [Indexed: 10/20/2022]
Abstract
Stimulated-echo acquisition mode (STEAM) is a key pulse sequences in MRI in general, and in cardiac imaging in particular. Fat suppression is an important feature in cardiac imaging to improve visualization and eliminate off-resonance and chemical-shift artifacts. Nevertheless, fat suppression comes at the expense of reduced temporal resolution and signal-to-noise ratio (SNR). The purpose of this study is to develop an efficient fat suppression method (Spectrally-Presaturated Modulation) for STEAM-based sequences to enable imaging with high temporal-resolution, high SNR, and no increase in scan time. The developed method is based on saturating the fat magnetization prior to applying STEAM modulation; therefore, only the water-content of the tissues is modulated by the sequence, resulting in fat-suppressed images without the need to run the fat suppression module during image acquisition. The potential significance of the proposed method is presented in two STEAM-based cardiac MRI applications: complementary spatial-modulation of magnetization (CSPAMM), and black-blood cine imaging. Phantom and in vivo experiments are conducted to evaluate the developed technique and compare it to the commonly implemented chemical-shift selective (CHESS) and water-excitation using spectral-spatial selective pulses (SSSP) fat suppression techniques. The results from the phantom and in vivo experiments show superior performance of the proposed method compared to the CHESS and SSSP techniques in terms of temporal resolution and SNR. In conclusion, the developed fat suppression technique results in enhanced image quality of STEAM-based images, especially in cardiac applications, where high temporal-resolution is imperative for accurate measurement of functional parameters and improved performance of image analysis algorithms.
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Affiliation(s)
- Ahmed S Fahmy
- Biomedical Engineering Department, Cairo University, Cairo, Egypt
| | | | - Nael F Osman
- Department of Radiology, Johns Hopkins University, Baltimore, USA
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Yee S. Segmentation of fat in MRI using a preparatory pair of rectangular RF pulses of opposite direction. Magn Reson Imaging 2016; 34:483-91. [DOI: 10.1016/j.mri.2015.11.006] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2015] [Revised: 11/06/2015] [Accepted: 11/17/2015] [Indexed: 10/22/2022]
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Marty B, Baudin PY, Reyngoudt H, Azzabou N, Araujo ECA, Carlier PG, de Sousa PL. Simultaneous muscle water T2 and fat fraction mapping using transverse relaxometry with stimulated echo compensation. NMR IN BIOMEDICINE 2016; 29:431-43. [PMID: 26814454 DOI: 10.1002/nbm.3459] [Citation(s) in RCA: 68] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/09/2015] [Revised: 10/20/2015] [Accepted: 11/13/2015] [Indexed: 05/27/2023]
Abstract
Skeletal muscle inflammation/necrosis and fat infiltration are strong indicators of disease activity and progression in many neuromuscular disorders. They can be assessed by muscle T2 relaxometry and water-fat separation techniques, respectively. In the present work, we exploited differences between water and fat T1 and T2 relaxivities by applying a bi-component extended phase graph (EPG) fitting approach to simultaneously quantify the muscle water T2 and fat fraction from standard multi-slice multi-echo (MSME) acquisitions in the presence of stimulated echoes. Experimental decay curves were adjusted to the theoretical model using either an iterative non-negative least-squares (NNLS) procedure or a pattern recognition approach. Twenty-two patients (age, 49 ± 18 years) were selected to cover a large range of muscle fat infiltration. Four cases of chronic or subchronic juvenile dermatomyositis (age, 8 ± 3 years) were investigated before and 3 months following steroid treatment. For control, five healthy volunteers (age, 25 ± 2 years) were recruited. All subjects underwent the MSME sequence and EPG fitting procedure. The EPG fitting algorithm allowed a precise estimation of water T2 and fat fraction in diseased muscle, even in the presence of large B1(+) inhomogeneities. In the whole cohort of patients, there was no overall correlation between water T2 values obtained with the proposed method and the fat fraction estimated inside muscle tissues (R(2) = 0.02). In the patients with dermatomyositis, there was a significant decrease in water T2 (-4.09 ± 3.7 ms) consequent to steroid treatment. The pattern recognition approach resulted in a 20-fold decrease in processing time relative to the iterative NNLS procedure. The fat fraction derived from the EPG fitting approach correlated well with the fat fraction derived from a standard three-point Dixon method (≈1.5% bias). The bi-component EPG fitting analysis is a precise tool to monitor muscle tissue disease activity and is able to handle bias introduced by fat infiltration and B1(+) inhomogeneities.
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Affiliation(s)
- Benjamin Marty
- Institute of Myology, NMR Laboratory, Paris, France
- CEA, DSV, I2BM, MIRCen, NMR Laboratory, Paris, France
| | | | - Harmen Reyngoudt
- Institute of Myology, NMR Laboratory, Paris, France
- CEA, DSV, I2BM, MIRCen, NMR Laboratory, Paris, France
| | - Noura Azzabou
- Institute of Myology, NMR Laboratory, Paris, France
- CEA, DSV, I2BM, MIRCen, NMR Laboratory, Paris, France
| | - Ericky C A Araujo
- Institute of Myology, NMR Laboratory, Paris, France
- CEA, DSV, I2BM, MIRCen, NMR Laboratory, Paris, France
| | - Pierre G Carlier
- Institute of Myology, NMR Laboratory, Paris, France
- CEA, DSV, I2BM, MIRCen, NMR Laboratory, Paris, France
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Stirnberg R, Brenner D, Stöcker T, Shah NJ. Rapid fat suppression for three-dimensional echo planar imaging with minimized specific absorption rate. Magn Reson Med 2015; 76:1517-1523. [DOI: 10.1002/mrm.26063] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Revised: 10/06/2015] [Accepted: 10/28/2015] [Indexed: 11/06/2022]
Affiliation(s)
- Rüdiger Stirnberg
- Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH; Jülich Germany
- German Centre for Neurodegenerative Diseases (DZNE); Bonn Germany
| | - Daniel Brenner
- Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH; Jülich Germany
- German Centre for Neurodegenerative Diseases (DZNE); Bonn Germany
| | - Tony Stöcker
- German Centre for Neurodegenerative Diseases (DZNE); Bonn Germany
- Department of Physics and Astronomy; University of Bonn; Bonn Germany
| | - N. Jon Shah
- Institute of Neuroscience and Medicine 4, Medical Imaging Physics, Research Centre Jülich GmbH; Jülich Germany
- Department of Neurology, Faculty of Medicine; RWTH Aachen University; JARA Aachen Germany
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Del Grande F, Santini F, Herzka DA, Aro MR, Dean CW, Gold GE, Carrino JA. Fat-suppression techniques for 3-T MR imaging of the musculoskeletal system. Radiographics 2015; 34:217-33. [PMID: 24428292 DOI: 10.1148/rg.341135130] [Citation(s) in RCA: 223] [Impact Index Per Article: 24.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Fat suppression is an important technique in musculoskeletal imaging to improve the visibility of bone-marrow lesions; evaluate fat in soft-tissue masses; optimize the contrast-to-noise ratio in magnetic resonance (MR) arthrography; better define lesions after administration of contrast material; and avoid chemical shift artifacts, primarily at 3-T MR imaging. High-field-strength (eg, 3-T) MR imaging has specific technical characteristics compared with lower-field-strength MR imaging that influence the use and outcome of various fat-suppression techniques. The most commonly used fat-suppression techniques for musculoskeletal 3-T MR imaging include chemical shift (spectral) selective (CHESS) fat saturation, inversion recovery pulse sequences (eg, short inversion time inversion recovery [STIR]), hybrid pulse sequences with spectral and inversion-recovery (eg, spectral adiabatic inversion recovery and spectral attenuated inversion recovery [SPAIR]), spatial-spectral pulse sequences (ie, water excitation), and the Dixon techniques. Understanding the different fat-suppression options allows radiologists to adopt the most appropriate technique for their clinical practice.
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Affiliation(s)
- Filippo Del Grande
- From the Russell H. Morgan Department of Radiology and Radiological Science, Johns Hopkins Hospital, Baltimore, Md (F.D.G., M.R.A., J.A.C.); Division of Radiological Physics, Department of Radiology, Clinic of Radiology and Nuclear Medicine, University of Basel Hospital, Basel, Switzerland (F.S.); Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, Md (D.A.H.); Department of Radiology, University of Florida College of Medicine, Gainesville, Fla (C.W.D.); and Departments of Radiology, Bioengineering, and Orthopaedic Surgery, Stanford University School of Medicine, Stanford, Calif (G.E.G.). Recipient of a Certificate of Merit award for an education exhibit at the 2012 RSNA Annual Meeting
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Abstract
Few tasks in imaging are more challenging than that of optimizing evaluations of the instrumented spine. The authors describe how applying fundamental and more advanced principles to postoperative spine computed tomography and magnetic resonance examinations mitigates the challenges associated with metal implants and significantly improves image quality and consistency. Newer and soon-to-be-available enhancements should provide improved visualization of tissues and hardware as multispectral imaging sequences continue to develop.
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Taviani V, Hernando D, Francois CJ, Shimakawa A, Vigen KK, Nagle SK, Schiebler ML, Grist TM, Reeder SB. Whole-heart chemical shift encoded water-fat MRI. Magn Reson Med 2013; 72:718-25. [PMID: 24186810 DOI: 10.1002/mrm.24982] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2013] [Revised: 09/12/2013] [Accepted: 09/12/2013] [Indexed: 12/21/2022]
Abstract
PURPOSE To develop and evaluate a free-breathing chemical-shift-encoded (CSE) spoiled gradient-recalled echo (SPGR) technique for whole-heart water-fat imaging at 3 Tesla (T). METHODS We developed a three-dimensional (3D) multi-echo SPGR pulse sequence with electrocardiographic gating and navigator echoes and evaluated its performance at 3T in healthy volunteers (N = 6) and patients (N = 20). CSE-SPGR, 3D SPGR, and 3D balanced-SSFP with chemical fat saturation were compared in six healthy subjects with images evaluated for overall image quality, level of residual artifacts, and quality of fat suppression. A similar scoring system was used for the patient datasets. RESULTS Images of diagnostic quality were acquired in all but one subject. CSE-SPGR performed similarly to SPGR with fat saturation, although it provided a more uniform fat suppression over the whole field of view. Balanced-SSFP performed worse than SPGR-based methods. In patients, CSE-SPGR produced excellent fat suppression near metal. Overall image quality was either good (7/20) or excellent (12/20) in all but one patient. There were significant artifacts in 5/20 clinical cases. CONCLUSION CSE-SPGR is a promising technique for whole-heart water-fat imaging during free-breathing. The robust fat suppression in the water-only image could improve assessment of complex morphology at 3T and in the presence of off-resonance, with additional information contained in the fat-only image.
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Affiliation(s)
- Valentina Taviani
- Department of Radiology, University of Wisconsin, Madison, Wisconsin, USA
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Jung BA, Weigel M. Spin echo magnetic resonance imaging. J Magn Reson Imaging 2013; 37:805-17. [PMID: 23526758 DOI: 10.1002/jmri.24068] [Citation(s) in RCA: 30] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2011] [Accepted: 01/11/2013] [Indexed: 11/07/2022] Open
Abstract
The spin echo sequence is a fundamental pulse sequence in MRI. Many of today's applications in routine clinical use are based on this elementary sequence. In this review article, the principles of the spin echo formation are demonstrated on which the generation of the fundamental image contrasts T1, T2, and proton density is based. The basic imaging parameters repetition time (TR) and echo time (TE) and their influence on the image contrast are explained. Important properties such as the behavior in multi-slice imaging or in the presence of flow are depicted and the basic differences with gradient echo imaging are illustrated. The characteristics of the spin echo sequence for different magnetic field strengths with respect to clinical applications are discussed.
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Affiliation(s)
- Bernd André Jung
- Department of Radiology, Medical Physics, University Medical Center, Freiburg, Germany.
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Goldfarb JW, Arnold-Anteraper S. Water-fat separation imaging of the heart with standard magnetic resonance bSSFP CINE imaging. Magn Reson Med 2013; 71:2096-104. [PMID: 23904254 DOI: 10.1002/mrm.24879] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2013] [Revised: 06/18/2013] [Accepted: 06/18/2013] [Indexed: 12/19/2022]
Abstract
PURPOSE To study balanced steady-state free precession CINE phase-sensitive water-fat separation imaging in four cardiac imaging planes to determine the necessary phase correction and image artifacts particular to this technique. METHODS Ten healthy volunteers and two subjects with known heart pathologies were studied with standard balanced steady-state free precession CINE imaging. Water-only and fat-only images were calculated using sign detection of the real part of the complex image after phase correction with constant and linear terms. Phase correction values were determined using both manual and automated methods. Differences in phase correction values between imaging planes, cardiac phases, coil elements, automated image reconstruction parameters as well as artifact scores between the automated and manual methods were studied with statistical tests. RESULTS Water-fat separation performed well in the heart after constant and linear phase correction. Both constant (p = 0.8) and linear x (p = 1) and y (p = 1) phase correction values did not vary significantly across cardiac phases, but varied significantly among the coils (p < 0.001) and imaging planes (p < 0.001). False water-fat separation artifacts were most frequent in the chest/back and also were present at the mitral and aortic valves. CONCLUSION Constant and linear phase correction is necessary to provide consistent results in standard imaging planes using a balanced steady-state free precession water-fat separation postprocessing algorithm applied to standard cardiac CINE imaging.
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Affiliation(s)
- James W Goldfarb
- Department of Research and Education, Saint Francis Hospital, Roslyn, New York, USA; Program in Biomedical Engineering, SUNY Stony Brook, Stony Brook, New York, USA
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Affiliation(s)
- Brian A Hargreaves
- Department of Radiology, Stanford University, 300 Pasteur Drive, Stanford, CA 94305, USA.
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A historical overview of magnetic resonance imaging, focusing on technological innovations. Invest Radiol 2013; 47:725-41. [PMID: 23070095 DOI: 10.1097/rli.0b013e318272d29f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023]
Abstract
Magnetic resonance imaging (MRI) has now been used clinically for more than 30 years. Today, MRI serves as the primary diagnostic modality for many clinical problems. In this article, historical developments in the field of MRI will be discussed with a focus on technological innovations. Topics include the initial discoveries in nuclear magnetic resonance that allowed for the advent of MRI as well as the development of whole-body, high field strength, and open MRI systems. Dedicated imaging coils, basic pulse sequences, contrast-enhanced, and functional imaging techniques will also be discussed in a historical context. This article describes important technological innovations in the field of MRI, together with their clinical applicability today, providing critical insights into future developments.
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ECG-gated multiecho Dixon fat-water separation in cardiac MRI: advantages over conventional fat-saturated imaging. AJR Am J Roentgenol 2012; 199:W74-83. [PMID: 22733934 DOI: 10.2214/ajr.11.7759] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
OBJECTIVE The purpose of this pictorial essay is to explore the advantages of multiecho Dixon fat-water separation techniques in cardiac MRI. The clinical indications, potential artifacts, and imaging findings with this technique are reviewed. CONCLUSION Multiecho Dixon fat-water separation can be used to help characterize cardiac masses, evaluate for myocardial lipomatous infiltration, and diagnose pericarditis. Advantages over conventional fat-saturation techniques include fewer artifacts from background inhomogeneity, improved contrast of microscopic fat, and capability for use in combination with cine and contrast-enhanced imaging.
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Sutter R, Ulbrich EJ, Jellus V, Nittka M, Pfirrmann CWA. Reduction of metal artifacts in patients with total hip arthroplasty with slice-encoding metal artifact correction and view-angle tilting MR imaging. Radiology 2012; 265:204-14. [PMID: 22923720 DOI: 10.1148/radiol.12112408] [Citation(s) in RCA: 107] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
PURPOSE To compare the new "warp" sequence (slice-encoding metal artifact correction [SEMAC], view-angle tilting [VAT], and increased bandwidth) for the reduction of both through-plane and in-plane magnetic resonance (MR) artifacts with current optimized MR sequences in patients with total hip arthroplasty (THA). MATERIALS AND METHODS The institutional review board issued a waiver for this study. Forty patients with THA were prospectively included. SEMAC, VAT, and increased bandwidth were applied by using the warp turbo-spin-echo sequence at 1.5 T. Coronal short tau inversion-recovery (STIR)-warp and transverse T1-weighted warp (hereafter, T1-warp) images, as well as standard coronal STIR and transverse T1-weighted sequence images optimized with high bandwidth (STIR-hiBW and T1-hiBW), were acquired. Fifteen additional patients were examined to compare the T1-warp and T1-hiBW sequence with an identical matrix size. Signal void was quantified. Qualitative criteria (distinction of anatomic structures, blurring, and noise) were assessed on a five-point scale (1, no artifacts; 5, not visible due to severe artifacts) by two readers. Abnormal imaging findings were recorded. Quantitative data were analyzed with a t test and qualitative data with a Wilcoxon signed rank test. RESULTS Signal void around the acetabular component was smaller for STIR-warp than STIR-hiBW images (21.6 cm2 vs 42.4 cm2; P=.0001), and for T1-warp than T1-hiBW images (17.6 cm2 vs 20.2 cm2; P=.0001). Anatomic distinction was better on STIR-warp compared with STIR-hiBW images (1.9-2.8 vs 3.6-4.6; P=.0001), and on T1-warp compared with T1-hiBW images (1.3-2.8 vs 1.8-3.2; P<.002). Distortion, blurring, and noise were lower with warp sequences than with the standard sequences (P=.0001). Almost half of the abnormal imaging findings were missed on STIR-hiBW compared with STIR-warp images (55 vs 105 findings; P=.0001), while T1-hiBW was similar to T1-warp imaging (50 vs 55 findings; P=.06). CONCLUSION STIR-warp and T1-warp sequences were significantly better according to quantitative and qualitative image criteria, but a clinically relevant artifact reduction was only present for STIR images.
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Affiliation(s)
- Reto Sutter
- Department of Radiology, Orthopedic University Hospital Balgrist, Forchstrasse 340, 8008 Zurich, Switzerland.
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Heilman JA, Derakhshan JD, Riffe MJ, Gudino N, Tkach J, Flask CA, Duerk JL, Griswold MA. Parallel excitation for B-field insensitive fat-saturation preparation. Magn Reson Med 2012; 68:631-8. [PMID: 22247080 PMCID: PMC4856011 DOI: 10.1002/mrm.23238] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/18/2010] [Revised: 08/22/2011] [Accepted: 09/07/2011] [Indexed: 11/11/2022]
Abstract
Multichannel transmission has the potential to improve many aspects of MRI through a new paradigm in excitation. In this study, multichannel transmission is used to address the effects that variations in B(0) homogeneity have on fat-saturation preparation through the use of the frequency, phase, and amplitude degrees of freedom afforded by independent transmission channels. B(1) homogeneity is intrinsically included via use of coil sensitivities in calculations. A new method, parallel excitation for B-field insensitive fat-saturation preparation, can achieve fat saturation in 89% of voxels with M(z) ≤ 0.1 in the presence of ± 4 ppm B(0) variation, where traditional CHESS methods achieve only 40% in the same conditions. While there has been much progress to apply multichannel transmission at high field strengths, particular focus is given here to application of these methods at 1.5 T.
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Affiliation(s)
- Jeremiah A Heilman
- Department of Physics, Case Western Reserve University, Cleveland, Ohio, USA.
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Ren AJ, Guo Y, Tian SP, Shi LJ, Huang MH. MR imaging of the spine at 3.0T with T2-weighted IDEAL fast recovery fast spin-echo technique. Korean J Radiol 2011; 13:44-52. [PMID: 22247635 PMCID: PMC3253402 DOI: 10.3348/kjr.2012.13.1.44] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2011] [Accepted: 08/03/2011] [Indexed: 11/22/2022] Open
Abstract
Objective To compare the iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) method with a fat-saturated T2-weighted (T2W) fast recovery fast spin-echo (FRFSE) imaging of the spine. Materials and Methods Images acquired at 3.0 Tesla (T) in 35 patients with different spine lesions using fat-saturated T2W FRFSE imaging were compared with T2W IDEAL FRFSE images. Signal-to-noise ratio (SNR)-efficiencies measurements were made in the vertebral bodies and spinal cord in the mid-sagittal plane or nearest to the mid-sagittal plane. Images were scored with the consensus of two experienced radiologists on a four-point grading scale for fat suppression and overall image quality. Statistical analysis of SNR-efficiency, fat suppression and image quality scores was performed with a paired Student's t test and Wilcoxon's signed rank test. Results Signal-to-noise ratio-efficiency for both vertebral body and spinal cord was higher with T2W IDEAL FRFSE imaging (p < 0.05) than with T2W FRFSE imaging. T2W IDEAL FRFSE demonstrated superior fat suppression (p < 0.01) and image quality (p < 0.01) compared to fat-saturated T2W FRFSE. Conclusion As compared with fat-saturated T2W FRFSE, IDEAL can provide a higher image quality, higher SNR-efficiency, and consistent, robust and uniform fat suppression. T2W IDEAL FRFSE is a promising technique for MR imaging of the spine at 3.0T.
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Affiliation(s)
- Ai-Jun Ren
- Department of Radiology, Navy General Hospital of PLA, Beijing 100048, People's [corrected] Republic of China.
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Abstract
OBJECTIVE The purpose of this article is to review some of the basic principles of imaging and how metal-induced susceptibility artifacts originate in MR images. We will describe common ways to reduce or modify artifacts using readily available imaging techniques, and we will discuss some advanced methods to correct readout-direction and slice-direction artifacts. CONCLUSION The presence of metallic implants in MRI can cause substantial image artifacts, including signal loss, failure of fat suppression, geometric distortion, and bright pile-up artifacts. These cause large resonant frequency changes and failure of many MRI mechanisms. Careful parameter and pulse sequence selections can avoid or reduce artifacts, although more advanced imaging methods offer further imaging improvements.
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Lenz C, Klarhöfer M, Scheffler K, Winter L, Sommer G. Assessing extracranial tumors using diffusion-weighted whole-body MRI. Z Med Phys 2011; 21:79-90. [DOI: 10.1016/j.zemedi.2010.06.004] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/31/2010] [Revised: 04/29/2010] [Accepted: 06/01/2010] [Indexed: 01/20/2023]
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Lu W, Pauly KB, Gold GE, Pauly JM, Hargreaves BA. Slice encoding for metal artifact correction with noise reduction. Magn Reson Med 2011; 65:1352-7. [PMID: 21287596 DOI: 10.1002/mrm.22796] [Citation(s) in RCA: 29] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 09/29/2010] [Accepted: 10/08/2010] [Indexed: 11/10/2022]
Abstract
Magnetic resonance imaging (MRI) near metallic implants is often hampered by severe metal artifacts. To obtain distortion-free MR images near metallic implants, SEMAC (Slice Encoding for Metal Artifact Correction) corrects metal artifacts via robust encoding of excited slices against metal-induced field inhomogeneities, followed by combining the data resolved from multiple SEMAC-encoded slices. However, as many of the resolved data elements only contain noise, SEMAC-corrected images can suffer from relatively low signal-to-noise ratio. Improving the signal-to-noise ratio of SEMAC-corrected images is essential to enable SEMAC in routine clinical studies. In this work, a new reconstruction procedure is proposed to reduce noise in SEMAC-corrected images. A singular value decomposition denoising step is first applied to suppress quadrature noise in multi-coil SEMAC-encoded slices. Subsequently, the singular value decomposition-denoised data are selectively included in the correction of through-plane distortions. The experimental results demonstrate that the proposed reconstruction procedure significantly improves the SNR without compromising the correction of metal artifacts.
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Affiliation(s)
- Wenmiao Lu
- School of Electrical and Electronic Engineering, Division of Information Engineering, Nanyang Technological University, Singapore.
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Postsurgical Spinal Magnetic Resonance Imaging With Iterative Decomposition of Water and Fat With Echo Asymmetry and Least-Squares Estimation. J Comput Assist Tomogr 2011; 35:16-20. [DOI: 10.1097/rct.0b013e3181f8d30d] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
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Hargreaves BA, Chen W, Lu W, Alley MT, Gold GE, Brau ACS, Pauly JM, Pauly KB. Accelerated slice encoding for metal artifact correction. J Magn Reson Imaging 2010; 31:987-96. [PMID: 20373445 DOI: 10.1002/jmri.22112] [Citation(s) in RCA: 74] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
PURPOSE To demonstrate accelerated imaging with both artifact reduction and different contrast mechanisms near metallic implants. MATERIALS AND METHODS Slice-encoding for metal artifact correction (SEMAC) is a modified spin echo sequence that uses view-angle tilting and slice-direction phase encoding to correct both in-plane and through-plane artifacts. Standard spin echo trains and short-TI inversion recovery (STIR) allow efficient PD-weighted imaging with optional fat suppression. A completely linear reconstruction allows incorporation of parallel imaging and partial Fourier imaging. The signal-to-noise ratio (SNR) effects of all reconstructions were quantified in one subject. Ten subjects with different metallic implants were scanned using SEMAC protocols, all with scan times below 11 minutes, as well as with standard spin echo methods. RESULTS The SNR using standard acceleration techniques is unaffected by the linear SEMAC reconstruction. In all cases with implants, accelerated SEMAC significantly reduced artifacts compared with standard imaging techniques, with no additional artifacts from acceleration techniques. The use of different contrast mechanisms allowed differentiation of fluid from other structures in several subjects. CONCLUSION SEMAC imaging can be combined with standard echo-train imaging, parallel imaging, partial-Fourier imaging, and inversion recovery techniques to offer flexible image contrast with a dramatic reduction of metal-induced artifacts in scan times under 11 minutes.
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Affiliation(s)
- Brian A Hargreaves
- Department of Radiology, Stanford University, Stanford, California 94305-5488, USA.
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Bley TA, Wieben O, François CJ, Brittain JH, Reeder SB. Fat and water magnetic resonance imaging. J Magn Reson Imaging 2009; 31:4-18. [DOI: 10.1002/jmri.21895] [Citation(s) in RCA: 249] [Impact Index Per Article: 16.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
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Magnetic resonance spectroscopic imaging and other emerging magnetic resonance techniques in prostate cancer. Prostate Cancer 2008. [DOI: 10.1017/cbo9780511551994.012] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
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Lu W, Hargreaves BA. Multiresolution field map estimation using golden section search for water-fat separation. Magn Reson Med 2008; 60:236-44. [PMID: 18581397 DOI: 10.1002/mrm.21544] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Many diagnostic MRI sequences demand reliable and uniform fat suppression. Multipoint water-fat separation methods, which are based on chemical-shift induced phase differences, have shown great success in the presence of field inhomogeneities. This work presents a computationally efficient and robust field map estimation method. The method begins with subsampling image data into a multiresolution image pyramidal structure, and then utilizes a golden section search to directly locate possible field map values at the coarsest level of the pyramidal structure. The field map estimate is refined and propagated to increasingly finer resolutions in an efficient manner until the full-resolution field map is obtained for final water-fat separation. The proposed method is validated with multiecho sequences where long echo-spacings normally impose great challenges on reliable field map estimation.
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Affiliation(s)
- Wenmiao Lu
- Department of Radiology, Stanford University, Stanford, CA 94305, USA.
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Brodsky EK, Holmes JH, Yu H, Reeder SB. Generalized k-space decomposition with chemical shift correction for non-Cartesian water-fat imaging. Magn Reson Med 2008; 59:1151-64. [PMID: 18429018 DOI: 10.1002/mrm.21580] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022]
Abstract
Chemical-shift artifacts associated with non-Cartesian imaging are more complex to model and less clinically acceptable than the bulk fat shift that occurs with conventional spin-warp Cartesian imaging. A novel k-space based iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) approach is introduced that decomposes multiple species while simultaneously correcting distortion of off-resonant species. The new signal model accounts for the additional phase accumulated by off-resonant spins at each point in the k-space acquisition trajectory. This phase can then be corrected by adjusting the decomposition matrix for each k-space point during the final IDEAL processing step with little increase in reconstruction time. The technique is demonstrated with water-fat decomposition using projection reconstruction (PR)/radial, spiral, and Cartesian spin-warp imaging of phantoms and human subjects, in each case achieving substantial correction of chemical-shift artifacts. Simulations of the point-spread-function (PSF) for off-resonant spins are examined to show the nature of the chemical-shift distortion for each acquisition. Also introduced is an approach to improve the signal model for species which have multiple resonant peaks. Many chemical species, including fat, have multiple resonant peaks, although such species are often approximated as a single peak. The improved multipeak decomposition is demonstrated with water-fat imaging, showing a substantial improvement in water-fat separation.
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Affiliation(s)
- Ethan K Brodsky
- Department of Radiology, University of Wisconsin-Madison, 600 Highland Avenue, Madison, WI 53792, USA.
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Lu W, Yu H, Shimakawa A, Alley M, Reeder SB, Hargreaves BA. Water-fat separation with bipolar multiecho sequences. Magn Reson Med 2008; 60:198-209. [PMID: 18581362 DOI: 10.1002/mrm.21583] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
Affiliation(s)
- Wenmiao Lu
- Department of Radiology, Stanford University, Stanford, CA 94305, USA.
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Reeder SB, McKenzie CA, Pineda AR, Yu H, Shimakawa A, Brau AC, Hargreaves BA, Gold GE, Brittain JH. Water-fat separation with IDEAL gradient-echo imaging. J Magn Reson Imaging 2007; 25:644-52. [PMID: 17326087 DOI: 10.1002/jmri.20831] [Citation(s) in RCA: 264] [Impact Index Per Article: 15.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022] Open
Abstract
PURPOSE To combine gradient-echo (GRE) imaging with a multipoint water-fat separation method known as "iterative decomposition of water and fat with echo asymmetry and least squares estimation" (IDEAL) for uniform water-fat separation. Robust fat suppression is necessary for many GRE imaging applications; unfortunately, uniform fat suppression is challenging in the presence of B(0) inhomogeneities. These challenges are addressed with the IDEAL technique. MATERIALS AND METHODS Echo shifts for three-point IDEAL were chosen to optimize noise performance of the water-fat estimation, which is dependent on the relative proportion of water and fat within a voxel. Phantom experiments were performed to validate theoretical SNR predictions. Theoretical echo combinations that maximize noise performance are discussed, and examples of clinical applications at 1.5T and 3.0T are shown. RESULTS The measured SNR performance validated theoretical predictions and demonstrated improved image quality compared to unoptimized echo combinations. Clinical examples of the liver, breast, heart, knee, and ankle are shown, including the combination of IDEAL with parallel imaging. Excellent water-fat separation was achieved in all cases. The utility of recombining water and fat images into "in-phase," "out-of-phase," and "fat signal fraction" images is also discussed. CONCLUSION IDEAL-SPGR provides robust water-fat separation with optimized SNR performance at both 1.5T and 3.0T with multicoil acquisitions and parallel imaging in multiple regions of the body.
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Affiliation(s)
- Scott B Reeder
- Department of Radiology, University of Wisconsin, Madison, Wisconsin 53792, USA.
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Kuo R, Panchal M, Tanenbaum L, Crues JV. 3.0 Tesla imaging of the musculoskeletal system. J Magn Reson Imaging 2007; 25:245-61. [PMID: 17260407 DOI: 10.1002/jmri.20815] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
High-field MRI at 3.0T is rapidly gaining clinical acceptance and experiencing more widespread use. The superiority of high-field imaging has clearly been demonstrated for neurological imaging. The impact of 3.0T imaging of the musculoskeletal system has been less dramatic due to complex optimization issues. Areas under consideration include coil technology, protocol modification, artifact reduction, and patient safety. In this article we review these issues and describe our experience with 3.0T musculoskeletal MRI. Fundamentally, an increased signal-to-noise ratio (SNR) is responsible for improved imaging at higher field strength. Increased SNR allows more headroom to adjust parameters that affect image resolution and examination time. It has been established that T1 relaxation time increases at 3.0T, while T2 time decreases. Consequently, scanner parameters require adjustment for optimization of images. Chemical shift and magnetic susceptibility artifacts are more pronounced and require special techniques to minimize the effect on image quality. Spectral fat saturation techniques can take advantage of the increased chemical shift. The specific absorption rate (SAR) and acoustic noise thresholds must be kept in mind at these higher fields. We additionally present some of the clinical issues we have experienced at 3.0T. A decision must be made as to whether to trade higher resolution for reduced scanning time. In general, we believe that routine imaging at 3.0T increases diagnostic confidence, especially for evaluations of cartilaginous and ligamentous structures.
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Affiliation(s)
- Raymond Kuo
- Radnet Management, Inc., Los Angeles, California 90025, USA
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Fuller S, Reeder S, Shimakawa A, Yu H, Johnson J, Beaulieu C, Gold GE. Iterative Decomposition of Water and Fat with Echo Asymmetry and Least-Squares Estimation (IDEAL) Fast Spin-Echo Imaging of the Ankle: Initial Clinical Experience. AJR Am J Roentgenol 2006; 187:1442-7. [PMID: 17114534 DOI: 10.2214/ajr.05.0930] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
OBJECTIVE Reliable, uniform fat suppression is important. Multiple approaches currently exist, many of which suffer from either suboptimal signal-to-noise ratio (SNR), or the inability to obtain consistent fat suppression around the ankle joint. Our purpose was to test iterative decomposition of water and fat with echo asymmetry and the least-squares estimation (IDEAL) method in combination with fast spin-echo imaging, which is able to achieve reliable high SNR images with uniform fat-water separation. SUBJECTS AND METHODS We compared IDEAL fast spin-echo with conventional fat-suppressed fast spin-echo imaging in 33 ankles in 32 patients. Quantitative measurements of SNR and contrast-to-noise ratio efficiency were made, and qualitative diagnostic image quality and fat-suppression scores were determined. RESULTS We found that the SNR efficiency for both cartilage and fluid was similar for both techniques, and fluid/cartilage contrast-to-noise ratio efficiency was higher with IDEAL fast spin-echo imaging. Fat suppression and diagnostic quality scores using the IDEAL method were superior (p < 0.01) to fat-suppressed fast spin-echo imaging. CONCLUSION IDEAL fast spin-echo imaging is a promising technique for MRI of the ankle.
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Affiliation(s)
- Samuel Fuller
- Department of Radiology, Grant Building S0-68B, Stanford University, 300 Pasteur Drive, Stanford, CA 94305-5105, USA
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Reeder SB, Yu H, Johnson JW, Shimakawa A, Brittain JH, Pelc NJ, Beaulieu CF, Gold GE. T1- and T2-weighted fast spin-echo imaging of the brachial plexus and cervical spine with IDEAL water–fat separation. J Magn Reson Imaging 2006; 24:825-32. [PMID: 16969792 DOI: 10.1002/jmri.20721] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
PURPOSE To compare the iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL) method with fat-saturated T1-weighted (T1W) and T2W fast spin-echo (FSE) and short-TI inversion recovery (STIR) imaging of the brachial plexus and cervical spine. MATERIALS AND METHODS Images acquired at 1.5T in five volunteers using fat-saturated T1W and T2W FSE imaging and STIR were compared with T1W and T2W IDEAL-FSE images. Examples of T1W and T2W IDEAL-FSE images acquired in patients are also shown. RESULTS T1W and T2W IDEAL-FSE demonstrated superior fat suppression (P<0.05) and image quality (P<0.05), compared to T1W and T2W fat-saturated FSE, respectively. SNR performance of T1W-IDEAL-FSE was similar to T1W FSE in the spinal cord (P=0.250) and paraspinous muscles (P=0.78), while T2W IDEAL-FSE had superior SNR in muscle (P=0.02) and CSF (P=0.02), and marginally higher cord SNR (P=0.09). Compared to STIR, T2W IDEAL-FSE demonstrated superior image quality (P<0.05), comparable fat suppression (excellent, P=1.0), and higher SNR performance (P<0.001). CONCLUSION IDEAL-FSE is a promising method for T1W and T2W imaging of the brachial plexus and cervical spine.
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Affiliation(s)
- Scott B Reeder
- Department of Radiology, University of Wisconsin, Madison, Wisconsin 53792-3252, USA.
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Reeder SB, Pineda AR, Wen Z, Shimakawa A, Yu H, Brittain JH, Gold GE, Beaulieu CH, Pelc NJ. Iterative decomposition of water and fat with echo asymmetry and least-squares estimation (IDEAL): application with fast spin-echo imaging. Magn Reson Med 2005; 54:636-44. [PMID: 16092103 DOI: 10.1002/mrm.20624] [Citation(s) in RCA: 529] [Impact Index Per Article: 27.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
Chemical shift based methods are often used to achieve uniform water-fat separation that is insensitive to Bo inhomogeneities. Many spin-echo (SE) or fast SE (FSE) approaches acquire three echoes shifted symmetrically about the SE, creating time-dependent phase shifts caused by water-fat chemical shift. This work demonstrates that symmetrically acquired echoes cause artifacts that degrade image quality. According to theory, the noise performance of any water-fat separation method is dependent on the proportion of water and fat within a voxel, and the position of echoes relative to the SE. To address this problem, we propose a method termed "iterative decomposition of water and fat with echo asymmetric and least-squares estimation" (IDEAL). This technique combines asymmetrically acquired echoes with an iterative least-squares decomposition algorithm to maximize noise performance. Theoretical calculations predict that the optimal echo combination occurs when the relative phase of the echoes is separated by 2pi/3, with the middle echo centered at pi/2+pik (k=any integer), i.e., (-pi/6+pik, pi/2+pik, 7pi/6+pik). Only with these echo combinations can noise performance reach the maximum possible and be independent of the proportion of water and fat. Close agreement between theoretical and experimental results obtained from an oil-water phantom was observed, demonstrating that the iterative least-squares decomposition method is an efficient estimator.
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Affiliation(s)
- Scott B Reeder
- Department of Radiology, Stanford University Medical Center, Stanford, California, USA.
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Szyszko TA, Bush J, Gishen P, Sellu D, Desouza NM. Endoanal magnetic resonance imaging of fistula-in-ano: a comparison of STIR with gadolinium-enhanced techniques. Acta Radiol 2005; 46:3-8. [PMID: 15841733 DOI: 10.1080/02841850510015947] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
Abstract
PURPOSE To compare a STIR sequence with gadolinium-enhanced techniques on endoanal magnetic resonance (MR) imaging of fistulas-in-ano by correlating the findings with those at surgery. MATERIAL AND METHODS Twenty-two consecutive patients with clinical suspicion of perianal sepsis were studied using an endoanal coil followed immediately by a phased array coil. T1-weighted precontrast and postcontrast and STIR images in transverse and coronal planes were produced with each coil and analysed by noting the presence and site of a collection, primary track, the position of any internal opening, and subcutaneous or supralevator extension. An "expert" and also a "trainee" radiologist assessed the images. Operative findings were similarly recorded. The Fisher exact test was used to compare imaging with surgery. Interobserver variation was calculated using a kappa statistic. RESULTS Of 22 patients with suspected fistulas, 8 were simple, 4 were complex, and 3 were superficial sinuses. Five had no anal pathology, 1 had anal excoriation, and 1 had a polyp. At surgery, 6 intersphincteric, 1 transsphincteric, 8 extrasphincteric, no supralevator collections, and 9 internal openings were noted. The overall sensitivity and specificity for detecting these were 75% and 64%, respectively, for STIR imaging, and 58.3% and 62.8% for gadolinium-enhanced imaging. There was good agreement between the "trainee" and the "expert" in the interpretation of images (kappa=0.7). CONCLUSION A STIR sequence is more sensitive overall than gadolinium-enhanced techniques on endoanal magnetic resonance imaging of fistulas-in-ano because of increased sensitivity in detecting the internal opening. A combination of endoanal and phased array techniques using STIR imaging sequences is valuable preoperative assessment in both simple and complex cases.
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Affiliation(s)
- T A Szyszko
- Department of Imaging, Hammersmith Hospitals NHS Trust, London, UK.
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