Can we avoid the traps of 3T imaging?

Transcription

1 Can we avoid the traps of 3T imaging? Poster No.: C-1473 Congress: ECR 2015 Type: Scientific Exhibit Authors: M. Kiss, J. Martos, L. R. Kozak, B. Lombay ; Budapest/HU, Miskolc/HU Keywords: MR physics, Neuroradiology brain, Computer applications, MRDiffusion/Perfusion, MR-Functional imaging, MR-Spectroscopy, Manometry DOI: /ecr2015/C-1473 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 29

2 Aims and objectives In recent years 3T MRI has become more and more common in the clinical practice and it increasingly occupies the place of 1.5T systems. Unfortunately transferring the 1.5T protocols to 3T systems were not really straightforward and sometimes not even successful [1]. There are several advantages of 3T MRI: faster sequences, new techniques and advanced hardware. Due to the growing number of 3T MRIs the clinical application spectrum have substantially broadened to almost all anatomical areas including e.g. musculoskeletal [2, 3], abdominal [4, 5], cardiac [6], angiographic [7, 8, 9], and wholebody imaging [10, 11]. Besides the many advantages, there are some disadvantages and artifacts e.g. high B0 and B1 inhomogeneity, chemical shift effects, artifacts from blood flow, magnetohydrodynamics-, susceptibility artifacts. In some cases contrast visualization is decreased [12, 13]. One of the main disadvantages of 3T scanners is the high specific absorption rate (SAR) [14], there are many articles dealing with SAR limit, and sequence optimization. To avoid the possible drawbacks many strategies have been described recently, but given the numerous drawbacks the question is still valid: is 3T clearly ready to meet all the clinical needs today? The purpose of this study to present the most relevant artifacts, present at 3T MRI, to review, compare and choose the best of the possible strategies, reducing them, if possible. We also aim to compare image artifacts and possible solutions 1.5-, and 3T MRI. Methods and materials Here we review imaging data of more than 400 patients including 40 children examined between and on a 1.5T-, (Magnetom Symphony, Siemens Healthcare, Erlangen, Germany) and two 3T (Magnetom Verio, Siemens Healthcare, Erlangen, Germany) MRI machines. Scans from different body region were systematically reviewed to show the main advantages, artifacts and their consequences, possible compensations and their effects (the latter mainly on the 3T systems, see Fig 1. / Table 1.). Problems in detail: Specific Absorption Rate reduction. Decreased contrast visualization between gray and white matter on T1weighted brain images. Page 2 of 29

3 Time-Of-Flight (TOF) MR angiography background suppression. Mitigating the susceptibility artifacts originating from metal implants. Decreased liquor signal intensity on T2-weighted lumbar spine images. In the first case we measured the Contrast to Noise Ratio (CNR) between the gray and white matter. A Region of Interest (ROI) approach was applied to measure the mean ± standard deviation. For the other cases 5 radiologist reviewed the images independently in a qualitative manner. Determining if image quality is acceptable upon applying solution based on Table 1. They also determined their subjective best solution for a given problem. In some cases we suggested other techniques/sequences to solve these imaging problems. Page 3 of 29

4 Fig. 1: Table 1. Important factors affecting image quality and possible compensations at 3T [15, 16, 17, 18, 19] Page 4 of 29

5 References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Images for this section: Page 5 of 29

6 Fig. 1: Table 1. Important factors affecting image quality and possible compensations at 3T [15, 16, 17, 18, 19] Page 6 of 29

7 Results SAR limit's problem Knowing and handling SAR limits are important in the clinical practice, especially at the abdomen, extremities and spine examinations to avoid the sudden stopping of measurement, due to exceeding the acceptable SAR. SAR can be easily reduced by reducing the slice number, voxel size or change other sequence parameter, and however these manipulations can sometimes seriously decrease image quality. To avoid this "trap" is better to change RF pulse type (from high/normal to low SAR), to reduce the turbo factor/echo train lengths or to increase the concatenations). T1 value: Contrast differentiation on T1-weighted brain Spin Echo images, on 1,5-, and 3T MRI system (Fig 2., Fig 3.). Fig. 2: T1-weighted Spin echo sequence about the brain on 1.5T (TR: 500 ms, TE: 11 ms). Page 7 of 29

8 References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Fig. 3: T1-weighted Spin echo sequence about the brain on 3T (TR: 620 ms, TE: 9 ms). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU There is clear contrast between the white-, and gray matter on 1.5T with some visible noise (Fig 2.), while contrast is diminished on at 3T - despite the better overall image quality (Fig 3.). Suggested solution: reducing the flip angle (FA) [17]. Lower the FA, improves CNR in some slices (Fig 4/a.) while not affecting other parts of the (Fig 4/b.). Page 8 of 29

9 Fig. 4: The results of lower FA (70 degree): visible contrast differentiation (a.). Contrast difference was lost on other slices (b.). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU We couldn't correct this problem of Spin Echo imaging, so we tried different sequences to find the best one of brain disorder analysis (Fig 5.). Page 9 of 29

10 Fig. 5: Four different types of T1-weighted sequences about the brain. The gray-, and white contrast visualization is invisible on the conventional Spin Echo (a.) and SPACE (b.) sequences. Good contrast is visible only the temporal-lobe on the 2D Flash sequence (c.). The best option is the MPRAGE sequence, with inversion time (d.). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Time-Of-Flight MR angiography - TOF MRA At 3T the TOF sequence provides superior spatial resolution, thus improved vessel contrast, better background tissues. However there are few cases, when background Page 10 of 29

11 suppression is not advantageous, e.g. to detect neurovascular compression, affecting the trigeminal nerve. It is easy to detect on 1.5T - TOF MRA, without MTC pulse. On 3T there are 2 two possible solutions: Decreasing the resolution. Reducing the flip angle Trigeminal nerve detection (Fig 6/a. white arrows) wasn't correct because of the image quality, but 3D VIBE (Volume Interpolated Breath-hold Examination) with fat suppression (Fig 6/b.) was successful for the correct identification of nerve. Fig. 6: TOF MRA: establishing the the presence of neurovascular compression is nearly impossible because of the too noisy image noise and the reduced visibility of the trigeminal nerve is viewless (a. - white arrows). The problem can be solved with FS VIBE sequence - the nerve is detectable (b. - red arrows). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Magnetic susceptibility This artifact mainly presents with high intensity on echo-planar diffusion weighted images (Fig 7/a). Possible solution: larger receiver bandwidth and/or a decreased echo time; even better solution: PAT (Parallel Acquisition Technique; Grappa and Sense). Using Page 11 of 29

12 PAT acquisition time was the same, the signal to noise ratio (SNR) were lower and artifacts were reduced successfully (Fig 7/b). Fig. 7: Diffusion weighted image with low TE and high receiver bandwidth, without PAT (a.) - with visible susceptibility artifacts (white arrows). Same sequences with PAT (Grappa) - the artifacts were reduced (b.). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Orthopedic metal implants in the spine may cause more extensive susceptibility artifacts at 3T than at 1.5T (Fig 8.). Page 12 of 29

13 Fig. 8: Susceptibility artifacts from metal implant at 3T, and 1.5T (a.). The artifacts appeared markedly on 3T images (b.). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU These could be reduce using conventional Turbo Spin Echo sequences with higher bandwidth (Fig 9/a. - WARP technique - Siemens), but flow artifacts will then be amplified (Fig 9/b). Flow artifacts can be reduced with a 3D SPACE (Sampling Perfection with Application optimized Contrasts using different flip angle Evolution) sequence (Fig 10.) with low turbo factor. Page 13 of 29

14 Fig. 9: T2-weighted axial images about the cervical spine - with metal implant. The susceptibility artifact appeared strongly on the gradient echo image (Fig 8/a). It could reduce with TSE sequence - however the flow artifacts were amplified (Fib 8/b). References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Fig. 10: T2-weighted SPACE axial and coronal images about the cervical spine - the flow artifacts were eliminated. References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Reduced Liquor Intensity Page 14 of 29

15 Signal intensity is much better on 3T than 1.5T. Of course we have to increase the TR at 3T. Interestingly there is a special artifact on the T2-weighted L-spine images - significant signal intensity reduction on the right or left side of the images (Fig 11/a.). Fig. 11: Fig 11. T2-weighted sagittalis L-spine images with significant signal decay on the left side. Fig 10/b show the same image after the correction. References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Possible solution: change concatenation (distribution of the slices to be measured over multiple measurements) values from 1 to 2, and apply a saturation band (Fig 11/b). This artifact is a typical 3T system issue, however with the use of more concatenation there is less slice cross talk and therefore less "saturation" in the slices. Images for this section: Page 15 of 29

16 Fig. 2: T1-weighted Spin echo sequence about the brain on 1.5T (TR: 500 ms, TE: 11 ms). Page 16 of 29

17 Fig. 3: T1-weighted Spin echo sequence about the brain on 3T (TR: 620 ms, TE: 9 ms). Fig. 4: The results of lower FA (70 degree): visible contrast differentiation (a.). Contrast difference was lost on other slices (b.). Page 17 of 29

18 Fig. 5: Four different types of T1-weighted sequences about the brain. The gray-, and white contrast visualization is invisible on the conventional Spin Echo (a.) and SPACE (b.) sequences. Good contrast is visible only the temporal-lobe on the 2D Flash sequence (c.). The best option is the MPRAGE sequence, with inversion time (d.). Page 18 of 29

19 Fig. 6: TOF MRA: establishing the the presence of neurovascular compression is nearly impossible because of the too noisy image noise and the reduced visibility of the trigeminal nerve is viewless (a. - white arrows). The problem can be solved with FS VIBE sequence - the nerve is detectable (b. - red arrows). Fig. 7: Diffusion weighted image with low TE and high receiver bandwidth, without PAT (a.) - with visible susceptibility artifacts (white arrows). Same sequences with PAT (Grappa) - the artifacts were reduced (b.). Page 19 of 29

20 Fig. 8: Susceptibility artifacts from metal implant at 3T, and 1.5T (a.). The artifacts appeared markedly on 3T images (b.). Fig. 9: T2-weighted axial images about the cervical spine - with metal implant. The susceptibility artifact appeared strongly on the gradient echo image (Fig 8/a). It could reduce with TSE sequence - however the flow artifacts were amplified (Fib 8/b). Page 20 of 29

21 Fig. 10: T2-weighted SPACE axial and coronal images about the cervical spine - the flow artifacts were eliminated. Fig. 11: Fig 11. T2-weighted sagittalis L-spine images with significant signal decay on the left side. Fig 10/b show the same image after the correction. Page 21 of 29

22 Conclusion Real and unavoidable problems play very important role in the sequence optimization. The SAR limit is a real "trap", because without change the sequence's parameters we will get noisy and unacceptable results. We suggest to modify the sequence's parameters instead of choosing another sequence(s). In our example the best way was to modify the RF-pulse type and to decrease the resolution. Great problem is to increase the contrast between the gray-, and white matter on the T1weighted Spin-Echo images. The lower flip angle could be a better route, but it didn't work on our systems. The only solution was using another sequence e.g. MPRAGE which apply Inversion Recovery technique to provide the contrast differentiation. We couldn't find optimal TOF's sequence values to identify the trigeminal nerve and determine the neurovascular compression. 3D VIBE sequence with fat suppression could be a solution. Using PAT sequences play an important role in reducing susceptibility artifacts on diffusion weighted sequences. In some cases however, the PAT caused significant artifacts, but it can be compensated. Susceptibility artifacts due to metal implants could be eliminated using TSE sequences while flow artifacts could be reduced with SPACE sequences, but in this case the turbo factors were limited. Finally we could compensate the T2-weighted L-spine intensity issue arising at 3T using changes in concatenation parameters. We summarize our results in two tables (Table 2. and Table 3. - see Fig 12. and Fig 13.). Page 22 of 29

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24 Fig. 12: Table 2. The usable and unusable solutions References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Fig. 13: Table 3. Avoidable and unavoidable problems and their solutions References: Neuroradiology, National Institute of Clinical Neuroscience, Department of Radiology; - Budapest/HU Images for this section: Page 24 of 29

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26 Fig. 12: Table 2. The usable and unusable solutions Fig. 13: Table 3. Avoidable and unavoidable problems and their solutions Page 26 of 29

27 Personal information References [1] Lawrence N. Tanenbaum: Clinical 3T MRI: Mastering and Challanges. Appl. Radiology 2006;35(11). [2] Filippo Del Grande, Francesco Santini, Daniel A. Herzka, Micheal R. Aro, Cooper W. Dean, Garry E. Gold, John A. Carrino: Fat-Suppression Techniques for 3T Imaging of the Musculoskeletal System. DOI: doi.org/ /rg [3] Ramnath RR. 3T MR imaging of the musculoskeletal system (Part II): clinical applications. Magn Reson Imaging Clin N Am 2006;14(1): [4] Kevin J. Chang, MD, and Ihab R. Kamel: Abdominal imaging at 3T: Challenges and solutions. Applied Radiology 2010;10: [5] Elmar M. Merkle and Brian M. Dale: Abdominal MRI at 3.0 T: The Basics Revisited. American Journal of Rontgenology. 2006;186: [6] John N. Oshinski, Jana G. Delfino Puneet Sharma, Ahmed M. Gharib and Roderic I. Pettigrew: Cardiovascular Magnetic Resonance at 3T: Current state of the art. Journal of Cardiovascular Magnetic Resonance 2010, 12:55. [7] Kolja M. Thielfelder, Georgios Meimarakis, Konstantin Nikolau, Wieland H. Sommer, Peter Schmitt, Philipp M. Kazmierczak, Maximilian F. Reiser and Daniel Theisen: NonContrast-Enhanced MR Angiograpghy at 3T in Patients with Advanced Peripheral Arterial Occlusive Disease. DOI: /journal.pone [8] K. Naela, J.P. Villablancaa, R. Saleha, W. Popea, A. Naela, G. Laubb and J.P. Finna: Contrast-Enhanced MRA at 3T in the Evaluation if intracranial Aneurysms: A Comparison with Time-Of-Flight MR Angiography. AJNR November : [9] Eftychia Z. Kapsalaki, Christos D. Rountas and Kostas N. Fountas: The Role of 3T MRA in the Detection of Intracranial Aneurysms. DOI: /2012/ Page 27 of 29

28 [10] Laura M. Fayad, Jaishri Blakeley, Scott Plotkin, Brigitte Widemann and Michael A. Jacobs: Whole Body MRI at 3T with Quantitative Diffusion Weighted Imaging and Contrast-Enhanced Sequences for the Characterization of Peripheral Lesions in Patients with Neurofibromatosis Type 2 and Schwannomatosis. DOI: /2013/ [11] Schmidt GP. Wintersperger B, Grase A, Baur-Melnyk A, Resier MF, Schoenberg SO.: High-resolution whole-body magnetic resonance imaging applications at 1,5 and 3T: a comparative study. Invest Radiology Jun;42(6): [12] Olaf Dietrich, Maximilian F. Reiser and Stefan Schoenberg: Artifacts in 3-Tesla MRI: Physical background and reduction strategies. Eur J Radiol 2008; 65(1): [13] Escher K, Shellock FG.: Evaluation of MRI artifacts at 3 Tesla for 38 commonly used cosmetics. Madn Reson Imaging 2013 Jun; 31(5): [14] Edelstein WA, Glover GH, Hardy CJ, Redington RW. The intrinsic signal-to-noise ratio in NMR imaging. Magn Reson Med 1986;3(4): [15] Fritz Schick: Whole-body MRI at high field: technical limits and clinical potential. DOI: /s [16] Vaishali V. Phalke, Sachin Gujar and Douglas J. Quint: Comparison of 3.0 versus 1.5T MR: Imaging of the spine. DOI: dx.doi.org/ /j.nic [17] Bernd L. Schmitz, Georg Grön, Florian Brausewetter, Martin H.K. Hoffmann, and Andrik J. Aschoff: Enhancing Gray-to-White Matter Contrast in 3T T1Spin-Echo Brain Scans by Optimizing Flip Angle. AJNR Am J Neuroradiol 26: , September [18] R. Javan, J.R. O'Rear, J. E. Machin; Fundamentals Behind the 10 most common Magnetic Resonance Imaging Artifacts with Correction Strategies and 10 High-Yield Points. DOI: /ecr2011/C [19] Charuta Dagia; Michael Ditchfield: 3T MRI in Pediatrics: Challanges and Clinical Applications. European Journal of Radiology, 68 (2008) [20] Matt A. Bernstein: Field Strength Dependence in MRI: Advantages and Artifacts at 3T. ( Page 28 of 29

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