Artefacts in body and breast MRI: lessons learned from second reading

Transcription

1 Artefacts in body and breast MRI: lessons learned from second reading Poster No.: C-0573 Congress: ECR 2013 Type: Scientific Exhibit Authors: M. Nadrljanski, P. Jovanovic, A. Jankovic, Z. C. Milosevic ; Belgrade/RS, Obrenovac/RS Keywords: Breast, Abdomen, MR physics, MR, Audit and standards, Diagnostic procedure, Artifacts DOI: /ecr2013/C-0573 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 25

2 Purpose An artefact is defined as any feature appearing in an image, which is not present in the original object, which is not an actual anatomic/pathological structure, masking true abnormalities or creating pseudo-lesions [1]. MRI is the non-invasive, radiationfree modality used in diagnostic imaging for over three decades, providing both, the indispensible images of anatomic / pathological structures and the functional data unavailable with other imaging modalities [2]. Artefacts in MRI appear as the result of complex interactions of different subsystems: the main magnet, gradient coils, radiofrequency transmitter and receiver, reconstruction gradient algorithm - the computer system [3]. Since 1972, when the magnetic resonance had been introduced into imaging, the technologic advances in the MRI system - components and architecture, including the different diagnostic applications of the modality and the introduction of the software solutions for image processing, different sources of potential artefacts and pitfalls. Zhuo and Gullapalli (2006) [3] propose the broad general classification of the sources of artefacts according to the subsystems of the MRI architecture: - Image-reconstruction related (limitations of the reconstruction algorithm) - System-related (due to transient effects of one or more subsystems) - Physiology related (due to complex subject-system interactions) Smith and Nayak (2010) [4] defined the common sources of MRI artefacts as follows: - Resonant offsets (Field inhomogeneity; Susceptibility; Chemical shift) - Hardware limitations (Gradient nonlinearities; Concomitant gradients; Timing errors; RF field nonuniformity; Limited dynamic range) - Motion and flow (Respiration; Cardiac cycle; Blood and CSF flow; Peristalsis and swallowing; Voluntary patient motion) - Miscellaneous (Aliasing, slice overlap, magic-angle RF interference; Truncation) Erasmus et al. (2004) [5] classify the artefacts based on their origin into three broad groups: - Patient-related MR artefacts (Motion artefacts; Flow; Metal artefacts) Page 2 of 25

3 - Signal-processing dependent (Chemical shift artefact; Partial volume; Wrap around; Gibbs phenomenon - ringing artefact) - Hardware-related (RF-quadrature; External magnetic field (B0) inhomogeneity; Gradient field artefacts (B1) inhomogeneity; RF inhomogeneity; Asymmetrical brightness; RF noise; RF tip angle inhomogeneity; Bounce point artefact; Surface coil artefacts; Sliceto-slice interference) There are other artefact-classification systems, proposed by other authors, covering the same artefacts classified somewhat differently or ion different order, as proposed by Morelli et al. (2011) [2], or Harvey et al. (2007) [6], focusing on the artefacts specific for breast MRI, while the mentioned three-category classification systems mostly overlap. The MRI artefacts are summarized in Tables 1-3, according to their origins. We analyzed the artefacts encountered during the second reading of the breast, abdominal and pelvic MRI-examinations of the outpatients, which were performed in other centers / cabinets. The second reading or the additional consultation was performed. Page 3 of 25

4 Images for this section: Table 1: Patient-related artefacts Table 2: Signal-processing artefacts Page 4 of 25

5 Table 3: Hardware-related artefacts Page 5 of 25

6 Methods and Materials We retrospectively analyzed 22 MRI exams of breast, abdomen and pelvis, performed in different centers / cabinets in the period: January September The examinations were recorded on the DVD in the centers where the examinations were performed and were analyzed on the 27-inch imac (Apple, Cupertino, California, USA) with the DICOM viewer OsiriX (OsiriX, Pixmeo, Geneva, Switzerland). The artefacts were analyzed according to the two classification systems. The first classification system used for the analysis of the artefacts (as described in Tables 1-3) is based on the origin of the artefacts, including the subject-related artefacts, the hardware and the signal-processing artefacts. The artefacts were then re-analyzed according to the impact on the quality of the image and the level of severity, according to the classification proposed by Fischer et al. [7], summarized in Table 4. Page 6 of 25

7 Images for this section: Table 4: Classification of artefacts according to the level of severity Page 7 of 25

8 Results In the 22 analyzed exams (6 abdominal MRI, 3 pelvic MRI, 11 breast MRI), the most common artefacts according to the classification system based on the artefact-origin were: motion-related (patient-related, Fig. 1-5), followed by signal processing artefacts (chemical shift, Fig. 6; wrap around or aliasing, Fig. 7-8) and hardware related artefacts (Fig. 9-14). According to the level of severity, all abdominal MRI exams (6/6; 100%), and pelvic exams (3/3; 100%) belonged to the Category 4 - unacceptable. Concerning the breast MRI examinations there were 11 examinations analyzed: (7/11; 64%) of breast MRI exams were classified as unacceptable - Category 4. The remaining examinations (4/11; 36%) were classified as the Category 3 - distinct. Page 8 of 25

9 Images for this section: Fig. 1: Ghosting artefact: increased signal of the ghosting artefact is best visible on the parts left or right of the structure Page 9 of 25

10 Fig. 2: Positioning artefact (arrowhead) and ghosting (arrow): loss of signal in multi-angle, multi-slice acquisition - the pre-excitation was for the adjacent slice Page 10 of 25

11 Fig. 3: DW-MRI (Diffusion-weighted MRI) ghosting artefact: a.) DWI - substantial ghosting artefacts limit the usefulness of the DWI and the use of the ADC maps b.) ADC map in the patient with locally advanced breast cancer (LABC) Page 11 of 25

12 Fig. 4: Phase-encoded motion artefact: numerous bands overlapping the image due to the abdominal wall movements during phase-encoding Page 12 of 25

13 Fig. 5: Motion-related artefact: coronal abdominal image obtained without breath hold; numerous breathing-related artefacts resulting in the diffuse image noise Page 13 of 25

14 Fig. 6: Chemical shift artefact: black and bright border Page 14 of 25

15 Fig. 7: Aliasing (wrap around) artefact: small field of view (FoV) leads to mismapping of the structures outside of the FoV, with the structure(s) being displaced to the opposite side Page 15 of 25

16 Fig. 8: Aliasing (wrap around) artefact: small field of view (FoV) leads to mismapping of the structures outside of the FoV, with the structure(s) being displaced to the opposite side Page 16 of 25

17 Fig. 9: Surface coil artefact (arrowhead): high signal at anterior abdominal wall with numerous motion artefacts (arrows) Page 17 of 25

18 Fig. 10: Artefact due to the coil displacement (arrow) with the signal flare (arrowhead) with the breast tissue near the coil element Page 18 of 25

19 Fig. 11: Slice overlap artefact (cross-slice): loss of signal in multi-angle, multi-slice acquisition - the pre-excitation was for the adjacent slice Page 19 of 25

20 Fig. 12: Moiré artefact: addition and cancellation of signals Page 20 of 25

21 Fig. 13: RF interference artefact (arrows): multiple high-intensity bands in the phaseencoding direction Page 21 of 25

22 Fig. 14: "Zebra" artefact (arrows): band-like oblique artefacts due to abrupt change from signal to non-signal Page 22 of 25

23 Conclusion Artefacts can easily simulate real lesions and mislead the radiologist. Recognizing the artefacts include their identification, understanding and avoidance, leading to corrections and improvement in quality. New techniques like ultrafast imaging and high-field MRI scanners (3T or higher) may involve the appearance of different kind and frequency of artefacts. It is worth mentioning that the MRI examinations no longer represent the structure-only imaging methods, but also provide the numerous data on functional aspects (DWI, PWI, MRS), enlarging thus the chances of artefacts to appear and influence the results, leading to possible misinterpretation. Page 23 of 25

24 References [1] Milosevic ZC, Nadrljanski M. Artefacts in digital full-field mammography. ECR 2011 Book of Abstracts (2011) Insights into Imaging 2: Suppl.1. S179 [2] Morelli JN, Runge VM, Ai F, et al. An Image-based Approach to Understanding the Physics of MR Artifacts. RadioGraphics, 2011;31: [3] Zhuo J, Gullapalli RP.MR Artifacts, Safety and Quality Control. RadioGraphics, 2006;26: [4] Smtih TB, Nayak KS. MRI artifacts and correction strategies. Imaging Med., 2010;2(4): [5] Erasmus LJ, Hurter D, Naude M, Kritzinger HG, Acho S. A short overview of MRI artefacts. SA Journal of Radiology, 2004;8(2): [6] Harvey JA, Hendrick ER, Coll JM, Nicholson BT, Burkholder BT, Cohen MA. Breast MR Imaging Artifacts: How to recognize and Fix Them. RadioGraphics, 2007;27:S131S145. [7] Fischer U, Baum F. Mammography Case Book. 100 Studies in the Breast Imaging. Stuttgart: Thieme, Page 24 of 25

25 Personal Information Corresponding author: Mirjan M. Nadrljanski, MD, M.Sc. Dept. of Diagnostic Imaging Institute of Oncology and Radiology of Serbia (IORS) Belgrade / RS dr.m.nadrljanski@gmail.com Page 25 of 25