Imaging
Figure 6: Clipped Aneurysm at the Anterior Communicating Artery
A A
Figure 7: Clipped Aneurysms at the Internal Carotid Posterior Communicating Arteries and at the Junction of the Anterior Choroid Artery and Internal Carotid Artery
B
B
A: A superior oblique view of a conventional 3D computed tomography angiography (3D CTA) image shows a clip at the anterior communication artery (AcomA), and does not clearly depict whether or not there are any remnant necks (white arrows, clip; white arrowheads, right anterior cerebral artery). B: A left anterior oblique view of the volume- rendered (VR) image by the application for bone elimination clearly depicts no remnant neck (white arrows, left anterior cerebral artery; white arrowheads, right anterior cerebral artery; single crossed white arrow, AcomA) of the aneurysm without a clip.
conventional 3D CTA with clips to replace IADSA, but 3D CTA with clip elimination could be significantly superior to conventional 3D CTA. 3D CTA using MDCT has the potential to replace IADSA to confirm complete or incomplete clipping of cerebral aneurysms in cases involving no more than one or two clips. MR angiography (MRA) also provides 2D and 3D images of aneurysms without bony structures. There are several limitations in imaging aneurysms by MRA.22
Flow-
related artefacts can result in under-estimation of the size of aneurysms. Even in larger aneurysms, turbulent flow and/or thrombosis within the aneurysm can cause poor visualisation of the aneurysm by MRA. However, MRA using 3 Tesla (3T) MR systems is able to clearly image small aneurysms.23–25
Further studies should
compare the current bone-free CTA technique with MRA. Moreover, to determine whether bone-free 3D CTA is a viable alternative to IADSA, detection of aneurysms should also be compared between 3D CTA and IADSA in a blinded study.
Conclusion
Bone-free 3D CTA using an image-processing application for the elimination of bones can improve delineation of cerebral aneurysms
1. Kouskouras C, et al., Neuroradiology, 2004;46: 842–50. 2. Uysal E, et al., Diagn Interv Radiol, 2005;11:77–82. 3. Pechlivanis I, et al., Acta Neurochir (Wien), 2005;147:1045–53. 4. Tipper G, et al., Clin Radiol, 2005;60:565–72. 5. Kato Y, et al., Acta Neurochir, 2002;144:715–22. 6. Agid R, et al., Neuroradiology, 2006;48:787–94. 7. Venema HW, et al., Radiology, 2001;218:893–8. 8. Moore EA, et al., Eur Radiol, 2001;11:137–41. 9. Jayakrishnan VK, et al., AJNR Am J Neuroradiol, 2003;24:451–5.
Thus, bone-free 3D CTA and conventional 3D CTA are complementary tools for imaging cerebral aneurysms near the skull base prior to surgery. This application can also eliminate clips in cases of clipped cerebral aneurysms. 3D CTA with the elimination of clips can improve the accuracy of detecting remnant necks after clipping surgery, and may be a viable alternative to IADSA for the detection of remnant necks in cases with single or double clips. n
Noriaki Tomura is an Associate Professor of Radiology and Chief of Neuroradiology at Akita University. He is board-certified in radiology and nuclear medicine, and received his MD from Akita University. His research interests are primarily in diagnostic neurology, head and neck radiology and nuclear medicine of the brain.
A left anterior oblique view of a conventional 3D computed tomography angiography (3D CTA) image (A) does not clearly show the remnant neck due to clips at the IC-PC (white arrows, clips; white arrowheads, left anterior cerebral artery; single crossed white arrow, left ICA; double crossed white arrow, left middle cerebral artery). A left anterior oblique view of the volume-rendered (VR) image (B) by the application for bone elimination clearly depicts a small part of a remnant neck (white arrow) of the aneurysm without clips.
near the skull base. This technique does not increase radiation exposure to patients, and remnant bones in the initial MIP images automatically acquired by the application for bone elimination can be easily removed through post-processing. Although parts of vessels are sometimes removed from the image along with the bones, these can be quickly and easily recovered through post-processing.
10. Abrahams JM, et al., Neurosurgery, 2002;51:264–9. 11. Kwon SM, et al., Comput Med Imag Graph, 2004;28:391–400. 12. van Straten M, et al., Am Assoc Phys Med, 2004;31:2924–33. 13. Tomandl BF, et al., AJNR Am J Neuroradiol, 2006;27:55–9. 14. Sakamoto S, et al., AJNR Am J Neuroradiol, 2006;27: 1332–7. 15. Tomura N, et al., Jpn J Radiol, 2009;27:31–6. 16. Sasiadek M, et al., Med Sci Monit, 2002;8:MT99–104. 17. Suryanarayanan S, et al., Image Processing, 2004:5370:410–19.
18. Lin T, et al., J Neurosurg, 1989;70:556–60. 19. Sasaki T, et al., J Neurosurg, 1994;80:58–63. 20. Dehdashti AR, et al., J Neurosurg, 2006;104:395–403. 21. Tomura N, et al., Clin Radiol, 2006;61;505–12 22. Gailoud P, et al., Neuroradiology, 2003;45:404–9. 23. Villablanca JP, Saleh R, AJNR Am J Neuroradiol, 2006;27:2118–21.
24. PH, Hui F, Sitoh YY, Ann Acad Med Singapore, 2007;36:388–93. 25. Miki H, Kiriyama I, Magn Reson Med Sci, 2008;7:169–78.
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