X-ray imaging fused with MRI offers the ability to provide dynamic, metabolic and/or high resolution soft tissue details with the interactivity or ability to use commonly available instruments and devices for interventional procedures.
One of the driving forces behind a combined imaging modality such as XMR is tit allows the high interactivity of X-ray and the ability to use non-MR compatible devices with the high soft-tissue definition created by MRI. As there is almost always a trade-off between spatial and temporal resolution in MRI, a higher temporal resolution can be achieved under X-ray angiography. Even with the introduction of spiral, radial, parallel imaging and compressed sense techniques, specialized hardware for rapid image reconstruction, and the use of sliding window reconstruction techniques, MRI can seldom obtain the temporal frame rates of X-ray angiography with high spatial resolution.
Initially, X-ray techniques were used for placement of catheters in the heart followed by interventions under MRI guidance.(4,5) This allowed the introduction of active and passive catheters and devices that had sufficient radiopacity for image guidance under X-ray, but did not require image registration for interventional MRI procedures. Many of the approved X-ray steerable catheters and devices contain ferrous braided materials or pull-wires that would heat when used for interventional MRI. Tuning and matching circuitry for actively visible MRI devices also added bulk and often rigidity to these devices.(6) Many of these devices also lacked guidewires for safe placement as well. As an alternative, passive devices were made of non-magnetic materials with more flexibility than MR-compatible materials, such as nitinol, and were doped with contrast agents to enable MR-visibility.(7) However, for cardiac applications, the inability to see long lengths of wires or catheters could make tracking of the devices in 3D difficult. One early device was used in clinical trials for pediatric interventions until the lack of visibility resulted in unrecognized wire breakage during MRI. Nonetheless, several commercial and academic research groups have successfully miniaturized these electronics and moving parts to provide MR safe compatible active devices that are undergoing preclinical applications or early clinical trials ranging from cardiac catheterization to cardiac biopsy to ablation.(8-14) Performing these procedures directly under MRI guidance has several advantages. In the case of cardiac ablation, late gadolinium enhancement(15) or thermometry(16) can be used to assess the degree of tissue ablation as well as visualizing cardiac perforation.
Thus, one of the advantages of XMR over MR-guided procedures is the ability to use “off-the-shelf” devices to perform interventional procedures. Even with specialized tables and angiographic suites that allowed the transfer of patients seamless from one modality to the other, registration of the 3D MRI images to the 2D angiographic images is required to create the MRI roadmap. Early registration methods consisted of matching of fiducial markers with both X-ray and MR visibility between multiple X-ray projections and MRI volumes(17) or optical techniques.(18) The earliest XFM studies were used to direct stem cell delivery to the heart (19) and target therapeutics.(17,20,21) The introduction of flat-panel X-ray angiographic systems that can be used to acquire ECG-gated, CT-like images and the incorporation of software for image fusion with pre-acquired MRI, radionuclide, and CT scans has vastly simplified this process and eliminated the need for distortion corrections required in image intensifier systems.(22) In addition, vendors are developing methodologies using limited projection images for reduced patient radiation exposure for multimodality image registration. One of the most obvious practical XMR procedures in the short term is using MRI to guide cardiac biopsy.(23) However, regardless of the ease of multimodality image fusion, misregistration will always exist. Therefore, procedures where 1- 2 mm of misregistration are of concern, such as mitral valve replacement, may use the MRI roadmap to be informative but still rely heavily on the angiographic data acquired in during real-time X-ray angiography.
The soft tissue detail from the MRI can be used to plan oblique angiographic imaging planes to further reduce radiation dose to the patient. However, one of the challenges is how to create an MRI roadmap from the feature rich MRI data. At a minimum, this requires segmentation of cine MRIs to create surface renderings. For full four-dimensional integration (3D plus time), the MRI volume must be synchronized to the ECG and respiratory motion. In the case of separate imaging series with vascular, function and viability information, e.g., coronary MRA, cine MRI and late gadolinium enhancement, a means to create a roadmap containing multiple features can be challenging. However, these roadmaps can clearly decrease procedure time and radiation doses. XFM has found the highest clinical utility in pediatric procedures where the concern for radiation exposure is the highest.(24) A recent example of ventricular septal defect closure using XFM allowed a more straight-forward antegrade rather than retrograde device placement.(25) It is anticipated that as augmented reality become more mainstream that fusion of MR with X-ray angiographic procedures will realize significant enhancements and expansion of in interventional procedures with reduced radiation exposure and increased safety.
1. Chong WKW, Lee SK, Terbrugge KG. 3T MRI - 3D DSA Fusion Technique on Posterior Cerebral Artery Dissecting Aneurysm: Understanding a Potential Pathophysiologic Mechanism. Interventional Neuroradiology 2006;12(3):215-221.
2. Park S, Song DY, Lee J. Deformable registration of X-ray to MRI for post-implant dosimetry in prostate brachytherapy. 2016. p 97860L-97860L-97866.
3. Nesvacil N, Potter R, Sturdza A, Hegazy N, Federico M, Kirisits C. Adaptive image guided brachytherapy for cervical cancer: a combined MRI-/CT-planning technique with MRI only at first fraction. Radiotherapy and oncology : journal of the European Society for Therapeutic Radiology and Oncology 2013;107(1):75-81.
4. Ratnayaka K, Faranesh AZ, Hansen MS, Stine AM, Halabi M, Barbash IM, Schenke WH, Wright VJ, Grant LP, Kellman P, Kocaturk O, Lederman RJ. Real-time MRI-guided right heart catheterization in adults using passive catheters. Eur Heart J 2013;34(5):380-389.
5. Razavi R, Hill DL, Keevil SF, Miquel ME, Muthurangu V, Hegde S, Rhode K, Barnett M, van Vaals J, Hawkes DJ, Baker E. Cardiac catheterisation guided by MRI in children and adults with congenital heart disease. Lancet 2003;362(9399):1877-1882.
6. Bell JA, Saikus CE, Ratnayaka K, Wu V, Sonmez M, Faranesh AZ, Colyer JH, Lederman RJ, Kocaturk O. A deflectable guiding catheter for real-time MRI-guided interventions. J Magn Reson Imaging 2012;35(4):908-915.
7. Krueger S, Schmitz S, Weiss S, Wirtz D, Linssen M, Schade H, Kraemer N, Spuentrup E, Krombach G, Buecker A. An MR guidewire based on micropultruded fiber-reinforced material. Magn Reson Med 2008;60(5):1190-1196.
8. Ratnayaka K, Saikus CE, Faranesh AZ, Bell JA, Barbash IM, Kocaturk O, Reyes CA, Sonmez M, Schenke WH, Wright VJ, Hansen MS, Slack MC, Lederman RJ. Closed-chest transthoracic magnetic resonance imaging-guided ventricular septal defect closure in swine. JACC Cardiovasc Interv 2011;4(12):1326-1334.
9. Rogers T, Ratnayaka K, Karmarkar P, Campbell-Washburn AE, Schenke WH, Mazal JR, Kocaturk O, Faranesh AZ, Lederman RJ. Real-time magnetic resonance imaging guidance improves the diagnostic yield of endomyocardial biopsy. JACC Basic Transl Sci 2016;1(5):376-383.
10. Carias M, Hynynen K. The evaluation of steerable ultrasonic catheters for minimally invasive MRI-guided cardiac ablation. Magn Reson Med 2014;72(2):591-598.
11. Ataollahi A, Karim R, Fallah AS, Rhode K, Razavi R, Seneviratne LD, Schaeffter T, Althoefer K. Three-Degree-of-Freedom MR-Compatible Multisegment Cardiac Catheter Steering Mechanism. IEEE Trans Biomed Eng 2016;63(11):2425-2435.
12. Raval AN, Karmarkar PV, Guttman MA, Ozturk C, Sampath S, DeSilva R, Aviles RJ, Xu M, Wright VJ, Schenke WH. Real-time magnetic resonance imaging-guided endovascular recanalization of chronic total arterial occlusion in a swine model. Circulation 2006;113.
13. Raval AN, Telep JD, Guttman MA, Ozturk C, Jones M, Thompson RB, Wright VJ, Schenke WH, DeSilva R, Aviles RJ. Real-time magnetic resonance imaging-guided stenting of aortic coarctation with commercially available catheter devices in Swine. Circulation 2005;112.
14. Kocaturk O, Saikus CE, Guttman MA, Faranesh AZ, Ratnayaka K, Ozturk C, McVeigh ER, Lederman RJ. Whole shaft visibility and mechanical performance for active MR catheters using copper-nitinol braided polymer tubes. J Cardiovasc Magn Reson 2009;11:29.
15. Suksaranjit P, Akoum N, Kholmovski EG, Stoddard GJ, Chang L, Damal K, Velagapudi K, Rassa A, Bieging E, Challa S, Haider I, Marrouche NF, McGann CJ, Wilson BD. Incidental LV LGE on CMR Imaging in Atrial Fibrillation Predicts Recurrence After Ablation Therapy. JACC Cardiovasc Imaging 2015;8(7):793-800.
16. de Senneville BD, Roujol S, Jais P, Moonen CT, Herigault G, Quesson B. Feasibility of fast MR-thermometry during cardiac radiofrequency ablation. NMR Biomed 2012;25(4):556-562.
17. de Silva R, Gutierrez LF, Raval AN, McVeigh ER, Ozturk C, Lederman RJ. X-ray fused with magnetic resonance imaging (XFM) to target endomyocardial injections: validation in a swine model of myocardial infarction. Circulation 2006;114(22):2342-2350.
18. Rhode KS, Hill DL, Edwards PJ, Hipwell J, Rueckert D, Sanchez-Ortiz G, Hegde S, Rahunathan V, Razavi R. Registration and tracking to integrate X-ray and MR images in an XMR facility. IEEE Trans Med Imaging 2003;22(11):1369-1378.
19. Azene NM, Ehtiati T, Fu Y, Flammang A, Guehring J, Gilson WD, Kedziorek DA, Cook J, P.V. J, Kraitchman DL. Intrapericardial delivery of visible microcapsules containing stem cells using XFM (X-ray fused with magnetic resonance imaging). Journal of Cardiovascular Magnetic Resonance 2011;13(S1):P26.
20. Hatt CR, Jain AK, Parthasarathy V, Lang A, Raval AN. MRI—3D ultrasound—X-ray image fusion with electromagnetic tracking for transendocardial therapeutic injections: In-vitro validation and in-vivo feasibility. Computerized Medical Imaging and Graphics 2013;37(2):162-173.
21. Kedziorek DA, Solaiyappan M, Walczak P, Ehtiati T, Fu Y, Bulte JW, Shea SM, Brost A, Wacker FK, Kraitchman DL. Using C-arm x-ray imaging to guide local reporter probe delivery for tracking stem cell engraftment. Theranostics 2013;3(11):916-926.
22. Gutierrez LF, Ozturk C, McVeigh ER, Lederman RJ. A practical global distortion correction method for an image intensifier based x-ray fluoroscopy system. Med Phys 2008;35.
23. McGuirt D, Mazal J, Rogers T, Faranesh AZ, Schenke W, Stine A, Grant L, Lederman RJ. X-ray Fused With Magnetic Resonance Imaging to Guide Endomyocardial Biopsy of a Right Ventricular Mass. Radiol Technol 2016;87(6):622-626.
24. Tzifa A, Schaeffter T, Razavi R. MR imaging-guided cardiovascular interventions in young children. Magn Reson Imaging Clin N Am 2012;20(1):117-128.
25. Ratnayaka K, Raman VK, Faranesh AZ, Sonmez M, Kim JH, Gutierrez LF, Ozturk C, McVeigh ER, Slack MC, Lederman RJ. Antegrade percutaneous closure of membranous ventricular septal defect using X-ray fused with magnetic resonance imaging. JACC Cardiovasc Interv 2009;2(3):224-230.