Usefulness of the Navigator-echo triggering Technique for Free-Breathing 3D MRCP

Usefulness of the Navigator-echo triggering Technique for Free-Breathing 3D MRCP Poster No.: C-1257 Congress: ECR 2012 Type: Scientific Exhibit Authors: K. Matsunaga, G. Ogasawara, K. Fujii, T. Irie, T. Yamane, K. Ishida, Y. Inoue; Sagamihara/JP Keywords: DOI: Biliary Tract / Gallbladder, Pancreas, MR, Comparative studies, Artifacts 10.1594/ecr2012/C-1257 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. www.myesr.org Page 1 of 14

Purpose Magnetic resonance cholangiopancreatography (MRCP) is a noninvasive imaging technique that provides detailed information on the anatomy and pathology of the biliary tree and pancreatic duct [1-3]. Breath-hold techniques or respiratory-triggering techniques are used to reduce motion artifacts in MRCP. The respiratory-triggered 3D MRCP technique can offer higher spatial resolution than the breath-hold technique and is widely used in clinical practice [4,5]. For respiratory triggering, movement of the abdominal wall is commonly monitored by a bellows rolled around the upper abdomen to monitor respiratory motion [6]. However, the motion of the abdominal wall does not always reflect that of the visceral organs faithfully, and the discrepancy between them may degrade the image quality. The navigatorecho triggering technique (navigator technique) is another method to monitor respiratory motion. This technique allows synchronization of data acquisition to the movement of visceral organs, by directly monitoring the movement of the right diaphragm with navigator echoes. It has been used mainly for cardiac imaging [7,8], and is introduced to upper abdominal imaging with the low flip angle sequences which avoid magnetization saturation inside the volume of interest [4]. Its superiority to the bellows technique for 3D MRCP has been reported in healthy volunteers [9]. In this study, we performed respiratory-triggered 3D MRCP with both navigator and bellows techniques in patients with biliary or pancreatic diseases. We compared the image quality, the visualization of the pancreaticobiliary tree and the clarity of the lesion, within a patient between the two methods. Methods and Materials Patients Institutional review board approval was obtained. Written informed consent was obtained before each examination. Forty patients (24 men and 16 women; mean age, 61.7 years; age range, 37-85 years) referred to MRCP for the evaluation of biliary or pancreatic diseases (Table 1). Study design Page 2 of 14

All the patients underwent 3D MRCP examinations using both bellows and navigator techniques. Four-hour fasting. Ingestion of negative oral contrast agent. Intramuscular injection of an antispasmodic agent. At the beginning of the examination, bellows was rolled around the upper abdomen. MRCP using the bellows technique was performed first, and, subsequently, MRCP using the navigator technique was done. MRCP A 1.5-Tesla system with eight-channel phased-array torso coil Respiratory-triggered 3D MRCP was performed with a 3D FRFSE sequence. TR/ TE = 2000-7000 ms/670.4 ms FOV = 34 x 34 cm matrix = 352 x 256 36-56 sections of 2.2-mm thickness parallel acquisition technique (reduction factor, 2) spectrally selected fat saturation In the navigator technique, the navigator was set on top of the right hemidiaphragm. 2D pencil-beam excitation 10-degree flip angle 10-cm length, 2-cm diameter acceptance window, ±2mm Partial maximum-intensity-projection (MIP) images of MRCP were created for. Data analysis Two independent board-certified radiologists visually evaluated the qualities of the 3D MRCP images using the bellows and navigator techniques in a blinded fashion. Differences between reviewers were resolved by consensus between them. The pancreaticobiliary tree was divided into 12 segments for the evaluation of the image quality (Table 2). The visualization of the 10 segments except the gallbladder and cystic duct was classified into four categories (excellent, good, fair and poor) on the MIP images. Page 3 of 14

The visualization of the gallbladder was classified into three categories (excellent, good and poor) on the MIP images. The visualization of the cystic duct was classified into three categories (excellent, good and poor) on the MIP and source images. The clarity of the lesion was compared between the two techniques in a side-by-side manner, on the MIP images. Source images were also used for the evaluation of the gallbladder lesion. Thirty-one lesions were identified in 26 patients, by referring to all available images including US, CT, MRI, and ERCP. The results of comparison were classified into the following categories: the navigator technique provided better quality, the two techniques provided equal quality, the bellows technique provided better quality and a lesion was not visualized on either images. Statistical analysis Wilcoxon signed-rank test was performed for statistical analysis of visual assessments. For the evaluation of the lesion clarity, all 31 lesions were evaluated as one group. The acquisition times were compared using the paired t-test. Images for this section: Page 4 of 14

Table 1: The clinical indications for MRCP examinations. Page 5 of 14

Results MRCP images were successfully acquired using both techniques in all patients. No significant difference in acquisition times was observed between the two techniques (Figure 1). The image quality was significantly better for the navigator technique than for the bellows technique in the following seven segments: the head, body and tail of the pancreatic duct; the right hepatic duct; the anterior and posterior segments of the right hepatic duct; and the cystic duct (Table 2, 3 Figure 2). The improvement of the image quality indicated better monitoring of respiratory motion using the navigator technique than using the bellows technique. The navigator technique tended to provide better image quality in the left side of the hepatic ducts; however, the difference failed to reach a statistical significance. The left hepatic lobe is moved and deformed by cardiac motion [10] in addition to respiratory motion, and improvement of correction for respiratory motion alone may not be effective for better visualization of the left side of the hepatic ducts. The clarity of the lesion was significantly better for the navigator technique than for the bellows technique (Table 4, Figure 3). Images for this section: Page 6 of 14

Fig. 1: Acquisition times for the bellows and navigator techniques. There was no significant difference between them. Means and standard deviations were presented. Page 7 of 14

Table 2: Image quality of the pancreaticobiliary tree. n = number of patients. Values are number of segments. a) Wilcoxon signed-rank test. *, P < 0.05; **, p < 0.01 Page 8 of 14

Table 3: Image quality of the cystic duct and gallbladder: n = number of patients. Values are number of segments. a) Wilcoxon signed-rank test. *: P < 0.05 Page 9 of 14

Fig. 2: A 43-year-old woman who had undergone cholecystectomy and choledochojejunostomy for pancreaticobiliary maljunction. (a) Bellows technique. (b) Navigator technique. The bile ducts of the right lobe and pancreatic duct are clearly visualized by the navigator technique (arrow head). But the bile ducts of the left lobe are still unclear (arrow). Page 10 of 14

Table 4: The clarity of the lesion. Values are number of lesions. The clarity of the lesions by the navigator technique was significantly better than by the bellows technique; all 31 lesions were evaluated as one group. P=0.0032 (Wilcoxon signed-rank test) Page 11 of 14

Fig. 3: A 67-year-old woman with branch duct type of intraductal papillary mucinous neoplasm in the pancreatic body. (a) Bellows technique. (b) Navigator technique. The multilocular cystic lesion in the pancreatic body is clearly visualized by the navigator technique (arrow). Page 12 of 14

Conclusion The navigator technique offered 3D MRCP images of higher quality than the bellows technique for the right side of the hepatic ducts, pancreatic ducts and cystic ducts. The navigator technique allowed clearer visualization of the pancreaticobiliary lesions. The navigator technique directly monitors respiratory motion of the right hemidiaphragm, which closely simulates that of the liver. The better quality of MRCP images appears to be attributable to this direct monitoring. References 1. Schaefer JF, Kirschner HJ, Lichy M, et al. Highly resolved free-breathing magnetic resonance cholangiopancreatography in the diagnostic workup of pancreaticobiliary diseases in infants and young children-initial experiences. Journal of pediatric surgery 2006;41:1645-1651. 2. Basaran C, Agildere AM, Donmez FY, et al. MR Cholangiopancreatography with T2- Weighted Prospective Acquisition Correction Turbo Spin-Echo Sequence of the Biliary Anatomy of Potential Living Liver Transplant Donors. AJR 2008;190:1527-1533. 3. Kinner S, Dechêne A, Ladd SC, et al. Comparison of different MRCP techniques for the depiction of biliary complications after liver transplantation. Eur Radiol 2010;20:1749-1756. 4. Asbach P, Klessen C, Kroencke TJ, et al. Magnetic resonance cholangiopancreatography using a free-breathing T2-weighted turbo spin-echo sequence with navigator-triggered prospective acquisition correction. Magnetic resonance imaging 2005; 23:939-945. 5. Choi JY, Lee JM, Lee JY, et al. Navigator-Triggered Isotropic Three-Dimensional Magnetic Resonance Cholangiopancreatography in the Diagnosis of Malignant Biliary Obstructions: Comparison With Direct Cholangiography JOURNAL OF MAGNETIC RESONANCE IMAGING 2008;27:94-101. Page 13 of 14

6. Soto JA, Barish MA, Alvarez O, et al. Detection of choledocholithiasis with MR cholangiography: comparison of three-dimensional fast spin-echo and single- and multisection half-fourier rapid acquisition with relaxation enhancement sequences. Radiology 2000;215:737-745. 7. Stuber M, Botnar RM, Danias PG, Kissinger KV, Manning WJ. Submillimeter threedimensional coronary MR angiography with real-time navigator correction: comparison of navigator locations. Radiology 1999;212:579-587. 8. Sakuma H, Ichikawa Y, Suzawa N, et al. Assessment of coronary arteries with total study time of less than 30 minutes by using whole-heart coronary MR angiography. Radiology 2005;237:316-321. 9. Morita S, Ueno E, Suzuki K, et al. Navigator-Triggered Prospective Acquisition Correction (PACE) Technique vs. Conventional Respiratory-Triggered Technique for Free-Breathing 3D MRCP: An Initial Prospective Comparative Study Using Healthy Volunteers. J. Magn. Reson. Imaging 2008;28:673-677. 10. Chung S, Breton E, Mannelli L, et al. Liver stiffness assessment by tagged MRI of cardiac-induced liver motion. Magnetic Resonance in Medicine 2011;65: 949-955. Personal Information Keiji Matsunaga MD. Department of Diagnostic Radiology, Kitasato University School of Medicine, Sagamihara, Japan. E-mail:kgmatsu@kitasato-u.ac.jp Page 14 of 14