Time-resolved 4D TWIST MR angiography of congenital heart and vessel anomalies: image quality and added diagnostic value compared to 3D MRA

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1 Time-resolved 4D TWIST MR angiography of congenital heart and vessel anomalies: image quality and added diagnostic value compared to 3D MRA Poster No.: C-1663 Congress: ECR 2012 Type: Scientific Paper Authors: P. Hunold 1, D. Michna 2, J. M. Theysohn 2, U. Neudorf 2, J. Barkhausen 1, F. M. Vogt 1, H. H. Quick 3 ; 1 Lübeck/DE, 2 Essen/DE, 3 Erlangen/DE Keywords: DOI: Cardiovascular system, Cardiac, Vascular, MR-Angiography, MR, Imaging sequences, Congenital /ecr2012/C-1663 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 11

2 Purpose MR imaging in combination with MR angiography has been established as a reliable technique in diagnostic work-up as well as follow-up of kids [1] and adults [2] with congenital heart and vessel anomalies (congenital heart disease, CHD). In fact, cardiac catheterization can be replaced by this non-invasive method in many cases. However, the demands for a comprehensive MR exam in CHD are challenging containing precise evaluation of cardiac morphology and function, detection and quantification of shunts, and reliable depiction of the great vessels. Recent advances in MRA encompass time-resolution which allows for dynamic acquisition and with adding physiology to morphology. One of those techniques is "TWIST" (Siemens). Purpose of the present study was to evaluate time-resolved contrast-enhanced 4D MR angiography (TWIST) compared to 3D MRA (FLASH) regarding image quality and added diagnostic value in patients with CHD. Methods and Materials Principles of TWIST-MRA (Time-resolved Angiography WIth Stochastic Trajectories): Fast image acquisition in TWIST is done by undersampling the k-space. The dynamic information is based on echo-sharing making it a 4D technique (3D + time): The center of k-space as responsible for image contrast is frequently sampled leading to a sequence of different contrasts depending on the bolus passage. On the other hand, the sharpnessencoding periphery of k-space is undersampled leading to short acquisition times. Each image is composed by one central k-space information ("A") with two or more periphery parts ("B") (Fig. 1). The temporal resolution of TWIST depends on the ratio of A to B (Fig. 2). Twenty-six pts (age, 26±16 yrs) with suspected or known CHD were included in the study. Indication was clinically driven in all cases. Patients underwent a comprehensive MRI protocol including cardiac cine MRI in long and short axes and contrast-enhanced MR angiography at 1.5T (Magnetom Avanto, Siemens). In all pts, 3D FLASH and 4D TWIST MRA were applied for intraindividual comparison. Figure 3 gives the scan parameters of the two sequences. For both MRA sequences, gadobutrol (Gadovist, Bayer) was used as Gd-based contrast material: single-dose (0.1 mmol/kg) in 3D FLASH, 5 cc in 4D TWIST. Quantitative comparison of the MRA images included SNR, CNR, and vessel wall delineation. Images were subjectively evaluated regarding image quality, artefacts, diagnostic value, added diagnostic value of 4D dynamic, additional information through 4D dynamic, and added level-of-confidence through 4D (Fig. 4). Page 2 of 11

3 Images for this section: Fig. 1: Schematic of TWIST sequence. "A" represents the center of k-space, whereas "B" represents the periphery of k-space. B is undersampled and, therefore, requires combination with one or more other B acquisitions. Each final image is composed by one part of A giving the contrast and two or more parts of B. Page 3 of 11

4 Fig. 2: Schematic of TWIST acquisition: Depending on how large A and B are chosen, different temporal resolutions of the sequence occur. Page 4 of 11

5 Fig. 3: Scan parameters of 3D FLASH and 4D TWIST MR angiography. Notice the difference in acquisition time per 3D data set. Page 5 of 11

6 Fig. 4: List of evaluated parameters for intraindividual comparison of the two sequences. Page 6 of 11

7 Results Concerning contrast-material volume, 3D FLASH required 10.8±5cc of gadobutrol, 4D TWIST was run with 5cc constantly. When evaluating quantitative measures, SNR (Fig. 5) and CNR (Fig. 6) were higher in the pulmonary trunc in 4D TWIST, but slightly higher in systemic arteries and great veins in 3D FLASH. No difference in vessel wall delineation was found between the two different sequences. 3D FLASH was judged slightly better in image quality (4.0±0.5 vs. 3.5±0.5) and artefacts (3.8±0.4 vs. 3.3±0.5) (Fig. 7). No difference in diagnostic value of the MRA in general was found (4.2±0.4 vs. 4.0±0.4). Interstingly, in 20/26 pts, added diagnostic value through the 4D dynamic was found regarding main diagnosis. Level-of.confidence in the diagnosis was higher in TWIST (Fig. 8). Figure 9 shows a list of patients and the added diagnostic yield by having the dynamic information through 4D imaging. Images for this section: Fig. 5: SNR comparison between 3D FLASH (red bars) and 4D TWIST (yellow bars), measured in different vessel regions. Page 7 of 11

8 Fig. 6: CNR comparison between 3D FLASH (red bars) and 4D TWIST (yellow bars), measured in different vessel regions. Fig. 7: Comparison of qualitative parameters in 3D FLASH and 4D TWIST concerning image quality. Page 8 of 11

9 Fig. 8: Added value of the dynamic acquisition: Subjective evaluation. Fig. 9: Added value through dynamic acquisition by 4D TWIST: List of the 20 patients, where higher diagnostic yield by the 4D acquisition was considered. Page 9 of 11

10 Conclusion Contrast-enhanced time-resolved 4D TWIST MRA yields robust images with high SNR and CNR. Compared to conventional 3D FLASH, multiple advantages are obvious: Dynamic information can be obtained - offering more physiological information in a morphologic technique. Less Gd contrast material is needed for adequate image quality. Not focus of this study, but well known is the fact that there are far less difficulties in bolus timing using 4D MRA. In the very special patient collective of CHD, added diagnostic value through the dynamic acquisition was found compared to 3D FLASH MRA. While recent data recommend the use of 4D MRA as a complimentary or specific tool [3,4], our study suggest full capabilities as a stand-alone MRA. So, the combination of the above-mentioned facts makes 4D TWIST MRA capable of serving as a routine tool in CHD. References [1] Ntsinjana HN et al. The Role of Cardiovascular Magnetic Resonance in Pediatric Congenital Heart Disease. J Cardiovasc Magn Res 2011; 13:51. [2] Kilner PJ et al. Recommendations for cardiovascular magnetic resonance in adults with congenital heart disease from the respective working groups of the European Society of Cardiology. Eur Heart J 2010; 31: [3] Mohrs OK et al. Time-Resolved Contrast-Enhanced MR Angiography of the Thorax in Adults with Congenital Heart Disease. Am J Roentgenol 2006; 187: [4] Fenchel M et al. Juvenile and Adult Congenital Heart Disease: Time-resolved 3D Contrast-enhanced MR Angiography. Radiology 2007; 244: Personal Information PD Dr. Peter Hunold University Hospital Schleswig-Holstein, Campus Lübeck Clinic for Radiology and Nuclear Medicine Ratzeburger Allee Lübeck Page 10 of 11

11 Germany Phone: Fax: Page 11 of 11