Dongyue Si1, Yanfang Wu2, Jie Yin2, Rui Guo3, Jingjing Xiao4, Bowei Liu1, Xue Lin2, Peng Gao2, Deyan Yang2, Quan Fang2, Jianwen Luo1, Daniel A. Herzka5,6, and Haiyan Ding1
1Center for Biomedical Imaging Research (CBIR), Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing, China, 2Department of Cardiology, Peking Union Medical College Hospital, Chinese Academy of Medical Sciences & Peking Union Medical College, Beijing, China, 3Department of Medicine, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, MA, United States, 4Department of Medical Engineering, Xinqiao Hosptial, Army Medical University, Chongqing, China, 5Department of Biomedical Engineering, Johns Hopkins School of Medicine, Baltimore, MD, United States, 6Cardiovascular Interventional Program, National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD, United States
Synopsis
Radiofrequency ablation (RFA) is a first-line
treatment for controlling atrial fibrillation (AF). Visualizing fibrotic tissues as
well as the surrounding anatomical structure could improve the delivery of therapy.
In this work, an independent navigator-gated three-dimensional dark-blood
phase-sensitive inversion recovery sequence was developed for atrial
visualization. Dark-blood was achieved by optimizing inversion recovery and T2-preparation
timing. Preliminary results from in vivo imaging in patients with
AF post RFA demonstrate that the proposed technique can clearly visualize the atrial
wall and scar formation. Both dark blood contrast and high resolution (1.25×1.25×3
mm3) were achieved.
INTRODUCTION
Atrial fibrillation (AF) is the most common
clinically significant cardiac arrhythmia. Isolating the pulmonary veins (PV)
by radiofrequency ablation (RFA) has become a first-line treatment for
controlling AF. Detailed visualization of atrial fibrosis and continuity of
delivered ablation lesions in conjunction with surrounding anatomy could
improve the both preprocedural decision making and post-procedural prognosis. 1-4
Late gadolinium enhancement (LGE) has been
widely used to image myocardial fibrosis. Inversion recovery (IR) or
phase-sensitive inversion recovery (PSIR) 5 are the most widely used
sequences for LGE. However, due to the extremely thin wall,1 imaging
the atrium is still challenging. In recent years, dark-blood PSIR imaging in
two- or three-dimensions (2D or 3D) using either T2-IR or magnetization
transfer-IR preparation have been proposed.6-8 Superior contrast
between myocardium and blood could improve delineation between the atrial wall
and the blood pool, increasing sensitivity to identify fibrosis.
The aim of this study was to develop an
independent navigator-gated9 3D dark-blood phase-sensitive inversion
recovery (DB-PSIR) sequence for atrial imaging. We hypothesize that the
combination of dark-blood contrast and high resolution achievable with 3D
imaging can better visualize atrial tissue in AF patients post RFA.METHODS
Pulse sequence
Figure 1 shows the diagram of the proposed DB-PSIR
sequence. Two ECG-triggered multi-shot 3D volumes are interleaved acquired
using spoiled gradient echo (SPGR) sequence. The first volume is prepared with the
combination of IR and T2-preparation (T2PREP) pre-pulses
to null normal myocardium and blood simultaneously. The durations between IR
and T2PREP (TD1) and between T2PREP and
imaging (IMG) (TD2) are calculated using Bloch equation simulations. The
second volume is the phase refence for PSIR reconstruction (REF)5. Before
data acquisition, fat suppression and an independent respiratory navigator are performed.
Independent navigators for the two volumes separately gate the corresponding
volumes with their own training templates ensuring a motion-compensated
reference volume and high scan efficiency9.
In vivo
experiments
As approved by the local institutional review
board, three AF patients (2 males, 60±1 yrs) were recruited 1-3 mo post RFA. Both independent navigator-gated
3D PSIR9 and the proposed 3D DB-PSIR sequences were acquired in axial
orientation at 3T (Philips Ingenia CX) 10 and 20 mins after contrast (Gd‐DTPA,
Magnevist, 0.2mmol/kg) injection, respectively. Typical imaging parameters were:
FOV 280×280×100 mm3,
TR/TE 5.2/2.6 ms, T2PREP echo time (TE) 30ms, voxel size 1.25×1.25×3 mm3
reconstructed into 0.73×0.73×1.5 mm3, SENSE acceleration factor 1.875,
FA 18° for IMG and 10° for REF,
acceptance window 5 mm. The ECG trigger delay (Ttrigger)
was determined from cine of the atrium. T1
values of the normal myocardium and blood pool were measured by modified
look‐locker inversion recovery (MOLLI) scouts10 and incorporated
into simulations. Corresponding T2 values were obtained from
literature, and set to 50 and 250 ms, for myocardium and blood respectively6.
Regions of interest (ROIs) were manually defined
on scar in atrium, blood and remote ventricular myocardium. Both endo- and
epi-myocardium were carefully avoided. The contrast to noise
ratio (CNR) were measured as the difference between mean signal intensity between
tissues over the standard deviation of background noise. RESULTS
Figure 2 showed the representative images
of 3D PSIR and the proposed DB-PSIR. The thin atrial wall was well delineated
from DB-PSIR images. A thin tissue layer between the atrium and aorta could be
appreciated which was difficult to identify from 3D PSIR (red arrow). The scar
to myocardium CNR in DB-PSIR was lower than that in PSIR (68.81 vs. 123.21),
but the corresponding scar to blood CNR in DB-PSIR was much higher than in PSIR
(67.01 vs. 0.55).
Figure 3 showed the finding of fibrosis tissue
around the left inferior pulmonary vein. Corresponding reformatted images
demonstrate RF ablation lesion. Again, DB-PSIR depicted the RFA lesion with
superior contrast from both atrial wall and blood pool. DISCUSSION
In this study, an independent navigator gated 3D
DB-PSIR sequence was developed and tested in vivo. The preliminary
result is promising by providing the detectable contrast between normal
myocardium and scar tissue on the atrium. The dark blood successfully removes
the contamination from adjacent blood signal. Clear differentiation of thin
atrial wall can be achieved with high spatial resolution. The independent
navigators on the IR-T2PREP prepared volume and reference volume presented both
robust PSIR reconstruction with improved reference motion compensation and time
efficiency. Minor inflow artifacts in the right PV blood pool (yellow arrows
Fig. 2) result from navigator excitation on the
right hemidiaphragm3. These can be addressed by placing the
navigator beam away from the right PV or performing the navigator after
acquisition.CONCLUSION
The proposed independent navigator-gated 3D DB-PSIR
sequence had an improved contrast between atrial myocardium and blood. The atrial
wall could be clearly delineated and scar from RF ablation lesions visualized. Differentiation
of fibrotic tissue from normal myocardium on atrium was feasible in AF patients
post RFA.Acknowledgements
No acknowledgement found.References
- Kolandaivelu A. Role of Cardiac Imaging (CT/MR)
Before and After RF Catheter Ablation in Patients with Atrial Fibrillation. J
Atr Fibrillation. 2012; 20;5(2):523
- Akoum N, WilberD, Hindricks G, Jais P, Cates J,
Marchlinski F, Kholmovski E, Burgon N, Hu N, Mont L, Deneke T, Duytschaever M,
Neumann T, Mansour M, Mahnkopf C, Hutchinson M, Herweg B, Daoud E, Wissner E,
Brachmann J, Marrouche NF. MRI assessment of ablation-induced scarring in
atrial fibrillation: Analysis from the DECAAF study. Journal of Cardiovascular
Electrophysiology, 2015;26(5), 473–480.
- Peters DC, Wylie JV, Hauser TH, Kissinger KV,
Botnar RM, Essebag V, Josephson ME, Manning WJ. Detection of Pulmonary Vein and
Left Atrial Scar after Catheter Ablation with Three-dimensional Navigator gated
Delayed Enhancement MR Imaging: Initial Experience. Radiology, 2007;243(3),
690–695.
- Taclas JE, Nezafat R, Wylie JV, Josephson ME,
Hsing J, Manning WJ, Peters DC. Relationship between intended sites of RF
ablation and post-procedural scar in AF patients, using late gadolinium
enhancement cardiovascular magnetic resonance, Heart Rhythm, 2010 (7), 489-496
- Kellman P, Arai AE, McVeigh ER, Aletras AH.
Phase-sensitive inversion recovery for detecting myocardial infarction using
gadolinium-delayed hyperenhancement. Magn Reson Med. 2002;47(2):372-383
- Kellman P, Xue H, Olivieri LJ, Cross RR, Grant
EK, Fontana M, Ugander M, Moon JC, Hansen MS. Dark blood late enhancement
imaging. J Cardiovasc Magn Reson. 2016;7;18(1):77
- Kim HW, Rehwald WG, Jenista ER, Wendell DC,
Filev P, van Assche L, Jensen CJ, Parker MA, Chen EL, Crowley ALC, Klem I, Judd
RM, Kim RJ. Dark-Blood Delayed Enhancement Cardiac Magnetic Resonance of
Myocardial Infarction. JACC Cardiovasc Imaging. 2018;11(12):1758-1769
- Ginami G, Lòpez K, Mukherjee RK, Neji R, Munoz
C, Roujol S, Mountney P, Razavi R, Botnar RM, Prieto C. Non-contrast enhanced
simultaneous 3D whole-heart bright-blood pulmonary veins visualization and
black-blood quantification of atrial wall thickness. Magn Reson Med.
2019;81(2):1066-1079
- Lee S, Schär M, Zviman M, Sena-Weltin V, Harouni
A, Kozerke S, McVeigh E, Halperin H, Herzka D. Free breathing independent
respiratory navigator-gated imaging: concurrent PSIR and T2-weighted 3D imaging
of the left ventricle. In Proceedings of the 19th Annual Meeting of ISMRM,
Montreal, Canada, 2011. p 19.
- Messroghli DR, Radjenovic A, Kozerke S, Higgins
DM, Sivananthan MU, Ridgway JP. Modified look-locker inversion recovery (MOLLI)
for high-resolution T 1 mapping of the heart. Magn Reson Med. 2004;52:141–146