Search

Cardiac magnetic resonance imaging (MRI) has been largely dependent on retrospective cine for data acquisition. Real-time imaging, although inferior in image quality to retrospective cine, is more informative about motion dynamics. We herein developed a real-time cardiac MRI approach to temporospatial characterization of left ventricle (LV) and right ventricle (RV) wall motion. This approach provided two temporospatial indices, temporal periodicity and spatial coherence, for quantitative assessment of ventricular function. In a cardiac MRI study, we prospectively investigated temporospatial characterization in reference to standard volumetric measurements with retrospective cine. The temporospatial indices were found to be effective for evaluating the difference of ventricular performance between the healthy volunteers and the heart failure (HF) patients (LV temporal periodicity 0.24 ± 0.037 vs. 0.14 ± 0.021; RV temporal periodicity 0.18 ± 0.030 vs. 0.10 ± 0.014; LV spatial coherence 0.52 ± 0.039 vs. 0.38 ± 0.040; RV spatial coherence 0.50 ± 0.036 vs. 0.35 ± 0.035; all in arbitrary unit). The HF patients and healthy volunteers were well differentiated in the scatter plots of spatial coherence and temporal periodicity while they were mixed in those of end-systolic volume (ESV) and ejection fraction (EF) from volumetric measurements. This study demonstrated the potential of real-time cardiac MRI for intricate analysis of ventricular function beyond retrospective cine.

Background Cardiovascular magnetic resonance (CMR) has been largely dependent on retrospective cine for image acquisition. Real-time imaging, although inferior in image quality to retrospective cine, is advantageous in examining temporospatial behaviors of cardiac motion over a series of sequential cardiac cycles. The presented work is a proof-of-concept of assessing cardiac function quantitatively with novel temporospatial indices in real-time CMR. Methods Fourier analysis was introduced for temporospatial characterization of real-time CMR signals arising from ventricular wall motion. Two quantitative indices, temporal periodicity and spatial coherence, were provided for function assessment in the left ventricle (LV) and right ventricle (RV). We prospectively investigated these temporospatial indices in a CMR study with healthy volunteers and heart failure (HF) patients. Results Real-time images were collected and analyzed in 12 healthy volunteers during exercise and at rest, and also in 12 HF patients at rest. The statistics indicated that the healthy volunteers presented an increase of temporal periodicity due to ventricular response to exercise (resting-state 0.24 ± 0.037 vs. exercising-state 0.31 ± 0.040 in LV; resting-state 0.18 ± 0.030 vs. exercising-state 0.25 ± 0.038 in RV; P 0.6, P

Magnetic resonance imaging (MRI) can measure cardiac response to exercise stress for evaluating and managing heart patients in the practice of clinical cardiology. However, exercise stress cardiac MRI have been clinically limited by the ability of available MRI techniques to quantitatively measure fast and unstable cardiac dynamics during exercise. The presented work is to develop a new real-time MRI technique for improved quantitative performance of exercise stress cardiac MRI. This technique seeks to represent real-time cardiac images as a sparse Fourier-series along the time. With golden-angle radial acquisition, parallel imaging and compressed sensing can be integrated into a linear system of equations for resolving Fourier coefficients that are in turn used to generate real-time cardiac images from the Fourier-series representation. Fourier-series reconstruction from golden-angle radial data can effectively address data insufficiency due to MRI speed limitation, providing a real-time approach to exercise stress cardiac MRI. To demonstrate the feasibility, an exercise stress cardiac MRI experiment was run to investigate biventricular response to in-scanner biking exercise in a cohort of sixteen healthy volunteers. It was found that Fourier-series reconstruction from golden-angle radial data effectively detected exercise-induced increase in stroke volume and ejection fraction in a healthy heart. The presented work will improve the applications of exercise stress cardiac MRI in the practice of clinical cardiology.

Purpose To develop and validate a technique for myocardial T1 mapping in patients with implantable cardioverter defibrillators (ICDs). Methods A MOLLI-based pulse sequence, named Wideband-FLASH-MOLLI, was developed by incorporating a fast low angle shot (FLASH) readout and a wideband inversion pulse. The performance of Wideband-FLASH-MOLLI was evaluated using phantom studies and validated in eight healthy volunteers and ten patients with ICDs at 1.5 Tesla. Comparisons were made between Wideband-FLASH-MOLLI, FLASH-MOLLI, and bSSFP-MOLLI sequences. Results In phantom studies, the maximum T1 estimation errors using Wideband-FLASH-MOLLI with and without an ICD were less than 3% for T1 range from 212 to 1673 ms. In all healthy volunteers, there was no significant native myocardial T1 estimation difference using Wideband-FLASH-MOLLI before and after the external attachment of an ICD to the body coil (1178 ± 27 ms versus 1174 ± 33 ms; P = 0.41). Due to the presence of an ICD, the magnitude images acquired using bSSFP-MOLLI and FLASH-MOLLI showed severe artifacts within the myocardium. In contrast, no or negligible device-induced artifacts were noted within the myocardial regions of the healthy volunteers or the patients with ICDs when using Wideband-FLASH-MOLLI. Conclusion This study demonstrates the feasibility of using Wideband-FLASH-MOLLI to mitigate image artifacts and to produce accurate myocardial T1 maps in patients with ICDs. Magn Reson Med 77:1495–1504, 2017. © 2016 International Society for Magnetic Resonance in Medicine

Background While low-field MRI is disadvantaged by a reduced signal-to-noise ratio (SNR) compared to higher fields, it has a number of useful features such as decreased SAR and shorter T1, and has shown promise for diagnostic imaging. This study demonstrates the feasibility of cardiac balanced steady-state free precession (bSSFP) MRI at 0.35 T and compares cardiac bSSFP MRI images at 0.35 T with those at 1.5 T. Methods Cardiac images were acquired in 7 healthy volunteers using an ECG-gated bSSFP cine sequence on a 0.35 T superconducting MR system as well as a clinical 1.5 T system. Blood and myocardium SNR and contrast-to-noise ratio (CNR) were computed. Subjective image scoring was used to compare the image quality between 0.35 and 1.5 T. Results Cardiac images at 0.35 T were successfully acquired in all volunteers. While the 0.35 T images were noisier than those at 1.5 T, blood, myocardium and papillary muscles could be clearly delineated. At 0.35 T, bSSFP images were acquired at flip angles as high as 150°. Maximum CNR was achieved at 130°. Image quality scoring showed that while at lower flip angles, the 0.35 T images had poorer quality than the 1.5 T, but with flip angles of 110 and 130, the image quality at 0.35 T had scores similar to those at 1.5 T. Conclusions This study demonstrates that cardiac bSSFP imaging is highly feasible at 0.35 T.

This work aims to demonstrate that radial acquisition with k-space variant reduced-FOV reconstruction can enable real-time cardiac MRI with an affordable computation cost. Due to non-uniform sampling, radial imaging requires k-space variant reconstruction for optimal performance. By converting radial parallel imaging reconstruction into the estimation of correlation functions with a previously-developed correlation imaging framework, Cartesian k-space may be reconstructed point-wisely based on parallel imaging relationship between every Cartesian datum and its neighboring radial samples. Furthermore, reduced-FOV correlation functions may be used to calculate a subset of Cartesian k-space data for image reconstruction within a small region of interest, making it possible to run real-time cardiac MRI with an affordable computation cost. In a stress cardiac test where the subject is imaged during biking with a heart rate of >100 bpm, this k-space variant reduced-FOV reconstruction is demonstrated in reference to several radial imaging techniques including gridding, GROG and SPIRiT. It is found that the k-space variant reconstruction outperforms gridding, GROG and SPIRiT in real-time imaging. The computation cost of reduced-FOV reconstruction is ~2 times higher than that of GROG. The presented work provides a practical solution to real-time cardiac MRI with radial acquisition and k-space variant reduced-FOV reconstruction in clinical settings.

Purpose To study the effects of cardiac devices on three-dimensional (3D) late gadolinium enhancement (LGE) MRI and to develop a 3D LGE protocol for implantable cardioverter defibrillator (ICD) patients with reduced image artifacts. Theory and Methods The 3D LGE sequence was modified by implementing a wideband inversion pulse, which reduces hyperintensity artifacts, and by increasing bandwidth of the excitation pulse. The modified wideband 3D LGE sequence was tested in phantoms and evaluated in six volunteers and five patients with ICDs. Results Phantom and in vivo studies results demonstrated extended signal void and ripple artifacts in 3D LGE that were associated with ICDs. The reason for these artifacts was slab profile distortion and the subsequent aliasing in the slice-encoding direction. The modified wideband 3D LGE provided significantly reduced ripple artifacts than 3D LGE with wideband inversion only. Comparison of 3D and 2D LGE images demonstrated improved spatial resolution of the heart using 3D LGE. Conclusion Increased bandwidth of the inversion and excitation pulses can significantly reduce image artifacts associated with ICDs. Our modified wideband 3D LGE protocol can be readily used for imaging patients with ICDs given appropriate safety guidelines are followed. Magn Reson Med, 2015. © 2015 Wiley Periodicals, Inc.

Author(s): Martin, Thomas; Wang, Yi; Rashid, Shams; Shao, Xingfeng; Moeller, Steen; Hu, Peng; Sung, Kyunghyun; Wang, Danny Jj | Abstract: Purpose:To develop a novel combination of controlled aliasing in parallel imaging results in higher acceleration (CAIPIRINHA) with integrated SSFP (CAIPI-iSSFP) for accelerated SSFP imaging without banding artifacts at 3T. Materials and Methods:CAIPI-iSSFP was developed by adding a dephasing gradient to the balanced SSFP (bSSFP) pulse sequence with a gradient area that results in 2π dephasing across a single pixel. Extended phase graph (EPG) simulations were performed to show the signal behaviors of iSSFP, bSSFP, and RF-spoiled gradient echo (SPGR) sequences. In vivo experiments were performed for brain and abdominal imaging at 3T with simultaneous multi-slice (SMS) acceleration factors of 2, 3 and 4 with CAIPI-iSSFP and CAIPI-bSSFP. The image quality was evaluated by measuring the relative contrast-to-noise ratio (CNR) and by qualitatively assessing banding artifact removal in the brain. Results:Banding artifacts were removed using CAIPI-iSSFP compared to CAIPI-bSSFP up to an SMS factor of 4 and 3 on brain and liver imaging, respectively. The relative CNRs between gray and white matter were on average 18% lower in CAIPI-iSSFP compared to that of CAIPI-bSSFP. Conclusion:This study demonstrated that CAIPI-iSSFP provides up to a factor of four acceleration, while minimizing the banding artifacts with up to a 20% decrease in the relative CNR.

Purpose To optimize and evaluate the respiratory motion-resolved, self-gated 4D-MRI using Rotating Cartesian K-space (ROCK-4D-MRI) method in a 0.35 T MRI-guided radiotherapy (MRgRT) system. Methods and materials The study included seven patients with abdominal tumors treated on the MRgRT system. ROCK-4D-MRI and 2D-CINE, was performed immediately after one of the treatment fractions. Motion quantification based on 4D-MRI was compared with those based on 2D-CINE. The image quality of 4D-MRI was evaluated against 4D-CT. The gross tumor volumes (GTV) were defined based on individual respiratory phases of both 4D-MRI and 4D-CT and compared for their variability over the respiratory cycle. Result The motion measurements based on 4D-MRI matched well with 2D-CINE, with differences of 1.04 ± 0.52 mm in the superior–inferior and 0.54 ± 0.21 mm in the anterior–posterior directions. The image quality scores of 4D-MRI were significantly higher than 4D-CT, with better tumor contrast (3.29 ± 0.76 vs. 1.86 ± 0.90) and less motion artifacts (3.57 ± 0.53 vs. 2.29 ± 0.95). The GTVs were more consistent in 4D-MRI than in 4D-CT, with significantly smaller GTV variability (9.31 ± 4.58% vs. 34.27 ± 23.33%). Conclusion Our study demonstrated the clinical feasibility of using the ROCK-4D-MRI to acquire high quality, respiratory motion-resolved 4D-MRI in a low-field MRgRT system. The 4D-MRI image could provide accurate dynamic information for radiotherapy treatment planning.

While communicating hydrocephalus (CH) is often characterized by increased pulsatile flow of cerebrospinal fluid (CSF) in the cerebral aqueduct, a clear-cut explanation for this phenomenon is lacking. Increased pulsatility of the entire cerebral vasculature including the cortical capillaries has been suggested as a causative mechanism. To test this theory, we used two-photon microscopy to measure flow pulsatility in neocortical capillaries 40 to 500 μm below the pial surface in adult rats with CH at 5 to 7 days (acute, n=8) and 3 to 5 weeks (chronic, n=5) after induction compared with intact controls ( n=9). Averaging over all cortical depths, no increase in capillary pulsatility occurred in acute (pulsatility index (PI): 0.15±0.06) or chronic (0.14±0.05) CH animals compared with controls (0.18±0.07; P=0.07). More specifically, PI increased significantly with cortical depth in controls ( r=0.35, P

Background Myocardial T1 mapping holds promise for non-invasive evaluation of diffuse fibrosis. Nevertheless, the widely used cardiac T1 mapping techniques, including MOLLI and SASHA, are generally not applicable to patients with implanted cardiac devices, such as implantable cardioverter defibrillators (ICDs) and pacemakers, due to large off-resonance induced by the device and the associated banding artifacts when using bSSFP readouts. We sought to develop and validate an improved technique for accurate myocardial T1 mapping in patients with implanted cardiac devices.

To develop and validate a technique for myocardial T1 mapping in patients with implantable cardioverter defibrillators (ICDs).A MOLLI-based pulse sequence, named Wideband-FLASH-MOLLI, was developed by incorporating a fast low angle shot (FLASH) readout and a wideband inversion pulse. The performance of Wideband-FLASH-MOLLI was evaluated using phantom studies and validated in eight healthy volunteers and ten patients with ICDs at 1.5 Tesla. Comparisons were made between Wideband-FLASH-MOLLI, FLASH-MOLLI, and bSSFP-MOLLI sequences.In phantom studies, the maximum T1 estimation errors using Wideband-FLASH-MOLLI with and without an ICD were less than 3% for T1 range from 212 to 1673 ms. In all healthy volunteers, there was no significant native myocardial T1 estimation difference using Wideband-FLASH-MOLLI before and after the external attachment of an ICD to the body coil (1178 ± 27 ms versus 1174 ± 33 ms; P = 0.41). Due to the presence of an ICD, the magnitude images acquired using bSSFP-MOLLI and FLASH-MOLLI showed severe artifacts within the myocardium. In contrast, no or negligible device-induced artifacts were noted within the myocardial regions of the healthy volunteers or the patients with ICDs when using Wideband-FLASH-MOLLI.This study demonstrates the feasibility of using Wideband-FLASH-MOLLI to mitigate image artifacts and to produce accurate myocardial T1 maps in patients with ICDs. Magn Reson Med 77:1495-1504, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

© 2015 IEEE. Cardiac electroanatomical mapping (EAM) to locate myocardial scar substrate during ventricular tachycardia (VT) ablation therapy is currently faced with a major limitation. The presence of epicardial fat leads to false-positive low-voltage maps that may interpreted as myocardial scar. Pre-procedural cardiac magnetic resonance (CMR) imaging can produce images of the heart in which both cardiac geometry and epicardial fat are particularly conspicuous. The goal of the present work is to build CMR based geometric models composed of a shell of the cardiac anatomy and epicardial fat. Herein, we first defined a black-blood imaging protocol that is feasible in patients with implanted devices. Then a semi-automated image segmentation method was developed and applied to extract ventricular surface anatomy and epicardial fat maps from which three-dimensional surfaces were built. The results suggest that deriving maps of epicardial fat from MRI data is feasible, accurate when compared to expert observers, and suitable for integration in a clinical catheter-based ablation procedure.

Background Late gadolinium enhancement (LGE) magnetic resonance imaging (MRI) of ventricular scar has been shown to be accurate for detection and characterization of arrhythmia substrates. However, the majority of patients referred for ventricular tachycardia (VT) ablation have an implantable cardioverter-defibrillator (ICD), which obscures image integrity and the clinical utility of MRI. Objective The purpose of this study was to develop and validate a wideband LGE MRI technique for device artifact removal. Methods A novel wideband LGE MRI technique was developed to allow for improved scar evaluation on patients with ICDs. The wideband technique and the standard LGE MRI were tested on 18 patients with ICDs. VT ablation was performed in 13 of 18 patients with either endocardial and/or epicardial approach and the correlation between the scar identified on MRI and electroanatomic mapping (EAM) was analyzed. Results Hyperintensity artifact was present in 16 of 18 of patients using standard MRI, which was eliminated using the wideband LGE and allowed for MRI interpretation in 15 of 16 patients. All patients had ICD lead characteristics confirmed as unchanged post-MRI and had no adverse events. LGE scar was seen in 11 of 18 patients. Among the 15 patients in whom wideband LGE allowed visualization of myocardium, 10 had LGE scar and 5 had normal myocardium in the regions with image artifacts when using the standard LGE. The left ventricular scar size measurements using wideband MRI and EAM were correlated with R2= 0.83 and P =.00003. Conclusion Wideband LGE MRI improves the ability to visualize myocardium for clinical interpretation, which correlated well with EAM findings during VT ablation. © 2014 Heart Rhythm Society.

Background Late gadolinium enhancement (LGE) cardiac MRI is the clinical gold standard for non-invasive characterization of myocardial scar [1]. However, up to 75% of patients who may benefit from LGE MRI have preexisting implanted cardiac devices such as implantable cardioverter defibrillators (ICD) and pacemakers (PM) [2]. The presence of an ICD produces hyper-intensity (HI) image artifacts in LGE (Figure 1) and can prevent assessment of myocardial scar. We recently proposed a wideband LGE MRI technique that removes these artifacts in ICD patients [3,4]. In this abstract, we present our two-center experience of using this wideband LGE sequence on a cohort of patients with ICDs who were referred to cardiac MRI.

Purpose: To propose and test a modified wideband late gadolinium enhancement (LGE) magnetic resonance (MR) imaging technique to overcome hyperintensity image artifacts caused by implanted cardiac devices. Materials and Methods: Written informed consent was obtained from all participants, and the HIPAA-compliant study protocol was approved by the institutional review board. Studies in phantoms and in a healthy volunteer were performed to test the hypothesis that the hyperintensity artifacts that are typically observed on LGE images in patients with implanted cardiac devices are caused by insufficient inversion of the affected myocardial signal. The conventional LGE MR imaging pulse sequence was modified by replacing the nonselective inversion pulse with a wideband inversion pulse. The modified LGE sequence, along with the conventional LGE sequence, was evaluated in 12 patients with implantable cardioverter defibrillators (ICDs) who were referred for cardiac MR imaging. Results: The ICD causes 2-6 kHz in frequency shift at locations 5-10 cm away from the device. This off-resonance falls outside the typical spectral bandwidth of the nonselective inversion pulse used in conventional LGE, which results in the hyperintensity artifact. In 10 of the 12 patients, the conventional LGE technique produced severe, uninterpretable hyperintensity artifacts in the anterior and lateral portions of the left ventricular wall. These artifacts were eliminated with use of the wideband LGE sequence, thereby enabling confident evaluation of myocardial viability. Conclusion: The modified wideband LGE MR imaging technique eliminates the hyperintensity artifacts seen in patients with cardiac devices. The technique may enable LGE MR imaging in patients with cardiac devices, in whom LGE MR imaging otherwise could not be used for diagnosis. © RSNA, 2013.

Background It has been well established that intracranial pulsatility, whether measured as parenchymal/intraventricular pressure or as cerebrospinal fluid (CSF) flow in the cerebral aqueduct, is often markedly elevated in patients with hydrocephalus. Attempts have been made to use this measure to predict outcome from shunt surgery, but its specificity is still questionable. The question of whether or not intracranial pulsatility plays a causative role in hydrocephalus or is merely an epiphenomenon related to intracranial compliance is similarly an unanswered question. As a first step toward answering this question, we hypothesized that aqueductal pulsatility would be reduced after increasing compliance following decompressive craniectomy. Materials and methods Communicating hydrocephalus was induced by injection of kaolin into the basal cisterns in five (n = 5) adult Sprague-Dawley rats; controls received similar saline injections. Flow pulsatility was studied at two weeks post-injection by cine phase contrast MRI prior to and immediately following bilateral craniectomy. Aqueductal stroke volume before and after craniectomy were compared. To minimize effects of extended anesthesia, the craniectomy was started prior to the first imaging scan without breaking through the bone completely. Animals were then moved to the scanner, imaged for the precraniectomy pulsatility measurements, and returned to the bench to complete the craniectomy. A bone flap (4 x 10 mm) was taken from each side over the parietal lobe. The dura mater was left intact, although small tears in the dura were noticed in some cases. A second scan was then obtained to measure post-craniectomy pulsatility. To ensure similar physiological state for the two scans, animals were intubated throughout and ventilated on O2/isoflurane. Following the second scan, the animals were euthanized.

Background We recently reported a lymphatic cerebrospinal fluid (CSF) absorption deficit in a kaolin model of communicating hydrocephalus in rats with ventricular expansion correlating negatively with the magnitude of the impediment to lymphatic function. However, it is possible that CSF drainage was not significantly altered if absorption at other sites compensated for the lymphatic defect. The purpose of this study was to investigate the impact of the lymphatic absorption deficit on global CSF absorption (CSF outflow resistance). Methods Kaolin was injected into the basal cisterns of Sprague Dawley rats. The development of hydrocephalus was assessed using magnetic resonance imaging (MRI). In one group of animals at about 3 weeks after injection, the movement of intraventricularly injected iodinated human serum albumin (125I-HSA) into the olfactory turbinates provided an estimate of CSF transport through the cribriform plate into nasal lymphatics (n = 18). Control animals received saline in place of kaolin (n = 10). In a second group at about 3.5 weeks after kaolin injection, intraventricular pressure was measured continuously during infusion of saline into the spinal subarachnoid space at various flow rates (n = 9). CSF outflow resistance was calculated as the slope of the steady-state pressure versus flow rate. Control animals for this group either received no injections (intact: n = 11) or received saline in place of kaolin (n = 8). Results Compared to saline injected controls, lateral ventricular volume in the kaolin group was significantly greater (0.087 ± 0.013 ml, n = 27 versus 0.015 ± 0.001 ml, n = 17) and lymphatic function was significantly less (2.14 ± 0.72% injected/g, n = 18 versus 6.38 ± 0.60% injected/g, n = 10). Additionally, the CSF outflow resistance was significantly greater in the kaolin group (0.46 ± 0.04 cm H2O.μL-1.min, n = 9) than in saline injected (0.28 ± 0.03 cm H2O.μL-1.min, n = 8) or intact animals (0.18 ± 0.03 cm H2O.μL-1.min, n = 11). There was a significant positive correlation between CSF outflow resistance and ventricular volume. Conclusions The data suggest that the impediment to lymphatic CSF absorption in a kaolin-induced model of communicating hydrocephalus has a significant impact on global CSF absorption. A lymphatic CSF absorption deficit would appear to play some role (either direct or indirect) in the pathogenesis of ventriculomegaly.

Background In communicating hydrocephalus (CH), where either there is no obvious physical blockage within the subarachnoid space, or the obstruction can be variable in location, explanations for the symptoms and clear-cut effective treatments have been elusive. A few investigators have begun to stress the importance of pulsatile vascular and CSF dynamics. While it is known that pulsatile flow through the cerebral aqueduct is often significantly elevated in hydrocephalus, a clear link between abnormal pulsations and ventriculomegaly has been yet to be established. The purpose of this study was to characterize the temporal changes in intracranial pulsatility in a novel model of CH.

Adult rats were in ected with kaolin in the basal cistern to impede cerebrospinal fluid flow and induce communicating hydrocephalus. Development and progress of was monitored using magnetic resonance imaging (MRI) for a period of over days. True FI P images were used to measure volume of the cerebral aqueduct and the lateral, third and fourth ventricles as well as hydrodynamic resistance of the aqueduct. Retrospectively gated phase contrast gradient echo images were used to measure stroke volume of F in the aqueduct, based on ventricular volumes, animals could be divided into groups where groups developed mild and severe hydrocephalus respectively, while roup did not. Ventricular volumes and stroke volumes of group increased over time, as expected, while in roup , ventricular volume increased but stroke volume increased and then decreased, a phenomenon that has not been reported before. Hydrodynamic resistance of aqueductal flow was found to correlate negatively with stroke volume for groups and , although at different levels.

Background Late gadolinium enhancement (LGE) cardiac MRI is the clinical gold standard for non-invasive assessment of myocardial viability and plays an important role in guiding catheter ablation of ventricular tachycardia (VT). The majority of VT patients have implanted cardiac devices such as implantable cardioverter defibrillators (ICDs). The presence of ICDs gives rise to strong off-resonance within the myocardium. This produces hyper-intensity (HI) artifacts in LGE, which can mask scar tissue, compromising the diagnostic value of LGE. Recent studies show that HI artifacts can be eliminated by using a wideband inversion recovery (IR) pulse in the LGE sequence. However, the current wideband LGE is a 2D sequence, which limits spatial resolution, especially slice thickness (8 mm). This is problematic for using LGE to guide catheter ablation of VT. High resolution LGE is feasible using a 3D LGE sequence. However, no prior studies have explored 3D LGE under the influence of strong off-resonance imposed by ICDs.

Background Late gadolinium enhancement (LGE) cardiac MRI is the clinical gold standard for non-invasive characterization of myocardial scar [1]. The LGE technique is a contrast enhanced inversion recovery (IR) FLASH sequence, and requires a priori knowledge of the initial inversion time (TI) to produce optimal contrast between healthy myocardium and scar substrate. The TI is typically assessed using a Look-Locker based TI scout sequence. Recent advances [2,3] have enabled successful application of LGE MRI to patients with cardiac implantable devices at our institution. Presence of cardiac devices, such as implantable cardioverter defibrillators (ICD), gives rise to severe offresonance in the myocardium. This produces banding artifacts in standard TI scout images which cannot be used to estimate the initial TI for LGE imaging. This can result in LGE images with poor contrast and delays in patient scanning. In this abstract, we present a modification to the standard TI scout sequence that prominently reduces artifacts in TI scout images. Methods The TI scout sequence is an inversion prepared cine sequence with TrueFISP readout. Severe off-resonance from an ICD produces severe banding artifacts in TrueFISP images. In addition, in IR sequences, severe off-resonance can prevent inversion of spins in the myocardium, giving rise to hyper-intensity artifacts [2,3]. Recently, we demonstrated that a wideband (3.8 kHz) inversion pulse can overcome this off-resonance effect and invert off-resonant spins sufficiently, thereby eliminating hyper-intensity artifacts [2,3]. We modified the TI scout sequence by replacing the conventional inversion pulse (bandwidth: 1.1 kHz) with a wideband inversion pulse (spectral bandwidth: 3.8 kHz). We also replaced the TrueFISP readout with a FLASH readout. The modified sequence was tested on a group of T1 phantoms and one ICD patient. Results Figure 1 shows phantom images of the modified TI scout sequence. The phantom results show that when a flip angle of 5° is used, the modified TI scout sequence can be used to determine the optimal TI quite accurately. At higher flip angles, larger TIs may be underestimated due to signal burn-off. Figure 2 demonstrates the banding artifacts produced when the standard TI scout sequence is used in an ICD patient. The modified TI scout sequence is able to remove these artifacts completely and allow effective determination of the optimal TI. Conclusions We have modified the TI scout sequence by implementing a wideband inversion pulse and FLASH readout. Phantom results and patient studies demonstrate that the modified sequence has none of the image artifacts that occur with the standard sequence, and produces a reliable estimation of inversion time. We expect that the new TI scout sequence will lead to improved application of LGE MRI in patients with implantable cardiac devices. Funding