A total of 1509 patients who had legacy pacemakers or defibrillators underwent 2103 MRIs according to a prespecified safety protocol. No long-term clinically significant adverse events were reported.
Purpose
To improve velocity‐to‐noise ratio (VNR) and dynamic velocity range of 4D flow magnetic resonance imaging (MRI) by using dual‐velocity encoding (dual‐venc) with k‐t generalized ...autocalibrating partially parallel acquisition (GRAPPA) acceleration.
Materials and Methods
A dual‐venc 4D flow MRI sequence with k‐t GRAPPA acceleration was developed using a shared reference scan followed by three‐directional low‐ and high‐venc scans (repetition time / echo time / flip angle = 6.1 msec / 3.4 msec / 15°, temporal/spatial resolution = 43.0 msec/1.2 × 1.2 × 1.2 mm3). The high‐venc data were used to correct for aliasing in the low‐venc data, resulting in a single dataset with the favorable VNR of the low‐venc but without velocity aliasing. The sequence was validated with a 3T MRI scanner in phantom experiments and applied in 16 volunteers to investigate its feasibility for assessing intracranial hemodynamics (net flow and peak velocity) at the major intracranial vessels. In addition, image quality and image noise were assessed in the in vivo acquisitions.
Results
All 4D flow MRI scans were acquired successfully with an acquisition time of 20 ± 4 minutes. The shared reference scan reduced the total acquisition time by 12.5% compared to two separate scans. Phantom experiments showed 51.4% reduced noise for dual‐venc compared to high‐venc and an excellent agreement of velocities (ρ = 0.8, P < 0.001). The volunteer data showed decreased noise in dual‐venc data (54.6% lower) compared to high‐venc, and improved image quality, as graded by two observers: fewer artifacts (P < 0.0001), improved vessel conspicuity (P < 0.0001), and reduced noise (P < 0.0001).
Conclusion
Dual‐venc 4D flow MRI exhibits the superior VNR of the low‐venc acquisition and reliably incorporates low‐ and high‐velocity fields simultaneously. In vitro and in vivo data demonstrate improved flow visualization, image quality, and image noise.
Level of Evidence: 2
Technical Efficacy: Stage 1
J. MAGN. RESON. IMAGING 2017;46:102–114
The purpose of this study was to evaluate the sensitivity of multiparametric cardiac magnetic resonance imaging (CMR) for the detection of acute cardiac allograft rejection (ACAR).
ACAR is currently ...diagnosed by endomyocardial biopsy, but CMR may be a noninvasive alternative because of its capacity for regional myocardial structure and function characterization.
Fifty-eight transplant recipients (mean age 47.0 ± 14.7 years) and 14 control subjects (mean age 47.7 ± 16.7 years) were prospectively recruited from August 2014 to May 2017 and underwent 97 CMR studies (83 transplant recipients, 14 control subjects) for assessment of global left ventricular function and myocardial T2, T1, and extracellular volume fraction (ECV). CMR studies were divided into 4 groups on the basis of biopsy grade: control subjects (n = 14), patients with no ACAR (no history of ACAR; n = 36), patients with past ACAR (history of ACAR; n = 24), and ACAR+ patients (active grade ≥1R ACAR; n = 23).
Myocardial T2 was significantly higher in patients with past ACAR compared with those with no ACAR (51.0 ± 3.8 ms vs. 49.2 ± 4.0 ms; p = 0.02) and in patients with no ACAR compared with control subjects (49.2 ± 4.0 ms vs. 45.2 ± 2.3 ms; p < 0.01). ACAR+ patients demonstrated increased T2 compared with the no ACAR group (52.4 ± 4.7 ms vs. 49.2 ± 4.0 ms, p < 0.01) but not compared with the past ACAR group. In contrast, ECV was significantly elevated in ACAR+ patients compared with transplant recipients without ACAR regardless of history of ACAR (no ACAR: 31.5 ± 3.9% vs. 26.8 ± 3.3% p < 0.01; past ACAR: 31.5 ± 3.9% vs. 26.8 ± 4.0% p < 0.01). Receiver operating characteristic curve analysis revealed that a combined model of age at CMR, global T2, and global ECV was predictive of ACAR (area under the curve = 0.84).
The combination of CMR-derived myocardial T2 and ECV has potential as a noninvasive tissue biomarker for ACAR. Larger studies during acute ACAR are needed for continued development of multiparametric CMR for transplant recipient surveillance.
Display omitted
Patients with bicuspid aortic valve (BAV) show altered hemodynamics in the ascending aorta that can be assessed by 4D flow MRI.
Comprehensive cardiac MRI was applied to test the hypothesis that ...BAV-mediated changes in aortic hemodynamics (wall shear stress WSS and velocity) are associated with parameters of left ventricular (LV) remodeling.
Retrospective data analysis.
Forty-nine BAV patients (mean age = 50.2 ± 13.5, 62% male).
Balanced steady-state free precession (bSSFP)-CINE, pre- and postcontrast T
mapping with modified Look-Locker inversion recovery (MOLLI), time-resolved 3D phase-contrast (PC) MRI with three-directional velocity encoding (4D flow MRI) at 1.5 and 3T.
Quantification of LV volumetric data and myocardial mass, extracellular volume fraction (ECV), aortic valve stenosis (AS), and regurgitation (AR). 3D aortic segmentation, quantification of peak systolic velocities, and 3D WSS in the ascending aorta (AAo), arch, and descending aorta (DAo).
Two-sided nonpaired t-test to compare subgroups. Pearson correlation coefficient for correlations between aortic hemodynamics and LV parameters.
Of the 49 BAV patients, 35 had aortic valve dysfunction (AS n = 7, AR n = 16, both AS and AR n = 12). Mean systolic WSS in the AAo, peak systolic velocities in the AAo and arch, and LV mass were significantly higher (P < 0.001) in the AS/AR group compared to the patients without AS/AR. In the complete group, we observed significant relationships between increased LV mass and elevated peak systolic velocity (r = 0.57, r = 0.58; P < 0.001) and WSS in the AAo and arch, respectively (r = 0.54, r = 0.46; P < 0.001). We detected an association between ECV and WSS in the AAo (r = 0.38, P = 0.02). These relations did not hold true for patients without AV dysfunction.
AS and AR in BAV patients have a major impact on elevated aortic peak velocities and WSS that were associated with parameters of LV remodeling.
3 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2017.
Oxidative stress is thought to play an important role in atherogenesis. The statin group of cholesterol-lowering drugs have been shown to reduce cardiovascular events and possess antioxidant ...properties. We aimed to assess the effects of simvastatin on a novel measure of prooxidant–antioxidant balance (PAB) in dyslipidemic patients. The PAB assay can measure the prooxidant burden and the antioxidant capacity simultaneously in one assay, thereby giving a redox index. We treated 102 dyslipidemic individuals with simvastatin, or a placebo in a double-blind, cross-over, placebo-controlled trial. PAB values were measured before and after each treatment period. Seventy-seven subjects completed the study. We found that statin therapy was associated with a significant reduction in PAB values (
P
< 0.001). This effect appeared to be independent of the cholesterol-lowering effects of statins. We conclude that serum PAB values are decreased by simvastatin therapy. Regarding previous reports on the elevation of PAB in conditions associated with oxidative stress, the PAB assay, along with other markers of oxidative stress, may be applied to estimate the extent of oxidative stress in patients, assessment of the antioxidative efficacy of medication such as statins and perhaps also for the identification of those individuals who need antioxidant therapy.
Studies reporting the safety of magnetic resonance imaging (MRI) in patients with a cardiac implantable electronic device (CIED) have mostly excluded examinations with the device in the magnet ...isocenter. The purpose of this study was to describe the safety of cardiac and thoracic spine MRI in patients with a CIED.
The medical records of patients with a CIED who underwent a cardiac or thoracic spine MRI between January 2011 and December 2014 were reviewed. Devices were interrogated before and after imaging with reprogramming to asynchronous pacing in pacemaker-dependent patients. The clinical interpretability of the MRI and peak and average specific absorption rates (SARs, W/kg) achieved were determined.
Fifty-eight patients underwent 51 cardiac and 11 thoracic spine MRI exams. Twenty-nine patients had a pacemaker and 29 had an implantable cardioverter defibrillator. Seventeen percent (n = 10) were pacemaker dependent. Fifty-one patients (89%) had non-MRI-conditional devices. There were no clinically significant changes in atrial and ventricular sensing, impedance, and threshold measurements. There were no episodes of device mode changes, arrhythmias, therapies delivered, electrical reset, or battery depletion. One study was prematurely discontinued due to a patient complaint of chest pain of which the etiology was not determined. Across all examinations, the average peak SAR was 2.0 ± 0.85 W/kg with an average SAR of 0.35 ± 0.37 W/kg. Artifact significantly limiting the clinical interpretation of the study was present in 33% of cardiac MRI studies.
When a comprehensive CIED magnetic resonance safety protocol is followed, the risk of performing 1.5-T magnetic resonance studies with the device in the magnet isocenter, including in patients who are pacemaker dependent, is low.
Background
Following heart transplantation (Tx), recipients are closely monitored using endomyocardial biopsy, which is limited by cost and invasiveness, and echocardiography, which is limited ...regarding detailed structural and functional evaluation.
Purpose
To test the feasibility of comprehensive structure–function cardiac MRI as a noninvasive modality to assess changes in myocardial structure and function.
Study Type
Prospective.
Subjects
MR was performed in 61 heart transplant recipients (age 47.9 ± 16.3 years, 39% female) and 14 age‐matched healthy controls (age 47.7 ± 16.7 years, 36% female).
Field Strength/Sequence
1.5T; 2D CINE steady state free precession (SSF)P imaging, T2‐mapping, pre‐ and postgadolinium contrast T1‐mapping, and tissue‐phase mapping (TPM).
Assessment
Quantification of myocardial T2 (as a measure of edema), pre‐ and post‐Gd T1 (allowing calculation of extracellular volume (ECV) to estimate interstitial expansion), and TPM‐based assessment of peak regional left ventricular (LV) velocities, dyssynchrony, and twist.
Statistical Tests
Comparisons between transplant recipients and controls were performed using independent samples t‐tests. Relationships between structural (T2, T1, ECV) and functional measures (myocardial velocities, dyssynchrony, twist) were assessed using Pearson correlation analysis.
Results
T2 and T1 were significantly elevated in transplant recipients compared to controls (global T2: 50.5 ± 3.4 msec vs. 45.2 ± 2.3 msec, P < 0.01; global T1: 1037.8 ± 48.0 msec vs. 993.8 ± 34.1 msec, P < 0.01). Systolic longitudinal function was impaired in transplant recipients compared to controls (reduced peak systolic longitudinal velocities, 2.9 ± 1.1 cm/s vs. 5.1 ± 1.2 cm/s, P < 0.01; elevated systolic longitudinal dyssynchrony, 60.2 ± 30.2 msec vs. 32.1 ± 25.1 msec, P < 0.01). Correlation analysis revealed a significant positive relationship between T2 and ECV (r = 0.45,P < 0.01). In addition, peak systolic longitudinal velocities demonstrated a significant inverse relationship with T2 (global r = –0.29, P = 0.02), and systolic radial dyssynchrony was positively associated with peak T2 and peak T1 (r = 0.26,P = 0.04; r = 0.27,P = 0.03).
Data Conclusion
MR techniques are sensitive to structural and functional differences in transplant recipients compared to controls. Structural (T2, T1) and functional (peak myocardial velocities, dyssynchrony) measures were significantly associated, suggesting a structure–function relationship of cardiac abnormalities following heart transplant.
Level of Evidence: 2
Technical Efficacy Stage: 2
J. Magn. Reson. Imaging 2019;49:678–687.
Background
Patients with bicuspid aortic valve (BAV) show altered hemodynamics in the ascending aorta that can be assessed by 4D flow MRI.
Purpose
Comprehensive cardiac MRI was applied to test the ...hypothesis that BAV‐mediated changes in aortic hemodynamics (wall shear stress WSS and velocity) are associated with parameters of left ventricular (LV) remodeling.
Study Type
Retrospective data analysis.
Population
Forty‐nine BAV patients (mean age = 50.2 ± 13.5, 62% male).
Field Strength/Sequence
Balanced steady‐state free precession (bSSFP)‐CINE, pre‐ and postcontrast T1 mapping with modified Look–Locker inversion recovery (MOLLI), time‐resolved 3D phase‐contrast (PC) MRI with three‐directional velocity encoding (4D flow MRI) at 1.5 and 3T.
Assessment
Quantification of LV volumetric data and myocardial mass, extracellular volume fraction (ECV), aortic valve stenosis (AS), and regurgitation (AR). 3D aortic segmentation, quantification of peak systolic velocities, and 3D WSS in the ascending aorta (AAo), arch, and descending aorta (DAo).
Statistical Tests
Two‐sided nonpaired t‐test to compare subgroups. Pearson correlation coefficient for correlations between aortic hemodynamics and LV parameters.
Results
Of the 49 BAV patients, 35 had aortic valve dysfunction (AS n = 7, AR n = 16, both AS and AR n = 12). Mean systolic WSS in the AAo, peak systolic velocities in the AAo and arch, and LV mass were significantly higher (P < 0.001) in the AS/AR group compared to the patients without AS/AR. In the complete group, we observed significant relationships between increased LV mass and elevated peak systolic velocity (r = 0.57, r = 0.58; P < 0.001) and WSS in the AAo and arch, respectively (r = 0.54, r = 0.46; P < 0.001). We detected an association between ECV and WSS in the AAo (r = 0.38, P = 0.02). These relations did not hold true for patients without AV dysfunction.
Data Conclusion
AS and AR in BAV patients have a major impact on elevated aortic peak velocities and WSS that were associated with parameters of LV remodeling.
Level of Evidence: 3
Technical Efficacy: Stage 3
J. Magn. Reson. Imaging 2017.
PDF
