Christine Mancini

T2-prepared SSFP improves diagnostic confidence in edema imaging in acute myocardial infarction compared to turbo spin echo.

T2‐weighted MRI of edema in acute myocardial infarction (MI) provides a means of differentiating acute and chronic MI, and assessing the area at risk of infarction. Conventional T2‐weighted imaging of edema uses a turbo spin‐echo (TSE) readout with dark‐blood preparation. Clinical applications of dark‐blood TSE methods can be limited by artifacts such as posterior wall signal loss due to through‐plane motion, and bright subendocardial artifacts due to stagnant blood. Single‐shot imaging with a T2‐prepared SSFP readout provides an alternative to dark‐blood TSE and may be conducted during free breathing. We hypothesized that T2‐prepared SSFP would be a more reliable method than dark‐blood TSE for imaging of edema in patients with MI. In patients with MI (22 acute and nine chronic MI cases), T2‐weighted imaging with both methods was performed prior to contrast administration and delayed‐enhancement imaging. The T2‐weighted images using TSE were nondiagnostic in three of 31 cases, while six additional cases rated as being of diagnostic quality yielded incorrect diagnoses. In all 31 cases the T2‐prepared SSFP images were rated as diagnostic quality, correctly differentiated acute or chronic MI, and correctly determined the coronary territory. Free‐breathing T2‐prepared SSFP provides T2‐weighted images of acute MI with fewer artifacts and better diagnostic accuracy than conventional dark‐blood TSE. Magn Reson Med 57:891–897, 2007. Published 2007 Wiley‐Liss, Inc.

Magnetic resonance imaging delineates the ischemic area at risk and myocardial salvage in patients with acute myocardial infarction.

Background—The area at risk (AAR) is a key determinant of myocardial infarction (MI) size. We investigated whether magnetic resonance imaging (MRI) measurement of AAR would be correlated with an angiographic AAR risk score in patients with acute MI. Methods and Results—Bright-blood, T2-prepared, steady-state, free-precession MRI was used to depict the AAR in 50 consecutive acute MI patients, whereas infarct size was measured on gadolinium late-contrast-enhancement images. AAR was also estimated by the APPROACH and DUKE angiographic jeopardy scores and ST-segment elevation score. Myocardial salvage was calculated as AAR minus infarct size. Results are mean±SD unless specified otherwise. Patients were 61±12 years of age, 76% had an ST-segment elevation MI, and 20% had a prior MI. All underwent MRI 4±2 days after initial presentation. The relation between MRI and the APPROACH angiographic estimates of AAR was similar (overall size relative to left ventricular mass was 32±12% vs 30±12%, respectively, P=0.33), correlated well (r=0.78, P<0.0001), and had a 2.5% bias on Bland-Altman analysis. The DUKE jeopardy score underestimated AAR relative to infarct size and was correlated less well with MRI (r=0.39, P=0.0055). ST-segment elevation score underestimated infarct size in 19 subjects (50%) and was not correlated with MRI (r=0.27, P=0.06). Myocardial salvage varied according to Thrombolysis in Myocardial Infarction flow grade at the end of angiography/percutaneous coronary intervention (P=0.04), and Thrombolysis in Myocardial Infarction flow grade was a univariable predictor of myocardial salvage (P=0.011). In multivariable analyses, infarct size was predicted by T2-prepared, steady-state, free-precession MRI (P<0.0001). Conclusions—T2-prepared, steady-state, free-precession MRI delineates the AAR and enables estimation of myocardial salvage when coupled with a measurement of infarct size.

High spatial and temporal resolution cardiac cine MRI from retrospective reconstruction of data acquired in real time using motion correction and resorting.

Cine MRI is used for assessing cardiac function and flow and is typically based on a breath‐held, segmented data acquisition. Breath holding is particularly difficult for patients with congestive heart failure or in pediatric cases. Real‐time imaging may be used without breath holding or ECG triggering. However, despite the use of rapid imaging sequences and accelerated parallel imaging, real‐time imaging typically has compromised spatial and temporal resolution compared with gated, segmented breath‐held studies. A new method is proposed that produces a cardiac cine across the full cycle, with both high spatial and temporal resolution from a retrospective reconstruction of data acquired over multiple heartbeats during free breathing. The proposed method was compared with conventional cine images in 10 subjects. The resultant image quality for the proposed method (4.2 ± 0.4) without breath holding or gating was comparable to the conventional cine (4.4 ± 0.5) on a five‐point scale (P = n.s.). Motion‐corrected averaging of real‐time acquired cardiac images provides a means of attaining high‐quality cine images with many of the benefits of real‐time imaging, such as free‐breathing acquisition and tolerance to arrhythmias. Magn Reson Med, 2009.

Fully Automatic, Retrospective Enhancement of Real- Time Acquired Cardiac Cine MR Images Using Image- Based Navigators and Respiratory Motion-Corrected Averaging

Real‐time imaging may be clinically important in patients with congestive heart failure, arrhythmias, or in pediatric cases. However, real‐time imaging typically has compromised spatial and temporal resolution compared with gated, segmented studies. To combine the best features of both types of imaging, a new method is proposed that uses parallel imaging to improve temporal resolution of real‐time acquired images at the expense of signal‐to‐noise ratio (SNR), but then produces an SNR‐enhanced cine by means of respiratory motion‐corrected averaging of images acquired in real‐time over multiple heartbeats while free‐breathing. The retrospective processing based on image‐based navigators and nonrigid image registration is fully automated. The proposed method was compared with conventional cine images in 21 subjects. The resultant image quality for the proposed method (3.9 ± 0.44) was comparable to the conventional cine (4.2 ± 0.99) on a 5‐point scale (P = not significant [n.s.]). The conventional method exhibited degraded image quality in cases of arrhythmias whereas the proposed method had uniformly good quality. Motion‐corrected averaging of real‐time acquired cardiac images provides a means of attaining high‐quality cine images with many of the benefits of real‐time imaging, such as free‐breathing acquisition and tolerance to arrhythmias. Magn Reson Med, 2007.

MultiContrast Delayed Enhancement (MCODE) improves detection of subendocardial myocardial infarction by late gadolinium enhancement cardiovascular magnetic resonance: a clinical validation study.

BackgroundMyocardial infarction (MI) documented by late gadolinium enhancement (LGE) has clinical and prognostic importance, but its detection is sometimes compromised by poor contrast between blood and MI. MultiContrast Delayed Enhancement (MCODE) is a technique that helps discriminate subendocardial MI from blood pool by simultaneously providing a T2-weighted image with a PSIR (phase sensitive inversion recovery) LGE image. In this clinical validation study, our goal was to prospectively compare standard LGE imaging to MCODE in the detection of MI.MethodsImaging was performed on a 1.5 T scanner on patients referred for CMR including a LGE study. Prospective comparisons between MCODE and standard PSIR LGE imaging were done by targeted, repeat imaging of slice locations. Clinical data were used to determine MI status. Images at each of multiple time points were read on separate days and categorized as to whether or not MI was present and whether an infarction was transmural or subendocardial. The extent of infarction was scored on a sector-by-sector basis.ResultsSeventy-three patients were imaged with the specified protocol. The majority were referred for vasodilator perfusion exams and viability assessment (37 ischemia assessment, 12 acute MI, 10 chronic MI, 12 other diagnoses). Forty-six patients had a final diagnosis of MI (30 subendocardial and 16 transmural). MCODE had similar specificity compared to LGE at all time points but demonstrated better sensitivity compared to LGE performed early and immediately before and after the MCODE (p = 0.008 and 0.02 respectively). Conventional LGE only missed cases of subendocardial MI. Both LGE and MCODE identified all transmural MI. Based on clinical determination of MI, MCODE had three false positive MI’s; LGE had two false positive MI’s including two of the three MCODE false positives. On a per sector basis, MCODE identified more infarcted sectors compared to LGE performed immediately prior to MCODE (p < 0.001).ConclusionWhile both PSIR LGE and MCODE were good in identifying MI, MCODE demonstrated more subendocardial MI’s than LGE and identified a larger number of infarcted sectors. The simultaneous acquisition of T1 and T2-weighted images improved differentiation of blood pool from enhanced subendocardial MI.

Characterization of myocardial T1-mapping bias caused by intramyocardial fat in inversion recovery and saturation recovery techniques

BackgroundQuantitative measurement of T1 in the myocardium may be used to detect both focal and diffuse disease processes such as interstitial fibrosis or edema. A partial volume problem exists when a voxel in the myocardium also contains fat. Partial volume with fat occurs at tissue boundaries or within the myocardium in the case of lipomatous metaplasia of replacement fibrosis, which is commonly seen in chronic myocardial infarction. The presence of fat leads to a bias in T1 measurement. The mechanism for this artifact for widely used T1 mapping protocols using balanced steady state free precession readout and the dependence on off-resonance frequency are described in this paper.MethodsSimulations were performed to illustrate the behavior of mono-exponential fitting to bi-exponential mixtures of myocardium and fat with varying fat fractions. Both inversion recovery and saturation recovery imaging protocols using balanced steady state free precession are considered. In-vivo imaging with T1-mapping, water/fat separated imaging, and late enhancement imaging was performed on subjects with chronic myocardial infarction.ResultsIn n = 17 subjects with chronic myocardial infarction, lipomatous metaplasia is evident in 8 patients (47%). Fat fractions as low as 5% caused approximately 6% T1 elevation for the out-of-phase condition, and approximately 5% reduction of T1 for the in-phase condition. T1 bias in excess of 1000 ms was observed in lipomatous metaplasia with fat fraction of 38% in close agreement with simulation of the specific imaging protocols.ConclusionsMeasurement of the myocardial T1 by widely used balanced steady state free precession mapping methods is subject to bias when there is a mixture of water and fat in the myocardium. Intramyocardial fat is frequently present in myocardial scar tissue due lipomatous metaplasia, a process affecting myocardial infarction and some non-ischemic cardiomyopathies. In cases of lipomatous metaplasia, the T1 biases will be additive or subtractive depending on whether the center frequency corresponds to the myocardium and fat being in-phase or out-of-phase, respectively. It is important to understand this mechanism, which may otherwise lead to erroneous interpretation.

Mechanisms for overestimating acute myocardial infarct size with gadolinium-enhanced cardiovascular magnetic resonance imaging in humans: a quantitative and kinetic study †

Aims It remains controversial whether cardiovascular magnetic resonance imaging with gadolinium only enhances acutely infarcted or also salvaged myocardium. We hypothesized that enhancement of salvaged myocardium may be due to altered extracellular volume (ECV) and contrast kinetics compared with normal and infarcted myocardium. If so, these mechanisms could contribute to overestimation of acute myocardial infarction (AMI) size. Methods and results Imaging was performed at 1.5T ≤ 7 days after AMI with serial T1 mapping and volumetric early (5 min post-contrast) and late (20 min post-contrast) gadolinium enhancement imaging. Infarcts were classified as transmural (>75% transmural extent) or non-transmural. Patients with non-transmural infarctions (n = 15) had shorter duration of symptoms before reperfusion (P = 0.02), lower peak troponin (P = 0.008), and less microvascular obstruction (P < 0.001) than patients with transmural infarcts (n = 22). The size of enhancement at 5 min was greater than at 20 min (18.7 ± 12.7 vs. 12.1 ± 7.0%, P = 0.003) in non-transmural infarctions, but similar in transmural infarctions (23.0 ± 10.0 vs. 21.9 ± 9.9%, P = 0.21). ECV of salvaged myocardium was greater than normal (39.5 ± 5.8 vs. 24.1 ± 3.1%) but less than infarcted myocardium (50.5 ± 6.0%, both P < 0.001). In kinetic studies of non-transmural infarctions, salvaged and infarcted myocardium had similar T1 at 4 min but different T1 at 8–20 min post-contrast. Conclusion The extent of gadolinium enhancement in AMI is modulated by ECV and contrast kinetics. Image acquisition too early after contrast administration resulted in overestimation of infarct size in non-transmural infarctions due to enhancement of salvaged myocardium.

Free-breathing T2* mapping using respiratory motion corrected averaging

BackgroundPixel-wise T2* maps based on breath-held segmented image acquisition are prone to ghost artifacts in instances of poor breath-holding or cardiac arrhythmia. Single shot imaging is inherently immune to ghost type artifacts. We propose a free-breathing method based on respiratory motion corrected single shot imaging with averaging to improve the signal to noise ratio.MethodsImages were acquired using a multi-echo gradient recalled echo sequence and T2* maps were calculated at each pixel by exponential fitting. For 40 subjects (2 cohorts), two acquisition protocols were compared: (1) a breath-held, segmented acquisition, and (2) a free-breathing, single-shot multiple repetition respiratory motion corrected average. T2* measurements in the interventricular septum and liver were compared for the 2-methods in all studies with diagnostic image quality.ResultsIn cohort 1 (N = 28) with age 51.4 ± 17.6 (m ± SD) including 1 subject with severe myocardial iron overload, there were 8 non-diagnostic breath-held studies due to poor image quality resulting from ghost artifacts caused by respiratory motion or arrhythmias. In cohort 2 (N = 12) with age 30.9 ± 7.5 (m ± SD), including 7 subjects with severe myocardial iron overload and 4 subjects with mild iron overload, a single subject was unable to breath-hold. Free-breathing motion corrected T2* maps were of diagnostic quality in all 40 subjects. T2* measurements were in excellent agreement (In cohort #1, T2*FB = 0.95 x T2*BH + 0.41, r2 = 0.93, N = 39 measurements, and in cohort #2, T2*FB = 0.98 x T2*BH + 0.05, r2 > 0.99, N = 22 measurements).ConclusionsA free-breathing approach to T2* mapping is demonstrated to produce consistently good quality maps in the presence of respiratory motion and arrhythmias.

Time resolved measure of coronary sinus flow following regadenoson administration

Objective To use velocity encoded phase contrast MRI to determine timing of peak myocardial blood flow to establish when CMR stress perfusion imaging should be performed after injection of regadenoson.

Regadenoson is a better myocardial vasodilator than dipyridamole in normal volunteers, but the data is less compelling in patients

Regadenoson is a selective Adenosine-2A receptor agonist and is used for myocardial perfusion imaging. Dipyridamole causes indirect vasodilation by inhibiting cellular reuptake of adenosine. The purpose of this study was to assess whether regadenoson is a better coronary vasodilator than dipyridamole in normal volunteers and in patients.