Motion-corrected free-breathing delayed enhancement imaging of myocardial infarction.

Following administration of Gd-DTPA, infarcted myocardium exhibits delayed enhancement and can be imaged using an inversion-recovery sequence. A conventional segmented acquisition requires a number of breath-holds to image the heart. Single-shot phase-sensitive inversion-recovery (PSIR) true-FISP may be combined with parallel imaging using SENSE to achieve high spatial resolution. SNR may be improved by averaging multiple motion-corrected images acquired during free breathing. PSIR techniques have demonstrated a number of benefits including consistent contrast and appearance over a relatively wide range of inversion recovery times (TI), improved contrast-to-noise ratio, and consistent size of the enhanced region. Comparison between images acquired using segmented breath-held turbo-FLASH and averaged, motion-corrected, free-breathing true-FISP show excellent agreement of measured CNR and infarct size. In this study, motion correction was implemented using image registration postprocessing rather than navigator correction of individual frames. Navigator techniques may be incorporated as well.     

Enhanced viability imaging: improved contrast in myocardial delayed enhancement using dual inversion time subtraction.

In delayed contrast-enhanced MRI for the assessment of myocardial viability, the TI time in a gated inversion-recovery segmented gradient echo sequence is usually selected to null signal from normal myocardium. Although this TI time generates good contrast between the enhancing infarcted tissue and normal myocardium, there is usually less contrast between the infarct and the blood pool. A subtractive technique utilizing two acquisitions at a long and short TI time is proposed to improve the delineation between infarct-blood and infarct-myocardium. The concept was demonstrated in six mongrel dogs with reperfused myocardial infarction. Infarct-normal myocardium contrast (signal difference) using the proposed enhanced viability imaging (ENVI) technique was 142 +/- 50% (P < 0.001) that of standard magnitude inversion recovery (IR), while at the same TI time for the primary image, infarct-blood contrast, was 247 +/- 136% (P < 0.002) that of magnitude IR. Accounting for increased noise due to the subtraction, signal difference-to-noise ratios (SDNR) did not show a significant change for infarct-myocardium but infarct-blood SDNR for ENVI was 174 +/- 105% that of magnitude-IR (P < 0.03). Thus, marked improvement in the delineation of the infarcted zone was noted over a range of TI times.     

Simultaneous myocardial and fat suppression in magnetic resonance myocardial delayed enhancement imaging

PURPOSE: To develop a method for fat suppression in myocardial delayed enhancement (MDE) studies that achieves effective signal intensity reduction in fat but does not perturb myocardial signal suppression. MATERIALS AND METHODS: A new approach to fat suppression that uses a spectrally-selective inversion-recovery (SPEC-IR) tip-up radio frequency (RF) pulse following the conventional nonselective IR RF pulse together with a second SPEC-IR RF pulse is proposed. The tip-up pulse restores the fat longitudinal magnetization after the nonselective IR pulse and allows the fat magnetization to recover more fully toward its equilibrium value, providing for better fat suppression by the second SPEC-IR RF pulse. This new approach was validated in phantom studies and in five patients. RESULTS: Effective fat suppression was achieved using the proposed technique with minimal impact on normal myocardial signal suppression. Mean fat suppression achieved using this approach was 67% +/- 8%, as measured in the chest wall immediately opposite the heart. CONCLUSION: The results indicate this modular-type approach optimizes fat suppression in myocardial delayed enhancement studies but does not perturb the basic IR pulse sequence or change basic acquisition parameters.     

Free-breathing, nongated real-time delayed enhancement MRI of myocardial infarcts: a comparison with conventional delayed enhancement

PURPOSE: To compare a free-breathing, nongated, and black-blood real-time delayed enhancement (RT-DE) sequence to the conventional inversion recovery gradient echo (IR-GRE) sequence for delayed enhancement MRI. MATERIALS AND METHODS: Twenty-three patients with suspected myocardial infarct (MI) were examined using both the IR-GRE and RT-DE imaging sequences. The sensitivity and specificity of RT-DE for detecting MI, using IR-GRE as the gold standard, was determined. The contrast-to-noise ratios (CNR) between the two techniques were also compared. RESULTS: RT-DE had a high sensitivity and specificity (94% and 98%, respectively) for identifying MI. The total acquisition time to image the entire left ventricle was significantly shorter using RT-DE than IR-GRE (5.6+/-0.9 versus 11.5+/-1.9 min). RT-DE had a slightly lower infarct-myocardium CNR but a higher infarct-blood CNR than IR-GRE imaging. Compared with IR-GRE, RT-DE accurately measured total infarct sizes. CONCLUSION: RT-DE can be used for delayed enhancement imaging during free-breathing and without cardiac gating.     

Phase-sensitive inversion recovery for detecting myocardial infarction using gadolinium-delayed hyperenhancement.

After administration of gadolinium, infarcted myocardium exhibits delayed hyperenhancement and can be imaged using an inversion recovery (IR) sequence. The performance of such a method when using magnitude-reconstructed images is highly sensitive to the inversion recovery time (TI) selected. Using phase-sensitive reconstruction, it is possible to use a nominal value of TI, eliminate several breath-holds otherwise needed to find the precise null time for normal myocardium, and achieve a consistent contrast. Phase-sensitive detection is used to remove the background phase while preserving the sign of the desired magnetization during IR. Experimental results are presented which demonstrate the benefits of both phase-sensitive IR image reconstruction and surface coil intensity normalization for detecting myocardial infarction (MI). The phase-sensitive reconstruction method reduces the variation in apparent infarct size that is observed in the magnitude images as TI is changed. Phase-sensitive detection also has the advantage of decreasing the sensitivity to changes in tissue T(1) with increasing delay from contrast agent injection.     

Quantitative assessment of myocardial scar in delayed enhancement magnetic resonance imaging

PURPOSE: To characterize the extent and distribution of left ventricular myocardial scar in delayed enhancement magnetic resonance imaging (MRI). MATERIALS AND METHODS: Delayed enhancement images from 18 patients were categorized into three groups based on myocardial scar appearance: discrete myocardial infarction (N = 10), diffuse fibrosis (N = 4), and circumferential endocardial scarring (N = 4). Images were segmented manually by two observers (twice by one observer) to identify nonviable myocardium. Scar was characterized by the following morphologic parameters: the relative area of nonviable myocardium (Percent Scar); a measure of scar cohesion (Patchiness); and the extent to which scar traversed the ventricle wall (Trans>50). RESULTS: The three scar parameters successfully discriminated between patient groups, although no one parameter was able to differentiate between all groups. The average bias between readers was approximately 3% for each parameter, and the average bias between repeated measurements was 1%. In addition, five patients exhibited regions of nonhyperenhanced nonviable myocardium that were expected to show hyperenhancement based upon their location within the infarct zone and appearance on cine images. CONCLUSION: Quantitative characterization of myocardial scar showed good interobserver and intraobserver agreement. However, the appearance of nonhyperenhanced scar in chronic ischemia is problematic for segmentation of delayed enhancement images.     

Improved delayed enhanced myocardial imaging with T2-Prep inversion recovery magnetization preparation

Purpose

To develop a magnetization preparation method that improves the differentiation of enhancing subendocardial infarction (MI) from ventricular blood for myocardial delayed‐enhancement (DE) magnetic resonance imaging (MRI).

Materials and Methods

T₂Prep‐IR is a magnetization preparation pulse that consists of a T₂ preparation (T₂Prep) followed immediately by a nonselective inversion recovery (IR) pulse. The first imaging excitation is then delayed an inversion time (TI) to allow nulling of normal myocardium in DE study. The amount of T₂ contrast is determined by the effective echo time of the T₂Prep pulse, TE_eff. TE_eff is selected to differentiate MI and blood that share similar T₁ values but have different T₂ values. The T₂Prep‐IR preparation was incorporated into a fast gradient echo sequence to produce an image with both T₁ and T₂ weighting. Simulations predict that this method will generate improved contrast between MI and chamber blood compared to conventional IR methods.

Results

Comparisons between images acquired using conventional IR and T₂Prep‐IR in patients with MI indicate that this new approach significantly improves the blood‐MI contrast (122 ± 32% higher than that of IR with P < 0.05).

Conclusion

Our preliminary patient studies confirm that this preparation is helpful for improved delineation of subendocardial infarction. J. Magn. Reson. Imaging 2008;28:1280–1286. © 2008 Wiley‐Liss, Inc.     

Motion corrected free-breathing delayed-enhancement imaging of myocardial infarction using nonrigid registration

PURPOSE: To develop and test an automatic free-breathing, delayed enhancement imaging method with improved image signal-to-noise ratio (SNR). MATERIALS AND METHODS: The proposed approach uses free-breathing, inversion-recovery single-shot fast imaging with steady precession (FISP) delayed-enhancement with respiratory motion compensation based on nonrigid image registration. Motion-corrected averaging is used to enhance SNR. RESULTS: Fully automatic, nonrigid registration was compared to previously validated rigid body registration that required user interaction. The performance was measured using the variance of edge positions in intensity profiles through the myocardial infarction (MI) enhanced region and through the right ventricular (RV) wall. Measured variation of the MI edge was 1.16 +/- 0.71 mm (N = 6 patients; mean +/- SD) for rigid body and 1.08 +/- 0.76 mm for nonrigid registration (no significant difference). On the other hand, significant improvement (P < 0.005) was found in the measurements at the RV edge where the SD was 2.06 +/- 0.56 mm for rigid body and 0.59 +/- 0.22 mm for nonrigid registration. CONCLUSION: The proposed approach achieves delayed enhancement images with high resolution and SNR without requiring a breathhold. Motion correction of free-breathing delayed-enhancement imaging using nonrigid image registration may be implemented in a fully automatic fashion and performs uniformly well across the full field of view (FOV).     

Fast, three-dimensional free-breathing MR imaging of myocardial infarction: a feasibility study.

Imaging delayed hyperenhancement of myocardial infarction is most commonly performed using an inversion recovery (IR) prepared 2D breathhold segmented k-space gradient echo (FGRE) sequence. Since only one slice is acquired per breathhold in this technique, 12-16 successive breathholds are required for complete anatomical coverage of the heart. This prolongs the overall scan time and may be exhausting for patients. A navigator-echo gated, free-breathing, 3D FGRE sequence is proposed that can be used to acquire a single slab covering the entire heart with high spatial resolution. The use of a new variable sampling in time (VAST) acquisition scheme enables the entire 3D volume to be acquired in 1.5-2 min, minimizing artifacts from bulk motion and diaphragmatic drift and contrast variations due to contrast media washout.     

Prediction of myocardial recovery by dobutamine magnetic resonance imaging and delayed enhancement early after reperfused acute myocardial infarction

The purpose was to study dobutamine magnetic resonance cine imaging (DOB-MRI) and delayed myocardial contrast enhancement (DE) early after reperfused acute myocardial infarction (AMI) for the predicion of segmental myocardial recovery and to find the optimal dose of dobutamine. Fifty patients (56±12 years, 42 males) with reperfused AMI underwent DOB-MRI and DE studies 3.5 (1–19) days after reperfusion. In DOB-MRI systolic wall thickening (SWT) was measured in 18 segments at rest and during dobutamine at 5, 10 and 20 μg*kg⁻¹*min⁻¹. Dysfunctional segments were identified and the extent of DE was measured for each segment. Segmental recovery was examined after 8 (5–15) months. Two hundred-forty-eight segments were dysfunctional with presence of DE in 193. DOB-MRI showed the best prediction of recovery at 10 μg*kg⁻¹*min⁻¹ of dobutamine with sensitivity of 67%, specificity of 63% and accuracy of 66% using a cut-off value for SWT of 2.0 mm. DE revealed a sensitivity of 68%, specificity of 65% and accuracy of 67% using a cut-off value of 46%. Combined analysis of DOB-MRI and DE did not improve diagnostic performance. Early prediction of segmental myocardial recovery after AMI is possible with DOB-MRI and DE. No improvement is achieved by dobutamine >10 μg*kg⁻¹*min⁻¹ or a combination of DOB-MRI and DE.     

Effect of inversion time on delayed-enhancement magnetic resonance imaging with and without phase-sensitive reconstruction

Purpose

To evaluate the consistency and inversion time (TI) independence of phase‐sensitive reconstruction (PSIR) delayed‐enhancement (DE) MRI in a clinical setting.

Materials and Methods

Mid‐ventricular short‐axis DE images were acquired in 25 patients using three TIs: 1) optimized to null viable myocardium, 2) 50 msec less than optimal TI, and 3) 50 msec greater than optimal TI. At each TI, images were acquired with PSIR and without magIR. In each image, percent scar was computed as the ratio of nonviable to total pixels in the left ventricle (LV).

Results

In the magIR images, percent scar was 23% ± 15% (optimal), 11% ± 11% (short), and 22% ± 15% (long). In PSIR images, percent scar was 25% ± 15% (optimal), 22% ± 15% (short), and 22% ± 14% (long). Percent scar was significantly underestimated in magIR images with short TI, but no statistically significant difference in percent scar was observed at the optimal or long TIs.

Conclusion

DE‐MRI is a robust imaging technique for clinical use. PSIR provided consistent image quality independently of TI, at least over the range of TIs evaluated in this study. However, neither image quality nor scar appearance in the PSIR images was significantly different from that in the magIR images when TI was at or above the null point of viable myocardium. J. Magn. Reson. Imaging 2005;21:650–655. © 2005 Wiley‐Liss, Inc.

     

Tissue characterization of myocardial infarction using T1rho: influence of contrast dose and time of imaging after contrast administration

PURPOSE: To determine whether contrast between acutely infarcted and normal myocardia in T1-rho-weighted cine TFE (T1rho-TFE) and delayed-enhancement (DE) images (measured using a metric percent enhancement (PE)) varied with the dose or time of imaging after contrast administration. MATERIALS AND METHODS: Eighteen patients with acute myocardial infarction (AMI) were randomly divided into three groups according to the dose of gadoversetamide (0.1, 0.2, or 0.3 mmol/kg) administered. After contrast administration, T1rho-TFE images were acquired at five and 40 minutes, and DE images were acquired at 10 and 30 minutes. RESULTS: For T1rho-TFE imaging the PE values at 40 minutes were 70+/-14, 98+/-14, and 105+/-41 at 0.1, 0.2, and 0.3 mmol/kg dose levels, which were significantly greater than the corresponding PEs at five minutes after contrast administration (44+/-12, 71+/-14, and 36+/-13). For DE and T1rho-TFE imaging the dose of contrast agent did not significantly affect the PE. However, with DE the PE tended to increase with the dose. At all dose levels, irreversible injury was more conspicuous in T1rho-TFE images acquired at 40 minutes than at five minutes after contrast. CONCLUSION: In T1rho-TFE, acute infarction was more conspicuous in images acquired at a later time point, and the PE did not vary with the contrast dose.     

A fast navigator-gated 3D sequence for delayed enhancement MRI of the myocardium: comparison with breathhold 2D imaging

PURPOSE: To develop a rapid navigator-gated three-dimensional (3DNAV) delayed-enhancement MRI (DE-MRI) sequence for myocardial viability assessment, and to evaluate its performance with breathhold two-dimensional (2DBH) DE-MRI sequence as the reference standard. MATERIALS AND METHODS: 2DBH DE-MRI was initiated 10 minutes after contrast administration and followed by 3DNAV DE-MRI in 23 patients at 1.5 T. Comparison was performed using three qualitative criteria (image quality score, diagnostic outcome, relative diagnostic confidence score) in all patients, and three quantitative criteria (infarct volume, infarct signal-to-noise ratio [SNR(inf)], and infarct-viable myocardium contrast-to-noise ratio [CNR(inf-myo)]) in patients with hyperenhanced myocardium. RESULTS: Compared to 2DBH DE-MRI, 3DNAV DE-MRI provided slightly better image quality, the same final diagnostic outcomes, and better relative diagnostic confidence score with 79% SNR(inf) improvement (P = 0.002) and 90% CNR(inf-myo) improvement (P = 0.004) in 39% less scan time (414 +/- 118 seconds for 2DBH and 251 +/- 93 seconds for 3DNAV). The measured infarct volumes demonstrated excellent correlation (18.9 +/- 19.0 mL for 2DBH DE-MRI vs. 17.6 +/- 19.0 mL for 3DNAV DE-MRI, r(2) = 0.998, P < 0.001, N = 7) and narrow limits of agreement (-1.3 +/- 1.8 mL). CONCLUSION: 3DNAV DE-MRI provides improved image quality and similar infarct detection in less scan time compared to the standard 2DBH DE-MRI.     

Inversion-recovery-prepared SSFP for cardiac-phase-resolved delayed-enhancement MRI.

Delayed-enhancement magnetic resonance imaging (DE-MRI) can be used to visualize myocardial infarction (MI). DE-MRI is conventionally acquired with an inversion-recovery gradient-echo (IR-GRE) pulse sequence that yields a single bright-blood image. IR-GRE imaging requires an accurate estimate of the inversion time (TI) to null the signal from the myocardium, and a separate cine acquisition is required to visualize myocardial wall motion. Simulations were performed to examine the effects of a steady-state free precession (SSFP) readout after an inversion pulse in the setting of DE-MRI. Using these simulations, a segmented IR-SSFP sequence was optimized for infarct visualization. This sequence yields both viability and wall motion images over the cardiac cycle in a single breath-hold. Viability images at multiple effective TIs are produced, providing a range of image contrasts. In a study of 11 patients, IR-SSFP yielded infarct sizes and left ventricular ejection fractions (LVEFs) similar to those obtained by IR-GRE and standard SSFP, respectively. IR-SSFP images yielded improved visualization of the infarct-blood border because of the simultaneous nulling of healthy myocardium and blood. T(1) (*) recovery curves were extracted from IR-SSFP images and showed excellent qualitative agreement with theoretical simulations.     

Percent infarct mapping for delayed contrast enhancement magnetic resonance imaging to quantify myocardial viability by Gd(DTPA)

Purpose

To demonstrate the advantages of signal intensity percent‐infarct‐mapping (SI‐PIM) using the standard delayed enhancement (DE) acquisition in assessing viability following myocardial infarction (MI). SI‐PIM quantifies MI density with a voxel‐by‐voxel resolution in clinically used DE images.

Materials and Methods

In canines (n= 6), 96 hours after reperfused MI and administration of 0.2 mmol/kg Gd(DTPA), ex vivo DE images were acquired and SI‐PIMs calculated. SI‐PIM data were compared with data from DE images analyzed with several thresholding levels using SI_remote+2SD, SI_remote+6SD, SI full width half maximum (SI_FWHM), and with triphenyl‐tetrazolium‐chloride (TTC) staining. SI‐PIM was also compared to R1 percent infarct mapping (R1‐PIM).

Results

Left ventricular infarct volumes (IV) in DE images, IV_SIremote+2SD and IV_SIremote+6SD, overestimated (P < 0.05) TTC by medians of 13.21 mL [10.2; 15.2] and 6.2 mL [3.79; 8.23], respectively. SI_FWHM, SI‐PIM, and R1‐PIM, however, only nonsignificantly underestimated TTC, by medians of ?0.10 mL [?0.12, ?0.06], ?0.86 mL [?1.04; 1.54], and ?1.30 mL [?4.99; ?0.29], respectively. The infarct‐involved voxel volume (IIVV) of SI‐PIM, 32.4 mL [21.2, 46.3] is higher (P < 0.01) than IIVVs of SI_FWHM 8.3 mL [3.79, 19.0]. SI‐PIM_FWHM, however, underestimates TTC (?5.74 mL [?11.89; ?2.52] (P < 0.01)). Thus, SI‐PIM outperforms SI_FWHM because larger IIVVs are obtained, and thus PIs both in the rim and the core of the infarcted tissue are characterized, in contradistinction from DE‐SI_FWHM, which shows mainly the infarct core.

Conclusion

We have shown here, ex vivo, that SI‐PIM has the same advantages as R1‐PIM, but it is based on the scanning sequences of DE imaging, and thus it is obtainable within the same short scanning time as DE. This makes it a practical method for clinical studies. J. Magn. Reson. Imaging 2010;32:859–868. © 2010 Wiley‐Liss, Inc.

     

Artifact suppression in imaging of myocardial infarction using B1-weighted phased-array combined phase-sensitive inversion recovery.

Regions of the body with long T1, such as cerebrospinal fluid (CSF), may create ghost artifacts on gadolinium-hyperenhanced images of myocardial infarction when inversion recovery (IR) sequences are used with a segmented acquisition. Oscillations in the transient approach to steady state for regions with long T1 may cause ghosts, with the number of ghosts being equal to the number of segments. B1-weighted phased-array combining provides an inherent degree of ghost artifact suppression because the ghost artifact is weighted less than the desired signal intensity by the coil sensitivity profiles. Example images are shown that illustrate the suppression of CSF ghost artifacts by the use of B1-weighted phased-array combining of multiple receiver coils.     

Phase‐sensitive inversion recovery for myocardial T1 mapping with motion correction and parametric fitting

The assessment of myocardial fibrosis and extracellular volume requires accurate estimation of myocardial T₁s. While image acquisition using the modified Look‐Locker inversion recovery technique is clinically feasible for myocardial T₁ mapping, respiratory motion can limit its applicability. Moreover, the conventional T₁ fitting approach using the magnitude inversion recovery images can lead to less stable T₁ estimates and increased computational cost. In this article, we propose a novel T₁ mapping scheme that is based on phase‐sensitive image reconstruction and the restoration of polarity of the MR signal after inversion. The motion correction is achieved by registering the reconstructed images after background phase removal. The restored signal polarity of the inversion recovery signal helps the T₁ fitting resulting in improved quality of the T₁ map and reducing the computational cost. Quantitative validation on a data cohort of 45 patients proves the robustness of the proposed method against varying image contrast. Compared to the magnitude T₁ fitting, the proposed phase‐sensitive method leads to less fluctuation in T₁ estimates. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Late gadolinium enhancement of acute myocardial infarction in mice at 7T: cine-FLASH versus inversion recovery

Purpose

To investigate myocardial infarction (MI), late gadolinium (Gd) enhancement (LGE), cardiovascular magnetic resonance imaging (CMRI) is used as the current gold standard for the in vivo diagnosis in patients and preclinical studies. While inversion recovery (IR) fast gradient echo LGE imaging is the preferred technique at clinical field strengths it remains to be investigated which is the best sequence at higher field strength. We therefore compared the IR technique against cine fast low shot angle (cine‐FLASH) for the quantification of MI size in mice at 7T in vivo.

Materials and Methods

Five mice were used to optimize cine‐FLASH and IR parameters. Nine mice were subsequently imaged with optimized parameters using both techniques 2–3 days after MI and ≈30 minutes post Gd injection.

Results

The difference in infarct size values was within 3.3% between the two CMRI techniques and within 7.5% of histological values by Bland–Altman analysis. Contrast‐to‐noise‐ratio between infarcted and normal tissue as well as blood was higher for cine‐FLASH with the additional benefit of a 2‐time‐fold shorter scan time than with the IR method. Furthermore, left ventricular function/volumes could be calculated from cine‐FLASH images before as well as after Gd injection.

Conclusion

In conclusion, cine‐FLASH LGE MRI represents an attractive alternative to IR LGE MRI for infarct size assessment in mice at high field strengths because it provides similar accuracy while being more robust, faster, and less user dependent. J. Magn. Reson. Imaging 2010;32:878–886. © 2010 Wiley‐Liss, Inc.     

Assessment of myocardial infarction in pigs using a rapid clearance blood pool contrast medium.

Delayed enhancement MRI using extracellular contrast media allows reliable detection of myocardial infarction. If blood pool contrast media like P792 (Vistarem, Guerbet, France), in addition to improving coronary MR angiography, can be shown to also produce delayed enhancement in myocardial infarction they could improve the prerequisites for a comprehensive cardiac MR examination. In this study reperfused myocardial infarction in five minipigs was imaged with an inversion-recovery fast low-angle shot sequence using P792 (0.013 mmol Gd/kg) and the extracellular contrast medium Gd-DOTA (Dotarem, 0.1 mmol Gd/kg, Guerbet). The infarction size determined on MRI using P792 (7.55 +/- 2.31 cm(2)) highly correlated both with histomorphometry (7.81 +/- 2.18 cm(2), r = 0.991, P < 0.002) and with MRI using Gd-DOTA (7.85 +/- 2.35 cm(2), r = 0.978, P < 0.005). Bland-Altman analysis showed that the limit of agreement of MRI using P792 compared to histomorphometry was 3.3 +/- 7.6% of the infarction size. The contrast-to-noise ratio between infarcted and remote myocardium was not significantly different between Gd-DOTA (5.9 +/- 2.4) and P792 (4.4 +/- 1.1, P = 0.5). The blood pool contrast medium P792 allows reliable assessment of viability with good contrast and accuracy.