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

3D whole-heart grey-blood late gadolinium enhancement cardiovascular magnetic resonance imaging

PURPOSE

To develop a free-breathing whole-heart isotropic-resolution 3D late gadolinium enhancement (LGE) sequence with Dixon-encoding, which provides co-registered 3D grey-blood phase-sensitive inversion-recovery (PSIR) and complementary 3D fat volumes in a single scan of < 7 min.

METHODS

A free-breathing 3D PSIR LGE sequence with dual-echo Dixon readout with a variable density Cartesian trajectory with acceleration factor of 3 is proposed. Image navigators are acquired to correct both inversion recovery (IR)-prepared and reference volumes for 2D translational respiratory motion, enabling motion compensated PSIR reconstruction with 100% respiratory scan efficiency. An intermediate PSIR reconstruction is performed between the in-phase echoes to estimate the signal polarity which is subsequently applied to the IR-prepared water volume to generate a water grey-blood PSIR image. The IR-prepared water volume is obtained using a water/fat separation algorithm from the corresponding dual-echo readout. The complementary fat-volume is obtained after water/fat separation of the reference volume. Ten patients (6 with myocardial scar) were scanned with the proposed water/fat grey-blood 3D PSIR LGE sequence at 1.5 T and compared to breath-held grey-blood 2D LGE sequence in terms of contrast ratio (CR), contrast-to-noise ratio (CNR), scar depiction, scar transmurality, scar mass and image quality.

RESULTS

Comparable CRs (p = 0.98, 0.40 and 0.83) and CNRs (p = 0.29, 0.40 and 0.26) for blood-myocardium, scar-myocardium and scar-blood respectively were obtained with the proposed free-breathing 3D water/fat LGE and 2D clinical LGE scan. Excellent agreement for scar detection, scar transmurality, scar mass (bias = 0.29%) and image quality scores (from 1: non-diagnostic to 4: excellent) of 3.8 ± 0.42 and 3.6 ± 0.69 (p > 0.99) were obtained with the 2D and 3D PSIR LGE approaches with comparable total acquisition time (p = 0.29). Similar agreement in intra and inter-observer variability were obtained for the 2D and 3D acquisition respectively.

CONCLUSION

The proposed approach enabled the acquisition of free-breathing motion-compensated isotropic-resolution 3D grey-blood PSIR LGE and fat volumes. The proposed approach showed good agreement with conventional 2D LGE in terms of CR, scar depiction and scan time, while enabling free-breathing acquisition, whole-heart coverage, reformatting in arbitrary views and visualization of both water and fat information.

Single breath-hold compressed sensing real-time cine imaging to assess left ventricular motion in myocardial infarction

PURPOSE

To evaluate the reliability of a real-time compressed sensing (CS) cine sequence for the detection of left ventricular wall motion disorders after myocardial infarction in comparison with the reference steady-state free precession cine sequence.

MATERIALS AND METHODS

One hundred consecutive adult patients referred for either initial work-up or follow-up by cardiac magnetic resonance (CMR) in the context of myocardial infarction were prospectively included. There were 77 men and 23 women with a mean age of 63.12±11.3 (SD) years (range: 29-89 years). Each patient underwent the reference segmented multi-breath-hold steady-state free precession cine sequence including one short-axis stack and both vertical and horizontal long-axis slices (SSFP_ref) and the CS real-time single-breath-hold evaluated sequence (CS_rt) providing the same slices. Wall motion disorders were independently and blindly assessed with both sequences by two radiologists, using the American Heart Association left ventricle segmentation. Paired Wilcoxon signed-rank test was used to search for differences in wall motion disorders conspicuity between both sequences and receiver operating characteristic curve (ROC) analysis was performed to assess the diagnosis performance of CS_rt sequence using SSFP_ref as the reference method.

RESULTS

Each patient had at least one cardiac segment with wall motion abnormality on SSFP_ref and CS_rt images. The 1700 segments analyzed with SSFP_ref were classified as normokinetic (360/1700; 21.2%), hypokinetic (783/1700; 46.1%), akinetic (526/1700; 30.9%) or dyskinetic (31/1700; 1.8%). Sensitivity and specificity of the CS sequence were 99.6% (95% CI: 99.1-99.9%) and 99.7% (95% CI: 98.5-100%), respectively. Area under ROC of CS_rt diagnosis performance was 0.997 (95% CI: 0.993-0.999).

CONCLUSION

CS real-time cine imaging significantly reduces acquisition time without compromising the conspicuity of left ventricular -wall motion disorders in the context of myocardial infarction.

[Optimal Imaging Method for Late Gadolinium-enhanced Cardiovascular Magnetic Resonance in Arrhythmic Cases]

We determined the procedure to reduce arrhythmia-related ghosting artifacts in the late gadolinium enhancement (LGE) imaging of cardiovascular magnetic resonance (CMR) in patients with arrhythmia by examining the causing factors using phantoms. Inversion recovery gradient echo and phase-sensitive inversion recovery (PSIR) sequences were compared under normal sinus rhythm and premature ventricular contraction (PVC) conditions. Under the PVC condition, trigger interval irregularly performed induced ghosting artifacts. A phase-corrected real image in PSIR, however; demonstrated an accurately positive contrast of pale LGE area indicative of mild fibrosis with minimal ghosting artifacts. The study results indicate that PSIR has an advantage for LGE CMR in patients with arrhythmia. Even without having PSIR method, the 2R-R method ensures consistency of contrast and enables reduction of ghost artifacts.

Ejection fraction in left bundle branch block is disproportionately reduced in relation to amount of myocardial scar

INTRODUCTION

The relationship between left ventricular (LV) ejection fraction (EF) and LV myocardial scar can identify potentially reversible causes of LV dysfunction. Left bundle branch block (LBBB) alters the electrical and mechanical activation of the LV. We hypothesized that the relationship between LVEF and scar extent is different in LBBB compared to controls.

METHODS

We compared the relationship between LVEF and scar burden between patients with LBBB and scar (n = 83), and patients with chronic ischemic heart disease and scar but no electrocardiographic conduction abnormality (controls, n = 90), who had undergone cardiovascular magnetic resonance (CMR) imaging at one of three centers. LVEF (%) was measured in CMR cine images. Scar burden was quantified by CMR late gadolinium enhancement (LGE) and expressed as % of LV mass (%LVM). Maximum possible LVEF (LVEFmax) was defined as the function describing the hypotenuse in the LVEF versus myocardial scar extent scatter plot. Dysfunction index was defined as LVEFmax derived from the control cohort minus the measured LVEF.

RESULTS

Compared to controls with scar, LBBB with scar had a lower LVEF (median [interquartile range] 27 [19-38] vs 36 [25-50] %, p < 0.001), smaller scar (4 [1-9] vs 11 [6-20] %LVM, p < 0.001), and greater dysfunction index (39 [30-52] vs 21 [12-35] % points, p < 0.001).

CONCLUSIONS

Among LBBB patients referred for CMR, LVEF is disproportionately reduced in relation to the amount of scar. Dyssynchrony in LBBB may thus impair compensation for loss of contractile myocardium.

Cardiac MRI and radionuclide ventriculography for measurement of left ventricular ejection fraction in ICD candidates

OBJECTIVE

Current guidelines provide left ventricular ejection fraction (LVEF) criterion for use of implantable cardioverter defibrillators (ICD) but do not specify which modality to use for measurement. We compared LVEF measurements by radionuclide ventriculography (RNV) vs cardiac MRI (CMR) in ICD candidates to assess impact on clinical decision making.

METHODS

This single-centre study included 124 consecutive patients referred for assessment of ICD implantation who underwent RNV and CMR within 30 days for LVEF measurement. RNV and CMR were interpreted independently by experienced readers.

RESULTS

Among 124 patients (age 64 ± 11 years, 77% male), median interval between CMR and RNV was 1 day; mean LVEF was 32 ± 12% by CMR and 33 ± 11% by RNV (p = 0.60). LVEF by CMR and RNV showed good correlation, but Bland-Altman analysis showed relatively wide limits of agreement (-12.1 to 11.4). CMR LVEF reclassified 26 (21%) patients compared to RNV LVEF (kappa = 0.58). LVEF by both modalities showed good interobserver reproducibility (ICC 0.96 and 0.94, respectively) (limits of agreement -7.27 to 5.75 and -8.63 to 6.34, respectively).

CONCLUSION

Although LVEF measurements by CMR and RNV show moderate agreement, there is frequent reclassification of patients for ICD placement based on LVEF between these modalities. Future studies should determine if a particular imaging modality for LVEF measurement may enhance ICD decision making and treatment benefit.

Dark-blood late gadolinium enhancement without additional magnetization preparation

BACKGROUND

This study evaluates a novel dark-blood late gadolinium enhancement (LGE) cardiovascular magnetic resonance imaging (CMR) method, without using additional magnetization preparation, and compares it to conventional bright-blood LGE, for the detection of ischaemic myocardial scar. LGE is able to clearly depict myocardial infarction and macroscopic scarring from viable myocardium. However, due to the bright signal of adjacent left ventricular blood, the apparent volume of scar tissue can be significantly reduced, or even completely obscured. In addition, blood pool signal can mimic scar tissue and lead to false positive observations. Simply nulling the blood magnetization by choosing shorter inversion times, leads to a negative viable myocardium signal that appears equally as bright as scar due to the magnitude image reconstruction. However, by combining blood magnetization nulling with the extended grayscale range of phase-sensitive inversion-recovery (PSIR), a darker blood signal can be achieved whilst a dark myocardium and bright scar signal is preserved.

METHODS

LGE was performed in nine male patients (63 ± 11y) using a PSIR pulse sequence, with both conventional viable myocardium nulling and left ventricular blood nulling, in a randomized order. Regions of interest were drawn in the left ventricular blood, viable myocardium, and scar tissue, to assess contrast-to-noise ratios. Maximum scar transmurality, scar size, circumferential scar angle, and a confidence score for scar detection and maximum transmurality were also assessed. Bloch simulations were performed to simulate the magnetization levels of the left ventricular blood, viable myocardium, and scar tissue.

RESULTS

Average scar-to-blood contrast was significantly (p < 0.001) increased by 99% when nulling left ventricular blood instead of viable myocardium, while scar-to-myocardium contrast was maintained. Nulling left ventricular blood also led to significantly (p = 0.038) higher expert confidence in scar detection and maximum transmurality. No significant changes were found in scar transmurality (p = 0.317), normalized scar size (p = 0.054), and circumferential scar angle (p = 0.117).

CONCLUSIONS

Nulling left ventricular blood magnetization for PSIR LGE leads to improved scar-to-blood contrast and increased expert confidence in scar detection and scar transmurality. As no additional magnetization preparation is used, clinical application on current MR systems is readily available without the need for extensive optimizations, software modifications, and/or additional training.

Influence of phase correction of late gadolinium enhancement images on scar signal quantification in patients with ischemic and non-ischemic cardiomyopathy

BACKGROUND

Myocardial fibrosis imaging using late gadolinium enhancement (LGE) cardiac magnetic resonance (CMR) has been validated as a quantitative predictive marker for response to medical, surgical, and device therapy. To date, all such studies have examined conventional, non-phase corrected magnitude images.  However, contemporary practice has rapdily adopted phase-corrected image reconstruction. We sought to investigate the existence of any systematic bias between threshold-based scar quantification performed on conventional magnitude inversion recovery (MIR) and matched phase sensitive inversion recovery (PSIR) images.

METHODS

In 80 patients with confirmed ischemic (N = 40), or non-ischemic (n = 40) myocardial fibrosis, and also in a healthy control cohort (N = 40) without fibrosis, myocardial late enhancement was quantified using a Signal Threshold Versus Reference Myocardium technique (STRM) at ≥2, ≥3, and ≥5 SD threshold, and also using the Full Width at Half Maximal (FWHM) technique. This was performed on both MIR and PSIR images and values compared using linear regression and Bland-Altman analyses.

RESULTS

Linear regression analysis demonstrated excellent correlation for scar volumes between MIR and PSIR images at all three STRM signal thresholds for the ischemic (N = 40, r = 0.96, 0.95, 0.88 at 2, 3, and 5 SD, p < 0.0001 for all regressions), and non ischemic (N = 40, r = 0.86, 0.89, 0.90 at 2, 3, and 5 SD, p < 0.0001 for all regressions) cohorts. FWHM analysis demonstrated good correlation in the ischemic population (N = 40, r = 0.83, p < 0.0001). Bland-Altman analysis demonstrated a systematic bias with MIR images showing higher values than PSIR for ischemic (3.3 %, 3.9 % and 4.9 % at 2, 3, and 5 SD, respectively), and non-ischemic (9.7 %, 7.4 % and 4.1 % at ≥2, ≥3, and ≥5 SD thresholds, respectively) cohorts. Background myocardial signal measured in the control population demonstrated a similar bias of 4.4 %, 2.6 % and 0.7 % of the LV volume at 2, 3 and 5 SD thresholds, respectively. The bias observed using FWHM analysis was -6.9 %.

CONCLUSIONS

Scar quantification using phase corrected (PSIR) images achieves values highly correlated to those obtained on non-corrected (MIR) images. However, a systematic bias exists that appears exaggerated in non-ischemic cohorts. Such bias should be considered when comparing or translating knowledge between MIR- and PSIR-based imaging.

Late gadolinium enhancement magnetic resonance imaging for the assessment of myocardial infarction: comparison of image quality between single and double doses of contrast agents

To compare the image quality of late gadolinium enhancement (LGE) cardiac magnetic resonance imaging (CMR) using a single dose of gadolinium contrast agent versus the conventional double dose for assessing myocardial infarction. This retrospective study examined 37 patients with chronic myocardial infarction who underwent LGE CMR using both inversion recovery (IR)-turbo fast low-angle shot magnitude-reconstructed and phase-sensitive images with two different dosages of gadolinium contrast agent: a single dose of 0.1 mmol/kg gadolinium-DTPA in 17 patients and a double dose of 0.2 mmol/kg in 20 patients. The contrast-to-noise ratio (CNR) and visual conspicuity between infarct and normal myocardium (CNRinfarct-normal, conspicuityinfarct-normal) and between infarct and left ventricular cavity (CNRinfarct-LVC, conspicuityinfarct-LVC) were compared. Interobserver agreement for the maximal transmural extent of infarction was also evaluated. CNRinfarct-normal was significantly higher with double-dose gadolinium contrast agent (15.5 ± 20.7 vs. 40.4 ± 16.1 in magnitude images and 9.5 ± 2.8 vs. 11.2 ± 2.7 in phase-sensitive images, P < 0.001) while conspicuityinfarct-normal showed no significant difference between the two groups (P > 0.05). Both CNRinfarct-LVC (7.7 ± 10.7 vs. -6.6 ± 19.0 in magnitude images and 4.1 ± 2.3 vs. -0.4 ± 4.1 in phase-sensitive images, P < 0.05) and conspicuityinfarct-LVC were significantly better with single-dose gadolinium contrast. Interobserver agreement for assessing the transmural extent of infarction was moderate in both groups: 0.591 for single-dose and 0.472 for double-dose. LGE CMR using a single dose of gadolinium contrast agent showed significantly better contrast between infarcted myocardium and left ventricular cavity lumen without a significant decrease in visual contrast between infarcted myocardium and normal myocardium, compared to a double dose.

Cardiac imaging techniques for physicians: late enhancement

Late enhancement imaging is used to diagnose and characterize a wide range of ischemic and nonischemic cardiomyopathies, and its use has become ubiquitous in the cardiac MR exam. As the use of late enhancement imaging has matured and the span of applications has widened, the demands on image quality have grown. The characterization of subendocardial MI now includes the accurate quantification of scar size, shape, and characterization of borders which have been shown to have prognostic significance. More diverse patterns of late enhancement including patchy, mid-wall, subepicardial, or diffuse enhancement are of interest in diagnosing nonischemic cardiomyopathies. As clinicians are examining late enhancement images for more subtle indication of fibrosis, the demand for lower artifacts has increased. A range of new techniques have emerged to improve the speed and quality of late enhancement imaging including: methods for acquisition during free breathing, and fat water separated imaging for characterizing fibrofatty infiltration and reduction of artifacts related to the presence of fat. Methods for quantification of T1 and extracellular volume fraction are emerging to tackle the issue of discriminating globally diffuse fibrosis from normal healthy tissue which is challenging using conventional late enhancement methods. The aim of this review will be to describe the current state of the art and to provide a guide to various clinical protocols that are commonly used.

Differentiation of myocardial scar from potential pitfalls and artefacts in delayed enhancement MRI

Delayed enhancement cardiac magnetic resonance (DE-CMR) imaging is used increasingly to identify and quantify focal myocardial scar. Our objective is to describe factors used in the interpretation of DE-CMR images and to highlight potential pitfalls and artefacts that mimic myocardial scar. Inversion recovery gradient recalled echo sequence is commonly accepted as the standard of reference for DE-CMR. There are also alternative sequences that can be performed in a single breath-hold or with free breathing. Radiologists need to be aware of factors affecting image quality, and potential pitfalls and artefacts that may generate focal hyperintense areas that mimic myocardial scar.

Optimization of myocardial nulling in pediatric cardiac MRI

BACKGROUND

Current protocols to determine optimal nulling time in late enhancement imaging using adult techniques may not apply to children.

OBJECTIVE

To determine the optimal nulling time in anesthetised children, with the hypothesis that this occurs earlier than in adults.

MATERIALS AND METHODS

Sedated cardiac MRI was performed in 12 children (median age: 12 months, range: 1-60 months). After gadolinium administration, scout images at 2, 3, 4 and 10 min and phase sensitive inversion recovery (PSIR) images from 5 to 10 min were obtained. Signal-to-noise ratio (SNR) and inversion time (TI) were determined. Quality of nulling was assessed according to a grading score by three observers. Data was analysed using linear regression, Kruskal-Wallis and quadratic-weighted kappa statistics.

RESULTS

One child with a cardiomyopathy had late enhancement. Good agreement in nulling occurred for scout images at 2 (κ = 0.69) and 3 (κ = 0.66) min and moderate agreement at 4 min (κ = 0.57). Agreement of PSIR images was moderate at 7 min (κ = 0.44) and poor-fair at other times. There were significant correlations between TI and scout time (r = 0.61, P < 0.0001), and SNR and kappa (r = 0.22, P = 0.017).

CONCLUSION

Scout images at 2-4 min can be used to determine the TI with little variability. Image quality for PSIR images was highest at 7 min and SNR optimal at 7-9 min. TI increases with time and should be adjusted frequently during imaging. Thus, nulling times in children differ from nulling times in adults when using standard adult techniques.

[Basic examination for three-dimensional phase-sensitive inversion recovery (3D PSIR) method by late gadolinium enhancement of non-breath-hold cardiac magnetic resonance image]

PURPOSE

We studied imaging parameters for the three-dimensional phase-sensitive inversion recovery by a late gadolinium enhancement (3D PSIR) method.

METHOD

In the 3D PSIR method using a 1.5 Tesla MRI system and a polyvinyl alcohol (PVA) gel phantom, we evaluated the relation of the signal intensity at multiple inversion times (TI), 100-500 ms; flip angles (FA), 15-35°; and segments, 20-45. In 30 patients with chronic myocardial infarction, we measured and compared the late gadolinium enhancement (LGE) image area of ratio for each of 3 sections on both 3D LGE images by a non-breath hold and two-dimensional inversion recovery (2D IR) method non-breath hold.

RESULT

In the 3D PSIR method, we recognized the signal intensity to make the width of step, maximum, and we recognized that the TI range, to keep the effective signal intensity difference constant, was limited on each phantom. The more this TI range decreased the bigger the difference in the FA and signal intensity. The set-up range of TI for the segment number remained the same. In the clinical setting, we recognized a good correlation between the 3D PSIR method (TI 300 ms, FA 20°) and the IR method (r=0.905, p<0.001). The imaging parameter that can be used in the clinical setting with the 3D PSIR method is FA 20° TI 200-300 ms, with the segment number adjusted by the cardiac cycle.

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, TEeff. TEeff 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.

Assessment of late gadolinium enhancement in nonischemic cardiomyopathy: comparison of a fast Phase-Sensitive Inversion Recovery Sequence (PSIR) and a conventional segmented 2D gradient echo recall (GRE) sequence--preliminary findings

BACKGROUND

Reliable detection of myocardial scarring in nonischemic cardiomyopathy is time-consuming using techniques that require determination of optimal inversion time. Therefore we evaluated an inversion-time-insensitive approach using a fast phase-sensitive inversion recovery (PSIR) sequence to detect and quantify late gadolinium enhancement (LGE).

PATIENTS AND METHODS

Twenty patients (mean age 40 years, 9 females) with nonischemic cardiomyopathy and evidence of LGE were evaluated. After administration of 0.2 mmol/kg gadolinium diethylene triamine pentaacetic acid, a segmented 2D inversion recovery turbo fast low-angle shot gradient echo recall (GRE) sequence [echo time (TE) 4.3 milliseconds, repetition time (TR) 750 milliseconds, alpha 30 degrees , voxel size 1.7 x 1.3 x 8-10 mm] was obtained and served as the standard of reference. Second, a fast multislice single-shot 2D PSIR sequence (TE 1.1 millisecond, TR 700 milliseconds, alpha 40 degrees , voxel size 2.5 x 1.7 x 8-10 mm) was acquired in the same slice positions. The PSIR(IR) images were used to analyze LGE. Altogether 53 short-axis slices with LGE were evaluated. Contrast-to-noise ratio and area of LGE were calculated and compared by 2 experienced readers. Image quality and confidence level for identification of LGE were rated on 5-point scales. Interobserver variability was evaluated in 10 patients.

RESULTS

All images were interpretable. Imaging time was reduced from 385 +/- 127 seconds to 20 +/- 3 seconds (P < 0.001). Contrast-to-noise ratio was 8.29 for PSIRmag and 12.07 for the conventional GRE images (P < 0.001). The mean area of LGE was 1.01 +/- 0.62 cm(2) for the GRE sequence and 1.10 +/- 0.62 cm(2) for PSIR(IR) (P = NS). The general linear model showed no interaction between the results and no significant difference of the mean (r = 0.09, mean difference 0.09 cm(2)). The overall interobserver variability of PSIR(IR) and GRE was excellent, with Pearson's correlation coefficients of r = 0.96 for PSIR(IR) and r = 0.98 for GRE. PSIR(IR) and conventional GRE were comparable in terms of image quality and confidence level (image quality: 1.6 +/- 0.67 vs. 1.5 +/- 0.93, P = NS; confidence level: 1.4 +/- 0.84 vs. 1.3 +/- 0.5; P = NS).

CONCLUSIONS

Fast PSIR sequences enable accurate detection and quantification of LGE in nonischemic cardiomyopathies. The examination time can be significantly shortened using the single-shot approach of the PSIR technique.

Contrast-enhanced magnetic resonance imaging in the assessment of myocardial infarction and viability

Contrast-enhanced magnetic resonance imaging (MRI) can be used to visualize the transmural extent of myocardial infarction with high spatial resolution. The aim of this review is to provide an overview of the use of contrast-enhanced MRI for characterization of ischemic myocardial injury in comparison to other imaging methods and its relevance in clinical syndromes related to coronary artery disease. Infarcted myocardium appears hyperenhanced compared with normal myocardium when imaged by a delayed-enhancement MRI technique with the use of an inversion-prepared T(1)-weighted sequence after injection of gadolinium chelates, such as gadolinium-diethylenetriamine pentaacetic acid. Experimental and clinical studies indicate that the extent of delayed enhancement is reproducible and closely correlates with the size of myocardial necrosis or infarct scar as determined by established in vitro and in vivo methods. Furthermore, MRI appears to be more sensitive than other imaging methods in detecting small subendocardial infarctions. The transmural extent of delayed enhancement potentially predicts functional outcome after revascularization in acute myocardial infarction and chronic ischemic heart disease, indicating that it can accurately discriminate between infarction and dysfunctional but viable myocardium. Further experience from clinical trials is needed to understand the association of delayed enhancement with clinical outcomes.

Comparison of the Extent of Delayed-Enhancement Cardiac Magnetic Resonance Imaging With and Without Phase-Sensitive Reconstruction at 3.0 T

OBJECTIVES

To evaluate phase-sensitive reconstructed images versus magnitude images generated by an inversion recovery pulse sequence for the determination of myocardial infarct size in delayed-enhancement cardiac magnetic resonance (DE-CMR) at 3 T.

MATERIALS AND METHODS

Thirty patients were examined at 3 T and DE images were obtained 10 minutes after contrast agent administration using a phase-sensitive breath-hold segmented inversion recovery gradient echo sequence. From magnitude and phase images, the percentage of hyperenhanced myocardium was expressed. Contrast-to-noise ratio (CNR) measurements were performed in hyperenhanced and normal myocardium.

RESULTS

We observed excellent correlation and concordance between hyperenhanced myocardium determined on phase-sensitive reconstructed and magnitude images. The mean CNR values were significantly higher in phase-sensitive reconstructed images compared with magnitude images (10.5 +/- 5.4 vs. 6.1 +/- 4.8; P < 0.001).

CONCLUSIONS

DE-CMR with phase-sensitive reconstruction at 3.0 T provides similar results to magnitude images, but with a significantly greater CNR between infarcted and normal myocardium.

Inversion recovery radial MRI with interleaved projection sets

The radial trajectory has found applications in cardiac imaging because of its resilience to undersampling and motion artifacts. Recent work has shown that interleaved and weighted radial imaging can produce images with multiple contrasts from a single data set. This feature was investigated for inversion recovery imaging of scar using a radial technique. The 2D radial imaging method was modified to acquire quadruply interleaved projection sets within each acquisition window of the cardiac cycle. These data were reconstructed using k-space weightings that used a smaller segment of the acquisition window for the central k-space data, the determinant of image contrast. This method generates four images with different T1 weightings. The novel approach was compared with noninterleaved radial imaging, interleaved radial without weightings, and Cartesian imaging in simulations, phantoms, and seven subjects with clinical myocardial infarction. The results show that during a typical acquisition window after an inversion pulse, magnetization changes rapidly. The interleaved acquisition provided better image quality than the noninterleaved radial acquisition. Interleaving with weighting provided better quality when the inversion time (TI) was shorter than optimal; otherwise, interleaving without weighting was superior. These methods enable a radial trajectory to be employed in conjunction with preparation pulses for viability imaging.