Myocardial first-pass perfusion cardiovascular magnetic resonance: history, theory, and current state of the art

Comprehensive review of artifacts in cardiac MRI and their mitigation

Cardiac magnetic resonance imaging (CMR) is an important clinical tool that obtains high-quality images for assessment of cardiac morphology, function, and tissue characteristics. However, the technique may be prone to artifacts that may limit the diagnostic interpretation of images. This article reviews common artifacts which may appear in CMR exams by describing their appearance, the challenges they mitigate true pathology, and offering possible solutions to reduce their impact. Additionally, this article acts as an update to previous CMR artifacts reports by including discussion about new CMR innovations.

Assessment of myocardial microvascular dysfunction in patients with different stages of diabetes mellitus: An adenosine stress perfusion cardiac magnetic resonance study

PURPOSE

To examine myocardial perfusion and T1 mapping indicesin individuals with type 2 diabetes mellitus (T2DM) at various stages of glycemic control and whether uncontrolled glycemic levels would worsen myocardial microvascular function.

METHOD

Cardiac magnetic resonance examinations were performed on 114 T2DM patients without obstructive coronary artery disease and 55 matched controls. Participants were further divided into four subgroups: Q1 (control); Q2 (prediabetes); Q3 (controlled T2DM) and Q4 (uncontrolled T2DM). The correlation between glycosylated hemoglobin (HbA1c) levels and myocardial perfusion parameters was evaluated.

RESULTS

Global myocardial perfusion reserve index (MPRI) was significantly reduced in the Q3 and Q4 subgroups compared to the Q1 or Q2 subgroup (all P<0.001). Compared with the Q1 subgroup, global stress T1 reactivity (stress ΔT1) was significantly reduced in the Q3 and Q4 subgroups (P=0.004 and < 0.001, respectively), but elevated in the Q2 subgroup (P=0.018). Global extracellular volume (ECV) was considerably higher in the Q2 subgroup and gradually rose in the Q3 and Q4 subgroups compared to the Q1 subgroup (P=0.011, 0.001, and 0.007, respectively). HbA1c levels correlated negatively with global MPRI and stress ΔT1, but positively with global ECV (β = -1.993, P<0.001; β = -0.180, P<0.001; and β = 0.127, P<0.001, respectively).

CONCLUSIONS

Global stress ΔT1 reduced in T2DM patients but rose in prediabetes patients. Compared to MPRI, the ECV parameter can indicate diabetes-induced coronary microvascular dysfunction earlier and persists throughout the disorder. Myocardial perfusion and T1 mapping at stress can be used to detect early signs of microvascular dysfunction and subclinical risk factors in patients with T2DM.

How to use MRI in cardiac disease with diastolic dysfunction?

Left ventricular (LV) diastolic dysfunction (DD) is an initially asymptomatic condition that can progress to heart failure, either with preserved or reduced ejection fraction. As such, DD is a growing public health problem. Impaired relaxation, the first stage of DD, is associated with altered LV filling. With progression, reducing LV compliance leads to restrictive cardiomyopathy. While cardiac magnetic resonance (CMR) imaging is the reference for LV systolic function assessment, transthoracic echocardiography (TTE) with Doppler flow measurements remains the standard for diastolic function assessment. Rather than simply replicating TTE measurements, CMR should complement and further advance TTE findings. We provide herein a step-by-step review of CMR findings in DD as well as imaging features which may help identify the underlying cause.

Improved reproducibility for myocardial ASL: Impact of physiological and acquisition parameters

PURPOSE

To investigate and mitigate the influence of physiological and acquisition-related parameters on myocardial blood flow (MBF) measurements obtained with myocardial Arterial Spin Labeling (myoASL).

METHODS

A Flow-sensitive Alternating Inversion Recovery (FAIR) myoASL sequence with bSSFP and spoiled GRE (spGRE) readout is investigated for MBF quantification. Bloch-equation simulations and phantom experiments were performed to evaluate how variations in acquisition flip angle (FA), acquisition matrix size (AMS), heart rate (HR) and bloodT 1 $$ {\mathrm{T}}_1 $$ relaxation time (T 1 , B $$ {\mathrm{T}}_{1,B} $$ ) affect quantification of myoASL-MBF. In vivo myoASL-images were acquired in nine healthy subjects. A corrected MBF quantification approach was proposed based on subject-specificT 1 , B $$ {\mathrm{T}}_{1,B} $$ values and, for spGRE imaging, subtracting an additional saturation-prepared baseline from the original baseline signal.

RESULTS

Simulated and phantom experiments showed a strong dependence on AMS and FA (R 2 $$ {R}^2 $$ >0.73), which was eliminated in simulations and alleviated in phantom experiments using the proposed saturation-baseline correction in spGRE. Only a very mild HR dependence (R 2 $$ {R}^2 $$ >0.59) was observed which was reduced when calculating MBF with individualT 1 , B $$ {\mathrm{T}}_{1,B} $$ . For corrected spGRE, in vivo mean global spGRE-MBF ranged from 0.54 to 2.59 mL/g/min and was in agreement with previously reported values. Compared to uncorrected spGRE, the intra-subject variability within a measurement (0.60 mL/g/min), between measurements (0.45 mL/g/min), as well as the inter-subject variability (1.29 mL/g/min) were improved by up to 40% and were comparable with conventional bSSFP.

CONCLUSION

Our results show that physiological and acquisition-related factors can lead to spurious changes in myoASL-MBF if not accounted for. Using individualT 1 , B $$ {\mathrm{T}}_{1,B} $$ and a saturation-baseline can reduce these variations in spGRE and improve reproducibility of FAIR-myoASL against acquisition parameters.

Phenotyping heart failure by cardiac magnetic resonance imaging of cardiac macro- and microscopic structure: state of the art review

Heart failure demographics have evolved in past decades with the development of improved diagnostics, therapies, and prevention. Cardiac magnetic resonance (CMR) has developed in a similar timeframe to become the gold-standard non-invasive imaging modality for characterizing diseases causing heart failure. CMR techniques to assess cardiac morphology and function have progressed since their first use in the 1980s. Increasingly efficient acquisition protocols generate high spatial and temporal resolution images in less time. This has enabled new methods of characterizing cardiac systolic and diastolic function such as strain analysis, exercise real-time cine imaging and four-dimensional flow. A key strength of CMR is its ability to non-invasively interrogate the myocardial tissue composition. Gadolinium contrast agents revolutionized non-invasive cardiac imaging with the late gadolinium enhancement technique. Further advances enabled quantitative parametric mapping to increase sensitivity at detecting diffuse pathology. Novel methods such as diffusion tensor imaging and artificial intelligence-enhanced image generation are on the horizon. Magnetic resonance spectroscopy (MRS) provides a window into the molecular environment of the myocardium. Phosphorus (31P) spectroscopy can inform the status of cardiac energetics in health and disease. Proton (1H) spectroscopy complements this by measuring creatine and intramyocardial lipids. Hyperpolarized carbon (13C) spectroscopy is a novel method that could further our understanding of dynamic cardiac metabolism. CMR of other organs such as the lungs may add further depth into phenotypes of heart failure. The vast capabilities of CMR should be deployed and interpreted in context of current heart failure challenges.

Role of Cardiovascular Imaging in Risk Assessment: Recent Advances, Gaps in Evidence, and Future Directions

Optimal risk assessment for primary prevention remains highly challenging. Recent registries have highlighted major discrepancies between guidelines and daily practice. Although guidelines have improved over time and provide updated risk scores, they still fail to identify a significant proportion of at-risk individuals, who then miss out on effective prevention measures until their initial ischemic events. Cardiovascular imaging is progressively assuming an increasingly pivotal role, playing a crucial part in enhancing the meticulous categorization of individuals according to their risk profiles, thus enabling the customization of precise therapeutic strategies for patients with increased cardiovascular risks. For the most part, the current approach to patients with atherosclerotic cardiovascular disease (ASCVD) is homogeneous. However, data from registries (e.g., REACH, CORONOR) and randomized clinical trials (e.g., COMPASS, FOURIER, and ODYSSEY outcomes) highlight heterogeneity in the risks of recurrent ischemic events, which are especially higher in patients with poly-vascular disease and/or multivessel coronary disease. This indicates the need for a more individualized strategy and further research to improve definitions of individual residual risk, with a view of intensifying treatments in the subgroups with very high residual risk. In this narrative review, we discuss advances in cardiovascular imaging, its current place in the guidelines, the gaps in evidence, and perspectives for primary and secondary prevention to improve risk assessment and therapeutic strategies using cardiovascular imaging.

A simplified method to correct saturation of arterial input function for cardiac magnetic resonance first-pass perfusion imaging: validation with simultaneously acquired PET

BACKGROUND

First-pass perfusion imaging in magnetic resonance imaging (MRI) is an established method to measure myocardial blood flow (MBF). An obstacle for accurate quantification of MBF is the saturation of blood pool signal intensity used for arterial input function (AIF). The objective of this project was to validate a new simplified method for AIF estimation obtained from single-bolus and single sequence perfusion measurements. The reference MBF was measured simultaneously on 13N-ammonia positron emission tomography (PET).

METHODS

Sixteen patients with clinically confirmed myocardial ischemia were imaged in a clinical whole-body PET-MRI system. PET perfusion imaging was performed in a 10-min acquisition after the injection of 10 mCi of 13N-ammonia. The MRI perfusion acquisition started simultaneously with the start of the PET acquisition after the injection of a 0.075 mmol/kg gadolinium contrast agent. Cardiac stress imaging was initiated after the administration of regadenoson 20 s prior to PET-MRI scanning. The saturation part of the MRI AIF data was modeled as a gamma variate curve, which was then estimated for a true AIF by minimizing a cost function according to various boundary conditions. A standard AHA 16-segment model was used for comparative analysis of absolute MBF from PET and MRI.

RESULTS

Overall, there were 256 segments in 16 patients, mean resting perfusion for PET was 1.06 ± 0.34 ml/min/g and 1.04 ± 0.30 ml/min/g for MRI (P = 0.05), whereas mean stress perfusion for PET was 2.00 ± 0.74 ml/min/g and 2.12 ± 0.76 ml/min/g for MRI (P < 0.01). Linear regression analysis in MBF revealed strong correlation (r = 0.91, slope = 0.96, P < 0.001) between PET and MRI. Myocardial perfusion reserve, calculated from the ratio of stress MBF over resting MBF, also showed a strong correlation between MRI and PET measurements (r = 0.82, slope = 0.81, P < 0.001).

CONCLUSION

The results demonstrated the feasibility of the simplified AIF estimation method for the accurate quantification of MBF by MRI with single sequence and single contrast injection. The MRI MBF correlated strongly with PET MBF obtained simultaneously. This post-processing technique will allow easy transformation of clinical perfusion imaging data into quantitative information.

Myocardial First-Pass Perfusion With Increased Anatomic Coverage at 3 T Using Autocalibrated Multiband Imaging

BACKGROUND

Myocardial first-pass perfusion (FPP) imaging is a useful cardiac MRI method for the diagnosis of coronary artery disease. However, conventional 2D multislice FPP acquisitions usually have gaps between myocardium slices, which limits the overall assessment of myocardial ischemia.

PURPOSE

To increase the anatomic coverage of myocardial FPP imaging at 3 T by implementing both autocalibrated multiband (MB) acquisition and k-t space acceleration with compress sensing (CS) reconstruction, without the need for additional reference scans.

STUDY TYPE

Phantom and prospective human studies.

PHANTOM/SUBJECTS

A T1MES (T1 Mapping and ECV Standardization in cardiovascular magnetic resonance) phantom and 20 subjects (12 healthy subjects and 8 patients, 10 males, age 42 ± 16 years).

FIELD STRENGTH/SEQUENCE

A 3 T/saturation recovery prepared gradient echo sequence with contrast administration.

ASSESSMENT

Phantom experiments were performed to compare the performance of autocalibrated MB-FPP with k-t acceleration using slice-GRAPPA and CS reconstructions. In vivo experiments were performed to compare the performance of conventional FPP (2.5× acceleration) with autocalibrated MB + CS-FPP (6× acceleration). In phantom experiments, the error maps were calculated. In in vivo experiments, the contrast ratio (CR) and blurring were quantitatively measured, while image quality, perceived signal-to-noise ratio (SNR), and artifact level were qualitatively graded by three cardiologists on a 4-point scale.

STATISTICAL TESTS

Wilcoxon signed-rank test, paired t-test. A P value <0.05 was considered statistically significant.

RESULTS

In phantom experiments, residual artifact was reduced using the MB + CS-FPP reconstruction method compared with using the MB + slice-GRAPPA reconstruction method. In in vivo experiments, the proposed autocalibrated MB + CS-FPP method demonstrated significantly higher CR (3.52 ± 0.78 vs 2.91 ± 0.81) and had significantly better perceived SNR (2.69 ± 0.29 vs 2.48 ± 0.31) compared to the conventional sequence. Compared with conventional FPP, MB + CS-FPP doubled the spatial coverage (MB + CS-FPP vs conventional FPP) without compromising the image quality (2.69 ± 0.26 vs 2.60 ± 0.30) or increasing the artifact level (2.60 ± 0.26 vs 2.52 ± 0.31).

CONCLUSION

Autocalibrated MB + CS-FPP improved the myocardial coverage and achieved comparable image quality with the same spatial resolution and scan time as conventional FPP and is a promising technique for clinical myocardial perfusion imaging.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 3.

Clinical and imaging characteristics of cardiac magnetic resonance presenting with myocardial infarction with non-obstructive coronary arteries in China

BACKGROUND

The characteristics are still unclear due to lack of systematic research on patients with myocardial infarction non-obstructive coronary arteries (MINOCA) in China. This study aimed to explore the clinical and imaging features of MINOCA patients.

METHODS

The patients who were diagnosed as suspected MI were studied. Cardiac magnetic resonance (CMR) was performed after coronary angiography or coronary computed tomographic angiography examination within one week. Myocardial infarction (MI) was determined by late gadolinium enhancement CMR.The patients with MI were divided into MINOCA and MICAD group according to whether the degree of coronary stenosis was greater than 50%. Cardiac function and imaging characteristics between the two groups were analyzed.

RESULTS

21 patients with MINOCA and 30 patients with myocardial infarction with obstructive coronary artery disease (MICAD) were analyzed. MINOCA patients were younger, and the electrocardiogram was commonly featured by non-ST-elevation. The parameters of left ventricular function were significantly different between the two groups including left ventricular ejection fraction, stroke volume, cardiac output, myocardial mass, and peak ejection rate (P < 0.05). Besides, MINOCA patients had smaller area of MI, less score of transmural extent, fewer involved segments. Furthermore, the transmural extent of MI in MINOCA patients was mainly grade I, that is, most of them were subendocardial MI, which was significantly negatively correlated with the amount of first-pass perfusion.

CONCLUSIONS

The clinical characteristics combined with imaging features of CMR may be effective to evaluate the cardiac function in order to make clinical decision for MINOCA patients in China.

Contrast-enhanced cine MR sequences in the assessment of myocardial hyperemia in acute myocarditis: can they help? A feasibility study

The study was designed to assess the accuracy of contrast-enhanced balanced steady-state free precession (cine-SSFP) CMR imaging sequences to exhibit myocardial hyperemia in acute myocarditis, which has for a long time been investigated in some centers using early gadolinium enhancement (EGE) sequence. Contrast-enhanced cine-SSFP (CESSFP) sequences were compared to precontrast cine-SSFP sequences to calculate the early cine-contrast enhancement in 36 consecutive patients with acute myocarditis and 36 controls matched for age and gender. Four-chamber views images were obtained in each subject before and after gadolinium injection. Absolute and relative left ventricular myocardial enhancement of the overall myocardium, then separately of the lateral wall and interventricular septum was analyzed in telediastole. Myocarditis patients displayed higher cine-SSFP absolute enhancement than controls (overall left ventricular myocardium 2.38 ± 0.33 vs 1.84 ± 0.31; lateral wall 2.45 ± 0.35 vs 1.83 ± 0.32; and septum 2.26 ± 0.29 vs 1.82 ± 0.29, p < 0.0001 for all). Less significant differences were observed for the relative enhancement (p < 0.05 for all). Using ROC curves, the optimal threshold value of absolute enhancement to diagnose acute myocarditis was 2.05 (sensitivity: 86%; specificity: 81%). Given the simplicity of use, contrast-enhanced cine-SSFP sequences should be used as an additional diagnostic tool to detect hyperemia in acute myocarditis patients.

A Slice-Low-Rank Plus Sparse (slice-L + S) Reconstruction Method for k-t Undersampled Multiband First-Pass Myocardial Perfusion MRI

PURPOSE

The synergistic use of k-t undersampling and multiband (MB) imaging has the potential to provide extended slice coverage and high spatial resolution for first-pass perfusion MRI. The low-rank plus sparse (L + S) model has shown excellent performance for accelerating single-band (SB) perfusion MRI.

METHODS

A MB data consistency method employing ESPIRiT maps and through-plane coil information was developed. This data consistency method was combined with the temporal L + S constraint to form the slice-L + S method. Slice-L + S was compared to SB L + S and the sequential operations of split slice-GRAPPA and SB L + S (seq-SG-L + S) using synthetic data formed from multislice SB images. Prospectively k-t undersampled MB data were also acquired and reconstructed using seq-SG-L + S and slice-L + S.

RESULTS

Using synthetic data with total acceleration rates of 6-12, slice-L + S outperformed SB L + S and seq-SG-L + S (N = 7 subjects) with respect to normalized RMSE and the structural similarity index (P < 0.05 for both). For the specific case with MB factor = 3 and rate 3 undersampling, or for SB imaging with rate 9 undersampling (N = 7 subjects), the normalized RMSE values were 0.037 ± 0.007, 0.042 ± 0.005, and 0.031 ± 0.004; and the structural similarity index values were 0.88 ± 0.03, 0.85 ± 0.03, and 0.89 ± 0.02 for SB L + S, seq-SG-L + S, and slice-L + S, respectively (P < 0.05 for both). For prospectively undersampled MB data, slice-L + S provided better image quality than seq-SG-L + S for rate 6 (N = 7) and rate 9 acceleration (N = 7) as scored by blinded experts.

CONCLUSION

Slice-L + S outperformed SB-L + S and seq-SG-L + S and provides 9 slice coverage of the left ventricle with a spatial resolution of 1.5 mm × 1.5 mm with good image quality.

Visualization of Concurrent Epicardial and Microvascular Coronary Artery Disease in a Patient with Systemic Lupus Erythematosus by Magnetic Resonance Imaging

ABSTRACT

We present a patient with history of systemic lupus erythematosus who presented with acute chest pain. Electrocardiography, invasive coronary angiography, and cardiac MRI were performed during the course of her evaluation. Invasive coronary angiography demonstrated obstructive disease in the diagonal system and cardiovascular MRI confirmed an anterior infarct consistent with the electrocardiographic findings. However, MRI also revealed focal inferoseptal hypoperfusion inconsistent with electrocardiographic and angiographic findings. Rather, these findings indicate the presence of concurrent microvascular coronary artery disease, which has a high prevalence among women with autoimmune disease.

Retrospective Detection and Suppression of Dark-Rim Artifacts in First-Pass Perfusion Cardiac MRI Enabled by Deep Learning

The dark-rim artifact (DRA) remains an important challenge in the routine clinical use of first-pass perfusion (FPP) cardiac magnetic resonance imaging (cMRI). The DRA mimics the appearance of perfusion defects in the subendocardial wall and reduces the accuracy of diagnosis in patients with suspected ischemic heart disease. The main causes for DRA are known to be Gibbs ringing and bulk motion of the heart. The goal of this work is to propose a deep-learning-enabled automatic approach for the detection of motion-induced DRAs in FPP cMRI datasets. To this end, we propose a new algorithm that can detect the DRA in individual time frames by analyzing multiple reconstructions of the same time frame (k-space data) with varying temporal windows. In addition to DRA detection, our approach is also capable of suppressing the extent and severity of DRAs as a byproduct of the same reconstruction-analysis process. In this proof-of-concept study, our proposed method showed a good performance for automatic detection of subendocardial DRAs in stress perfusion cMRI studies of patients with suspected ischemic heart disease. To the best of our knowledge, this is the first approach that performs deep-learning-enabled detection and suppression of DRAs in cMRI.Clinical Relevance- Our approach enables clinicians to provide a more accurate diagnosis of ischemic heart disease by detecting and suppressing subendocardial dark-rim artifacts in first-pass perfusion cMRI datasets.

Clinical Application of Dynamic Contrast Enhanced Perfusion Imaging by Cardiovascular Magnetic Resonance

Functionally significant coronary artery disease impairs myocardial blood flow and can be detected non-invasively by myocardial perfusion imaging. While multiple myocardial perfusion imaging modalities exist, the high spatial and temporal resolution of cardiovascular magnetic resonance (CMR), combined with its freedom from ionising radiation make it an attractive option. Dynamic contrast enhanced CMR perfusion imaging has become a well-validated non-invasive tool for the assessment and risk stratification of patients with coronary artery disease and is recommended by international guidelines. This article presents an overview of CMR perfusion imaging and its clinical application, with a focus on chronic coronary syndromes, highlighting its strengths and challenges, and discusses recent advances, including the emerging role of quantitative perfusion analysis.

Diagnostic Accuracy of Spiral Whole-Heart Quantitative Adenosine Stress Cardiovascular Magnetic Resonance With Motion Compensated L1-SPIRIT

BACKGROUND

Variable density spiral (VDS) pulse sequences with motion compensated compressed sensing (MCCS) reconstruction allow for whole-heart quantitative assessment of myocardial perfusion but are not clinically validated.

PURPOSE

Assess performance of whole-heart VDS quantitative stress perfusion with MCCS to detect obstructive coronary artery disease (CAD).

STUDY TYPE

Prospective cross sectional.

POPULATION

Twenty-five patients with chest pain and known or suspected CAD and nine normal subjects.

FIELD STRENGTH/SEQUENCE

Segmented steady-state free precession (SSFP) sequence, segmented phase sensitive inversion recovery sequence for late gadolinium enhancement (LGE) imaging and VDS sequence at 1.5 T for rest and stress quantitative perfusion at eight short-axis locations.

ASSESSMENT

Stenosis was defined as ≥50% by quantitative coronary angiography (QCA). Visual and quantitative analysis of MRI data was compared to QCA. Quantitative analysis assessed average myocardial perfusion reserve (MPR), average stress myocardial blood flow (MBF), and lowest stress MBF of two contiguous myocardial segments. Ischemic burden was measured visually and quantitatively.

STATISTICAL TESTS

Student's t-test, McNemar's test, chi-square statistic, linear mixed-effects model, and area under receiver-operating characteristic curve (ROC).

RESULTS

Per-patient visual analysis demonstrated a sensitivity of 84% (95% confidence interval [CI], 60%-97%) and specificity of 83% [95% CI, 36%-100%]. There was no significant difference between per-vessel visual and quantitative analysis for sensitivity (69% [95% CI, 51%-84%] vs. 77% [95% CI, 60%-90%], P = 0.39) and specificity (88% [95% CI, 73%-96%] vs. 80% [95% CI, 64%-91%], P = 0.75). Per-vessel quantitative analysis ROC showed no significant difference (P = 0.06) between average MPR (0.68 [95% CI, 0.56-0.81]), average stress MBF (0.74 [95% CI, 0.63-0.86]), and lowest stress MBF (0.79 [95% CI, 0.69-0.90]). Visual and quantitative ischemic burden measurements were comparable (P = 0.85).

DATA CONCLUSION

Whole-heart VDS stress perfusion demonstrated good diagnostic accuracy and ischemic burden evaluation. No significant difference was seen between visual and quantitative diagnostic performance and ischemic burden measurements.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

CMR for myocardial characterization in ischemic heart disease: state-of-the-art and future developments

Ischemic heart disease and its sequelae are one of the major contributors to morbidity and mortality worldwide. Over the last decades, technological developments have strengthened the role of noninvasive imaging for detection, risk stratification, and management of patients with ischemic heart disease. Cardiac magnetic resonance (CMR) imaging incorporates both functional and morphological characterization of the heart to determine presence, acuteness, and severity of ischemic heart disease by evaluating myocardial wall motion and function, the presence and extent of myocardial edema, ischemia, and scarring. Currently established clinical protocols have already demonstrated their diagnostic and prognostic value. Nevertheless, there are emerging imaging technologies that provide additional information based on advanced quantification of imaging biomarkers and improved diagnostic accuracy, therefore potentially allowing reduction or avoidance of contrast and/or stressor agents. The aim of this review is to summarize the current state of the art of CMR imaging for ischemic heart disease and to provide insights into promising future developments.

Impact of the Choice of Native T1 in Pixelwise Myocardial Blood Flow Quantification

BACKGROUND

Quantification of myocardial blood flow (MBF) from dynamic contrast-enhanced (DCE) MRI can be performed using a signal intensity model that incorporates T1 values of blood and myocardium.

PURPOSE

To assess the impact of T1 values on pixelwise MBF quantification, specifically to evaluate the influence of 1) study population-averaged vs. subject-specific, 2) diastolic vs. systolic, and 3) regional vs. global myocardial T1 values.

STUDY TYPE

Prospective.

SUBJECTS

Fifteen patients with chronic coronary heart disease.

FIELD STRENGTH/SEQUENCE

3T; modified Look-Locker inversion recovery for T1 mapping and saturation recovery gradient echo for DCE imaging, both acquired in a mid-ventricular short-axis slice in systole and diastole.

ASSESSMENT

MBF was estimated using Fermi modeling and signal intensity nonlinearity correction with different T1 values: study population-averaged blood and myocardial, subject-specific systolic and diastolic, and segmental T1 values. Myocardial segments with perfusion deficits were identified visually from DCE series.

STATISTICAL TESTS

The relationships between MBF parameters derived by different methods were analyzed by Bland-Altman analysis; corresponding mean values were compared by t-test.

RESULTS

Using subject-specific diastolic T1 values, global diastolic MBF was 0.61 ± 0.13 mL/(min·g). It did not differ from global MBF derived from the study population-averaged T1 (P = 0.88), but the standard deviation of differences was large (0.07 mL/(min·g), 11% of mean MBF). Global diastolic and systolic MBF did not differ (P = 0.12), whereas global diastolic MBF using systolic (0.62 ± 0.13 mL/(min·g)) and diastolic T1 values differed (P < 0.05). If regional instead of global T1 values were used, segmental MBF was lower in segments with perfusion deficits (bias = -0.03 mL/(min·g), -7% of mean MBF, P < 0.05) but higher in segments without perfusion deficits (bias = 0.01 mL/(min·g), 1% of mean MBF, P < 0.05).

DATA CONCLUSION

Whereas cardiac phase-specific T1 values have a minor impact on MBF estimates, subject-specific and myocardial segment-specific T1 values substantially affect MBF quantification.

LEVEL OF EVIDENCE

3 TECHNICAL EFFICACY STAGE: 3.

Comparison of two dipyridamole infusion protocols for myocardial perfusion imaging in subjects with low likelihood of significant obstructive coronary artery disease

BACKGROUND

Myocardial perfusion imaging (MPI) with positron emission tomography allows accurate measurements of myocardial blood flow (MBF). Stress MBF thresholds have been proposed to provide diagnostic and prognostic information in different pathology. Most studies relying on dipyridamole use a 5-minute infusion protocol, while current guidelines recommend a 4-minute infusion. The purpose of this study is to compare the effects of different dipyridamole infusion times on stress MBF.

METHODS

The charts of 2,207 patients who underwent rubidium-82 MPI were retrospectively reviewed and 147 subjects with low likelihood of significant coronary artery disease (CAD) defined as calcium score = 0, body mass index < 45 kg·m-2, and summed stress score ≤ 3 were included. Of those, 65 were imaged with a 4-minute dipyridamole infusion (0.56 mg·kg-1) protocol and 82 with a 5-minute protocol (0.70 mg·kg-1).

RESULTS

Stress MBF (3.23±0.76 vs 3.02±0.71 mL·min-1·g-1, P = 0.09), myocardial flow reserve (2.70±0.67 vs 2.85±0.74, P = 0.20), and coronary vascular resistance index (30±10 vs 31±9 mmHg × g × min·mL-1, P = 0.38) were not significantly different between the two protocols. The 5-minute protocol was associated with higher prevalence of symptoms (92.7% vs 81.5%, P = 0.04) and greater decrease in systolic blood pressure (- 9 vs - 6 mmHg, P = 0.03).

CONCLUSIONS

The 4-minute and 5-minute dipyridamole infusion protocols produce comparable myocardial flow response, hemodynamic changes, and symptoms, in subjects with low likelihood of significant obstructive CAD.

Cardiac magnetic resonance imaging myocardial perfusion reserve index in heart transplant patients

OBJECTIVE

To compare the myocardial perfusion reserve index (MPRI) measured during stress cardiac magnetic resonance imaging (MRI) with regadenoson in patients with heart transplants versus in patients without heart transplants.

MATERIAL AND METHODS

We retrospectively compared 20 consecutive asymptomatic heart transplant patients without suspicion of microvascular disease who underwent stress cardiac MRI with regadenoson and coronary computed tomography angiography (CTA) to rule out cardiac allograft vasculopathy versus 16 patients without transplants who underwent clinically indicated stress cardiac MRI who were negative for ischemia and had no signs of structural heart disease. We estimated MPRI semiquantitatively after calculating the up-slope of the first-pass enhancement curve and dividing the value obtained during stress by the value obtained at rest. We compared MPRI in the two groups. Patients with positive findings for ischemia on stress cardiac MRI or significant coronary stenosis on coronary CTA were referred for conventional coronary angiography.

RESULTS

More than half the patients remained asymptomatic during the stress test. Stress cardiac MRI was positive for ischemia in two heart transplant patients; these findings were confirmed at coronary CTA and at conventional coronary angiography. Patients with transplants had lower end-diastolic volume index (59.3±15.2 ml/m² vs. 71.4±15.9 ml/m² in those without transplants, p=0.03), lower MPRI (1.35±0.19 vs. 1.6±0.28 in those without transplants, p=0.003), and a less pronounced hemodynamic response to regadenoson (mean increase in heart rate 13.1±5.4 bpm vs. 28.5±8.9 bpm in those without transplants, p <0.001).

CONCLUSION

Stress cardiac MRI with regadenoson is safe. In the absence of epicardial coronary artery disease, patients with heart transplants have lower MPRI than patients without transplants, suggesting microvascular disease. The hemodynamic response to regadenoson is less pronounced in patients with heart transplants than in patients without heart transplants.

Perceived Dark Rim Artifact in First-Pass Myocardial Perfusion Magnetic Resonance Imaging Due to Visual Illusion

OBJECTIVE

To demonstrate that human visual illusion can contribute to sub-endocardial dark rim artifact in contrast-enhanced myocardial perfusion magnetic resonance images.

MATERIALS AND METHODS

Numerical phantoms were generated to simulate the first-passage of contrast agent in the heart, and rendered in conventional gray scale as well as in color scale with reduced luminance variation. Cardiac perfusion images were acquired from two healthy volunteers, and were displayed by the same gray and color scales used in the numerical study. Before and after k-space windowing, the left ventricle (LV)-myocardium boarders were analyzed visually and quantitatively through intensity profiles perpendicular the boarders.

RESULTS

k-space windowing yielded monotonically decreasing signal intensity near the LV-myocardium boarder in the phantom images, as confirmed by negative finite difference values near the board ranging -1.07 to -0.14. However, the dark band still appears, which is perceived by visual illusion. Dark rim is perceived in the in-vivo images after k-space windowing that removed the quantitative signal dip, suggesting that the perceived dark rim is a visual illusion. The perceived dark rim is stronger at peak LV enhancement than the peak myocardial enhancement, due to the larger intensity difference between LV and myocardium. In both numerical phantom and in-vivo images, the illusory dark band is not visible in the color map due to reduced luminance variation.

CONCLUSION

Visual illusion is another potential cause of dark rim artifact in contrast-enhanced myocardial perfusion MRI as demonstrated by illusory rim perceived in the absence of quantitative intensity undershoot.

Extended quantitative dynamic contrast-enhanced cardiac perfusion imaging in mice using accelerated data acquisition and spatially distributed, two-compartment exchange modeling

The objective of the present work was to improve data acquisition and quantification of dynamic contrast-enhanced perfusion imaging in the in vivo murine heart. Four-fold undersampled data were acquired in 14 mice and reconstructed using k-t SPARSE. A two-compartment exchange model was employed to provide additional characterization of myocardial tissue based on compartment volumes and the permeability surface area product. The feasibility of the proposed method was tested using compartment-based analysis of contrast-enhanced perfusion data acquired with intravascular and extracellular contrast agents. A significantly different permeability surface area product was measured for the intravascular versus extracellular contrast agent (0.13-0.15 ml/g/min vs 0.86-0.88 ml/g/min). The reduced extravasation also resulted in significantly smaller interstitial volumes of the intravascular versus extracellular agent (9.8-11% vs 45-47%). No difference was found for myocardial blood flow (6.5-7.2 ml/g/min vs 6.0-7.0 ml/g/min). The results presented here show that two-compartment exchange modeling in the in vivo murine heart is feasible and gives access to tissue parameters beyond myocardial blood flow.

Long-Term Prognostic Value of Stress Perfusion Cardiovascular Magnetic Resonance Imaging

PURPOSE OF REVIEW

The purpose of this review is to analyze the long-term prognostic value of stress perfusion cardiovascular magnetic resonance (CMR) in patients with suspected or known coronary artery disease (CAD).

RECENT FINDINGS

Stress perfusion CMR provides high diagnostic accuracy for detection of CAD, with high sensitivity and relatively lower specificity. A normal stress perfusion CMR examination is highly predictive of overall low patient risk. Conversely, abnormal stress perfusion CMR results are associated with mortality and increased risk for adverse cardiac-related events. Stress perfusion CMR is a useful and robust tool for risk reclassification across different CAD risk categories, and most significant for patients of intermediate risk. Stress CMR is reliable for excluding clinically significant coronary artery disease in patients presenting with low-risk acute chest pain. An ischemic burden threshold of less than 1.5 cardiac segments has been found to be most appropriate for safe deferral from revascularization therapy. A stress perfusion CMR-guided strategy has been shown to be noninferior compared to fractional flow reserve (FFR) for revascularization in patients with stable CAD. In clinical practice, CMR offers a multiplicity of useful techniques besides stress perfusion which may add significant prognostic value when combined with the findings of the stress test itself. Stress perfusion CMR is an accurate noninvasive diagnostic test for patients with suspected CAD and provides strong prognostic value across different risk categories.

Complete Free-breathing Adenosine Stress Cardiac MRI Using Compressed Sensing and Motion Correction: Comparison of Functional Parameters, Perfusion, and Late Enhancement with the Standard Breath-holding Examination

PURPOSE

To compare free-breathing (FB) stress cardiac MRI examinations with the reference standard breath-holding (BH) examination.

MATERIALS AND METHODS

A total of 40 consecutive patients were enrolled prospectively and were examined with 3-T MRI. Functional imaging, perfusion, and late gadolinium enhancement (LGE) sequences were performed in BH and FB by using compressed sensing and in-line motion correction. Left ventricle (LV) and right ventricle (RV) functional parameters in BH and FB examinations were compared by using Bland-Altman plots and linear mixed models. Subjective image quality was assessed with a five-point scale (1 = nondiagnostic, 5 = very good). For perfusion and LGE imaging, diagnostic confidence was rated with a three-point scale (1 = low, 3 = high), and image quality was rated with a five-point scale (1 = nondiagnostic, 5 = very good). The Wilcoxon test was used to compare image quality and diagnostic confidence.

RESULTS

Bland-Altman plots showed good agreement for LV and RV functional parameters in BH and FB sequences. Subjective image quality was significantly better with the BH sequences in the LV (P < .01) but was comparable in the RV (P > .99). Scanning time was 218 seconds (range, 130-385 seconds) for cine BH and 16 seconds (range, 11-27 seconds) for cine FB. Extent of perfusion defects, LGE, and diagnostic confidence was comparable between groups. Scanning time was 371 seconds (range, 239-502 seconds) for the LGE BH sequence and 189 seconds (range, 122-286 seconds) for the LGE FB sequence.

CONCLUSION

FB adenosine stress cardiac MRI delivers diagnostic image quality and could represent an alternative for use in patients who are unable to meet the demands of multiple BHs and long examination times.© RSNA, 2019.

Simulation of the Perfusion of Contrast Agent Used in Cardiac Magnetic Resonance: A Step Toward Non-invasive Cardiac Perfusion Quantification

This work presents a new mathematical model to describe cardiac perfusion in the myocardium as acquired by cardiac magnetic resonance (CMR) perfusion exams. The combination of first pass (or contrast-enhanced CMR) and late enhancement CMR is a widely used non-invasive exam that can identify abnormal perfused regions of the heart via the use of a contrast agent (CA). The exam provides important information to the diagnosis, management, and prognosis of ischemia and infarct: perfusion on different regions, the status of microvascular structures, the presence of fibrosis, and the relative volume of extracellular space. This information is obtained by inferring the spatiotemporal dynamics of the contrast in the myocardial tissue from the acquired images. The evaluation of these physiological parameters plays an important role in the assessment of myocardial viability. However, the nature of cardiac physiology poses great challenges in the estimation of these parameters. Briefly, these are currently estimated qualitatively via visual inspection of images and comparison of relative brightness between different regions of the heart. Therefore, there is a great urge for techniques that can help to quantify cardiac perfusion. In this work, we propose a new mathematical model based on multidomain flow in porous media. The model is based on a system of partial differential equations. Darcy's law is used to obtain the pressure and velocity distribution. CA dynamics is described by reaction-diffusion-advection equations in the intravascular space and in the interstitial space. The interaction of fibrosis and the CA is also considered. The new model treats the domains as anisotropic media and imposes a closed loop of intravascular flow, which is necessary to reproduce the recirculation of the CA. The model parameters were adjusted to reproduce clinical data. In addition, the model was used to simulate different scenarios: normal perfusion; endocardial ischemia due to stenosis in a coronary artery in the epicardium; and myocardial infarct. Therefore, the computational model was able to correlate anatomical features, stenosis and the presence of fibrosis, with functional ones, cardiac perfusion. Altogether, the results suggest that the model can support the process of non-invasive cardiac perfusion quantification.

Haemodynamic effects of pharmacologic stress with adenosine in patients with left ventricular systolic dysfunction

BACKGROUND

In patients with heart failure, downregulation of adenosine receptor gene expression and impaired adenosine-related signal transduction may result in a diminished response to adenosine. This may have implications for cardiac stress testing. We evaluated the haemodynamic response to intravenous adenosine in patients with left ventricular systolic dysfunction (LVSD) undergoing stress cardiovascular magnetic resonance imaging (CMR).

METHODS AND RESULTS

We retrospectively examined 497 consecutive patients referred for clinical stress CMR. Blood pressure and heart rate responses with intravenous adenosine were compared in patients with normal, mild-moderately impaired and severely impaired LV systolic function (ejection fraction [EF] > 55%, 36-55% and < 35%, respectively). Following 2 min of adenosine infusion, there was a significant difference between the groups in the heart rate change from baseline, with a diminished heart rate response in patients with LVSD (p < 0.001). An increase in the dose of adenosine (up to 210 μg/kg/min) was required to achieve a sufficient haemodynamic response in more patients with severe LVSD (41%) than those with mild-moderately impaired and normal LV systolic function (24% and 19%, respectively, p < 0.001). Even with increased doses of adenosine in subjects with severe LVSD, peak haemodynamic response remained blunted. With multivariate analysis age (p < 0.001) and LVEF (p = 0.031) were independent predictors of heart rate response to adenosine.

CONCLUSION

Patients with reduced LVEF referred for stress CMR may have a blunted heart rate response to adenosine. Further study is warranted to determine whether this may be associated with reduced diagnostic accuracy and also the potential utility of further dose increases or alternative stressors.

Quantitative myocardial first-pass cardiovascular magnetic resonance perfusion imaging using hyperpolarized [1-13C] pyruvate

BACKGROUND

The feasibility of absolute myocardial blood flow quantification and suitability of hyperpolarized [1-13C] pyruvate as contrast agent for first-pass cardiovascular magnetic resonance (CMR) perfusion measurements are investigated with simulations and demonstrated in vivo in a swine model.

METHODS

A versatile simulation framework for hyperpolarized CMR subject to physical, physiological and technical constraints was developed and applied to investigate experimental conditions for accurate perfusion CMR with hyperpolarized [1-13C] pyruvate. Absolute and semi-quantitative perfusion indices were analyzed with respect to experimental parameter variations and different signal-to-noise ratio (SNR) levels. Absolute myocardial blood flow quantification was implemented with an iterative deconvolution approach based on Fermi functions. To demonstrate in vivo feasibility, velocity-selective excitation with an echo-planar imaging readout was used to acquire dynamic myocardial stress perfusion images in four healthy swine. Arterial input functions were extracted from an additional image slice with conventional excitation that was acquired within the same heartbeat.

RESULTS

Simulations suggest that obtainable SNR and B0 inhomogeneity in vivo are sufficient for the determination of absolute and semi-quantitative perfusion with ≤25% error. It is shown that for expected metabolic conversion rates, metabolic conversion of pyruvate can be neglected over the short duration of acquisition in first-pass perfusion CMR. In vivo measurements suggest that absolute myocardial blood flow quantification using hyperpolarized [1-13C] pyruvate is feasible with an intra-myocardial variability comparable to semi-quantitative perfusion indices.

CONCLUSION

The feasibility of quantitative hyperpolarized first-pass perfusion CMR using [1-13C] pyruvate has been investigated in simulations and demonstrated in swine. Using an approved and metabolically active compound is envisioned to increase the value of hyperpolarized perfusion CMR in patients.

Association of cardiovascular risk factors on myocardial perfusion and fibrosis in asymptomatic individuals: cardiac magnetic resonance study

Background Myocardial perfusion reserve index (MPRI) and extracellular volume fraction (ECV) on cardiac magnetic resonance (CMR) are known to quantify coronary microvascular dysfunction and myocardial fibrosis, respectively. Purpose To demonstrate that cardiovascular risk factors such as hypertension, diabetes, hyperlipidemia, and smoking are correlated with MPRI and ECV on CMR in asymptomatic individuals. Material and Methods Between October 2013 and July 2014, 196 individuals underwent CMR. After excluding those with chest pain, arrhythmia, and obstructive coronary artery disease, participants were divided into five groups: those without risk factor (n = 26) and those with one (n = 43), two (n = 35), three (n = 24), or four (n = 6) risk factors. MPRI and ECV were obtained on perfusion CMR and pre- and post-T1 mapping, respectively. Results A total of 134 asymptomatic individuals (109 men, 25 women; mean age = 54.4 ± 7.08 years; body mass index [BMI] = 24.96 ± 2.76 kg/m²; Framingham risk score [FRS] = 7.71 ± 5.21) were included. The Jonckheere-Terpstra test demonstrated trends of increasing BMI, FRS, and left ventricular mass index (all P values < 0.001), but decreasing MPRI ( P = 0.001) with increasing numbers of risk factors. Stepwise multiple linear regression demonstrated that an increasing number of cardiovascular risk factors was an independent predictor of MPRI ( P = 0.001). However, there was no significant association between the number of risk factors and ECV ( P = 0.99). Conclusion We demonstrated that an increasing number of cardiovascular risk factors is significantly associated with reduced MPRI, but not with ECV on CMR.

Assessment of Myocardial Perfusion at Rest and During Stress Using Dynamic First-Pass Contrast-Enhanced Magnetic Resonance Imaging in Healthy Dogs

Objective: To assess the feasibility of myocardial perfusion analysis in healthy dogs using dynamic contrast-enhanced cardiac magnetic resonance (DCE-MR) imaging at rest and during simulated stress with two doses of adenosine.

Animals: Ten healthy beagle dogs.

Procedures: Dogs were anesthetized and positioned in dorsal recumbency in a 3.0 Tesla MR scanner. Electrocardiogram-triggered dynamic T1-weighted ultrafast gradient echo images of three slices in short-axis orientation of the heart were acquired during breath holds and the first pass of gadolinium contrast. Image acquisition was performed after 4 min infusion of 140 μg/kg/min and 280 μg/kg/min adenosine and, after a washout period, without adenosine, respectively. Images were processed by dividing each slice into 6 radial segments and perfusion analysis was performed from signal intensity-time data.

Results: No differences in perfusion parameters were found between segments within any of the slices, but significant differences were found between slices for peak enhancement, accumulated enhancement, and the maximum upslope. In addition, significant differences were found within each slice between data at rest and during adenosine-induced stress for the relative and absolute maximum upslope, relative peak enhancement, time to peak, and accumulated enhancement although inter-individual variation was large and no difference was found between the two stress tests for some parameters.

Conclusion and Clinical Relevance: Results of this study showed that rest and stress myocardial perfusion can be assessed using DCE-CMR in dogs using the methods described. Both, adenosine dose and slice appear to affect perfusion parameters in healthy dogs and individual response to adenosine was variable.

Incremental Value of Magnetic Resonance Imaging in Further Characterizing Hypodense Mediastinal and Paracardiac Lesions Identified on Computed Tomography

Mediastinal and paracardiac lesions are usually first diagnosed on a chest radiograph or echocardiogram. Often, a computed tomography is obtained to further delineate these lesions. CT may be suboptimal for evaluation of enhancement characteristics and direct extension into the adjacent mediastinal structures. With its intrinsic superior soft-tissue characterization, magnetic resonance imaging (MRI) can better delineate these lesions, their internal tissue characteristics, and identify adhesion/invasion into adjacent structures. This pictorial essay provides a brief synopsis of the key MRI sequences and their utility in further characterizing mediastinal and paracardiac lesions.

Impact of incomplete ventricular coverage on diagnostic performance of myocardial perfusion imaging

In the context of myocardial perfusion imaging (MPI) with cardiac magnetic resonance (CMR), there is ongoing debate on the merits of using technically complex acquisition methods to achieve whole-heart spatial coverage, rather than conventional 3-slice acquisition. An adequately powered comparative study is difficult to achieve given the requirement for two separate stress CMR studies in each patient. The aim of this work is to draw relevant conclusions from SPECT MPI by comparing whole-heart versus simulated 3-slice coverage in a large existing dataset. SPECT data from 651 patients with suspected coronary artery disease who underwent invasive angiography were analyzed. A computational approach was designed to model 3-slice MPI by retrospective subsampling of whole- heart data. For both whole-heart and 3-slice approaches, the diagnostic performance and the stress total perfusion deficit (TPD) score-a measure of ischemia extent/severity-were quantified and compared. Diagnostic accuracy for the 3-slice and whole-heart approaches were similar (area under the curve: 0.843 vs. 0.855, respectively; P = 0.07). The majority (54%) of cases missed by 3-slice imaging had primarily apical ischemia. Whole-heart and 3-slice TPD scores were strongly correlated (R² = 0.93, P < 0.001) but 3-slice TPD showed a small yet significant bias compared to whole-heart TPD (- 1.19%; P < 0.0001) and the 95% limits of agreement were relatively wide (- 6.65% to 4.27%). Incomplete ventricular coverage typically acquired in 3-slice CMR MPI does not significantly affect the diagnostic accuracy. However, 3-slice MPI may fail to detect severe apical ischemia and underestimate the extent/severity of perfusion defects. Our results suggest that caution is required when comparing the ischemic burden between 3-slice and whole-heart datasets, and corroborate the need to establish prognostic thresholds specific to each approach.

Applications of cardiac magnetic resonance imaging in sickle cell disease

Cardiac magnetic resonance imaging (CMR) has evolved from an effective research tool to a non-invasive clinical modality with versatile applications. The accuracy of volume measurements and functional assessment and the ability to identify unique myocardial tissue characteristics non-invasively are the primary advantages of CMR. The use of CMR in sickle cell disease (SCD) has been limited clinically to myocardial iron assessment. The use of other CMR applications to characterize the cardiac pathology in SCD is slowly emerging but remains limited to research level. In this review, we discuss some of the applications of CMR in studying cardiovascular diseases and its potential uses in SCD for research and clinical purposes.

Recent Advances in Cardiovascular Magnetic Resonance: Techniques and Applications

Cardiovascular magnetic resonance imaging has become the gold standard for evaluating myocardial function, volumes, and scarring. Additionally, cardiovascular magnetic resonance imaging is unique in its comprehensive tissue characterization, including assessment of myocardial edema, myocardial siderosis, myocardial perfusion, and diffuse myocardial fibrosis. Cardiovascular magnetic resonance imaging has become an indispensable tool in the evaluation of congenital heart disease, heart failure, cardiac masses, pericardial disease, and coronary artery disease. This review will highlight some recent novel cardiovascular magnetic resonance imaging techniques, concepts, and applications.

Hyperpolarized 13C urea myocardial first-pass perfusion imaging using velocity-selective excitation

BACKGROUND

A velocity-selective binomial excitation scheme for myocardial first-pass perfusion measurements with hyperpolarized 13C substrates, which preserves bolus magnetization inside the blood pool, is presented. The proposed method is evaluated against gadolinium-enhanced 1H measurements in-vivo.

METHODS

The proposed excitation with an echo-planar imaging readout was implemented on a clinical CMR system. Dynamic myocardial stress perfusion images were acquired in six healthy pigs after bolus injection of hyperpolarized 13C urea with the velocity-selective vs. conventional excitation, as well as standard 1H gadolinium-enhanced images. Signal-to-noise, contrast-to-noise (CNR) and homogeneity of semi-quantitative perfusion measures were compared between methods based on first-pass signal-intensity time curves extracted from a mid-ventricular slice. Diagnostic feasibility is demonstrated in a case of septal infarction.

RESULTS

Velocity-selective excitation provides over three-fold reduction in blood pool signal with a two-fold increase in myocardial CNR. Extracted first-pass perfusion curves reveal a significantly reduced variability of semi-quantitative first-pass perfusion measures (12-20%) for velocity-selective excitation compared to conventional excitation (28-93%), comparable to that of reference 1H gadolinium data (9-15%). Overall image quality appears comparable between the velocity-selective hyperpolarized and gadolinium-enhanced imaging.

CONCLUSION

The feasibility of hyperpolarized 13C first-pass perfusion CMR has been demonstrated in swine. Comparison with reference 1H gadolinium data revealed sufficient data quality and indicates the potential of hyperpolarized perfusion imaging for human applications.

Coronary calcification compromises myocardial perfusion irrespective of luminal stenosis

Aim

The aim of this study was to evaluate the relationship between coronary artery calcification (CAC) assessed by multi-detector computed tomography (MDCT) and myocardial perfusion assessed by cardiac magnetic resonance imaging (CMR) in a group of symptomatic patients.

Method

Retrospective analysis of 120 patients (age 65.1 ± 8.9 years, 88 males) who presented with atypical chest pain to Bethanien Hospital, Frankfurt, Germany, between 2007 and 2010 and who underwent CAC scoring using MDCT, CMR, and conventional coronary angiography. Patients were divided into those with high-grade (HG) stenosis (n = 67, age 65.1 ± 9.4 years) and those with no-HG stenosis (n = 53, age 65.1 ± 8.6 years).

Results

There were more males with HG stenosis (82.1% vs. 62.3%, p = 0.015), in whom the percentage and number of abnormal perfusion segments were higher at rest (37.3% vs. 17%, p = 0.014) but not different with stress (p = 0.83) from those with no-HG stenosis. Thirty-four patients had myocardial perfusion abnormalities at rest and 26 patients developed perfusion defects with stress. Stress-induced myocardial perfusion defects were 22.4% sensitive and 79.2% specific for detecting HG stenosis. The CAC score was lower in patients with no-HG stenosis compared to those with HG stenosis (p < 0.0001). On the ROC curve, a CAC score of 293 had a sensitivity of 71.6% and specificity of 83% in predicting HG stenosis [(AUC 0.80 (p < 0.0001)]. A CAC score of 293 or the presence of at least 1 segment myocardial perfusion abnormality was 74.6% sensitive and 71.7% specific in detecting HG stenosis, the respective values for the 2 abnormalities combined being 19.4% and 90.6%. The severity of CAC correlated with the extent of myocardial perfusion in the patient group as a whole with stress (r = 0.22, p = 0.015), particularly in those with no-HG stenosis (r = 0.31, p = 0.022). A CAC score of 293 was 31.6% sensitive and 87.3% specific in detecting myocardial perfusion abnormalities.

Conclusion

In a group of patients with exertional angina, coronary calcification is more accurate in detecting high-grade luminal stenosis than myocardial perfusion defects. In addition, in patients with no stenosis, the incremental relationship between coronary calcium score and the extent of myocardial perfusion suggests coronary wall hardening as an additional mechanism for stress-induced angina other than luminal narrowing. These preliminary findings might have a clinical impact on management strategies of these patients other than conventional therapy.

Effect of pulmonary hyperinflation on central blood volume: An MRI study

Pulmonary hyperinflation attained by glossopharyngeal insufflation (GPI) challenges the circulation by compressing the heart and pulmonary vasculature. Our aim was to determine the amount of blood translocated from the central blood volume during GPI. Cardiac output and cardiac chamber volumes were assessed by magnetic resonance imaging in twelve breath-hold divers at rest and during apnea with GPI. Pulmonary blood volume was determined from pulmonary blood flow and transit times for gadolinium during first-pass perfusion after intravenous injection. During GPI, the lung volume increased by 0.8±0.6L (11±7%) above the total lung capacity. All cardiac chambers decreased in volume and despite a heart rate increase of 24±29 bpm (39±50%), pulmonary blood flow decreased by 2783±1820mL (43±20%). The pulmonary transit time remained unchanged at 7.5±2.2s and pulmonary blood volume decreased by 354±176mL (47±15%). In total, central blood volume decreased by 532±248mL (46±14%). Voluntary pulmonary hyperinflation leads to ∼50% decrease in pulmonary and central blood volume.

Gadolinium-based contrast agents in pediatric magnetic resonance imaging

Gadolinium-based contrast agents can increase the accuracy and expediency of an MRI examination. However the benefits of a contrast-enhanced scan must be carefully weighed against the well-documented risks associated with administration of exogenous contrast media. The purpose of this review is to discuss commercially available gadolinium-based contrast agents (GBCAs) in the context of pediatric radiology. We discuss the chemistry, regulatory status, safety and clinical applications, with particular emphasis on imaging of the blood vessels, heart, hepatobiliary tree and central nervous system. We also discuss non-GBCA MRI contrast agents that are less frequently used or not commercially available.

Myocardial stress perfusion magnetic resonance: initial experience in a pediatric and young adult population using regadenoson

BACKGROUND

Dipyridamole and adenosine are traditional pharmacological stressors for myocardial perfusion. Regadenoson, a selective adenosine A2A agonist, has a lower side effect profile with lower incidence of bronchospasm and bradycardia. There is a growing need for myocardial perfusion assessment within pediatrics. There is no report on the utility of regadenoson as a stress agent in children.

OBJECTIVE

To observe the safety and feasibility of regadenoson as a pharmacologic stressor for perfusion cardiac MR in a pilot cohort of pediatric patients weighing more than 40 kg who have congenital heart disease and pediatric acquired heart disease.

MATERIALS AND METHODS

We reviewed our initial experience with regadenoson stress cardiac MR in 31 pediatric patients 15.8 ± 1.7 years (range 12-22 years) with congenital heart disease and acquired heart disease. Mean patient weight was 60 ± 15 kg (range of 40-93 kg). All patients underwent cardiac MR because of concern for ischemia. The cohort included a heterogeneous group of patients at a pediatric institution with potential risk for ischemia. Subjects' heart rate and blood pressure were monitored and pharmacologic stress was induced by injection of 400 mcg of regadenoson. We evaluated their hemodynamic response and adverse effects using changes in vital signs and onset of symptoms. A pediatric cardiologist and radiologist qualitatively assessed myocardial perfusion and viability images.

RESULTS

One child was unable to complete the stress perfusion portion of the examination, but did complete the remaining portion of the CMR. Resting heart rate was 72 ± 14 beats per minute (bpm) and rose to peak of 124 ± 17 bpm (95 ± 50% increase, P < 0.005) with regadenoson. Image quality was considered good or diagnostic in all cases. Three patients had irreversible perfusion defects. Four patients had reversible perfusion defects. Nine of the patients underwent cardiac catheterization with angiography and the findings showed excellent agreement.

CONCLUSION

Regadenoson might be a safe and feasible pharmacologic stress agent for use in cardiac MR in older pediatric patients with congenital heart disease and acquired heart disease. The ease of use as a bolus and the advantage of a prolonged hyperemia make its use appealing in pediatrics. In a limited number of cases, regadenoson stress perfusion showed excellent agreement with cardiac catheterization. Regadenoson might be a viable pharmacologic stress agent in this population.

Cardiac Imaging in Heart Failure with Comorbidities

Imaging modalities stand at the frontiers for progress in congestive heart failure (CHF) screening, risk stratification and monitoring. Advancements in echocardiography (ECHO) and Magnetic Resonance Imaging (MRI) have allowed for improved tissue characterizations, cardiac motion analysis, and cardiac performance analysis under stress. Common cardiac comorbidities such as hypertension, metabolic syndromes and chronic renal failure contribute to cardiac remodeling, sharing similar pathophysiological mechanisms starting with interstitial changes, structural changes and finally clinical CHF. These imaging techniques can potentially detect changes earlier. Such information could have clinical benefits for screening, planning preventive therapies and risk stratifying patients. Imaging reports have often focused on traditional measures without factoring these novel parameters. This review is aimed at providing a synopsis on how we can use this information to assess and monitor improvements for CHF with comorbidities.

Stress perfusion magnetic resonance imaging to detect coronary artery lesions in children

BACKGROUND

Stress perfusion cardiovascular magnetic resonance (CMR) is used widely in adult ischemic heart disease, but data in children is limited. We sought to evaluate feasibility, accuracy and prognostic value of stress CMR in children with suspected coronary artery disease (CAD).

METHODS

Stress CMR was reviewed from two pediatric centers over 5 years using a standard pharmacologic protocol. Wall motion abnormalities, perfusion deficits and late enhancement were correlated with coronary angiogram (CAG) when available, and clinical status at 1 year follow-up for major adverse cardiovascular events (MACE; coronary revascularization, non-fatal myocardial infarction and death due to CAD) was recorded.

RESULTS

Sixty-four stress perfusion CMR studies in 48 children (10.9 ± 4.8 years) using adenosine; 59 (92%) and dipyridamole; 5 (8%), were reviewed. Indications were Kawasaki disease (39%), post arterial switch operation (12.5%), post heart transplantation (12.5%), post anomalous coronary artery repair (11%), chest pain (11%), suspected myocarditis or CAD (3%), post coronary revascularization (3%), and others (8%). Twenty-six studies were performed under sedation. Of all studies performed, 66% showed no evidence of ischemia or infarction, 28% had perfusion deficits and 6% had late gadolinium enhancement (LGE) without perfusion deficit. Compared to CAG, the positive predictive value (PPV) of stress CMR was 80% with negative predictive value (NPV) of 88%. At 1 year clinical follow-up, the PPV and NPV of stress CMR to predict MACE were 78 and 98%.

CONCLUSION

Stress-perfusion CMR, in combination with LGE and wall motion-analysis is a feasible and an accurate method of diagnosing CAD in children. In difficult cases, it also helps guide clinical intervention by complementing conventional CAG with functional information.

Imaging Techniques for the Assessment of Myocardial Perfusion

One of the most significant causes of heart failure is coronary heart disease and subsequent left ventricular dysfunction. The prognosis and perioperative mortality are influenced by left ventricular function, which is also an important predictor marker following revascularization. The evaluation of myocardial perfusion is of utmost importance in patients who present several symptoms before choosing cardiac catheterization as treatment. The evaluation of myocardial perfusion and myocardial viability leads to superior diagnostic and treatment algorithms, thus resulting in an important improvement in the outcomes of patients with coronary artery disease. Color Doppler myocardial imaging, single-photon emission computed tomography (SPECT), contrast perfusion echocardiography, positron emission computed tomography (PET) and magnetic resonance imaging (MRI) are currently used methods for assessing myocardial perfusion. This review aims to summarize the benefits and disadvantages of each of these techniques.

Breathing Maneuvers as a Vasoactive Stimulus for Detecting Inducible Myocardial Ischemia - An Experimental Cardiovascular Magnetic Resonance Study

BACKGROUND

Breathing maneuvers can elicit a similar vascular response as vasodilatory agents like adenosine; yet, their potential diagnostic utility in the presence of coronary artery stenosis is unknown. The objective of the study is to investigate if breathing maneuvers can non-invasively detect inducible ischemia in an experimental animal model when the myocardium is imaged with oxygenation-sensitive cardiovascular magnetic resonance (OS-CMR).

METHODS AND FINDINGS

In 11 anesthetised swine with experimentally induced significant stenosis (fractional flow reserve <0.75) of the left anterior descending coronary artery (LAD) and 9 control animals, OS-CMR at 3T was performed during two different breathing maneuvers, a long breath-hold; and a combined maneuver of 60s of hyperventilation followed by a long breath-hold. The resulting change of myocardial oxygenation was compared to the invasive measurements of coronary blood flow, blood gases, and oxygen extraction. In control animals, all breathing maneuvers could significantly alter coronary blood flow as hyperventilation decreased coronary blood flow by 34±23%. A long breath-hold alone led to an increase of 97±88%, while the increase was 346±327% (p<0.001), when the long breath-hold was performed after hyperventilation. In stenosis animals, the coronary blood flow response was attenuated after both hyperventilation and the following breath-hold. This was matched by the observed oxygenation response as breath-holds following hyperventilation consistently yielded a significant difference in the signal of the MRI images between the perfusion territory of the stenosis LAD and remote myocardium. There was no difference between the coronary territories during the other breathing maneuvers or in the control group at any point.

CONCLUSION

In an experimental animal model, the response to a combined breathing maneuver of hyperventilation with subsequent breath-holding is blunted in myocardium subject to significant coronary artery stenosis. This maneuver may allow for detecting severe coronary artery stenosis and have a significant clinical potential as a non-pharmacological method for diagnostic testing in patients with suspected coronary artery disease.

The role of stress cardiac magnetic resonance in women

Coronary artery disease (CAD) is the leading cause of death in women. Nevertheless, extensive evidence demonstrates under-diagnosis and under-treatment of women for suspected or known ischemic heart disease (IHD). Stress cardiac magnetic resonance (CMR) is becoming readily available and offers significant advantages over other stress imaging modalities. The high spatial and temporal resolution of CMR provides the unique ability to identify subendocardial ischemia, viability, and the presence of microvascular disease. Furthermore, CMR is free from ionizing radiation, and image quality is not compromised by attenuation artifacts or patient size. Over the past two decades, evidence-based data have demonstrated the high diagnostic and prognostic performance of stress CMR in the context of IHD, often superior to other stress imaging techniques. Importantly, ad hoc studies confirmed these results in women with known or suspected IHD. Stress CMR warrants consideration as the modality of choice for women requiring an imaging test for ischemia given its strong evidence base, superior test characteristics, comprehensive nature, and unique ability to characterize both epicardial and microvascular disease.

Prognostic Benefit of Cardiac Magnetic Resonance Over Transthoracic Echocardiography for the Assessment of Ischemic and Nonischemic Dilated Cardiomyopathy Patients Referred for the Evaluation of Primary Prevention Implantable Cardioverter–Defibrillator Therapy

Background—

The aim of this study was to determine the prognostic benefit of cardiac magnetic resonance (CMR) over transthoracic echocardiography (TTE) in ischemic cardiomyopathy and nonischemic dilated cardiomyopathy patients evaluated for primary prevention implantable cardioverter–defibrillator therapy.

Methods and Results—

We enrolled 409 consecutive ischemic and dilated cardiomyopathy patients (mean age: 64±12 years; 331 men). All patients underwent TTE and CMR, and left ventricle end-diastolic volume, left ventricle end-systolic volume, and left ventricle ejection fraction (LVEF) were evaluated. In addition, late gadolinium enhancement was also assessed. All patients were followed up for major adverse cardiac events (MACE) defined as a composite end point of long runs of nonsustained ventricular tachycardia, sustained ventricular tachycardia, aborted sudden cardiac death, or sudden cardiac death. The median follow-up was 545 days. CMR showed higher left ventricle end-diastolic volume (mean difference: 43±22.5 mL), higher left ventricle end-systolic volume (mean difference: 34±20.5 mL), and lower LVEF (mean difference: −4.9±10%) as compared to TTE ( P <0.01). MACE occurred in 103 (25%) patients. Patients experiencing MACE showed higher left ventricle end-diastolic volume, higher left ventricle end-systolic volume, and lower LVEF with both imaging modalities and higher late gadolinium enhancement per-patient prevalence as compared to patients without MACE. At multivariable analysis, CMR-LVEF ≤35% (hazard ratio=2.18 [1.3–3.8]) and the presence of late gadolinium enhancement (hazard ratio=2.2 [1.4–3.6]) were independently associated with MACE ( P <0.01). A model based on CMR-LVEF ≤35% or CMR-LVEF ≤35% plus late gadolinium enhancement detection showed a higher performance in the prediction of MACE as compared to TTE-LVEF resulting in net reclassification improvement of 0.468 (95% confidence interval, 0.283–0.654; P <0.001) and 0.413 (95% confidence interval, 0.23–0.63; P <0.001), respectively.

Conclusions—

CMR provides additional prognostic stratification as compared to TTE, which may have direct impact on the indication of implantable cardioverter–defibrillator implantation.

A look-locker acquisition scheme for quantitative myocardial perfusion imaging with FAIR arterial spin labeling in humans at 3 tesla

PURPOSE

A novel method for quantitative measurement of myocardial blood flow (MBF) using arterial spin labeling (ASL) in a single breath-hold is presented, evaluated by simulations, phantom studies and in vivo studies and tested for reproducibility and variability.

METHODS

A flow-sensitive alternating inversion recovery (FAIR) ASL method with Look-Locker readout (LL-FAIR-ASL) was implemented at 3 tesla. Scans were performed on 10 healthy volunteers and MBF measured in three slices. The method was investigated for reproducibility by Bland-Altman analysis and statistical measures, the coefficients of reproducibility (CR) and variation (CV) are reported.

RESULTS

The MBF values for the basal, mid, and apical slices were 1.04 ± 0.40, 1.06 ± 0.46, and 1.06 ± 0.38 ml/g/min, respectively (mean ± SD), which compare well with literature values. The CV across all scans, 43%, was greater than the between-session and within-session values, at 16 and 13%, respectively, for the mid-ventricular slice. The change in MBF required for detection, from the CR, was 61% between-session and 53% within-session for the mid-ventricle.

CONCLUSION

This study shows the feasibility of the LL-FAIR-ASL method for the quantification of MBF. The statistical measures reported will allow the planning of future clinical research studies involving rest and stress measurements. Magn Reson Med 78:541-549, 2017. © 2016 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

The Use of Cardiac Magnetic Resonance in Patients with Suspected Coronary Artery Disease: A Clinical Practice Perspective

Cardiac magnetic resonance imaging (CMR) is a useful diagnostic imaging modality in patients with known or suspected coronary artery disease (CAD). It provides unique information not available from other modalities, however, it is complex. CMR is not a single technique. Instead, it consists of multiple distinct techniques and a lack of understanding of which techniques to perform and how to interpret the findings in combination limits its efficacy and widespread use. Conversely, its multiparametric nature can provide a comprehensive assessment with the potential for higher accuracy than is achievable by other modalities. Moreover, its ability to directly assess myopathic processes often contributes insights that change patient management. In this article we provide a brief technical overview and focus on specific clinical scenarios in patients with known or suspected CAD. We highlight the multiparametric nature of CMR and discuss cases which illustrate the unique information that CMR can contribute.