Retrospective Electrocardiography-Gated Real-Time Cardiac Cine MRI at 3T: Comparison with Conventional Segmented Cine MRI

Accelerated cardiac magnetic resonance imaging using deep learning for volumetric assessment in children

BACKGROUND

Ventricular volumetry using a short-axis stack of two-dimensional (D) cine balanced steady-state free precession (bSSFP) sequences is crucial in any cardiac magnetic resonance imaging (MRI) examination. This task becomes particularly challenging in children due to multiple breath-holds.

OBJECTIVE

To assess the diagnostic performance of accelerated 3-RR cine MRI sequences using deep learning reconstruction compared with standard 2-D cine bSSFP sequences.

MATERIAL AND METHODS

Twenty-nine consecutive patients (mean age 11 ± 5, median 12, range 1-17 years) undergoing cardiac MRI were scanned with a conventional segmented 2-D cine and a deep learning accelerated cine (three heartbeats) acquisition on a 1.5-tesla scanner. Short-axis volumetrics were performed (semi-)automatically in both datasets retrospectively by two experienced readers who visually assessed image quality employing a 4-point grading scale. Scan times and image quality were compared using the Wilcoxon rank-sum test. Volumetrics were assessed with linear regression and Bland-Altman analyses, and measurement agreement with intraclass correlation coefficient (ICC).

RESULTS

Mean acquisition time was significantly reduced with the 3-RR deep learning cine compared to the standard cine sequence (45.5 ± 13.8 s vs. 218.3 ± 44.8 s; P < 0.001). No significant differences in biventricular volumetrics were found. Left ventricular (LV) mass was increased in the deep learning cine compared with the standard cine sequence (71.4 ± 33.1 g vs. 69.9 ± 32.5 g; P < 0.05). All volumetric measurements had an excellent agreement with ICC > 0.9 except for ejection fraction (EF) (LVEF 0.81, RVEF 0.73). The image quality of deep learning cine images was decreased for end-diastolic and end-systolic contours, papillary muscles, and valve depiction (2.9 ± 0.5 vs. 3.5 ± 0.4; P < 0.05).

CONCLUSION

Deep learning cine volumetrics did not differ significantly from standard cine results except for LV mass, which was slightly overestimated with deep learning cine. Deep learning cine sequences result in a significant reduction in scan time with only slightly lower image quality.

Evaluation of left ventricular and left atrial volumetric function from native MR multislice 4D flow magnitude data

OBJECTIVES

To assess the feasibility, precision, and accuracy of left ventricular (LV) and left atrial (LA) volumetric function evaluation from native magnetic resonance (MR) multislice 4D flow magnitude images.

MATERIALS & METHODS

In this prospective study, 60 subjects without signs or symptoms of heart failure underwent 3T native cardiac MR multislice 4D flow and bSSFP-cine realtime imaging. LV and LA volumetric function parameters were evaluated from 4D flow magnitude (4D flow-cine) and bSSFP-cine data using standard software to obtain end-diastolic volume (EDV), end-systolic volume (ESV), ejection-fraction (EF), stroke-volume (SV), LV muscle mass (LVM), LA maximum volume, LA minimum volume, and LA total ejection fraction (LATEF). Stroke volumes derived from both imaging methods were further compared to 4D pulmonary artery flow-derived net forward volumes (NFV). Methods were compared by correlation and Bland-Altman analysis.

RESULTS

Volumetric function parameters from 4D flow-cine and bSSFP-cine showed high to very high correlations (r = 0.83-0.98). SV, LA volumes and LATEF did not differ between methods. LV end-diastolic and end-systolic volumes were slightly underestimated (EDV: -2.9 ± 5.8 mL; ESV: -2.3 ± 3.8 mL), EF was slightly overestimated (EF: 0.9 ± 2.6%), and LV mass was considerably overestimated (LVM: 39.0 ± 11.4 g) by 4D flow-cine imaging. SVs from both methods correlated very highly with NFV (r = 0.91 in both cases) and did not differ from NFV.

CONCLUSION

Native multislice 4D flow magnitude data allows precise evaluation of LV and LA volumetric parameters; however, apart from SV, LV volumetric parameters demonstrate bias and need to be referred to their respective normal values.

CLINICAL RELEVANCE STATEMENT

Volumetric function assessment from native multislice 4D flow magnitude images can be performed with routinely used clinical software, facilitating the application of 4D flow as a one-stop-shop functional cardiac MR exam, providing consistent, simultaneously acquired, volume and flow data.

KEY POINTS

• Native multislice 4D flow imaging allows evaluation of volumetric left ventricular and atrial function parameters. • Left ventricular and left atrial function parameters derived from native multislice 4D flow data correlate highly with corresponding standard cine-derived parameters. • Multislice 4D flow-derived volumetric stroke volume and net forward volume do not differ.

Fast acquisition of left and right ventricular function parameters applying cardiovascular magnetic resonance in clinical routine - validation of a 2-shot compressed sensing cine sequence

Objectives. To evaluate if cine sequences accelerated by compressed sensing (CS) are feasible in clinical routine and yield equivalent cardiac morphology in less time. Design. We evaluated 155 consecutive patients with various cardiac diseases scanned during our clinical routine. LV and RV short axis (SAX) cine images were acquired by conventional and prototype 2-shot CS sequences on a 1.5 T CMR. The 2-shot prototype captures the entire heart over a period of 3 beats making the acquisition potentially even faster. Both scans were performed with identical slice parameters and positions. We compared LV and RV morphology with Bland-Altmann plots and weighted the results in relation to pre-defined tolerance intervals. Subjective and objective image quality was evaluated using a 4-point score and adapted standardized criteria. Scan times were evaluated for each sequence. Results. In total, no acquisitions were lost due to non-diagnostic image quality in the subjective image score. Objective image quality analysis showed no statistically significant differences. The scan time of the CS cines was significantly shorter (p < .001) with mean scan times of 178 ± 36 s compared to 313 ± 65 s for the conventional cine. All cardiac function parameters showed excellent correlation (r 0.978-0.996). Both sequences were considered equivalent for the assessment of LV and RV morphology. Conclusions. The 2-shot CS SAX cines can be used in clinical routine to acquire cardiac morphology in less time compared to the conventional method, with no total loss of acquisitions due to nondiagnostic quality.

TRIAL REGISTRATION

ISRCTN12344380. Registered 20 November 2020, retrospectively registered.

Real-Time Spiral CMR Is Superior to Conventional Segmented Cine-Imaging for Left-Ventricular Functional Assessment in Patients with Arrhythmia

(1) Background: Segmented Cartesian Cardiovascular magnetic resonance (CMR) often fails to deliver robust assessment of cardiac function in patients with arrhythmia. We aimed to assess the performance of a tiny golden-angle spiral real-time CMR sequence at 1.5 T for left-ventricular (LV) volumetry in patients with irregular heart rhythm; (2) Methods: We validated the real-time sequence against the standard breath-hold segmented Cartesian sequence in 32 patients, of whom 11 presented with arrhythmia. End-diastolic volume (EDV), end-systolic volume (ESV), stroke volume (SV), and ejection fraction (EF) were assessed. In arrhythmic patients, real-time and standard Cartesian acquisitions were compared against a reference echocardiographic modality; (3) Results: In patients with sinus rhythm, good agreements and correlations were found between the segmented and real-time methods, with only minor, non-significant underestimation of EDV for the real-time sequence (135.95 ± 30 mL vs. 137.15 ± 31, p = 0.164). In patients with arrhythmia, spiral real-time CMR yielded superior image quality to the conventional segmented imaging, allowing for excellent agreement with the reference echocardiographic volumetry. In contrast, in this cohort, standard Cartesian CMR showed significant underestimation of LV-ESV (106.72 ± 63.51 mL vs. 125.47 ± 72.41 mL, p = 0.026) and overestimation of LVEF (42.96 ± 10.81% vs. 39.02 ± 11.72%, p = 0.039); (4) Conclusions: Real-time spiral CMR improves image quality in arrhythmic patients, allowing reliable assessment of LV volumetry.

Comparison of cardiac volumetry using real-time MRI during free-breathing with standard cine MRI during breath-hold in children

BACKGROUND

Cardiac real-time magnetic resonance imaging (RT-MRI) provides high-quality images even during free-breathing. Difficulties in post-processing impede its use in clinical routine.

OBJECTIVE

To demonstrate the feasibility of quantitative analysis of cardiac free-breathing RT-MRI and to compare image quality and volumetry during free-breathing RT-MRI in pediatric patients to standard breath-hold cine MRI.

MATERIALS AND METHODS

Pediatric patients (n = 22) received cardiac RT-MRI volumetry during free breathing (1.5 T; short axis; 30 frames per s) in addition to standard breath-hold cine imaging in end-expiration. Real-time images were binned retrospectively based on electrocardiography and respiratory bellows. Image quality and volumetry were compared using the European Cardiovascular Magnetic Resonance registry score, structure visibility rating, linear regression and Bland-Altman analyses.

RESULTS

Additional time for binning of real-time images was 2 min. For both techniques, image quality was rated good to excellent. RT-MRI was significantly more robust against artifacts (P < 0.01). Linear regression revealed good correlations for the ventricular volumes. Bland-Altman plots showed a good limit of agreement (LoA) for end-diastolic volume (left ventricle [LV]: LoA -0.1 ± 2.7 ml/m², right ventricle [RV]: LoA -1.9 ± 3.4 ml/m²), end-systolic volume (LV: LoA 0.4 ± 1.9 ml/m², RV: LoA 0.6 ± 2.0 ml/m²), stroke volume (LV: LoA -0.5 ± 2.3 ml/m², RV: LoA -2.6 ± 3.3 ml/m²) and ejection fraction (LV: LoA -0.5 ± 1.6%, RV: LoA -2.1 ± 2.8%).

CONCLUSION

Compared to standard cine MRI with breath hold, RT-MRI during free breathing with retrospective respiratory binning offers good image quality, reduced image artifacts enabling fast quantitative evaluations of ventricular volumes in clinical practice under physiological conditions.

Differences in left ventricular and left atrial function assessed during breath-holding and breathing

PURPOSE

To analyze differences in systolic and diastolic left ventricular (LV) as well as left atrial (LA) function parameters obtained from identical cardiac magnetic resonance (MR) imaging techniques during inspiratory breath-holding and breathing (breath-hold to breathing differences).

METHOD

56 subjects without signs of heart failure (23/33 male/female, age 58 ± 14 years) underwent 3 T MR cine real-time and transmitral phase contrast imaging with the same spatial and temporal resolution during inspiratory breath-holding and free breathing. LV and LA volumetric function parameters were derived from segmentation of cine series, transmitral peak velocities and early-diastolic myocardial peak velocity from phase contrast series. Corresponding breath-hold and breathing parameters were compared by Bland-Altman analysis; repeatability of breath-hold and breathing measurements was quantified by variance component analysis. p < 0.05 was regarded as statistically significant.

RESULTS

Mean differences between results obtained during inspiratory breath-holding vs. breathing were significant for LV volumetric function (end-diastolic volume=-7 mL, p = 0.002; end-systolic volume=-7 mL, p < 0.001; ejection fraction = 3 %, p < 0.001; peak ejection rate = 22 mL/s, p = 0.002; early-diastolic peak filling rate=-34 mL/s, p = 0.025), LA volumetric function (maximum volume=-6 mL, p < 0.001; total ejection fraction=-4%, p < 0.001; active ejection fraction=-2%, p = 0.013; before contraction ejection fraction=-4%, p < 0.001) and early-diastolic velocities (transmitral=-6 cm/s, p < 0.001; tissue velocity=-1.8 cm/s, p < 0.001). Standard deviations of breath-hold-to-breathing differences exceeded the corresponding repeatabilities of breath-hold and breathing measurements.

CONCLUSIONS

Systolic and diastolic LV and LA function parameters acquired during inspiratory breath-holding and breathing differ, and large inter-individual breath-hold-to-breathing variations are possible. Thus, the breathing state should be taken into account, especially when comparing results in patient follow-up acquired in different respiratory states.

Retrospective respiratory motion correction in cardiac cine MRI reconstruction using adversarial autoencoder and unsupervised learning

The aim of this study was to develop a deep neural network for respiratory motion compensation in free-breathing cine MRI and evaluate its performance. An adversarial autoencoder network was trained using unpaired training data from healthy volunteers and patients who underwent clinically indicated cardiac MRI examinations. A U-net structure was used for the encoder and decoder parts of the network and the code space was regularized by an adversarial objective. The autoencoder learns the identity map for the free-breathing motion-corrupted images and preserves the structural content of the images, while the discriminator, which interacts with the output of the encoder, forces the encoder to remove motion artifacts. The network was first evaluated based on data that were artificially corrupted with simulated rigid motion with regard to motion-correction accuracy and the presence of any artificially created structures. Subsequently, to demonstrate the feasibility of the proposed approach in vivo, our network was trained on respiratory motion-corrupted images in an unpaired manner and was tested on volunteer and patient data. In the simulation study, mean structural similarity index scores for the synthesized motion-corrupted images and motion-corrected images were 0.76 and 0.93 (out of 1), respectively. The proposed method increased the Tenengrad focus measure of the motion-corrupted images by 12% in the simulation study and by 7% in the in vivo study. The average overall subjective image quality scores for the motion-corrupted images, motion-corrected images and breath-held images were 2.5, 3.5 and 4.1 (out of 5.0), respectively. Nonparametric-paired comparisons showed that there was significant difference between the image quality scores of the motion-corrupted and breath-held images (P < .05); however, after correction there was no significant difference between the image quality scores of the motion-corrected and breath-held images. This feasibility study demonstrates the potential of an adversarial autoencoder network for correcting respiratory motion-related image artifacts without requiring paired data.

Guideline for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging-Part 1: Standardized Protocol

Cardiac magnetic resonance (CMR) imaging is widely used in many areas of cardiovascular disease assessment. This is a practical, standard CMR protocol for beginners that is designed to be easy to follow and implement. This protocol guideline is based on previously reported CMR guidelines and includes sequence terminology used by vendors, essential MR physics, imaging planes, field strength considerations, MRI-conditional devices, drugs for stress tests, various CMR modules, and disease/symptom-based protocols based on a survey of cardiologists and various appropriate-use criteria. It will be of considerable help in planning and implementing tests. In addressing CMR usage and creating this protocol guideline, we particularly tried to include useful tips to overcome various practical issues and improve CMR imaging. We hope that this document will continue to standardize and simplify a patient-based approach to clinical CMR and contribute to the promotion of public health.

Guidelines for Cardiovascular Magnetic Resonance Imaging from the Korean Society of Cardiovascular Imaging-Part 2: Interpretation of Cine, Flow, and Angiography Data

Cardiovascular magnetic resonance imaging (CMR) is expected to be increasingly used in Korea due to technological advances and the expanded national insurance coverage of CMR assessments. For improved patient care, proper acquisition of CMR images as well as their accurate interpretation by well-trained personnel are equally important. In response to the increased demand for CMR, the Korean Society of Cardiovascular Imaging (KOSCI) has issued interpretation guidelines in conjunction with the Korean Society of Radiology. KOSCI has also created a formal Committee on CMR guidelines to create updated practices. The members of this committee review previously published interpretation guidelines and discuss the patterns of CMR use in Korea.

Feasibility of real-time cine cardiac magnetic resonance imaging to predict the presence of significant retrosternal adhesions prior to redo-sternotomy

BACKGROUND

Injury to vital structures posterior to the sternum is a complication associated with redo sternotomy in congenital cardiac surgery. The goal of our study was a novel evaluation of real-time cine cardiovascular magnetic resonance (CMR) to predict the presence of significant retrosternal adhesions of cardiac and vascular structures prior to redo sternotomy in patients with congenital heart disease.

METHODS

Twenty-three patients who had prior congenital heart surgery via median sternotomy had comprehensive CMR studies prior to redo sternotomy. The real time cine (RTC) sequence that was used is an ungated balanced steady-state free precession (bSSFP) sequence using SENSitivity Encoding for acceleration with real-time reconstruction. Spontaneously breathing patients were instructed to take deep breaths during the acquisition whilst increased tidal volumes were delivered to mechanically ventilated patients. All patients underwent redo cardiac surgery subsequently and the presence and severity of retrosternal adhesions were noted at the time of the redo sternotomies.

RESULTS

Median age at the time of CMR and operation were 5.5 years (range, 0.2-18.4y) and 6.1 years (range, 0.3-18.8y) respectively. There were 15 males and 8 females in the study group. Preoperative retrosternal adhesions were identified on RTC in 13 patients and confirmed in 11 (85%) at the time of surgery. In only 2 patients, no adhesions were identified on CMR but were found to have significant retrosternal adhesions at surgery; false positive rate 15% (CI 0.4-29.6%), false negative rate 20% (CI 3.7-36.4%). The total classification error of the real time cine sequence was 17% (CI 1.7-32.4%) with an overall accuracy of 83% (CI 67.7-98.4%). Standard breath-hold cine images correlated poorly with surgical findings and did not increase the diagnostic yield.

CONCLUSIONS

RTC imaging can predict the presence of significant retrosternal adhesions and thus help in risk assessment prior to redo sternotomy. These findings complement the surgical planning and potentially reduce surgical complications .