Cardiac magnetic resonance imaging for the interventional cardiologist

What Matters in Radiological Image Segmentation? Effect of Segmentation Errors on the Diagnostic Related Features

Segmentation is a crucial step in extracting the medical image features for clinical diagnosis. Though multiple metrics have been proposed to evaluate the segmentation performance, there is no clear study on how or to what extent the segmentation errors will affect the diagnostic related features used in clinical practice. Therefore, we proposed a segmentation robustness plot (SRP) to build the link between segmentation errors and clinical acceptance, where relative area under the curve (R-AUC) was designed to help clinicians to identify the robust diagnostic related image features. In experiments, we first selected representative radiological series from time series (cardiac first-pass perfusion) and spatial series (T2 weighted images on brain tumors) of magnetic resonance images, respectively. Then, dice similarity coefficient (DSC) and Hausdorff distance (HD), as the widely used evaluation metrics, were used to systematically control the degree of the segmentation errors. Finally, the differences between diagnostic related image features extracted from the ground truth and the derived segmentation were analyzed, using the statistical method large sample size T-test to calculate the corresponding p values. The results are denoted in the SRP, where the x-axis indicates the segmentation performance using the aforementioned evaluation metric, and the y-axis shows the severity of the corresponding feature changes, which are expressed in either the p values for a single case or the proportion of patients without significant change. The experimental results in SRP show that when DSC is above 0.95 and HD is below 3 mm, the segmentation errors will not change the features significantly in most cases. However, when segmentation gets worse, additional metrics are required for further analysis. In this way, the proposed SRP indicates the impact of the segmentation errors on the severity of the corresponding feature changes. By using SRP, one could easily define the acceptable segmentation errors in a challenge. Additionally, the R-AUC calculated from SRP provides an objective reference to help the selection of reliable features in image analysis.

Multimodality imaging in aortic stenosis

Aortic stenosis (AS) is the most common cardiac valve lesion in the adult population, with an incidence increasing as the population ages. Accurate assessment of AS severity is necessary for clinical decision-making. Echocardiography is currently the diagnostic method of choice for assessing and managing AS. Transthoracic echocardiography is usually sufficient in most situations. Transesophageal echocardiography and stress echocardiography may also be utilized when there is inadequate image quality and/or discordance in the results and the clinical presentation. There is a role for other imaging modalities such as cardiac computed tomography, magnetic resonance imaging, and catheterization in selected cases. The following describes in some detail the role of these modalities in the diagnosis and assessment of AS.

Evaluation of aortic stenosis using cardiovascular magnetic resonance: a systematic review & meta-analysis

BACKGROUND

As the average age of patients with severe aortic stenosis (AS) who receive procedural intervention continue to age, the need for non-invasive modalities that provide accurate diagnosis and operative planning is increasingly important. Advances in cardiovascular magnetic resonance (CMR) over the past two decades mean it is able to provide haemodynamic data at the aortic valve, along with high fidelity anatomical imaging.

METHODS

Electronic databases were searched for studies comparing CMR to transthoracic echocardiography (TTE) and transoesophageal echocardiography (TEE) in the diagnosis of AS. Studies were included only if direct comparison was made on matched patients, and if diagnosis was primarily through measurement of aortic valve area (AVA).

RESULTS

Twenty-three relevant, prospective articles were included in the meta-analysis, totalling 1040 individual patients. There was no significant difference in AVA measured as by CMR compared to TEE. CMR measurements of AVA size were larger compared to TTE by an average of 10.7% (absolute difference: + 0.14cm2, 95% CI 0.07-0.21, p < 0.001). Reliability was high for both inter- and intra-observer measurements (0.03cm2 +/- 0.04 and 0.02cm2 +/- 0.01, respectively).

CONCLUSIONS

Our analysis demonstrates the equivalence of AVA measurements using CMR compared to those obtained using TEE. CMR demonstrated a small but significantly larger AVA than TTE. However, this can be attributed to known errors in derivation of left ventricular outflow tract size as measured by TTE. By offering additional anatomical assessment, CMR is warranted as a primary tool in the assessment and workup of patients with severe AS who are candidates for surgical or transcatheter intervention.

Future perspectives of nanoparticle-based contrast agents for cardiac magnetic resonance in myocardial infarction

Cardiac Magnetic Resonance (CMR), thanks to high spatial resolution and absence of ionizing radiation, has been widely used in myocardial infarction (MI) assessment to evaluate cardiac structure, function, perfusion and viability. Nevertheless, it suffers from limitations in tissue and assessment of myocardial pathophysiological changes subsequent to MI. In this issue, nanoparticle-based contrast agents offer the possibility to track biological processes at cellular and molecular level underlying the various phases of MI, infarct healing and tissue repair. In this paper, first we examine the conventional CMR protocol and its findings in MI patients. Next, we looked at how nanoparticles can help in the imaging of MI and give an overview of the major approaches currently explored. Based on the presentation of successful nanoparticle applications as contrast agents (CAs) in preclinical and clinical models, we discuss promises and outstanding challenges facing the field of CMR in MI, their translational potential and clinical application.

Regular cocaine use is associated with increased systolic blood pressure, aortic stiffness and left ventricular mass in young otherwise healthy individuals

BACKGROUND

The cardiovascular impact of cocaine use in otherwise healthy individuals who consider themselves 'social' users is not well established.

METHODS/RESULTS

Twenty regular cocaine users and 20 control subjects were recruited by word-of-mouth. Cardiovascular magnetic resonance was performed to assess cardiac and vascular structure and function. Cocaine users had higher systolic blood pressure compared to non-users (134±11 vs 126±11 mmHg, p = 0.036), a finding independent of age, body surface area, smoking and alcohol consumption. Cocaine use was associated with increased arterial stiffness - reflected by reduced aortic compliance (1.3±0.2 vs 1.7±0.5 cm2×10-2.mmHg-1, p = 0.004), decreased distensibility (3.8±0.9 vs 5.1±1.4 mmHg-1.10-3, p = 0.001), increased stiffness index (2.6±0.6 vs 2.1±0.6, p = 0.005), and higher pulse wave velocity (5.1±0.6 vs 4.4±0.6 m.s-1, p = 0.001). This change in aortic stiffness was independent of vessel wall thickness. Left ventricular mass was 18% higher in cocaine users (124±25 vs 105±16 g, p = 0.01), a finding that was independent of body surface area, and left atrial diameter was larger in the user group than controls (3.8±0.6 vs 3.5±0.3 cm, p = 0.04). The increased left ventricular mass, systolic blood pressure and vascular stiffness measures were all associated with duration and/or frequency of cocaine use. No late gadolinium enhancement or segmental wall motion abnormalities were seen in any of the subjects.

CONCLUSIONS

Compared with the non-user control cohort, cocaine users had increased aortic stiffness and systolic blood pressure, associated with greater left ventricular mass. These measures are all well known risk factors for premature cardiovascular events, highlighting the dangers of cocaine use, even in a 'social' setting, and have important public health implications.

Utility of cardiac magnetic resonance in assessing right-sided heart failure in sarcoidosis

BACKGROUND

Cardiac involvement in sarcoidosis is associated with a poor prognosis. In patients with right sided heart failure, differentiating between cor-pulmonale, or cardiac sarcoidosis has important implications to management.

CASE PRESENTATION

We present the case of a patient with severe but stable pulmonary sarcoidosis and new onset right sided heart failure despite only mild elevations of pulmonary artery pressure. CMR demonstration of extensive right ventricular fibrosis with associated dilatation and hypokinesis was a key finding for prognosis and management of the patient.

CONCLUSION

Cardiac magnetic resonance (CMR) is the preferred investigation in the diagnosis of cardiac sarcoidosis, allowing assessment of myocardial inflammation and fibrosis, as well as function, in a manner not matched by other technologies.