Assessment of cardiac function: magnetic resonance and computed tomography

Assessment of deep learning segmentation for real-time free-breathing cardiac magnetic resonance imaging at rest and under exercise stress

In recent years, a variety of deep learning networks for cardiac MRI (CMR) segmentation have been developed and analyzed. However, nearly all of them are focused on cine CMR under breathold. In this work, accuracy of deep learning methods is assessed for volumetric analysis (via segmentation) of the left ventricle in real-time free-breathing CMR at rest and under exercise stress. Data from healthy volunteers (n = 15) for cine and real-time free-breathing CMR at rest and under exercise stress were analyzed retrospectively. Exercise stress was performed using an ergometer in the supine position. Segmentations of two deep learning methods, a commercially available technique (comDL) and an openly available network (nnU-Net), were compared to a reference model created via the manual correction of segmentations obtained with comDL. Segmentations of left ventricular endocardium (LV), left ventricular myocardium (MYO), and right ventricle (RV) are compared for both end-systolic and end-diastolic phases and analyzed with Dice's coefficient. The volumetric analysis includes the cardiac function parameters LV end-diastolic volume (EDV), LV end-systolic volume (ESV), and LV ejection fraction (EF), evaluated with respect to both absolute and relative differences. For cine CMR, nnU-Net and comDL achieve Dice's coefficients above 0.95 for LV and 0.9 for MYO, and RV. For real-time CMR, the accuracy of nnU-Net exceeds that of comDL overall. For real-time CMR at rest, nnU-Net achieves Dice's coefficients of 0.94 for LV, 0.89 for MYO, and 0.90 for RV and the mean absolute differences between nnU-Net and the reference are 2.9 mL for EDV, 3.5 mL for ESV, and 2.6% for EF. For real-time CMR under exercise stress, nnU-Net achieves Dice's coefficients of 0.92 for LV, 0.85 for MYO, and 0.83 for RV and the mean absolute differences between nnU-Net and reference are 11.4 mL for EDV, 2.9 mL for ESV, and 3.6% for EF. Deep learning methods designed or trained for cine CMR segmentation can perform well on real-time CMR. For real-time free-breathing CMR at rest, the performance of deep learning methods is comparable to inter-observer variability in cine CMR and is usable for fully automatic segmentation. For real-time CMR under exercise stress, the performance of nnU-Net could promise a higher degree of automation in the future.

Relationship of Aortic Stiffness to Exercise and Ventricular Volumes in Single Ventricles

BACKGROUND

Patients with single ventricle (SV) may often undergo aortic reconstruction that creates a stiff large vessel, increasing afterload and affecting exercise performance. The objective of this study was to determine the relationship of pulse wave velocity (PWV) and distensibility in reconstructed and normal aortic arches after Fontan with exercise variables.

METHODS

PWV and distensibility of the descending aorta at the level of the diaphragm (DAo) were calculated with real-time exercise cardiac magnetic resonance in 48 patients with SV after Fontan (18 after aortic reconstruction; 30 without aortic reconstruction) and compared with metabolic exercise stress test variables.

RESULTS

PWV was greater in the reconstructed group than in the non-reconstructed group (median 4.4 m/s [range: 2.3 to 9.8 m/s] versus 3.6 [range: 2.6 to 6.3 m/s], respectively, p = 0.003). Statistically significant inverse correlations were found between PWV and end-diastolic, end-systolic, and stroke volumes at rest and at exercise in the reconstructed group. In addition, inverse correlations also existed in the reconstructed group between distensibility of the DAo and the exercise variables such as peak oxygen pulse (R = 0.56, p = 0.02), peak oxygen consumption (R = 0.63, p = 0.008), oxygen consumption at ventilatory anaerobic threshold (R = 0.48, p = 0.04), and peak work (R = 0.54, p = 0.02). Similar correlations were not seen in patients with non-reconstructed aortas.

CONCLUSIONS

Patients with SV with reconstructed aortas have increased aortic stiffness, increasing afterload on the ventricle. Native DAo stiffness distal to the reconstruction is inversely correlated with exercise performance, presumably to decrease impedance mismatch to maintain homogeneity of the aortic wall. This information suggests a possible mechanism for decreased exercise performance in patients with SV with aortic reconstructions.

MRI of right atrial function after catheter ablation of atrial flutter

RATIONALE AND OBJECTIVES

Catheter ablation of the cavotricuspid isthmus (CTI) is an effective treatment of right atrial flutter. The objective of this study was to evaluate the changes in CTI length and right atrial (RA) function after radiofrequency ablation of isthmus-dependent atrial flutter (isthmus ablation).

MATERIALS AND METHODS

Magnetic resonance imaging was obtained in 14 patients (2 female, mean age 59 +/- 9) before and after isthmus ablation (mean delay 80 +/- 175 days) using steady-state free precession cine magnetic resonance imaging in right anterior oblique view orientation. Right atrial function (maximum/minimum right atrial volumes, stroke volume, ejection fraction) and maximum/minimum length of the CTI were measured.

RESULTS

After isthmus ablation, maximum RA volume decreased by 13% (P = .02) and minimum RA volume by 22% (P = .01), whereas stroke volume and ejection fraction did not increase significantly (P = .4 and .2, respectively). After ablation, the maximum length of the CTI showed a significant decrease of 19% (P < .001) and the minimum length a decrease of 24% (P < .001). A linear correlation between change in CTI length and number of energy applications during ablation could not be observed (r = .605, P = .22 for minimum length; r = .384, P = .18 for maximum length). After eliminating the outliers in the number of energy applications, a significant correlation between energy applications and change in CTI systolic length was found (r = .808, P = .008).

CONCLUSION

Magnetic resonance imaging to visualize right atrial size and function in right anterior oblique orientation was successfully performed and easy to evaluate for volumetric analysis and determination of CTI length. Scarring of the CTI with the use of catheter ablation leads to a significant and linear decrease in its length and to a subsequent reduction of right atrial volumes, whereas functional parameters such as stroke volume/ejection fraction did not change significantly.

CT and MRI of acute thoracic cardiovascular emergencies

A wide spectrum of acute cardiovascular disorders is seen in patients who are hospitalized in a critical care setting. Imaging plays a central role in the diagnosis and management of these conditions. The most frequently used imaging remains chest radiography; however, more advanced modalities, including coronary angiography, echocardiography, and radioisotope scintigraphy, have well established roles in the assessment of patients in the critical care setting. More recently, multidetector row CT (MDCT) and MRI are being used increasingly for evaluation of coronary artery disease, cardiac structure and function, coronary artery anomalies, cardiac masses, pericardial disease, valvular disease, postoperative cardiovascular abnormalities, venous thromboembolism and acute aortic syndromes, often with other ancillary findings that can provide important clinical information. The three most common life-threatening cardiovascular processes in which advanced imaging plays a role, particularly CT, are discussed, including pulmonary embolism, aortic dissection, and coronary artery disease.

Comparison of left and right ventricular volume measurement using the Simpson's method and the area length method

PURPOSE

To compare ventricular volume measurement using a volumetric approach in the three standard cardiac planes and ventricular volume estimation by a geometrical model, the Area-Length method (ALM).

MATERIALS AND METHODS

Fifty-six healthy volunteers were examined (27 males, 29 females) on a 1.5T MR-unit with ECG-triggered steady state free precision (SSFP) Cine-MR sequences and parallel image acquisition. Multiple slices in standardized planes including the short-axis view (sa), 4-chamber view (4ch), left and right 2-chamber views (2ch) were used to cover the whole heart. End-systolic and end-diastolic ventricular volumes (EDV, ESV), stroke volume (SV), and ejection fraction (EF) were calculated with Simpson's rule in all planes and with ALM in the 2ch and 4ch planes. Global function parameters measured in the sa plane were compared with those obtained in the other imaging planes.

RESULTS

A very good correlation is observed when comparing functional parameters calculated with Simpson's rule in all imaging planes: for instance, the mean EDV/ESV of the left and right ventricle of the female population group measured in sa, 4ch, and 2ch: left ventricle EDV/ESV 114.3/44.4, 120.9/46.5, and 117.7/45.3 ml; right ventricle EDV/ESV 106.6/46.0, 101.2/41.1, and 103.5/43.0 ml. Functional parameters of the left ventricle calculated with ALM in 2ch and 4ch correlate to parameters obtained in sa with Simpson's rule in the range of 5-10%: for instance, the EDV/ESV of the left ventricle of the male population group measured in the sa, 4ch, and 2ch: 160.3/63.5, 163.1/59.0, and 167.0/65.7 ml. Functional parameters of the right ventricle measured with ALM in 4ch are 40-50% lower and calculated in 2ch almost double as high as compared with the parameters obtained in sa with Simpson's rule: for instance, male right ventricular EDV/ESV measured in sa, 4ch, and 2ch: 153.4/68.1, 97.5/34.5, and 280.2/123.2 ml. The EF correlates for all imaging planes measured with the Simpson's rule in both ventricles and using ALM in the left ventricle except for males with an overestimation of less than 6%. The EF of the right ventricle is calculated higher using ALM in 4ch and 2ch compared to the EF calculated in sa: female/male EF of the right ventricle measured in the sa, 4ch, and 2ch: 56.8/55.7, 66.0/65.0, and 60.0/57.0%.

CONCLUSION

In the setting of healthy volunteers the ALM method should not be used in 2ch and 4ch planes of the right ventricle because of lacking correlation of global functional parameters compared to those obtained in the sa plane. Using Simpson's rule functional parameters correlate well to each other in the different imaging planes.

Cardiac CT of the transplanted heart: indications, technique, appearance, and complications

Effective antirejection therapy and infection control have significantly improved the long-term survival of heart transplant recipients, but coronary allograft vasculopathy remains an important limiting factor. Most heart transplant recipients undergo annual coronary angiography for the detection of allograft vasculopathy, which is often clinically silent. Angiography allows detection of vasculopathy only indirectly, with depiction of the lumen, and does not depict the wall thickening and intimal hyperplasia that typify this disease; the procedure also is invasive and is associated with a 1%-2% risk of complication. In contrast, electrocardiographically gated multidetector computed tomography (CT) can provide a comprehensive and noninvasive evaluation of the transplanted heart in a single study. Cardiac CT enables evaluation of the coronary artery lumen and wall and thus may be used for screening, diagnosis, grading, and follow-up of coronary allograft vasculopathy. It also may be used to detect other posttransplantation complications, such as malignancy and infection, and to assess cardiac and vascular anastomoses and cardiac function. However, special strategies may be needed to reduce the transplant heart rate so as to obtain images of diagnostic quality.

ACR clinical statement on noninvasive cardiac imaging

Coronary artery disease and other acquired and congenital cardiac diseases are major medical and socio-economic problems. Historically, imaging has had a critical role in the diagnosis and evaluation of acquired and congenital cardiac disease. Advances in computed tomography (CT), with multidetector CT and electron beam CT technology, and magnetic resonance (MR) imaging, now make it possible to noninvasively image the coronary arteries, cardiac chambers, valves, myocardium, and pericardium and assess cardiac function, and CT and MR imaging are becoming increasingly important in the evaluation of cardiac disease. Radiologists, because of their extensive experience in CT and MR imaging, have an important role in imaging cardiac patients using these modalities. This clinical statement of the ACR discusses various technical and patient safety issues related to cardiac CT and MR imaging, and it suggests appropriate qualifications for radiologists until such time as ACR practice guidelines for the performance of cardiac CT and cardiac MR imaging are written and approved through the usual ACR process. It stresses that the interpreting physician is responsible for examining not only the cardiac structures of interest but also all the visualized noncardiac structures and must report any clinically relevant abnormalities of these adjacent structures.

Cardiopulmonary bypass for adults with congenital heart disease: pitfalls for perfusionists

The fixed incidence of congenital heart defects and improved survival have resulted in increasing numbers of adults with congenital heart disease (CHD) who have undergone complex repairs and/or palliations. Eventually, there will be more adults with CHD than children. They will require cardiac surgical interventions associated with progression of their CHD or for age-related disease, such as coronary revascularization. During bypass, anatomical shunts may exist within or without the heart. Left-to-right shunts can result in dramatically lower systemic blood flow than pump flow due to 'steal', while pulmonary edema ensues due to excessive pulmonary flow. Right-to-left shunts carry risks of massive air embolism and double or triple venous cannulation may be necessary. Cannulation of composite reconstructed aortas may be difficult, risking dissection or aortic obstruction, and double arterial cannulation may be indicated. Aberrant coronary arterial and venous anatomy may .preclude adequate myocardial preservation with common techniques and can be complicated by aortic insufficiency. Valves and conduits may exhibit failure. Conventional monitoring, such as central venous oximetry, may be misleading. Monitoring, such as serial lactate measurement, near-infrared spectroscopy and transcranial Doppler blood velocity, offer advantages for such patients. The perfusionist needs to be aware of such conditions as much congenital aberrancy may present unexpectedly during cardiac surgery.

Assessment of cardiac function by electron-beam computed tomography

The measurement of parameters relating to the assessment of cardiac function and morphology are critically important prognostic determinates in patients with known or suspected cardiac disease, such as coronary artery disease and myocardial infarction. Similarly, the measurement of indices, such as ejection fraction and myocardial mass, are key in assessing the efficacy of therapy in patients with valvular, coronary artery and intrinsic myocardial diseases. Electron-beam computed tomography has been proven to be a reliable and accurate modality for measuring a host of parameters relating to cardiac function. This article reviews the unique technologic design of the electron-beam computed tomography scanner and specifically addresses how this technology has enabled electron-beam computed tomography to become the gold standard for the quantification of cardiac function.

Congestive Heart Failure: A Review and Case Report From a Chiropractic Teaching Clinic

OBJECTIVE

To discuss the case of a 62-year-old woman with congestive heart failure (CHF), precipitated by a previous arteriovenous malformation, and to review the clinical presentation, pathophysiology, and treatment options for patients with CHF.

CLINICAL FEATURES

The patient complained of pain, rapid weight gain, and shortness of breath. The index event for this patient was known to be an arteriovenous malformation. Biventricular cardiomegaly with pulmonary venous hypertension was evident on chest radiographs.

INTERVENTION AND OUTCOME

The patient received both medical care (drug therapy) and chiropractic care (manipulation and soft tissue techniques to alleviate symptoms and discomfort).

CONCLUSION

Patients with known and undiagnosed CHF may visit the chiropractic physician; thus, knowledge of comprehensive care, differential diagnosis, and continuity of care are important. Chiropractic management may be helpful in alleviating patient discomfort. Further clinical investigations may help to clarify the role of complementary and alternative care in the diagnosis and treatment of CHF.

Current awareness in NMR in biomedicine

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.