Assessment of Chronic Aortic Dissection:Contribution of Different ECG-Gated Breath-Hold MRI Techniques

Society for Cardiovascular Magnetic Resonance/European Society of Cardiovascular Imaging/American Society of Echocardiography/Society for Pediatric Radiology/North American Society for Cardiovascular Imaging Guidelines for the use of cardiovascular magnetic resonance in pediatric congenital and acquired heart disease : Endorsed by The American Heart Association

Cardiovascular magnetic resonance (CMR) has been utilized in the management and care of pediatric patients for nearly 40 years. It has evolved to become an invaluable tool in the assessment of the littlest of hearts for diagnosis, pre-interventional management and follow-up care. Although mentioned in a number of consensus and guidelines documents, an up-to-date, large, stand-alone guidance work for the use of CMR in pediatric congenital 36 and acquired 35 heart disease endorsed by numerous Societies involved in the care of these children is lacking. This guidelines document outlines the use of CMR in this patient population for a significant number of heart lesions in this age group and although admittedly, is not an exhaustive treatment, it does deal with an expansive list of many common clinical issues encountered in daily practice.

Society for Cardiovascular Magnetic Resonance/European Society of Cardiovascular Imaging/American Society of Echocardiography/Society for Pediatric Radiology/North American Society for Cardiovascular Imaging Guidelines for the Use of Cardiac Magnetic Resonance in Pediatric Congenital and Acquired Heart Disease: Endorsed by The American Heart Association

Cardiovascular magnetic resonance has been utilized in the management and care of pediatric patients for nearly 40 years. It has evolved to become an invaluable tool in the assessment of the littlest of hearts for diagnosis, pre-interventional management and follow-up care. Although mentioned in a number of consensus and guidelines documents, an up-to-date, large, stand-alone guidance work for the use of cardiovascular magnetic resonance in pediatric congenital 36 and acquired 35 heart disease endorsed by numerous Societies involved in the care of these children is lacking. This guidelines document outlines the use of cardiovascular magnetic resonance in this patient population for a significant number of heart lesions in this age group and although admittedly, is not an exhaustive treatment, it does deal with an expansive list of many common clinical issues encountered in daily practice.

Effects of pulmonary endarterectomy on pulmonary hemodynamics in chronic thromboembolic pulmonary hypertension, evaluated by interventricular septum curvature

The interventricular septum curvature, measured in images of electrocardiogram-gated 320-slice multidetector computed tomography, is reportedly useful and less invasive than right heart catheterization, as it could provide clues regarding pulmonary arterial pressure in patients with chronic thromboembolic pulmonary hypertension. Although pulmonary endarterectomy is an efficient treatment for chronic thromboembolic pulmonary hypertension, the interventricular septum curvature in patients who have received pulmonary endarterectomy has not been evaluated. We evaluated whether the interventricular septum curvature on electrocardiogram-gated 320-slice multidetector computed tomography can predict pulmonary hemodynamics in chronic thromboembolic pulmonary hypertension even after pulmonary endarterectomy. We studied 40 patients with chronic thromboembolic pulmonary hypertension (60.5 ± 9.7 years; 30 females), who underwent pulmonary endarterectomy at Chiba University Hospital between December 2010 and July 2018. To measure the interventricular septum curvature, we prepared left ventricular short-axis tomographic images from 4D images of electrocardiogram-gated 320-slice multidetector computed tomography. We calculated the radius of interventricular septum and determined the interventricular septum curvature in both the systolic and diastolic phases. We compared the interventricular septum curvature with pulmonary hemodynamics measured by right heart catheterization before and after pulmonary endarterectomy. After pulmonary endarterectomy, the correlations of the interventricular septum curvature with mean pulmonary arterial pressure, systolic pulmonary arterial pressure, and pulmonary vascular resistance disappeared, although the interventricular septum curvature was correlated with these pulmonary hemodynamic parameters before pulmonary endarterectomy. Changes in systolic interventricular septum curvature revealed significant correlations with changes in mean pulmonary arterial pressure, systolic pulmonary arterial pressure and pulmonary vascular resistance. Diastolic interventricular septum curvature also showed significant correlations with preoperative pulmonary hemodynamics, but not with postoperative pulmonary hemodynamics. Changes in the interventricular septum curvature after pulmonary endarterectomy could estimate the efficacy of pulmonary endarterectomy, although the interventricular septum curvature after pulmonary endarterectomy showed no significant correlations with pulmonary hemodynamics. Additionally, our findings confirmed that the interventricular septum curvature before pulmonary endarterectomy could be used to evaluate the severity of disease.

MRI in Chronic Aortic Dissection: A Systematic Review and Future Directions

The acute event of thoracic aortic dissection carries with it high mortality and morbidity. Despite optimal initial surgical or medical management strategies, the risk of further complications in the long-term, including aneurysmal dilatation and false lumen (FL) expansion, are not insignificant. Adequate follow-up of such conditions requires dedicated imaging where relevant prognostic indicators are accurately assessed. We perform a systematic review of the literature and report the current evidence for the use of magnetic resonance imaging (MRI) in assessment of chronic aortic dissection. We then make a comparison with traditional imaging modalities including computed tomography and echocardiography. We discuss new ways in which MRI may extend existing aortic assessment, including identification of blood-flow dynamics within the TL and FL using phase-contrast imaging.

Visualization of through-plane blood flow measurements obtained from phase-contrast MRI

The purpose of this work was to develop a visualization method for concurrent observation of both velocity and magnitude data obtained from through-plane velocity measurements using phase-contrast magnetic resonance imaging. Magnitude and velocity images were combined using an opacity transfer function (OTF) where the opacity was a function of a velocity range defined by the velocity encoding (v (enc)) parameter. Measured velocities were color-coded according to a predefined color scale and then combined into one image with the gray-scale magnitude image according to the OTF. In the combined images, simultaneous information of velocity and anatomy was presented. The proposed visualization method facilitated the understanding of how the measured blood flow was related to the underlying anatomy. Results are shown where the method is used to visualize blood flow measurements in the ascending aorta and the aortic valve. Adjustments of the OTF render possible identification of the peak velocities and their localization. Forward and backward blood flow is easily shown when applying appropriate OTF and color-coding. An advantage when using the proposed method is the ability of developing standardized protocol settings since the velocity information is quantitative and not relative as is the case for data obtained from the magnitude images. The intended application of the visualization method is the analysis of common flow studies used in the diagnosis of different cardiovascular diseases.

Imaging of the thoracic aorta

Three-dimensional vascular imaging techniques offer a significant advantage over traditional imaging techniques. Spatial resolution of current state-of-the-art allows sufficient depiction of anatomical detail. Pre-operative planning of complex endovascular procedures is facilitated by state-of-the-art imaging. Cone-beam CT holds great promise in guiding complex endovascular procedures.

Imaging features of intramural hematoma of the aorta

Intramural hematoma (IMH) is defined as localized hemorrhage within the aortic wall and is included in the acute aortic syndrome spectrum with aortic dissection and penetrating aortic ulcer. The mortality from IMH is similar to classic aortic dissection (21%). 16% of patients with IMH will evolve to classic aortic dissection over time. Despite this confusion exists regarding the precise definitions and radiologic features of IMH versus penetrating ulcers with mural thrombus and overt aortic dissection.

Cardiovascular applications of phase-contrast MRI

OBJECTIVE

The purpose of this study was to review and illustrate various clinical applications of phase-contrast MRI.

CONCLUSION

Cardiac MRI has emerged as a valuable noninvasive clinical tool for evaluation of the cardiovascular system. Phase-contrast MRI has a variety of established applications in quantifying blood flow and velocity and several emerging applications, such as evaluation of diastolic function and myocardial dyssynchrony.

The role of noninvasive vascular imaging in splanchnic and mesenteric pathology

Traditionally, catheter angiography (CA) has been the mainstay of diagnosis for mesenteric arterial diseases. However, CA is invasive and is associated with complications that result from the procedure itself, depending on the experience of the operators, site of vascular access, ionized radiation that could be significant when combined with interventional procedures, and administered contrast material. During the past 2 decades, technical improvements in computed tomography (CT) and magnetic resonance hardware and methods have contributed new, noninvasive tools, specifically CT angiography (CTA) and 3-dimensional gadolinium-enhanced magnetic resonance angiography (3D Gd-MRA). This article outlines the current applications, strengths, and weaknesses of CTA and 3D Gd-MRA in imaging of the mesenteric vessels.

Assessment of thoracic aortic dimensions in an experimental setting: comparison of different unenhanced magnetic resonance angiography techniques with electrocardiogram-gated computed tomography angiography for possible application in the pediatric population

PURPOSE

To compare different unenhanced magnetic resonance angiography (MRA) techniques for quantitative evaluation of vessel lumen in an experimental setting in young pigs whose dimensions allow for a comparison with a pediatric population.

MATERIAL AND METHODS

Magnetic resonance imaging was performed in 5 healthy ventilated pigs at 1.5 T. Three different electrocardiogram (ECG)-triggered sequences were applied for MRA: [TSE-Db] T2-weighted dark-blood TurboSpinEcho (2.0 x 1.1 x 4 mm3); [trueFISP] 2D-steady-state-free-precession (2.2 x 1.8 x 2 mm3); [NAV] respiratory-gated, T2-prepared 3D-trueFISP (1.3 x 1.3 x 1.3 mm3). ECG-gated-CT angiography (CTA) (16-row CT, 1 mm collimation) served as the standard of reference. The vessel lumen was measured at 7 positions perpendicularly angulated to the vessel wall on multiplanar reformations: ascending aorta (P1), the aortic arch before (P2) and after (P3) the origin of the first supraaortic branch, the aortic arch after the origin of the second supraaortic branch (P4), the descending aorta at the level of the diaphragm (P5), and the first and second supraaortic branches (P6, P7).

RESULTS

Percentage differences in the vessel area determined by MRA reformation compared with CTA-reformation were 10% +/- 20% and 35% +/- 27% (TSE-Db), -4% +/- 13% and 20% +/- 24% (trueFISP), and -3% +/- 13% and -10% +/- 19% (NAV), for positions P1 to P5 and P6 to P7, respectively. A significant difference from CTA was found for TSE-Db at all positions, and for trueFISP only at positions P6 and P7.

CONCLUSIONS

Unenhanced MRA techniques allow for a reliable assessment of the dimensions of the thoracic aorta compared with CTA as the standard of reference. Using ECG-gating and navigator techniques, the free-breathing approach showed the best agreement with CTA. This technique may therefore be the most useful in the pediatric age group allowing for true 3D data acquisition with its inherent postprocessing possibilities.

Comparison of different MRI techniques for the assessment of thoracic aortic pathology: 3D contrast enhanced MR angiography, turbo spin echo and balanced steady state free precession

PURPOSE

The purpose of this study was to compare two non-contrast 2D techniques with the current contrast-enhanced MRI standard 3D technique for the routine assessment of thoracic aortic pathologies.

METHODS

One hundred patients with suspected or known thoracic aortic diseases were examined with a 1.5 T scanner using 2D turbo spin echo (TSE), 2D balanced steady state free precession (balanced SSFP) and 3D contrast-enhanced MR angiography (CE-MRA). The diameters of the aorta at predefined levels were measured. The feasibility to visualize the aortic root and supra-aortic branches was tested. All morphologic abnormalities of the aorta, the aortic wall and the aortic valve, as well as image quality of TSE and balanced SSFP influencing the diagnosis were analysed.

RESULTS

Compared to CE-MRA, balanced SSFP and TSE allowed for the detection of a significantly higher number of relevant pathologies (thickened aortic wall and signs of emergency) in less time. No significant differences were found among the sequences for the identification of aneurysms, dissection membranes and thrombi. No single technique was able to address all clinically relevant issues. TSE was associated with a better image quality compared to balanced SSFP, which however did not translate into a significantly improved diagnostic accuracy.

CONCLUSION

The total number of pathologic findings was higher using 2D TSE and balanced SSFP when compared to 3D CE-MRA. None of the techniques applied could address all clinically relevant issues. The major drawback of TSE is its relatively long scanning time while balanced SSFP is associated with more artifacts.

[Long-term MRI follow-up of aortic dissection in 56 patients: therapeutic impact]

PURPOSE

To retrospectively assess the value of MRI in long-term follow-up of aortic dissection (AD) and its impact on therapy.

MATERIALS AND METHODS

Comparison of clinical progression and analysis of 215 MRI examinations performed on 56 patients in our center from 1991 to 2002.

RESULTS

Twenty-six patients (46%) had AD complications: 14 (54%) were asymptomatic and eight (31%) had subsequent surgical repair (native aorta upstream prosthesis disease in three patients and aneurismal dilatation of false lumen in five cases). Of the eight patients with secondary surgery, five (63%) were clinically asymptomatic. The delay between initial dissection and secondary surgery was less than 5 years in five patients and exceeded 10 years in three cases. The remaining 30 patients (54%) had unmodified radiological findings after a mean follow-up of 3.5 years (6 months to 9 years).

CONCLUSION

MRI depicted AD complications in long-term follow-up of sometimes asymptomatic patients, allowing for adaptation of surgical treatment in 26 cases (46%).

Applications of phase-contrast flow and velocity imaging in cardiovascular MRI

A review of cardiovascular clinical and research applications of MRI phase-contrast velocity imaging, also known as velocity mapping or flow imaging. Phase-contrast basic principles, advantages, limitations, common pitfalls and artefacts are described. It can measure many different aspects of the complicated blood flow in the heart and vessels: volume flow (cardiac output, shunt, valve regurgitation), peak blood velocity (for stenosis), patterns and timings of velocity waveforms and flow distributions within heart chambers (abnormal ventricular function) and vessels (pulse-wave velocity, vessel wall disease). The review includes phase-contrast applications in cardiac function, heart valves, congenital heart diseases, major blood vessels, coronary arteries and myocardial wall velocity.