MR blood flow measurement. Clinical application in the heart and circulation

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.

Standardized image interpretation and post-processing in cardiovascular magnetic resonance - 2020 update : Society for Cardiovascular Magnetic Resonance (SCMR): Board of Trustees Task Force on Standardized Post-Processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post-Processing of the Society for Cardiovascular Magnetic Resonance (SCMR). The aim of the Task Force is to recommend requirements and standards for image interpretation and post-processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate. It is an update of the original recommendations published 2013.

Velocity quantification by electrocardiography-gated phase contrast magnetic resonance imaging in patients with cardiac arrhythmia: a simulation study based on real time transesophageal echocardiography data in atrial fibrillation

OBJECTIVE

To systematically investigate the impact of beat-to-beat variations on electrocardiography (ECG)-gated multibeat flow imaging with phase contrast (PC) magnetic resonance imaging (MRI) based on real time in vivo transesophageal echocardiography (TEE) data in patients with known arrhythmia.

METHODS

Real-time 2-dimensional Doppler TEE was performed in five patients with atrial fibrillation (4 men, age = 64 ± 8.7 years). The TEE data provided real-time left atrial (LA) and left ventricular (LV) flow velocities in consecutive cardiac cycles with different RR interval durations. The PC MRI acquisitions were simulated from the TEE velocity measures by constructing time-resolved k-space data for segmented sampling schemes typically used for ECG-gated 2-dimensional PC MRI. Each simulation was repeated 100 times to minimize effects from data that may be weighted to a particular beat in the center of k-space. The resulting LA and LV velocities were compared to the average TEE velocities and data from individual cardiac cycles.

RESULTS

Despite beat-to-beat variations of velocities in TEE data, ECG-gated flow imaging with MRI could reproduce persistent average LA and LV mean velocities within 7.0% to 7.4% compared to TEE.

CONCLUSIONS

The PC MRI velocity measurements in patients with varying RR interval durations are not significantly different from time-averaged real-time velocity data for a typical segmented k-space data acquisition schemes. Though beat-to-beat variations in atrial velocities that were observed with TEE cannot be detected with ECG-gated multibeat PC MRI, it can reliably assess average flow patterns across multiple beats.

Standardized image interpretation and post processing in cardiovascular magnetic resonance: Society for Cardiovascular Magnetic Resonance (SCMR) board of trustees task force on standardized post processing

With mounting data on its accuracy and prognostic value, cardiovascular magnetic resonance (CMR) is becoming an increasingly important diagnostic tool with growing utility in clinical routine. Given its versatility and wide range of quantitative parameters, however, agreement on specific standards for the interpretation and post-processing of CMR studies is required to ensure consistent quality and reproducibility of CMR reports. This document addresses this need by providing consensus recommendations developed by the Task Force for Post Processing of the Society for Cardiovascular MR (SCMR). The aim of the task force is to recommend requirements and standards for image interpretation and post processing enabling qualitative and quantitative evaluation of CMR images. Furthermore, pitfalls of CMR image analysis are discussed where appropriate.

Phase-contrast MRI and applications in congenital heart disease

A review of phase-contrast magnetic resonance imaging techniques, with specific application to congenital heart disease, is presented. Theory, pitfalls, advantages, and specific examples of multiple, well-described congenital heart disease presentations are discussed.

Comprehensive 4D velocity mapping of the heart and great vessels by cardiovascular magnetic resonance

BACKGROUND

Phase contrast cardiovascular magnetic resonance (CMR) is able to measure all three directional components of the velocities of blood flow relative to the three spatial dimensions and the time course of the heart cycle. In this article, methods used for the acquisition, visualization, and quantification of such datasets are reviewed and illustrated.

METHODS

Currently, the acquisition of 3D cine (4D) phase contrast velocity data, synchronized relative to both cardiac and respiratory movements takes about ten minutes or more, even when using parallel imaging and optimized pulse sequence design. The large resulting datasets need appropriate post processing for the visualization of multidirectional flow, for example as vector fields, pathlines or streamlines, or for retrospective volumetric quantification.

APPLICATIONS

Multidirectional velocity acquisitions have provided 3D visualization of large scale flow features of the healthy heart and great vessels, and have shown altered patterns of flow in abnormal chambers and vessels. Clinically relevant examples include retrograde streams in atheromatous descending aortas as potential thrombo-embolic pathways in patients with cryptogenic stroke and marked variations of flow visualized in common aortic pathologies. Compared to standard clinical tools, 4D velocity mapping offers the potential for retrospective quantification of flow and other hemodynamic parameters.

CONCLUSIONS

Multidirectional, 3D cine velocity acquisitions are contributing to the understanding of normal and pathologically altered blood flow features. Although more rapid and user-friendly strategies for acquisition and analysis may be needed before 4D velocity acquisitions come to be adopted in routine clinical CMR, their capacity to measure multidirectional flows throughout a study volume has contributed novel insights into cardiovascular fluid dynamics in health and disease.

Towards comprehensive assessment of mitral regurgitation using cardiovascular magnetic resonance

Cardiovascular magnetic resonance (CMR) is increasingly used to assess patients with mitral regurgitation. Its advantages include quantitative determination of ventricular volumes and function and the mitral regurgitant fraction, and in ischemic mitral regurgitation, regional myocardial function and viability. In addition to these, identification of leaflet prolapse or restriction is necessary when valve repair is contemplated. We describe a systematic approach to the evaluation of mitral regurgitation using CMR which we have used in 149 patients with varying etiologies and severity of regurgitation over a 15 month period. Following standard ventricular cine acquisitions, including 2, 3 and 4 chamber long axis views and a short axis stack for biventricular function, we image movements of all parts of the mitral leaflets using a contiguous stack of oblique long axis cines aligned orthogonal to the central part of the line of coaptation. The 8-10 slices in the stack, orientated approximately parallel to a 3-chamber view, are acquired sequentially from the superior (antero-lateral) mitral commissure to the inferior (postero-medial) commissure, visualising each apposing pair of anterior and posterior leaflet scallops in turn (A1-P1, A2-P2 and A3-P3). We use balanced steady state free precession imaging at 1.5 Tesla, slice thickness 5 mm, with no inter-slice gaps. Where the para-commissural coaptation lines curve relative to the central region, two further oblique cines are acquired orthogonal to the line of coaptation adjacent to each commissure. To quantify mitral regurgitation, we use phase contrast velocity mapping to measure aortic outflow, subtracting this from the left ventricular stroke volume to calculate the mitral regurgitant volume which, when divided by the left ventricular stroke volume, gives the mitral regurgitant fraction. In patients with ischemic mitral regurgitation, we further assess regional left ventricular function and, with late gadolinium enhancement, myocardial viability. Comprehensive assessment of mitral regurgitation using CMR is feasible and enables determination of mitral regurgitation severity, associated leaflet prolapse or restriction, ventricular function and viability in a single examination and is now routinely performed at our centre. The mitral valve stack of images is particularly useful and easy to acquire.

Magnetic resonance (MR) imaging and MR angiography for evaluation and follow-up of hepatic artery banding in patients with hepatic involvement of hereditary hemorrhagic telangiectasia

BACKGROUND

We describe findings obtained by magnetic resonance angiography (MRA) and magnetic resonance imaging (MRI) for evaluation and follow-up after hepatic artery banding in patients with hepatic involvement of hereditary hemorrhagic telangiectasia (HHT).

METHODS

Abdominal MRA and liver MRI were performed in three patients with HHT as clinically defined by Curacao criteria. One patient underwent MRA and MRI twice for preinterventional evaluation and follow-up, one patient for preinterventional evaluation, and one patient for postinterventional evaluation. Hepatic vascular involvement of the disease and postinterventional vascular anatomy were evaluated by two radiologists by consensus.

RESULTS

Hepatic vascular involvement with perfusion disorders and arteriosystemic shunts was found in all three patients. MRA and MRI allowed diagnostic characterization of hepatic vascular disease (three of three), preinterventional evaluation of complex vascular anatomy and variants (two of two), and postinterventional follow-up of hepatic artery banding (two of two).

CONCLUSION

In preinterventional evaluation and postinterventional follow-up, MRA and MRI allows characterization of complex hepatic vascular alterations of HHT and, hence, is an alternative to other imaging modalities in the diagnosis, clinical decision making, and follow-up of HHT.

Coarctation of the aorta: pre and postoperative evaluation with MRI and MR angiography; correlation with echocardiography and surgery

AIMS

To compare MRI and MRA with Doppler-echocardiography (DE) in native and postoperative aortic coarctation, define the best MR protocol for its evaluation, compare MR with surgical findings in native coarctation.

MATERIALS AND METHODS

136 MR studies were performed in 121 patients divided in two groups: Group I, 55 preoperative; group II, 81 postoperative. In group I, all had DE and surgery was performed in 35 cases. In group II, DE was available for comparison in 71 cases. MR study comprised: spin-echo, cine, velocity-encoded cine (VEC) sequences and 3D contrast-enhanced MRA.

RESULTS

In group I, diagnosis of coarctation was made by DE in 33 cases and suspicion of coarctation and/or aortic arch hypoplasia in 18 cases. Aortic arch was not well demonstrated in 3 cases and DE missed one case. There was a close correlation between VEC MRI and Doppler gradient estimates across the coarctation, between MRI aortic arch diameters and surgery but a poor correlation in isthmic measurements. In group II, DE detected a normal isthmic region in 31 out of 35 cases. Postoperative anomalies (recoarctation, aortic arch hypoplasia, kinking, pseudoaneurysm) were not demonstrated with DE in 50% of cases.

CONCLUSIONS

MRI is superior to DE for pre and post-treatment evaluation of aortic coarctation. An optimal MR protocol is proposed. Internal measurement of the narrowing does not correspond to the external aspect of the surgical narrowing.

Noninvasive assessment of blood flow based on magnetic resonance global coherent free precession

BACKGROUND

Magnetic resonance global coherent free precession (GCFP) is a new technique that produces cine projection angiograms directly analogous to those of x-ray angiography noninvasively and without a contrast agent. In this study, we compared GCFP blood flow with "gold standards" to determine the accuracy of noninvasive GCFP blood flow measurements.

METHODS AND RESULTS

The relationship between GCFP blood flow and true blood flow defined by invasive ultrasonic flow probe and by phase contrast velocity encoded MRI (VENC) was studied in anesthetized dogs (n=6). Blood flow was controlled by use of a hydraulic occluder around the left iliac artery. GCFP images were acquired by selectively exciting the abdominal aorta and visualizing temporal blood flow into the iliac arteries. GCFP flow was similar to ultrasonic blood flow at baseline (131.3+/-44.8 versus 114.8+/-34.2 mL/min), during occlusion (10.8+/-5.1 versus 6.5+/-7.2 mL/min), during reactive hyperemia (191.4+/-100.7 versus 260.3+/-138.7 mL/min), during the new resting state (135.5+/-52.4 versus 117.8+/-24.1 mL/min), and during partial occlusion (61.4+/-36.4 versus 49.3+/-13.1 mL/min, P=NS for all). Results comparing GCFP flow with VENC were similar. Statistical analysis revealed that GCFP flow was related to mean blood flow assessed by the flow probe (P<0.0001) and by VENC (P<0.0001). In the control right iliac artery, conversely, GCFP measurements were unaffected throughout all left iliac interventions (P=NS).

CONCLUSIONS

GCFP blood flow is linearly related to true blood flow for a straight, cylindrical blood vessel without branches. Although more complex geometries imply a qualitative rather than a quantitative relationship, the data nevertheless suggest that GCFP may serve as the basis for a new form of noninvasive stress testing.

Accelerated dynamic Fourier velocity encoding by exploiting velocity-spatio-temporal correlations

OBJECTIVE

To describe how the information content in a Fourier velocity encoding (FVE) scan can be transformed into a very sparse representation and to develop a method that exploits the compactness of the data to significantly accelerate the acquisition.

MATERIALS AND METHODS

For validation, fully sampled FVE datasets were acquired in phantom and in vivo experiments. Fivefold and eightfold acceleration was simulated by using only one fifth or one eighth of the data for reconstruction in the proposed method based on the k-t BLAST framework. Reconstructed images were compared quantitatively to those from the fully sampled data.

RESULTS

Velocity spectra in the accelerated datasets were comparable to the spectra from fully sampled datasets. The detected peak velocities remained accurate even at eightfold acceleration, and the overall shape of the spectra was well preserved. Slight temporal smoothing was seen in the accelerated datasets.

CONCLUSION

A novel technique for accelerating time-resolved FVE scan is presented. It is possible to accelerate FVE to acquisition speeds comparable to a standard time-resolved phase-contrast scan.

[Pericardium and cardiac valves: value of MRI and Multislice CT]

Color Doppler echocardiography has limitations, particularly in the assessment of valvular regurgitation and pericardial diseases. MRI, with the help of three dimensional morphologic data, dynamic acquisitions with cine techniques and functional evaluation with flow sensitive techniques can be envisioned as a complementary noninvasive procedure able to provide the complete information required for planning therapeutic options. Qualitative as well as accurate and reproducible quantitative information (volume measurements, cardiac function and flow velocity profiles) are unique for the evaluation of the severity of valve or pericardial diseases. Multislice CT is unique in precisely demonstrating valvular and pericardial calcifications. This article reviews both imaging techniques used in assessing valvular and pericardial disease and discusses the advantages and limitations of these techniques in current clinical applications.

Cardiovascular magnetic resonance imaging: current and emerging applications

Magnetic resonance (MR) imaging is gaining importance in cardiology as the newest, most complex, and rapidly emerging noninvasive test of choice for patients with a multitude of cardiovascular problems. It has long been recognized to provide an accurate and reliable means of assessing the function and anatomy of the heart and great vessels, but its emerging role as one of the dominant imaging modalities in other aspects of cardiology such as perfusion imaging, atherosclerosis imaging, and coronary artery imaging cannot be understated. As MR technology evolves, newer therapeutic applications are also being developed, including specific MR-compatible catheters for electrophysiology studies/ablation as well as interventional cardiology related procedures, which may alter the way we practice cardiology in the future. Also, MR is entering an important phase in its evolution, with an anticipated exponential growth in its current applications and through the development of newer molecular imaging applications. It is anticipated that such developments will be coupled to the utilization of molecular markers to index biologic processes to allow for their in vivo visualization. This combination of biochemical markers and imaging methodology will also usher in an era of molecular imaging during which much progress in the diagnosis and treatment of cardiovascular disease is anticipated.

Assessment of valve disease: qualitative and quantitative

Evaluation of valve disease has changed significantly with the development of color Doppler echocardiography. Nevertheless, this technique has limitations, particularly in the assessment of valvular regurgitation. MR imaging, with its ability to provide three-dimensional morphologic data, dynamic cine information, and functional evaluation with flow-sensitive techniques, can be envisioned as a complementary noninvasive modality, able to provide the complete information required for planning therapeutic options. With MR imaging, qualitative as well as accurate and reproducible quantitative information such as volume measurements, cardiac function, and flow velocity profiles are unique for the evaluation of the severity of valve disease. This article reviews the different MR imaging techniques used in assessing valvular heart disease and discusses the advantages and limitations of these techniques in current clinical applications in comparison with classical imaging methods.

Cardiac MR imaging

There has been tremendous progress for MR imaging depiction of cardiac morphology and function. Further advances toward achieving faster acquisition with real-time imaging, higher resolution for plaque imaging, and quantitative analysis are taking place at a rapid pace.

Estimation of left ventricular performance through temporal pressure variations measured by MR velocity and acceleration mappings

PURPOSE

To describe a method for assessing pressure variation vs. time (dp/dt) using blood flow acceleration measured by MRI, and to demonstrate its applicability in estimating left ventricular (LV) function.

MATERIALS AND METHODS

The method was tested in vitro using a pulsatile phantom, and a strong correlation was found between transducer and MRI determinations of dp/dt (r = 0.98). Selected aortic flow parameters were then measured in 10 patients and the results were compared with transducer measurements of the LV dp/dt.

RESULTS

The correlation coefficients for the reference estimations of global myocardial function and MRI were 0.59 for aortic velocity, 0.74 for aortic acceleration, and 0.86 for aortic dp/dt.

CONCLUSION

MR measurements of velocity and acceleration within the ascending aorta offer a noninvasive method for determining indices, such as the aortic dp/dt, that are closely correlated with the global myocardial contractility function.

Effect of acquisition parameters on the accuracy of velocity encoded cine magnetic resonance imaging blood flow measurements

PURPOSE

To investigate the effect of acquisition parameters on the accuracy of 2D velocity encoded cine magnetic resonance imaging (VEC MRI) flow measurements.

MATERIALS AND METHODS

Using a pulsatile flow phantom, through-plane flow measurements were performed on a flexible vessel made of polyvinyl alcohol cryogel (PVA), a material that mimics the MR signal and biomechanical properties of aortic tissue.

RESULTS

Repeated VEC MRI flow measurements (N = 20) under baseline conditions yielded an error of 0.8 +/- 1.5%. Slice thickness, angle between flow and velocity encoding directions, spatial resolution, velocity encoding range, and radio frequency (RF) flip angles were varied over a clinically relevant range. Spatial resolution had the greatest impact on accuracy, with a 9% overestimation of flow at 16 pixels per vessel cross-section.

CONCLUSION

VEC MRI proved to be an accurate and reproducible technique for pulsatile flow measurements over the range of acquisition parameters examined as long as sufficient spatial resolution was prescribed.

Phase contrast MRI with improved temporal resolution by view sharing: k-space related velocity mapping properties

Phase contrast techniques in combination with k-space segmented CINE imaging are widely used for the quantitative assessment of blood flow or tissue motion. The temporal resolution of the corresponding pulse sequences plays an important role concerning the potential of the method to fully detect time resolved flow or motion patterns. A further improvement of temporal or spatial resolution in phase contrast CINE MRI can be achieved by the application of view sharing. Based on simulations with point-spread-functions resulting from different cyclic flow or motion patterns an analysis of view sharing techniques in combination with phase contrast MRI is presented. Velocity mapping properties and the role of different k-space regions concerning the resulting values in the phase images and thus encoded velocities were investigated. It could be shown that the velocity induced phase shifts in phase contrast techniques are mainly encoded in the central sections of k-space which makes view sharing also suitable for velocity mapping. As a result the use of appropriate sampling and data acquisition schemes permits the assessment of flow or motion patterns with significantly improved temporal resolution without loss of functional information. In addition phantom measurements with an oscillation phantom were performed in order to validate the simulation results and to demonstrate the potential of view sharing techniques to accelerate phase contrast imaging and improve the detection of the underlying flow or motion dynamics.

Effect of breath holding on blood flow measurement using fast velocity encoded cine MRI

Breath-hold MR measurement of cardiac output was compared with results from respiratory triggered MR acquisitions, since flow measurement during breath-holding may be different from physiological blood flow. Cardiac output during large lung volume breath-holding (4.47 +/- 0.63 l/min in the aorta and 4.53 +/- 0.59 l/min in the pulmonary artery) was significantly lower than that measured during normal breathing (6.09 +/- 0.49 l/min and 6.48 +/- 0.67 l/min, P < 0.01). In contrast, no significant difference was found between measurements conducted with small lung volume breath-holding (5.87 +/- 0.53 l/min and 6.41 +/- 0.75 l/min) and normal breathing. In conclusion, breath-hold MR flow measurement using small lung volume by shallow inspiration can provide a blood flow quantification that is close to physiological blood flow. Magn Reson Med 45:346-348, 2001.

Detection and quantification of valvular heart disease with dynamic cardiac MR imaging

Magnetic resonance (MR) imaging is rapidly gaining acceptance as an accurate, reproducible, noninvasive method for optimal assessment of structural and functional parameters in patients with valvular heart disease. The severity of valvular regurgitation can be evaluated with cine gradient-echo MR imaging, which allows measurement of the area of the signal void corresponding to the abnormal flow jet. Alternatively, this modality can be used to obtain ventricular volumetric measurements and calculate the regurgitant fraction, or velocity-encoded cine (VEC) MR imaging can be used to quantify regurgitant blood flow. The severity of valvular stenosis can be determined by evaluating the flow jet and associated findings with either modality or by using VEC MR imaging to calculate the transvalvular pressure gradient and valve area. Dynamic MR imaging allows accurate assessment of ventricular function and comprehensive evaluation of pathophysiologic changes. In addition, good interstudy reproducibility suggests a role for VEC MR imaging in assessing the effects of therapeutic intervention and monitoring regurgitant fraction, thereby helping in surgical planning and the prevention of ventricular dysfunction. With greater cost-effectiveness and the increasing availability of new hardware and more advanced techniques, MR imaging will become a routine procedure in valvular heart disease.

Morphologic and functional evaluation of congenital heart disease by magnetic resonance imaging

Magnetic resonance imaging (MRI) has evolved sufficiently to be recognized as a useful complementary noninvasive method to echocardiography in the evaluation of congenital heart disease (CHD). In some cases, MRI is superior to other imaging modalities, particularly in the evaluation of thoracic aortic anomalies and in defining the anatomy of central pulmonary arteries; it is also the procedure of choice in the postoperative follow-up of patients with CHD. Recent technological advances permit not only morphological evaluation (provided by spin-echo and MR angiographic techniques) but functional and flow information (provided by fast cine-GE and velocity-encoded sequences), causing it to be recognized by pediatric cardiologists and cardiac surgeons as an unavoidable technique for pre- and postoperative evaluation of some CHD. This review describes the various techniques used in the evaluation of CHD with emphasis on recent developments as well as recognized clinical applications. J. Magn. Reson. Imaging 1999;10:639-655.