Phase-contrast Flow Quantification Research Articles

Cerebral Arterial Pulsatility and Global White Matter Microstructure Impact Spatial Working Memory in Older Adults With and Without Cardiovascular Risk Factors.

Aging is associated with an increased prevalence of vascular health conditions that are linked to a disruption in the cerebral vasculature and white matter microstructural organization. In people with cardiovascular risk factors, increased cerebral arterial pulsatility is associated with poorer white matter microstructural organization and cognitive functioning. This study examines the relationship among arterial pulsatility, white matter microstructural organization, and cognitive ability in a healthy adult lifespan sample. One hundred and eighty-nine adults were divided into a younger adult (<50 years, n = 97) and older adult (>50 years, n = 92). The latter were further subdivided into two subgroups with (CV+, n = 25) and without (CV−, n = 67) cardiovascular risk factors. Arterial pulsatility was measured using cardiac-gated phase-contrast flow quantification sequence and three indexes of whole-brain white matter microstructural organization [i.e., fractional anisotropy (FA), radial diffusivity (RaD), mean diffusivity (MD)] were derived from diffusion-weighted imaging (DWI). Cognitive ability was assessed using global cognitive functioning (MoCA) and a measure of working memory [sensitivity (d′) from a 2-back task]. Neither the whole group analysis nor the younger adult group showed an association between measures of arterial pulsatility, global white matter microstructural organization, and cognition. In older adults, higher MD and RaD were associated with increased arterial pulsatility and poorer working memory performance. The indirect pathway from arterial pulsatility to working memory performance via both MD and RaD measures was significant in this group. Interestingly, a comparison of CV+ and CV− subgroups showed that this mediating relationship was only evident in older adults with at least one CV risk factor. These findings are consistent with cardiovascular risk factors as underlying arterial, white matter, and cognitive decline in cognitively normal older adults.

Stationary tissue background correction increases the precision of clinical evaluation of intra-cardiac shunts by cardiovascular magnetic resonance

We aimed to evaluate the clinical utility of stationary tissue background phase correction for affecting precision in the measurement of Qp/Qs by cardiovascular magnetic resonance (CMR). We enrolled consecutive patients (n = 91) referred for CMR at 1.5T without suspicion of cardiac shunt, and patients (n = 10) with verified cardiac shunts in this retrospective study. All patients underwent phase contrast flow quantification in the ascending aorta and pulmonary trunk. Flow was quantified using two semi-automatic software platforms (SyngoVia VA30, Vendor 1; Segment 2.0R4534, Vendor 2). Measurements were performed both uncorrected and corrected for linear (Vendor 1 and Vendor 2) or quadratic (Vendor 2) background phase. The proportion of patients outside the normal range of Qp/Qs was compared using the McNemar’s test. Compared to uncorrected measurements, there were fewer patients with a Qp/Qs outside the normal range following linear correction using Vendor 1 (10% vs 18%, p < 0.001), and Vendor 2 (10% vs 18%, p < 0.001), and following quadratic correction using Vendor 2 (7% vs 18%, p < 0.001). No patient with known shunt was reclassified as normal following stationary background correction. Therefore, we conclude that stationary tissue background correction reduces the number of patients with a Qp/Qs ratio outside the normal range in a consecutive clinical population, while simultaneously not reclassifying any patient with known cardiac shunts as having a normal Qp/Qs. Stationary tissue background correction may be used in clinical patients to increase diagnostic precision.

Magnetic Particle Imaging for High Temporal Resolution Assessment of Aneurysm Hemodynamics.

PurposeThe purpose of this work was to demonstrate the capability of magnetic particle imaging (MPI) to assess the hemodynamics in a realistic 3D aneurysm model obtained by additive manufacturing. MPI was compared with magnetic resonance imaging (MRI) and dynamic digital subtraction angiography (DSA).Materials and MethodsThe aneurysm model was of saccular morphology (7 mm dome height, 5 mm cross-section, 3–4 mm neck, 3.5 mm parent artery diameter) and connected to a peristaltic pump delivering a physiological flow (250 mL/min) and pulsation rate (70/min). High-resolution (4 h long) 4D phase contrast flow quantification (4D pc-fq) MRI was used to directly assess the hemodynamics of the model. Dynamic MPI, MRI, and DSA were performed with contrast agent injections (3 mL volume in 3 s) through a proximally placed catheter.Results and Discussion4D pc-fq measurements showed distinct pulsatile flow velocities (20–80 cm/s) as well as lower flow velocities and a vortex inside the aneurysm. All three dynamic methods (MPI, MRI, and DSA) also showed a clear pulsation pattern as well as delayed contrast agent dynamics within the aneurysm, which is most likely caused by the vortex within the aneurysm. Due to the high temporal resolution of MPI and DSA, it was possible to track the contrast agent bolus through the model and to estimate the average flow velocity (about 60 cm/s), which is in accordance with the 4D pc-fq measurements.ConclusionsThe ionizing radiation free, 4D high resolution MPI method is a very promising tool for imaging and characterization of hemodynamics in human. It carries the possibility of overcoming certain disadvantages of other modalities like considerably lower temporal resolution of dynamic MRI and limited 2D characteristics of DSA. Furthermore, additive manufacturing is the key for translating powerful pre-clinical techniques into the clinic.

SU-E-I-61: An Efficient and Practical MR Flow Quantification Quality Assurance Method

Purpose: To develop and validate a novel flow quantification quality assurance (QA) method based on a multi-directional flow phantom driven by a power injector and a fast measurement protocol. Methods: An improved MR flow phantom driven power injector was designed and constructed by immersing a 3D loop of acrylic tubes in a bath stationary saline. A power injector equipped with clinical MR scanner can be used to deliver 60 ml of saline at a nominal flow rate of 2ml/sec. A fast 2D phase contrast flow quantification protocols was optimized to measure the through-plane flow rate in three orthogonal orientations in less than 24 sec. At the same time, the actual amount of saline injected was measured to calibrate the output of power injector and to determine the true flow rate more accurately. Such method was tested and evaluated on a 3.0T clinical MR scanner (Siemens TIM Trio). Results: Eight repeat flow quantification QA measurements and power injector output calibration were performed. The measured flow rates were +2.31±0.05 ml/s and −2.21±0.10 ml/s in the H/F direction, +2.37±0.11 ml/s and −2.68±0.15 ml/s in the A/P direction and +2.35±0.11 ml/s and −2.63±0.06 ml/s in the R/L direction. The calibrated true flow rate was 1.937±0.004 ml/s. The flow quantifications in all direction are highly reproducible, but significantly different from the reference value. Conclusion: A novel method of MR flow quantification quality assurance using a advanced flow phantom driven by a power injector combined with an optimized fast measurement protocol was validated. Since most clinical MR scanners are already equipped with a power injector and the entire procedure is very quick and simple, there should be little barrier for its wide-spread implementation. Research Support from Siemens

Validation of segmented and real-time EPI phase contrast flow quantification against segmented gradient echo sequences

Background MR based Flow Quantification is an established method for measuring cardio-pulmonary haemodynamics, but is challenging to perform in situations where it may be advantageous to asses real-world physiological behavior, for example in exercise. The availability of a new real time flow quantification sequence presents the opportunity to measure velocity and flow without these challenges. This study is a preliminary validation of the method as a precursor to use of the sequence in subjects undergoing assessment of induced haemodynamic change by exercise and preload alteration. Methods

A global multiscale mathematical model for the human circulation with emphasis on the venous system

We present a global, closed-loop, multiscale mathematical model for the human circulation including the arterial system, the venous system, the heart, the pulmonary circulation and the microcirculation. A distinctive feature of our model is the detailed description of the venous system, particularly for intracranial and extracranial veins. Medium to large vessels are described by one-dimensional hyperbolic systems while the rest of the components are described by zero-dimensional models represented by differential-algebraic equations. Robust, high-order accurate numerical methodology is implemented for solving the hyperbolic equations, which are adopted from a recent reformulation that includes variable material properties. Because of the large intersubject variability of the venous system, we perform a patient-specific characterization of major veins of the head and neck using MRI data. Computational results are carefully validated using published data for the arterial system and most regions of the venous system. For head and neck veins, validation is carried out through a detailed comparison of simulation results against patient-specific phase-contrast MRI flow quantification data. A merit of our model is its global, closed-loop character; the imposition of highly artificial boundary conditions is avoided. Applications in mind include a vast range of medical conditions. Of particular interest is the study of some neurodegenerative diseases, whose venous haemodynamic connection has recently been identified by medical researchers.

WE‐C‐116‐09: A Novel Flow Quantification Quality Assurance Method Using Power Injector

Purpose: To develop a practical flow quantification quality assurance method based on a simple and compact flow phantom driven by a power injector. Methods: A flow phantom was made using acrylic with U‐shaped tubes built inside the chamber and immersed in stationary saline. A MR power injector equipped with the MR scanner was used to inject up to 110 mL of saline through the tube with 4.76 mm inner diameter at a precise rate of 2.00+/−0.01 mL/s. 2D phase contrast flow quantification was performed with a single imaging slice of 10mm perpendicular to the straight sections of the U‐shape tube on two different models of 1.5T MR scanners (Siemens Espree and Aera). Flow rates in two opposite directions were measured from phase contrast images using Siemens ARGUS software. Eight repeat measurements were performed for each scanner. Results: The flow rates measured on the Espree scanner were +2.15+/−0.06 mL/s with 7.45% difference from the 2mL/s flow rate provided by the power injector and −2.17+/−0.03mL/s with 8.7% difference. On the Aera scanner, the flow rates were +1.90+/−0.03mL/s with 4.8% difference from the 2mL/s produced by the power injector and −1.99+/−0.02mL/s with 0.6% difference. The measured flow rates were different from the true flow rate for both scanners and the error were different between scanners. Conclusion: Our proposed method of quality assurance using a simple flow phantom driven by a power injector was able to detect the errors in flow quantification for both scanner as well as the difference between two scanners. Such method can be implemented on many clinical MR scanners already equipped with a power injector.

Quantification of thoracic aorta blood flow by magnetic resonance imaging during supine cycling exercise of increasing intensity

Background Cardiac magnetic resonance imaging (MRI) may be used for the diagnosis and follow-up of diseases affecting the thoracic aorta (TA). Typically, patients are imaged at rest. Quantifying TA blood flow distribution during activity may improve understanding of disease impact by assessing possible factors contributing to exercise intolerance. Blood flow quantification during exercise MRI, though, has heretofore been complicated by prolonged MRI scan times, motion artifact, and gradient field inhomogeneities. We developed a protocol for phase-contrast (PC) MRI flow quantification in the TA and head and neck arteries during three-tiered supine cycling submaximal exercise. Methods PC-MRI was acquired in the ascending aorta (AAo) and innominate (IA), left common carotid (LCCA), and left subclavian (LSA) arteries using a 1.5T Siemens MAGNETOM ® Symphony magnet. Six healthy volunteers (28±2 years) were imaged during rest and supine pedaling of an MRI-compatible cycle to reach 130%, 150%, and 170% of resting heart rate (HR130 ,H R150 ,H R170). Scan parameters balanced image quality with acquisition time, accounting for subject positioning in the magnet and motion from pedaling. Time-resolved volumetric blood flow was calculated from PC-MRI data and estimated in the descending aorta (dAo). Flow quantification included cardiac index from AAo flow, arterial normalized mean flow (NMF,L/min/m 2 ) and flow distribution (FD,% of AAo flow). Significance of flow quantification between HRs and rest was tested post-hoc with Student’s t-test. Results Cardiac index increased linearly (r 2 =0.99) from 3.1±0.3 to 5.2±0.3 L/min/m 2 from rest to HR170 (p<0.05). HR increased to 111±5.9 bpm and workload to 38±9 watts at HR170. In the dAo, NMF increased linearly with respect to HR (r 2 =0.99) by 46%, 72%, and 93% with significance at all levels (Table 1). The IA showed significant increase in NMF of 39% at HR170 compared to rest. Increases in NMF

Magnetic resonance imaging signatures of vascular pathology in multiple sclerosis

Venous vascular contributing factors to multiple sclerosis (MS) have been known for some time. Only recently has the scope of their potential role become more apparent with the theory of chronic cerebrospinal venous insufficiency (CCSVI). As research expands to further explore the role of vascular pathology in the MS population, it is expedient to review the evidence from an imaging perspective. In this paper, we review the current state-of-the-art methods using magnetic resonance imaging (MRI) as applied to imaging MS patients and CCSVI. This includes evaluating imaging signatures of vascular structure and flow as well as brain iron content. Upon review of the literature, we find that extracranial venous anomalies including stenosis, venous malformations, and collateralization of flow in the major veins of the neck have been observed to be prevalent in the MS population. Abnormal flow has been reported in MS patients both in major vessels using phase-contrast flow quantification and in the brain using perfusion-weighted imaging. We discuss the role of quantitative flow imaging and its potential in assessing possible biomarkers for abnormal flow. Finally, it has been suggested that the presence of high iron content may indirectly indicate progression of existing vascular pathology. To that end, we review the use of susceptibility-weighted imaging in monitoring iron in the thalamus, basal ganglia, and MS lesions.

Applications of phase-contrast velocimetry sequences in cardiovascular imaging

To describe and illustrate the main applications of phase-contrast flow quantification in cardiovascular imaging. Phase-contrast velocimetry sequences provide an accurate, reliable, reproducible and non-invasive study of blood flow, information which is sometimes not available from other investigation methods. The haemodynamic information obtained from these complement MRI angiography images. They appear to have a range of clinical applications, firstly improving pathophysiological understanding but also contributing to the treatment and follow-up strategy after surgical or endovascular treatment.

CMR real-time, free-breathing, phase contrast flow quantification: a novel approach to assess ventricular coupling in constrictive pericarditis

Background/objective Constrictive pericarditis (CP) is an important cause of heart failure; however, with accurate diagnosis and directed treatment it is potentially curable. Cardiac magnetic resonance imaging (CMR) has played a diagnostic role, primarily by allowing assessment of pericardial morphology but with limited depiction of physiological changes. We sought to examine the feasibility of a novel CMR approach that enables real-time phase contrast (RT-PC) assessment of discordant respirophasic changes in trans-mitral and tricuspid flow velocity the signature findings in CP due to enhanced ventricular interdependence. Method Patients referred to the CMR lab pre-pericardectomy or for assessment of suspected CP were included. Following routine CMR examination for CP, transmitral (MV) and tricuspid valve (TV) flow velocities were simultaneously obtained by through-plane RT-PC imaging during unrestricted respiration using a slice position to include both valves (Figure 1) with the following parameters: TR/TE=13.7ms/2.5ms, water excitation pulse with flip angle=25, 10mm slice thickness, 160x120 matrix, EPI factor=15, TSENSE rate=2, slice thickness=10mm, and VENC=150cm/s. Shared velocity encoding was used to achieve an effective temporal

Visualization and Quantification of Flow and Velocity Fields in Intracranial Arteriovenous Malformations Using Phase-Contrast MR Angiography

The objective of this study was to describe postprocessing tools for MR phase-contrast flow quantification images and apply those tools to cerebral arteriovenous malformations (AVMs) to visualize blood flow dynamics noninvasively. Inflow and outflow zones were clearly depicted at different regions in the AVM. The processed images showed flow patterns including vortical flow and variations in velocity over the cardiac cycle. Particle tracking gave an impression of the overall flow state and of the venous drainage system in particular.

In‐plane velocity encoding with coherent steady‐state imaging

Standard phase-contrast flow quantification (PC-FQ) using radiofrequency (RF) spoiled steady-state (SS) incoherent gradient-echo sequences have a relatively low signal-to-noise ratio (SNR). Unspoiled SS coherent (SSC) gradient-echo sequences have a higher intrinsic SNR and are T2/T1 weighted so that blood has a relatively large signal compared to other tissues. An SSC sequence that was modified to allow in-plane velocity encoding is presented. Velocity encoding was achieved by inverting the readout gradients. This offers the benefit that there is no resultant increase in repetition time (TR), which avoids increased sensitivity to off-resonance artifacts when conventional velocity-encoding methods using separate velocity-encoding gradients are extended to SSC sequences. The results of standard PC-FQ and the new method from in vitro experiments of constant and sinusoidal flow, and in vivo imaging of the carotid artery were compared. Vector field maps and paths obtained from particle-tracking calculations based on the velocity-encoded images were used to visualize the velocity data. The technique has the potential to increase the precision of PC-FQ measurements.

Spiral laminar flow in the abdominal aorta: a predictor of renal impairment deterioration in patients with renal artery stenosis?

Spiral or helical arterial blood flow patterns have been widely observed in both animals and humans. The absence of spiral flow has been associated with carotid arterial disease. The aim of this study was to detect the presence of aortic spiral flow using magnetic resonance imaging (MRI) and to evaluate the relationship of the presence of spiral aortic flow with renal arterial disease and renal function in the follow-up of patients with suspected renal atheromatous disease. Prospective study of 100 patients with suspected renal arterial disease and 44 patient controls. Using a 1.5 T MRI unit (Siemens Symphony), phase contrast flow quantification and three-dimensional contrast enhanced MR angiography of the abdominal aorta were performed. Renal arterial stenoses (RAS) were classified minimal, moderate or severe. Renal function was followed at 3 months before and 6 months after MRI. Non-spiral flow was more prevalent in patients with more severe RAS. Renal impairment progressed significantly in severe RAS without spiral flow (P = 0.0065), but did not progress significantly in severe RAS with spiral flow (P = 0.12). In minimal or moderate RAS with or without spiral flow there was no significant progression (P = 0.16, 0.13, 0.47, 0.092, respectively). Aortic spiral blood flow can be assessed with MRI. Lack of aortic spiral blood flow in patients with severe RAS is associated with significant short-term renal function deterioration. Determination of blood flow patterns may be a useful indicator of renal impairment progression in patients with suspected renal artery stenosis.

Differential diagnosis of arachnoid cyst from subarachnoid space enlargement by phase-contrast cine MRI.

To reveal the relationship of brain motion and cerebrospinal fluid (CSF) flow by phase-contrast cine MRI, and to evaluate this technique in differentiating between arachnoid cysts and subarachnoid space enlargement. Using a phase-contrast cine MRI pulse sequence, we measured brain motion and CSF flow during the cardiac cycle in 10 healthy volunteers and 10 patients with MRI-suspected arachnoid cyst or subarachnoid space enlargement. CSF stroke volume curve was illustrated according to flow quantification, and time-signal intensity curve was traced. The two curves were compared. This study showed that brain motion was due to the volume difference between arterial and venous blood flow during a cardiac cycle, and thus drives CSF pulsation. Arachnoid cysts and subarachnoid space enlargement carried different curve patterns, demonstrating that phase-contrast MRI and flow quantification can be a useful and reliable technique for non-invasive evaluation of brain motion and CSF flow. Arachnoid cysts can be successfully differentiated using phase-contrast cine MRI from subarachnoid space enlargement.

Improved phase-contrast flow quantification by three-dimensional vessel localization

In this paper, a method of three-dimensional (3D) vessel localization is presented to allow the identification of a vessel of interest, the selection of a vessel segment, and the determination of a slice orientation to improve the accuracy of phase-contrast magnetic resonance (PCMR) angiography. A marching-cube surface-rendering algorithm was used to reconstruct the 3D vasculature. Surface-rendering was obtained using an iso-surface value determined from a maximum intensity projection (MIP) image. This 3D vasculature was used to find a vessel of interest, select a vessel segment, and to determine the slice orientation perpendicular to the vessel axis. Volumetric flow rate (VFR) was obtained in a phantom model and in vivo using 3D localization with double oblique cine PCMR scanning. PCMR flow measurements in the phantom showed 5.2% maximum error and a standard deviation of 9 mL/min during steady flow, 7.9% maximum error and a standard deviation of 13 mL/min during pulsatile flow compared with measurements using an ultrasonic transit-time flowmeter. PCMR VFR measurement error increased with misalignment at 10, 20, and 30 degrees oblique to the perpendicular slice in vitro and in vivo. The 3D localization technique allowed precise localization of the vessel of interest and optimal placement of the slice orientation for minimum error in flow measurements.

Carotid artery stenosis: clinical efficacy of MR phase-contrast flow quantification as an adjunct to MR angiography.

To assess the utility of magnetic resonance (MR) flow quantification in the evaluation of suspected carotid artery stenosis. Fifty-five patients referred for angiography and 10 healthy volunteers underwent Doppler ultrasound, three-dimensional time-of-flight MR angiography, and MR phase-contrast flow quantification to measure peak systolic velocity (PSV) and volumetric flow rate (VFR) in the common and internal carotid arteries distal to the stenosis. PSV and VFR were significantly lower in the severely (> or = 70%) stenosed internal carotid arteries (P < .05). The VFR ratio (internal carotid artery-common carotid artery) achieved 91% overall accuracy for detection of severe stenosis. Combination of flow data with results of MR angiography yielded sensitivity of 100% (95% confidence interval, 78%-100%) with a modest loss in specificity. Doppler and MR measurements of PSV in the common carotid artery showed significant correlation: volunteers, r = .73; patients, r = .64. MR flow quantification provides information about the hemodynamic significance of carotid stenosis. As an adjunct to MR angiography, it may be useful in enabling differentiation of occlusions from critical stenoses.