On the Temporal Fidelity of Nonlinear Inverse Reconstructions for Real- Time MRI – The Motion Challenge

Frahm, Jens; Schätz, Sebastian; Untenberger, Markus; Zhang, S.; Voit, Dirk; Merboldt, Klaus‐Dietmar; Sohns, Jan M; Lotz, Joachim; Uecker, Martin

doi:10.2174/1874347101408010001

Cited by 41 publications

(46 citation statements)

References 24 publications

(35 reference statements)

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“…The valveless nature of these venous plexus vessels probably enhances the direct pressure transmission greatly (Henriques, 1962). In addition, the well established link of the CSF compartment to the peripheral lymphatic system (Boulton et al, 1996;Johnston et al, 2004;Koh et al, 2005) implies a connection to respiration as a main constituent of the external lymph pump known to regulate lymphatic backflow to the venous system, in particular from cervical regions (SchmidSchönbein, 1990). This indirect mechanism may provide another contribution to CSF flux that is in line with a respiration-dependent modulation.…”

Section: Discussionmentioning

confidence: 99%

Inspiration Is the Major Regulator of Human CSF Flow

et al. 2015

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The mechanisms behind CSF flow in humans are still not fully known. CSF circulates from its primary production sites at the choroid plexus through the brain ventricles to reach the outer surface of the brain in the subarachnoid spaces from where it drains into venous bloodstream and cervical lymphatics. According to a recent concept of brain fluid transport, established in rodents, CSF from the brain surface also enters the brain tissue along para-arterial routes and exits through paravenous spaces again into subarachnoid compartments. This unidirectional flow is mainly driven by arterial pulsation. To investigate how CSF flow is regulated in humans, we applied a novel real-time magnetic resonance imaging technique at high spatial (0.75 mm) and temporal (50 ms) resolution in healthy human subjects. We observed significant CSF flow exclusively with inspiration. In particular, during forced breathing, high CSF flow was elicited during every inspiration, whereas breath holding suppressed it. Only a minor flow component could be ascribed to cardiac pulsation. The present results unambiguously identify inspiration as the most important driving force for CSF flow in humans. Inspiratory thoracic pressure reduction is expected to directly modulate the hydrostatic pressure conditions for the low-resistance paravenous, venous, and lymphatic clearance routes of CSF. Furthermore, the experimental approach opens new clinical opportunities to study the pathophysiology of various forms of hydrocephalus and to design therapeutic strategies in relation to CSF flow alterations.

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Section: Discussionmentioning

confidence: 99%

Inspiration Is the Major Regulator of Human CSF Flow

et al. 2015

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“…1,4,[26][27][28][29][30][31][32][33] While real-time MRI studies of cardiac function and flow offer general advantages over ECG-synchronized cine MRI techniques, which include free breathing, beat-to-beat analyses and dynamic access to physiological interventions, the NLINV method adds adequate temporal and spatial resolution as demonstrated in previous work. [16][17][18][19][20][21][22] On the other hand, a potential limitation of the proposed method, which currently hampers its widespread availability, is the high computational demand of NLINV reconstructions. However, this challenge has successfully been met by the development of a fully integrated bypass GPU computer to the commercial MRI system.…”

Section: Discussionmentioning

confidence: 99%

“…22 Excellent spatiotemporal acuity even of small and fast-moving objects was obtained for NLINV reconstructions without temporal filter.…”

Section: 21mentioning

confidence: 90%

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Real-time phase-contrast flow MRI of the ascending aorta and superior vena cava as a function of intrathoracic pressure (Valsalva manoeuvre)

Kowallick

Joseph²,

Unterberg‐Buchwald³

et al. 2014

BJR

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Objective: Real-time phase-contrast flow MRI at high spatiotemporal resolution was applied to simultaneously evaluate haemodynamic functions in the ascending aorta (AA) and superior vena cava (SVC) during elevated intrathoracic pressure (Valsalva manoeuvre). Methods: Real-time phase-contrast flow MRI at 3 T was based on highly undersampled radial gradient-echo acquisitions and phase-sensitive image reconstructions by regularized non-linear inversion. Dynamic alterations of flow parameters were obtained for 19 subjects at 40-ms temporal resolution, 1.33-mm in-plane resolution and 6-mm section thickness. Real-time measurements were performed during normal breathing (10 s), increased intrathoracic pressure (10 s) and recovery (20 s).Results: Real-time measurements were technically successful in all volunteers. During the Valsalva manoeuvre (late strain) and relative to values during normal breathing, the mean peak flow velocity and flow volume decreased significantly in both vessels (p , 0.001) followed by a return to normal parameters within the first 10 s of recovery in the AA. By contrast, flow in the SVC presented with a brief (1-2 heartbeats) but strong overshoot of both the peak velocity and blood volume immediately after pressure release followed by rapid normalization. Conclusion: Real-time phase-contrast flow MRI may assess cardiac haemodynamics non-invasively, in multiple vessels, across the entire luminal area and at high temporal and spatial resolution. Advances in knowledge: Future clinical applications of this technique promise new insights into haemodynamic alterations associated with pre-clinical congestive heart failure or diastolic dysfunction, especially in cases where echocardiography is technically compromised.The Valsalva manoeuvre attempts to increase the intrathoracic pressure by a forceful expiration against a closed glottis, typically for a few seconds. The resulting haemodynamic response is characterized by a sinusoidal waveform of arterial pressure and stroke volume. The pattern is caused by an acute increase in intrathoracic pressure (Phase 1), a decreased stroke volume secondary to decreased venous return (Phase 2), an acute decrease of intrathoracic pressure during early recovery (Phase 3) and a subsequent increase in stroke volume accompanied by a reflex bradycardia (Phase 4). 3 In general, however, the clinical relevance of the Valsalva manoeuvre suffers from difficulties in the non-invasive quantification of blood flow dynamics and the inability to assess haemodynamic functions simultaneously in the superior vena cava (SVC) and with respect to left-ventricular outflow. 4 Moreover, because the manoeuvre is inevitably associated with a forced and increased breathing frequency during strain release, echocardiographic studies may be compromised by the lack of an appropriate acoustic window.On the other hand, MRI techniques have emerged as a new diagnostic standard for simultaneous evaluation of leftventricular and right-ventricular function. 5 In particular,

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“…13,14 Magnitude images and phase-contrast maps were obtained online using a server with 2 Â 4 graphics processing units (sysGen/TYAN Octuple-GPU, 2x Intel Westmere E5620 processor, 48 GB RAM, Sysgen, Bremen, Germany) which was fully integrated into the reconstruction pipeline of the commercial MRI system. 17,18 Two sequential images with and without a bipolar velocity-encoding gradient (VENC ¼ 200 cm/s) were resolution, and 6 mm section thickness. Although not required for data acquisition, the electrocardiography (ECG) was co-registered to facilitate the post-acquisition flow analysis using preliminary experimental software that allowed for treatment of multiple cardiac cycles (Qflow 5.4, MEDIS, Leiden, The Netherlands).…”

Section: Real-time Phase-contrast Flow Mrimentioning

confidence: 99%

Real-time phase-contrast flow MRI of haemodynamic changes in the ascending aorta and superior vena cava during Mueller manoeuvre

et al. 2014

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AIM: To evaluate the potential of real-time phase-contrast flow magnetic resonance imaging (MRI) at 40 ms resolution for the simultaneous determination of blood flow in the ascending aorta (AA) and superior vena cava (SVC) in response to reduced intrathoracic pressure (Mueller manoeuvre).MATERIALS AND METHODS: Through-plane flow was assessed in 20 healthy young subjects using real-time phase-contrast MRI based on highly undersampled radial fast low-angle shot (FLASH) with image reconstruction by regularized non-linear inversion. Haemodynamic alterations (three repetitions per subject ¼ 60 events) were evaluated during normal breathing (10 s), inhalation with nearly closed epiglottis (10 s), and recovery (20 s).RESULTS: Relative to normal breathing and despite interindividual differences, reduced intrathoracic pressure by at least 30 mmHg significantly decreased the initial peak mean velocity (averaged across the lumen) in the AA by À24 AE 9% and increased the velocity in the SVC by þ28 AE 25% (p < 0.0001, n ¼ 23 successful events). Respective changes in flow volume per heartbeat were À25 AE 9% in the AA and þ49 AE 44% in the SVC (p < 0.0001, n ¼ 23). Flow parameters returned to baseline during sustained pressure reduction, while the heart rate was elevated by 10% (p < 0.0001) after the start (n ¼ 24) and end (n ¼ 17) of the manoeuvre. CONCLUSIONS: Real-time flow MRI during low intrathoracic pressure non-invasively revealed quantitative haemodynamic adjustments in both the AA and SVC.

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On the Temporal Fidelity of Nonlinear Inverse Reconstructions for Real- Time MRI – The Motion Challenge

Cited by 41 publications

References 24 publications

Inspiration Is the Major Regulator of Human CSF Flow

Inspiration Is the Major Regulator of Human CSF Flow

Real-time phase-contrast flow MRI of the ascending aorta and superior vena cava as a function of intrathoracic pressure (Valsalva manoeuvre)

Real-time phase-contrast flow MRI of haemodynamic changes in the ascending aorta and superior vena cava during Mueller manoeuvre

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