A novel sequence for simultaneous measurement of whole-brain static and dynamic MRA, intracranial vessel wall image, and T1 -weighted structural brain MRI.

PURPOSE: To propose a highly time-efficient imaging technique named improved simultaneous noncontrast angiography and intraplaque hemorrhage (iSNAP) for simultaneous assessment of lumen, vessel wall, and blood flow in intracranial arteries. METHODS: iSNAP consists of pulsed arterial spin labeling preparations and 3D golden angle radial acquisition. Images were reconstructed by k-space weighted image contrast (KWIC) method with optimized data-sharing strategies. Dynamic MRA for blood flow assessment was obtained from iSNAP by reconstruction at multiple inversion times and image subtraction, static MRA by both image subtraction approach and phase-sensitive inversion recovery technique, and vessel wall images by both reconstruction at zero-crossing time-point of blood and phase-sensitive inversion recovery. A T1 -weighted brain MRI was also reconstructed from iSNAP. Preliminary comparison of iSNAP against the dedicated dynamic MRA sequence 4D-TRANCE, MRA/vessel wall imaging sequence SNAP, and vessel wall imaging sequence T1 -weighted VISTA was performed in healthy volunteers and patients. RESULTS: iSNAP has whole-brain coverage and takes ~6.5 min. The dedicated reconstruction strategies are feasible for each iSNAP image contrast and beneficial for image SNR. iSNAP-dynamic MRA yields similar dynamic flow information as 4D-TRANCE and allows more flexible temporal resolution. The 2 types of iSNAP static MRA images complement each other in characterizing both proximal large arteries and distal small arteries. Depiction of vessel wall lesions in iSNAP vessel wall images is better than SNAP and may be similar to T1 -weighted VISTA, although the images are slightly blurred. CONCLUSION: iSNAP provides a time-efficient evaluation of intracranial arteries and may have great potential for comprehensive assessment of intracranial vascular conditions using a single sequence.

Intracranial simultaneous noncontrast angiography and intraplaque hemorrhage (SNAP) MRA: Analyzation, optimization, and extension for dynamic MRA.

PURPOSE: Simultaneous noncontrast angiography and intraplaque (SNAP) imaging, as a noncontrast-enhanced MRA technique, may not provide consistent vessel visualization for intracranial artery imaging among subjects. This study aims to investigate the underlying mechanism and extend SNAP to dynamic MRA. METHODS: The cause of the instability of intracranial SNAP-MRA was investigated through theoretical analysis and simulations. The scan parameters, including TI and flip angle, were optimized for reliable imaging. In vivo experiments were conducted to validate the simulation results. The simulation results were correlated with real intracranial blood flow by introducing the concept of blood travel time, and intracranial SNAP-MRA was revealed to reflect the cerebral blood expanse region in 5 TI. A new noncontrast-enhanced dynamic MRA technique, termed 4D SNAP-MRA, was proposed and demonstrated through in vivo scans. RESULTS: The cause of the instability of intracranial SNAP-MRA was proved to be the slow or fast blood flow in the imaging slab. This instability can be mitigated by adjusting TI and flip angle in the SNAP sequence. The proposed 4D SNAP-MRA can provide dynamic visualization of the cerebral blood circulation and cerebral hemodynamic information such as blood travel time. CONCLUSION: The 3D SNAP-MRA with optimal imaging parameters can generate cerebral angiography with hemodynamic information, and the 4D SNAP-MRA provides dynamic visualization of the cerebral blood circulation.

Noncontrast enhanced four-dimensional dynamic MRA with golden angle radial acquisition and K-space weighted image contrast (KWIC) reconstruction.

PURPOSE: To explore the feasibility of 2D and 3D golden-angle radial acquisition strategies in conjunction with k-space weighted image contrast (KWIC) temporal filtering to achieve noncontrast enhanced dynamic MRA (dMRA) with high spatial resolution, low streaking artifacts and high temporal fidelity. METHODS: Simulations and in vivo examinations in eight normal volunteers and an arteriovenous malformation patient were carried out. Both 2D and 3D golden angle radial sequences, preceded by spin tagging, were used for dMRA of the brain. The radial dMRA data were temporally filtered using the KWIC strategy and compared with matched standard Cartesian techniques. RESULTS: The 2D and 3D dynamic MRA image series acquired with the proposed radial techniques demonstrated excellent image quality without discernible temporal blurring compared with standard Cartesian based approaches. The image quality of radial dMRA was equivalent to or higher than that of Cartesian dMRA by visual inspection. A reduction factor of up to 10 and 3 in scan time was achieved for 2D and 3D radial dMRA compared with the Cartesian-based counterparts. CONCLUSION: The proposed 2D and 3D radial dMRA techniques demonstrated image quality comparable or even superior to those obtained with standard Cartesian methods, but within a fraction of the scan time.

Dynamic Imaging of Aortic Pathologies: Review of Clinical Applications and Imaging Protocols.

The past decade has seen significant advances in dynamic imaging of the aorta. Today's vascular surgeons have the opportunity to choose from a wide array of imaging modalities to evaluate different aortic pathologies. While vascular ultrasound and aortography are considered to be the bread and butter imaging modalities, newer dynamic imaging techniques provide time-resolved information in various aortic pathologies. However, despite growing evidence of their advantages in the literature, they have not been routinely adopted. In order to understand the role of these emerging modalities, one must understand their principles, advantages, and limitations in the context of various clinical scenarios. In this review, we provide an overview of dynamic imaging techniques for aortic pathologies and describe various dynamic computed tomography and magnetic resonance imaging protocols, clinical applications, and potential future directions.

Utility of dynamic MRA in the evaluation of male erectile dysfunction.

PURPOSE: To assess the efficacy of time-resolved MR angiography (MRA) in evaluating penile vasculature in patients with clinically suspected vascular anomalies contributing to their erectile dysfunction correlating with penile doppler ultrasound (PDUS) findings and clinical outcomes after surgical intervention. METHODS: Men (n = 26) with signs of early vascular shunting on PDUS underwent time-resolved, contrast-enhanced (0.1 mMol/kg gadobutrol at 1 ml/s followed by saline flush) 3-dimensional spoiled gradient echo T1-weighted MRA sequence performed over 3 min with 4.6 s frame rate after intracavernosal injection of an erectogenic agent. Additional T1- and T2-weighted sequences were performed for anatomic co-localization and tissue characterization. MRA images were evaluated for early filling of draining veins as well as arteriovenous malformations and fistulas and correlated with findings at surgery. RESULTS: 29 MRA examinations on 26 patients (mean age 39 years) demonstrated abnormal early venous drainage (n = 22) as well as diminutive/delayed cavernosal enhancement (n = 3), incomplete tumescence (n = 2), and combined arterial inflow/venous outflow disease (n = 1). The MRA had a concordance of 85.2% at determining the presence, or lack thereof of a shunt/AVM when compared to PDUS. CONCLUSIONS: Time-resolved MRA allows for both temporal and spatial resolution with visualization of both arterial and venous abnormalities which may be suggested with a screening PDUS examination. This technique allows us to provide detailed anatomic information prior to any surgical intervention.