4D time‐resolved MR angiography with keyhole (4D‐TRAK): More than 60 times accelerated MRA using a combination of CENTRA, keyhole, and SENSE at 3.0T

Abstract

Purpose: To present a new 4D method that is designed to provide high spatial resolution MR angiograms at subsecond temporal resolution by combining different techniques of view sharing with parallel imaging at 3.0T. Materials and Methods:In the keyhole-based method, a central elliptical cylinder in k-space is repeated n times (keyhole) with a random acquisition (CENTRA), and followed by the readout of the periphery of k-space. 4D-MR angiography with CENTRA keyhole (4D-TRAK) was combined with parallel imaging (SENSE) and partial Fourier imaging. In total, a speed-up factor of 66.5 (6.25 [CENTRA keyhole] ϫ 8 [SENSE] ϫ 1.33 [partial Fourier imaging]) was achieved yielding a temporal resolution of 608 ms and a spatial resolution of (1.1 ϫ 1.4 ϫ 1.1) mm 3 with whole-brain coverage 4D-TRAK was applied to five patients and compared with digital subtraction angiography (DSA).Results: 4D-TRAK was successfully completed with an acceleration factor of 66.5 in all five patients. Sharp images were acquired without any artifacts possibly created by the transition of the central cylinder and the reference dataset. MRA findings were concordant with DSA.Conclusion: 4D time-resolved MRA with keyhole (4D-TRAK) is feasible using a combination of CENTRA, keyhole, and SENSE at 3.0T and allows for more than 60 times accelerated MRA with high spatial resolution. CONTRAST-ENHANCED MR angiography (MRA) is routinely used for imaging of the vascular system in many centers (1,2). Although techniques of contrast-enhanced MRA have continuously improved in the past, there is still a demand for acquiring both high spatial resolution and high temporal resolution at the same time, as is achieved in single projection techniques such as digital subtraction angiography (DSA). It has been demonstrated that very high spatial resolution images without venous contamination can be obtained in contrast-enhanced MRA of the supraaortic arteries by starting to acquire phase-encoding in or near the center of k-space (elliptical centric (3) / CENTRA (4)). Nevertheless, these methods primarily do not contain dynamic information. Additional dynamic information, however, is clinically required or at least desired in many MRA applications (eg, MRA of cerebral arteriovenous malformations [cAVM], MRA of the foot, MRA of hemodialysis shunts, etc) to allow insight into filling and outflow of the contrast agent in the vessels. In this study a new method is presented which is designed to provide 4D contrast-enhanced MRA with high spatial resolution and more than 60 times accelerated temporal resolution by combining CENTRA with the keyhole method (5), partial Fourier, and SENSE (6) at 3.0T. In addition, an update of the literature on time-resolved MRA is given and our method is compared to currently available techniques of time-resolved MRA. MATERIALS AND METHODS Patient StudiesBetween April and September 2005, five patients (two men, three women; age range: 23-59 years, mean age: 35 years) were included in this feasibility study. All patients presented with cerebral art...

Quality-Evaluation Scheme for Cerebral Time-Resolved 3D Contrast-Enhanced MR Angiography Techniques

“…Diagnostic confidence index grading of images was recommended by most authors 4,11,12,17,21,31,33,35 because an initial appraisal is necessary before a more specific evaluation. The grading provides an immediate estimate of the level of diagnostic accuracy of the images to characterize possible vascular disease.…”

“…The artifacts were correlated with the diagnostic confidence index in our study, and this confirmed the literature data suggesting that artifacts may degrade image quality and lead to misinterpretation. 11,14,22,28,30,31,33 The type of artifacts, such as aliasing, ringing, movement, or vascular edge, must be specified because it is influenced by the TR-3D-CE-MRA strategy used. 11,35,[37][38][39] Arterial-to-venous separation, assessed with a semiquantitative scale, 5,11,12,30,34 provides a quick evaluation of the practical temporal resolution (ie, the ability of TR-3D-CE-MRA to detect rapid arteriovenous shunt involved in certain vascular malformations).…”

“…4,11,12,14,17,21,31,33,35 Grading was as follows: 0, no vascular study possible; 1, vascular study possible but with low diagnostic confidence; 2, vascular study possible with adequate diagnostic confidence; and 3, vascular study possible with high diagnostic confidence.…”

“…The region of interest was chosen to cover a large part of the vascular lumen with careful exclusion of voxels containing partial volume and to provide an easily reproducible location. 3,24 We defined arterial and venous SI and arteriovenous contrast with methods excluding noise estimation 3,11,12,24 because of the inhomogeneous distribution of noise throughout the image due to parallel imaging. 36 Arterial and venous SI curves were obtained, and 4 quantitative parameters were plotted (Fig 1): 1) Maximum arterial SI.…”

Anomalous Venous Blood Flow and Iron Deposition in Multiple Sclerosis

“…Finally, the latest and most promising technique is 4D MRI angiography, which may make it possible to measure blood flow in cerebral veins, helping to confirm and/or correlate the transcranial Doppler hemodynamic parameters described above (Eddleman et al, 2009;Spuentrup et al, 2009;Willinek et al, 2008).…”