Tailoring the flow sensitivity of fast spin‐echo sequences for noncontrast peripheral MR angiography

Abstract

There has recently been renewed interest in noncontrast techniques for peripheral MR angiography following the discovery of an association between gadolinium-based contrast agents and nephrogenic systemic fibrosis in patients with renal insufficiency. The ''fresh blood imaging'' technique proposed by Miyazaki et al. involves the subtraction of two three-dimensional fast spin-echo image sets, one acquired in systole, when the arteries appear dark due to flow-related dephasing, and the other obtained in diastole, when the arteries are brighter. Our goal was to investigate how parameters of the fast spin-echo sequence influence its flow sensitivity, and how that in turn impacts the depiction of large and small arteries. Results from phantom experiments and human studies in the calf suggest that the flow sensitivity is governed largely by the flip angle of the radiofrequency refocusing pulses. The area of the spoiler gradients has a lesser effect, and at low flip angles the echo time plays a role. These parameters can be optimized to obtain good depiction of the calf arteries in healthy subjects. It remains to be seen whether they provide sufficient control over flow sensitivity to achieve diagnostic-quality images in other vascular beds and in the presence of pathology. Magn Reson Med 64:1098-1108,

Intracranial arterial wall imaging using three‐dimensional high isotropic resolution black blood MRI at 3.0 Tesla

“…(ii) The use of low FA refocusing pulses causes the formation of simulated echoes, which store magnetization along the longitudinal axis and exhibits a complicated phase evolution between the longitudinal and transverse planes that results in signal loss (17). Furthermore, the FA impacts flow-related signal loss, and a smaller FA leads to greater flow suppression (17,23).…”

Non‐contrast enhanced MR angiography: Physical principles

“…The motion sensitivity of cardiac-gated 3D FSE NCE-MRA techniques is influenced by the choice of refocusing flip angle (55). The refocusing flip angle affects the relative depiction of fast-flowing blood in large arteries versus slow-flowing blood in smaller branch arteries, as illustrated in Figure 4 and exemplified in Figure 5.…”

Comparison of Nonenhanced MR Angiographic Subtraction Techniques for Infragenual Arteries at 1.5 T: A Preliminary Study

“…The fast SE approach is commercially available and relies on systolic spin dephasing from fast arterial flow (13)(14)(15)(16). Systolic arterial flow dephasing is paramount for accurate depiction of distal peripheral vessels and can be adjusted by altering the flip angle (FA) used to refocus transverse spins, with smaller FAs imparting greater sensitivity to slow flow (17). Incorporation of variable-refocusing FAs (18) (hereafter, variable FAs) increases P eripheral arterial disease (PAD) affects approximately 8 million patients in the United States, with prevalence projected to increase as the population ages (1).…”