Variable-density velocity-selective magnetization preparation for non-contrast-enhanced peripheral MR angiography

• Published in: Australasian physical & engineering sciences in medicine Vol. 47; no. 4; pp. 1763 - 1771
• Main Authors: Kim, Minyoung, Hwang, Inpyeong, Choi, Seung Hong, Park, Jaeseok, Shin, Taehoon
• Format: Journal Article
• Language: English
• Published: Cham Springer International Publishing 01.12.2024; Springer Nature B.V
• Subjects: Adult; Angiography; Background noise; Biological and Medical Physics; Biomedical and Life Sciences; Biomedical Engineering and Bioengineering; Biomedicine; Biophysics; Contrast Media; Density; Excitation; Fourier transforms; Humans; Magnetic resonance; Magnetic Resonance Angiography; Magnetization; Male; Medical and Radiation Physics; Medical imaging; Sampling; Signal to noise ratio; Velocity; Velocity distribution; Non-contrast-enhanced magnetic resonance angiography; RF pulse design; Magnetization preparation; Velocity-selective excitation
• ISSN: 2662-4729; 0158-9938; 2662-4737; 2662-4737; 1879-5447
• DOI: 10.1007/s13246-024-01464-3

Velocity-selective (VS) magnetization preparation has shown great promise for non-contrast-enhanced (NCE) magnetic resonance angiography (MRA) with the ability to generate positive angiographic contrast directly using a single 3D acquisition. However, existing VS-MRA methods have an issue of aliased saturation around a certain velocity, known as velocity field-of-view (vFOV), which can cause undesired signal loss in arteries. This study aimed to develop a new version of the VS preparation pulse sequence that overcomes the aliased saturation problem in conventional VS preparation. Utilizing the fact that an excitation profile is the Fourier transform of excitation k-space sampling, we sampled the k-space in a non-uniform fashion by scaling gradient pulses accordingly to have aliased excitation diffused over velocity. The variable density sampling function was numerically optimized to maximize the average of the velocity passband signal while minimizing its variance. The optimized variable density VS magnetization was validated through Bloch simulations and applied to peripheral NCE MRA in healthy subjects. The in-vivo experiments showed that the proposed variable density VS-MRA significantly lowered arterial signal loss observed in conventional VS-MRA, as evidenced by a higher arterial signal-to-noise ratio (58.50 ± 14.29 vs. 55.54 ± 12.32; p  < 0.05) and improved artery-to-background contrast-to-noise ratio (22.75 ± 7.57 vs. 20.60 ± 6.51; p  < 0.05).