Improved Visualization of Intracranial Vessels by Gradient Moment Nulling in Hybrid of Opposite-contrast Magnetic Resonance Angiography (HOP MRA)

Abstract

Hybrid of opposite-contrast (HOP) magnetic resonance angiography (MRA) is a new method that combines the advantages of 3-dimensional (3D) time-of-flight (TOF) MRA and black-blood (BB) MRA without prolonging acquisition time. In phantom and clinical studies, we focused on image differences when we applied gradient moment nulling (GMN) to 2 or 3 axes in the first echo. We made an original phantom with a semicircular tube of 3- and 5-mm internal diameter, with flow rate in the tube of 0, 20, 60, 80, or 120 cm/s. In original images of the phantom obtained with TOF MRA and flow-sensitive BB MRA and in filter frequency-weighted subtraction (FWS) processed images acquired with HOP MRA, we measured the contrast-to-noise ratio (CNR) of both the inside and outside of the tubes. In FWS processed images with GMN applied to 2 axes, the CNR was high at various flow rates in both straight and bending portions of the tubes in comparison with TOF images. In a clinical study in 15 patients, we evaluated vessel visualization in images obtained using conventional TOF MRA with magnetization transfer contrast (MTC) and HOP MRA. In clinical studies, visualization scores of HOP MRA were equivalent to those of conventional TOF MRA in the bilateral internal carotid arteries (ICA) and inferior in the basilar arteries. However, visualization of the peripheral portion of the middle cerebral artery (MCA) improved significantly in HOP MRA with GMN applied to 2 and 3 axes. Visualization of the main trunk of the ICA and MCA was superior in HOP MRA with GMN applied to 2 axes. HOP MRA with 2-axis GMN may be useful for excellent visualization of both major arteries and peripheral vessels in the head.