Nonlinear excitation profiles for three-dimensional inflow MR angiography

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Cardiovascular Imaging

Background:

• Three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA) is crucial for visualizing blood vessels.
• Achieving uniform signal intensity across the entire imaging slab is a key challenge in MRA.
• Conventional radiofrequency (RF) pulses and TONE pulses have limitations in providing consistent vessel signal.

Purpose of the Study:

• To numerically calculate a novel RF excitation pulse with a nonlinear profile for 3D TOF MRA.
• To evaluate the performance of this new pulse, termed the optform pulse, in achieving uniform vessel signal.
• To compare the efficacy of the optform pulse against conventional RF pulses and TONE pulses.

Main Methods:

• Numerical calculation of a nonlinear RF excitation pulse (optform pulse) designed for uniform vessel signal.
• Acquisition of MRA data in a healthy volunteer, focusing on lower leg and carotid/vertebral arteries.
• Comparison of signal homogeneity achieved by the optform pulse versus conventional methods.

Main Results:

• The optform pulse was successfully calculated to provide a uniform vessel signal across the excitation volume.
• MRA acquisitions demonstrated superior signal homogeneity with the optform pulse in both lower leg and carotid/vertebral arteries.
• The effectiveness of the optform pulse was evident despite a tenfold difference in flow velocity ranges between the two anatomical regions.

Conclusions:

• The numerically calculated optform pulse offers a significant advancement for 3D TOF MRA.
• This novel pulse provides superior vessel signal homogeneity compared to conventional RF and TONE pulses.
• The optform pulse demonstrates robust performance across varying physiological conditions, enhancing MRA quality.