Volunteer imaging was performed on a healthy male volunteer (age 70 years) using an eight-channel knee coil on a 3T GE HDxt clinical MR scanner. The 3D Cones sequence uses a unique k-sampling trajectory that samples data along twisting evenly spaced paths on cone surfaces in 3D (11 (link)). It samples data starting from the center of k-space and twists outward from there with the data acquisition starting as soon as possible after the RF excitation. Both RF and gradient spoiling are used to crush the remaining transverse magnetization after each data acquisition. Inversion preparation and excitation was performed using a 8.6 ms Silver-Hoult adiabatic inversion pulse (12 ) with a bandwidth of ∼1.5 kHz, and 300 μs duration hard excitation RF pulse, respectively. The TI was set to approximately the null point of fat at θ = 50°. Relevant sequence parameters were field of view (FOV) = 15 cm, matrix 256 × 256, slice thick = 5 mm, TE = 30 μs, TR = 50 ms, N = 5, τ = 5 ms, TI = 20 ms, and θ = 10° –80°.
Further experiments were performed on the same volunteer (but during a separate scan session) to highlight the scan time savings that can be acquired using the multispoke approach. To minimize scan time, anisotropic FOV encoding together with slab-selection excitation was used to excite and encode only regions of interest. The slab selective RF pulse was a 600 μs minimum-phase Shinnar–Le Roux pulse with peak RF power near the end of the pulse. Using the same number of k-space spokes, several inversion prepared images were obtained using different values of N. Relevant sequence parameters were FOV = 15 cm, matrix 256 × 256, slice thick = 5 mm, 10 slices, TE = 30 μs, TR = 80 ms, τ = 5 ms, θ = 30°, and TI = optimum. SNR of the images was measured as the mean signal in a region of interest (ROI), divided by the standard deviation of the noise.
Further experiments were performed on the same volunteer (but during a separate scan session) to highlight the scan time savings that can be acquired using the multispoke approach. To minimize scan time, anisotropic FOV encoding together with slab-selection excitation was used to excite and encode only regions of interest. The slab selective RF pulse was a 600 μs minimum-phase Shinnar–Le Roux pulse with peak RF power near the end of the pulse. Using the same number of k-space spokes, several inversion prepared images were obtained using different values of N. Relevant sequence parameters were FOV = 15 cm, matrix 256 × 256, slice thick = 5 mm, 10 slices, TE = 30 μs, TR = 80 ms, τ = 5 ms, θ = 30°, and TI = optimum. SNR of the images was measured as the mean signal in a region of interest (ROI), divided by the standard deviation of the noise.
