Further, in all cases the unwanted excitation decays rapidly as |B1+| increases. Note that the |Mxy||Mxy| patterns shown in Fig. 6 are Hermitian symmetric about the |B1+| axis, and are therefore displayed only for positive selleck chemicals llc off-resonance frequencies. Fig. 7 shows the BIR-4 comparison results. A 4.7 ms, TB = 4 |B1+|-selective pulse was designed to excite a 45° tip angle, with a passband width of 0.4 Gauss/1.7 kHz, and ripples δ1,e=0.01δ1,e=0.01 and δ2,e=0.4δ2,e=0.4. The high δ2,eδ2,e was used to reflect the fact that the stopband above the passband was a ‘don’t-care’ region. The passband was placed as close to |B1+|=0 as possible, so direct weighted-least squares dual-band FIR filter

design was used to design the ββ filter. Two BIR-4 pulses were then designed: one with the same 4.7 ms duration as the |B1+|-selective pulse, and one longer 5.9 ms pulse. The 4.7 ms BIR-4 pulse design used ΔωRF0=100π/T radians/s, β=10β=10, and κ=tan-120κ=tan-120[25]. These parameters were empirically selected to match the threshold |B1+| and passband ripple of the |B1+|-selective pulse. The 5.9 ms BIR-4 pulse design used the same ΔωRF0 and ββ, but its longer duration enabled use of a less-aggressive κ=tan-115κ=tan-115. All pulses are plotted in Fig. 7a. Note that there is a π+π/8π+π/8 phase shift (not shown) between the central and outer lobes of the BIR-4 Selleckchem Veliparib pulses’

A(t)A(t) waveforms, to affect the 45° tip angle. Fig. 7b plots the |Mxy||Mxy| profile of each pulse at 0 Hz. All three pulses have approximately the

same threshold |B1+|, and approximately the same ripple across the passband. The longer 5.9 ms BIR-4 pulse achieved the same threshold |B1+| as the 4.7 ms BIR-4 pulse, without requiring a large κκ. Fig. 7c compares the off-resonance sensitivity of the three pulses. The pulses all have similar off-resonance sensitivity near |B1+|=0, in the transition up to their passbands. In the passband, the |B1+|-selective pulse appears to have similar off-resonance sensitivity to the 4.7 ms BIR-4 pulse, but the 5.9 ms BIR-4 pulse is significantly more robust to off-resonance than either 4.7 ms pulse. The proposed algorithm extends the attractive properties of nearly the Shinnar–Le Roux algorithm to the design of |B1+|-selective pulses. These include speed and the ability to predict slice profile characteristics analytically, and to thereby make tradeoffs between pulse parameters before ever designing a pulse and evaluating it. This eliminates the need for a guess-and-check approach to pulse design and makes the design process more accessible to non-experts. Further, previous methods for |B1+|-selective pulse design focused on the design of the y-component of the RF field, and assumed that the amplitude of the overall field was independent of that component [9] and [10].