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1.
Fig. 7

Fig. 7. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Representative TRAMP 13C data overlays with and without a super-STEP (beff = 119.4 s/mm2). The STEP highlights the lactate in the tumor.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
2.
Fig. 1

Fig. 1. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

(A) STEAM: Conventional STE formation. (B) Super-STEAM: Super-STE encoding and conventional excitation. (C) Super-STEAM: Super-STE encoding and super-STE excitation. (D) Super-STEP: Super-STE encoding and super-STE refocusing to MZ. It can be followed by any imaging sequence. The solid lines indicate magnetization that contributes to the final signal, while the dashed components are not observed, as they are either crushed or have zero net signal, averaged across φ.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
3.
Fig. 5

Fig. 5. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Phantom tests of the B1 response for STE and super-STE. (A) Comparison for various STEAM encoding schemes (Fig. 1A,B). (B) Comparison for various STEP schemes (Fig. 1D). The dashed lines are simulated profiles and X’s are acquired data, corrected for T2 relaxation of the phantom. Note that the simulation curves include B1 variations for all pulses, including the excitation pulses.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
4.
Fig. 3

Fig. 3. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Comparison between different encoding pulse trains (left), combined with different refocusing methods (right - only refocused signal components shown). Both super-STE designs outperform the conventional 90°-90° by storing more magnetization in MencZ (left). Both the super-STE excitation and and STEP improve the signal, with the final magnetization refocused along MX or MZ. (The schemes from Fig. 1A,B are shown in “90° Excitation”, Fig. 1C in “Super-STE Excitation”, and Fig. 1D in “STEP”).

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
5.
Fig. 9

Fig. 9. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Preliminary liver tumor model 13C data overlays with and without a super-STEP (beff = 119.4 s/mm2). (Color scale is same as Fig. 7.) In this experiment, 13C-urea was co-polarized with [1-13C]-pyruvate and both compounds were injected. As in the TRAMP, the STEP highlights the lactate in the tumor. The urea signal is also better localized to the tumor with the perfusion weighting, suggesting it is better perfused into the tumor tissue compared with other tissues.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
6.
Fig. 8

Fig. 8. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

(A) The average metabolite amplitudes across several organs in normal (N = 4) and transgenic prostate tumor mice (N = 4) show how the distribution is affected by the super-STEP (beff = 119.4 s/mm2). The tumor lactate was the largest metabolite signal across the entire animal. The preparation significantly suppressed metabolites in the kidneys and liver (* indicates p < .05). The delineation of prostate tumors (squares) and liver tumors (circles) was significantly improved with the STEP, as measured by the (B) mean lactate : pyruvate in the tumors (p < .05) and (C) the maximum tumor lactate : maximum normal tissue lactate (p < .05), where the kidneys and liver were used for a normal tissue reference.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
7.
Fig. 6

Fig. 6. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

In vivo comparison between conventional and super STE methods. (A) Metabolite amplitudes for conventional STEAM (Fig. 1A) and super-STEAM encoding (Fig. 1B, sech 180°, ΔT = 1.65ms, N = 12), normalized by the measured polarization, in a normal rat. The least-squares linear fits show the metabolite amplitude correlation between the two experiments, demonstrating that the contrast was similar. (B) STEAM (90°-90°) and super-STEP metabolite amplitudes (b = beff = 9.95 s/mm2), normalized by polarization, in a normal mouse. Again, the linear fits show reasonable correlation. Using the super-STEAM encoding and super-STEP approaches had significantly increased SNR.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
8.
Fig. 4

Fig. 4. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Simulated Menc preserved for SLR super-STE designs with various numbers of pulses. (T1 = ∞. N = 2 is conventional 90°-90° STE.) (A) As the pulse train length increases, T2 decay can outweigh the improved encoding efficiency. (B) Diffusion-weighting as a function of normalized diffusion (Eq. 21). This assumed isotropic diffusion and Tdead = 0 for two different mixing time durations (solid/dashed). As expected, there is more diffusion-weighting for longer pulse trains, although the super-STE shape is more complex than the STE. The SLR and sech train designs also vary, particularly at larger diffusion coefficients.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
9.
Fig. 2

Fig. 2. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Comparison of continuous pulses (dashed) and gapped pulse trains (solid lines) magnetization profiles. (A) Rectangular 180° and 90°-90° (conventional STE encoding). (B) Hyperbolic secant (sech) 180° inversion pulse and its gapped pulse train version (super-STE encoding) which creates a square-wave in MZ. The real and imaginary RF components are black and gray, respectively. (C) Sech super-STE profile, (φ(x⃗, f)), in response to B1 variations. The profile deviates noticably when there is 60% of the nominal B1 ampliude, but is practically indistinguishable from the nominal response for 80%, 120% (not shown), and 140% (not shown) amplitudes. (D) Gapped pulse train off-resonance profile for rectangular subpulses. The pulse train profile (solid lines) reflects the modulation of (φ(x⃗, f)) by the subpulse profile (dashed lines). The profile depends on the subpulse shape and TrfT. The subpulse profile was calculated in the small-tip regime and scaled appropriately.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.
10.
Fig. 10

Fig. 10. From: Generating Super Stimulated-Echoes in MRI and their Application to Hyperpolarized C-13 Diffusion Metabolic Imaging.

Simulation comparison between SE, STE and super-STE diffusion sequences, assuming a typical clinical system maximum gradient strength of 4 G/cm, neglecting gradient ramps, and a single-exponential model for the super-STE (Eq. 26). (A) For hyperpolarized 13C-pyruvate imaging with estimated in vivo relaxation rates. The dashed gray lines indicate the approximate b-value threshold where a super-STE approach is advantageous over a SE. The colored dashed lines demonstrate key tradeoffs: (left) The STE and super-STE have less signal as T1 is shortened due to mixing time relaxation. (right) Increased RF pulse dead-time reduces signal for all sequences, and the loss is greater in the super-STE due to a larger number of pulses used. (B) 1H diffusion for several tissue types with Tdead = 2 ms. For skeletal muscle and cartilage, which have shorter T2s, the super-STE is advantageous for large b-values.

Peder E. Z. Larson, et al. IEEE Trans Med Imaging. ;31(2):265-275.

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