Whole-brain chemical exchange saturation transfer imaging with optimized turbo spin echo readout

FIGURE S1 Source S₀ images spanning the whole BSA phantom from the proposed 3D SPACE-CEST sequence. No discernible artifact exists throughout the SPACE-CEST source images, reflecting the robustness of the proposed sequence

FIGURE S2 The APTw images spanning the whole BSA phantom from the proposed 3D SPACE-CEST sequence. Minor artifacts occur at edge slices on the APTw images, possibly reflecting the deteriorating B₀ field homogeneity

FIGURE S3 Source S₀ images (A) and corresponding B₀ offset maps (B) spanning the whole brain of a normal volunteer from the proposed SPACE-CEST sequence using the constant flip angle refocusing mode. These images were ordered at a finer equidistant resolution than those shown in Figure 4. Red arrows indicate noticeable B₀ inhomogeneity at the tissue–air interface

FIGURE S4 Sagittal APTw images calculated from source images and B₀ maps as shown in Figure 4. Skull stripping was performed to render only the brain volume. High-quality APTw maps spanning the whole brain were obtained with the proposed SPACE-CEST sequence, attesting its feasibility for in vivo applications

FIGURE S5 Transverse APTw images calculated from retrospectively reconstructed source images and B₀ maps in a transverse orientation. The original source images and B₀ maps are shown in Figure 4. Whole-brain isotropic imaging with the SPACE-CEST sequence allows convenient retrospective multiplanar reconstruction

FIGURE S6 Coronal APTw images calculated from retrospectively reconstructed source images and B₀ maps in a coronal orientation. The original source images and B₀ maps are shown in Figure 4. Whole-brain isotropic imaging with the SPACE-CEST sequence allows convenient retrospective multiplanar reconstruction

FIGURE S7 The fluid-attenuated inversion recovery images (A) and corresponding APTw maps from the proposed SPACE-CEST (B) sequences done on the second newly diagnosed brain tumor patient. The SPACE-CEST sequence used the constant flip angle refocusing mode. Red arrows indicate the brain tumor regions

FIGURE S8 The SPACE-CEST source images acquired with nominal turbo factors of 140 (A) and 90 (B) from the patient shown in Figure 7. The acquisition window of the SPACE readout module was reduced from 369 ms to 239 ms when decreasing the nominal turbo factor from 140 to 90. However, little improvement in spatial resolution was achieved (Supporting Information Figure S8B versus S8A), which corroborates the established conclusion that the SPACE readout module can support long acquisition duration up to 1 second, as noted in Ref. 39

FIGURE S9 The SPACE-CEST source images acquired with nominal turbo factors of 140 (A,B) and 90 (C), and in-plane resolution of 2.8 × 2.8 mm² (A,C) and 1.4 × 1.4 mm² (B) from the BSA phantom shown in Figure 2. Little improvement in spatial resolution was achieved when reducing the turbo factor from 140 to 90 (Supporting Information Figure S9C versus S9A), which is consistent with the results in Supporting Information Figure S8. However, noticeable improvement in spatial resolution was achieved when doubling the in-plane resolution without changing the turbo factor (Supporting Information Figure S9B versus S9A). Thus, one should probably consider using higher spatial resolution than 2.8 × 2.8 × 2.8 mm³ used here instead of shortening the turbo factor, if interested in reducing the blurriness. However, further investigation needs to be done to study the causes of blurriness in the future