Ultrashort-T2* mapping at 7 tesla using an optimized pointwise encoding time reduction with radial acquisition (PETRA) sequence at standard and extended echo times

Figures

• 

  Fig 1. Example high-resolution PETRA knee image, with comparison to a conventional-TE DESS sequence image. Sagittal images of one participant’s knee from the fat-suppressed PETRA series at 0.34 mm isotropic resolution (A) and from the fat-suppressed dual-echo steady state (DESS) at 0.30 mm isotropic resolution (B). These images illustrate the difference in signal, and resulting differences in contrast between conventional and zero echo-time sequences, in the patellar tendon, cruciate ligaments, and other ultrashort-T2* tissues in these images. Zero echo-time series can enhance visualization of certain structures, supplementing the visualization provided by series with more conventional tissue contrast.

• 

  Fig 2. Sagittal PETRA images all acquired in a single participant knee, acquired using the parameters listed in S1 Table. Low-resolution images acquired at TE = 0.07 msec with (A) and without (B) fat suppression, at TE = 0.58 msec with (C) and without (D) fat suppression, and high-resolution images at TE = 0.07 msec with (E) and without (F) fat suppression. Note the off-resonance artifacts appearing as double lines and thick low/high signal borders around tissue interfaces (e.g., patellar tendon-infrapatellar fat pad interface, muscle-fat interfaces, etc.).

• 

  Fig 3. MnCl2 phantom plots. Plots showing examples of median measured (round markers) and fitted signal (dashed line) based on estimated ultrashort-T2* signal versus TE for three MnCl2 phantom solutions from two (top and bottom plots for each region) scans (a), the relationship between mean 1/T2* and MnCl2 concentration, averaged over two scans (b), the relationship between mean signal and collagen concentration at TE = 0.07 msec, averaged over three scans (c). Error bars represent the interquartile range within each subregion for signal versus TE plots and the standard deviation between scans for the 1/T2* and signal versus concentration plots.

• 

  Fig 4. Ultrashort-T2* map and corresponding R2 map for one knee for two different scan sessions. Images and maps for one participant’s knee scanned in two sessions, grouped by scan session and labeled as Scan 1 (top two rows) and Scan 2 (bottom two rows). Images for each scan include an example PETRA image at TE = 0.07 msec, ultrashort-T2* map in msec calculated using 7 TE values and R2 fit goodness map for the 7-TE fit in the masked ROIs (upper row of each set), and the ultrashort-T2* map in msec calculated using 3 TE values and R2 fit goodness map for the 3-TE fit in the masked ROIs (bottom row of each set).

• 

  Fig 5. Example T2* curves. Plots of the median measured (round markers) and fitted (dashed line) signal based on estimated ultrashort-T2* signal versus TE for the measured knee tissue regions from two scans of a single participant’s knee (10 days between scans). The points and for signal decay curves fitted to all seven TE values are shown in black and the points and signal decay curves fitted to a subset of three TE values are shown in red. Error bars represent the interquartile range within each subregion.