Fig. 2.

Image and maps from a low-grade tumor in an 11-year-5-month-old girl with a pilocytic astrocytoma (classified as grade I) scanned at center 4 on a 1.5-T Achieva (Philips, Best, the Netherlands). a Pre-contrast axial T2-weighted MR image (turbo spin-echo sequence, repetition time/echo time [TR/TE] = 6,070/100 ms, number of signals averaged [NSA] = 3, acquired with 4-mm slice thickness and 10% slice gap, reformatted to the dynamic susceptibility-contrast acquisition of 3.5-mm slice thickness, no gap and 3.4×3.4-mm in-plane resolution) on which the tumor region of interest is defined. b Post-contrast axial T1-weighted MR image (spin-echo sequence, TR/TE=676/12 ms, NSA=2, acquired with 4-mm slice thickness, 10% gap, reformatted as in (a) shows high signal in the tumor. c–e Uncorrected (c) and leakage-corrected (d) relative cerebral blood volume (rCBV) maps and K₂ map (e) acquired in axial plane. Dynamic susceptibility-contrast data were acquired with an sPRESTO sequence (TR/TE=17/25 ms, flip angle 7^o, with 30 slices at 3.4×3.4×3.5-mm resolution). The uncorrected rCBV map shows a black hole indicating negative values in the tumor. After correction, rCBV is shown to increase. The K₂ map shows very high values within the tumor compared to surrounding normal tissue. Uncorrected median rCBV was negative prior to leakage correction (−9.83 vs. 2.97), K₂ was 0.168. sPRESTO sensitivity-encoded Philips principles of echo-shifting with a train of observations