Fig. 7.
The tag-on and tag-off acquisitions using a TEeff of (a, c, and e) 30 ms and (b, d, and f) 300 ms. (a) and (b) are coronal images and their enlarged anatomic images of TEeff of 30 ms and 300 ms, respectively. (c) and (d) show the acquisition sequence showing the contrast-determined time of TEeff of 30 ms and 300 ms by red line, and their various TI images, respectively. The fusion image with TI 500 ms was used with tagged MRI color images covering the entire SSS region including upper PSD, lower PSD, and SSS at a slice of 3D images using various TI periods. Both TEeff of 30 ms and 300 ms show tagged CSF signals at the upper PSD, lower PSD, and SSS, while showing dark blood signals (yellow arrows) throughout TI periods. Tagged MRI signal curves of both TEeff of (e) 30 ms and (f) 300 ms show similar tagged MRI curves; tagged MRI signal increase (wash-in) and decrease (wash-out) were both around 1100–1300 ms, with similar PH. However, MTT was a bit longer, rCFF and rCFV were higher in data obtained at TEeff of 300 ms, as compared to TEeff of 30 ms. MTT was increased by approximately 270 ms, which is the difference between TEeff of 300 ms and 30 ms. This may be due to adding an extra contrast-determined time of TEeff to the TI period. During the TEeff of 300 ms period, tagged signals within the 3D slab may travel in multiple directions to increase tagged MRI outflow measures. Regarding the baseline of (f) TEeff of 300 ms, it is a non-zero baseline due to the lower signal but higher contrast (more T2-weighted) at TEeff of 300 ms, as compared to TEeff of 30 ms. From the Equation (1), lower signal in the ROI due to the long TEeff is likely to introduce an extra signal bias like a ratio of small signals in both numerator and denominator. To correct this bias, we have added an extra data point (SIR = 0% at TI = 0 ms) based on the assumption that no signal is present at TI = 0 ms. Dotted green line shows the corrected curve fit with zero starting point with the corresponding tagged fluid metrics in the parentheses. CSF, cerebrospinal fluid; MTT, mean transit time; PH, peak height; PSD, parasagittal dura; rCFF, relative CSF flow; rCFV, relative CSF volume; SIR, signal increase ratio; SSS, superior sagittal sinus; TEeff, effective TE; TI, inversion time.