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AJNR - American Journal of Neuroradiology

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MR Blood Oxygenation Level–Dependent Signal Differences in Parenchymal and Large Draining Vessels: Implications for Functional MR Imaging

Timo Krings^,a, Stephan G. Erberich^a, Florian Roessler^a, Jürgen Reul^a and Armin Thron^a

^a From the Department of Neuroradiology and the Interdisciplinary Center for Clinical Research—Central Nervous System, University Hospital of the Technical University, Aachen, Germany.

View larger version (45K): [in a new window]   FIG 1. MR signal time courses for parenchyma, sulcal veins, and bridging veins for single subject in two different functional runs (hand clenching) (S1). Each diamond represents MR signal at one time-point. Temporal resolution of the sequence was 2.2 s/image. Mean percent signal changes increase as a function of vessel size. Note low test-retest variability of percent signal changes within the same subject.

View larger version (128K): [in a new window]   FIG 2. MR signal time course correlation with contrast-enhanced T1-weighted scans and phase-contrast MR angiography (S5). Contrast-enhanced studies reliably show sulcal and superficial veins, whereas the phase-contrast MR angiography with given flow sensitivity demonstrates vessels the size of large bridging veins. Significant change in MR signal (S) is seen in bridging veins even close to superior sagittal sinus. From this data, one can presume that dilution of increased oxyhemoglobin content and therefore decay of S takes place when bridging veins enter large draining sinuses. Arrows point at sulcal veins, arrowheads at large bridging veins.

View larger version (39K): [in a new window]   FIG 3. MR signal time courses for parenchyma, sulcal veins, and bridging veins for subject scanned with higher temporal resolution (556 ms/image) during hand clenching. With a finer temporal resolution, the differences in onset of significant task related MR signal changes between vessels of different diameter can be visualized.

View larger version (138K): [in a new window]   FIG 4. Functional MR and MR signal time course. This patient was evaluated for presurgical planning of a space-occupying lesion near central sulcus (Astrocytoma III) (S7). The first fMR imaging study shows dual activation in slice of interest with parenchymal activation located in close proximity to tumor. A stereotactic biopsy was performed after which the patient suffered from transient mild paresis of the small right hand muscles. A postbiopsy MR image demonstrates that the biopsy involved a previously activated region posterior to the lesion. Functional study again shows dual activation with parenchymal activation close to biopsy tract and lateral venous activity unaffected by biopsy. This case illustrates the importance of differentiating task-related hemodynamic changes of small parenchymal venules and large draining veins.