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AJNR - American Journal of Neuroradiology

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Arteriovenous Shunt Visualization in Arteriovenous Malformations with Arterial Spin-Labeling MR Imaging

R.L. Wolf^a, J. Wang^a,b, J.A. Detre^a,b, E.L. Zager^c and R.W. Hurst^a,c

^a Department of Radiology, University of Pennsylvania Medical Center, Philadelphia, Pa
^b Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, Pa
^c Department of Neurosurgery, University of Pennsylvania Medical Center, Philadelphia, Pa

View larger version (20K): [in this window] [in a new window]   Fig 1. Image evaluation and shunt approximation for a right hemisphere AVM. A, CASL perfusion M maps show bright signal intensity in the sagittal sinus and right transverse sinus (arrowheads) and in draining veins (arrows) adjacent to the nidus (open arrows). B, A small region of interest (red circle) placed in the left basal ganglia is used for each patient to measure mean M (BGmean) and SD (BGSD). A threshold is generated (empirically chosen as threshold = BGmean + 8 *BGSD) above which voxels are labeled as shunt voxels to create a mask (blue voxels) for the AVM and draining vessels. The AV shunt fraction is estimated by multiplying the mean M in the mask by the number of voxels in the mask, then dividing by the mean M in the entire brain multiplied by all labeled voxels. C, Registered 2D TOF MRA source images (no superior saturation band) are reviewed to verify reasonable selection of AVM and draining vessels (open and closed arrows).

View larger version (45K): [in this window] [in a new window]   Fig 2. AVM before (top) and 2 days after (bottom) partial embolization (patient 1). CASL M images (A, D) show decrease in AV shunt (arrows, D), estimated decrease from 23% to 20%. Superficial venous drainage is identified, including the superior sagittal sinus and sphenobasal sinus on both studies (open arrowheads, A). Of interest, despite intense signal intensity in the sphenobasal sinus, this corresponds to a relatively small venous structure on DSA (black arrowhead, C). DSA lateral projections (C, F) and 3D TOF MRA collapsed maximum intensity projection images (B, E) confirm decreased flow in a portion of AVM, especially the posterior-superior portion (white arrowhead, E).

View larger version (37K): [in this window] [in a new window]   Fig 3. Susceptibility artifact resulting from the presence of embolic material, thrombus, and/or hemorrhage (patient 1). CASL source images from 4 imaging locations are shown.

View larger version (49K): [in this window] [in a new window]   Fig 4. Multiple postlabeling delay times (200–1500 ms): effect on ASL signal intensity in the AVM (patient 1). M (T1-corrected) measured in regions of interest for the AVM (diamond), sagittal sinus (triangle), right MCA territory (box), and entire brain (circle) at each delay is plotted (above), with M maps from 1 imaging location at multiple delays for comparison (below). ASL signal intensity is relatively stable in global measures over the entire brain and in the MCA at longer delays as expected. Signal intensity decreases in AVM and increases in sagittal sinus as delay increases.

View larger version (18K): [in this window] [in a new window]   Fig 5. Regional changes in CBF compared with extent of AV shunt. = contralateral – ipsilateral CBF in measured regions of interest in white matter near the AVM, the cortex near the AVM, the thalamus, and the basal ganglia. A, Cortical gray matter CBF values are negatively but weakly correlated with percent AV shunt and are not significant. (B) values in white matter (R2 = 0.70, F = 11.58, P = .02) are negatively correlated (blood flow in adjacent ipsilateral white matter increases as percent shunt increased). Basal ganglia values (C) show little change in CBF with the size of the AV shunt, but thalamic CBF (D) appears to decrease ipsilaterally as percent AV shunt increases (R2 = 0.74, F = 14.19, P = .01).