Flow void

Absence of the normal flow-void in large veins should raise suspicion of CVST, but this sign is unreliable, as it also appears with slow flow. 

On the other hand, thrombus characteristics as discussed above might also mask the presence of an acute CVST since the hypointense visualization of acute thrombus (< 3 days) on T2-weighted sequences might be mistaken as a flow void (Fig. 18.3). The same is true for old organized or partially recanalized sinus thrombosis (Fig. 18.9). 

Binder Sulfur Marshall Stability Flow Voids (%) Coefficient of... 

Venous malformations consist of collections of venous channels and a large draining vein. Most are asymptomatic but they may present with hemorrhage into the ventricles, or seizures. On contrast CT, the draining vein may appear as a linear enhancing streak, but a flow void on MRl is more sensitive. The definitive diagnosis is made on the venous phase of a cerebral angiogram. 

The earliest ischemic change on conventional MRI, immediately detectable, is loss of the normal flow void in the affected artery, the MRI equivalent of the hyperdense artery sign on... 

Vapor formation rates in rapidly heated systems have been measured by Faneuff, McLean, and Scherrer (FI) and Cole (C4) for wires in a stationary liquid pool, and by Johnson et al. (Jl, J2, Tl) for a metal ribbon suspended in a channel flow. Void growth rates in a volume-heated boiling system were studied by Lipkis, Liu, and Zuber (L8). In practice the total vapor volume... 

Hyperacute (0-6 h) T2 shows loss of signal flow void FLAIR shows vessel high signal GRE T2 shows blooming susceptibility Occurs within minutes of the infarct... 

Fig. 6.1 Basilar occlusion, (a) The T2 weighted image shows loss of the signal flow void in the basilar artery in this patient with basilar occlusion and hyperacute pontine infarct. No parenchymal abnormality is noted at this early time point, (b) Coronal MIP image from the CT angiogram demonstrates the occlusion as a filling defect (arrow)...

Fig. 5.15. Bridging vascular sign in a pedunculated leiomyoma. Tl-weighted contrast-enhanced fat-suppressed sagittal image depicts a large pedunculated subserosal leiomyoma originating from the uterine fundus. Flow-voids are seen within the vessel stalk (arrow). A second intramural leiomyoma in the anterior wall is seen displacing the endometrial stripe. (Reproduced with permission from [223])...

Flow voids in the periphery (best seen on Tl-weighted images) indicate the perifi-broid plexus vessels... 

Torashima M, Yamashita Y, Matsuno Y, Takahashi M, Nakahara K, Onitsuka Y, Ohtake H, Tanaka N, Okamura H (1998) The value of detection of flow voids between the uterus and the leiomyoma with MRI. J Magn Reson Imaging 8 427-431... 

The true AL is larger because of the tortuous path and use of the hydraulic radius predicts too large a v. Experimental data show that the constant should be 150, which gives the Blako-Kozeny equation for laminar flow, void fractions less than 0.5, efifective particle diameter Dp, and Nr, p < 10. 

Fractionated voiding is caused by hypoactivity of the detrusor muscle and voiding consists of several unsustained detrusor contractions each with its own flow. Voiding frequency tends to be low bladder capacity is large. 

Fig. 6. H2 and CO yields in the MDR reaction (filled symbols reduction under reactant flow, void symbols reduction under H2 flow).

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