collaterals are formed. Numerous such collateral pathways Flow volume in the azygos venous system was quantioccur; clinically, the most relevant are gastroesophageal varitated with Cine-phase contrast (PC) velocity mapping ces. Hemorrhage from gastroesophageal varices is the main in volunteers and compared with patients with known complication and leading cause of death in patients with porportal hypertension, who were referred for transjugular tal hypertension. 4 Although a multitude of clinical, laboraintrahepatic portosystemic shunt (TIPS) placement.tory, and endoscopic parameters have been evaluated for risk Subsequently, the TIPS-induced hemodynamic effects stratification with regard to variceal hemorrhage, their clinion portal and azygos flow were analyzed. To assess intracal usefulness has been limited. 1,5-12 and intersubject variability, flow in the azygos veins wasBecause gastroesophageal collaterals drain into the azymeasured in each of 10 normal subjects at three different gous system, measurement of the flow therein reflects the times. Subsequently, portal and azygos flow was quantidegree of gastroesophageal collateralization. 13 Several autated in 20 patients with portal hypertension, before and thors have demonstrated an increased azygous flow in paafter TIPS placement. All imaging was performed on a tients with portal hypertension [14][15][16][17] and revealed an associa-1.5-tesla magnetic resonance imaging (MRI) system. tion between the risk of variceal hemorrhage and highly Azygos flow was measured transaxially at the midthoelevated azygous flow. 17 The clinical significance of these racic level. Cine-PC flow measurements of the main porfindings was limited, however, by the invasive nature of the tal vein followed morphological evaluation of the portal employed continuous thermodilution flow measurement techvenous system with axial and coronal breath-held magnique. net resonance angiogram. Azygos flow in normal subPhase contrast (PC) velocity mapping allows for the direct jects was characterized by high inter-and low intrasubquantitative evaluation of flow dynamics. The phase of proton ject variability. Azygos flow in patients with portal spins is modulated by altering the first moment of the maghypertension was significantly higher (P õ .001). Follownetic field in any direction. The gradient modulation causes ing successful TIPS placement in 18 patients, Cine-PC spins moving in the encoded direction to acquire a phase revealed a mean decrease in azygos flow of 46.3% (P õ shift, which is proportional to velocity. Cine-PC flow mea-.001) and a 134% (P õ .001) increase of portal flow. Resurements have been validated in vitro 18 as well as in vivo, 19-23 flecting the complexity of portal hemodynamics, there including the portal vein. 5,24,25 Combined with Cine-imaging, was no correlation between the changes in the portal this technique provides a two-dimensional velocity map in a and azygos systems. In 2 patients with early occlusion cross-section with good temporal resolution. 27 of TIPS, docume...