Rapid flow through the imaging plane produces a bright signal, whereas slow flow or in-plane flow can produce a dark signal due to signal saturation [59]. On axial 2-D time-of-flight images, the jugular veins, right brachiocephalic vein, and superior vena cava are oriented in the superior-inferior direction and produce a bright signal, whereas the left brachiocephalic vein and subclavian 3 Suspected Upper-Extremity Deep Vein Thrombosis veins are oriented in-plane and produce a darker signal, often requiring sagittal 2-D time-of-flight images for best assessment. Breathing artifacts may also impair imaging quality [11,59,60]. Phase-contrast flow imaging has not been widely used for upper-extremity venography because of the slow flows that must be detected [59]. IV gadolinium-based contrast agents [59] can be administered during acquisition of 2-D or 3-D T1-weighted gradient-echo images with fat saturation to produce a very bright signal in patent vessels [45,61,62]. A 90- to 120- second delay is required after injection to allow the contrast bolus to enter the venous or equilibrium phase [47,59] and to generate an MRV. MRV has proven very useful to evaluate the central venous structures, which cannot be directly imaged by US, but US or venography are still preferred to image the more peripheral veins. A few IV contrast agents persist longer in the vessels and have been useful to image the venous structures. Fibrin-specific MR contrast agents can further enhance all thrombi and may even detect thrombi not readily visible in noncontrast imaging [63]. The dynamic filling of vessels by IV contrast agents can be imaged with time-resolved techniques. Such techniques can reduce both IV contrast volume and acquisition time while improving specificity when used as an adjunct to conventional MR sequences [64,65].
Suspected Upper Extremity Deep Vein Thrombosis. Rapid flow through the imaging plane produces a bright signal, whereas slow flow or in-plane flow can produce a dark signal due to signal saturation [59]. On axial 2-D time-of-flight images, the jugular veins, right brachiocephalic vein, and superior vena cava are oriented in the superior-inferior direction and produce a bright signal, whereas the left brachiocephalic vein and subclavian 3 Suspected Upper-Extremity Deep Vein Thrombosis veins are oriented in-plane and produce a darker signal, often requiring sagittal 2-D time-of-flight images for best assessment. Breathing artifacts may also impair imaging quality [11,59,60]. Phase-contrast flow imaging has not been widely used for upper-extremity venography because of the slow flows that must be detected [59]. IV gadolinium-based contrast agents [59] can be administered during acquisition of 2-D or 3-D T1-weighted gradient-echo images with fat saturation to produce a very bright signal in patent vessels [45,61,62]. A 90- to 120- second delay is required after injection to allow the contrast bolus to enter the venous or equilibrium phase [47,59] and to generate an MRV. MRV has proven very useful to evaluate the central venous structures, which cannot be directly imaged by US, but US or venography are still preferred to image the more peripheral veins. A few IV contrast agents persist longer in the vessels and have been useful to image the venous structures. Fibrin-specific MR contrast agents can further enhance all thrombi and may even detect thrombi not readily visible in noncontrast imaging [63]. The dynamic filling of vessels by IV contrast agents can be imaged with time-resolved techniques. Such techniques can reduce both IV contrast volume and acquisition time while improving specificity when used as an adjunct to conventional MR sequences [64,65].