Contrast-enhanced MR venography (MRV) techniques are either high resolution or time resolved [47,51]. MRI can image the vessel lumen, the vessel wall, the surrounding structures, and assess for the presence of flow in the vessel. Thrombus can also be imaged directly [52]. Nephrogenic systemic sclerosis has been associated with exposure to some brands of gadolinium-based contrast agents in patients with renal failure [53]. Spin-echo techniques produce black-blood images [33,50] on which thrombus displays high intravascular signal often accompanied by venous enlargement. The high signal decreases after 6 months, and the technique is less useful for chronic thrombus [54]. This imaging technique is not always consistent and is affected by a variety of flow artifacts [50]. Newer double inversion-recovery techniques provide more reliable black-blood imaging [47]. Black-blood imaging is also useful to image the vessel wall, where scan parameters can be adjusted to enhance either T1 or T2 weighting. Balanced gradient-echo techniques produce bright-blood images on which acute thrombus is relatively isointense to blood, making the sequence insensitive to detect acute thrombus [55,56]. The signal of thrombus varies in intensity over time. Cardiac-gated 3-D steady-state free precession and fast spin-echo techniques also produce bright-blood images. Because steady-state free precession images are T1/T2 weighted, visibility of clots depends on the age of thrombus. The weighted subtraction of fast spin-echo images in various phases of the cardiac cycle can help differentiate transient flow artifacts from true filling defects that persist over the cardiac cycle. Both techniques have been implemented for noncontrast MR angiography and appear promising [57-59]. Using time of flight to image veins is usually limited to a 2-D technique.
Suspected Upper Extremity Deep Vein Thrombosis. Contrast-enhanced MR venography (MRV) techniques are either high resolution or time resolved [47,51]. MRI can image the vessel lumen, the vessel wall, the surrounding structures, and assess for the presence of flow in the vessel. Thrombus can also be imaged directly [52]. Nephrogenic systemic sclerosis has been associated with exposure to some brands of gadolinium-based contrast agents in patients with renal failure [53]. Spin-echo techniques produce black-blood images [33,50] on which thrombus displays high intravascular signal often accompanied by venous enlargement. The high signal decreases after 6 months, and the technique is less useful for chronic thrombus [54]. This imaging technique is not always consistent and is affected by a variety of flow artifacts [50]. Newer double inversion-recovery techniques provide more reliable black-blood imaging [47]. Black-blood imaging is also useful to image the vessel wall, where scan parameters can be adjusted to enhance either T1 or T2 weighting. Balanced gradient-echo techniques produce bright-blood images on which acute thrombus is relatively isointense to blood, making the sequence insensitive to detect acute thrombus [55,56]. The signal of thrombus varies in intensity over time. Cardiac-gated 3-D steady-state free precession and fast spin-echo techniques also produce bright-blood images. Because steady-state free precession images are T1/T2 weighted, visibility of clots depends on the age of thrombus. The weighted subtraction of fast spin-echo images in various phases of the cardiac cycle can help differentiate transient flow artifacts from true filling defects that persist over the cardiac cycle. Both techniques have been implemented for noncontrast MR angiography and appear promising [57-59]. Using time of flight to image veins is usually limited to a 2-D technique.