Intravascular Ultrasound in the diagnosis and treatment of chronic cerebrospinal venous insufficiency

Technical considerations

Intravascular ultrasound is a technique that places within a hollow structure, such as a vein or artery, a catheter or a wire containing a miniaturized phased array ultrasonic transducer that sends out frequencies of 10 to 50 megahertz and then captures reflections off near objects. The catheter or wire is 3.2-8.2 French in diameter and is attached externally to a cart that performs the reformations and calculations. The systems are also equipped with a motorized unit that can retract the catheter at a fixed rate. The device can be introduced through a sheath of 6-9 Fr diameters and advanced over a 0.01inch-0.038 inch guidewire by either over the wire or rapid exchange techniques. (11)

Images that are created are cross sectional B-mode images with resolution of 110-150 microns and penetration of about 20 millimeters. In addition to cross sectional images, modern units can create longitudinal reformations that some believe provide images that are more revealing views of length of stenosis and degree of narrowing. However, this requires use of a motorized catheter driver. Some vendors have now made available wires that can capture hemodynamic data such as Doppler flow rates, pressures and gradients. Assessment of stenotic and microvascular resistance is now possible, although the utility of this information in CCSVI is not established.

Other methodologies include ChromaFlo and VH (Virtual Histology). Chromaflow detects blood flow and represents it on imaging with a red color. Thus this non-quantifiable presentation of flow aids in differentiating tissue types that are similar to flowing blood on the B-mode images.  VH-IVUS is a spectrum analysis of IVUS-derived radiofrequency (RF) data acquired at the top of the R wave. It allows reconstruction of a color coded map showing a more detailed analysis of plaque composition and morphology. It is suggested that VH-IVUS has the ability to detect lesions that predict high risk lesions in coronary artery disease. It is possible that such manipulations may distinguish various tissue types in CCSVI and may be able to predict response to angioplasty. However this feature does not yet exist.

Finally, IVUS presents a real-time cross sectional view. During that interrogation it is possible to analyze various questionable areas of the venous anatomy while performing a variety of physiological maneuvers such as Valsalva and reverse Valsalva, inspiration and expiration, flexion and extension and varying degrees of rotation. We shall see that there is great advantage to such maneuvers in the evaluation of CCSVI.