3D Visualization of Arteries and Veins

Deep venous thrombosis (DVT) occurs in approximately two out of every 1,000 people, predominately in those over 60 years of age, and present diagnostic techniqes are both invasive and painful. In DVT, a blood clot developes in the deep veins in the leg. The clot, which is called a thrombus, blocks the blood flow through the vein. In addition, portions of the clot may break away from the vein wall and travel through the veins into the lung, where it can lodge in a pulmonary artery causing a life threatening embolism.

Fig. 1: IDL-rendered image showing the arteries and veins of the pelvis. Thrombosis is demonstrated using a 3-D overlay of magnetic resonance direct clot imaging (yellow) onto combined magnetic resonance venography and arteriography (red and blue). The subtraction technique isolates venous and arterial phases using timing information after a contrast bolus is given into a periheral vein. Direct clot imaging isolates fresh clot as high signal on a background of suppressed blood and fat signal. 3-D overlay is then possible so that the relative positions of the vessels and thrombus can be appreciated. Images credit Queens Medical Centre

At present, x-ray venography is one of the standard techniques used to image the deep veins of the leg and pelvis. Venography, however, has it's drawbacks. It is invasive as it involves injecting contrast media directly into the veins of the foot. It can be painful and difficult to perform if the patient's legs are swollen.

Three-dimensional, dynamic contrast-enhanced MRI (DCE-MRI) is an alternative technique which is less invasive because the contrast media can be injected into a vein in the arm. Using DCE-MRI is difficult, because when it is used on veins, the contribution of the arteries ans well as the veins are both enhanced by the contrast agent, making it difficult to decern between the two. The images need additional post-processing to separate those contributions.

Dr. Anne Martel of Queens Medical Centre in the UK developed an MRI-based, non-invasive alternative to the commonly-performed venography. Medical Physicist Anne Martel and her colleagues have built an IDL application which enables hospital clinicians to more accurately analyze contrast-enhanced MRI images to gain new insight into the causes and treatment options of DVT. Dr. Martel uses several IDL routines to perform specific functions in her custom application. A GUI allows hospital clinicians to select representative arterial and venous pixels from a dynamic sequence of 3D images to separate the arterial and venous information. The team then wrote another IDL procedure that uses this information to carry out factor analysis and generate 3D arterial and venous images, and developed another GUI to read the 3D data sets and display the data in the form of a 3D surface rendered object. This second GUI allows the user to control all aspects of the 3D display, including the orientation of both the image objects and the light sources used to illuminate the object.

The users of this application are hospital personnel, such as radiographers, clinicians, and radiologists who typically have limited computer experience. The clinician can can carry out all of the steps necessary to separate the arterial and venous images and to display them as 3D objects with this custom-built application.