There is an increasing interest in using MR imaging as a means of guiding endovascular procedures due to MR's
unparalleled soft tissue characterization capabilities and its ability to assess functional parameters such as blood flow and
tissue perfusion. In order to evaluate the potential safety risk of catheter heating, we performed in vitro testing where we
measured heat deposition in sample non-ferrous 5F catheters ranging in length from 80cm - 110cm within a gel
phantom. To identify the conditions for maximum heat deposition adjacent to catheters, we measured (1) the effect of
variable immersed lengths, (2) the effect of variable SAR, and (3) whether heating varied along the catheter shaft. Net
temperature rise per scan and initial rate of temperature rise were determined for all configurations. The temperature
recordings clearly and consistently demonstrated the correlations between MR scanning under the three variable
conditions and heat deposition. Our overall maximum heating condition, which combined the maximum heating
conditions of all three variables, was modest (<2°C/min), but well above the temperature response of the gel well away
from the catheter. Reduced SAR acquisitions effectively limited these temperature rises, and RF exposure levels of
0.2W/kg produced little detectible temperature change over the 2 minute MR acquisitions studied here. A combination
of SAR limits and imaging duty cycle restrictions appear to be sufficient to permit MR imaging in catheterized patients
without concern for thermal injury.
Conventional evaluation of the significance of vascular disease has focused on estimates of geometric factors. There is now substantial interest in investigating whether the onset and progression of vascular pathology can be related to hemodynamic factors. Current imaging modalities have excellent capabilities in delineating the geometric boundaries of the vascular lumen. Advanced non-invasive imaging modalities such as Multi Detector CT and MRI are also able to define the extent of disease within the vessel wall and to provide information on the composition of thrombotic and atherosclerotic components. Finally, it is also possible to use imaging techniques to measure flow velocities across the lumen of vessels of interest, and to determine the pulsatile variation of these velocities through the cardiac cycle. Despite these advanced capabilities, imaging alone is unable to determine important features of the vascular hemodynamics such as wall shear stress or pressure distributions. However, the information on lumenal geometry and the inlet and outlet flow conditions can be used as input into numerical simulation models that are able to predict those quantities. These Computational Fluid Dynamics models can be used to predict hemodynamic parameters on a patient-specific basis. It is therefore possible to use non-invasive imaging methods to follow the progression of vascular disease over time, and to relate changes in lumenal and wall structure to calculated hemodynamic descriptors. This approach can be used not only to understand the natural progression of vascular disease, but as a tool to predict the likely outcome of a surgical intervention.