Heart disease and stroke are caused primarily by arterial stenoses. Since the 1950's X-ray angiography has been the primary method of diagnosing the presence and significance of arterial stenoses. While extremely useful, x-ray angiography is invasive and often requires large doses of nephrotoxic contrast agents. We have developed a new MRI technique which produces cine movie analogous to those of x-ray angiography noninvasively and without a contrast agent. The technique involves specific changes to the well-known steady state free precession (SSFP) MRI pulse sequence. This new technique, which we term """"""""Dynamic Magnetic Resonance Selective Angiography"""""""" (DMRSA), involves exciting protons within moving blood as they travel through a slice in space and, simultaneously, acquiring two-dimensional projection images which allow direct visualization of the blood as it fills the distal vasculature and its branches. The efficiency of the technique is intrinsically high both because excitation and imaging are performed simultaneously and because new spins are continuously """"""""pumped"""""""" into the distal vasculature as blood flows through the excitation slice. The images are acquired in cine (movie) format such that pulsatile blood flow is directly visualized. Like invasive angiography, DMRSA allows specific blood vessels to be selectively interrogated. We show preliminary data demonstrating that blood can be visualized after traveling up to 16 cm outside the excitation slice, and that temporal filling of branch vessels is directly observed. We show that we have developed an understanding of the underlying physical principles sufficient to allow us to modify the basic DMRSA pulse sequence in such a way that artifacts characteristic of our early implementations of the technique are eliminated. We show example images in a patient in which the aorta and renal arteries are visualized in the same manner as in x-ray angiography. We show large animal data strongly suggesting that that DMRSA can be used to noninvasively determine the functional significance of arterial stenoses. Based on our preliminary data we believe this technique has wide potential application. We propose to optimize DMRSA image quality (Aim 1), to test the hypothesis that the functional significance of arterial stenoses can be determined by comparing vessel filling distances under pharmacologic stress to those at rest (Aim 2), and to evaluate the ability of DMRSA to non-invasively detect coronary artery disease (Aim 3).
| Klem, Igor; Rehwald, Wolfgang G; Heitner, John F et al. (2005) Noninvasive assessment of blood flow based on magnetic resonance global coherent free precession. Circulation 111:1033-9 |
