Noninvasive Determination of Coronary Blood Flow Velocity With Cardiovascular Magnetic Resonance in Patients After Stent Deployment

Purpose: To assess constant and pulsatile flow velocity within the lumen of a peripheral NiTi stent using phase velocity mapping for comparison with independent assessments of flow velocity in a phantom model. Materials and Methods:A 9 ϫ 20-mm stent installed in flexible tubing was placed in a phantom filled with stationary fluid. Constant and pulsatile flow (produced by a pump programmed to produce a simulation of the carotid artery flow) was assessed using phase velocity mapping at 4.1 T (for constant flow) and at 1.5 T (for pulsatile flow). In all cases 256 ϫ 256 gradient echo phase velocity maps were acquired. For the pulsatile flow condition, cine images with acquisition gated to the pump cycle were acquired with 40 msec temporal resolution across the simulated cardiac cycle. Computed flow volume rates were compared with fluid volume collection for the constant flow model, and with ultrasonic Doppler flow meter measurements for the pulsatile model. Results:The data showed that volume flow rate assessments by phase velocity mapping agreed with independent measurements within 10% to 15%. MR AND CT ANGIOGRAPHY are routinely used in the assessment of vascular patency and in-stent pathology. However, both provide only morphologic information and require exposure to ionizing radiation. MRI traditionally has been limited in its ability to assess vascular stent patency due to susceptibility artifacts and radiofrequency shielding. It has been shown that stents made from nickel-titanium (NiTi) alloys produce susceptibility artifacts of smaller extent than those produced by similar devices made from stainless steel. Self-expanding NiTi device placement procedures are also less likely to result in vessel wall damage, since a high-pressure balloon deployment system is not required in order to conform the stent to the vessel wall. NiTi self-expanding devices presently account for 100% of carotid and femoral artery stenting procedures and 70% of saphenous vein bypass graft stenting procedures (1). ConclusionWith the inherent signal-to-noise ratio (SNR) and spatial resolution of MRI, characterization of arterial anatomy with MRI is superior to that obtained with carotid duplex ultrasound scanning (2). Advances in fast MRI techniques enable comprehensive study of both cardiac morphology, function, blood flow, perfusion (3), and also coronary artery bypass graft function (4,5).The present study examined the quantitative assessment of flow through the lumen of a NiTi stent. The device was of a size typical for use in peripheral arteries and bypass grafts to provide for a larger number of pixels for flow computation than would be possible in a coronary-sized device given typical pixel resolutions in patient studies.Since utilization of MRI through stented regions has been limited, this study attempted flow measurements through a NiTi stent in both continuous and more clinically relevant pulsatile flows. The aim of this study was to demonstrate the feasibility of using MRI through metallic stents in quantitative determinations ...

Section: Discussionsupporting

confidence: 53%

Section: Discussionmentioning

confidence: 93%

Section: Discussionmentioning

confidence: 99%

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Magnetic resonance phase velocity mapping through NiTi stents in a flow phantom model

Walsh

Holton

Brott

et al. 2004

“…Moreover, measurements performed in close proximity to the stent can reduce the accuracy of the measurements. Nagel et al (9) have shown that measurements at least 1 cm distal to the stent are not influenced by stainless-steel coronary arterial stents. In our study, we measured proximal aortic flow 2 cm distal to the coarctation in order to have a site below the stent placement and to avoid any flow jet from the coarctation.…”

Section: Discussionmentioning

confidence: 99%

Phase contrast MR imaging to measure changes in collateral blood flow after stenting of recurrent aortic coarctation: Initial experience

Pujadas

Reddy

Weber

et al. 2006

Purpose:To assess the feasibility of using phase contrast magnetic resonance (PC-MR) imaging to measure the change in collateral blood flow early after stenting of aortic coarctation. Materials and Methods:A total of 10 consecutive patients with coarctation of the aorta underwent MR imaging, X-ray angiography, and stent placement. PC-MR at two sites in the descending aorta was performed before and early after stenting in order to estimate collateral inflow to the descending thoracic aorta. The collateral flow and collateral flow percentage before and after stent placement were compared.Results: Before stenting, the mean proximal aortic flow ϭ 43.9 Ϯ 14.6 mL/second; mean distal flow ϭ 54.2 Ϯ 10 mL/second; collateral flow ϭ 10.2 Ϯ 6.8 mL/second; and collateral flow percentage ϭ 30.1 Ϯ 27.9%. After stenting, the mean proximal aortic flow ϭ 62.1 Ϯ 17.9 mL/second; mean distal flow ϭ 60 Ϯ 19 mL/second; collateral flow ϭ -1.9 Ϯ 3.7 mL/second; and collateral flow percentage ϭ -3.3 Ϯ 6.8%. Conclusion:PC-MR can be used to measure changes in collateral circulation after stent treatment of coarctation of the aorta.

“…The flow velocity reserve was 2.26 Ϯ 0.49 at one month and 1.52 Ϯ 0.09 (P Ͻ 0.05) at six months after stent implantation in subjects with restenosis. In a recent study by Nagel et al (83), coronary flow velocity reserve in the artery distal to the stent was measured with MR in 38 patients after successful stent placements. Using a threshold of 1.2 for MR flow velocity reserve, a sensitivity of 83% and a specificity of 94% were achieved for detecting Ն75% stenoses on coronary angiography.…”

Section: Mr Flow Measurement In Coronary Circulationmentioning

confidence: 99%

Magnetic resonance imaging for ischemic heart disease

Sakuma

2007

Cardiac MRI has long been recognized as an accurate and reliable means of evaluating cardiac anatomy and ventricular function. Considerable progress has been made in the field of cardiac MRI, and cardiac MRI can provide accurate evaluation of myocardial ischemia and infarction (MI). Late gadolinium (Gd)-enhanced MRI can clearly delineate subendocardial infarction, and the assessment of transmural extent of infarction on late enhanced MRI has been shown to be useful in predicting functional recovery of dysfunctional myocardium in patients after MI. Stress first-pass contrast-enhanced (CE) myocardial perfusion MRI can be used to detect subendocardial ischemia, and recent studies have demonstrated the high diagnostic accuracy of stress myocardial perfusion MRI for detecting significant coronary artery disease (CAD). Free-breathing, whole-heart coronary MR angiography (MRA) was recently introduced as a method that can provide visualization of all three major coronary arteries within a single three-dimensional (3D) acquisition. With further improvements in MRI techniques and the establishment of a standardized study protocol, cardiac MRI will play a pivotal role in managing patients with ischemic heart disease.