MRI Techniques for Cardiovascular Imaging

Over the last several years, cardiovascular MRI has benefited from a number of technical advances which have improved routine clinical imaging techniques. As a result, MRI is now well positioned to realize its longstanding promise of becoming the comprehensive cardiac imaging test of choice in many clinical settings. This may be achieved using a combination of basic advanced techniques. In this overview, the basic cardiac MRI techniques which are clinically useful are reviewed, and the recent technical advances which are clinically promising are described. These advances include routine black blood and cine bright blood techniques that are high speed (slice), multislice whole heart perfusion imaging methods, and recently emerging real-time imaging methodologies. J Magn. Reson. Imaging 1999;10:590–601. © 1999 Wiley-Liss, Inc

Slice Location Dependence of Aortic Regurgitation Measurements with MR Phase Velocity Mapping

Although several methods have been used clinically to assess aortic regurgitation (AR), there is no “gold standard” for regurgitant volume measurement. Magnetic resonance phase velocity mapping (PVM) can be used for noninvasive blood flow measurements. To evaluate the accuracy of PVM in quantifying AR with a single imaging slice in the ascending aorta, in vitro experiments were performed by using a compliant aortic model. Attention was focused on determining the slice location that provided the best results. The most accurate measurements were taken between the aortic valve annulus and the coronary ostia where the measured (Y) and actual (X) flow rate had close agreement (Y = 0.954 × + 0.126, r2 = 0.995, standard deviation of error = 0.139 L/min). Beyond the coronary ostia, coronary flow and aortic compliance negatively affected the accuracy of the measurements. In vivo measurements taken on patients with AR showed the same tendency with the in vitro results. In making decisions regarding patient treatment, diagnostic accuracy is very important. The results from this study suggest that higher accuracy is achieved by placing the slice between the aortic valve and the coronary ostia and that this is the region where attention should be focused for further clinical investigation

Quantification of Mitral Regurgitation With MR Phase-Velocity Mapping Using a Control Volume Method

Reliable diagnosis and quantification of mitral regurgitation are important for patient management and for optimizing the time for surgery. Previous methods have often provided suboptimal results. The aim of this in vitro study was to evaluate MR phase-velocity mapping in quantifying the mitral regurgitant volume (MRV) using a control volume (CV) method. A number of contiguous slices were acquired with all three velocity components measured. A CV was then selected, encompassing the regurgitant orifice. Mass conservation dictates that the net inflow into the CV should be equal to the regurgitant flow. Results showed that a CV, the boundary voxels of which excluded the region of flow acceleration and aliasing at the orifice, provided accurate measurements of the regurgitant flow. A smaller CV provided erroneous results because of flow acceleration and velocity aliasing close to the orifice. A large CV generally provided inaccurate results because of reduced velocity sensitivity far from the orifice. Aortic outflow, orifice shape, and valve geometry did not affect the accuracy of the CV measurements. The CV method is a promising approach to the problem of quantification of the MRV

Evaluation of the Precision of Magnetic Resonance Phase Velocity Mapping for Blood Flow Measurements

Evaluating the in vivo accuracy of magnetic resonance phase velocity mapping (PVM) is not straightforward because of the absence of a validated clinical flow quantification technique. The aim of this study was to evaluate PVM by investigating its precision, both in vitro and in vivo, in a 1.5 Tesla scanner. In the former case, steady and pulsatile flow experiments were conducted using an aortic model under a variety of flow conditions (steady: 0.1–5.5 L/min; pulsatile: 10–75 mL/cycle). In the latter case, PVM measurements were taken in the ascending aorta of ten subjects, seven of which had aortic regurgitation. Each velocity measurement was taken twice, with the slice perpendicular to the long axis of the aorta. Comparison between the measured and true flow rates and volumes confirmed the high accuracy of PVM in measuring flow in vitro (p \u3e 0.85). The in vitro precision of PVM was found to be very high (steady: y = 1.00x + 0.02, r = 0.999; pulsatile: y = 0.98x + 0.72, r = 0.997; x: measurement #1, y: measurement #2) and this was confirmed by Bland-Altman analysis. Of great clinical significance was the high level of the in vivo precision (y = 1.01x − 0.04, r = 0.993), confirmed statistically (p = 1.00). In conclusion, PVM provides repeatable blood flow measurements. The high in vitro accuracy and precision, combined with the high in vivo precision, are key factors for the establishment of PVM as the “gold-standard” to quantify blood flow

Evidence generation and reproducibility in cell and gene therapy research: A call to action.

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