G. Engels

Evaluation of left ventricular inflow and volume by MR

Considerable progress has been achieved during the past few years in the evaluation of intracardial blood flow by MR. Similar to ultrasound Doppler, it is possible now to registrate parameters of left ventricular diastolic filling as E/A ratio, velocity time integral of A- to E-wave (A(area)/E(area)), or isovolumetric relaxation time index. A total of 24 patients (7 women, 17 men, aged 24-69 yr) were examined, 5 of whom suffered from a hypertensive heart disease, 5 from a coronary heart disease, and 7 from mitral valve stenosis of various degree; 7 showed normal findings. E/A-ratio, A(area)/E(area), as well as isovolumetric relaxation time (IVRT) were evaluated by two different examiners on the same day by MR and ultrasound-Doppler, showing correlation factors of .89 for E/A ratio, .67 for A(area)/E(area), and .76 for IVRT in comparing both techniques. Additionally, to test the potential for making left ventricular function diagnoses from MR, time-volume curves for normal cases and patients with hypertrophic and dilated cardiomyopathy were elaborated by a computer-assisted 3D imaging technique. This technique showed good concordance with the results from cardiac catheterization or radionuclide ventriculography.

Phase-mapping technique for the evaluation of aortic valve stenosis by MR

New MR-techniques for quantitative blood flow registration such as phase-mapping (a two-dimensional space-resolved technique with a time-averaged measurement of blood flow) or RACE (real-time acquisition and evaluation of blood flow in one-dimensional space projection) are available for the diagnosis of valvular heart disease. Initial results of grading aortic valve stenosis by these methods are shown in comparison to continuous wave Ultrasound-Doppler. Two groups of 15 patients were examined by RACE or phase-mapping, 12 respectively 8 of whom suffered from an aortic valve stenosis. The shape of blood flow profiles as well as grading of aortic valve stenosis show high concordance when comparing the results of MR and Doppler technique. Good reliability and practicability of the demonstrated MR-method are shown. With respect to the results of RACE and phase-mapping the development of an alternative and competing MR-method for the evaluation of valvular heart disease and shunt diagnostics seems possible.

Quantification of aortic valvular insufficiency by MRI

Flow-encoded MRI sequences nowadays allow a quantitative evaluation of blood flow in any slice position. For the first time there is the possibility of determining quantitatively the volumes of both left ventricular ejection and regurgitation over the aortic valve in a non-invasive ways, thus obtaining the regurgitation fraction as a reliable measure for the evaluation of aortic valvular insufficiencies. The quantitative assessment of aortic valvular insufficiencies was carried out by MRI and compared with the diagnosis by means of Doppler ultrasound and in some cases by cardiac catheter also. The new MRI method is characterized by a good correlation with the clinical grading of aortic valvular insufficiencies. It should be possible to develop a new non-invasive standard for quantifying aortic valvular insufficiencies.

MR measurements of Gd-DTPA kinetics for estimation of myocardial perfusion

By administering gadolinium-diethylenetriamine-penta-acetic acid (Gd-DTPA) in conjunction with the Turbo-Flash sequence, the authors assessed the potential of dynamic contrast-enhanced ultrafast magnetic resonance imaging (MRI) to detect and quantify reductions in myocardial perfusion secondary to stenosis and hyperemia induced by Dipyridamole. In ten subjects and three dogs signal intensity-time curves were generated in regions of interest over myocardium. A one-compartment model was introduced to describe the kinetics of Gd-DTPA. The first results indicate that measurements of Gd-DPTA kinetics seem of potential value for the non-invasive assessment of myocardial perfusion.<<ETX>>