[Left ventricular short-axis plane for magnetic resonance imaging: its clinical importance and applications]

Abstract

Left ventricular short-axis images were obtained by ECG-gated magnetic resonance imaging (MRI) in nine patients with hypertrophic cardiomyopathy and seven patients with chest pain, all of whom had diagnostic cardiac catheterization including angiography. The accuracy and usefulness of the short-axis image in MRI for measuring wall thickness and dimension and for calculating ejection fraction were evaluated. All patients were examined on an examination couch in the right anterior oblique position in optimal positions to obtain the left ventricular long-axis images in the Z-X plane (conventional coronal plane). Next, the paraxial mode was used to obtain the short-axis images by rotating the Y-Z plane (conventional sagittal plane) around the Y axis. The intervals between the trigger on the middle point of the upstroke of the R wave and the 90 degree pulse of saturation recovery spin echo sequence were 40 msec and 340 msec with a 34 msec echo delay time for the end-diastolic and end-systolic images, respectively. Short-axis images in MRI in end-diastole were utilized to measure wall thickness and dimension in patients with hypertrophic cardiomyopathy and the measurements obtained were compared with those of echocardiography. As for calculating ejection fraction in patients with chest pain, the length of the left ventricular long axis (L) was measured using the MRI long-axis image. The intraventricular sectional area at four levels (S1, S2, S3, S4) were measured using the MRI short-axis image in end-diastole and in end-systole. Left ventricular end-diastolic and end-systolic volumes were calculated using the following formula: V = 1/2 X (L -4.5) X S1 + 1.5 X (S1 + S2 + S3) + 1/3 X 1/2 X (L -4.5) X S4. Ejection fraction by MRI was compared with that by cardiac catheterization (single plane, area-length method). The measurements of wall thickness and dimension by MRI correlated well with those by echocardiography (r = 0.97, p less than 0.01). Ejection fraction calculated by MRI correlated significantly with that by cardiac catheterization (r = 0.82, p less than 0.05). We concluded that the left ventricular short-axis image in MRI is satisfactorily accurate for measuring wall thickness and dimension, and useful for evaluating the left ventricular ejection fraction.