Modified RV short axis series--a new method for cardiac MRI measurement of right ventricular volumes.

PURPOSE: The current standard image orientation employed in the MRI assessment of right ventricular volumes uses a series of short axis cine acquisitions located with respect to a horizontal long axis view with the first slice placed across the atrio-ventricular valve plane at end diastole. Inherent inaccuracies are encountered with the use of this image orientation due to difficulty in defining the tricuspid valve and the border between atrium and ventricle on the resultant images. Our experience indicates that because the tricuspid valve is usually not in-plane in the slice the atrio-ventricular margin is difficult to distinguish. This leads to inaccuracies in measurements at the base of the RV and miscalculation of the RV volume. The purpose of this study was to assess an alternative method of image orientation aimed at increasing the accuracy of RV volume measurements using current commercially available CMRI sequences. This technique, the modified RV short axis series, is oriented to the outflow tract of the right ventricle. METHOD: We undertook a prospective study of 50 post cardiac transplant patients. A series of LV short axis multi-slice cine acquisition FIESTA images was acquired using the current standard technique. From this data set, LV and RV stroke volumes were derived on an Advantage Windows workstation using planimetry of the endocardial and epicardial borders in end systole and end diastole. Our new technique involved obtaining a set of multi-slice cine acquisition FIESTA images in a plane perpendicular to a line from the centre of the pulmonary valve to the apex of the RV. Planimetry of the RV was then performed and a stroke volume calculated using the same method of analysis. RV stroke volumes obtained from both techniques were compared with LV stroke volumes. Three operators independently derived RV data sets. RESULTS: On the images acquired with the new technique, the tricuspid valve was easier to define leading to more accurate and reproducible planimetry of ventricular borders. RV stroke volumes calculated from the new method showed better agreement with LV stroke volumes than with the current method. These results were consistent across the three operators. CONCLUSIONS: This new method improves visualisation of the tricuspid valve and makes analysis easier and less prone to operator error than the current standard technique for MRI assessment of RV volumes.

Eye shape in emmetropia and myopia.

PURPOSES: To determine axial, vertical, and horizontal eye dimensions in myopic and emmetropic eyes by using magnetic resonance imaging (MRI) and to relate these to different ocular expansion models of myopia development. METHODS: The internal length (cornea to retina), height and width (both retina to retina) were measured in emmetropic and myopic eyes (up to -12 D) of 88 participants aged 18 to 36 years. Participants were positioned supine in a clinical MRI scanner. The fixation target was imaged straight ahead of the subject by an overhead 45 degrees inclined mirror. Eye images were acquired with a 7.5-cm receive-only radio frequency surface coil. Axial (horizontal through middle of eye) and sagittal (vertical through visual axis) sections were taken with a T(1)-weighted fast spin-echo sequence. RESULTS: With an increase in myopic refractive correction, myopic eyes became much larger in all three dimensions, but more so in length (0.35 mm/D, 95% confidence interval [CI] 0.28-0.40) than in height (0.19 mm/D, 95% CI 0.09-0.29) and more so in height than in width (0.10 mm/D, 95% CI 0.01-0.20). Based on height and length dimensions, 25% and 29% of myopic eyes exclusively fitted global expansion and axial elongation models, respectively. Based on width and length dimensions, 17% and 39% of myopic eyes exclusively fitted the global expansion and axial elongation models, respectively. CONCLUSIONS: Although there are considerable individual variations, in general myopic eyes are elongated relative to emmetropic eyes, more in length than in height and even less in width. Approximately a quarter of the myopic participants fitted each of the global expansion or axial elongation model exclusively. The small proportions are due primarily to the large variability in the dimensions of emmetropic eyes.