Effects of slice thickness and head rotation when measuring glioma sizes on MRI: in support of volume segmentation versus two largest diameters methods.

This paper presents a study of the effects of scanning parameters variability when assessing glioma sizes on MRI. A database of lesions of various shapes and sizes, segmented on 3D-SPGR MRI images, was acquired on 65 patients with low-grade glioma. Simulations of large slice thickness and patient's head rotation were performed, allowing us to study their influence on two size indices: the bi-dimensional diameter product index (computed with the two largest diameters method) and the equivalent diameter index (computed with the volume segmentation method). Results show that thick slices and axial plane rotation can induce average (maximal) uncertainties on the bi-dimensional diameter product index between 32 and 6 % (150 %) for small and large tumors (size range 0.5-286 ml). The uncertainty on the equivalent diameter index, for the same categories of tumors, drops below 8 and 0.1 % (23 %). This study shows that the volume segmentation method is subject to less variability inherent to scanning conditions compared to the two largest diameters method. It also emphasizes the need for strict clinical guidelines on the replication of scanning conditions when performing MRI follow-ups on patients harboring small tumors. These implications await confirmation on a series of real patients being re-scanned with FLAIR MRI.

Postoperative assessment of left ventricular function by two-dimensional strain (speckle tracking) after paediatric cardiac surgery.

BACKGROUND: Left ventricular (LV) dysfunction may complicate paediatric cardiac surgery with cardiopulmonary bypass, notably after long aortic cross-clamping (ACC). Assessment of occult myocardial injury by conventional echocardiographic variables may be difficult in the postoperative period. AIMS: To evaluate the feasibility of two-dimensional (2D) strain in the postoperative period, and to assess the effect of ACC duration on this variable. METHODS: Thirty-three paediatric patients (age<18years) with congenital heart disease undergoing cardiac surgery with cardiopulmonary bypass were included in this prospective single-centre study. Daily echocardiography was performed from the day before surgery to the fifth postoperative day. LV ejection fraction and LV 2D strain were measured. The cohort was divided into three groups according to ACC duration (group 1:<30minutes; group 2: 30-80minutes; group 3:>80minutes). RESULTS: Mean age and weight were 4.2±2.5years and 15.1±5.2kg, respectively. Feasibilities of longitudinal, circumferential and radial strains were good, and quite similar to conventional variables. Compared with conventional variables, intra- and interobserver agreements regarding 2D strain were better (r=0.916, P<0.001 and r=0.855, P<0.001 for longitudinal strain versus r=0.156, P=0.54 and r=0.064, P=0.80 for LV ejection fraction by Simpson's method). Postoperative evolution of longitudinal and circumferential strains was significantly different between the three groups (P<0.001), whereas there was no difference using conventional variables. CONCLUSION: Postoperative LV 2D strain is a feasible and reproducible method. Strain measurements seem to indicate correlation with ACC duration.