Influence of Signal Intensity Non-Uniformity on Brain Volumetry Using an Atlas-Based Method

OBJECTIVE: Many studies have reported pre-processing effects for brain volumetry; however, no study has investigated whether non-parametric non-uniform intensity normalization (N3) correction processing results in reduced system dependency when using an atlas-based method. To address this shortcoming, the present study assessed whether N3 correction processing provides reduced system dependency in atlas-based volumetry. MATERIALS AND METHODS: Contiguous sagittal T1-weighted images of the brain were obtained from 21 healthy participants, by using five magnetic resonance protocols. After image preprocessing using the Statistical Parametric Mapping 5 software, we measured the structural volume of the segmented images with the WFU-PickAtlas software. We applied six different bias-correction levels (Regularization 10, Regularization 0.0001, Regularization 0, Regularization 10 with N3, Regularization 0.0001 with N3, and Regularization 0 with N3) to each set of images. The structural volume change ratio (%) was defined as the change ratio (%) = (100 x [measured volume - mean volume of five magnetic resonance protocols] / mean volume of five magnetic resonance protocols) for each bias-correction level. RESULTS: A low change ratio was synonymous with lower system dependency. The results showed that the images with the N3 correction had a lower change ratio compared with those without the N3 correction. CONCLUSION: The present study is the first atlas-based volumetry study to show that the precision of atlas-based volumetry improves when using N3-corrected images. Therefore, correction for signal intensity non-uniformity is strongly advised for multi-scanner or multi-site imaging trials.

Echocardiographic Evaluation of Regional Wall Motion Nonuniformity and Phase Difference in Asymmetric Septal Hypertrophy

BACKGROUND: A regional wall motion nonuniformity and a phase difference between LV posterior wall motion and transmitral flow are present during normal rapid filling period and are thought to be an evidence for involvement of ventricular restoring forces. To assess the role of nonuniformity on diastolic funtional impairment of asymmetric septal hypertrophy(ASH), the time relations between left ventricular regional wall motions and filling velocity were studied. METHOD: We measured the time intervals from A2 to peak rate of LV posterior wall(short axis) thinning(A2-(-)dpw/dt), peak rate of medial mitral annulus (long axis dimension) lengthening(A2-dL/dt) and peak mitral flow(A2-E) by M-mode and Doppler echocardiography. Result: In ASH patients, A2-(-)dpw/dt(106+/-6msec, mean SE) and the regional wall motion nonuniformity((-)dpw/dt-dL/dt, 89+/-11msec, mean SE) were increased significantly when compared with normal control values(88+/-4, 28+/-5msec, mean SE, p<0.01,respectively).In normal controls, peak mitral flow velocity lagged peak rate of regional wall motion, so the phase differences were present((-)dpw/dt-E :71+/-8msec, dL/dt-E:44+/-6msec). In ASH patients, (-)dpw/dt-E was present(90+/-16msec) but dL/dt-E was not present or reversed(-21+/-18 msec). So these chacteristic phase differences were disturbed. CONCLUSION: These data suggested that the relaxation nonuniformity of regional wall motion in ASH may act as an energy dissipating factor of restoring forces during rapid filling period.

Echocardiographic Measurement of Early Diastolic Time Intervals in Patients with Hypertension: With Reference to Regional Nonuniformity and Restoring Forces

BACKGROUND: It is known that left ventricular(LV) wall motion is not uniform even in normal heart, and the restoring forces make phase differences between LV wall motion and mitral flow velocity during rapid filling period. METHOD: To investigate the regional nonuniformity and restoring forces in 46 patients with hypertension(HT)(group:normal wall thickiness.n=12,II:LVH with fractional shortening(FS)>25%. n=22. III:FS<25%.n=12). We measured the time intervals from A2 to peak thinning rate point of LV posterior wall(A2-(-)dpw/dt).to mitral flow starting point (IRT).and to peak mitral flow velocity(A2-E) by M-mode and Doppler echocardiography. RESULTS: The noniformity((-)dpW/dt-dL/dt)and phase differance((-)dpw/dt-E) were increased in HT(control:HT.22+/-7.8 vs. 49+/-5.2msec, 63+/-4.5 vs, 86+/-6.2msec, p<0.05 respectively).In group comparison, nonuniformity increased in group II and III(group I: group II, III, 35+/-5.1 vs. 50+/-7.1,70+/-14msec, p<0.05 respectively). but phase difference increased only in group II(groupII: group I, III, 93+/-6.0 vs. 75+/-5.2, 80+/-20msec, p<0.05, respectively). CONCLUSION: We interpreted these data that in HT with hypertrophy or not, the nonuniformity of LV wall motion working on the restoring forces which can be expressed as phase difference between LV wall motion and mitral flow. But in HT with hypertensive heart failure group, no significant changes of phase difference and it's suggest that other mechanism could be also working on early diastolic filling.