Hewlett-Packard Workstations Research Articles

The Effects of FreeSurfer Version, Workstation Type, and Macintosh Operating System Version on Anatomical Volume and Cortical Thickness Measurements

FreeSurfer is a popular software package to measure cortical thickness and volume of neuroanatomical structures. However, little if any is known about measurement reliability across various data processing conditions. Using a set of 30 anatomical T1-weighted 3T MRI scans, we investigated the effects of data processing variables such as FreeSurfer version (v4.3.1, v4.5.0, and v5.0.0), workstation (Macintosh and Hewlett-Packard), and Macintosh operating system version (OSX 10.5 and OSX 10.6). Significant differences were revealed between FreeSurfer version v5.0.0 and the two earlier versions. These differences were on average 8.8±6.6% (range 1.3–64.0%) (volume) and 2.8±1.3% (1.1–7.7%) (cortical thickness). About a factor two smaller differences were detected between Macintosh and Hewlett-Packard workstations and between OSX 10.5 and OSX 10.6. The observed differences are similar in magnitude as effect sizes reported in accuracy evaluations and neurodegenerative studies.The main conclusion is that in the context of an ongoing study, users are discouraged to update to a new major release of either FreeSurfer or operating system or to switch to a different type of workstation without repeating the analysis; results thus give a quantitative support to successive recommendations stated by FreeSurfer developers over the years. Moreover, in view of the large and significant cross-version differences, it is concluded that formal assessment of the accuracy of FreeSurfer is desirable.

Simulation of Optical Fiber Transmission Systems Using SPW on an HP Workstation

In this article, an intensity modulation-direct detection (IM-DD) optical fiber transmission system is simulated and investigated using a signal processing worksystem (SPW) on a Hewlett-Packard (HP) workstation. The optical fiber transmission system simulated includes a laser diode source, a single-mode fiber and a positive-intrinsic-negative (p-i-n) photodiode receiver model. Simulation methods are pre sented on the optical source waveforms, fiber attenuation and dispersion, and receiver noise. The end-to-end performance of a typical trans mission system is also presented. In the simula tion, models can be made as detailed as neces sary and computer waveforms can be compared directly to measured waveforms. Measured data can be used to accurately characterize functional components, such as sources, fibers and detectors. The impact of noise on the per formance of the transmission system can be observed. SPW software and its usage on HP workstations are introduced.