Diffusion-weighted imaging in normal pancreas: Apparent diffusion coefficient test-retest repeatability

Background The assessment of apparent diffusion coefficient (ADC) repeatability is important to body diffusion weighted imaging (DWI). However, data onto evaluating the repeatability of ADC values for normal pancreas are limited. The aim of this study was to evaluate the ADC test-retest repeatability of the normal pancreas.Methods Twenty-six healthy volunteers (mean 47.6 years; 13 men) were included and scanned twice with reposition using a DWI sequence at 3.0-T. ADCs of the pancreatic head, body and tail for two DWIs were measured by two readers. The mean ADCs of the pancreatic head, body and tail were calculated as the global pancreatic ADC. Test-retest repeatability and agreement of ADC measurement were evaluated by the Bland-Altman analysis, intra-class correlation coefficient (ICC) and coefficient of variation (CV).Results The global pancreatic ADC showed the best test-retest repeatability (mean difference ± limits of agreement were 0.05 ± 0.25×10 -3 mm 2 /s; ICC, 0.79; CV, 6%). Test-retest repeatabilities for ADC of pancreatic head, body or tail were scattered, with mean difference ± limits of agreement between two tests were 0.03 ± 0.47, 0.05 ± 0.42 and 0.06 ± 0.31 (×10 -3 mm 2 /s), respectively (ICCs, 0.81, 0.52 and 0.68; CVs, 9%, 8% and 8%). Both intra-observer repeatability and inter-observer reproducibility were acceptable for whole pancreas between ADC measurements of the two DWIs.Conclusions ADC values of the pancreas are technically challenging and repeatability is variable. Cautions should be taken when interpreting longitudinal clinical changes in ADC values of the normal pancreas because the measurements do have an inherent variability by locations.

Full information ADC test procedures using sinusoidal excitation, implemented in MATLAB and LabVIEW

Analog-to-digital converters and the need to test these devices appeared simultaneously. Thus, ADC circuit realizations and test methods evolved also simultaneously. In the last decades several techniques have been elaborated and spread worldwide. These are available in IEEE standards and in the literature as well. However, standard methods do not support the recognition of incorrect measurement settings. Accurate test results require careful choice of settings and calculated quality parameters of the ADC under test are very sensitive to imperfections of the measurement setup. In addition, the requirements are different for each test technique and the restrictions can even be contradicting (e.g. overdrive is recommended for histogram test and contraindicated for FFT test). This paper presents solutions to perform the commonly used methods reliably and some advanced methods to increase the performance of ADC quality parameter estimation. Implementations of the proposed algorithms are presented as well, with URL for download.

Testing of High-Resolution Analog-to-Digital Converters Using Segmentation and Optimized Low-Precision DAC

The main challenges of high-resolution ADC testing are the huge number of samples and the expensive test equipment, especially the requirement of high linearity signal source. In this paper, the scaling and segmentation algorithm which combines SEIR with windows is introduced for high-resolution ADC test. The new approach is validated by simulation with a 24-bit sigma-delta ADC. INL error of the proposed method is ±0.2LSB, which is less than the SEIR method of ±0.5LSB,and less than the histogram method of ±0.3LSB. About 20 million samples are required in the proposed method, which is about 30 times less than the traditional histogram method.