Trade off study on different envelope detectors for B-mode imaging

Generation of B-mode images involves envelope detection of the RF signals. Various detection algorithms are available. A trade of between performance, price, and complexity determines the choice of algorithm in an ultrasound system. A Hilbert transform (HT) and a subsequent computation of the magnitude give the ideal envelope, but the approach (IDE) is expensive and complex. A rectifier (REC) is a simple, low-cost solution, but the performance is severely degraded (especially in dynamic imaging). This study has investigated the possibility of providing a detector with a complexity and cost close to REC, while maintaining performance close to IDE. Two low-cost detectors have been implemented and evaluated on in-vivo data. The first approach is an expansion of the rectifier with a median filter (ERM). The second detector (TAS) approximates the HT by a time delay and the magnitude by a weighted sum of the real and imaginary signals. The four detectors were evaluated on in-vivo data acquired with a B-K Medical 2102 scanner interfaced to the sampling system RASMINE. Three data sets were acquired with three different center frequencies. Hundred images were acquired as the transducer was moved across the liver and the carotid artery of a 30 years old healthy male. The root-mean-square (RMS) error relative to the IDE, and a visual inspection determine the performance. For the 3.5 MHz data sets RMSE´s of 15.7%, 1.6%, and 1.9% are obtained with REC, ERM, and TAS, respectively. The performance is similar to the two other data sets. Close to envelope detection is therefore obtainable with a simple detector (ERM or TAS), which is less complex and costly.