Article

Optimal transmit phasing on tissue background suppression in contrast harmonic imaging.

Department of Electrical Engineering, National Taiwan University of Science and Technology, Taipei, Taiwan.
Ultrasound in medicine & biology (Impact Factor: 2.46). 07/2008; 34(11):1820-31. DOI: 10.1016/j.ultrasmedbio.2008.04.010
Source: PubMed

ABSTRACT Ultrasonic harmonic imaging provides superior image quality than linear imaging and has become an important diagnostic tool in many clinical applications. Nevertheless, the contrast-to-tissue ratio (CTR) in harmonic imaging is generally limited by tissue background signal comprising both the leakage harmonic signal and the tissue harmonic signal. Harmonic leakage generally occurs when a wideband transmit pulse is used for better axial resolution. In addition, generation of tissue harmonic signal during acoustic propagation also decreases the CTR. In this paper, suppression of tissue background signal in harmonic imaging is studied by selecting an optimal phase of the transmit signal to achieve destructive cancellation between the tissue harmonic signal and the leakage harmonic signal. With the optimal suppression phase, our results indicate that the tissue signal can be significantly reduced at second harmonic band, whereas the harmonic amplitude from contrast agents shows negligible change with the selection of transmit phase. Consequently, about 5-dB CTR improvement can be achieved from effective reduction of tissue background amplitude in optimal transmit phasing.

0 Bookmarks
 · 
66 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Assessment of US ability to identify subcutaneous nodular lesions using conventional B mode imaging (CBMI) and tissue second harmonic imaging (THI). Three different types of equipment were used (Philips Envisor HDC, Philips HD 11 XE and GE Logic E) with 12-13 MHz probes and THI probes with variable frequency. One experienced operator studied 31 patients (24 women, 7 men, mean age 49 ± 15) with 52 subcutaneous nodular lesions of which 43 were palpable and 9 were nonpalpable. Statistical analysis was carried out using chi-square test. 19/52 subcutaneous nodular lesions were hyperechoic, 10/52 were isoechoic and 23/52 were hypoechoic. Of the hyperechoic nodules, 8/19 (42%) (p < 0.005) were not detected using THI, as they "disappeared" when THI was activated. Of the isoechoic nodules only 1/10 was not detected using THI, and of the hypoechoic nodules only 2/23 were not detected. Of the nodular lesions detected using CBMI and also using THI (41/52), 16/41 were shown more clearly using THI than using BMCI. No nodule was detected with the exclusive use of THI. The statistical significance of the "disappearing" lesions (p < 0.005), mainly hyperechoic (42%), at the activation of THI must lead to a reconsideration of routine activation of THI during the entire US examination in the evaluation of subcutaneous lesions in order to avoid the risk of missing important lesions. The present results suggest that both BMCI and THI should be used in the study of subcutaneous lesions.
    Journal of Ultrasound 09/2011; 14(3):152-6.
  • [Show abstract] [Hide abstract]
    ABSTRACT: The impulse response of a transducer can be rep- resented in the frequency domain by its complex analog, the transfer function. The amplitude transfer function is measured regularly in contrast to the phase transfer function (PTF). Applications for the PTF range from adjusting the emitted pulse shape for coding based imaging to the optimization of ultrasound contrast imaging methods based on destructive interference. A number of acoustic methods to measure a transducer's PTF ex- ists, but they usually require accurate distance and acoustic wave speed measurements. Small discrepancies in these cause large phase errors. We present a pulse-echo method to measure a trans- ducer's PTF without needing a measurement of the wave travel distance and speed. We generalize it to rectangular transducers. In our method the transducer is excited by a monofrequency sine burst with a rectangular envelope. The transducer initially vibrates at resonance (transient regime) prior to the forcing frequency (steady state regime). The PTF value of the system is the difference between the phases deduced from the transient and the steady state regimes at different forcing frequencies. As the PTF is calculated from a relative difference measuring the wave travel distance or speed is unnecessary. The approach assumes linear wave propagation and uses a pulse-echo setup. The method was tested on a custom built single element transducer (square: 13 x 13 mm, center frequency 4 MHz, no backing or matching layers). The results were compared with KLM model simulations. Also, we phase calibrated a hydrophone, which was then used to measure the PTF of the square transducer. The simulated and measured resonance frequencies differed by 0.17 MHz. The mean PTF difference between simulation and measurements was 7 - 14 . The method's reproducibility was 15 . The PTF of the transducer was measured with good reproducibility, without measuring the wave travel distance or speed of sound in the medium. Our simple setup requires basic laboratory ultrasound equipment. Index Terms—phase; pulse-echo; hydrophone; rectangular transducers; transducer calibration.
    01/2010;
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The rapid progress of molecular imaging (MI) and the application of nanotechnology in medicine have the potential to advance the foundations of diagnosis, treatment, and prevention of diseases. Although MI and biomedical nanotechnology are still in a formative phase in China, much has been achieved over the last decade. This article provides a commentary on the development and current status of nanomedicine in China, with a selective focus on Chinese nanoparticle synthesis technology, the development of imaging equipment, and the preclinical application of novel MI probes. WIREs Nanomed Nanobiotechnol 2011 DOI: 10.1002/wnan.156 For further resources related to this article, please visit the WIREs website.
    Wiley Interdisciplinary Reviews Nanomedicine and Nanobiotechnology 08/2011; · 5.68 Impact Factor