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  • SAGE Publications  (4)
  • 2005-2009  (4)
  • 1
    In: Ultrasonic Imaging, SAGE Publications, Vol. 31, No. 3 ( 2009-07), p. 183-200
    Abstract: Acoustic radiation force impulse (ARFI) imaging has been demonstrated to be capable of visualizing changes in local myocardial stiffness through a normal cardiac cycle. As a beating heart involves rapidly-moving tissue with cyclically-varying myocardial stiffness, it is desirable to form images with high frame rates and minimize susceptibility to motion artifacts. Three novel ARFI imaging methods, pre-excitation displacement estimation, parallel-transmit excitation and parallel-transmit tracking, were implemented. Along with parallel-receive, ECG-gating and multiplexed imaging, these new techniques were used to form high-quality, high-resolution epicardial ARFI images. Three-line M-mode, extended ECG-gated three-line M-mode and ECG-gated two-dimensional ARFI imaging sequences were developed to address specific challenges related to cardiac imaging. In vivo epicardial ARFI images of an ovine heart were formed using these sequences and the quality and utility of the resultant ARFI-induced displacement curves were evaluated. The ARFI-induced displacement curves demonstrate the potential for ARFI imaging to provide new and unique information into myocardial stiffness with high temporal and spatial resolution.
    Type of Medium: Online Resource
    ISSN: 0161-7346 , 1096-0910
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2009
    detail.hit.zdb_id: 2012028-X
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  • 2
    Online Resource
    Online Resource
    SAGE Publications ; 2009
    In:  Ultrasonic Imaging Vol. 31, No. 3 ( 2009-07), p. 201-213
    In: Ultrasonic Imaging, SAGE Publications, Vol. 31, No. 3 ( 2009-07), p. 201-213
    Abstract: Shear wave elasticity imaging (SWEI) was employed to track acoustic radiation force impulse (ARFI)-induced shear waves in the mid-myocardium of the left ventricular free wall (LVFW) of a beating canine heart. Shear waves were generated and tracked with a linear ultrasound transducer that was placed directly on the exposed epicardium. Acquisition was ECG-gated and coincided with the mid-diastolic portion of the cardiac cycle. Axial displacement profiles consistent with shear wave propagation were clearly evident in all SWEI acquisitions (i.e., those including an ARFI excitation); displacement data from control cases (i.e., sequences lacking an ARFI excitation) offered no evidence of shear wave propagation and yielded a peak absolute mean displacement below 0.31 μm after motion filtering. Shear wave velocity estimates ranged from 0.82 to 2.65 m/s and were stable across multiple heartbeats for the same interrogation region, with coefficients of variation less than 19% for all matched acquisitions. Variations in velocity estimates suggest a spatial dependence of shear wave velocity through the mid-myocardium of the LVFW, with velocity estimates changing, in limited cases, through depth and lateral position.
    Type of Medium: Online Resource
    ISSN: 0161-7346 , 1096-0910
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2009
    detail.hit.zdb_id: 2012028-X
    Location Call Number Limitation Availability
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  • 3
    In: Multiple Sclerosis Journal, SAGE Publications, Vol. 11, No. 1 ( 2005-02), p. 41-45
    Abstract: Background: Once weekly interferon β-1a for multiple sclerosis (OWIMS) demonstrated modest, but significant, magnetic resonance imaging (MRI) benefit of once-weekly (qw) interferon (IFN) β-1a at 48 weeks, but no significant effect on relapses. Objective: An OWIMS extension permitted assessment of longer-term efficacy/safety of qw IFN β-1a in relapsing-remitting multiple sclerosis (RRMS). Methods: Placebo patients were rerandomized to IFN β-1a, 22 or 44 mcg qw, for two additional 48-week intervals. Primary outcome was MRI lesion activity. Relapse rate and other MRI measures were secondary outcomes. Results: After three years, median (mean) T2 lesion count/patient/scan was 1.3 (2.6) for 44 mcg, 1.7 (3.3) for 22 mcg, 1.7 (3.4) for placebo/22 mcg, 2.0 (3.6) for placebo/44 mcg (all differences not significant). Annualized relapse rates were lowest for 44 mcg (0.77) versus other groups (0.83-0.86, not significant). Persistent neutralizing antibodies did not affect relapse rates, but MRI active lesions were increased in antibody-positive patients receiving 44 mcg compared to antibody negative patients. Conclusions: In RRMS, once weekly IFN β-1a, particularly 44 mcg, can induce a significant MRI, but not relapse, effect, compared with placebo. No significant dose effect was seen. In contrast to the significant effect observed with three-times-weekly dosing of subcutaneous IFN β-1a compared with placebo, this study confirms the lack of meaningful clinical benefit with once-weekly dosing.
    Type of Medium: Online Resource
    ISSN: 1352-4585 , 1477-0970
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2005
    detail.hit.zdb_id: 2008225-3
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  • 4
    Online Resource
    Online Resource
    SAGE Publications ; 2009
    In:  Ultrasonic Imaging Vol. 31, No. 1 ( 2009-01), p. 17-30
    In: Ultrasonic Imaging, SAGE Publications, Vol. 31, No. 1 ( 2009-01), p. 17-30
    Abstract: Acoustic radiation force (ARF) has become a common excitation mechanism in elasticity imaging. The high acoustic intensities and subsequent generation of harmonics, however, hamper the effectiveness of using conventional radiofrequency (rf) tracking to investigate the dynamics of tissues and catheter-based transducers, especially during the excitation. Optical tracking, on the other hand, does not utilize acoustic echo and thus is not affected by ARF-generated interference. Additionally, it is able to track equally well in two dimensions, something that rf tracking is unable to do. Despite the inherent near-field scattering that will likely preclude optical (i.e., visible spectrum) tracking from supplanting current ultrasound-based methods in a clinical setting, it could offer valuable new tools in the pursuit of a better understanding of ARF-induced dynamic responses. We utilized an optically-based method to track the dynamic response resulting from an ARF-induced excitation on the surface of a tissue-mimicking phantom and on an unbounded catheter. These tracking data were then compared to tracking data obtained from the conventional rf tracking method. Both impulsive and harmonic (i.e., amplitude-modulated) excitations were investigated. In general, there was good agreement between the conventional (i.e., ultrasound-based) and optically-based tracking methods. Disparities between displacement estimates from the two tracking methods is thought to be a result of the finite length of the tracking marker, which was assumed to move as an infinitesimal point, and aberration of reflected light due to surface waves. Given the reasonable agreement seen for the harmonic and impulsive excitation cases, an optical tracking method could be insightful in future investigations of tissue/transducer response to ARF-induced excitations in controlled experimental settings.
    Type of Medium: Online Resource
    ISSN: 0161-7346 , 1096-0910
    Language: English
    Publisher: SAGE Publications
    Publication Date: 2009
    detail.hit.zdb_id: 2012028-X
    Location Call Number Limitation Availability
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