Ultrasound in medicine & biology
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Ultrasound Med Biol · Jul 2009
Diagnostic ultrasound at MACH 20: retroperitoneal and pelvic imaging in space.
An operationally available diagnostic imaging capability augments spaceflight medical support by facilitating the diagnosis, monitoring and treatment of medical or surgical conditions, by improving medical outcomes and, thereby, by lowering medical mission impacts and the probability of crew evacuation due to medical causes. Microgravity-related physiological changes occurring during spaceflight can affect the genitourinary system and potentially cause conditions such as urinary retention or nephrolithiasis for which ultrasonography (U/S) would be a useful diagnostic tool. This study describes the first genitourinary ultrasound examination conducted in space, and evaluates image quality, frame rate, resolution requirements, real-time remote guidance of nonphysician crew medical officers and evaluation of on-orbit tools that can augment image acquisition. ⋯ Real-time and still U/S images received at Mission Control Center in Houston were of sufficient quality for the images to be diagnostic for multiple potential genitourinary applications. Microgravity-based ultrasound imaging can provide diagnostic quality images of the retroperitoneum and pelvis, offering improved diagnosis and treatment for onboard medical contingencies. Successful completion of complex sonographic examinations can be obtained even with minimally trained nonphysician ultrasound operators, with the assistance of ground-based real-time guidance.
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Ultrasound Med Biol · Jul 2009
Detectability of small blood vessels with high-frequency power Doppler and selection of wall filter cut-off velocity for microvascular imaging.
Power Doppler imaging of physiologic and pathologic angiogenesis is widely used in preclinical studies to track normal development, disease progression and treatment efficacy but can be challenging given the presence of small blood vessels and slow flow velocities. Power Doppler images can be plagued with false-positive color pixels or undetected vessels, thereby complicating the interpretation of vascularity metrics such as color pixel density (CPD). As an initial step toward improved microvascular quantification, flow-phantom experiments were performed to establish relationships between vessel detection and various combinations of vessel size (160, 200, 250, 300 and 360 microm), flow velocity (4, 3, 2, 1 and 0.5 mm/s) and transducer frequency (30 and 40 MHz) while varying the wall filter cut-off velocity. ⋯ Color pixel density vs. wall filter cut-off curves from analogous in vivo experiments exhibited the same shape, including a distinct CPD plateau. The similar shape of the flow-phantom and in vivo curves suggests that the presence of a plateau in vivo can be used to identify the best-estimate CPD value that can be treated as a quantitative vascularity metric. The ability to identify the best CPD estimate is expected to improve quantification of angiogenesis and anti-vascular treatment responses with power Doppler.
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Ultrasound Med Biol · Jul 2009
Ultrasonographic evaluation of hyoid-larynx approximation in dysphagic stroke patients.
Hyoid-larynx approximation is an essential part of the swallowing process, and is related to airway protection. We aimed to evaluate the reliability of ultrasonographic examination of hyoid-larynx approximation and measure the approximation in stroke patients with or without dysphagia. Fifteen normal subjects and 40 stroke patients with or without dysphagia admitted to the Department of Rehabilitation Medicine of a tertiary hospital between July 2006 and February 2007 participated in this study. ⋯ Among stroke patients, hyoid-larynx approximation was less in the dysphagia group than in the nondysphagia group. In conclusion, ultrasound can quantitatively measure hyoid-larynx approximation with good reliability. Hyoid-larynx approximation was significantly reduced in stroke patients with dysphagia.
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Ultrasound Med Biol · Jul 2009
Simulation of intracranial acoustic fields in clinical trials of sonothrombolysis.
Two clinical trials have used ultrasound to improve tPA thrombolysis in patients with acute ischemic stroke. The Combined Lysis of Thrombus in Brain Ischemia Using Transcranial Ultrasound and Systemic tPA (CLOTBUST) trial reported accelerated recanalisation of the middle cerebral artery (MCA) in patients with symptoms of MCA infarction, which were monitored with 2-MHz transcranial Doppler. In CLOTBUST, there was no increased bleeding as evidenced by cranial computed tomography. ⋯ This simulated pressure is below the threshold for both inertial and stable acoustic cavitation but likewise lower than any acoustic pressure that has been reported as sufficient for effective sonothrombolysis. Simulating the pressure field of ultrasound protocols for clinical trials of sonothrombolysis may help explain mechanisms of adverse effects. Such simulations could prove useful in the initial design and optimization of future protocols for this promising therapy of ischemic stroke.