Biomedical subjects

Anne L Hall

Publications and source records attributed to Anne L Hall.

4 recordsLinked to original sources

PubMed2006

Vector Doppler imaging of a spinning disc ultrasound Doppler phantom.

Vector Doppler methods are used to obtain angle independent in-plane velocity information. Velocity magnitude as well as direction are reconstructed from regular steered colour flow and from split-aperture Doppler acquisitions. Spatially resolved in-plane velocity was obtained through Doppler colour flow mode and subsequent data triangulation. A depth-invariant constant Doppler angle was achieved by using a depth expanding transmit-receive Doppler aperture. Velocities of up to 50 cm s(-1) and 360 degrees vector velocity directions were measured. This was achieved by creating a spinning solid disc phantom. Such a phantom was built to allow underwater mounting and spinning of a solid disc-shaped ultrasound phantom (maximum velocity of 50 cm s-1). Doppler triangulation was realised by steered Doppler and by a split-aperture approach. Results of both imaging methods are shown. Split-aperture results showed errors of less then 10% for velocity magnitude estimation and less then 2.5 degrees for directional information.

Humans↗

PubMed2006

In vivo perfusion estimation using subharmonic contrast microbubble signals.

OBJECTIVE: The purpose of this study was to quantify perfusion in vivo using contrast-enhanced subharmonic imaging (SHI). METHODS: A modified LOGIQ 9 scanner (GE Healthcare, Milwaukee, WI) operating in gray scale SHI mode was used to measure SHI time-intensity curves in vivo. Four dogs received intravenous contrast bolus injections (dose, 0.1 mL/kg), and renal SHI was performed. After 3 contrast agent injections, a microvascular staining technique based on stable (nonradioactive) isotope-labeled microspheres (BioPhysics Assay Laboratory Inc, Worcester, MA) was used to quantify the degree of perfusion in 8 sections of each kidney. Low perfusion states were induced by ligating surgically exposed segmental renal arteries followed by contrast agent injections and microvascular staining. Digital clips were transferred to a personal computer, and SHI time-intensity curves were acquired in each section using Image-Pro Plus software (Media Cybernetics, Silver Spring, MD). Subharmonic fractional blood volumes were calculated, and the perfusion was estimated from the initial slope of the fractional blood volume uptake averaged over 3 injections. Subharmonic perfusion data were compared with the gold standard (ie, the microspheres) using linear regression analysis. RESULTS: In vivo gray scale SHI clearly showed flow and, thus, perfusion in the kidneys with almost complete suppression of tissue signals. In total, 270 SHI time-intensity curves were acquired, which reduced to 94 perfusion estimates after averaging. Subharmonic perfusion estimates correlated significantly with microsphere results (r = 0.57; P < .0001). The best SHI perfusion estimates occurred for high perfusion states in the anterior of the kidneys (r = 0.73; P = .0001). The corresponding root mean square error was 2.4%. CONCLUSIONS: Subharmonic perfusion estimates have been obtained in vivo. The perfusion estimates were in reasonable to good agreement with a microvascular staining technique.

Albumins↗

PubMed2006

Measurement of volumetric flow.

OBJECTIVE: The purpose of this study was to evaluate a 3-dimensional (3D) sonographic method for the measurement of volumetric flow under conditions of known flow rates and Doppler angles. METHODS: A GE/Kretz Voluson 730 system (GE Healthcare, Milwaukee, WI) and RAB2-5 probe were used to acquire 3D Doppler measurements in a custom flow phantom. Blood-mimicking fluid circulated by a computer-controlled pump provided a range of flow velocities (2-15 mL/s). A 6-axis positioning system maneuvered the ultrasound probe through a range of angles (40 degrees-70 degrees and 110 degrees -140 degrees) with respect to the tube (orthogonal to the tube being 90 degrees). Volume data sets were obtained spanning 29 degrees lateral and 20 degrees elevational angles encompassing the flow tube in a scanning time of less than 10 seconds. Power Doppler data were used to correct for partial volume effects. RESULTS: Using a single angle (110 degrees) with respect to the flow tube, measured and actual volume flow rates were within the 95% confidence interval over the full range of flow rates. At flow rates of 5 and 10 mL/s, the measured volume flow rates were all within +/-15% of actual values for the range of angles tested and also stayed within the 95% confidence interval. CONCLUSIONS: Direct comparisons of volume flow rates estimated with 3D sonography and known flow rates showed that the method has good accuracy. Subsequent comparisons under pulsatile and in vivo conditions will be needed to verify this performance for clinical applications.

Blood Flow Velocity↗

PubMed2005

Real-time excitation-enhanced ultrasound contrast imaging.

A new nonlinear contrast specific imaging modality, excitation-enhanced imaging (EEI) has been implemented on commercially-available scanners for real-time imaging. This novel technique employs two acoustic fields: a low-frequency, high-intensity ultrasound field (the excitation field) to actively condition contrast microbubbles, and a second lower-intensity regular imaging field applied shortly afterwards to detect enhanced contrast scattering. A Logiq 9 scanner (GE Healthcare, Milwaukee, WI) with a 3.5C curved linear array and an AN2300 digital ultrasound engine (Analogic Corporation, Peabody, MA) with a P4-2 phased array transducer (Philips Medical Systems, Bothell, WA) were modified to perform EEI on a vector-by-vector basis in fundamental and pulse inversion harmonic grayscale modes. Ultrasound contrast microbubbles within an 8 mm vessel embedded in a tissue-mimicking flow phantom (ATS Laboratories, Bridgeport, CT) were imaged in vitro. While video intensities of scattered signals from the surrounding tissue were unchanged, video intensities of echoes from contrast bubbles within the vessel were markedly enhanced. The maximum enhancement achieved was 10.4 dB in harmonic mode (mean enhancement: 6.3 dB; p = 0.0007). In conclusion, EEI may improve the sensitivity of ultrasound contrast imaging, but further work is required to assess the in vivo potential of this new technique.

Albumins↗