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Biomedical subjects

Paul L Carson

Publications and source records attributed to Paul L Carson.

14 recordsLinked to original sources
PubMed2006

Spatial control of gas bubbles and their effects on acoustic fields.

Because microbubbles can enhance therapy, such as by cavitation or by thermal means, treatment could be confined with localization of microbubbles. This spatial control can be achieved by the vaporization of liquid-filled droplets present throughout the medium in a process known as acoustic droplet vaporization (ADV). Bubbles in the form of an orthogonal plane or "wall" can thus be created and can scatter ultrasound to enhance the proximal acoustic field while shielding distal tissues. To investigate the possible effects of a preexistent bubble wall, tissue-mimicking polyacrylamide gels embedded with perfluorocarbon droplets were insonified under various conditions. The preliminary results presented in this paper show that a bubble wall can successfully cause proximal ADV at approximately half the transmitted pressures that are required without the use of a bubble wall, while also serving as a viable shield against ADV and potential damage in distal areas. The results seen here in a gel medium are promising and suggest further development in vivo is needed.

Acrylic Resins↗
PubMed2006

Refill model of rabbit kidney vasculature.

A refill model previously developed in flow phantoms was modified to simulate the refill of cortical and medullary rabbit kidney tissues. The highly structured kidney tissues were accounted for by considering refill both within and across the scan-plane. Refill curves were acquired with ultrasound contrast from rabbit kidneys using high MI disruption pulses followed by low MI real-time imaging. The comparison of the real medullary and cortical tissues with their corresponding models resulted in an RMS error of 11% and 18%, respectively, indicating that simple assumptions about a tissue's vascular structure are predictive of refill behaviour. Tissue classification images were generated using the refill models and an exponential simplification. These images were indistinguishable and matched what is expected of a kidney, indicating that the primary distinguishing characteristic between kidney tissue types is mean transit time. However, the vascular model is useful in predicting and explaining tissue properties that affect refill behavior.

Animals↗
PubMed2006

Imaging of joints with laser-based photoacoustic tomography: an animal study.

Photoacoustic tomography (PAT), a nonionizing, noninvasive, laser-based technology was adapted to joint imaging for the first time. Pulsed laser light in the near-infrared region was directed toward a joint with resultant ultrasonic signals recorded and used to reconstruct images that present the optical properties in subsurface joint tissues. The feasibility of this joint imaging system was validated on a Sprague Dawley rat tail model and verified through comparison with histology. With sufficient penetration depth, PAT realized tomographic imaging of a joint as a whole organ noninvasively. Based on the optical contrast, various intra- and extra-articular tissues, including skin, fat, muscle, blood vessels, synovium and bone, were presented successfully in images with satisfactory spatial resolution that was primarily limited by the bandwidth of detected photoacoustic signals rather than optical diffusion as occurs in traditional optical imaging. PAT, with its intrinsic advantages, may provide a unique opportunity to enable the early diagnosis of inflammatory joint disorders, e.g., rheumatoid arthritis, and to monitor therapeutic outcomes with high sensitivity and accuracy.

Acoustics↗
PubMed2005

Acoustic droplet vaporization for temporal and spatial control of tissue occlusion: a kidney study.

Acoustic droplet vaporization (ADV) has been introduced with the potential application of tumor treatment via occlusion and subsequent necrosis. New Zealand White rabbits were anesthetized, and their left kidney was externalized. An imaging array and single-element transducer were positioned in a tank with direct access to the kidney's vasculature and renal artery. Filtered droplet emulsions (diameter <6 microm) were injected intra-arterially (IA) into the left heart during insonification of the renal artery, and the extent of blood flow reduction by ADV was compared to the untreated right kidney. Flow cytometry (using colored microspheres) of kidney tissue samples and reference blood from the femoral artery allowed the quantitative estimation of regional blood flow. A maximum regional blood flow reduction in the treated region of >90% and an average organ perfusion reduction of >70% was achieved using ADV. After treatment of the left kidney, the control kidney on the contralateral side showed a maximum decrease in regional blood flow of 18% relative to the pre-ADV baseline. Image-based hyper-echogenicity from ADV of IA injections was monitored for approximately 90 minutes, and cortex perfusion was reduced by >60% of its original value for more than 1 hour. This could be enough time for the onset of cell death and possible tumor treatment via ischemic necrosis. Moreover, currently used radiofrequency tissue ablation-based tumor treatment could benefit from ADV due to the decreased heat loss via vascular cooling.

Animals↗
PubMed2005

Functional imaging with intraoperative ultrasound: detection of somatosensory cortex in dogs with color-duplex sonography.

OBJECTIVE: To evaluate the capability of intraoperative color-duplex sonography to detect eloquent flow-activated areas and their anatomic relationship in dogs. METHODS: After craniotomy, the sensory cortex of eight dogs was identified by recording the highest amplitude detected with a grid electrode evoked with somatosensory evoked potential stimulation of the nervus ischiadicus. A 7.5-MHz linear array transducer was placed on the dura, and eight images were taken in color-coded capture mode during baseline and somatosensory evoked potential stimulation of the ipsilateral (nonevoked) and contralateral (evoked) sensory cortex. The differences in flow velocity intensities were statistically compared (Wilcoxon test) in three arbitrary velocity ranges and across all colored pixels in a region of interest between baseline and stimulation in both hemispheres. RESULTS: Comparing both hemispheres during stimulation, the evoked sensory cortex demonstrated an increase of 10% in the number of counted colored pixels during stimulation, whereas the number of counted colored pixels in the ipsilateral sensory cortex decreased by 2% (P < 0.05), indicating an overall increase in measured flow during stimulation. Comparing differences during nonstimulation and stimulation in single hemispheres, the lowest of the three velocity ranges (approximately 10-20 mm/s) demonstrated a statistically significant (P = 0.01) increase during stimulation, whereas no change was observed during stimulation in the ipsilateral hemisphere. This increase has been confirmed by regional cerebral blood flow measurement with colored microspheres. CONCLUSION: This study indicates, for the first time, the capability of intraoperative ultrasound to detect functionally important areas during evoked stimulation.

Animals↗
PubMed2005

Sonographic evaluation of early-stage breast cancers that undergo neoadjuvant chemotherapy.

OBJECTIVE: We prospectively evaluated low-stage breast cancers treated with neoadjuvant chemotherapy using whole-volume sonography and color Doppler imaging. METHODS: Thirty-four women with breast cancer (mean maximum size, 2.4 cm) received neoadjuvant chemotherapy with doxorubicin and docetaxel. Targeted whole-volume sonography of tumor sites was performed before and after chemotherapy to assess mass size, color pixel speed-weighted density, and American College of Radiology Breast Imaging Reporting and Data System sonographic characteristics. After chemotherapy, tumor sites were excised by lumpectomy or mastectomy. RESULTS: Three (11.3%) of 34 patients had a complete histologic response. After chemotherapy, correlation was r = 0.716 between final histologic and sonographic sizes. Compared with histologic residual tumors, sonography had 4 false-negative results, 3 false-positive results, and 27 true-positive results (sensitivity, 87%), with no false-negative results among a subgroup of tumors of 7 mm and larger (sensitivity, 100%). The 3 cases with false-positive results were histologic fibrosis or biopsy changes. Mean speed-weighted density was 0.015 before and 0.0082 after chemotherapy (P = .03). After chemotherapy, vascularity was less common within (P = .06) or adjacent to (P = .009) masses or in tumor sites (P = .05). Prechemotherapy variables of gray scale characteristics and vascularity were compared with final histologic size, and all had P > .20. CONCLUSIONS: Postchemotherapy sensitivity of sonography was high for residual tumors of 7 mm or larger. Correlation was moderate between histologic and sonographic final tumor sizes. False-positive results were caused by fibrosis or biopsy-related changes. False-negative results occurred with residual tumor size of 6 mm or smaller. After chemotherapy, vascularity usually decreased, and this was not specific for complete response. Before chemotherapy, no vascular or gray scale feature at initial imaging predicted complete responders.

Adult↗
PubMed2004

Sound speed estimation using automatic ultrasound image registration.

A mismatch between the sound speed assumed for beamforming and scan conversion and the true sound speed in the tissue to be imaged can lead to significant defocusing and some geometric distortions in ultrasound images. A method is presented for estimating the average sound speed based on detection of these distortions using automatic registration of overlapping, electronically steered images. An acrylamide gel phantom containing vaporized dodecafluoropentane droplets as point targets was constructed to evaluate the technique. Good agreement (rms deviation <0.4%) was found between the sound speeds measured in the phantom using a reference pulse-echo technique and the image-based sound speed estimates. A significant improvement in accuracy (rms deviation <0.1%) was achieved by including the simulated sound field of the probe rather than assuming straight acoustic beams and propagation according to ray acoustics.

Algorithms↗
PubMed2004

Potential of microbubbles for use as point targets in phase aberration correction.

Bubbles can be produced by vaporization of perfluorocarbon droplets of a few microm diameter. These bubbles can reach over 100 microm in diameter and their backscatter is calculated to be well more than 10 dB above that of several organ tissues. At appropriate sizes, small acoustic amplitudes, and diagnostic frequencies (2-15 MHz), bubbles can be approximated by the nonrigid sphere-scattering solution employed here. This paper concerns the bubble size and its implications on the backscatter amplitude and the phase error introduced in diagnostic ultrasound when assuming that the bubble acts as a point target for phase aberration correction.

Algorithms↗
PubMed2004

On the acoustic vaporization of micrometer-sized droplets.

This paper examines the vaporization of individual dodecafluoropentane droplets by the application of single ultrasonic tone bursts. High speed video microscopy was used to monitor droplets in a flow tube, while a focused, single element transducer operating at 3, 4, or 10 MHz was aimed at the intersection of the acoustical and optical beams. A highly dilute droplet emulsion was injected, and individual droplets were positioned in the two foci. Phase transitions of droplets were produced by rarefactional pressures as low as 4 MPa at 3 MHz using single, 3.25 micros tone bursts. During acoustic irradiation, droplets showed dipole-type oscillations along the acoustic axis (average amplitude 1.3 microm, independent of droplet diameter which ranged from 5 to 27 microm). The onset of vaporization was monitored as either spot-like, within the droplet, or homogeneous, throughout the droplet's imaged cross section. Spot-like centers of nucleation were observed solely along the axis lying parallel to the direction of oscillation and centered on the droplet. Smaller droplets required more acoustic intensity for vaporization than larger droplets, which is consistent with other experiments on emulsions.

Acoustics↗
PubMed2004

Combination of digital mammography with semi-automated 3D breast ultrasound.

This paper describes work aimed at combining 3D ultrasound with full-field digital mammography via a semi-automatic prototype ultrasound scanning mechanism attached to the digital mammography system gantry. Initial efforts to obtain high x-ray and ultrasound image quality through a compression paddle are proving successful. Registration between the x-ray mammogram and ultrasound image volumes is quite promising when the breast is stably compressed. This prototype system takes advantage of many synergies between the co-registered digital mammography and pulse-echo ultrasound image data used for breast cancer detection and diagnosis. In addition, innovative combinations of advanced US and X-ray applications are being implemented and tested along with the basic modes. The basic and advanced applications are those that should provide relatively independent information about the breast tissues. Advanced applications include x-ray tomosynthesis, for 3D delineation of mammographic structures, and non-linear elasticity and 3D color flow imaging by ultrasound, for mechanical and physiological information unavailable from conventional, non-contrast x-ray and ultrasound imaging.

Adult↗
PubMed2002

Rapid elastic image registration for 3-D ultrasound.

A Subvolume-based algorithm for elastic Ultrasound REgistration (SURE) was developed and evaluated. Designed primarily to improve spatial resolution in three-dimensional compound imaging, the algorithm registers individual image volumes nonlinearly before combination into compound volumes. SURE works in one or two stages, optionally using MIAMI Fuse software first to determine a global affine registration before iteratively dividing the volume into subvolumes and computing local rigid registrations in the second stage. Connectivity of the entire volume is ensured by global interpolation using thin-plate splines after each iteration. The performance of SURE was quantified in 20 synthetically deformed in vivo ultrasound volumes, and in two phantom scans, one of which was distorted at acquisition by placing an aberrating layer in the sound path. The aberrating layer was designed to induce beam aberrations reported for the female breast. Synthetic deformations of 1.5-2.5 mm were reduced by over 85% when SURE was applied to register the distorted image volumes with the original ones. Registration times were below 5 min on a 500-MHz CPU for an average data set size of 13 MB. In the aberrated phantom scans, SURE reduced the average deformation between the two volumes from 1.01 to 0.30 mm. This was a statistically significant (P = 0.01) improvement over rigid and affine registration transformations, which produced reductions to 0.59 and 0.50 mm, respectively.

Algorithms↗
PubMed2002

In vivo droplet vaporization for occlusion therapy and phase aberration correction.

The objective was to determine whether a transpulmonary droplet emulsion (90%, <6 microm diameter) could be used to form large gas bubbles (>30 microm) temporarily in vivo. Such bubbles could occlude a targeted capillary bed when used in a large number density. Alternatively, for a very sparse population of droplets, the resulting gas bubbles could serve as point beacons for phase aberration corrections in ultrasonic imaging. Gas bubbles can be made in vivo by acoustic droplet vaporization (ADV) of injected, superheated, dodecafluoropentane droplets. Droplets vaporize in an acoustic field whose peak rarefactional pressure exceeds a well-defined threshold. In this new work, it has been found that intraarterial and intravenous injections can be used to introduce the emulsion into the blood stream for subsequent ADV (B- and M-mode on a clinical scanner) in situ. Intravenous administration results in a lower gas bubble yield, possibly because of filtering in the lung, dilution in the blood volume, or other circulatory effects. Results show that for occlusion purposes, a reduction in regional blood flow of 34% can be achieved. Individual point beacons with a +24 dB backscatter amplitude relative to white matter were created by intravenous injection and ADV.

Acoustics↗