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Biomedical subjects

F Forsberg

Publications and source records attributed to F Forsberg.

15 recordsLinked to original sources
PubMed1996

Endosonographic and color Doppler flow imaging alterations observed within irradiate rectal cancer.

PURPOSE: To correlate the endosonographic and color Doppler flow imaging alterations observed in irradiated rectal cancers with the pathologic features of radiation response, and to evaluate the potential impact of altered blood flow on the integrity of the surgical anastomosis. METHODS AND MATERIALS: Endosonography with color and pulsed wave Doppler was performed on 20 rectal cancer masses before and after high dose preoperative radiation (XRT). Pre- and post-XRT observations included comparing alterations in tumor size, sonographic echotexture, color Doppler flow, and pulsatility indices. Comparisons were made with pathologic findings in the irradiated specimens and with the incidence of anastomotic failure. RESULTS: Compared to pre-XRT observations, irradiated rectal cancers decreased in size and became either mixed in echogenicity with less apparent color Doppler flow (16 of 20) or unchanged in color Doppler flow and echotexture (4 of 20). Those with less flow (16 of 20) were imaged later (mean = 90.2 +/- 12.1 days) than those without change in color Doppler flow (mean = 21.7 +/- 2.7 days). Pathologically, the group of four without change in color Doppler signal had features of acute inflammation which were not observed in 16 of 20 imaged later. Based on pulsatility index measurements, both high and low resistance vessels were detected and confirmed by immunohistochemical staining, and features of postradiation obliterative vasculitis were observed. Only one primary anastomosis in 14 patients with decreased flow failed. CONCLUSIONS: The sonographic and color Doppler flow imaging alterations observed within irradiated rectal cancer correlated with changes of postradiation obliterative vasculitis. The apparent diminished local blood flow within high and low resistance vessels post-XRT did not result in an increased incidence of anastomotic failures.

Aged↗
PubMed1996

Quantitative ultrasonic diagnosis of silicone breast implant rupture: an in vitro feasibility study.

Ultrasound is useful in evaluating the integrity of silicone breast implants. However, extensive operator experience is required. A system for computer-assisted diagnosis is being developed to reduce operator dependence. Feasibility was examined by measuring the ultrasonic properties of breast implants in vitro. Silicone gels from 45 explanted implants (26 intact and 19 ruptured) were placed in sealed acoustic test chambers and 60 RF A-lines were acquired from each. Velocity of sound, attenuation and integrated backscatter (IB) were estimated. Receiver operating characteristic (ROC) analysis was performed. The mean speed of sound was 1060 m/s +/- 50.1 m/s in intact implants and 1115 m/s +/- 74.3 m/s in ruptured ones (p < 0.003). Differences in attenuation were not statistically significant. The mean IB was -83.9 dB +/- 7.94 dB in intact and -77.2 dB +/- 9.07 dB in ruptured implants (p < 0.006). The area under the ROC curve (Az) was 0.70 and 0.73 for IB and velocity, respectively, while combining the two yielded Az = 0.81. Changes in speed of sound and IB, with changes in integrity of breast implants, have been demonstrated in vitro. The results indicate the potential for quantitative assessment of silicone breast implants performed in vivo.

Breast Implants↗
PubMed1996

Studies on the use of non-Rayleigh statistics for ultrasonic tissue characterization.

The research groups at Drexel University and Thomas Jefferson University had proposed the use of non-Rayleigh statistics for tissue characterization. Previous work based on the hypothesis that the envelope of the backscattered echosignal from abnormal regions of the tissue is more likely to be K-distributed than Rayleigh distributed, used the parameter of the K-distribution, M, to distinguish between regions containing benign or malignant masses and normal ones. In this work the B-scan breast images of 19 patients were studied using this approach. Previous studies have also been extended to exploit the existence of non-uniform phase characteristics of the echosignal from scatterers with some regular spacings, such as those in a periodic or quasi-periodic alignment. Computer simulations were carried out to show that the phase statistics deviate significantly from uniform in the range of (0, 2 pi) if the imaging region contained a number of periodically aligned (regular lattice) scatterers along with a collection of randomly distributed scatterers resulting in a quasi-periodic arrangement. This methodology was then applied to B-scan images of the breasts to distinguish between benign and malignant masses. If benign lesions show some sort of quasi-periodic or regular structures in the tissue, they will present non-uniform phase characteristics while more randomly structured malignant masses will have uniform phase characteristics. It is seen that the K-distribution may be used to identify the abnormal regions in the breast images and information on the phase may be used to further separate the abnormal regions into benign and malignant ones.

Breast Neoplasms↗
PubMed1996

Color amplitude imaging: preliminary results using vascular sonographic contrast agents.

Conventional (mean Doppler frequency shift) color Doppler imaging and a new method of displaying blood flow in color that uses the amplitude of the Doppler signal were utilized to evaluate three vascular sonographic contrast agents. To compare the two color flow detection modalities, a total of 20 pairs of contrast agent injections were performed while imaging a variety of abdominal organs and tumors in experimental animal models. The 20 paired injections were scored independently to indicate whether color amplitude imaging better demonstrated the effects of contrast enhancement (n = 14), both techniques were equivalent in demonstrating the effects of contrast enhancement (n = 4), or color Doppler imaging better demonstrated the effects of contrast enhancement (n = 2). These results indicate that compared to color Doppler imaging, color amplitude imaging improved visualization of both normal and abnormal blood flow in 70% of these cases (P < 0.0001). Specifically, with contrast enhancement of the Doppler signals, organ vascularity and regional differences in parenchymal blood flow were better demonstrated with color amplitude imaging than with color Doppler imaging. In addition, since color amplitude imaging is nondirectional and less angle dependent than color Doppler imaging, it was possible to visualize vessel continuity more completely and to demonstrate vessel branching more clearly with this modality. However, owing to the lack of directivity and poor temporal resolution, information obtained with color amplitude imaging appears to be complementary to that of color Doppler imaging. In conclusion, color amplitude imaging is a reliable method of determining the effectiveness of vascular sonographic contrast agents and should be considered one of the primary flow imaging modalities used for the assessment of these agents.

Animals↗
PubMed1995

Volume flow estimation using time domain correlation and ultrasonic flowmetry.

A comparison of two volumetric blood flow measurement techniques, CVI-Q (based on time domain correlation) and ultrasonic flowmetry, has been performed in vitro and in vivo. A pulsatile flowpump was used to simulate carotid and femoral type waveforms which were measured simultaneously using the two methods. Five dogs had their common carotid and femoral arteries exposed, and the instantaneous maximum volume flow and the mean flow were measured. Each vessel was partially occluded halfway through the experiment, simulating a 90% stenosis. In vitro, both techniques achieved absolute errors below +/- 5% for flow rates over 100 mL/min, but ultrasonic flowmetry had statistically significant larger errors for slower flow rates. In vivo correlation coefficients ranging from 0.73 to 0.95 were obtained with regression line slopes close to unity. The two techniques were in reasonable agreement, but with standard deviations of 20% to 28%. These studies indicate that noninvasive CVI-Q measurements of blood flow in the carotid and femoral arteries are linear and accurate compared to invasive ultrasonic flowmetry.

Algorithms↗
PubMed1995

Parenchymal enhancement and tumor visualization using a new sonographic contrast agent.

The purpose of this study was to assess the ability of a sonographic contrast agent to increase parenchymal echogenicity and improve tumor visibility. The agent is an emulsion that changes at body temperature from nonechogenic submicrometer liquid droplets to echogenic 1 to 5 microns microbubbles, capable of transversing the pulmonary and capillary circulations. Peripheral venous injections (dosages of 0.05 to 0.8 ml/kg) were administered to five woodchucks (three with multiple hepatomas), 12 rabbits (with renal VX-2 tumors), and four dogs. Ultrasonograms were acquired from kidney, liver, tumors (including tumor vessels) and normal vessels. Uptake and washout curves were generated via videodensitometry. Finally, Doppler shifts from a cuff transducer around the celiac trunk were analyzed to provide an in vivo dose-response curve. Vascular enhancement, including hepatoma and VX-2 tumor vessels, was seen for 2 to 3 min. Maximum enhancement was 18.7 dB for a 0.6 ml/kg dose. Enhancement of normal liver and kidney parenchyma was observed in all three species for up to 20 min. Small hepatomas became more echogenic centrally, but larger tumors showed no increase in central echogenicity. In conclusion, improved tumor visibility and parenchymal enhancement was demonstrated in animals.

Animals↗
PubMed1994

Ultrasound contrast agents: a review.

During the past 25 years, many attempts have been made to establish effective ultrasound contrast agents for both cardiac and noncardiac applications. The ideal ultrasound contrast agent would be: (a) nontoxic; (b) injectable intravenously; (c) capable of passing through the pulmonary, cardiac and capillary circulations; and (d) stable for recirculation. A variety of potential ultrasound contrast agents have been or are now under development. Present and future ultrasound contrast agents should provide for increased diagnostic capabilities in a variety of normal and abnormal vessels and organs throughout the body. These agents will enhance tumor vascularity, delineate areas of ischemia, as well as improve visualization of vascular stenosis. Future developments with modification of ultrasound equipment should increase the capabilities of these agents to improve imaging as well as Doppler sensitivity.

Biophysical Phenomena↗
PubMed1994

Artifacts in ultrasonic contrast agent studies.

Intravenously injected ultrasonic contrast agents making use of encapsulated gas microbubbles have excellent clinical potential for both color and spectral Doppler studies. However, a number of artifacts are associated with sonographic contrast agent measurements. Three artifacts were identified: (1) color "blooming," (2) increased maximum Doppler shift, and (3) spectral "bubble noise." Experiments have been conducted with Albunex and Levovist. These agents were injected into rabbits and humans to allow the cause of the artifacts to be established. Color blooming occurs soon after the bolus injection and is seen as gray scale pixels changing to color display. This is caused by the increase in flow signal strength. The apparent increase in the maximum Doppler shift frequency is due to the limited dynamic range of the spectral display. Only signals above a certain threshold are visible. As the Doppler signal power is enhanced, the highest frequency visible also increases. Finally, very large excursions can sometimes be seen in the spectral display (bubble noise). These might be due to either the breakdown of microbubbles or individual very large bubbles. The color blooming and bubble noise artifacts are easily identifiable and will not influence diagnostic management. The increase in peak Doppler shifts is more troublesome as it prevents comparison of spectral parameters obtained before and after injection of contrast agent.

Albumins↗
PubMed1994

Endorectal color and duplex imaging of the normal rectal wall and rectal masses.

This study investigates the ability of endorectal ultrasonography aided by color flow and pulse wave Doppler techniques to identify submucosal arterial plexuses of the normal rectal wall and to detect vessels supplying rectal wall masses. Color flow and pulsed wave Doppler analysis of 62 normal submucosal arterial plexuses and vessels feeding rectal wall masses (one rectal endometriosis and seven rectal cancers) was performed. The color signals from normal submucosal arterial plexuses and the one case of rectal endometriosis were judged to be sparse or decreased in comparison to color signals from rectal cancers. The median and mean P1 values for normal submucosal arterial plexuses were significantly greater than those for the central feeding vessels or small peripheral vessels within rectal masses. Our experience with color and duplex endorectal ultrasonography suggests that different vascular structures exist in normal persons compared to those in rectal wall masses. Pathologically, rectal cancers possess vessels with and without a smooth muscle layer, which may produce the high and low resistance signals identified by pulse Doppler.

Adult↗
PubMed1993

Galactose-based intravenous sonographic contrast agent: experimental studies.

A galactose-based sonographic contrast agent, which produces stable microbubbles capable of traversing the cardiopulmonary circulation, was used to enhance Doppler signals in blood vessels of varying size after intravenous injection. A series of experiments using dogs, rabbits, and woodchucks was conducted to establish the ability of the agent to enhance the reflectivity of normal tissue, tumor tissue, and blood. Although no enhancement was perceptible in tissue on the sonogram, significant enhancement of color and spectral Doppler signals was demonstrated in a variety of vessels. These included the aorta, vena cava, and portal vein as well as such small vessels as those of the retina of the eye, renal cortex, liver parenchyma, and gallbladder wall. Both spectral and color Doppler enhancement was shown in naturally occurring woodchuck hepatomas. Peak Doppler signal enhancement after bolus injection was approximately 10 dB with a dose of 0.01 ml/kg. Recirculation of the agent provided enhancement after intravenous bolus injection for more than 3 min. With a steady intravenous infusion of 0.2 ml/min/kg, Doppler signal enhancement of about 14 dB was maintained continuously for more than 5 min. The results of these animal experiments, in particular in small vessels and with recirculation after intravenous injection, suggest excellent potential for future clinical applications.

Angiography↗
PubMed1991

Accuracy of colour Doppler ultrasound velocity measurements in small vessels.

Colour Doppler ultrasound offers the possibility of imaging small vessels not visible by B-mode alone. The colour Doppler image of velocities allows the course of small vessels to be imaged in the X-Y plane of the scan provided the Doppler frequency shift is of sufficient magnitude. This permits alignments of the Doppler cursor, allowing angle correction to provide true velocity measurements from the Doppler shift obtained. Before attempting to make velocity measurements, however, it is essential to be aware of the possible error in the Z plane caused by the thickness of the Doppler sample volume. To quantify this source of error, hydrophone and flow-rig measurements were performed on an Acuson 128 colour Doppler scanner with both 5 MHz linear-array and 3.5 MHz phased-array transducers. Measurements of the transmitted pulses using a point hydrophone showed that both probes employ approximately 3.5 MHz Doppler pulses (in both colour and pulsed Doppler modes). The two transducers have the same axial resolution. In colour Doppler mode the axial length of the sample volume increases automatically with depth by up to 0.5 mm. Measurements of colour and pulsed Doppler signal strength were obtained in a controlled flow rig. Both transducers produced accurate colour flow images of the phantom at their optimum depths; flow velocity errors due to Z-plane thickness are less than 5%. There was, however, substantial error outside these optimum conditions (up to 20%).

Arteries↗
PubMed1991

Assessment of hybrid speckle reduction algorithms.

A consequence of employing coherent detection methods in medical ultrasound imaging systems is the occurrence of interference effects in the received echo field, which produce the speckle artefact. Speckle can severely degrade the information content of the image, and its efficient removal from ultrasound pulse-echo images is the focus of a number of research projects. Traditionally, the approach towards speckle reduction in pulse-echo images has been based on two classes of technique, either employing some form of spatial/frequency compounding or a data (image) filter. Both approaches have inherent shortcomings, and two alternative techniques are suggested here: 'local frequency diversity' and 'frequency differencing'. These algorithms deterministically identify where speckle occurs, and correct for speckle only within short, localized, corrupted segments of the A-line. This provides the potential for real-time implementation. Simulated and clinical in vivo images have been obtained, and the capabilities of the alternative speckle reduction algorithms are assessed against the more conventional approaches.

Algorithms↗