Biomedical subjects

James B. Seward

Publications and source records attributed to James B. Seward.

7 recordsLinked to original sources

PubMed1999

Transvascular Imaging: Feasibility Study Using a Vector Phased Array Ultrasound Catheter.

BACKGROUND: Transvascular imaging is defined as the acquisition of anatomic and functional information of structures lying beyond the confines of a vascular conduit within which the imaging device resides. Interrogating structures surrounding the vascular conduit is the subject of this feasibility study using a novel underblood, phased array ultrasound-tipped catheter. METHODS: An intravascular catheter (10-F, 3.2-mm-diameter, four-way articulation) tipped with a 5.5- to 10-MHz frequency agile, vector phased array transducer with full Doppler capability (Sequoia, Acuson) was used. The imaging transducer has a wide range of tissue penetration (2 mm to >10 cm from the lens). The catheter was introduced via an 11-Fr femoral venous sheath into the inferior and superior vena cavae and right heart chambers. As the catheter was advanced, attention was directed to visualization of structures surrounding the vessel in which the catheter resided. RESULTS: From the cavae and femoral vein the thoracic, abdominal and femoral arteries could be easily imaged. Anatomy that was visualized included the liver, hepatic veins, gallbladder, and mesenteric vessels. Normal and pathological anatomy and Doppler physiology could be readily appreciated. Doppler (i.e., pulsed- and continuous-wave, color flow, and tissue Doppler) fostered unique transvascular physiological hemodynamic and flow assessment. CONCLUSION: Transvascular imaging is feasible in human subjects using this 10-Fr catheter tipped with a 5.5- to 10-MHz vector phased array transducer. Intravascular navigation to a desired location within the body and the performance of diagnostic or therapeutic procedures at a remote site under direct ultrasound visualization are possible. Full Doppler capability extends the concept of transvascular hemodynamic and physiological assessment.

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PubMed1999

Rapid Three-Dimensional Myocardial Contrast Echocardiography: Volumetric Quantitation of Nonperfused Myocardium After Intravenous Contrast Administration.

Current acquisition methods for quantitative three-dimensional myocardial contrast echocardiography require long acquisition times and therefore require the invasive administration of deposit contrast agents administered intra-arterially or into the left atrium. This study addressed the feasibility of obtaining accurate and precise quantitative volumetric measurements of nonperfused myocardium after an intravenous bolus of echocardiographic contrast agent using a rapid three-dimensional myocardial contrast echocardiographic acquisition technique. An open-chest pig model of acute left anterior descending coronary artery (LAD) occlusion was used. After LAD ligature, an intravenous bolus of contrast agent was given and images were obtained over a 12-second period using a continuously rotating transducer placed at the apical position. There was no significant microbubble destruction during the rotational acquisition period as measured by differences in mean gray scale values of apical, mid, and basal myocardial regions between the first and last image frames of acquisition. Calculated volumes of nonperfused myocardium demonstrated significant agreement and correlation (mean difference +/- SD = -0.30 +/- 1.71 cm(3); r = 0.89; P < 0.01; y = 1.06x - 1.08) with anatomic specimens. When expressed as percent of total LV volume being nonperfused, the mean difference +/- SD was 2.1 +/- 3.6%, r = 0.94, P < 0.01, and y = 1.33x - 4.08. We conclude that accurate and precise measurements of nonperfused myocardium after an acute LAD coronary artery occlusion can be obtained after the intravenous bolus administration of a contrast material when a rapid 12-second acquisition with a continuously rotating transducer is used.

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PubMed1998

Three-Dimensional Imaging Used for Virtual Dissection, Image Banking and Physical Replication of Anatomy and Physiology.

Historically, techniques of dissection have been used to aid in our understanding of human anatomy, physiology, and pathology. However, these techniques alter the structures and fine details being studied. New advances in computer technology, imaging equipment, data acquisition, processing, storage, and display now allow multidimensional imaging. Interactive computer programs can electronically display both static three-dimensional and higher-dimensional images that retain features such as motion, pressure, and temporal change. Multidimensional images can be reconstructed and manipulated using different holographic, stereolithographic, or interactive two-dimensional displays. We describe the unique potential of multidimensional reconstruction, virtual dissection, and replication of cardiovascular structures using ultrasound data. Ultrasound technology has the advantage of depicting both anatomy and physiology. The ability to perform virtual dissection and surgery in the living patient without disruption of anatomy or physiology provides the clinician with a powerful new tool for diagnosis, teaching, and therapeutics.

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PubMed1998

Three-Dimensional Echocardiography: Precision and Accuracy of Left Ventricular Volume Measurement Using Rotational Geometry with Variable Numbers of Slice Resolution.

We developed a new, rapid (6 seconds) acquisition technique allowing collection of approximately six through nine apical rotational tomograms for three-dimensional (3-D) echocardiography. To justify an appropriate sampling density for precise and accurate measurement of chamber volumes in left ventricles with complicated shape, we designed a validation study in vitro using six canine heart specimens with irregular, asymmetric left ventricles with known volumes (28.5 to 104.3 ml; mean, 71.2 ml). The number of equally spaced slices were incrementally deleted from the original high resolution scans (48 slices) to 2 slices in 3-D reconstruction. We created subgroups of 48- and 36-, 24- and 16-, 12- and 8-, 6- and 4-, and 3- and 2-component slices to compare left ventricular (LV) volumes measured in 3-D images with different slice resolution with the reference standard measured in the specimen. The accuracy and precision of LV volume were relatively constant in the subgroup of 4- and 6- through 36- and 48-component slices. When the subgroup with 6- and 4-component slices was used, the correlation was r = 0.991, P < 0.0001, root-mean-square percent error of 5.0%, bias of 0.5 +/- 3.7 ml, and interobserver variability of 5.0%. With the reduction in component slices equal or less than three, the accuracy decreased significantly (root-mean-square percent error = 8.1% and bias = -2.0 +/- 5.7 ml) compared with higher slice resolutions. This study demonstrated that 3-D echocardiography using apical rotational techniques can accurately quantify LV volume in the canine heart specimens with irregular shapes with as few as 4-6 axial slices. The rapid 3-D acquisition technique is therefore anticipated to yield precise and accurate LV volumetry.

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PubMed1997

Absent Pulmonary Valve: Echocardiographic Features.

Congenital absence of the pulmonary valve, a rare anomaly, is characterized by absent or rudimentary pulmonary valve, often with annular stenosis, and aneurysmal dilatation of the pulmonary arteries. This defect is most commonly an accompaniment of tetralogy of Fallot but occasionally occurs alone. Four patients with this abnormality were examined by two-dimensional echocardiography at the Mayo Clinic. Doppler echocardiography provided hemodynamic assessment of the magnitude of outflow obstruction and valve regurgitation. The two-dimensional echocardiographic and Doppler features of absent or rudimentary pulmonary valve provided diagnostic information sufficient to proceed directly to surgical correction.

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PubMed1997

Reference Techniques for Left Ventricular Volume Measurement by Three-Dimensional Echocardiography: Determination of Precision, Accuracy, and Feasibility.

The use of multiple in vitro reference methods to validate three-dimensional (3-D) echocardiographic techniques makes comparison difficult. In an attempt to establish a reference standard, we studied precision, accuracy, and feasibility of a true left ventricular (LV) volume measurement in six dog heart specimens using three techniques, called fluid, sheath, and cast. LV volumes ranged from 30 to 105 mL. Intraobserver variability was minimal in all combinations (1.26% to 2.8%) with a statistically insignificant tendency to higher values in the cast method. The cast method, however, exhibited significantly higher interobserver variability (5.78%) as compared to that ranging from 1.47% to 1.59% in the remaining two techniques. Regression analysis demonstrated high correlations among the three techniques assessed by 95% confidence limits and correlation coefficient (R(2) > 0.98, P < 0.01). Mean differences among the techniques (0.12 to 1.08 mL) were not significant. The fluid technique was easy to perform. The sheath technique required some practice. The cast method was sensitive to accurate preparation of a gelatin mixture. We conclude that the fluid and sheath techniques are precise, accurate, and feasible. We recommend their use as reference standards in laboratory LV volume measurement. Validation 3-D echocardiographic studies using either of these two techniques will be comparable. Although the accuracy of the cast technique is excellent, its lower precision makes it a second choice. It could be used in cases where an LV cavity cast is required and higher interobserver variability is acceptable.

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PubMed1997

Pericardiocentesis Guided by Two-Dimensional Echocardiography.

Echodirected pericardiocentesis has become the method of choice for the initial treatment of clinically significant pericardial effusions since it was introduced into the regular practice at the Mayo Medical Center in April 1980. Between April 1980 and January 1, 1994, 610 consecutive two-dimensional (2-D) echodirected pericardiocenteses were performed at the Mayo Clinic. There have been no deaths in the series of consecutive cases. In the first 500 consecutive cases examined in detail, there were five serious complications and 18 nonthreatening complications. Echodirected pericardiocentesis is a safe, humane, and cost-effective means of performing a pericardial tap. Excellent results have been obtained even with a large number of physician operators. This technique is well suited to the primary care setting. Physicians performing this procedure should be familiar with reading and performing 2-D echocardiography. Qualified physicians can be trained, fairly easily, to perform echodirected pericardiocentesis.

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