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Biomedical subjects

W Stanford

Publications and source records attributed to W Stanford.

At least 73 records · Page 4Linked to original sources
PubMed1994

Evaluation of cardiac function with ultrafast computed tomography.

Ultrafast computed tomography (UFCT) possesses many features that make it uniquely capable in performing measurements of cardiac function. Over the years, numerous validation studies have verified UFCT's ability to provide qualitative and quantitative information about cardiac performance. Documented accuracy and reproducibility in measuring functional parameters, such as volume, mass, contractility, and cardiac output, make UFCT a valuable tool in cardiac imaging.

Cardiac Output↗
PubMed1993

Nonangiographic assessment of coronary artery bypass graft patency.

Coronary artery bypass graft patency can be assessed using the indirect techniques of evaluating patients' symptoms and exercise tolerance, changes in stress electrocardiogram, radioisotope regional perfusion, and myocardial wall contraction. The direct techniques assess graft patency directly by visualizing grafts using conventional computed tomography (CT), ultrafast CT, magnetic resonance imaging, digital subtraction angiography, and echocardiography. The advantages and disadvantages of each of these modalities are reviewed. At the present time, ultrafast CT and possibly magnetic resonance imaging and Doppler appear to be the only techniques besides angiography that can consistently evaluate bypass graft patency. Although they have the advantage of being minimally invasive, they cannot show graft stenosis or sequential graft patency. These techniques are best used in following patients after coronary bypass graft surgery and ruling out graft closure as the source of chest pain.

Angina Pectoris↗
PubMed1993

Accurate preoperative diagnosis of pericardial constriction using cine computed tomography.

OBJECTIVES: The purpose of this study was to determine the accuracy of cine computed tomography in the diagnosis of constrictive pericarditis. BACKGROUND: Constrictive pericarditis is characterized by abnormalities of both cardiac structure and function. Accurate diagnosis requires detection of both a thickened pericardium and abnormal ventricular diastolic filling. At present, no one diagnostic technique has demonstrated sufficient accuracy in this setting. Cine computed tomography is a relatively new cardiac imaging mode with very high time and spatial resolution that has the potential to accurately diagnose constrictive pericarditis. METHODS: Twelve consecutive patients were retrospectively identified who had catheterization findings suggestive of constrictive physiology, had undergone a cine computed tomographic examination and had pathologic data that delineated the status of the pericardium. Group 1 (with constrictive pericarditis; n = 5) had surgical confirmation of thickened pericardium and improved clinically after pericardiectomy. Group 2 (no constrictive pericarditis; n = 7) had cardiomyopathy with normal pericardium. Seven normal volunteers (Group 3) were also studied. Cine computed tomograms were obtained for the entire heart (8-mm slices, 17 frames/s, nonionic contrast medium). Pericardial thickness was measured at 10 degrees intervals at three ventricular levels in each subject. The rapidity of diastolic filling was assessed by calculating the percent filling fraction in early diastole. RESULTS: Pericardial thickness was 10 +/- 2 mm (mean +/- SD) in Group 1, 2 +/- 1 mm in Group 2 and 1 +/- 1 mm in Group 3 (p < 0.05, constrictive pericarditis vs. no constrictive pericarditis). Left ventricular filling fraction was 83 +/- 6% in Group 1, 62 +/- 9% in Group 2 and 44 +/- 5% in Group 3. Right ventricular filling fraction was 93 +/- 5% in Group 1, 62 +/- 14% in Group 2 and 35 +/- 6% in Group 3 (p < 0.05, Group 1 vs. Groups 2 and 3). Both indexes provided a clear-cut distinction between patients with and without constriction. CONCLUSIONS: Cine computed tomography simultaneously provides both anatomic and physiologic data that allow accurate preoperative diagnosis of pericardial constriction.

Adult↗
PubMed1993

Utility of ultrafast computed tomography in the detection of thoracic aortic aneurysms and dissections.

The millisecond image acquisition time characteristic of the ultrafast computed tomography (UFCT) scanner makes it an ideal modality for evaluating patients with suspected vascular lesions of the thoracic aorta. Unlike conventional CT, the UFCT electron beam technology produces images with excellent resolution, minimal respiratory artifact, and superior vascular enhancement. This report discusses the (1) basic characteristics of the UFCT scanner as they relate to the imaging of the thoracic aorta, (2) UFCT appearances of uncomplicated and complicated aneurysms and dissections, (3) appropriate CT protocols used in the work-up of suspected thoracic aortic disease, and (4) strengths and weaknesses of other imaging modalities compared with UFCT.

Aortic Dissection↗
PubMed1993

Importance of left atrial baroreceptors in the cardiopulmonary baroreflex of normal humans.

In animals, sympathetic responses to orthostasis are regulated in part by cardiopulmonary afferents arising from atrial and ventricular baroreceptors. To determine the relative importance of these baroreceptor regions in the cardiopulmonary baroreflex of normal humans, simultaneous measurements of left atrial and right and left ventricular volumes (cine computed tomography), invasive hemodynamics, forearm vascular resistance (plethysmography), and efferent sympathetic nerve activity to muscle (microneurography) were obtained under control conditions and with nonhypotensive lower body negative pressure (-10 mmHg, LBNP-10) in nine normal human subjects. LBNP-10 did not alter heart rate or mean systemic arterial pressure, but it did produce significant decreases in pulmonary artery diastolic and right atrial pressures. This reduction in cardiac filling pressures resulted in efferent sympathoexcitation evidenced by increases in forearm vascular resistance and efferent sympathetic nerve activity to the muscle. LBNP-10 did not alter end-diastolic volume of the left or the right ventricle. Similarly, ventricular stroke volume was unchanged during LBNP-10, as assessed by cine computed tomography or thermodilution techniques. In contrast, LBNP-10 resulted in a significant decrease in left atrial volume. Thus, LBNP produced a significant decrease in cardiac filling pressures and left atrial volumes with resultant reflex sympathoexcitation, whereas ventricular volumes were unchanged. These observations suggest an important role for left atrial (nonventricular) baroreceptor afferents in the cardiopulmonary baroreflex of normal humans.

Adult↗
PubMed1993

Expiratory collapse of the trachea presenting as worsening asthma.

A 50-year-old woman with lifelong asthma had nearly total expiratory collapse of her distal trachea. The signs and symptoms were similar to those of asthma except for a pronounced upper airway component to her wheezing and the immediate onset of dyspnea on exertion. Surgical repair led to significant improvement in symptoms and resolution of tracheal collapse on expiration. Ultrafast computed tomography was a valuable adjunct to bronchoscopy in diagnosis and management. Expiratory collapse of the trachea should be considered in the differential diagnosis of wheezing and intractable reactive airway disease.

Asthma↗
PubMed1993

Coronary artery calcification: clinical significance and current methods of detection.

Coronary artery disease affects 1,500,000 Americans each year; 500,000 of these will die. The earliest detectable lesion of coronary atherosclerosis is the fatty streak. Later, crescent-shaped lipid plaques occur, which may rupture and produce either progressive stenosis or sudden occlusion with myocardial infarction. Calcium is deposited early in the formation of the atherosclerotic plaque, and calcification can be used as a marker of the atherosclerotic process. Many imaging techniques can be used to detect calcification of coronary arteries. The most promising are fluoroscopy, ultrafast CT, and intravascular sonography. Detection of calcification is most valuable in persons less than 40 years old in whom modification of risk factors may be important. In addition, the progression and possible regression of calcification can be used as an indicator of the atherosclerotic process. The absence of calcification in coronary arteries may diminish the need for further testing.

Calcinosis↗
PubMed1993

Coronary artery visualization using ultrafast computed tomography.

The advantages and limitations of ultrafast computed tomography in the imaging of normal and pathologic conditions of the coronary artery are discussed. The scanner's speed, resolution, and lack of significant motion artifact enhance the visualization of coronary arteries. Coronary artery calcification also is well visualized, and coronary artery fistuli, coronary bypass graft patency, and Kawasaki disease can be assessed accurately using contrast-enhanced flow studies. The inability to image stenoses and the lack of longitudinal images detract from its usefulness. Future scanner upgrades to provide increased resolution and thinner slices should improve the scanner's ability to evaluate the coronary artery.

Coronary Disease↗
PubMed1992

Ultrafast computed tomography in experimental pulmonary embolism.

Computed tomography (CT) has proven useful in the diagnosis of central pulmonary embolism; however, its ability to detect peripheral emboli has not been established. The authors evaluate the usefulness of ultrafast CT (UFCT) in detecting experimental peripheral pulmonary emboli. Three Gelfoam emboli measuring 0.7 x 1.5 cm were introduced into the pulmonary arteries of each of seven dogs, and contiguous, 3-mm, axial UFCT images from the lung apex to the base were obtained after the administration of a contrast bolus. After scanning, the dogs were killed, and the locations of the emboli were determined by a pulmonary pathologist blinded to the imaging results. Concomitantly, the locations of the emboli on the UFCT images were determined by consensus of three chest radiologists blinded to the autopsy results. All 21 emboli were identified on UFCT images; the locations of the emboli corresponded exactly with the autopsy findings. The authors conclude that UFCT can reliably detect Gelfoam emboli in second- to fourth-division pulmonary vessels. Further studies are needed to determine if in vivo blood clots can be similarly visualized.

Animals↗
PubMed1992

Cardiac anatomy instruction by ultrafast computed tomography versus cadaver dissection.

RATIONALE AND OBJECTIVES: This prospective study was designed to determine to what extent an ultrafast computed tomography (UFCT) videotape of the heart could enhance or substitute for cadaver dissection in teaching anatomy to first-year medical students. METHODS: A student population (n = 180) was randomized into four groups. Group 1 (control) received no instruction, group 2 viewed the videotape, group 3 participated in cardiac dissection, and group 4 performed cardiac dissection and viewed the videotape. After randomized instruction, each group was tested with 10 UFCT static cardiac images and 8 cardiac cadaver specimens. A different population consisting of nonrandomized fourth-year medical students also was tested. RESULTS: The results point to an interaction between instruction and the manner in which it was assessed. There was more carryover from the videotape-acquired knowledge to specimens than from dissection-acquired knowledge to UFCT images. CONCLUSIONS: Cardiac UFCT instruction resulted in dramatically improved image testing performance. This image-acquired knowledge was not sufficiently transferred to cardiac specimen identification; thus, videotape instruction should not replace dissection for teaching cardiac anatomy. Video provided instruction benefits beyond that gained through general clinical experience.

Audiovisual Aids↗
PubMed1992

Minimum scan speeds for suppression of motion artifacts in CT.

Cardiac and ventilatory motions cause artifacts at chest computed tomography (CT). To determine how short the scan times on third-generation units must be to avoid such artifacts, motion was measured with fast and ultrafast CT scans. Minimum detectable motion was then determined. The longest scan time that avoided a barely perceptible artifact was calculated by dividing the minimum detectable motion by the peak physiologic velocity. The posterior left ventricular wall moved at a maximum velocity of 52.5 mm/sec, necessitating a scan time of 19.1 msec or less to avoid artifact. Lung vessels near the heart moved at 40.5 mm/sec for a scan time of 24.7 msec or less. During quiet breathing, pulmonary vessels moved at 10.7 mm/sec for a scan time of 93.5 msec or less. The authors conclude that the shortest scan time on third-generation units (0.6 second) cannot prevent all artifacts arising from motion in the chest. Even ultrafast scan times (50 msec) are not short enough to eliminate artifacts on these units. Thus, reduction of motion artifacts will require techniques other than fast scanning.

Artifacts↗
PubMed1991

Fungal pulmonary infections after bone marrow transplantation: evaluation with radiography and CT.

The authors reviewed 55 pairs of chest radiographs and computed tomographic (CT) studies obtained in 33 febrile bone marrow transplant (BMT) recipients. The images were read separately, without knowledge of the clinical diagnosis. Twenty-one episodes of fungal infection were documented. One chest radiograph showed a pneumonia-like opacity, and 17 showed nodular opacities, five with cavitation. In 20 of 21 episodes, CT showed nodules with cavitation (n = 7), halo (n = 4), hazy margin (n = 5), air bronchogram (n = 2), cluster of fluffy nodules (n = 1), or sharp margin (n = 1). In none of the nine bacteremic episodes, however, were there opacities on chest radiographs or CT studies. CT studies demonstrating complicated nodules in febrile BMT patients strongly suggest a fungal infection, whereas negative CT studies suggest bacteremia or non-filamentous fungal infection of nonpulmonary origin. CT appears to add useful information to radiographic analysis during the assessment of febrile episodes in BMT patients, especially when invasive diagnostic procedures pose a high risk.

Adult↗
PubMed1991

High-resolution ultrafast chest CT in the clinical management of febrile bone marrow transplant patients with normal or nonspecific chest roentgenograms.

Plain chest roentgenograms may be normal or show nonspecific abnormalities during the frequent febrile episodes that occur in patients after bone marrow transplantation. In this group, ultrafast 10-mm and 3-mm high-resolution CT scans were prospectively performed in 33 patients to determine if useful information was provided that either changed the patient's clinical management or added confidence to the clinical diagnosis. The 36 symptomatic episodes that occurred in 33 patients included fever in 20 episodes and fever combined with cough, dyspnea, chest pain, or rales in 16. Fourteen chest roentgenograms were interpreted as normal, and 22 were interpreted as demonstrating nonspecific changes; however, none of the roentgenograms was considered helpful in that they did not provide sufficient information for further management. In 2 of 14 episodes in patients with normal chest roentgenograms and in 9 of 22 episodes in patients with nonspecific chest roentgenograms, CT scanning resulted in a change in clinical management that included performing bronchoscopy, increasing or changing antibiotic coverage, starting white blood cell transfusions, requesting surgical biopsy, or a combination of these. In 1 of 14 episodes in patients with normal chest roentgenograms and in 8 of 22 episodes in patients with nonspecific roentgenograms, CT added confidence to the diagnosis. In the remaining 16 episodes, CT scans provided no additional information. We conclude that in many instances, noncontrast ultrafast chest CT scans can provide information that may either change a patient's clinical management or more clearly establish the extent of pulmonary disease.

Adult↗
PubMed1991

The evaluation of coronary bypass graft patency: direct and indirect techniques other than coronary arteriography.

Patients having one or more coronary artery bypass graft operations constitute an important part of the practice of cardiac radiology. Bypass graft patency can be determined by indirect and direct methods. The indirect imaging methods include radionuclide ventriculography, thallium-201 scintigraphy, and positron emission tomography. The direct methods include conventional CT, ultrafast CT, MR imaging, digital subtraction angiography, and Doppler sonography. This review discusses the advantages and limitations of these methods and attempts to define the relative importance of each of these techniques in the evaluation of bypass graft patency.

Coronary Angiography↗
PubMed1991

Ultrafast computed tomography in assessing coronary bypass grafts.

The evaluation of chest pain in the postoperative coronary artery bypass graft patient is an important part of the cardiologist's and cardiothoracic surgeon's practice. Ultrafast computed tomography, by virtue of its speed and 0.75- to 1.5-mm spatial resolution, can detect graft patency with sensitivities of 93% to 96% and specificities of 86% to 100% in 94.2% of patients studied. Although image resolution is insufficient to demonstrate graft stenosis or sequential anastomoses, ultrafast computed tomography is becoming an increasingly important, minimally invasive imaging modality for the evaluation of coronary artery bypass graft patency.

Coronary Angiography↗