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Biomedical subjects

B A Angelsen

Publications and source records attributed to B A Angelsen.

At least 19 recordsLinked to original sources
PubMed1992

Intravascular ultrasonographic appearance of angiographically normal arteries related to age and the occurrence of vascular disease.

In 22 individuals (mean age 52 years) the ultrasonographic images of arteries defined as normal by arteriography were studied and related to the age and medical history of the patients. The series was divided into 2 groups: patients with clinical manifestation of atherosclerosis and patients without a history of arterial disease. The study included 6 young patients (mean age 14 years) referred for angiographic documentation of abolished intracranial circulation. A typical 3-layered appearance of the arterial wall was found in young healthy individuals as well as in adult and elderly subjects. There was no difference in the ultrasonographic appearance of muscular and elastic arteries. In patients with extensive obstructive atherosclerosis affecting other parts of the arterial tree, a segment of the iliac artery can have the same appearance as seen in young healthy individuals. There are indications that severe hypertension can result in a thickening of the middle low-echogenic layer of the arterial wall. In patients with chronic renal insufficiency, small calcifications in the middle layer were a typical finding.

Adolescent↗
PubMed1991

Tissue characterization with intra-arterial ultrasound: special promise and problems.

Although we are able to identify many tissue types based on the screen image in intravascular ultrasound, there is additional information in the ultrasound signal which could be of assistance in characterization and identification of tissue. Intravascular ultrasound has several special characteristics which affect tissue characterization. These include the high transducer frequency, small transducers, short and relatively uniform path to the tissue, and limited tissue types to identify. These characteristics influence the results obtained by absolute backscatter, local statistics, frequency dependent backscatter, and angle dependency of backscatter. These effects are both positive and negative, and in many cases can be observed in clinical imaging. Another area of tissue characterization which can be performed with ultrasound is measurement of arterial wall elasticity. This can be of importance in the evaluation of mechanisms of dilatation, and the potential for complications.

Arteries↗
PubMed1991

Intravascular ultrasound guidance for catheter-based coronary interventions.

Intravascular ultrasound is a new method for visualizing the details of vascular pathology, providing high resolution images of plaque and thrombus. This review summarizes the potential applications of ultrasound imaging in the guidance of balloon angioplasty, atherectomy, laser ablation and stenting. Ultrasound differs from angiography and angioscopy in its ability to penetrate below the surface of the vessel lumen, demonstrating specific aspects about the distribution and composition of plaque. Because the different layers of the arterial wall have different acoustic properties, ultrasound catheters are able to define the layers of normal wall in comparison with plaque. Particularly in combination with therapeutic techniques designed to remove or ablate plaque, ultrasound may prove useful in maximizing the amount of plaque treated and minimizing trauma to normal vessel wall components. Combined imaging/therapeutic devices are in the pilot phase of development and show promise for enhancing the safety and efficacy of the catheter devices.

Angioplasty, Balloon, Coronary↗
PubMed1991

Flow estimation using ultrasound imaging (color M-mode) and computer postprocessing.

We have developed a method to calculate flow noninvasively in blood vessels using color Motion-mode (M-mode) and computer postprocessing. The velocity of each point in the cross-sectional area of the vessel was found from the color M-mode recording by correcting for angle both distances and velocities and by assuming a symmetrical circular velocity field. Volume flow was then found by integrating the velocity field at 5-ms intervals through the cardiac cycle. In a cardiovascular hydromechanical model, a correlation of 0.99 and p value of less than 0.001 were found between estimated and measured flow in the model (n = 8). In 20 healthy individuals, we made 31 investigations in the common carotid (CCA), internal carotid (ICA), and external carotid (ECA) artery, comparing flow in the CCA with the added flow in the ICA and ECA. The values (CCA versus ICA + ECA) correlated with r = 0.91 and p less than 0.01. Repeated investigations (n = 8) in one individual gave flow estimates of 495 +/- 50 ml/min in the CCA, 304 +/- 45 ml/min in the ICA, and 165 +/- 37 ml/min in the ECA (means +/- SD). This article shows that this system can make accurate estimation of blood flow to the brain noninvasively.

Blood Flow Velocity↗
PubMed1991

Sensitivity and speed of colour Doppler flow mapping compared with continuous wave Doppler for the detection of ventricular septal defects.

Twenty nine patients (aged from three months to 37 years) with confirmed or suspected ventricular septal defects were studied separately by three examiners who used colour flow mapping and imaging, or continuous wave Doppler and imaging, or a combined reference examination. Colour flow mapping identified 19 of the 25 patients with a ventricular septal defect, continuous wave Doppler echocardiography identified 18, and the combined reference examination identified 24. Two of four patients without ventricular septal defect had a false positive result with colour flow mapping and none had a false positive result with continuous wave Doppler examination. During the reference examination continuous wave Doppler identified 24 patients with ventricular septal defects and colour flow mapping identified 23. In two patients a second ventricular septal defect was found by colour flow mapping, and confirmed by continuous wave Doppler. There was no significant difference in time to diagnosis between the two techniques. Colour flow mapping aids identification of multiple ventricular septal defects but is not faster and has lower specificity than continuous wave Doppler. A combination of the two techniques gave the highest sensitivity and specificity.

Adolescent↗
PubMed1990

Estimation of arterial compliance in aortic regurgitation: three methods evaluated in pigs.

Three methods for measuring arterial compliance when aortic regurgitation is present are examined. The first two methods are based on a Windkessel model composed of two elements, compliance C and resistance R. Arterial compliance was estimated from diastolic pressure waveforms and diastolic regurgitant flow for one method, and from systolic aortic pressure waveforms and systolic flow for the other method. The third method was based on a three-element Windkessel model, composed of characteristic resistance r, compliance C and resistance R. In this method arterial compliance was calculated by adjusting the model to the modulus and phase of the first harmonic term of the aortic input impedance. The three methods were compared and validated in six anaesthetised pigs over a broad range of aortic pressures. The three methods were found to give quantitatively similar estimates of arterial compliance at mean aortic pressures above 60 mm Hg. Below 60 mm Hg, estimates of arterial compliance varied widely, probably because of poor validity of the Windkessel models in the low pressure range.

Animals↗
PubMed1990

Quantification of aortic regurgitation by Doppler echocardiography: a new method evaluated in pigs.

We have developed a method to quantify aortic regurgitant orifice and volume, based on measurements of the velocity of the regurgitant jet, aortic systolic flow, the systolic and diastolic arterial pressures, a Windkessel arterial model, and a parameter estimation technique. In six pigs we produced aortic regurgitant flows between 2.1 and 17.8 ml per beat, i.e. regurgitant fractions from 0.06 to 0.58. Pulmonary and aortic flows were measured with electromagnetic flow probes, aortic pressure was measured invasively, and the regurgitant jet velocity was obtained with continuous-wave Doppler. The parameter estimation procedure was based on the Kalman filter principle, resulting primarily in an estimate of the regurgitant orifice area. The area was multiplied by the velocity integral of the regurgitant jet to estimate regurgitant volume. A strong correlation was found between the regurgitant volumes obtained by parameter estimation and the electromagnetic flow measurement. These results from our study in pigs suggest that it may be possible to quantify regurgitant orifice and volume in patients completely noninvasively from Doppler and blood pressure measurements.

Animals↗
PubMed1990

Autocorrelation length of normal and myopathic human myocardium measured by acoustic microscopy: implications for clinical ultrasonic tissue characterization.

The pattern of acoustic speckle present in ultrasonic images of tissue may be affected by pathological changes in the tissue. To investigate the possibility for such an effect in dilated cardiomyopathy, we examined acoustic micrographs of frozen sections of normal (autopsy) and myopathic (transplant recipient) human myocardium. The resulting images were digitized, and the major axis autocorrelation length calculated for each image. For the normal specimens (n = 75, four patients), the mean autocorrelation length was 37 +/- 18 microns, with the maximum value of 92 microns. The myopathic specimens (n = 64, four patients) had a mean of 52 +/- 19 microns, with a maximum of 100 microns. We conclude that the changes in structure between normal and myopathic myocardium are significant (p less than 0.001), but on so small a scale in relation to the wave length of clinical ultrasound that there will only be changes in the intensity of the backscattered signal, not the pattern of speckle.

Acoustics↗
PubMed1990

Estimation of regurgitant volume and orifice in aortic regurgitation combining CW Doppler and parameter estimation in a Windkessel-like model.

A method for noninvasive estimation of regurgitant orifice and volume in aortic regurgitation is proposed and tested in anesthetized open chested pigs. The method can be used with noninvasive measurement of regurgitant jet velocity with continuous wave ultrasound Doppler measurements together with cuff measurements of systolic and diastolic systemic pressure in the arm. These measurements are then used for parameter estimation in a Windkessel-like model which include the regurgitant orifice as a parameter. The aortic volume compliance and the peripheral resistance are also included as parameters measurements in the open chest pigs are used. Electromagnetic flow measurements in the ascending aorta and pulmonary artery are used for control, and a correlation between regurgitant volume obtained from parameter estimation and electromagnetic flow measurements of 0.95 over a range from 2.1 to 17.8 mL is obtained.

Animals↗
PubMed1989

Analysis of backscattered ultrasound from normal and diseased arterial wall.

Intra-arterial ultrasonic imaging has several features which affect the feasibility of clinical tissue characterization when compared with trans-thoracic ultrasound. The short distance from transducer to tissue, fluid path, high frequencies, and special characteristics of the tissues of interest all contribute to making practical tissue characterization by measurement of the backscattered signal more probable in intra-arterial imaging. The properties of backscattered ultrasound, and methods of characterizing such signals, are discussed with special reference to intra-arterial applications.

Acoustics↗
PubMed1989

The initial clinical evaluation of a transesophageal system with pulsed Doppler, continuous wave Doppler, and color flow imaging based on an annular array technology.

The application of transesophageal echocardiography (TEE) offers access to a great deal of important clinical information regarding cardiovascular anatomy and physiology. Two applications which have not been reported and would appear to be of interest are continuous wave Doppler capabilities and the implementation of higher frequency transducers. A TEE system designed at the Institute of Biomedical Engineering in Trondheim, which is based on an annular array technology, offers these capabilities. We evaluated this instrument in the clinical setting in a series of 30 patients to test the probe function in terms of the tissue and flow imaging quality with a 7.5 MHz carrier frequency, and to report on the implementation of a continuous wave Doppler modality in a TEE probe. We found that the annular array method permitted the use of high frequency probes for tissue and flow imaging which resulted in excellent image resolution, and that shifting the carrier frequency of the transducer to a lower frequency permitted the optimization of the Doppler sensitivity. The continuous wave Doppler was used to measure abnormal blood flow velocities in excess of 5.0 m/s, and was particularly useful in the operating room as velocity measurements could be obtained without compromising the sterile field. The results of our evaluation indicate that high imaging frequencies and continuous wave Doppler can be applied by an annular array TEE transducer.

Adolescent↗
PubMed1989

Cross sectional early mitral flow velocity profiles from colour Doppler.

Instantaneous cross sectional flow velocity profiles from early mitral flow in 10 healthy men were constructed by time interpolation of the velocity data from each point in sequentially delayed two dimensional digital Doppler ultrasound maps. This interpolation allows correction of the artificially produced skewness of velocities across the flow sector caused by the time taken to scan the flow sector for velocity recording of pulsatile blood flow. These results suggested that early mitral flow studied in an apical four chamber view is variably skewed both at the leaflet tips and at the annulus. The maximum flow velocity overestimated the cross sectional mean velocity at the same time by a factor of 1.2-2.2. Also the maximum time velocity integral overestimated the cross sectional mean time velocity integral to the same extent. This cross sectional skew must be taken into account when calculation of blood flow is based on recordings with pulsed wave Doppler ultrasound from a single sample volume.

Adolescent↗
PubMed1977

Diagnosis of valvular heart disease using transcutaneous Doppler ultrasound.

An ultrasonic Doppler instrument capable of measuring mean and maximum velocities inside a small sample volume is presented. The instrument has been used for determining velocities in normal and diseased heart valves. A method is described for identifying the different heart valves, based on their relation to one another as well as the form of the velocity curve. The pressure drop across the mitral valve can be determined from the maximum velocity and the mean velocity can be used to determine the degree of aortic insufficiency. Recordings of mean and maximum velocities can give an indication of the form of the whole spectrum, thus making complete frequency analysis unnecessary for most purposes.

Aorta, Thoracic↗
PubMed1976

Transcutaneous measurement of blood flow velocity in the human aorta.

A Doppler velocity meter for measuring blood flow velocity in the human aorta is described. Using pulsed ultrasound, this instrument allows the velocity to be measured at selected depths. The instrument has been tested in laboratory experiments, and appears to give accurate estimates of mean flow velocity for both steady and pulsatile flows. Flow velocities and estimates of stroke volume have been obtained from the ascending aorta in 18 patients. It is suggested that at present only relative values for flow and flow velocity can be measured. A method for obtaining absolute values for these parameters, based on scanning in the aortic arch, is proposed.

Angina Pectoris↗
PubMedDate not supplied

The velocity distribution in the aortic anulus in normal subjects: a quantitative analysis of two-dimensional Doppler flow maps.

The velocity distribution in the aortic anulus is commonly assumed to be uniform. A skewed velocity profile may have consequences for the accuracy of volume flow estimates by the Doppler echocardiographic technique. To assess this issue, the velocity distribution in the aortic anulus in 12 normal subjects was studied by computer analysis of digital velocity data from two-dimensional Doppler ultrasound flow maps. The velocity profiles in the aortic anulus were found to be flat but slightly skewed, with the highest velocities toward the septum. There was little interindividual variation. Our findings imply that the centerline velocity is the best estimate for the spatial mean velocity at the aortic anulus in normal subjects. The importance of this finding in patients is unknown. In normal subjects, the results suggest that stroke volume might be overestimated by approximately 15% by Doppler echocardiography if the cross-sectional velocity profile is not accounted for.

Adult↗