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Biomedical subjects

N Bom

Publications and source records attributed to N Bom.

At least 73 records · Page 4Linked to original sources
PubMed1991

Backscatter directivity and integrated backscatter power of arterial tissue.

A 27 MHz transducer, mounted on an ultrasonic microscope, was used to quantify the dependence of backscatter power on the angle of incidence of arterial vessels. Due to variations in the angle of incidence significant variations in backscatter power were found in the intima, the muscular and elastic media, the adventitia and the external elastic lamina. The muscular and the elastic media show anisotropic behaviour in their angle dependence, i.e. the extent of the angle dependence depends on the direction of angle variation. This anisotropic nature is probably caused by the dominant orientation of smooth muscle cells or elastin fibers in these tissue layers. Measurements on 13 specimens of the iliac artery showed that each tissue type of the vessel has its own specific angle dependent behaviour. In the future this property might be used for quantitative tissue characterization.

Humans↗
PubMed1991

Principles and recent developments in ultrasound contrast agents.

The behaviour of gas bubbles and gas encapsulated spheres as echographic contrast agents is reviewed. Compared with rigid spheres, gas bubbles are superior scattering agents and they offer a number of useful properties which can be exploited in a variety of ways. The analysis of their velocity of sound, back-scatter intensity, second harmonic emission and resonant frequency opens up new perspectives in the development of contrast agents for echocardiographic research with potential clinical applications.

Contrast Media↗
PubMed1991

The relative contributions of myocardial wall thickness and ischemia to ultrasonic myocardial integrated backscatter during experimental ischemia.

The purpose of this study was to assess the empirical relationship between myocardial integrated backscatter (IB) and myocardial wall thickness (WT) in normal myocardium. A second object was to estimate the additional contribution to acute ischemic integrated backscatter levels given this relationship. Myocardial IB measurements and simultaneous myocardial WT measurements were made in 16 open-chested pigs with intact coronary circulation (normal myocardium) and 10 min after the flow in the left anterior descending coronary artery had been reduced to 20% of its baseline value (ischemic myocardium). Measurements were made 50 times during one cardiac cycle and averaged over 10 cardiac cycles. IB and WT measurements were normalized with respect to the nonischemic end-diastolic values. The relationship between IB and WT in normal myocardium was estimated in every individual pig by simple linear regression. Estimates of IB during ischemia were calculated on the basis of this relationship and the ischemic WT measurements. Differences of the estimator and the actual measurement made during ischemia depict the actual contribution of the state of acute ischemia, without the influence of WT. The slope of the relationship between IB and WT during normal myocardial contraction ranged from -0.16 to 0.03 dB/% (mean = -0.036 dB/%, SD = 0.06 dB/%). The additional contribution of ischemia ranged from -3.84 to 5.56 dB (mean = 0.31 dB, SD = 2.72 dB). It was concluded that the average contribution of ischemia to IB measurements is insignificant if the IB dependency on WT is removed from the data and that the higher level of ischemic IB measurements can be explained by the decrease in wall thickness during ischemia and not by the ischemia itself.

Animals↗
PubMed1991

Influence of attenuation on measurements of ultrasonic myocardial integrated backscatter during cardiac cycle (an in vitro study).

The purpose of this study was to investigate the dependence of ultrasonic integrated backscatter (IB) and attenuation in myocardium on wall thickness in a state of acute ischemia. Therefore, an in vitro experiment was set up in which attenuation, IB and wall thickness of a piece of freshly excised myocardium could be measured almost simultaneously. The myocardium was taken from 11 Yorkshire pigs (25-30 kg) that were killed less than 45 min before the experiment. The myocardium was placed in the far field of an ultrasound transducer (3.2-7.2 MHz) and then compressed by a stainless steel sphere. Data were processed off-line. Backscatter and attenuation were also measured as a function of frequency at 100% and 75% wall thickness, respectively. Both attenuation and IB varied during compression. Attenuation had an initial value of 2.19 +/- 0.76 dB/cm and a slope of 0.015 +/- 0.017 dB/cm% wall thickness. IB had an initial value of -76.9 +/- 2.7 dB and a slope of -0.12 +/- 0.07 dB/% wall thickness. After subtracting the influence of the attenuation from the IB the initial value of IB was -74.0 +/- 2.7 dB and the slope -0.08 +/- 0.07 dB/% wall thickness. Attenuation appeared to have a linear dependency on frequency. Backscatter appeared not to increase with increasing frequency without correction of the spectrum for the frequency dependent insonified volume.

Animals↗
PubMed1991

Cyclic changes of blood echogenicity in high-frequency ultrasound.

Ultrasound images from human arteries obtained in vivo with an intravascular 30 MHz ultrasound imaging device show that blood echogenicity changes during the cardiac cycle. Quantitative measurements of blood echogenicity during the cardiac cycle suggest that these variations may be related to changes in the state of erythrocyte aggregation, which are induced by varying shear rate.

Blood Flow Velocity↗
PubMed1991

Angle-dependent backscatter from the arterial wall.

The anisotropic nature of intra-arterial echographic images is reported, and the source of this anisotropy is investigated using postmortem human iliac arteries. A 27 MHz transducer, mounted on an ultrasonic microscope, is used to quantify the angular dependence of the backscatter power versus the angle of incidence, and these results are correlated with histological findings. Besides the observed differences in the acoustic response of morphologically different tissues, significant variations in backscatter power are found in both media and internal elastic lamina due to variations in the angle of incidence. This angle dependence is caused by the dominant orientation of fibers in tissue layers and by the shape and size various scattering particles. The results indicate that long microscopic structures with one main orientation are responsible for the backscattered signal and that the angular-dependent response is related to the histologically determined orientation of these fibers. These results may have an impact on the assessment of intra-arterial echographic images.

Blood Vessels↗
PubMed1990

Ultrasonic myocardial integrated backscatter and myocardial wall thickness in animal experiments.

The purpose of this study was to distinguish between normal and ischemic myocardium using ultrasonic integrated backscatter (IB) measurements and to relate IB with myocardial wall thickness. IB was measured in 9 open-chested Yorkshire pigs (24-30 kg) before, after 30 minutes of partial occlusion of the proximal left anterior descending coronary artery (LADCA), and after 60 minutes of subsequent reperfusion. The ultrasound transducer (4 MHz) was sutured onto the epicardial surface perfused by the LADCA. IB measurements were made with a repetition rate of 50 times per heart rate simultaneously with a left ventricular pressure signal. Myocardial wall thickness was measured off-line. The measurements of integrated backscatter, left ventricular pressure and wall thickness were based on mean values of ten subsequent cardiac cycles. End-systolic IB measurements were 5.3 dB higher during occlusion as compared to the reference measurements (7.1 +/- 3.2 dB versus 1.8 +/- 2.6 dB; p = 0.002). No statistically significant differences were found in end-systolic IB measurements. End-systolic wall thickness was 5 mm smaller during occlusion as compared to the reference measurements (7.2 +/- 1.4 mm versus 12.2 +/- 1.2 mm; p less than 0.001). Simple linear regression analysis showed a statistically significant inverse relationship between IB measurements and wall thickness in 21 out of the 23 sequences in which wall thickness could be measured. End-systolic IB measurements are favourable to distinguish acute ischemic myocardium from normal myocardium. There is a distinct inverse relationship between IB and myocardial wall thickness.

Animals↗
PubMed1990

Enhanced morphological diagnosis in infective endocarditis by transoesophageal echocardiography.

Thirty three consecutive patients with clinically suspected endocarditis were studied by both precordial cross sectional echocardiography and transoesophageal echocardiography. The diagnostic value of both techniques was assessed. The data were compared with findings at operation in 25 patients. In 21 patients with native valve endocarditis precordial echocardiography showed evidence of vegetations in six patients and suggested their presence in nine. Transoesophageal echocardiography identified vegetations in 18 patients. Complications were seen in four patients at precordial echocardiography and in nine patients at transoesophageal echocardiography. Precordial echocardiography did not show vegetations in any of the 12 patients with prosthetic valve endocarditis whereas transoesophageal echocardiography showed vegetations in four. Complications were seen in four patients at precordial echocardiography and in 10 at transoesophageal echocardiography. Echocardiographic findings were confirmed at operation in all 25 operated patients. In two patients both echocardiographic techniques had missed the perforation of the cusps of the aortic valve that was seen at operation, but this had no effect on patient management. Transoesophageal echocardiography is the best diagnostic approach when infective endocarditis is suspected in patients with either native or prosthetic valves.

Adolescent↗
PubMed1990

The design, construction and clinical evaluation of a small phased array transducer for intraoperative echocardiography.

A small probe for cardiac surgery was developed and clinically tested. The probe is built as a phased array transducer with 64 elements with a centerfrequency of 5 MHz. The transducertip is connected with a handle by a flexible yet steerable shaft. This shaft has a length of 10 cm and can be set in a desired shape. Good quality images were obtained in all patients. The first study suggest many applications for a small probe in intraoperative echocardiography.

Cardiac Surgical Procedures↗
PubMed1989

Early and recent intraluminal ultrasound devices.

The history of intraluminal echography dates back to the very beginning of diagnostic ultrasound. Over the years many fascinating ideas and applications of catheter tip or gastroscopic tube tip mounted transducers have been described. This chapter surveys these methods, subdividing them into a) measurements; b) Doppler and c) imaging. The survey ranges from early work of Cieszynski on the feasibility of echocardiography to more recent intra-arterial catheter tip Doppler with guidewire and balloon as described by Serruys. Examples of ultrasound catheter tip echography in combination with other techniques such as angioscopy, laser ablation and spark erosion are also described. Today practical approaches are limited to imaging only. The three major approaches for catheter tip echo imaging are described and compared. This paper concludes with the results of automatic contour analysis of the inner arterial boundaries.

Cardiac Catheterization↗
PubMed1989

Intravascular echographic assessment of vessel wall characteristics: a correlation with histology.

In vivo application of intravascular high frequency ultrasonic imaging for peripheral and coronary artery disease is a promising technique for vascular surgeons, radiologists and cardiologists. This report demonstrates in vitro results obtained with a high frequency imaging catheter (40 MHz) in 70 human specimens including arteries with and without atherosclerosis, veins, coronary artery bypass grafts and vascular prosthetic material. Correlation between the ultrasonic images and the histologic characteristics of the corresponding vessel wall tissue and lumen geometry was established. In addition, the effect of intervention techniques i.e. balloon angioplasty, spark erosion and laser were studied with ultrasound and histology. It is anticipated that development of such a catheter imaging technique has potential for diagnostic imaging and for combination with therapeutic systems.

Angioplasty, Balloon↗
PubMed1989

Imaging artifacts in mechanically driven ultrasound catheters.

Mechanically driven catheter tip echo systems presently operate with a flexible shaft. Rotation power from a proximally mounted motor is transferred via this shaft to the rotating echo tip element. In practice, the tip does not identically 'follow' the rotation of the motor due to low torsional rigidity of the shaft, which creates artifacts in the displayed cross-sectional image. In order to visualize curved arteries such as the coronary arteries, a compromise is necessary between the required low flexural rigidity and a high torsional rigidity. In this report the image artifacts of mechanically driven systems are presented that are related to catheter tip motion. The properties of a spiral drive-shaft and a solid drive-shaft have been compared for rotational speed of 1000 and 3000 revolutions per minute (rpm), and for straight as well as strongly curved catheters. By way of example, the periodic angle error varies from 25 degrees top-top in a straight catheter to 80 degrees top-top when the catheter is curved with R = 20 mm, using a spiral drive-shaft at 1000 rpm.

Angioplasty, Balloon↗
PubMed1989

Transesophageal Doppler color flow imaging in the detection of native and Björk-Shiley mitral valve regurgitation.

Regurgitant blood flow of mitral valves was studied by transesophageal Doppler color flow echocardiographic imaging in 11 healthy volunteers (Group 1), 25 cardiac patients with a native mitral valve (Group 2), 10 patients with a normally functioning Björk-Shiley mitral prosthesis without clinical evidence of mitral regurgitation (Group 3) and 10 patients with angiographic or surgical evidence of Björk-Shiley mitral valve regurgitation (Group 4). Holosystolic regurgitant color jets were classified as type I or type II. The data were compared with results obtained with precordial techniques, i.e., continuous wave and Doppler color flow echocardiographic imaging (Groups 1 to 4) and left ventricular angiography or surgery (Groups 2 and 4). In Group 1, transesophageal Doppler color flow imaging revealed no mitral regurgitant flow in 7 of the 11 patients and a type I jet in 4 patients that was detected in only 1 patient by precordial techniques. In Group 2, angiography showed no mitral regurgitation in 20 patients and documented mitral regurgitation in 5. Transesophageal Doppler color flow imaging detected in 4 of the 20 patients a type I jet that was not visualized with precordial techniques in 2 patients. Type II jets were detected by the transesophageal technique in all five patients with proven mitral regurgitation and were also visualized with precordial echocardiography. All patients in Group 3 showed two identical type I jets that were not detected with precordial echocardiography.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

[Videodensitometry in echoencephalography of premature infants].

In 22 premature children (12 normal prematures and 10 with brain pathology) echodensity was measured as average grey scale values. For performing the measurements, echoencephalograms were recorded on videotape and analysed by an IBM-AT computer and a high resolution framegrabber. An evident difference of echodensity was measured between normal parenchyma, skull, fresh cerebral haemorrhages and cerebral oedema.

Brain↗
PubMed1988

Myocardial backscatter analysis in animal experiments.

This paper describes the instrumentation and data analysis procedures for cardiac tissue characterization by a backscatter method. Experimental results obtained with a 'button' transducer in direct contact with the myocardium are discussed.

Animals↗