Time Gain Compensation Research Articles

The use of an infrared touch-screen to control the sensitivity of ultrasound scanners in clinical practice.

Real-time ultrasound involves rapid scanning through the body and easy control manipulation is essential. The sensitivity settings of a scanner (also referred to as the time gain compensation (TGC) settings) are crucial in obtaining good image quality. However, many ultrasound scanners only allow the operator a limited scope for adjusting the sensitivity, and often it is only possible to change the slope or overall level of the TGC or to alter the TGC at a few depth ranges. No commercially available scanners allow the operator to alter the sensitivity in small regions of the image despite the common experience that a diagnosis is often made by examining in detail a particular area of an image. One approach to this problem is to automate fully the sensitivity controls (McDicken et al, 1974; DeClercq & Maginness, 1975; Pye et al, 1988). Another approach is to make the sensitivity controls more flexible and easier to use. In order to explore the potential of more flexible methods of sensitivity control, an infrared touch-screen has been used in conjunction with a microcomputer to control the sensitivity of a real-time scanner. This system has been evaluated clinically in routine obstetric scanning. The touch-screen is manufactured by Microvitec Ltd, and comprises an array of infrared emitters and detectors plus control logic mounted in a frame that fits around a 14-inch monitor screen. The maximum resolution of the array is 120 divisions horizontally by 90 vertically.

Image and Signal Processing in Diagnostic Ultrasound Imaging

An overview of signal-processing techniques used in the acquisition, display, manipulation, and analysis of echo scan data is presented. The principles of time-gain compensation, selective enhancement, log compression, fill-in interpolation, edge enhancement, image updating, write zoom, gray scale mapping, black/white inversion, freeze frame, frame averaging, read zoom, thresholding, contrast enhancement, filtering, and region-of-interest definition are reviewed. The concept of gray scale mapping, which dictates how the stored scan data are displayed, is explained with many illustrative examples.

Method and apparatus for compensation during ultrasound examination

The time-gain function of an ultrasound receiver for medical examinations is modified to compensate for different attenuation characteristics in body structures. The slope of the time-gain function is increased at times associated with pulse transmission through the highly attenuating body wall and may be decreased at times associated with pulse transmission through fluid filled body structures. The time-gain compensation, in combination with probe focus compensation and a highly linear receiver transfer function provides sharply increased diagnostic quality. The location and attenuating characteristics of body structures may be determined from a prior knowledge of their depth within the body or from distinctive signatures in ultrasound echos.

Ultrasound integrated backscatter tissue characterization of remote myocardial infarction in human subjects

To determine whether quantitative ultrasound tissue characterization differentiates normal myocardial regions from segments of remote infarction, 32 consecutive patients with a diagnosis of previous myocardial infarction were evaluated. Images were obtained in real time with a modified two-dimensional ultrasound system capable of providing continuous signals in proportion to the logarithm of integrated backscatter along each A line. In 15 patients, adequate parasternal long-axis images that delineated both normal and infarct segments were obtained with standard time-gain compensation. Image data were analyzed to yield both magnitude and delay (electrocardiographic R wave to nadir normalized for the QT interval) of the cyclic variation of backscatter.Cyclic variation was present in 55 of 56 normal myocardial sites, averaging (mean ± SEM) 3.2 ± 0.2 dB in magnitude and exhibiting a mean normalized delay of 0.87 ± 0.03. The magnitude of cyclic variation in infarct segments was significantly reduced to 1.1 ± 0.2 dB (42 sites), and the delay was markedly increased to 1.47 ± 0.12 (21 sites) (p < 0.0001 for both). In 20 of 42 infarct sites, no cyclic variation was detectable. Thus, ultrasound tissue characterization quantitatively differentiated infarct segments from normal myocardium in patients with remote myocardial infarction.

Frequency- and depth-dependent compensation of ultrasonic signals

The resolution in ultrasonic images decreases with depth when using traditional time-gain compensation (TGC) of the received signal. To reduce this effect, both frequency-dependent and depth-dependent compensation is introduced. A time-varying digital filtering method is presented for this purpose, which is based on Wiener filtering. Images obtained from a simulated tissue equivalent are presented and the frequency-compensated images are compared to conventional TGC-compensated images. It is shown that the improvement in resolution using frequency-dependent compensation is considerable when the signal-to-noise ratio in the received signal is high.

4662380 Adaptive time gain compensation system for ultrasound imaging

4662380 Adaptive time gain compensation system for ultrasound imaging

A high frequency peak detector for u.s. test pulses

To determine whether quantitative ultrasound tissue characterization differentiates normal myocardial regions from segments of remote infarction, 32 consecutive patients with a diagnosis of previous myocardial infarction were evaluated. Images were obtained in real time with a modified two-dimensional ultrasound system capable of providing continuous signals in proportion to the logarithm of integrated backscatter along each A line. In 15 patients, adequate parasternal long-axis images that delineated both normal and infarct segments were obtained with standard time-gain compensation. Image data were analyzed to yield both magnitude and delay (electrocardiographic R wave to nadir normalized for the QT interval) of the cyclic variation of backscatter.Cyclic variation was present in 55 of 56 normal myocardial sites, averaging (mean ± SEM) 3.2 ± 0.2 dB in magnitude and exhibiting a mean normalized delay of 0.87 ± 0.03. The magnitude of cyclic variation in infarct segments was significantly reduced to 1.1 ± 0.2 dB (42 sites), and the delay was markedly increased to 1.47 ± 0.12 (21 sites) (p < 0.0001 for both). In 20 of 42 infarct sites, no cyclic variation was detectable. Thus, ultrasound tissue characterization quantitatively differentiated infarct segments from normal myocardium in patients with remote myocardial infarction.

Focal periportal sparing in hepatic fatty infiltration: a cause of hepatic pseudomass on US.

An unusual pattern of hepatic fatty infiltration was detected sonographically in 31 patients over a 1.5-year period. At appropriate gain settings and time gain compensation, the liver parenchyma demonstrated diffuse increased echogenicity except for a solitary hypoechoic area with relatively distinct margins, usually located in the medial segment of the left hepatic lobe. This hypoechoic periportal focus varied in size between 1.5 and 5 cm and was typically ovoid, but was occasionally spherical or irregular in shape. Eight patients with such foci underwent percutaneous needle biopsy because of concern that there was a space-occupying mass. Microscopic examination of specimens from the hypoechoic periportal region revealed normal hepatic parenchymal cells, while tissue samples from the surrounding liver had high fat levels. In the remaining 23 patients, correlative radiologic studies supported the diagnosis of fatty liver and excluded a central-mass lesion. A localized area of normal hepatic tissue should be considered among the possible diagnoses when a circumscribed hypoechoic periportal area is demonstrated within a fatty liver.

Ultrasound mammography: effects of focal zone placement.

In order to avoid serious pitfalls in the diagnosis of breast masses by sonography, it is important to understand the effects of technical factors such as focal zone placement and time gain compensation.

Physical factors influencing quantitation of two-dimensional contrast echo amplitudes

Measurement errors that may interfere with quantitation by the new myocardial contrast two-dimensional echocardiographic technique were examined in a simplified in vitro model consisting of a 50 cc blood-filled balloon with supplemental controlled injection of 0.2 to 2.6 cc of sonicated dextrose 70%. The blood-contrast mixture in the balloon volume was imaged with two-dimensional echocardiography and discrete regions were studied for both magnitude and time course of echo intensities. Preliminary evidence indicates that a regional contrast echo intensity measurement is significantly modified by contrast-related ultrasound attenuation in intervening regions and by the amount and mode of contrast material injection. Thus, injection of 1.2 cc contrast material resulted in substantially higher peak echo intensity and a more rapid decay than injection of 0.8 or 0.6 cc. These measurements were also found to be influenced by the echographic system signal processing and time-gain compensation which contribute to nonlinear and unevenly compensated image distribution of echo amplitudes. Other factors are discussed, including transducer-related image resolution and image texture, contrast agent bubble size and persistence and computer methods for standardized selection of region of interest and analysis of the regional contrast intensity decay curve.

Signal processing equipment for ultrasonic visualization

In megahertz ultrasonic echoscopy of objects, echoscopes having a time gain compensation facility are often used. To ensure that a uniform ultrasonic echo signal is obtained at a predetermined depth (5) within an object, the present invention varies the sensitivity of the time gain compensation for each pulse of ultrasonic energy (8) used to obtain an echogram of the object. The present invention may include means to vary the slope of the time gain compensation so that at other predetermined depths (6) within the object, echo signals of respective intensities are received, thus overcoming problems due to shadowing by ultrasonically highly absorbing regions of the object. The main application of the invention is in medical diagnosis.

B‐MODE GRAY‐SCALE ULTRASOUND: IMAGING ARTIFACTS AND INTERPRETATION PRINCIPLES

The production and identification of gray‐scale ultrasonic imaging artifacts and some basic principles of ultrasonic interpretation are reviewed, discussed, and demonstrated with canine ultrasonograms. Imaging artifacts produced by ultrasound matter interactions include:reverberations, shadowing, through transmission and refractive and reflective zones. Technical imaging artifacts discussed include: off‐normal incidence defects, echo displacement, and improper time gain compensation settings. Interpretation principles to distinguish mass lesions, cystic structures, and calculi within abdominal parenchymal organs are presented.

Sonographic tissue texture: influence of transducer focusing pattern.

The ultrasonic beam profile pattern is not accurately known for most transducers in clinical use. A simple scan of an easily available phantom permits the clinician to determine the focusing pattern of his own transducer and equipment. Disregarding other operator-controllable parameters such as the time-gain compensation, output, and system sensitivity, the true echo pattern of a tissue is not accurately represented until the distance of the region of narrowest beam focus is reached. The fine speckled echo pattern commonly seen in uniform organs near the transducer is largely artifactual due to interference phenomena in the near field of the acoustic beam. Closest approximation of true texture is not displayed until near the depth at which the narrowest focus occurs. Beyond that depth, broad, coarser patterns can be expected.

Physical factors influencing numerical echo-amplitude data extracted from B-scan ultrasound images.

The replacement of analog-scan converters by digital-scan converters in commercially available B-scan ultrasound equipment provides easily available numerical echo-amplitude data from regions or organs of interest, once the image has been created. These values vary with, and are influenced by, a variety of physical variables, including transducer power output, time-gain compensation, signal threshold, preprocessing digital signal level assignment, frequency, and acoustic beam width. Unless vigorous efforts are made to standardize these variables, clinical reports using numerical analysis as disease descriptors should be viewed critically.

Technical factors influencing the imaging of small anechoic cysts by B-scan ultrasound.

Ultrasound examination of small cysts in vivo and in vitro has demonstrated that several factors can interfere with recognition of their true anechoic nature. Reverberation and the effects of the beam width can interact with adjacent acoustic reflectors to produce artifactual echoes. Sonic enhancement in distal tissues varies with time gain compensation, frequency, and the position of the focal zone. If the operator is aware of this problem, he can compensate for these effects and thereby improve diagnostic accuracy.

Characterization of medical ultrasonic transceivers. Gain transfer characteristics and their applications.

Abstract The concept of gain transfer characteristics of medical ultrasonic transceivers is presented. Transfer characteristics relate the peak echo amplitude at the output of the receiver to the attenuation of a reproducible reference echo, at discrete time gain compensation (TGC) voltage levels. A method is shown for the determination of the transfer characteristics, and their numerous applications are described.

Visualization of orbital tissues using various echographic techniques

Abstract Seventeen different ultrasonic A -scan techniques were used for ultrasonography of intact human orbits to find technical parameters which are most suitable to exhibit identifiable echoes from the posterior sclera, the surface of the external eye muscles and the orbital bones simultaneously. Contact coupling of the transducer probes to a number of preselected examination points at the anterior surface of the globe (horizontal plane) was applied to each of the techniques studied. The echograms were compared to an anatomic scheme developed specially for the purpose. The ultrasonic beam was initially directed rectangularly to the opposite sclera; subsequently attempts were made to pick up presumed muscle or bone echoes of higher amplitudes by tilting the transducer slightly within the horizontal plane. The tilting was limited by the requirement to maintain a high scleral echo amplitude. The best echograms were recorded using our modified echograph 7100 MA (Kretztechnik, Austria) with well-defined time-gain compensation and a 6 MHz probe.

Calibration and quality control in diagnostic ultrasound

Methods for calibrating ultrasound equipment and techniques for evaluating the consistency of operation of A-, B- and M-mode pulse-echo ultrasound apparatus, were presented. Equipment parameters to be included in these procedures include system sensitivity and noise level, time gain compensation, A-mode display linearity, B- and M-mode grey scale, longitudinal and lateral resolution, depth calibration, B-mode position alignment, initial and strong-interface dead zones and power output. Calibration and test procedures used in the laboratory were described, and their correlation with the recently adopted interim standards of the American Institute of Ultrasound in Medicine discussed.

Multiscan echocardiography. I. Technical description.

The principle of a prototype multiple element echocardiographic instrument is described. The major goal of this system is instantaneous visualization of moving cross-sections of the heart. As a result a direct impression of cardiac anatomy and dimensions may be obtained. The transducer contains 20 small acoustic elements positioned in a row. System characteristics and transducer details are given. A flexible five lever time-gain compensation unit which permits independent gain setting for specific depth ranges is described. Recording modes include video tape, photographic, film and line scan techniques. The signal from any selected element of the Multiscan transducer may be recorded in the conventional time-motion display, thus combining Multiscan capabilities with conventional echocardiographic techniques.