the of the magnitude, i.e., intensity, of the field.) It is shown that Rayleigh statistics govern the fist-order behavior of the magnitude; and the autocorrelation of the resulting image speckle is obtained by the methodof Middleton. The corresponding power spectrum follows immediately by Fourier transformation. Theoretical and experimentally determined autocorrelation functions and power spectra derived from B-scans of a scattering phantom containing many scatterers per resolution cell are presented. These functions lead naturally to the definition of the average speckle spot or cell sue, and this inturn is comparable to the resolution cell. Each independent speckle servesas a degreeof freedom that determines the number of samples of tissue available over a target.As the speckle cell size decreases this number increases in a manner predictable from the physical parameters of the cell size. However, it is found that the speckle cellis broadened, the degrees of freedom diminished, when the object structureis correlated. This yields the possibilityof deducing information about the object structure from the second-order statistics of the speckle texture, in addition to that obtainable from the fiistorder statistics.

Statistics of Speckle in Ultrasound B-Scans

Fetal umbilical artery flow velocity waveforms and placental resistance: pathological correlation.

Fetal umbilical artery flow velocity waveforms and placental resistance : Clinical significance

We propose a robust wavelet domain method for noise filtering in medical images. The proposed method adapts itself to various types of image noise as well as to the preference of the medical expert; a single parameter can be used to balance the preservation of (expert-dependent) relevant details against the degree of noise reduction. The algorithm exploits generally valid knowledge about the correlation of significant image features across the resolution scales to perform a preliminary coefficient classification. This preliminary coefficient classification is used to empirically estimate the statistical distributions of the coefficients that represent useful image features on the one hand and mainly noise on the other. The adaptation to the spatial context in the image is achieved by using a wavelet domain indicator of the local spatial activity. The proposed method is of low complexity, both in its implementation and execution time. The results demonstrate its usefulness for noise suppression in medical ultrasound and magnetic resonance imaging. In these applications, the proposed method clearly outperforms single-resolution spatially adaptive algorithms, in terms of quantitative performance measures as well as in terms of visual quality of the images.

A versatile wavelet domain noise filtration technique for medical imaging

https://www.gastrojournal.org/article/0016-5085(85)90569-4/pdf

Measurement of Gastric Emptying Time by Real-Time Ultrasonography

Fetal umbilical venous flow measured in utero by pulsed Doppler and B-mode ultrasound: I. Normal pregnancies

Using pulsed Doppler and B-mode ultrasonic techniques, umbilical venous flow has been measured for the first time under essentially normal physiological conditions. In normal pregnancies, the flow per unit fetal weight remains essentially constant at 110–120 ml/min/kg for most of the pregnancy. In pregnancies with complications, however, abnormally low or high flow values are frequently observed. Low flow values correlate strongly with retarded fetal growth, and with increased incidences of antenatal hypoxia, neonatal morbidity and neonatal death. In some circumstances high flow values suggest the presence of a compensatory mechanism. The results reported here suggest that umbilical flow can be used to separate all fetuses, whether growth retarded or not, into “low risk” and “high risk” groups with better sensitivity and accuracy than existing methods. In addition, low flow values have been measured an average of one week before growth retardation or fetal hypoxia were indicated by the conventional methods. A possible strategy for the diagnostic use of umbilical flow measurements is outlined.

Umbilical venous flow in normal and complicated pregnancy

Grey scale echography portrays the internal echoes originating from small impedance discontinuities formed by the structural organisation of soft tissue. These internal echoes are independent of inclination whilst their size and distribution is specific to the type of tissue examined. Thus normal and pathological tissues are portrayed with a differing appearance allowing their identification on the echograms. The principle of selecting a range of magnitudes of echoes for display on a restricted dynamic range of a display unit is described as well as methods used for compensating for the factors that effect the magnitude of echoes. Grey scale echography gives a new active role to simple scanning and a comparison of the features of simple and compound scanning is made. The simples and most reliable application of grey scale echography is the differentiation between cystic and solid structures and the criteria used in this application are discussed. The classification of soft tissue is more difficult, normal soft tissues being classified primarily by the appearance of the internal echoes, whilst the classification of localized pathological processes is based on the appearance of both the internal and the boundary echoes. The diagnosis of diffuse pathological conditions is the most difficult and is based on the change in the normal structural echo pattern.

William J. Garrett

Papers

Fetal umbilical venous flow measured in utero by pulsed Doppler and B-mode ultrasound: I. Normal pregnancies

Umbilical venous flow in normal and complicated pregnancy

Principles and classification of soft tissues by grey scale echography.

The diagnosis of fetal hydronephrosis, megaureter and urethral obstruction by ultrasonic echography.

Placental aging monitored by gray scale echography