Michael Halliwell

Ultrasonic Doppler studies of the breast

The growth of a malignant tumour depends on vascularisation. The ultrasonic Doppler method can detect the blood flow associated with malignant breast tumours, the signals differing qualitatively from those due to benign lesions. Several descriptors of the Doppler signals were tested; benign and malignant lesions are best separated by the difference between the maximum systolic frequencies from suspect and contralateral sites. Corresponding main arterial sites are reliably coincident in normal breast pairs. Consideration of the powers and frequency spectra of Doppler signals leads to the rejection of models of tumour vascularisation giving Doppler signals based on capillary perfusion and on a single feed artery. The data are compatible with a multiple feed artery model, and this is supported by a contrast angiogram. Doppler ultrasound may be useful as a preliminary screening method, in the management of patients with radiologically dense breasts or diffuse dysplasia, and for monitoring unexcised tumours undergoing hormone therapy.

Ultimate limits in ultrasonic imaging resolution

According to elementary theory, the resolution of an ultrasonic imaging system increases with the ultrasonic frequency. However, frequency is limited by frequency-dependent attenuation. For imaging at any required depth, resolution improvement beyond the limit imposed by ultrasonic frequency can be obtained by increasing the ultrasonic intensity. This is itself, however, dependent on safety considerations and the effects of nonlinearity. In homogeneous media, image resolution increases with decreasing f-number. Particularly at low f-numbers, however, tissue inhomogeneity leads to a deterioration in image quality. Inhomogeneity may also be considered in terms of phase aberration. It has been found that for a given aperture, image degradation due to phase aberration is worse at higher frequencies. Schemes have been proposed for correction of this problem, but so far model systems do not lend themselves to clinical application. Deconvolution is unsatisfactory, speed correction is impracticable and synthetic aperture scanning and holography are virtually useless in biological tissues. Ultrasound-computed tomography has had only limited success. Speckle reduction can improve target detectability, but at the expense of resolution. Time-frequency control provides a useful partial solution to the problem of resolution reduction resulting from attenuation. It is clear that improved resolution would result in significant clinical benefits. An optimisation system for aperture size and ultrasonic frequency is proposed with signal averaging for resolution enhancement of a defined object area. This would have a compact ultrasonic beam and would allow frame rate to be traded for resolution, by means of signal averaging.

Fusion of 2-D images using their multiscale edges

A new framework for fusion of 2D images based on their multiscale edges is described in this paper. The new method uses the multiscale edge representation of images proposed by Mallat and Hwang (1992). The input images are fused using their multiscale edges only. Two different algorithms for fusing the point representations and the chain representations of the multiscale edges (wavelet transform modulus maxima) are given. The chain representation has been found to provide numerous new alternatives for image fusion, since edge graph fusion techniques can be employed to combine the images. The new framework encompasses different levels, i.e. pixel and feature levels, of image fusion in the wavelet domain.

The differentiation of bile ducts and blood vessels using a pulsed Doppler system

Abstract Anechoic hepatic ducts are readily visualized by grey-scale ultrasound although differentiation of dilated bile ducts from portal veins can remain a problem. The supplementary use of a pulse-Doppler interfaced to a β-scanner as an aid to differentiation is investigated in a series of ten normal subjects and twenty patients presenting with suspected obstructive jaundice. The Doppler diagnoses were found to be in good agreement with the conclusions of more conventional methods such as endoscopic retrograde cholangio-pancreatography and liver biopsy.

Incoherent imaging using continuous wave ultrasound. A preliminary study using bovine intervertebral discs

As an object rotates with respect to a stationary planar ultrasonic beam, the scattering centres within the object return echoes that are Doppler-shifted in frequency by amounts depending on the velocities of the individual scatterers. The backscattered echo amplitude at any particular frequency is the line integral of the scattered radiation at the cross-range corresponding to that frequency. The amplitude as a function of frequency can be interpreted as a tomographic projection. A tomographic reconstruction algorithm can produce an image of the distribution of scattering centres in the insonified object from these projections. This paper describes the development and characterisation of a microscanner to investigate the approach of using continuous wave ultrasound for three-dimensional cross-sectional imaging. The results of preliminary tissue investigation, conducted using bovine coccygeal intervertebral discs, are described. The radial imaging resolution improves as the Doppler frequency resolution improves but the circumferential resolution degrades proportionally. As the number of projections increases, there is a finite increase in image quality. Two- and three-dimensional images of the intervertebral disc reveal an alternate light and dark banding pattern that is characteristic of the laminar structure of the annulus fibrosus.

Continuous wave ultrasonic doppler tomography

In continuous wave ultrasonic Doppler tomography (DT), the ultrasonic beam moves relative to the scanned object to acquire Doppler-shifted frequency spectra which correspond to cross-range projections of the scattering and reflecting structures within the object. The relative motion can be circular or linear. These data are then backprojected to reconstruct the two-dimensional image of the object cross section. By using coherent processing, the spatial resolution of ultrasonic DT is close to an order of magnitude better than that of traditional pulse-echo imaging at the same ultrasound frequency.

Doppler Ultrasonic Imaging

The method of image reconstruction using the backprojection technique employed to create X-ray CT scans has been successfully applied to reconstruct images of targets rotating in a continuous wave ultrasonic beam.

Physiological control of splanchnic blood flow by adrenaline: studies during acute hypoglycaemia in man.

Superior mesenteric artery blood flow (SMABF) increases significantly during and after the hypoglycaemia reaction in healthy humans. To investigate the mechanisms controlling this phenomenon, SMABF and plasma catecholamines were measured in healthy human volunteers. In 10 controls, hypoglycaemia was induced by insulin infusion (2.5 m-units.min-1.kg-1). In six subjects, beta-blockade by propranolol infusion (0.7 microgram.min-1.kg-1) preceded insulin infusion and was continued throughout the study. Following the hypoglycaemia reaction, the glucose nadir was similar in both groups. In controls, increases in SMABF [42.4+/-6.1% (mean+/-S.E.M.); P<0. 001], cardiac output (34.3+/-2.3%; P<0.001) and pulse rate (from 63. 9+/-2.7 to 82.5+/-3.1 beats/min; P<0.001) occurred. Superior mesenteric artery resistance fell by 32.4+/-3.3% (P<0.001). Under beta-blockade, decreases in SMABF (34.8+/-2.9%; P<0.001) and pulse rate (from 59.5+/-0.2 to 51.8+/-2.2 beats/min; P<0.001) occurred. Superior mesenteric artery resistance increased (peak +30.8+/-12.3%; not significant). Subjects showed greater increases in adrenaline (P<0.006) and noradrenaline (P<0.022) concentrations than controls. Mesenteric hyperaemia associated with hypoglycaemia in man appears to be mediated by a beta-adrenergic mechanism that is activated by increased circulating levels of adrenaline.

Large Area Doppler Array for the Rapid Investigation of the Breast

Breast cancer is an unfortunately common affliction especially in the western world where it represents the major cause of death in women between 40 and 45 years of age. The annual death rate is 27 per 100,000 of population and, during their lifetimes, one in 13 of all women will be affected by the disease (Silverberg, 1980). Despite improvements in surgery, radiotherapy and chemotherapy an apparent slight increase in incidence has resulted in the overall mortality remaining constant over the last 50 years. About half of all the individuals presenting with a malignant lump in their breast will die within five years. However, if consideration is given only to those individuals with small lumps (about 1 cm in diameter as opposed to the average presentation size of 3 cm), then treatment can give an over 90 per cent cure rate (Haagensen, 1971). The difference arises because of the occurrence of distant metastases. The likelihood of metastases increases with size so that any technique which results in the earlier detection of breast lumps will lead to an improved overall survival and reduce the personal tragedy that is often caused by this disease.

An Effect of Scatterer Size on Reflex Transmission Imaging

Reflex transmission imaging (RTI) (Green and Arditi, 1985) permits images, which are effectively transmission images of attenuation, to be made with a single transducer. The RTI process is initiated when a brief ultrasonic pulse is launched into the tissue from a well-focused transducer. With reference to Fig. 1, only reflected and scattered waves from a selected zone beyond the focal region are amplified, digitized and integrated. Echoes from outside this zone are ignored. The value of the integral of backscattered signal received at the transducer is strongly dependent on the attenuation at the focus. RTI can be performed with B-scan equipment with a highly focused beam, and affords the capability to generate orthographic transmission images in a selected plane that can be directly correlated with the B-scan on an adjacent display. Its orientation relative to the body is the same as that of a C-scan (constant depth scan). A reflection C-scan can be made simultaneously with RTI, further expanding the potential diagnostic capability. Tissue attenuation is an important factor in ultrasound tissue characterization, and it can in principle be determined by RTI. RTI has been applied at 5 MHz to show structure in the lamb kidney (Green and Arditi, 1985) and 4 MHz to detect renal calculi (Green et al., 1991). It seems that RTI has not been used in medical application at frequencies higher than about 20 MHz (Guittet et al., 2000).