Bristol General Hospital

About: Bristol General Hospital is a healthcare organization based out in Bristol, United Kingdom. It is known for research contribution in the topics: Ultrasonic sensor & Doppler effect. The organization has 246 authors who have published 271 publications receiving 5414 citations.

Sonoporation, drug delivery, and gene therapy

Abstract: Ultrasound is a very effective modality for drug delivery and gene therapy because energy that is non-invasively transmitted through the skin can be focused deeply into the human body in a specific location and employed to release drugs at that site. Ultrasound cavitation, enhanced by injected microbubbles, perturbs cell membrane structures to cause sonoporation and increases the permeability to bioactive materials. Cavitation events also increase the rate of drug transport in general by augmenting the slow diffusion process with convective transport processes. Drugs and genes can be incorporated into microbubbles, which in turn can target a specific disease site using ligands such as the antibody. Drugs can be released ultrasonically from microbubbles that are sufficiently robust to circulate in the blood and retain their cargo of drugs until they enter an insonated volume of tissue. Local drug delivery ensures sufficient drug concentration at the diseased region while limiting toxicity for healthy tissues. Ultrasound-mediated gene delivery has been applied to heart, blood vessel, lung, kidney, muscle, brain, and tumour with enhanced gene transfection efficiency, which depends on the ultrasonic parameters such as acoustic pressure, pulse length, duty cycle, repetition rate, and exposure duration, as well as microbubble properties such as size, gas species, shell material, interfacial tension, and surface rigidity. Microbubble-augmented sonothrombolysis can be enhanced further by using targeting microbubbles.

Ultrasonic Doppler studies of the breast

Abstract: 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.

Absorption and dispersion of ultrasound in biological tissue

Abstract: Absorption of ultrasound is the process of conversion of vibrational energy into heat. In biological soft tissues, the absorption coefficients are roughly proportional to the frequency; typically α = 1 dB cm −1 MHz −1 . The velocities in soft tissues are similar, being about 1,500 msec − . Classical viscosity theory cannot explain this form of absorption. A relaxation process is associated with a range of frequency over which there is dispersion in velocity—from a low value at low frequencies to a high value at high frequencies—and a maximum in the absorption per wavelength. Experimental data, particularly for haemoglobin solutions, indicate that absorption and dispersion in biological materials are due to relaxation processes distributed over a range of frequencies. The dispersion is small, and usually negligible in relation to variations and uncertainties of measurement. The natures of the relaxation processes which are involved have yet to be resolved; possibilities include solvent-solute interactions and disturbances in H-bonding equilibria. Lung has a lower velocity than that of solid tissues, whereas that of bone is higher; both have higher values of absorption.