Catálogo de publicaciones - libros

Any US equipment includes Doppler facilities capable of providing information about moving structures inside the human body. In most cases, the primary interest is in the investigation of blood flow dynamics, since this may be helpful for early diagnosis of cardiovascular diseases. However, there is also an increasing interest in tracking the movements of human tissues, since such movements can give an indirect evaluation of their elastic properties, which are valuable indicators of the possible presence of pathologies. This paper aims at presenting an overview of the different ways in which the Doppler technique has been developed and used in medical ultrasound (US), from early continuous wave (CW) systems to advanced pulsed wave (PW) colour-Doppler equipment. In particular, the most important technical features and clinical applications of CW, single-gate PW, multi-gate PW and flow-imaging systems are reviewed. The main signal processing approaches used for detection of Doppler frequencies are described, including time-domain and frequency-domain (spectral) methods, as well as novel strategies like, e.g., harmonic Doppler mode, which have been recently introduced to exploit the benefits of US contrast agents.

While the use of contrast agents in other imaging modalities (X ray, MRI, PET, …) has been routinely accepted for many years, the development and commercialization of contrast agents designed specifically for ultrasound imaging has occurred only very recently. As in the other imaging modalities, the injection of contrast agents during an ultrasound examination is intended to facilitate the detection and diagnosis of specific pathologies. Contrast agents efficiency is based on the backscattering of ultrasound by microbubbles. These microparticules are intravenously injected in the blood flow. After an introduction and generalities on ultrasound contrast agents (UCA) the microbubble physics in an acoustic field will be developed. Second, physics characteristics of contrast agents will be compared (bubbles with or without shell, gas nature, size distribution). Influence of acoustic pressure on the behaviour of the microparticules (linear, non linear and destruction) will be discussed. Finally, a review of specific imaging adapted to contrast agent properties as harmonic imaging, pulse inversion imaging will be presented.

This paper describes the image formation in medical ultrasound for the case of scattering media. The texture statistics are dominated by speckle formation which results from random interference of backscattered echoes. The effects of spatial, fixed and adaptive, filtering, as well as, of grey scale encoding on the detection of lesions are analytically described and illustrated with representative images.

This paper describes the methods applied in a software package developed by the authors for use in a performance testing protocol for medical ultrasound equipment. The history of performance testing of medical ultrasound equipment is briefly reviewed. This paper is confined to the testing of performance of usage aspects, i.e. imaging performance and Doppler velocity estimation performance. Simple test objects are used which have a long life expectancy. The tests performed both in fundamental and in (tissue) harmonic modes when applicable are spatial resolution, contrast sensitivity, and clutter. The concept of a computational observer is used to define the lesion signal to-noise ratio and the tissue-to-clutter ratio. Further imaging performance features are penetration depth, slice thickness and geometric conformity of display. Pulsed Doppler velocity measurement features tested are: sensitivity, depth and 3D size of the sample volume, velocity measurement, channel separation. The whole performance measurement protocol as well as the quantitative measurements in the digitized images are implemented in software, together with the graphs and data obtained from the measurements.

Elastography is a new ultrasound-based imaging technique that provides images (called elastograms) of internal strain in soft tissues under a static compression. The strain is related to the stiffness of the tissues, which is in turn related to the pathological state of tissues. For example, it has been known for long that breast and prostate cancer are stiffer than normal tissues, and palpation is a standard medical practice.

This paper begins with an overview and a description of the interactions between ultrasound and biological tissues encountered during treatment protocols. In a second part of this seminar, two clinical applications of therapeutic ultrasound will be described in details: -Kidney stone destruction by ultrasound (lithotripsy) and High Intensity Focused Ultrasound for treating prostate cancer (HIFU).

The post-processing of 2D or 3D ultrasound data is a very attractive research field to envisage an automatic analysis and/or quantitative measurements. For example, quantitative volume parameters recovery is a unique mean of making objective reproducible and operator independent diagnosis. Thus, it is important to perform a successful segmentation. Among the large variety of post processing devoted to ultrasound data, different segmentation approaches are discussed here and illustrated by some examples.

IVUS is used for diagnostics, therapy guidance and scientific purposes. It is the only clinical available technique that can assess plaque burden and free lumen diameter at high accuracy. Contrast angiography, which was the golden standard before IVUS, can only give a shadow projection of the lumen. Especially with the advent of 3D IVUS using pull backs it became an important tool for monitoring treatment and follow up of interventions like balloon angioplasty and placing of stents (wire prostheses that are used to prevent the arterial wall from recoiling). 3D IVUS in combination with biplane angiography allows assessment of true 3D reconstructions of arteries, pre and post treatment. Using computational fluid dynamics the velocity profile and thus the shear stress at the vascular wall can be calculated. This can be related to biological markers, which gives insight in formation of atherosclerosis, restenosis and remodelling.

In Cardiology the first use on ultrasound was described in 1953 by Inge Edler and Helmuth Herz in Lund, Sweden. They used the M-mode technique which is, in brief, the registration of moving echoes as recorded in a single ultrasound beam. Two dimensional (2D) real time echography appeared in the late sixties with mechanically and electronically swept spoundbeams. The linear- and phased array approaches are examples of electronic real time systems which today represent the majority of apparatus. Use of frequency analyses of the echoes allowed indication of blood velocity over the 2D image. This is called Colour Doppler where a colour coding separates velocity towards the transducer from blood velocity away from the transducer. This is very powerful since now 2D geometry becomes available together with the blood flow information. Echo contrast is an old technique to enhance the echo image at the location of the contrast fluid. This fluid contains small gas containing bubbles. Present use aims at better identification of cardiac chambers contours as well as myocardial perfusion. Semi invasive is the Trans Oesophageal Isographic (TEE) approach. Here a transducer is mounted at the tip of a long tube. It allows contact with the heart with improved image quality. The IntraVascular Ultrasound System (IVUS) uses echography at the tip of a catheter. Following this, techniques for real time 3D will be presented and a brief description of portable echo equipment is given.

In this paper the different techniques of radionuclide application in medicine will be outlined in some details. The corresponding chemical requirements such as radionuclide purity, pharmaceutical requirements, carrier influence and others will be underlined. An overview will be given on the different production modes of radionuclides based on reactors, small or medium cyclotrons, high-energy particle accelerators and short outlook on future aspects of medical isotope application will be given.