Transducers in medical ultrasound: Part Three. Transducer applications in echocardiology

A comparison is made between phased arrays and mechanical sector scanners in transcutaneous echocardiographic applications. Aspects such as contact area, beam control, side lobes, grating lobes and image quality are discussed in the context of transducer frequency. The incorporation of simultaneous acquisition of Doppler velocity information and display of M-mode signals is considered. Transoesophageal and intraoperative scanning systems for cardiology are also compared, in particular linear arrays, phased arrays and mechanical scanners, and their advantages and disadvantages in relation to the above mentioned aspects are discussed. The general conclusion is that electronic sector scanners may have a considerably improved cost/benefit ratio in the near future and thereby will become the leading systems for echocardiography.     

Transducers in medical ultrasound: Part Two. Vibration modes, matching layers and grating lobes

The performance of transducers used for medical diagnosis depends to a great extent on matching layer, backing impedance and geometry of the active surface. In this paper special attention is given to the element vibrational modes, the optimum matching, the grating lobe and change of the real acoustic impedance into an imaginary impedance as a function of the product of the width and wavelength. Grating lobes on the echo image and the effect of a mismatch of the matching layer are illustrated. Suggestions are made for the design of linear and phased array transducers considering the above-mentioned aspects.     

An investigation of a spread energy method for medical ultrasound systems. Part one: theory and investigation.

A medical ultrasound device using a Golay code is proposed and investigated theoretically. The code enables the spread energy method to be used to help overcome the restraints of the parameters of resolution, peak power and penetration.     

Radiation technology in medicine: Part 1. medical accelerators

Ionizing radiation is widely used in medicine today. Sources of ionizing radiation include X-ray tubes, natural and artificial isotopes, and accelerators [1, 2]. This review describes the role of accelerator technology and nuclear physics methods in cancer treatment. It presents an analysis of the data that have been published in scientific articles and reports, materials of the IAEA, and other places over the course of the past 5 decades.     

An investigation of a spread energy method for medical ultrasound systems. Part two: proposed system and possible problems.

A medical ultrasound device using a Golay code is proposed and investigated theoretically. The code enables the spread energy method to be used to help overcome the restraints of the parameters of resolution, peak power and penetration.     

Performance testing of medical ultrasound equipment: fundamental vs. harmonic mode

Assessment of the performance of medical ultrasound equipment is generally based on the image quality in fundamental mode. Recent development of the so-called tissue harmonic imaging (THI) mode induces the need for assessment of differences in the quality of imaging in THI vs. fundamental imaging mode. Quality features to be tested are sensitivity (penetration depth), spatial resolution, contrast resolution, lesion signal-to-noise ratio, and tissue-to-clutter ratio (TCR). These features are explained and examples are shown. The main conclusion from a comparison of the results for the two imaging modes might be that when using THI improvement of TCR, in particular in the near field, is obtained at the expense of a loss in axial resolution. Furthermore, lesion detection is not significantly improved.