Peripheral Vascular Ultrasound - part 1 pot

[...]... Speed of ultrasound 6 Generation of ultrasound waves 7 Pulsed ultrasound 7 Frequency content of pulses 8 Beam shape 9 Interaction of ultrasound with surfaces 9 Loss of ultrasound energy in tissue 11 Producing an ultrasound image 12 Amplification of received ultrasound echoes 13 Dynamic range, compression curves and gray-scale maps 14 Transducer designs and beam forming 15 Focusing the beam 18 Image... periodic displacement of these particles (Fig 2.1B) The size, or amplitude, 6 PERIPHERAL VASCULAR ULTRASOUND Transducer off Table 2 .1 Speed of sound in different tissues Medium Air Water (20° C) Fat Blood Muscle Bone Soft tissue (average) A Transducer on B Displacement of particles Depth λ C 330 14 80 14 50 15 70 15 80 3500 15 40 taken for the wave to move forwards through the medium by one wavelength is... whereas ultrasound is scattered by rough surfaces (B) and small structures (C) Attenuation coefficient at 1 MHz (dB cm 1) Water (20° C) Fat Blood Muscle Bone Soft tissue (average) 0.2 60 20 15 0 10 00 70 11 PERIPHERAL VASCULAR ULTRASOUND Aortic valve leaflets Chest wall Chest wall Right ventricle Septum Depth 12 Anterior mitral valve leaflet Posterior mitral valve leaflet Pericardium Time Aorta Anterior mitral... bone (Fig 10 .12 ) and bowel gas, leading to an acoustic shadow beyond Table 2.2 shows the ratio of the reflected to incident wave amplitude for a range of reflecting interfaces 9 10 PERIPHERAL VASCULAR ULTRASOUND The path along which the reflected ultrasound travels will also affect the amplitude of the signal detected by the transducer If the beam is perpendicular to the interface, the reflected ultrasound. .. during 1 second (s) and is given by: f ϭ ϩ Excess pressure Speed of sound (m/s) Depth Ϫ D Figure 2 .1 A: A medium consisting of evenly distributed particles B: The positions of the particles change (shown here at a given point in time) as the ultrasound wave passes through the medium C: The amplitude of the particle displacement D: Excess pressure of these displacements is shown in Figure 2.1C As the particles...2 PERIPHERAL VASCULAR ULTRASOUND therapeutic procedures, such as angioplasty, rather than diagnostic angiograms Vascular ultrasound examinations rely on the use of ultrasound to produce a black and white anatomical image that can demonstrate the presence of disease along an arterial wall or the presence of thrombus in a vein Doppler ultrasound can provide a functional... has moved Ultrasound is a longitudinal wave, as the displacement of the particles within the medium is in the same direction as that in which the wave is travelling Figure 2 .1 shows a medium with particles distributed evenly within it The position of the particles within the medium will change as a sound wave passes through it, causing local periodic displacement of these particles (Fig 2.1B) The size,... understanding of the role of vascular ultrasound in relation to these other techniques for investigating vascular disorders In addition, it is important to know about the different radiological and surgical techniques used to treat peripheral vascular disease 3 This page intentionally left blank 5 Chapter 2 Ultrasound and imaging INTRODUCTION CHAPTER CONTENTS Introduction 5 Nature of ultrasound 5 Wavelength... neighbor’s hi-fi bass through the partition wall better than the treble PRODUCING AN ULTRASOUND IMAGE Ultrasound imaging uses information contained in reflected and scattered signals received by the transducer If it is assumed that the speed of the ultrasound through the tissue is constant, it is possible to predict the distance from a reflective boundary or scattering particle to the transducer When an ultrasound. .. transmit a larger amplitude ultrasound pulse, thus increasing the amplitude of reflections However, increasing the output power causes the patient to be exposed to more ultrasound energy The alternative is to amplify the received signal, but there is a limit at which the amplitude of the received signal is no greater than the background noise, and at which 13 14 PERIPHERAL VASCULAR ULTRASOUND A Amplitude . disease 11 1 10 . Duplex assessment of upper extremity arterial disease 13 3 11 . Duplex assessment of aneurysms 14 5 12 . Anatomy of the lower limb venous system and assessment of venous insufficiency 16 3 13 image 12 Amplification of received ultrasound echoes 13 Dynamic range, compression curves and gray-scale maps 14 Transducer designs and beam forming 15 Focusing the beam 18 Image resolution 19 Tissue. Wendy, Tony and June Prelims.qxd 1~ 9~04 17 : 01 Page ii Peripheral Vascular Ultrasound HOW, WHY AND WHEN SECOND EDITION Abigail Thrush MSc Medical Physicist, Department of Clinical Physics, St