Evaluation of Intravascular Ultrasound Catheter-Based Transducers Using the Resolution Integral.

Intravascular ultrasound (IVUS) catheters are a specialist imaging modality used in the assessment of cardiovascular disease. The ultrasound transducer may either be of single-element mechanical or phased-array design. Because of their design and operating frequencies (10-45 MHz), evaluation of the imaging performance is not possible with commercially available ultrasound test objects. An existing test object, the Edinburgh Pipe Phantom, was modified to allow measurement of resolution integral (R), depth of field (Lr) and characteristic resolution (Dr) of IVUS catheters. In total, seven IVUS catheters, from two manufacturers and of both single-element mechanical and phased-array design, were tested to provide a measure of performance over different frequencies and technologies. Measurements of R for the tested IVUS catheters ranged from 11.9 to 18.8. The modified Edinburgh Pipe Phantom therefore allows catheter-based ultrasound probes to be evaluated scientifically and their performance to be seen in relation to other similar ultrasound technologies such as pre-clinical ultrasound and endoscopic ultrasound.

The effect of back reflections on the acoustic power delivered by physiotherapy ultrasound machines.

Physiotherapy ultrasound is used widely for the treatment of soft tissue injuries. The ultrasonic treatment heads are all highly resonant devices and may therefore be sensitive to the levels of acoustic back reflection that they experience. However, the extent to which reflections affect acoustic power during clinical use has not been reported in the literature and is not addressed in current technical standards. This study investigated the effect of physiological levels of acoustic reflection on 29 physiotherapy treatment heads from a total of 21 machines and 6 manufacturers. A range of membranes were constructed and used to mimic the levels of acoustic reflections that occur during treatment. The results obtained showed that almost half of the heads tested (45%) had deviations in acoustic power of more than 15% compared with free-field measurements. Four heads (17%) had deviations in power of more than 25%. We recommend that the susceptibility of physiotherapy ultrasound machines to acoustic reflections be addressed in the relevant technical standards. Also, it is appropriate for tests to be carried out during design and manufacture, and by the purchaser during their acceptance testing.