The Imaging Performance of Diagnostic Ultrasound Scanners Using the Edinburgh Pipe Phantom to Measure the Resolution Integral - 15 Years of Experience.

The grayscale imaging performance of a total of 368 different scanner/transducer combinations from 39 scanner manufacturers measured over a period of 15 years is presented. Performance was measured using the resolution integral, a single figure-of-merit to quantify ultrasound imaging performance. The resolution integral was measured using the Edinburgh Pipe Phantom. Transducers included single element, linear, phased, curvilinear and multi-row arrays. Our results demonstrate that the resolution integral clearly differentiates between transducers with varying levels of performance. Two further parameters were also derived from the resolution integral: characteristic resolution and depth of field. We demonstrate that these two parameters can successfully characterize individual transducer performance and differentiate between transducers designed for different clinical and preclinical applications. In conclusion, the resolution integral is an effective metric to quantify and monitor grayscale imaging performance in clinical practice.

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.

An ultrasound mini-balance for measurement of therapy level ultrasound.

This paper describes a cost-effective method for measuring acoustic power using a radiation force balance. The device is based around a long established balance design with a gantry arrangement fitted with an absorbing target. The notion of this balance design is that it can easily be constructed from materials that would be readily available within a clinical or industrial environment. The mini-balance was calibrated using a transfer standard against an NPL Reference balance, so a comparison of the performance between the two systems could be assessed. The measurements were completed at 1 MHz and 3 MHz and over the acoustic power range of 1 W to 15 W. The results show the acoustic power measured on the mini-balance to be within 5% of the reference measurements made on the NPL Balance. A separate systematic uncertainty budget is also presented based on studies made on the balance and on similar systems. The overall expanded uncertainty was calculated to be within 14% at 1 W level, decreasing with increasing power level to 7.4% above 5 W.

Quality assurance testing of transoesophageal echocardiography probes.

INTRODUCTION: In response to an ultrasound imaging issue with transoesophageal echocardiography probes, a testing protocol was developed to check features pertinent to the operation of these probes. The imaging problem was detected in multiple probes of the same make and model. METHODS: Over a two-year period, a series of 26 probes of this model were tested at acceptance, then three to six months later before being replaced due to a defect. A range of visual, mechanical and electrical tests were performed. Image tests comprised low-contrast penetration measurements and a comparison of phantom images at regular intervals to highlight artefacts in both B-mode and colour Doppler imaging. RESULTS: Of the 26 defective probes replaced, 7 suffered mechanical/electrical problems, 5 of which prevented imaging results being obtained. Low-contrast penetration reduction of greater than 5% occurred in 14 probes. B-mode artefacts were observed on 12 probes and Doppler noise artefacts on 6 probes. No faults were found on five probes. The manufacturer addressed the imaging problem identified and of the seven subsequent probes supplied, only one suffered an imaging fault. CONCLUSIONS: The implementation of a quality assurance protocol for transoesophageal echocardiography probes resulted in cost savings on replacements/repairs. When provided with the evidence gathered, the manufacturer supplied 23 probes under warranty or as loan equipment. The regular testing of the probes substantially reduced the impact of downtime and poor diagnosis from this equipment on the clinical service.

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.