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Joyce Joy, Prof Sandy Cochran Institute of Medical Science & Technology Dundee Dynamic Characterisation of 2D/3D/4D Medical Ultrasound Imaging The limitations of quality assurance of ultrasound imaging systems are well recognized [1]. Novel phantoms have been developed to aid repeatability and to quantify different parameters. One such phantom is the Edinburgh pipe phantom [2]. This phantom permits the calculation of a single figure of merit; the “resolution integral” (RI). This has been shown to be consistent, reliable and correlated with clinical perception. However it fails to provide completely non-subjective results as it still requires manual scanning and judgment of targets; in addition, this is again time consuming. The work reported here is an approach to automate testing for ultrasound devices. The project was initiated with first preliminary prototypes built and tests carried out on them by Blair et al [3]. A new improved design and a working prototype has been developed, as reported here to overcome the drawbacks and to automate the process based on the resolution integral which can produce non-subjective and repeatable results for each combination of imaging system and transducer array. The dynamic phantom makes use of a pair of 0.3 mm diameter nylon targets in a test tank which is filled with fluid (Fig 1). The ultrasonic probe under test is mounted in a fixture that holds it. The transducer is just dipped into the fluid so as to image the pair of targets whose range and separation can be independently controlled via motors. The motion from the motors is coupled to the targets using magnets. The image from the scanner under test is acquired and analysed by the controlling software to calculate RI. The analysis flowchart is shown in Fig. 3. No manual intervention is required once the phantom is set and launched. Furthermore, there is no subjectivity in the measurement, as it is entirely automated. However, there was lag in the internal magnets following the outer magnets. To overcome this, the design was then modified by replacing the magnets with arms holding the targets (Fig 2). This new design has still to be tested. There are different approaches to validate the image quality of ultrasound systems. These tests are carried out manually and are very time consuming. The other main drawbacks are subjectivity and poor repeatability of the results. This is of concern as ultrasound imaging systems are increasingly used in a variety of specialties for diagnosis and treatment management and users may be less expert than in the past. Care has to be taken to ensure that machines are operating to specification as a sub-optimal scanner could lead to missed pathologies or misdiagnoses. A total of 21 ultrasound imaging systems in clinical use for different applications in Ninewells Hospital, NHS Tayside, UK, were tested with different imaging system - transducer array combinations. Each system was tested many times to make sure that the resolution integral values are the same for all the same system- transducer combination. With the names of these systems and their host departments anonymized, the systems have been classified to indicate their expected performance range based on three parameters, the age of the system, the frequency range of the transducers tested and the price range. The tests were carried out at three different depth settings indicated as low (5 – 30 mm), medium (10 – 70 mm) and high (50 – 120 mm). Low Medium High DEPTH The modified dynamic phantom will be used to analysis the clinical ultrasound systems in the near future. We also intend to make some changes in the set up my moving the electronics to the sides and attaching a probe holder. [1] Boyden, Julie, “Is Quality Assurance of ultrasound equipment necessary? - the benefits and objections” in: BMUS Bulletin, Vol. 11, No. 1,pp. 30-32, 2003 [2] E.L. Madsen and L. Ernest , “Quality Assurance for Grey-Scale Imaging” Ultrasound in Medicine & Biology, Vol. 26, Supplement 1, pp S48 – S50, 2000 [3] M.Blair, S.Cochran, G.A.Corner and D.MacLennan “A Novel Dynamic Ultrasound Test Object using Feedback to Automate Quality Assurance” UK IPEM “Quality Assurance of Ultrasound Scanners”, York, 2006 INTRODUCTION PROBLEM Prof George Corner Medical Physics NHS Tayside David Lines Diagnostic Sonar Ltd Livingston, Edinburgh METHODOLOGY Ultrasound Transducer Magnets to move the targets Control board& Power circuit Stepper motors Fig1. Dynamic phantom-initial design Fig 2. Dynamic phantom with arms holding the targets- Arms holding the targets Initialize Start Move vertically Move horizontally Grab image Start iterations Image processing Resolved Move back one step Save Image Return Target position NO YES ANALYSIS OF CLINICAL ULTRASOUND SYSTEMS Fig 4 a) Depth vs. RI plot for 5 different transducers b) RI’s of different ultrasound systems tested Fig 3 a) Flowchart for the dynamic phantom analysis b) Top- Print screen version of the lab view program showing resolved targets, Bottom- unresolved targets. REFERENCES I would like to express my sincere gratitude to Florian Riedel and Alexander Valente for their immense effort in making the first model of the dynamic phantom. ACKNOWLEDGEMENT FUTURE WORK Resolution Integral
