Phantoms for Diagnostic Ultrasound Equipment
Edinburgh Pipe Phantom
Developed by the NHS Lothian Medical Physics Department, and demonstrated at the "York" ultrasound meeting this phantom gives medical physicists a method of monitoring the performance of a diagnostic ultrasound scanner over time or comparing the performance of one diagnostic ultrasound scanner against another
The Edinburgh Pipe Phantom is a measurement tool that allows ultrasound greyscale performance to be characterised for a particular ultrasound scanner / transducer combination, and with imaging techniques such as harmonic imaging, speckle reduction and compound imaging. The phantom consists of a series of fluid-filled cylindrical voids (pipes) embedded in a tissue-mimicking material (TMM) which is contained in a rigid enclosure. The pipes are parallel and inclined at an angle of 50 degrees relative to the base of the phantom.
Quantities known as the Resolution Integral, Depth of Field and Characteristic Resolution are used to characterise transducer performance. The Resolution Integral is essentially the ratio of penetration to lateral & elevation resolution, measured from the surface of the phantom through the full depth range of the image. Depth of Field defines a region of optimum resolution, and Characteristic Resolution is representative of the lateral & elevation resolution within the Depth of Field. The three quantities are related by the expression Resolution Integral = Depth of Field / Characteristic Resolution. Measurements are carried out by assessing the minimum and maximum depths at which each pipe can be visualised. The number of visible pipes will depend on ultrasonic frequency and the properties of the scanner / transducer combination.
Further details of the analysis method can be found in the following publications:
· The Resolution Integral: visual and computational approaches to characterizing ultrasound images” PMB, Vol 55, 5067-5088.
· Moran C M, Smart S, Ellis W, Pye S D. Characterising the performance of a high resolution ultrasound scanner for pre-clinical ultrasound imaging. Proc 2008 IEEE Ultrasonics Symposium pp1724-1727
· Pye S D, Ellis W, MacGillivray T. Medical ultrasound: a new metric of performance for grey-scale imaging. Journal of Physics: Conf Series 1; 2004, 187-192
· Enclosure: constructed of Perspex (plexiglass) with a 10mm thickness of Precision Acoustics F28 Acoustic Absorber at the base
· Number of pipes: 12 in total – 2x0.42mm, 2x0.56mm, 1 of all other sizes
· Pipe diameters (mm): 0.42, 0.56, 0.72, 1.0, 1.5, 2.0, 3.0, 4.0, 6.0, 7.9
· Acoustic properties of the IEC TMM used in the phantom are described in Ramnarine et al. Construction and geometric stability of physiological wall-less stenosis phantoms. Ultrasound Med Biol; 2001, 27 245-250
The phantom consists of a series of "pipes" which when scanned can be resolved. The results are analysed using an algorithm to minimise subjectivity in the results.
For a PDF file with more details on the analysis contact David Bell, at firstname.lastname@example.org