title: Recognising small image quality differences for ultrasound probes and the potential of misdiagnosis due to undetected side lobes.
abstract: BACKGROUND
  Ultrasonic imaging is an integral and routine procedure in many medical applications. An increased awareness of the need for quality assurance in this field has led to numerous tests being proposed. Due to the complexity of the problem, the tests directly measuring the important parameters of resolution and contrast of low-echoic structures are not unified, often more qualitative than quantitative, and are performed at large periodic intervals. Uniform sensitivity of an array transducer is a necessary but insufficient requirement for imaging quality of an ultrasound probe. Good probe uniformity should in no way be confused with meaning the ultrasound probe is working as it should.
  
  
  METHODS
  In this paper, side lobes in the elevation direction and side and grating lobes in the lateral direction are discussed. Both may provide uniform element response across the scanner, yet result in a loss of resolution and contrast. To resolve problems of these resolution and contrast-relevant parameters being overlooked, a crossed filament phantom is introduced.
  
  
  RESULTS
  The cross-filament phantom provides the determination of resolution- and contrast-relevant parameters of a scanner, by directly measuring the main, side and grating-lobes of the beam in 3D. The main lobe 3D-data allows the determination of lateral and elevational resolution at different depths and thus the focal settings. In combination with the side and grating lobe information, the contrast for a small non-echoic object (i.e. a cyst) in an echoic environment may be explained.
  
  
  CONCLUSIONS
  We argue that regarding system acceptance, system baseline quality assurance and routine quality assurance, the analysis of the beam shape should be part of the comprehensive assessment. Combining the results with void resolution and contrast measurements is recommended.
authors.affiliation: Institute of Applied Physics, Vienna University of Technology, Austria.
authors.forename: Georg
authors.initials: G
authors.lastname: Doblhoff
authors.affiliation: Tissue Characterization Consulting, Timelkam, Austria.
authors.forename: Jaroslav
authors.initials: J
authors.lastname: Satrapa
authors.affiliation: Northern Physics Services, Hexham, Northumberland, UK.
authors.forename: Philip
authors.initials: P
authors.lastname: Coulthard
keywords: Ultrasound image quality; beam shape; contrast; filament phantom; grating lobes; resolution; side lobes; uniformity; void phantom