Objective measurements of image quality.

Tissue harmonic imaging (THI) and compound imaging have been reported clinically to improve contrast resolution, tissue differentiation and overall image quality. However, there have been limited studies to date to quantify objectively the improvements in image quality achieved with these new imaging techniques. The aim of this study was to quantify differences in image quality that exist between conventional B-mode imaging, harmonic imaging, compound imaging and harmonic compound imaging. An ATL HDI 5000 scanner with three probes (C5-2, L7-4 and L12-5) was tested with two different types of test object, the Gammex-RMI model 404 GS LE and the Gammex-RMI 403 GS LE. The measurement limitations associated with subjective analysis methods were not present in this study because an automated image analysis program was used to determine the image quality parameters. Therefore, subtle differences between the four imaging modes could be detected. Significant improvements in lateral resolution and slice thickness as a function of depth were found with THI. Contrast resolution and anechoic target detection improved with compound imaging, and harmonic compound imaging improved lateral resolution, slice thickness as a function of depth and contrast resolution.