Slice thickness measurements.

A new slice thickness test object is discussed, with results of feasibility tests using 13 transducers from six different commercial scanners presented. Both inplane beamwidth and slice thickness measurements could be easily performed and interpreted. For proper equipment gain settings the slice thickness measurement results were found to be independent of receiver gain with a tissue-mimicking (TM) fill in the test object. This is explained by a simple model in which test object low-amplitude internal fill echoes effectively act as an invariant measurement reference level with respect to the slice thickness profile echoes. This model also predicts that in clinical images the inplane lateral resolution (and slice thickness) will be governed by the local image contrast between adjacent tissues as well as the beam profile. Slice thickness measurement results from various types of real-time transducers demonstrate their inherent slice thickness focal characteristics.