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Effect of Line Spacing and Ratemeter Averaging on Lesion Detection

The Johns Hopkins University, Applied Physics Laboratory, Silver Spring, Maryland
The Johns Hopkins Medical Institutions, Baltimore, Maryland

Correspondence: For reprints contact: A. G. Schulz, The Johns Hopkins University, Applied Physics Laboratory, 8621 Georgia Ave., Silver Spring, Md. 20910.

ABSTRACT

Spatial integration resulting from proper adjustment of line spacing values appears to aid in the detection of focal lesions in photorecords of rectilinear scanning. Similar improvement possibilities exist with independent ratemeter smoothing. There is good correlation between the gains in detection and in the corresponding integration lengths associated with averaging along and perpendicular to the path of the scan. For the specific lesion sizes in this study detection performance with a line spacing of 0.32 cm is 10–15% better than that at 0.16 cm. Wider line spacing did not give further improvement.

An additional improvement of 10% in detecting small focal lesions is obtained by spatial integration along the path of the scan. The best space constant value is about 0.3 cm. For the size lesions studied, unidirectional scanning provided no change in detectabiity compared to normal bidirectional scanning. Scalloping is not a significant factor for this problem for space constant values up to 0.5 cm.

Where post-scan data processing is not available or in use rectilinear scanning instruments should offer the clinician independent variable time smoothing so that the counting rate may be smoothed before recording without the complex interplay of contrast enhancement that now exists in many of the older designs.