OBJECTIVE: To determine the relationship between X-ray image quality as reflected by the gray scale range and the reliability of measuring intervertebral angles.

DESIGN: Intrarater reliability evaluation.

SETTING: Image processing laboratory.

PATIENTS: Digitized images of fluoroscopic AP lumbar motion sequences obtained from eight patients.

INTERVENTION: Ten consecutive measurements of a single intervertebral angle in each subject related to gray scale range and midpoint gray level. The results were compared to measurements from an osseous lumbar spine calibration model.

MAIN OUTCOME MEASURES: Variance of intervertebral angles in relation to gray scale range and midpoint level.

RESULTS: No relationship was found between reliability of intervertebral angles and image parameters.

CONCLUSION: For radiographs of diagnostic quality the gray scale range and midpoint level over the area of interest does not affect the reliability of coordinate marking.

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