Objective:To investigate the influence of the type and extentofhead motion on subtraction image quality of 64-slice volume CT digital subtraction angiography(VCTDSA). Methods:Forty-four consecutive patients(18 male

26 female;mean age

(52.6±17.6) years)underwent VCTDSA for the evaluation of cerebral vascular disorders. We performed the scanning with two different registration methods:test bolus injection without head fixation and registration with rigid head fixation. Imaging data of two different scan modes were then analyzed. The type and extent of head motion between two scan modes as well as the manifestation

degree of artifacts after subtraction were evaluated. Results:There were three forms of head motion during test bolus scan:intra-lamina(r77.3%)

inter-lamina(r4.5%)and mixed motion (18.2%). High density motion artifacts of subtraction images were observed near the border of the anatomic structures. Motion artifacts were obviously reduced by head fixation. With head fixation approach

the subtraction angiograms without motion artifact increased from 13.6% to 59.1%

and images with moderately to severe artifacts reduced from 47.1% to 11.4%. Conclusion:There were three forms of head motion without head fixation

and different form motion artifacts were observed after subtraction. Head fixation prevents motion artifacts and greatly improves subtraction image quality.