Background:
Positron emission tomography (pet) attenuation correction (ac) using computed tomography (ct) can be affected by respiratory motion: hi-speed ct captures 1 point of the respiratory cycle while pet emission data averages many cycles. we quantified the changes in apparent myocardial uptake due to this respiratory-induced ct attenuation mismatch.
Methods:
Twenty-two patients undergoing fluorine-18 fluorodeoxyglucose (fdg) pet/ct received 3 sequential ct scans at normal resting end-inspiration (ct(inspir)), ending expiration (ct(expir)), and at midvolume between end-expiration and end-inspiration (ct(midvol)). a pneumotachometer measured absolute changes in lung volume. seven subjects also underwent a 3-minute transmission scan with a 68ge rotating rod source (rrs). the pet emission data set was reconstructed up to 4 times using ct(expir), ct(inspir), ct(midvol), and rrs ac maps. relative heart position and cardiac uptake was measured for each ct attenuation correction.
Results:
Respiratory motion produced marked changes in global and regional myocardial uptake. changes were large in the lateral and anterior regions at the lung-soft tissue interface (up to 30% using ct(inspir) compared to ct(expir) for ac) and smaller in the septal region (10% or less). data corrected with ct(expir) agreed best with the rrs.
Conclusion:
Respiratory effects can introduce large inhomogeneities in apparent myocardial uptake when ct is used for attenuation correction.