Effective methods to correct contrast agent-induced errors in PET quantification in cardiac PET/CT.
In combined PET/CT studies, x-ray attenuation information from the CT scan is generally used for PET attenuation correction. Iodine-containing contrast agents may induce artifacts in the CT-generated attenuation map and lead to an erroneous radioactivity distribution on the corrected PET images. This study evaluated 2 methods of thresholding the CT data to correct these contrast agent-related artifacts.


METHODS
PET emission and attenuation data (acquired with and without a contrast agent) were simulated using a cardiac torso software phantom and were obtained from patients. Seven patients with known coronary artery disease underwent 2 electrocardiography-gated CT scans of the heart, the first without a contrast agent and the second with intravenous injection of an iodine-containing contrast agent. A 20-min PET scan (single bed position) covering the same axial range as the CT scans was then obtained 1 h after intravenous injection of (18)F-FDG. For both the simulated data and the patient data, the unenhanced and contrast-enhanced attenuation datasets were used for attenuation correction of the PET data. Additionally, 2 threshold methods (one requiring user interaction) aimed at compensating for the effect of the contrast agent were applied to the contrast-enhanced attenuation data before PET attenuation correction. All PET images were compared by quantitative analysis.


RESULTS
Regional radioactivity values in the heart were overestimated when the contrast-enhanced data were used for attenuation correction. For patients, the mean decrease in the left ventricular wall was 23%. Use of either of the proposed compensation methods reduced the quantification error to less than 5%. The required time for postprocessing was minimal for the user-independent method.


CONCLUSIONS
The use of contrast-enhanced CT images for attenuation correction in cardiac PET/CT significantly impairs PET quantification of tracer uptake. The proposed CT correction methods markedly reduced these artifacts; additionally, the user-independent method was time-efficient.
Büther
Florian
F
Department of Nuclear Medicine, University of Münster, Münster, Germany. butherf@uni-muenster.de
Stegger
Lars
L
Dawood
Mohammad
M
Range
Felix
F
Schäfers
Michael
M
Fischbach
Roman
R
Wichter
Thomas
T
Schober
Otmar
O
Schäfers
Klaus P
KP
D016477:Artifacts; D003287:Contrast Media; D003324:Coronary Artery Disease / Q000000981:diagnostic imaging*; D019788:Fluorodeoxyglucose F18; D006321:Heart / Q000000981:diagnostic imaging*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D007472:Iohexol / Q000031:analogs & derivatives; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000379:methods; D019275:Radiopharmaceuticals; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods
D003287:Contrast Media; D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18; D007472:Iohexol; C038192:iopromide