Comparison of Standard-Dose vs Low-Dose Attenuation Correction CT on Image Quality and Positron Emission Tomographic Attenuation Correction

Objective

To determine if low-dose attenuation correction computed tomography (CTAC) 1) provides images with acceptable anatomic definition and noise compared with standard-dose CTAC and 2) provides acceptable positron emission tomographic attenuation correction.

Methods

Positron emission tomography/computed tomography was performed on 78 patients. Forty-three patients underwent CTAC with tube current based on a standard weight-based scale. A second group of 35 patients underwent CTAC with tube current based on a low-dose weight-based scale. In a blinded review, two radiologists rated each examination for anatomic definition and image noise at 4 major anatomic levels using a 5-point scale. To evaluate for correct positron emission tomographic attenuation correction at the standard and reduced radiation doses on CTAC, water phantom studies using both imaging techniques were performed and compared.

Results

Patients who underwent low-dose CTAC received a mean 60.6% reduction in radiation dose compared with those who underwent standard-dose CTAC (P < .0001). Low-dose CTAC demonstrated statistically significant poorer ratings for anatomic detail and noise at each of the 4 anatomic levels (P < .0001) compared with standard-dose CTAC. Scans were graded acceptable for diagnostic interpretation if scores for image noise and anatomic definition were greater than 3 at all anatomic levels. There was a significant difference between the number of acceptable diagnostic scans in the standard-dose group (88.4%) compared with the low-dose group (17.1%) (P < .0001). There was no statistical difference in attenuation correction values in low-dose and standard-dose attenuation correction maps of the water phantom.

Conclusion

Low-dose CTAC significantly reduced the effective dose while providing optimal positron emission tomographic attenuation correction. However, because of decreased image quality, low-dose CTAC was not acceptable for diagnostic interpretation.

Key Words: PET/CT, radiation dose, attenuation correction CT