Vikram Krishnasetty MD, Presenter: Nothing to Disclose

Ali A. Bonab PhD, Abstract Co-Author: Nothing to Disclose

Alan Fischman, Abstract Co-Author: Nothing to Disclose

Elkan F. Halpern PhD, Abstract Co-Author: Nothing to Disclose

Suzanne L. Aquino MD, Abstract Co-Author: Nothing to Disclose

To determine if low dose attenuation correction CT (CTAC) (1)provides images with acceptable anatomic definition and noise as compared with standard dose CTAC; and (2)provides proper PET attenuation correction.

Combined PET-CT exams were performed on 78 patients. The first group of 43 patients received a CTAC with tube current based on a standard weight based scale. The second group of 35 patients received a CTAC with tube current based on a maximally reduced radiation dose weight based scale. In a blinded review, two radiologists rated the randomized CTAC for anatomic definition and image noise in major anatomic landmarks of the thoracic inlet, mediastinum, abdomen, and pelvis using a 5 point scale (1, unacceptable; 2, substandard; 3, acceptable; 4, above average; 5, superior). To evaluate for proper PET attenuation correction at the standard and reduced radiation dose CTAC levels, studies were performed on a water phantom using both imaging techniques. The attenuation correction maps were then compared. Statistical analysis of the data using Wilcoxen (Rank Sums) and Chi-squared tests were performed.

Low dose CTAC demonstrated a mean 60.6% reduction in the dose-length product as compared to standard dose CTAC (p<0.0001). As compared to low dose CTAC images, standard dose CTAC demonstrated better anatomic detail and noise in each of the four anatomic levels (p<0.0001). Scans were deemed acceptable for diagnostic interpretation if all scores for image noise and anatomic definition were ≥ 3. 88.4% of the standard dose CTAC and 17.1% of low dose CTAC were classified as acceptable. There was a statistical difference between the number of acceptable scans in the high dose group versus the low dose group(p<0.0001). There was no statistical difference of attenuation correction values in low dose and high dose attenuation correction maps of a water phantom.

1)Low dose CTAC are adequate for PET attenuation correction. 2)Low dose CTAC alone are not acceptable for diagnostic purposes.

Low dose CTAC as part of a PET/CT exam is not suitable for diagnostic interpretation but can reduce total radiation dose when performed in conjunction with a full dose diagnostic CT.

Krishnasetty, V, Bonab, A, Fischman, A, Halpern, E, Aquino, S, Comparison of Standard Dose versus Low Dose Attenuation Correction CT on Image Quality and PET Attenuation Correction.  Radiological Society of North America 2006 Scientific Assembly and Annual Meeting, November 26 - December 1, 2006 ,Chicago IL. http://archive.rsna.org/2006/4436381.html