DETECT - Dual energy transmission estimation CT - for improved attenuation correction in SPECT and PET

Accurate attenuation correction is a vital component of any quantitative Emission CT (ECT) study, especially I-131-mIBG SPECT where accurate activity concentration measurements are required for dosimetry calculations. Conventional CT is often used to obtain an attenuation map, which is then scaled to the I-131 emission energy (364, KeV). Scaling inaccuracies due to the increased photoelectric component of the attenuation coefficients of bone af: CT energies lead to an overestimate of activity. Dual Energy CT is more accurate but must be justified against increased cost, scan time and dose to the patient. We propose a method (DETECT) of obtaining two attenuation maps from a single CT scan using a conventional CT scanner operating at 120 and 140 kVp for alternate slices. Each map's missing slices are reconstructed using weighted linear interpolation. The effect of the x-ray beam spectrum has been investigated by simulated scaling using the CT spectra and by a phantom study. Assuming a perfect emission detector, segmented abdominal CT data predicts a mean activity overestimate of 2+/-3% for DETECT compared to 12+/-5% for the standard single energy (120 kVp) CT method when scaled to 364 keV, suggesting that DETECT can offer reliable attenuation correction with no dose or user penalty.