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 ¹³¹I-mIBG SPECT where accurate activity measurements are required for dosimetry calculations. Conventional CT is often used to obtain an attenuation map, which is then scaled to the ¹³¹I emission energy (364 keV). Scaling inaccuracies due to the increased photoelectric component of the attenuation coefficients of bone at 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