Method to minimize dose for CT attenuation correction in SPECT

With the recent introduction of hybrid SPECT/CT systems, with diagnostic multi-slice CT (Computed Tomography) capabilities the CT dose delivered to the patient may become an issue, as attenuation compensation in SPECT using co-registered CT data becomes more common in clinical practice. In general, any CT data can be converted to a volume of linear attenuation coefficients (LAC), also referred to as the "attenuation map", or mu-map. We investigated the range of CT settings that minimize the dose to the patient and allow for CT image quality that is appropriate for attenuation correction. SPECT/CT registration issues are outside the scope of this work, and we assume that the objects are perfectly registered. Various phantoms are used to analyze both CT and attenuation-corrected SPECT image quality, where the CT data itself is used to generate the mu-maps. Conclusion: The effective dose to the patient from a CT scan for the purpose of SPECT AC can be lowered to at least 30% to 50% without affecting the image quality of the SPECT AC, using CT derived mu-maps, if an appropriate scan protocol with a very smooth (MTF at 50%: 1.0 Ip/cm) CT reconstruction kernel is used. A further clinical investigation is needed to confirm these findings in clinical practice