SPECT/CT: Increase your diagnostic potential

Objectives Demonstrate improvement of SPECT/CT with minor changes to factory settings. Compare image quality of SPECT/CT,1mm and 5mm aquisitions, with Diagnostic CT. Present exposure values for SPECT/CT.

Methods We examined the factory settings for our 16 slice SPECT/CT and its image fusion software. Initially data was aquired with 1.2mm CT dector and reconstructed at 5mm. These settings where adjusted to 0.6mm and 1mm. Recon increment was lowered to 0.7mm. With thin slice aqcuisition ref. mAs was increased to 25 from 15. No changes in Kev were made(Siemens exposure control calbrated at 130 Kev). Image fusion software was reprogrammed to slice match 1mm CT with NM reconstruction. The study group was filtered for both SPECT/CT and Diagnostic CT with similar CT volumes(Chest, Spinal etc). SPECT/CT 1mm quality and exposure were compared to both the 5mm technique and Diagnostic CT at our facility.

Results Radiologists were extremely pleased with the improvement of image quality. The 1mm SPECT/CT techinque provided greater detail and resolution. Step artefact was removed from sagittal and cornonal reconstructions. For the study group 1mm technique increased expsoures 40% on average from the 5mm factory default. Exposure values for SPECT/CT compared to Diagnostic CT at our facility are as follows; L/spine 9% of Diagnostic CT dose, Chest 24%, Abd/Pel 15%. See Tbl.1

Conclusions With each case patients receive multi-slice CT exposure whether it be from 5mm or 1mm SPECT/CT aquisitions. At our facility the benefit of clinically useful images greatly out weighted the slight increase in exposure. Our goal was simply to demonstrate the quality of imaging possible with SPECT/CT

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CT Exposures

DLP Corr. Fact. Chest 0.017, L/S 0.015, Pel 0.019 Spect/CT 130Kev, ref. mAs 15(5mm) or 25(1mm) Diagnostic CT 120Kv, mA range 10-500