The need to reduce radiation exposure of patients has become a central issue in cardiac imaging due to the increasing number of cardiovascular diagnostic procedures and therapeutic interventions performed every year. Attenuation correction by CT improves the accuracy of MPI, but increases the patient radiation dose due to the need of a double CT acquisition for stress/rest imaging.
AIM OF THE STUDY was to evaluate the opportunity of using a single CT acquired for attenuation correction purposes (AC) of stress/rest SPECT/CT.
Twenty five Tc 99m tetrofosmin low-dose stress-rest SPECT/TC studies with perfusion defects were processed by using 2 methods: 1) standard method (M1) applying a CT (S-CT) for AC of stress SPECT (S-SPECT) and a second CT (R-CT) for AC of rest SPECT (R-SPECT); 2) method 2 (M2) using the S-CT for AC of both S and R SPECT. The transaxial reconstruction was performed by iterative method with scatter and attenuation correction and a resolution recovery algorithm. 11 out of 25 (44%) stress-rest SPECT studies were performed by using a 1-Day protocol. The mean effective dose due to a single CT acquisition was extimated to be 0.8 mSv.
The summed rest score was 7.52± 0.58 (SRS1) by M1 and 7.76±8.68 (SRS2) by M2 (F=N.S), whereas the summed stress score was unchanged 13.84±10.64 (SSS). The summed difference score was 6.2±4.76 (SDS1) with M1 and 5.24 ±4.95 (SDS2) with M2 (F= N.S).
Moreover, the extension of the perfusion defect at rest was 12.4±11.6 by using M1 and 12.4±11.7 with M2 (F=N.S); after stress the extension of the perfusion defect was 19.9 ±16.2 with M1 and 20 ± 16.1 by using M2 (F=N.S).
Our data suggest that using a single CT acquisition in comparison to a double Ct acquisition only minimal differences are observed, which are within the range of the test reproducibility. A single CT scan can be used to correct for attenuation stress-rest cardiac SPECT studies minimizing radiation exposure of patients without decreasing the accuracy of myocardial perfusion imaging.