Optimisation of protocol for low dose CT-derived attenuation correction in myocardial perfusion SPECT imaging

Abstract

Our results indicate that reliable attenuation maps (mu-maps) of the thorax can be obtained even with the use of very low tube current. In our study, radiation exposure in CT-based AC for myocardial perfusion SPECT was substantially lowered (60% reduction). This is of particular importance in high-risk patients who may have to undergo follow-up scans and in research studies on volunteers. The procedure introduced is relatively simple and can be transferred to other SPECT/CT devices, which allow adjustment of tube current.

Accurate localization of incidental findings on the computed tomography attenuation correction image

“…This finding concurs with a previous patient based study, where a 1mA attenuation map was acquired at rest and a 2.5mA attenuation map at stress; both image sets revealed abnormal findings at a rate of 9.7% [12]. The patient based study and our work both describe potential dose saving in the region of 60%.…”

“…In our (static) phantom study we did not set out to determine the effect of respiratory motion on lesion detection. Variation in respiratory motion can be great, both within subjects and between them [30,31] but previous work comparing 2.5mA attenuation maps at stress and 1mA attenuation maps at rest saw equal detection rates (9.7%) of abnormal findings [12]. In this work the authors do comment that the attenuation map, with a rotation time of 14 seconds was sampled over approximately 3 respiratory cycles.…”

“…Variation of tube current has no impact on tissue attenuation values and Hounsfield Units (HU) -the resultant attenuation maps are therefore largely independent of mA [9,10,11,12]. However, the impact of varying mA on lesion detection is less clear and this deserves investigation because of the potential dose saving at lower mA values.…”

Spect/Ct

“…Koepfli et al (65) and a recent study with SPECT/CT confirmed these findings (66). However, a potential misalignment between emission and transmission data poses the risk of incomplete correction and thus artificial perfusion defects and requires careful quality control to avoid reconstruction artifacts.…”

Cardiac SPECT/CT Imaging: CT Attenuation Correction and SPECT/CT Hybrid Imaging

“…Using SPECT/CT hybrid systems increases the specificity of myocardial SPECT to 80-90% [9]. SPECT/CT studies have shown that low-dose CT acquisitions are also feasible for CTAC [25]. The main limitation of CTAC is misregistration between myocardial SPECT and CT attenuation maps due to respiratory and cardiac motion [24,26].…”