Myocardial Perfusion Imaging with a Solid-State Camera: Simulation of a Very Low Dose Imaging Protocol

Abstract

High sensitivity dedicated cardiac systems cameras provide an opportunity to lower injected doses for SPECT myocardial perfusion imaging (MPI), but the exact limits for lowering doses have not been determined. List mode data acquisition allows for reconstruction of various fractions of acquired counts, allowing a simulation of gradually lower administered dose. We aimed to determine the feasibility of very low dose MPI by exploring the minimal count level in the myocardium for accurate MPI. Methods Seventy nine patients were studied (mean body mass index 30.0 ± 6.6, range 20.2–54.0 kg/m2) who underwent 1-day standard dose 99mTc-sestamibi exercise or adenosine rest/stress MPI for clinical indications employing a Cadmium Zinc Telluride dedicated cardiac camera. Imaging time was 14-min with 803 ± 200 MBq (21.7 ± 5.4mCi) of 99mTc injected at stress. To simulate clinical scans with lower dose at that imaging time, we reframed the list-mode raw data to have count fractions of the original scan. Accordingly, 6 stress equivalent datasets were reconstructed corresponding to each fraction of the original scan. Automated QPS/QGS software was used to quantify total perfusion deficit (TPD) and ejection fraction (EF) for all 553 datasets. Minimal acceptable count was determined based on previous report with repeatability of same-day same-injection Anger camera studies. Pearson correlation coefficients and SD of differences with TPD for all scans were calculated. Results The correlations of quantitative perfusion and function analysis were excellent for both global and regional analysis on all simulated low-counts scans (all r ≥0.95, p<0.0001). Minimal acceptable count was determined to be 1.0 million counts for the left ventricular region. At this count level, SD of differences was 1.7% for TPD and 4.2% for EF. This count level would correspond to a 92.5 MBq (2.5 mCi) injected dose for the 14 min acquisition. Conclusion 1.0 million myocardial count images appear to be sufficient to maintain excellent agreement quantitative perfusion and function parameters as compared to those determined from 8.0 million count images. With a dedicated cardiac camera, these images could be obtained over 10 minutes with an effective radiation dose of less than 1 mSv without significant sacrifice in accuracy.

Absolute myocardial blood flow quantification with SPECT/CT: Is it possible?

“…It is estimated that over 300 of these scanners are currently in use-a number that is increasing by about 100 per year 22 and already surpassing the number of cardiac PET scanners. To date, these new techniques have been utilized primarily to reduce the routine scan time and radiation dose, 23,24 or achieve ultra-low radiation dose (\1 mSv) stress-only imaging 25 at standard times (10-12 minutes). The increased count sensitivity of these systems offers also a great advantage for the dynamic flow imaging.…”

Quantification with normal limits: New cameras and low-dose imaging

“…14 In that study, the normal patients' list-mode raw data obtained from CZT SPECT scanner are reframed to simulate low-count images. They demonstrate that a progressive decrease of the left ventricular count levels leads to an increase of the segmental interpatient variation of the normal limits.…”

Automatic evaluation of myocardial perfusion on SPECT: Need for “Normality”

“…12,13 Finally, the introduction of dedicated cardiac cameras built around solid-state Cadmium-Zinc-Telluride (CZT) detectors has represented a real revolution in the field of nuclear cardiac imaging, allowing reducing consistently both the radiation burden and acquisition time of MPI, while maintaining if not improving the overall diagnostic capability. 7,14,15 Because of the absence of the photomultipliers tubes, CZT cameras are consistently less bulky than traditional SPECT devices, increasing patients comfort while reducing overall logistic needs. Nevertheless, while performing consistently better than Anger cameras, CZT devices still constitute a limited fraction of the working nuclear cardiac cameras, mainly because of the higher initial costs of this technology.…”