IQ SPECT Allows a Significant Reduction in Administered Dose and Acquisition Time for Myocardial Perfusion Imaging: Evidence from a Phantom Study

Abstract

We recently demonstrated in a clinical trial the ability of a new protocol, IQ SPECT, to acquire myocardial perfusion imaging (MPI) studies in a quarter of the time (12 s/view) of the standard protocol, with preserved diagnostic accuracy. We now aim to establish the lower limit of radioactivity that can be administered to patients and the minimum acquisition time in SPECT MPI using an IQ SPECT protocol, while preserving diagnostic accuracy. Methods: An anthropomorphic cardiac phantom was used to acquire clinical rest scans with a simulated in vivo distribution of 99m Tc-tetrofosmin at full dose (740 MBq) and at doses equal to 50%, 25%, and 18%. For each dose, 2 sets of images were acquired, with and without a transmural defect (TD). Variable acquisition times were also used for each dose. We analyzed raw data and reconstructed images, including no correction and correction for attenuation (AC), for scatter (SC), or for both (ACSC). Images were evaluated qualitatively and quantitatively in order to assess left ventricle (LV) wall thickness (full width at half maximum of the medial sections), TD, and cavity contrast in the LV wall. Data were compared across different acquisition times within the same dose and across doses with the same acquisition time. Results: Images were visually scored as very-good quality except those acquired with 4 s/view or less at 100% dose and 6 s/view or less with 50%, 25%, or 18% dose, due to falsepositive defects. LV wall thickness was not significantly different among all acquisitions. Cavity contrast remained unchanged within the same dose for all images and tended to be higher in AC and ACSC images. TD contrast remained unchanged within the same dose for all images. In SC and no-correction images, contrast was constant for all doses. AC images had significantly higher TD contrast values, and ACSC images showed a drop in TD contrast for a 50% dose. Conclusion: IQ SPECT effectively preserved both image quality and quantitative measurements with reduced acquisition time or administered dose in a phantom study. These findings suggest that approximately one eighth of the time, compared with standard protocols with a full dose, or a lower dose at an acquisition time of 12 s/view can be applied in MPI without the loss of diagnostic accuracy.

How to use cardiac IQ•SPECT routinely? An overview of tips and tricks from practical experience to the literature

“…Other workers have confirmed this finding in both phantom studies [5] and clinical studies [6]. The phantom study also confirmed that either the activity or the acquisition duration can be reduced.…”

Diagnostic Performance of Attenuation-Corrected Myocardial Perfusion Imaging for Coronary Artery Disease: A Systematic Review and Meta-Analysis

“…When considering radiation, dose from radionuclide transmission sources is less than from SPECT/CT (11). However, a lower radiation dose from SPECT/CT has been achieved by reducing x-ray tube current and incorporating new reconstruction methods and new protocols (39,43,44). Also RAC is time consuming.…”

New techniques, distinctive population, unique normal databases

“…9 The use of IQÁSPECT to reduce imaging time and/ or radiopharmaceutical dose has been demonstrated in phantoms and in patients. 7,10 In one study based on patient images, Lyon et al compared attenuation corrected stress SPECT to IQÁSPECT using a dose of 925-1100 MBq (25-30 mCi) Tc-99m sestamibi. Several different count levels were simulated for IQÁSPECT, and evaluated using system and count level specific normal files.…”

“…This design allows increased sensitivity over the heart where it is most needed but avoids truncation of the body. 7 It is important that the heart be properly positioned in the region of highest magnification of both collimators throughout acquisition. While slight mispositioning may be tolerable, poor patient set-up may be less forgiving than standard parallel-hole collimation.…”