Advances in dual respiratory and ECG-gated SPECT imaging

Abstract

In the current issue of Journal of Nuclear Cardiology, Kortelainen et al report that a new method of acquiring dual respiratory and ECG-gated SPECT myocardial perfusion data reduces artifacts due to respiratory motion while leaving asynchrony measurements derived from the data unaltered. 1 As the improvements reported were modest and only observed in a subset of subjects, a relevant question to ask is whether the additional equipment needed and patient preparation logistics would significantly improve patient outcomes. Is pulmonary motion actually a significant problem in nuclear cardiology imaging, requiring a solution?There is a long history of exploring data acquisition and processing methods to detect and compensate for the repositioning of organ systems due to breathing in scintigraphic imaging, notably for PET studies to improve the detection of tumors involved in lung cancer. 2 In the realm of cardiac imaging, it was recognized as early as 1989 that changes in breathing patterns over time could degrade Tl-201 SPECT myocardial image quality if data acquisition was initiated too early following treadmill exercise, 3 the remedy for which was to delay the start of imaging. Even with this change in technique, myocardial motion due to normal breathing patterns has been shown to degrade image quality and affect quantified myocardial perfusion. 4 In 2009, several papers appeared documenting the effect of respiratory motion on SPECT perfusion assessment and proposing solutions. [5][6][7] Now, in conjunction with protocols involving imaging the heart while it is in a stressed state, corrections for breathing motion have been shown to improve accuracy not only of relative myocardial perfusion evaluation but also of absolute myocardial blood flow quantitative measurements as derived from Rb-82 PET data. 8 There are advantages to ECG-gating both rest and stress PET data, and newer rest/stress SPECT protocols are being implemented such that the heart is in a genuinely different physiologic state during stress SPECT acquisition, 9 raising the prospect that it may become important to detect and correct for changes in breathing patterns induced by stress.Initially, the main focus of Tl-201 and Tc-99m-sestamibi SPECT imaging was relative myocardial perfusion assessment, but with ECG-gating, additional parameters can be measured as well, including LV ejection fraction, 10 volumes, wall thickening by way of partial volume effects, 11 and regional asynchrony. 12 Multiple different approaches are possible in acquiring SPECT data with ECG-gating, and effects of gating errors and arrhythmias on quantified parameters have been reported. 13 By the same token, several different approaches to handle cardiac displacement to account for breathing motion are possible. With these new approaches to incorporate information regarding pulmonary motion, attention now has broadened to assessing the effects of pulmonary gating errors and breathing motion not only on myocardial perfusion but on the other parameters as well. This account by Kort...

Myocardial perfusion imaging with retrospective gating and integrated correction of attenuation, scatter, respiration, motion, and arrhythmia

“…23 Electrocardiogram gating to exclude arrhythmic heartbeats is essential when imaging a beating heart and further correction of respiratory motion might improve image quality and patient-by-patient variability. 24 – 26 However, the combined effects of such corrections have yet to be determined and they are not necessarily applied in clinical practice. We found that the integrated corrections for the SPECT images using a list-mode data acquisition are technologically and clinically feasible and significantly improved image quality by visual assessment without any noticeable pitfalls.…”

“…Lastly, although improving quantitative values by integrating all possible correction methods is desirable, whether pursuing true quantitation would definitively improve clinical diagnostic ability requires further investigation. 26 …”