Introduction Identification of myocardial ischaemia & the need for mechanical intervention has increasingly become dependent on measurements of coronary artery flow in terms of FFR, CMR & IMR at invasive coronary angiography & coronary flow reserve (CFR) at CTCA, in addition to anatomy & standard perfusion scanning. CFR measured by PET imaging has been available for some time & has shown additional prognostic value over myocardial perfusion imaging alone. Unfortunately, PET has limited clinical availability. The advent of solid state gamma cameras has increased count sensitivity & temporal resolution. Thus, it is possible to perform measurements of global & regional CFR & myocardial blood flow (MBF) from a dynamic SPECT acquisition. Adding CFR measurements to a SPECT myocardial perfusion scan may be particularly useful for patients with triple vessel disease or suspected microvascular angina ((µVA) with so called ‘matched’ defects. The measurement requires dynamic imaging with stress & at rest, from the moment of injection of myocardial perfusion tracer – Diagram 1 Detailed tissue kinetic modelling is used to estimate absolute MBF & CFR. The dynamic data is processed using a Leppo net retention model on the GE Alcyone software suite. The Renkin-Crone flow model is used to convert the retention ratio to MBF. CFR is then calculated as the ratio of hyperaemic to rest absolute MBF.
Results Table 1We have now performed 49 SPECT MPS’s with flow measurements, as part of clinical service, on a GE Discovery NM530c scanner.Reason for referral was divided into possible µVA, ACP & TCP. Of those with possible µVA, not all had had coronary angiography to support the diagnosis. However, whilst most had normal standard myocardial perfusion scans, half had evidence of abnormal CFR supporting the potential diagnosis in these cases & increasing the identification of potential ischaemia from 20% with standard MPS to 80% with CFR.In patients with ACP, the addition of CFR to standard SPECT MPS, had a lesser impact, increasing the suggestion of ischaemia from 23% to 35%.In patients with TCP, although 60% of previous angiograms had been normal, again the addition of CFR increased identification of potential ischaemia from 23% of patients using standard SPECT MPS, to 72% with CFR assessment.
Conclusions The addition of non-invasive flow assessment to standard SPECT MPS increases the identification of potential ischaemia in patients with potential µVA or TCP, presumably due to identifying flow reduction in ‘matched’ ischaemic defects which may be missed on standard perfusion scanning. However, whilst CFR has less advantages in terms of additional information in patients with ACP, it may increase confidence in the exclusion of ischaemia.
Conflict of Interest none
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