Dynamic SPECT Measurement of Absolute Myocardial Blood Flow in a Porcine Model

Abstract

Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) provide incremental diagnostic and prognostic information over relative perfusion alone. Recent development of dedicated cardiac SPECT cameras with better sensitivity and temporal resolution make dynamic SPECT imaging more practical. In this study, we evaluate the measurement of MBF using a multipinhole dedicated cardiac SPECT camera in a pig model of rest and transient occlusion at stress using 3 common tracers: 201 Tl, 99m Tc-tetrofosmin, and 99m Tc-sestamibi. Methods: Animals (n 5 19) were injected at rest/stress with 99m Tc radiotracers (370/1,100 MBq) or 201 Tl (37/110 MBq) with a 1-h delay between rest and dipyridamole stress. With each tracer, microspheres were injected simultaneously as the gold standard measurement for MBF. Dynamic images were obtained for 11 min starting with each injection. Residual resting activity was subtracted from stress data and images reconstructed with CT-based attenuation correction and energy window-based scatter correction. Dynamic images were processed with kinetic analysis software using a 1-tissue-compartment model to obtain the uptake rate constant K 1 as a function of microsphere MBF. Results: Measured extraction fractions agree with those obtained previously using ex vivo techniques. Converting K 1 back to MBF using the measured extraction fractions produced accurate values and good correlations with microsphere MBF: r 5 0.75-0.90 (P , 0.01 for all). The correlation in the MFR was between r 5 0.57 and 0.94 (P , 0.01). Conclusion: Noninvasive measurement of absolute MBF with stationary dedicated cardiac SPECT is feasible using common perfusion tracers. St udies using PET have demonstrated that absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR 5 stress/ rest MBF) provide incremental diagnostic and prognostic information over relative perfusion alone (1-4). Imaging of myocardial perfusion is much more commonly performed with SPECT than with PET, but MBF measurements are not typically acquired.Measuring MBF is difficult with standard SPECT cameras because of the need for attenuation and scatter correction and the need to rotate around the patient for 3-dimensional imaging. Recent studies have shown that it is possible to obtain an index of the MFR without a direct measure of MBF using a combination of dynamic planar followed by static SPECT acquisitions (5) and that this can provide some prognostic information (6). Other studies have demonstrated that rapid camera rotation can provide dynamic tomographic data and hence a measure of MFR (7) and the arterial input function (8), suggesting that accurate measures of MBF could be possible (9). The practicality of measuring MBF has increased greatly, however, with the advent of dedicated cardiac cameras.Dedicated cardiac cameras such as the DSPECT system (Spectrum Dynamics Medical Inc.) or the Discovery NM 530c/ 570c cameras (GE Healthcare) have greatly improved sensitivity and do not rotate around the patient (10). These features allow d...

Absolute Myocardial Blood Flow and Flow Reserve Assessed by Gated SPECT with Cadmium–Zinc–Telluride Detectors Using 99mTc-Tetrofosmin: Head-to-Head Comparison with 13N-Ammonia PET

“…Our results demonstrate that quantification of dynamic SPECT MPI on modern CZT cameras is technically feasible but without specific correction for the different extraction fraction and metabolism of Previous studies exploring quantification of MBF with dynamic planar scintigraphy in humans (18)(19)(20)(21)(22)(23)(24)(25) and with dynamic SPECT in experimental animals (26)(27)(28) have documented the limitations of conventional g-cameras for the dynamic acquisition of datasets required for MBF quantification. The introduction of CZT cameras without the need of detector rotation has allowed proving the concept of dynamic image acquisition for MBF quantification in a recent animal study using microspheres as a standard of reference (6). A recent study has confirmed the feasibility and reproducibility of kinetic analysis of myocardial tracer uptake with a CZT device (29), although no standard of reference for perfusion quantification was available.…”

“…The recent advances in SPECT technology including semiconductor detector material (cadmium zinc telluride [CZT]) allow acquisition in a nonrotating mode and therefore acquisition of time-activity curves. This may enable absolute MBF and MFR estimation by SPECT as recently shown in experimental animal models (6), which may pave the way for its implementation in clinical routine (7). More knowledge on the impact of the tracer properties on the values obtained from quantification is crucial.…”

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

“…26 Wells et al have applied dynamic flow quantification analysis as described by Klein et al to animal images obtained with high-efficiency MPI, demonstrating very good correlations of MBF with invasive microsphere measurements. 27 …”

Dynamic SPECT: evolution of a widely available tool for the assessment of coronary flow reserve

“…Further studies are needed to assess whether availability of transmission to correct for attenuation may enable better modelling of 99m Tc-labelled tracer kinetics. In addition, the new technology with superior sensitivity allows a significant reduction in the administered dose of 99m Tc-labelled tracers [21][22][23], which should also be applied to dynamic SPECT in future studies.With the increasing abundance of dedicated cardiac cameras with solid-state detectors, this technology offers great promise for CFR quantification with dynamic SPECT. However, further studies are needed for validation of this technique with PET measurements in large patient cohorts and with low administered activities, to establish its role in the clinical work-up of patients with known or suspected CAD and to provide data equivalent to the large body of data already accumulated for blood flow quantitation with PET tracers.…”

“…Further studies are needed to assess whether availability of transmission to correct for attenuation may enable better modelling of 99m Tc-labelled tracer kinetics. In addition, the new technology with superior sensitivity allows a significant reduction in the administered dose of 99m Tc-labelled tracers [21][22][23], which should also be applied to dynamic SPECT in future studies.…”