Gated SPECT imaging to detect changes in myocardial blood flow during progressive coronary occlusion

Quantitative Assessment of Myocardial Blood Flow with SPECT

The quantitative assessment of myocardial blood flow (MBF) and coronary flow reserve (CFR) may be useful for the functional evaluation of coronary artery disease, allowing judgment of its severity, tracking of disease progression, and evaluation of the anti-ischemic efficacy of therapeutic strategies. Quantitative estimates of myocardial perfusion and CFR can be derived from single-photon emission computed tomography (SPECT) myocardial perfusion images by use of equipment, tracers, and techniques that are available in most nuclear cardiology laboratories. However, this method underestimates CFR, particularly at high flow rates. The recent introduction of cardiac-dedicated gamma cameras with solid-state detectors provides very fast perfusion imaging with improved resolution, allowing fast acquisition of serial dynamic images during the first pass of a flow agent. This new technology holds great promise for MBF and CFR quantification with dynamic SPECT. Future studies will clarify the effectiveness of dynamic SPECT flow imaging.

Quantitation of myocardial blood flow and myocardial flow reserve with 99mTc-sestamibi dynamic SPECT/CT to enhance detection of coronary artery disease

PURPOSE

Conventional dual-head single photon emission computed tomography (SPECT)/CT systems capable of fast dynamic SPECT (DySPECT) imaging have a potential for flow quantitation. This study introduced a new method to quantify myocardial blood flow (MBF) and myocardial flow reserve (MFR) with DySPECT scan and evaluated the diagnostic performance of detecting coronary artery disease (CAD) compared with perfusion using invasive coronary angiography (CAG) as the reference standard.

METHODS

This study included 21 patients with suspected or known CAD who had received DySPECT, ECG-gated SPECT (GSPECT), and CAG (13 with ≥ 50% stenosis in any vessel; non-CAD group: 8 with patent arteries or < 50% stenosis). DySPECT and GSPECT scans were performed on a widely used dual-head SPECT/CT scanner. The DySPECT imaging protocol utilized 12-min multiple back-and-forth gantry rotations during injections of (99m)Tc-sestamibi (MIBI) tracer at rest or dipyridamole-stress stages. DySPECT images were reconstructed with full physical corrections and converted to the physical unit of becquerels per milliliter. Stress MBF (SMBF), rest MBF (RMBF), and MFR were quantified by a one-tissue compartment flow model using time-activity curves derived from DySPECT images. Perfusion images were processed for GSPECT scan and interpreted to obtain summed stress score (SSS) and summed difference score (SDS). Receiver-operating characteristic (ROC) analyses were conducted to evaluate the diagnostic performance of flow and perfusion.

RESULTS

Using the criteria of ≥ 50% stenosis as positive CAD, areas under the ROC curve (AUCs) of flow assessment were overall significantly greater than those of perfusion. For patient-based analysis, AUCs for MFR, SMBF, SSS, and SDS were 0.91 ± 0.07, 0.86 ± 0.09, 0.64 ± 0.12, and 0.59 ± 0.13. For vessel-based analysis, AUCs for MFR, SMBF, SSS, and SDS were 0.81 ± 0.05, 0.76 ± 0.06, 0.62 ± 0.07, and 0.56 ± 0.08, respectively.

CONCLUSION

The preliminary data suggest that MBF quantitation with a conventional SPECT/CT system and the flow quantitation method is a clinically effective approach to enhance CAD detection.

Quantification of Myocardial Perfusion Reserve Using Dynamic SPECT Imaging in Humans: A Feasibility Study

Myocardial perfusion imaging (MPI) is well established in the diagnosis and workup of patients with known or suspected coronary artery disease (CAD); however, it can underestimate the extent of obstructive CAD. Quantification of myocardial perfusion reserve with PET can assist in the diagnosis of multivessel CAD. We evaluated the feasibility of dynamic tomographic SPECT imaging and quantification of a retention index to describe global and regional myocardial perfusion reserve using a dedicated solid-state cardiac camera.

METHODS

Ninety-five consecutive patients (64 men and 31 women; median age, 67 y) underwent dynamic SPECT imaging with (99m)Tc-sestamibi at rest and at peak vasodilator stress, followed by standard gated MPI. The dynamic images were reconstructed into 60-70 frames, 3-6 s/frame, using ordered-subsets expectation maximization with 4 iterations and 32 subsets. Factor analysis was used to estimate blood-pool time-activity curves, used as input functions in a 2-compartment kinetic model. K1 values ((99m)Tc-sestamibi uptake) were calculated for the stress and rest images, and K2 values ((99m)Tc-sestamibi washout) were set to zero. Myocardial perfusion reserve (MPR) index was calculated as the ratio of the stress and rest K1 values. Standard MPI was evaluated semiquantitatively, and total perfusion deficit (TPD) of at least 5% was defined as abnormal.

RESULTS

Global MPR index was higher in patients with normal MPI (n = 51) than in patients with abnormal MPI (1.61 [interquartile range (IQR), 1.33-2.03] vs. 1.27 [IQR, 1.12-1.61], P = 0.0002). By multivariable regression analysis, global MPR index was associated with global stress TPD, age, and smoking. Regional MPR index was associated with the same variables and with regional stress TPD. Sixteen patients undergoing invasive coronary angiography had 20 vessels with stenosis of at least 50%. The MPR index was 1.11 (IQR, 1.01-1.21) versus 1.30 (IQR, 1.12-1.67) in territories supplied by obstructed and nonobstructed arteries, respectively (P = 0.02). MPR index showed a stepwise reduction with increasing extent of obstructive CAD (P = 0.02).

CONCLUSION

Dynamic tomographic imaging and quantification of a retention index describing global and regional perfusion reserve are feasible using a solid-state camera. Preliminary results show that the MPR index is lower in patients with perfusion defects and in regions supplied by obstructed coronary arteries. Further studies are needed to establish the clinical role of this technique as an aid to semiquantitative analysis of MPI.