Reduced dose measurement of absolute myocardial blood flow using dynamic SPECT imaging in a porcine model.
OBJECTIVE
Absolute myocardial blood flow (MBF) and myocardial flow reserve (MFR) measurements provide important additional information over traditional relative perfusion imaging. Recent advances in camera technology have made this possible with single-photon emission tomography (SPECT). Low dose protocols are desirable to reduce the patient radiation risk; however, increased noise may reduce the accuracy of MBF measurements. The authors studied the effect of reducing dose on the accuracy of dynamic SPECT MBF measurements.


METHODS
Nineteen 30-40 kg pigs were injected with 370 + 1110 MBq of Tc-99m sestamibi or tetrofosmin or 37 + 111 MBq of Tl-201 at rest + stress. Microspheres were injected simultaneously to measure MBF. The pigs were imaged in list-mode for 11 min starting at the time of injection using a Discovery NM 530c camera (GE Healthcare). Each list file was modified so that 3/4, 1/2, 1/4, 1/8, 1/16, and 1/32 of the original counts were included in the projections. Modified projections were reconstructed with CT-based attenuation correction and an energy window-based scatter correction and analyzed with FlowQuant kinetic modeling software using a 1-compartment model. A modified Renkin-Crone extraction function was used to convert the tracer uptake rate K1 to MBF values. The SPECT results were compared to those from microspheres.


RESULTS
Correlation between SPECT and microsphere MBF values for the full injected activity was r ≥ 0.75 for all 3 tracers and did not significantly degrade over all count levels. The mean MBF and MFR and the standard errors in the estimates were not significantly worse than the full-count data at 1/4-counts (Tc99m-tracers) and 1/2-counts (Tl-201).


CONCLUSIONS
Dynamic SPECT measurement of MBF and MFR in pigs can be performed with 1/4 (Tc99m-tracers) or 1/2 (Tl-201) of the standard injected activity without significantly reducing accuracy and precision.
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Rachel
R
Timmins
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Ran
R
Klein
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Julia
J
Petryk
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Brian
B
Marvin
Nordion, Inc., Ottawa, Ontario K2K 1X8, Canada.
Lihui
L
Wei
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Robert A
RA
deKemp
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
Terrence D
TD
Ruddy
Division of Cardiology, University of Ottawa Heart Institute, Ottawa, Ontario K1Y4W7, Canada.
R Glenn
RG
Wells
D000818:Animals; D003326:Coronary Circulation; D005260:Female; D007091:Image Processing, Computer-Assisted; D011829:Radiation Dosage; D013552:Swine; D015899:Tomography, Emission-Computed, Single-Photon / Q000379:methods*