Study of cardiac ejection fraction and volume measurements using a dynamic cardiac phantom and SPECT

A dynamic cardiac phantom and single photon emission computed tomography (SPECT) imaging were used to obtain ejection fraction (EF) and left ventricular volume measurements. The dynamic cardiac phantom consists of two ventricles with a volume of approximately 58 ml each at 1 atm. pressure. This latex and rubber-foam phantom was connected to a pulsatile flow pump via noncompliant plastic tubing. A Tc-99m pertechnetate and water solution was used to fill the left ventricle, and 10 ml, 18.5 ml, and 33 ml were added to the ventricular chamber so that three ejection fractions of 14.7%, 24.1%, and 36.2% were produced. A triple camera system with three different collimators was used for planar and SPECT scans. Low energy high resolution (LEHR), ultrahigh resolution (LEUR), and super high resolution (LESR) parallel hole collimators were used. The simulated heart rate was between 82 and 89 beats per min. SPECT scans of twenty frames per R-R interval were obtained from a simulated ECG signal and 10 beats per angle were used to acquire the data for 120 steps at 3 degree intervals. The acquired data were reconstructed using filtered backprojection (FBP) and a Hamming window with a high cutoff frequency of 0.7 cycle/cm. Two different attenuation coefficients, 0.11 and 0.15 cm^-1, were applied for the attenuation correction and compared. The EF measurements from the LEHR planar images agree well with the actual EF. The volume estimations by pixel summing method produced the best estimations with a threshold of about 50% of the peak value within the ROI. Overall, the calibrated count method yielded the most reliable estimations in EF and volume measurements. First-pass measurements using a multicrystal camera were performed by standard acquisition and processing software. Acquisition consisted of 2000 continuous planar images of 25 milliseconds each. The first-pass measurements showed that EF calculations were more accurate using first-single beat data rather than the average of several beats. The dynamic cardiac phantom is useful for evaluating methods for cardiac function measurements, testing reconstruction algorithms with attenuation corrections, and studying collimator characteristics.