An investigation of a sinogram discontinuity artifact on myocardial perfusion imaging

Our purpose was to find out the cause of an unusual distinct break seen on a patient's sinogram despite within-tolerance results on all quality assurance tests during myocardial perfusion imaging (MPI) and corrective measures.

SPECT quality control is a prerequisite to obtaining high-quality diagnostic images. Daily uniformity and energy-peaking tests and weekly center-of-rotation (COR) tests are run to check the performance of the SPECT system. A distinct break in the sinogram of an MPI study was noticed for 1 patient, despite routine quality control tests that showed the system to be well within tolerance limits. Critical inspection of the γ-camera revealed that the 2 detector heads did not make complete contact with each other at a 90° position and that a gap of as much as 10.0 mm was left between the 2 edges of the detectors even though COR testing showed the system to be within tolerance limits. After this gap had been minimized (-10-mm position), the MPI study of this patient was repeated.

Reduction of the gap between detectors corrected the sinogram discontinuity. On the MPI study, the break in the sinogram existed because the 2 detectors were not acquiring the data at the same position in their useful fields of view. When one of the detectors was tilted to exactly 45°, the gap was reduced and the data were acquired at the same useful field of view for both detectors.

The sinogram artifact may arise even after perfect COR calibration, and in the reported case, the discontinuity in the sinogram was rectified by correcting the angle of the detectors. Meticulous investigation for artifacts must be performed to minimize the probability of false results.