8th Baltic Congress of Radiology

Nuclear Medicine

oral abstract

Myocardial perfusion imaging (MPI) on single-photon emission computed tomography (SPECT) is one of the most common performed and trusted modalities in the diagnosis and risk assessment in patients with stable ischemic heart disease. The introduction of SPECT cameras equipped with high-efficiency Cadmium-zinc-telluride (CZT) detectors has allowed a reduction of acquisition time and injected radiotracers dose, as well as improving image quality and diagnostic accuracy. Dedicated cardiac CZT camera possess some limitation that are related to the intrinsic architecture of the camera, whereas all-purpose CZT SPECT cameras overcome some of those limitations. The possibility to discretely compose the camera set-up and the protocols for acquisition, reconstruction and post-processing, including many techniques of quantification, results in a heterogeneous outcome of procedures that basic are the same. These issues are significant in the diagnostic work-up of a certain patient. However, that scientific investigations in the setting of multicentre trials could be greatly compromised by these factors. Standardisation and harmonisation of procedures needs to be further pursued and developed in both healthcare studies and in the clinical settings to improve the comparability of results between institutions. While some data have demonstrated the feasibility of MPI on the all-purpose cameras, however, there are only limited scientific publications referencing detailed studies on MPI comparison between CZT gamma cameras. In present study we compared whole body CZT SPECT-CT camera to a dedicated cardiac CZT camera for myocardial perfusion imaging using phantoms in order to identify and optimize protocols.

We used cardiac insert phantom with an artificial defect imitation in anterior wall on SPECT. Additional combination of NEMA phantom with cardiac insert within was scanned for more realistic depiction of a heart in a background activity. Cardiac insert phantom was filled with 3 MBq of 99mTc solution in a myocardial 110 ml volume interstice, in contrast 0.8 MBq was used for a filling of 60 ml ventricle space. NEMA phantom for a simulating a hot background activity was filled with 25 MBq in its volume. The acquisition was performed using two different systems D-SPECT Cardio (Spectrum Dynamics, 2017) and NM/CT 870 CZT (GE Healthcare, 2021). Image acquisition was done performing the standard clinical protocols settings. In D-SPECT the phantom was placed in about 25 cm distance to the detector from cardiac insert centre, energy window was setted at 14015 keV for a total 1.1 million count amount. Accordingly, for NM/CT 870 CZT the parameters were 140.5 ±10 keV energy window, 60 projections per head over 180, 20 seconds per each projection, used matrix 64x64. The phantoms placed at 30 cm distance from the detectors by recording the total number of counts detected during a 11-minute acquisition. Image quality assessment was carried out objectively by measuring contrast-to-noise ratio (CNR) which is related to the contrast or signal difference between an object of interest and the image background. CNR was measured using an open source software ImageJ. Images quality was assessed independently by three nuclear medicine radiologists in accordance with international guidelines.

Image quality can be investigated in two ways, objectively based on physical measurements and subjectively through psychophysical assessments. After the comparison of the two systems the main differences of CNR, uniformity and spatial resolution were found Psychophysical assessments of the images also showed significant difference between the systems.

Our preliminary results suggest that MPI acquired with an all-purpose CZT SPECT camera is feasible, comparing with the dedicated cardiac camera technology, meantime imaging quality is depended on dosing, acquisition protocols and reconstruction parameters. Moreover, in order to harmonize the scanners, it is necessary to increase the radiotracer dose for all-purpose CZT camera. Depending on the results of image acquisition and reconstruction the further steps in harmonization of dedicated cardiac-centred gamma camera and all-purpose SPECT system should be taken. The optimization and harmonization work must be done separately for each device taking in account the reconstruction algorithms.

Myocardial perfusion imaging is one the most common and highly sensitive functional imaging procedures performed in a nuclear medicine department. In present study we compared all-purpose CZT SPECT-CT camera to a dedicated cardiac CZT camera. The study was performed using phantoms. Contrast-to-noise ratio, uniformity and spatial resolution and psychophysical assessments were done. Due to differences of the systems, some parameters could not be harmonized.

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