Effects of a novel additional neck-shield and time of flight on quality of cerebral imaging in ¹⁵O-labeled gas inhalation study

Objectives Activity outside the field of view degrades image quality in 3D PET scanner. The present study aimed to reveal combined effects of a novel additional neck-shield made of tungsten rubber and time of flight (TOF) algorithm on image quality of 3D PET in ¹⁵O-labeled gas inhalation study.

Methods ¹⁵O-gas images were acquired using three emission-scans with ¹⁵O-labeled CO₂, O₂ and CO gas inhalation in two healthy volunteers. All images were acquired by Discovery 710 PET/CT (GE Healthcare) with and without neck-shield and reconstructed using 3D-OSEM and 3D-OSEM + TOF. Regional cerebral blood flow (CBF), oxygen extraction fraction (OEF) and cerebral metabolic rates of oxygen (CMRO₂) were calculated from ¹⁵O-gas images and arterial blood sampling by PET autoradiographic method. Noise equivalent count rate (NECR) was calculated from PET count rates. Mean values and standard deviation (SD) to calculate signal to noise ratios (SNRs) were measured in 10-mm diameter circular ROIs covered the cortical ribbons on cortices of cerebellum and cerebrum with CBF, OEF and CMRO₂ images. One-way ANOVA was applied to the group comparison of SNR in each ROI.

Results The random count rates decreased 47% and NECRs increased approximately half again using neck-shield. The SNRs without TOF were increased using the neck-shield. A significant difference (p < 0.05) was found between shield (-) and TOF (-) and shield (+) and TOF (-) in SNR of OEF.

Conclusions The image quality based PET count rate was dramatically improved by the novel additional neck-shield. The image quality based SNR was improved significantly in OEF using the neck-shield.