Selection of optimal collimator for 1-day basal/acetazolamide brain perfusion SPECT

Objectives Basal/acetazolamide-challenged brain perfusion SPECT is very useful to assess cerebral perfusion and vascular reserve. However, as there is a tradeoff between sensitivity and spatial resolution in the selection of collimator, the selection of optimal collimator is crucial. In this study, we examined three collimators to select optimal one for 1-day brain perfusion SPECT.

Methods Three collimators, low energy high resolution-parallel beam (LEHR-PAR), ultra resolution-fan beam (LEUR-FAN) and super fine-fan beam (LESFR-FAN), were tested for 1-day imaging using Triad XLT 9 (TRIONIX). The SPECT images of Hoffman 3D brain phantom filled with Tc-99m of 170 MBq and a normal volunteer were acquired with a protocol of 50 kcts/frame and detector rotation of 3 degree. FBP reconstruction with Butterworth filter (cut-off frequencies, 0.3 to 0.5) was performed. The quantitative and qualitative assessments for three collimators were performed.

Results The blind tests showed that LESFR-FAN provided the best image quality for Hoffman brain phantom and the volunteer. However, images for all the collimator were evaluated as ‘acceptable. On the other hand, in order to meet the equivalent signal-to-noise ratio (SNR), total acquisition time or radioactivity dose for LESFR-FAN must have been increased up to almost twice of that for LEUR-FAN and LEHR-PAR. The volunteer test indicated that total acquisition time could be reduced approximately by 10 to 14 min in clinical practice using LEUR-FAN and LEHR-PAR without significant loss on image quality, in comparison with LESFR-FAN.

Conclusions Although LESFR-FAN provides the best image quality, it requires significantly more acquisition time than LEUR-FAN and LEHR-PAR to provide reasonable SNR. Since there is no significant clinical difference between three collimators, LEUR-FAN and LEHR-PAR can be recommended as optimal collimators for 1-day brain perfusion imaging with respect to image quality and SNR