Abstract
We aimed to investigate the image quality of the U-SPECT5/CT E-Class a micro single-photon emission computed tomography (SPECT) system with two large stationary detectors for visualization of rat hearts and bones using clinically available 99mTc-labelled tracers. Sensitivity, spatial resolution, uniformity and contrast-to-noise ratio (CNR) of the small-animal SPECT scanner were investigated in phantom studies using an ultra-high-resolution rat and mouse multi-pinhole collimator (UHR-RM). Point source, hot-rod, and uniform phantoms with 99mTc-solution were scanned for high-count performance assessment and count levels equal to animal scans, respectively. Reconstruction was performed using the similarity-regulated ordered-subsets expectation maximization (SROSEM) algorithm with Gaussian smoothing. Rats were injected with ~ 100 MBq [99mTc]Tc-MIBI or ~ 150 MBq [99mTc]Tc-HMDP and received multi-frame micro-SPECT imaging after tracer distribution. Animal scans were reconstructed for three different acquisition times and post-processed with different sized Gaussian filters. Following reconstruction, CNR was calculated and image quality evaluated by three independent readers on a five-point scale from 1 = “very poor” to 5 = “very good”. Point source sensitivity was 567 cps/MBq and radioactive rods as small as 1.2 mm were resolved with the UHR-RM collimator. Collimator-dependent uniformity was 55.5%. Phantom CNR improved with increasing rod size, filter size and activity concentration. Left ventricle and bone structures were successfully visualized in rat experiments. Image quality was strongly affected by the extent of post-filtering, whereas scan time did not have substantial influence on visual assessment. Good image quality was achieved for resolution range greater than 1.8 mm in bone and 2.8 mm in heart. The recently introduced small animal SPECT system with two stationary detectors and UHR-RM collimator is capable to provide excellent image quality in heart and bone scans in a rat using standardized reconstruction parameters and appropriate post-filtering. However, there are still challenges in achieving maximum system resolution in the sub-millimeter range with in vivo settings under limited injection dose and acquisition time.
Highlights
Preclinical single-photon emission computed tomography (SPECT) imaging is an evolving field full of challenges
High spatial resolution can improve the diagnostic value of SPECT scans if sufficient image quality is achieved, which is affected by the choice of collimator[12], reconstruction algorithm[5,13], post-reconstruction filter[13] and injection dose[14]
This study aims to examine the preclinical applicability and image quality of the recently introduced microSPECT system for rat imaging under in vivo conditions using [ 99mTc]Tc-MIBI17 and [ 99mTc]Tc-HMDP18,19 with a pre-set similarity-regulated ordered-subsets expectation maximization (SROSEM) reconstruction algorithm and Gaussian post-filtering
Summary
Preclinical single-photon emission computed tomography (SPECT) imaging is an evolving field full of challenges. The introduction of pinhole collimation opened up new applications for small-animal SPECT imaging[1,2,3] and with the development of multi-pinhole collimation, high spatial resolution in the sub-millimeter range with acceptable sensitivity was p ossible[3,4,5,6]. For animal SPECT imaging, bigger size of the organs is an advantage of rats over mice, the higher soft tissue attenuation and scattering, as well as requirement of larger bore and transaxial size, might have negative impact on precise imaging. This study aims to examine the preclinical applicability and image quality of the recently introduced microSPECT system for rat imaging under in vivo conditions using [ 99mTc]Tc-MIBI17 and [ 99mTc]Tc-HMDP18,19 with a pre-set SROSEM reconstruction algorithm and Gaussian post-filtering
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