Abstract
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Objectives: The uMI780 and the first total-body uEXPLORER scanner which are produced by Shanghai United Imaging Healthcare are both based on the SiPM detectors. The former PETCT system has a transaxial and axial FoV of 700 mm and 300 mm. In the uEXPLORER scanner, the transaxial FoV is the same as uMI780, but it has a much longer axial FoV, reaching 1940 mm. It will provide extremely high sensitivity for clinical imaging and scientific research. Here, we characterize the image quality compared with uMI780 and the uEXPLORER scanner.
Methods: In the following study, the acquisition time was extended to eliminate the effect of the decay of 18F. First, we used a uniform phantom (150 mm × 2000 mm) filled with 18F to study the noise performance in two scanners. A single-bed scan (2.5mins) and a multi-bed (9 beds, 17s per bed) scan with overlap 32% was performed with uMI780. Following, the data was acquired for 2.5 minutes in uEXPLORER. The images were reconstructed with all physics corrections for further noise analysis. Then the contrast recovery coefficient (CRC) with iterations was evaluated with various axial position and acquisition time for the uEXPLORER and uMI780. The phantoms and scanning protocol were prepared according to the National Electrical Manufacturers Association (NEMA) NU 2-2012 standard. The clinical benefit of uEXPLORER was further assessed with a 65 kg, 61 years old male volunteer. The volunteer was injected with 7.85 mCi FDG, and first scanned with uMI780 (2 mins/bed, 8 beds) and then scanned for about 16 minutes in uEXPLORER after 60-min rest. The common reconstruction parameters including subsets = 20, reconstruction matrix = 256×256, reconstructed FoV = 600 mm were used in all the mentioned study.
Results: Fig. 1 gives the uniform phantom and noise evaluation with uMI780 and uEXPLORER. It is obvious that the uEXPLORER has a 5.5-fold reduction in the noise compared to multi-bed scanning and 1.5-fold reduction compared to single bed scanning with uMI780 at the center plane of axial FoV. This means the uEXPLORER can support clinical images with a more than 25-fold sensitivity gain than a multi-bed scan with uMI780. Fig. 2 suggests that the CRC is consistent along the axial FoV and over different acquisition time. This demonstrates that the uEXPLORER can provide the uniform lesion detection ability along axial FoV. Compared with uMI780, uEXPLORER has a higher CRC over all the iterations for all the hot spheres. For comparison, the reconstructed images of the volunteer for scanning with uMI780 and uEXPLORER, are shown in Fig. 3. Obviously, the uEXPLORER provides a significant reduction in the noise standard deviation compared with a multi-bed scan with uMI780.
Conclusions: The uEXPLORER scanner can be able to provide clinical images with low noise standard deviation, high contrast, and uniform lesion detection ability along the whole axial FoV.
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