Optimization of ^99mTc whole‐body SPECT/CT image quality: A phantom study

Abstract

Purpose Investigate the impact of acquisition time and reconstruction parameters on single‐photon emission computed tomography/computed tomography (SPECT/CT) image quality with the ultimate aim of finding the shortest possible acquisition time for clinical whole‐body SPECT/CT (WB‐SPECT/CT) while maintaining image quality Methods The National Electrical Manufacturers Association (NEMA) image quality measurements were performed on a SPECT/CT imaging system using a NEMA International Electrotechnical Commission (IEC) phantom with spherical inserts of varying diameter (10–37 mm), filled with 99mTc in activity sphere‐to‐background concentration ratio of 8.5:1. A gated acquisition was acquired and binned data were summed to simulate acquisitions of 15, 8, and 3 s per projection angle. Images were reconstructed on a Hermes (HERMES Medical Solutions AB, Stockholm, Sweden) workstation using eight subsets and between 4 and 24 iterations of the three‐dimensional (3D) ordered subset expectation maximization (OSEM) algorithm. Reconstructed images were post‐smoothed with 3D Gaussian filter ranging from 0 to 12 mm full‐width at half maximum (FWHM). Contrast recovery, background variability, and contrast‐to‐noise ratio were evaluated Results As expected, the spheres were more clearly defined as acquisition time and count statistics improved. The optimal iteration number and Gaussian filter were determined from the contrast recovery convergence and level of noise. Convergence of contrast recovery was observed at eight iterations while 12 iterations yielded stabilized values at all acquisition times. In addition, it was observed that applying 3D Gaussian filter of 8–12 mm FWHM suppressed the noise and mitigated Gibbs artifacts. Background variability was larger for small spheres than larger spheres and the noise decreased when acquisition time became longer. A contrast‐to‐noise ratio >5 was reached for the two smallest spheres of 10 and 13 mm at acquisition times of 8 s Conclusion Optimized reconstruction parameters preserved image quality with reduce acquisition time in present study. This study suggests an optimal protocol for clinical 99mTc SPECT/CT can be reached at 8 s per projection angle, with data reconstructed using 12 iterations and eight subset of the 3D OSEM algorithm and 8 mm Gaussian post‐filter.

Transition to Fast Whole-Body SPECT/CT Bone Imaging: An Assessment of Image Quality

“…Consistent with our result, a previous study [ 14 ] showed the sphere’s deformation became more apparent with the short acquisition time using NEMA IEC Body phantom with irregularly shaped lesion simulating inserts. In our study, the high noise induced by low counts in images at 360 s and 180 s was the principal cause of poor image quality.…”

“…This technique has been demonstrated by Bailey and Kalemis [ 19 ], using an electrocardiography (ECG) simulator as an external trigger to generate non-physiological gating, resulting in essentially identical yet statistically distinct partitioned datasets at reduced acquisition time. A more in depth discussion of this technique can be found in our previous work [ 14 ].…”

“…Reduction of SPECT/CT image time would therefore aid the introduction of WB-SPECT/CT into clinical routine by reducing the likelihood of patient motion as well as bringing the total study acquisition time down to approximately the same as current PBS protocols. In recent studies, fast SPECT protocols have shown promise on reducing imaging time without loss of diagnostic quality [ 14 , 15 ]. In addition, it is possible to substitute “true” PBS with re-projected “synthetic” PBS derived from the WB-SPECT/CT, as has been done previously with lung imaging [ 16 , 17 ].…”

Detection of prostate cancer bone metastases with fast whole-body 99mTc-HMDP SPECT/CT using a general-purpose CZT system

“…Diagnostic performance being unaffected by the acquisition time was most likely caused by the preserved high lesion contrast in the images with short acquisition times (Table 2 ). The reconstruction parameters of the 50-, 32-, and 26-min images were similar to those suggested to be optimal by Alqahtani et al [ 16 ], except post-processing filtering was increased for the 32- and 26-min images.…”

“…Gregoire et al evaluated visual image quality [ 11 ]. Alqahtani et al optimized reconstruction parameters to preserve image quality with reduced acquisition time [ 16 ]. Zacho et al demonstrated fast partial-body bone SPECT/CT as an add-on to whole-body planar bone scintigraphy [ 15 , 17 ].…”