Improving the detectability of overactive glands in dual-phase parathyroid SPECT/CT: a Monte Carlo simulation study

Abstract

Objective. SPECT-CT is a standard procedure conducted before minimally invasive surgery for the treatment of primary hyperthyroidism. In order to improve image quality, it is important to know how defect detectability is influenced by acquisition and processing parameters. The objective of this study is to continue prior physical phantom optimization studies by performing Monte Carlo simulations for the dual phase parathyroid SPECT-CT protocol using a digital anthropomorphic phantom. Methods. The dual phase parathyroid SPECT-CT imaging procedure with 99mTc-Sestamibi was simulated using the previously extensively validated SIMIND software for the first time. An anthropomorphic ZUBAL based phantom was built to represent an adenoma. Its diameter was set to 0.76 cm which corresponded to more than three times the pixel size and the target-to-background ratio was set to 16:1 based on previous studies. Four different collimators were tested. Contrast-tonoise (CNR) values were determined for different scatter correction options and processing parameter values. The OSEM algorithm was used for image reconstruction. Results. CNR values were improved from about zero (LEGP collimator, 16 iterations, attenuation correction: on, scatter correction: off) up to 3.7 (LEUHR collimator, 16 iterations, attenuation correction: on, scatter correction: off). The subjective visual assessment of detectability on simulated images agreed with the quantitative CNR values. Conclusion. Higher resolution collimators gave better CNR as confirmed by similar studies. The effect of scatter correction was found beneficial only if both the resolution and sensitivity of the collimator were relatively high. This is a significant finding since there is a shortage of definitive guideline on the use of scatter correction for parathyroid SPECT imaging.

IMPROVING THE QUANTIFICATION ACCURACY OF Tc-99m MIBI DUAL-PHASE PARATHYROID SPECT/CT: A MONTE CARLO SIMULATION STUDY

“…The dual-phase parathyroid Tc-99m-MIBI SPECT imaging protocol was used per previous parathyroid studies [40,41]. Specifically, Siemens Symbia Intevo Gamma Camera was chosen for the study.…”

“…The simulated phantom was filled with water. The pixel size for the phantom was 0.24mm according to previous studies ( [40,41]) while the entire phantom is sized 128x128x128 pixels. The adenoma is simulated as a uniform sphere with an offset ~1.5cm from the center situated on the upper central portion of the cylinder.…”

“…This technique allows us to administer scatter correction after the reconstruction, thus giving us a chance to compare it against its nonscatter corrected counterpart. Three energy windows were set-up with the primary photopeak at 140 keV [41].…”

“…Single photon emission computed tomography (SPECT) visualizes the radioactivity distribution across the human body on a field of view (FOV). Traditionally, SPECT is seen as a qualitative imaging technique that has low special resolution and high noise in regions of interest [45,41]. Since the recent development of iterative reconstruction algorithms, SPECT has joined others as a quantitative imaging modality providing an accurate quantitative representation of radioactivity in the body.…”

“…Siemens Collimator specifications including septal properties. Sensitivity is set according to Tc99m[41].…”