Factors affecting the repeatability of gamma camera calibration for quantitative imaging applications using a sealed source

Abstract

Several applications in nuclear medicine require absolute activity quantification of single photon emission computed tomography images. Obtaining a repeatable calibration factor that converts voxel values to activity units is essential for these applications. Because source preparation and measurement of the source activity using a radionuclide activity meter are potential sources of variability, this work investigated instrumentation and acquisition factors affecting repeatability using planar acquisition of sealed sources. The calibration factor was calculated for different acquisition and geometry conditions to evaluate the effect of the source size, lateral position of the source in the camera field of-view (FOV), source-to-camera distance (SCD), and variability over time using sealed Ba-133 sources. A small region of interest (ROI) based on the source dimensions and collimator resolution was investigated to decrease the background effect. A statistical analysis with a mixed-effects model was used to evaluate quantitatively the effect of each variable on the global calibration factor variability. A variation of 1 cm in the measurement of the SCD from the assumed distance of 17 cm led to a variation of 1–2% in the calibration factor measurement using a small disc source (0.4 cm diameter) and less than 1% with a larger rod source (2.9 cm diameter). The lateral position of the source in the FOV and the variability over time had small impacts on calibration factor variability. The residual error component was well estimated by Poisson noise. Repeatability of better than 1% in a calibration factor measurement using a planar acquisition of a sealed source can be reasonably achieved. The best reproducibility was obtained with the largest source with a count rate much higher than the average background in the ROI, and when the SCD was positioned within 5 mm of the desired position. In this case, calibration source variability was limited by the quantum noise.

Multi-centre evaluation of accuracy and reproducibility of planar and SPECT image quantification: An IAEA phantom study

“…The standard deviations within one study and one site were, for each trial, much smaller than the variation of results between the sites. This indicates that modern scintillation cameras provide stable data for repeated studies [34,35]. …”

Reference values of mandibular condyles metabolic activity: A study using 99mTc‐MDP single‐photon emission computed tomography

“…Taking into account the technical factors of the SPECT test, including the dose of the radiopharmaceutical, gamma camera calibration and individual factors such as the presence of a bone metabolic disease, renal function, body weight and food intake that may influence the results, [38][39][40] the uptake was measured in a fixed ROI, adding five trans-axial tomographic slides representing the total size of the condyle. This technique reduces intra-operator and inter-operator variability.…”

3-D Image-Based Dosimetry in Radionuclide Therapy

“…Zhao et al [29] compared the performance of different calibration methods and concluded that a planar acquisition of a point source was sufficiently accurate when scatter and background correction was included in the determination of the calibration factor. Anizan et al [27], [28] investigated the use of sealed 133 Ba sources as 131 I surrogates, with detailed analysis of the factors affecting the repeatability and stability. A general uncertainty analysis of the calibration procedure was also undertaken [34].…”