Evaluation of penetration and scattering components in conventional pinhole SPECT: phantom studies using Monte Carlo simulation

Abstract

In quantitative pinhole SPECT, photon penetration through the collimator edges (penetration), and photon scattering by the object (object scatter) and collimator (collimator scatter) have not been investigated rigorously. Monte Carlo simulation was used to evaluate these three physical processes for different tungsten knife-edge pinhole collimators using uniform, hotspot and donut phantoms filled with 201Tl, 99mTc, 123I and 131I solutions. For the hotspot phantom, the penetration levels with respect to total counts for a 1 mm pinhole aperture were 78%, 28% and 23% for 131I, 123I and 99mTc, respectively. For a 2 mm aperture, these values were 65% for 131I, 16% for 123I and 12% for 99mTc. For all pinholes, 201Tl penetration was less than 4%. The evaluated scatter (from object and collimator) with a hotspot phantom for the 1 mm pinhole was 24%, 16%, 18% and 13% for 201Tl, 99mTc, 123I and 131I, respectively. Summation of the object and collimator scatter for the uniform phantom was approximately 20% higher than that for the hotspot phantom. Significant counts due to penetration and object and collimator scatter in the reconstructed image were observed inside the core of the donut phantom. The collimator scatter can be neglected for all isotopes used in this study except for 131I. Object scatter correction for all radionuclides used in this study is necessary and correction for the penetration contribution is necessary for all radionuclides but 201Tl.

Toward Quantitative Small Animal Pinhole SPECT: Assessment of Quantitation Accuracy Prior to Image Compensations

“…While this knowledge and the proposed compensation methods may be used to facilitate quantitative preclinical SPECT, some unique characteristics of small animal SPECT imaging, such as the routine use of pinhole collimators (as compared to parallel-hole collimators in clinical imaging) and the vastly smaller size of rodents (as compared to human), are expected to make a difference in terms of how one may approach the problem. For example, there have been recent efforts implementing attenuation correction methods for quantitative small animal pinhole SPECT without taking measures to reduce the effects of scatter [12–14]. The scatter effects were deemed negligible, especially in I-125 rodent imaging.…”

Coregistration of Magnetic Resonance and Single Photon Emission Computed Tomography Images for Noninvasive Localization of Stem Cells Grafted in the Infarcted Rat Myocardium

“…In contrast to clinical situations, the gamma-ray scatter and attenuation are usually found to be secondary and relatively negligible in small animal SPECT imaging. In a previous study by Deloar et al [27], for example, photons scattered by the pinhole collimator were only 3.0% of total counts, relative to the edge penetration of 23% and primary counts of 61%. A refined simulation model that accounts for the scattering and attenuation would represent the future direction of this study.…”

Pinhole X-ray fluorescence imaging of gadolinium and gold nanoparticles using polychromatic X-rays: a Monte Carlo study

“…69,70 Since our system was modeled by benchmarking the pinhole SPECT system, which detects much higher energy photons than K-shell XRF photons, [52][53][54][55][56] further investigation in optimizing the system design -such as collimator design, X-ray filter, and tube potential -is needed to reduce the dose level and improve the image quality. In addition, if the aforementioned 2D pixelated detectors with high-energy resolution are commercially available, discrete XRF peaks can be analytically separated from the background photons.…”

“…38 The model was benchmarked against the design and the dimension of the pinhole, as well as the type and the pixel size of the detector commonly used in preclinical pinhole SPECT. [52][53][54][55][56] A cylindrical water phantom in the middle, as shown in Figure 1A, had a diameter of 5 cm and a height of 5 cm each. Four cylindrical water columns, 1 cm in diameter and 3 cm in height, containing GdNPs or AuNPs of different concentrations (0.01 wt%, 0.03 wt%, 0.06 wt%, and 0.09 wt%) were placed in the water phantom, as shown in Figure 1B.…”