Modeling of high-energy contamination in SPECT imaging using Monte Carlo simulation

Cot, Albert; Jané, E.; Sempau, J.; Falcon, Carles; Bullich, Santiago; Pavı́a, Javier; Calviño, F.; Ros, Domènec

doi:10.1109/tns.2006.870174

Cited by 16 publications

(11 citation statements)

References 11 publications

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“…Even though generating a table of depth-dependent CDRs with very low noise requires their computation only once, it is still computationally demanding [2]. There have been some efforts to develop faster MC simulations that include the septal penetration and collimator scatter response [9], [11], [15], but using a MC simulator as a forward projector involves high computational complexity [14]. In addition, one should validate the MC simulation by comparison of simulated energy spectra and PSFs with experimental measurements.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, one should validate the MC simulation by comparison of simulated energy spectra and PSFs with experimental measurements. For higher-energy photons it has been shown that it is important to carefully model all components of the SPECT detector system (collimator, back compartment, shielding) to get good agreement between measurement and simulation [9], [16], [17]. Even small discrepancies between collimator specification provided by the manufacturer and the actual dimensions of the collimator can lead to significant mismatch between measurement and simulation.…”

Section: Introductionmentioning

confidence: 99%

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Correction for Collimator-Detector Response in SPECT Using Point Spread Function Template

Chun

Fessler

Dewaraja

2013

IEEE Trans. Med. Imaging

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Compensating for the collimator-detector response (CDR) in SPECT is important for accurate quantification. The CDR consists of both a geometric response and a septal penetration and collimator scatter response. The geometric response can be modeled analytically and is often used for modeling the whole CDR if the geometric response dominates. However, for radionuclides that emit medium or high-energy photons such as I-131, the septal penetration and collimator scatter response is significant and its modeling in the CDR correction is important for accurate quantification. There are two main methods for modeling the depth-dependent CDR so as to include both the geometric response and the septal penetration and collimator scatter response. One is to fit a Gaussian plus exponential function that is rotationally invariant to the measured point source response at several source-detector distances. However, a rotationally-invariant exponential function cannot represent the star-shaped septal penetration tails in detail. Another is to perform Monte-Carlo (MC) simulations to generate the depth-dependent point spread functions (PSFs) for all necessary distances. However, MC simulations, which require careful modeling of the SPECT detector components, can be challenging and accurate results may not be available for all of the different SPECT scanners in clinics. In this paper, we propose an alternative approach to CDR modeling. We use a Gaussian function plus a 2-D B-spline PSF template and fit the model to measurements of an I-131 point source at several distances. The proposed PSF-template-based approach is nearly non-parametric, captures the characteristics of the septal penetration tails, and minimizes the difference between the fitted and measured CDR at the distances of interest. The new model is applied to I-131 SPECT reconstructions of experimental phantom measurements, a patient study, and a MC patient simulation study employing the XCAT phantom. The proposed model yields up to a 16.5 and 10.8% higher recovery coefficient compared to the results with the conventional Gaussian model and the Gaussian plus exponential model, respectively.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Correction for Collimator-Detector Response in SPECT Using Point Spread Function Template

Chun

Fessler

Dewaraja

2013

IEEE Trans. Med. Imaging

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“…The aim of this study was to evaluate the image quality and quantify the impact of high energy contamination for each isotope. High energy contamination [4,5] ends up in the main energy window by one or by a combination of the following effects: scatter in the object, Compton effect in the crystal, penetration of the collimator, and backscatter from the camera end parts (light guides, PMTs, lead ending).…”

Section: Introductionmentioning

confidence: 99%

Comparison of Image Quality of Different Iodine Isotopes (I-123, I-124, and I-131)

Rault

Vandenberghe

Holen

et al. 2007

Cancer Biotherapy and Radiopharmaceuticals

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I-131 is a frequently used isotope for radionuclide therapy. This technique for cancer treatment requires a pre-therapeutic dosimetric study. The latter is usually performed (for this radionuclide) by directly imaging the uptake of the therapeutic radionuclide in the body or by replacing it by one of its isotopes, which are more suitable for imaging. This study aimed to compare the image quality that can be achieved by three iodine isotopes: I-131 and I-123 for single-photon emission computed tomography imaging, and I-124 for positron emission tomography imaging. The imaging characteristics of each isotope were investigated by simulated data. Their spectrums, point-spread functions, and contrast-recovery curves were drawn and compared. I-131 was imaged with a high-energy all-purpose (HEAP) collimator, whereas two collimators were compared for I-123: low-energy high-resolution (LEHR) and medium energy (ME). No mechanical collimation was used for I-124. The influence of small high-energy peaks (>0.1%) on the main energy window contamination were evaluated. Furthermore, the effect of a scattering medium was investigated and the triple energy window (TEW) correction was used for spectral-based scatter correction. Results showed that I-123 gave the best results with a LEHR collimator when the scatter correction was applied. Without correction, the ME collimator reduced the effects of high-energy contamination. I-131 offered the worst results. This can be explained by the large amount of septal penetration from the photopeak and by the collimator, which gave a low spatial resolution. I-124 gave the best imaging properties owing to its electronic collimation (high sensitivity) and a short coincidence time window.

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“…The model for high energy detection was also considered to be Gaussian [8]: Here, Xo and Yo are the coordinates of the perpendicular projection of the source point on the detector plane, x andy are coordinates for any point on this plane, b is a parameter determining the width of the Gaussian function and A represents its amplitude. Parameters A and b were measured from planar images of a small sphere containing 0.30 MBq of IS F, placed at increasing distances from 1 to 6 cm, at intervals of 1 cm.…”

Section: Displays the Spect System Andmentioning

confidence: 99%

“…In previous works, HE response functions based on MC simulation have been developed for human imaging gamma cameras and incorporated into SimSET [8], [5], [6]. While MC modeling of backscattering areas is a useful method, its accuracy is often compromised by the need to reduce 978-1-4673-0120-6/111$26.00 ©2011 IEEE computation time, and current models could still be improved [9].…”

Section: Introductionmentioning

confidence: 99%

Monte Carlo simulation of small animal SPECT studies with <sup>123</sup>I-labeled radiotracers using high and low energy photons in a modified version of SimSET

Roé-Vellvé

Cot

Ros

et al. 2011

2011 IEEE Nuclear Science Symposium Conference Record

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Small-animal molecular imaging is a prominent field of research, and SPECT plays an important role within it. Evaluation of imaging systems and reconstruction algorithms in SPECT imaging often involves Monte Carlo simulations, and SimSET is a widely used code for emission tomography simulation. 1231 is a frequently used radionuclide in human and small animal studies. It emits a main yield of 159 keY photons, which are used for imaging, but it also has a low contribution of higher energy photons, which generate non-negligible noise in SPECT studies. The aim of this work was to implement experiment-based high-and low-energy response functions for a small animal SPECT system, to incorporate them into SimSET and to car'?; out a preliminary validation of the simulator obtained for 231 labeled radiotracers. Experimental measurements with 99 mTc were carried out to characterize 159 keY detection of 1231. Since most of the relevant high-energy (HE) lines of 1231 are close to 511 keY, the detector response to HE photons was characterized with the 511 keY photons from positron-electron annihilation subsequent to 1 8 F decay. Once the obtained response functions were incorporated into SimSET, experimental and simulated images of capillaries and small spheres containing 1231 were generated at various distances. Efficiency and spatial resolution were estimated from these images. The values from simulated images are close to the experimental ones, with deviations of under 10% in efficiency and under 6% in spatial resolution.

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Modeling of high-energy contamination in SPECT imaging using Monte Carlo simulation

Cited by 16 publications

References 11 publications

Correction for Collimator-Detector Response in SPECT Using Point Spread Function Template

Correction for Collimator-Detector Response in SPECT Using Point Spread Function Template

Comparison of Image Quality of Different Iodine Isotopes (I-123, I-124, and I-131)

Monte Carlo simulation of small animal SPECT studies with <sup>123</sup>I-labeled radiotracers using high and low energy photons in a modified version of SimSET

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