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  • 1.
    Larsson, Anne
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Transmission-dependent convolution subtraction of 99m-Tc-HMPAO rCBF SPECT - a Monte Carlo study2005In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 52, no 1, p. 231-237Article in journal (Refereed)
    Abstract [en]

    Transmission-dependent convolution subtraction has been shown to be useful when correcting for malpositioned scattered events in single photon emission computed tomography (SPECT). The method is based on convolution subtraction but includes a matrix of scatter fractions instead of a global scatter fraction. In this study, this method is evaluated for regional cerebral blood flow SPECT with 99mTc-hexamethyl propylene-amine oxime (HMPAO) by using Monte Carlo simulations. Different geometries for generating the scatter fractions as a function of the attenuation path length are studied and compared. The most optimal value of the exponential describing the falloff of the monoexponential scatter kernel is determined for each geometry. The method is also compared with convolution subtraction with a global scatter fraction. It is shown that the most optimal of the tested geometries is a homogeneous activity distribution. A scatter kernel with an exponential of 0.15 pixel-1 is most optimal for this geometry. A comparison with convolution subtraction shows that transmission-dependent convolution subtraction can give more accurate results if used with optimal parameters.

  • 2. Ljungberg, Michael
    et al.
    Larsson, Anne
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Johansson, Lennart
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    A new collimator simulation in SIMIND based on the delta-scattering technique2005In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 52, no 5, p. 1370-1375Article in journal (Refereed)
    Abstract [en]

    To use conventional ray tracing methods in Monte Carlo simulation of the collimator in a scintillation camera system can be time consuming. It is however necessary to take collimator interactions into account when simulating radionuclides emitting high-energy photons that can penetrate the septa in the collimator. In this work a statistical collimator algorithm, based on the Delta-Scattering method, is evaluated using 123I. The evaluation is performed by comparing results from Monte Carlo simulations and measurements for a scintillation camera system, using point sources and a nonhomogeneous brain phantom. A good agreement can be seen for both images and energy spectra.

  • 3.
    Mähler, Emma
    et al.
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Sundström, Torbjörn
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Diagnostic Radiology.
    Axelsson, Jan
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Larsson, Anne
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Detecting small liver tumors with In-111-Pentetreotide SPECT-A Collimator study based on Monte Carlo simulations2012In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 59, no 1, p. 47-53Article in journal (Refereed)
    Abstract [en]

    In In-111- pentetreotide single-photon emission computed tomography (SPECT), the tumor-to-background-uptake ratio is generally high. The noise is, however, also usually on a high level, and in combination with the low spatial resolution of SPECT, this may lead to difficulties in the detection of small tumors. This is especially the case in regions with a relatively high background activity, such as in the liver, which is a common region for somatostatin-positive metastases. Visually detecting the small tumors is important for a successful treatment of the cancer disease. In this paper, we compare three different parallel-hole collimators for In-111-pentetreotide SPECT regarding contrast as a function of image noise for a phantom simulating small tumors in liver background. The corresponding contrast-to-noise ratios are also presented. All raw-data projections are produced using Monte Carlo simulations. The collimators are of type low-energy general-purpose (LEGP), extended LEGP (ELEGP), and medium-energy general-purpose (MEGP). Reconstructions were performed with OSEM both with and without model-based compensation. Of the investigated collimators, the ELEGP collimator proved to be the most optimal for the smallest tumors, both with and without model-based compensation included in the reconstruction. It is also shown that model-based compensation outperforms the conventional reconstruction technique.

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