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  • 1.
    Bornefalk, Hans
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Lewin, John H.
    Danielsson, Mats
    Lundqvist, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Improved dual-energy imaging with electronic spectrum splittingIn: Medical physics (Lancaster), ISSN 0094-2405Article in journal (Refereed)
  • 2.
    Åslund, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics.
    Lundqvist, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    AEC for scanning digital mammography based on variation of scan velocity2005In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 32, no 11, p. 3367-3374Article in journal (Refereed)
    Abstract [en]

    A theoretical evaluation of nonuniform x-ray field distributions in mammography was conducted. An automatic exposure control (AEC) is proposed for a scanning full field digital mammography system. It uses information from the leading part of the detector to vary the scan velocity dynamically, thus creating a nonuniform x-ray field in the scan direction. Nonuniform radiation fields were also created by numerically optimizing the scan velocity profile to each breast's transmission distribution, with constraints on velocity and acceleration. The goal of the proposed AEC is to produce constant pixel signal-to-noise ratio throughout the image. The target pixel SNR for each image could be set based on the breast thickness, breast composition, and the beam quality as to achieve the same contrast-to-noise ratio between images for structures of interest. The results are quantified in terms of reduction in entrance surface air kerma (ESAK) and scan time relative to a uniform x-ray field. The theoretical evaluation was performed on a set of 266 mammograms. The performance of the different methods to create nonuniform fields decreased with increased detector width, from 18% to 11% in terms of ESAK reduction and from 30% to 25% in terms of scan time reduction for the proposed AEC and detector widths from 10 to 60 mm. Some correlation was found between compressed breast thickness and the projected breast area onto the image field. This translated into an increase of the ESAK and decrease of the scan time reduction with breast thickness. Ideally a nonuniform field in two dimensions could reduce the entrance dose by 39% on average, whereas a field nonuniform in only the scanning dimension ideally yields a 20% reduction. A benefit with the proposed AEC is that the risk of underexposing the densest region of the breast can be virtually eliminated.

  • 3.
    Åslund, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics.
    Lundqvist, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Evaluation of an AEC system for scanning photon counting mammography based on variation of scan velocityIn: Medical physics (Lancaster), ISSN 0094-2405Article in journal (Other academic)
  • 4.
    Åslund, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics.
    Lundqvist, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Physical characterization of a scanning photon counting digital mammography system based on Si-strip detectors2007In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 34, no 6, p. 1918-1925Article in journal (Refereed)
    Abstract [en]

    The physical performance of a scanning multislit full field digital mammography system was determined using basic image quality parameters. The system employs a direct detection detector comprised of linear silicon strip sensors in an edge-on geometry connected to photon counting electronics. The pixel size is 50 mu m and the field of view 24 x 26 cm(2). The performance was quantified using the presampled modulation transfer function, the normalized noise power spectrum and the detective quantum efficiency (DQE). Compared to conventional DQE methods, the scanning geometry with its intrinsic scatter rejection poses additional requirements on the measurement setup, which are investigated in this work. The DQE of the photon counting system was found to be independent of the dose level to the detector in the 7.6-206 mu Gy range. The peak DQE was 72% and 73% in the scan and slit direction, respectively, measured with a 28 kV W-0.5 mm Al anodefilter combination with an added 2 mm Al filtration.

  • 5.
    Åslund, Magnus
    et al.
    KTH, School of Engineering Sciences (SCI), Physics.
    Cederström, Björn
    KTH, School of Engineering Sciences (SCI), Physics.
    Lundqvist, Mats
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Scatter rejection in multislit digital mammography2006In: Medical physics (Lancaster), ISSN 0094-2405, Vol. 33, no 4, p. 933-940Article in journal (Refereed)
    Abstract [en]

    The scatter to primary ratio (SPR) was measured on a scanning multislit full-field digital mammography system for different thickness of breast equivalent material and different tube voltages. Scatter within the detector was measured separately and was found to be the major source of scatter in the assembly. Measured total SPRs below 6% are reported for breast range 3-7 cm. The performance of the multislit assembly is compared to other imaging geometries with different scatter rejection schemes by using the scatter detective quantum efficiency.

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