Impact of low-dose CT scan in dual timepoint investigations: a phantom study

M A Micheelsen, Mikael Jensen

    Research output: Contribution to journalConference articleResearchpeer-review


    Dual timepoint FDG takeup investigations have a potential for separating malignant lymph nodes from non-malignant in certain cases of suspected lung cancer. One hour seems to be the optimal time interval between the two scans (50-120 min). Many of the new PET scanners benefit from image fusion with a CT image and also use the CT for attenuation correction. In any practical hospital setting, 1 hour is too long to occupy the scanner bed and a second CT procedure thus becomes necessary. This study tries to validate to what extent the dose/quality of the second CT scan can be lowered, without compromising attenuation correction, lesion detection and quantification. Using a standard NEMA phantom with the GE Discovery PET/CT scanner, taken in and out between scan sessions, we have tried to find the minimal CT dose necessary for the second scan while still reaching tissue activity quantification within predetermined error limits. For a hot sphere to background activity concentration ratio of 1:5, the average uptake (normalised by the time corrected input activity concentration) in a sphere of 6 cm3 was found to be 0.90 ± 0.08 for the standard scan, yielding a dose of 5.5 mGy, and 0.90 ± 0.14 for a scan with lowest possible mAs product and lowest possible kV, yielding a dose of 0.65 mGy. With an insignificant increase in the uncertainty in the uptake measurement, we can get an order of magnitude reduction for the CT dose.
    Original languageEnglish
    Book seriesJournal of Physics: Conference Series
    Issue number1
    Pages (from-to)012009
    Publication statusPublished - 2011
    EventInternational Conference on Image Optimisation in Nuclear Medicine - Atlantica Aeneas Resort, Ayia Napa, 23–26 Mar
    Duration: 1 Jan 2011 → …


    ConferenceInternational Conference on Image Optimisation in Nuclear Medicine
    CityAtlantica Aeneas Resort, Ayia Napa, 23–26 Mar
    Period01/01/2011 → …


    • Hevesy Laboratory


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