Frequently Asked Questions

  1. Does the use of pinholes increase the sensitivity of the U-SPECT?
    Yes it does, particularly for small objects. The U-SPECT II has 75 pinholes, all focusing on the same small volume such as the mouse heart, brain or spine to maximize photon detection yield. That way one can acquire many photons from a specific area of interest which results in ultra-high image resolution and sensitivity with low image noise.

  2. So only a very small area can be scanned?
    No, by stepping the animal bed through the collimator tube using an XYZ micro-manipulator a larger part or the entire animal can be scanned. Using this scanning focus method (SFM) we have superior resolution, both in focused imaging and in total body imaging.  SFM can successfully be used in dynamic total body imaging.

  3. Why do some U-SPECT collimators have gold pinholes?
    Compared with the more commonly used lead or tungsten, gold pinhole apertures have high stopping power, which  significantly reduces blurring caused by radiation penetration in the aperture edge material. This is why a high resolution can even be maintained with high energy photons from isotopes like In-111.

  4. Why is it beneficial to use such big detectors for such small animals ?   
    To deal with various types of resolution degradation in pinhole systems large image magnification factors are needed, which corresponds to a large pinhole-to-detector distance (See F. Beekman and F. van der Have, “The Pinhole, gateway to ultra-high resolution three-dimensional radionuclide imaging”, Eur. J. Nucl. Med. & Mol. Im. 2007). U-SPECT-II has by far the highest magnification factor in the market. In combination with 360◦ angular detector coverage and zero movement errors in the detectors we get unsurpassed resolution and sensitivity, but it requires a large detector area. Three 15” x 20” detectors with advanced list mode acquisition electronics are used.

  5. Could the use of overlapping further increase sensitivity of U-SPECT?
    Yes, in such a case a U-SPECT collimator could contain hundreds of pinholes. However, independent research conducted at UZ-Leuven (Vunckx et al , IEEE Trans. Med. Imaging. 2008) and at University Medical Centre Utrecht has shown that such a sensitivity increase is only artificial. In the overlapping projections there is photon information loss. Overlap (or multiplexing) for small animal SPECT almost never results in a better resolution or better noise properties. Instead, overlap of projection may lead to serious image artifacts.

  6. How long does a scan take?
    This depends on the scan volume, the radiopharmaceutical, the required image detail, and the dose. A cardiac perfusion scan showing a beating mouse heart typically  ranges between  a couple of minutes up to an hour.

  7. What is the time resolution and minimum scan time?
    The minimum scan time can be very short  because no detector movements are needed with U-SPECT. In theory scanning times of 0.0001s are possible. However, due to dose limitations 30 sec for dynamic tracer imaging, and 5 to 30 minutes for static imaging are being used in practice. (See “Movies of dopamine transporter occupancy with ultra-high resolution focusing pinhole SPECT” Mol. Psych, 2007) . With gating much better time resolutions are being achieved in practice. Scan time does not depend on limitations in the systems hard- or software.

  8. The pictures you show are very nice but isn’t the dose so high that it will have immediate side effects?
    The doses we use are never that high. One of the main ideas of using microSPECT imaging is to keep the animal alive and reduce the use of animals!
    It is up to the researcher to determine the dose and balance between the required image quality and the acceptable dose level. We refer for example to the scientific article “U-SPECT-II: An Ultra-High-Resolution Device for Molecular Small-Animal Imaging” by F. van der have et al., where images based on high as well as low dose are shown with extremely high quality.

  9. Which isotopes can be used?
    A wide variety of isotopes can be imaged, including I-125. The energy range is 30-400 keV (so including In-111).

  10. Is triggering possible?
    Yes, multiple triggering: e.g. ECG, respiratory and a user defined mode. Of course the reconstruction algorithm includes these trigger signals. MILabs offers accessory equipment to monitor the animal. The monitored parameters are: ECG, respiration and temperature.

  11. Can the U-SPECT be combined with a micro-CT system?
    Yes it can. MILabs offers a separate CT system, called U-CT. MILabs has not chosen to by default integrate the two systems fully, as separate systems offer more flexibility: one can use the two systems simultaneously (see Beekman and Hutton, “Multi-modality imaging on track”, (Editorial)  Eur. J. Nucl. Med. Mol. Im, 2007. The same bed is used and moving the animal from one system to the other and it the combination is therefore very convenient. Various Image fusion tools are available..

  12. What do I have to do if I want to scan a rat instead of a mouse?
    You have to exchange the collimator and click-off the bed. This takes only a few minutes. The system automatically detects which bed and collimator is mounted and it will adapt the system parameters.

  13. What are the cameras in front for?
    The cameras produce an optical image of the animal which is displayed on the screen.
    On this image the scan volume can be set. Now the system knows exactly how to position the bed in order to focus all pinholes on the desired scan volume. 
    When starting the acquisition the bed automatically moves to this position. This way one can choose a minimal volume of interest in order to obtain maximum sensitivity.

  14. How long will the installation take?
    The installation is in the one week range, which includes calibration. Scans are being made already after or within a week.

  15. What about maintenance, how much time a year does it cost?
    Because the U-SPECT is a stationary system mechanical maintenance is minimal. With a standard configuration basic maintenance requires only one week per year.